observations and modeling of banded orographic convection radar images and numerical simulations of three shallow convective precipitation events over the coastal range in western oregon are presented in one of these events unusually well defined quasi stationary banded formations produced large precipitation enhancements in favored locations while varying degrees of band organization and lighter precipitation accumulations occurred in the other two cases the difference between the more banded and cellular cases appeared to depend on the vertical shear within the orographic cap cloud and the susceptibility of the flow to convection upstream of the mountain numerical simulations showed that the rainbands which appeared to be shear parallel convective roll circulations that formed within the unstable orographic cap cloud developed even over smooth mountains however these banded structures were better organized more stationary and produced greater precipitation enhancement over mountains with small scale topographic obstacles low amplitude random topographic roughness elements were found to be just as effective as more prominent subrange scale peaks at organizing and fixing the location of the orographic rainbands

microbial community distribution in sediments from the mount elbert gas hydrate stratigraphic test well alaska north slope we studied the microbial communities collected from hydrate bearing sediments on the north slope of alaska to determine how abiotic variables e g grain size hydrate presence formation fluid gases may correspond to the type and distribution of microbes in the sediments the cores were acquired from sub permafrost eocene 46 55 million year old sediments in the bpxa doe usgs mount elbert gas hydrate stratigraphic test well within which hydrates are believed to have formed 1 5 mya forty samples eight of which originally contained hydrates were acquired from depths of ca 606 666 m below land surface five drilling fluid samples acquired from the same depth range were included in the analysis as a control for possible contamination by drilling fluid microbes during the drilling and handling of cores dna was extracted from 15 samples typically 1 ng dna g sediment was recovered and then amplified using polymerase chain reaction with primers specific for bacterial and archaeal 16s rdna genes which indicates the likelihood that microbes were present in all analyzed samples only bacterial dna amplicons were detected terminal restriction fragment length polymorphism t rflp was used to measure bacterial diversity in the respective samples non metric multidimensional scaling nms was used to determine the abiotic variables that may have influenced bacterial diversity nms analysis revealed that the microbial taxa present in the sediment were distinct from the taxa present in the drilling fluids suggesting that the sediments were not contaminated by the drilling fluids multi response permutation procedures mrpp found no significant difference between three sample groups identified a priori as being from within a hydrate zone outside of hydrate zone or on the edge of a hydrate non hydrate zone according to downhole nuclear magnetic resonance spectroscopy logs however among the several other abiotic parameters that were evaluated mud gas methane concentration and variables related to hydrate presence e g chloride concentration salinity and resistivity appeared to define the arrangement of microbial community signatures in plots resulting from nms analysis communities from hydrate and non hydrate layers each contained unique taxa as determined by the t rflp assay

upstream effects of mesoscale mountains abstract the alpine experiment alpex has revealed that low level air is typically diverted around the alps without reaching the mountaintop in pursuit of an understanding of the physical basis of this phenomenon and of its generality we have explored the characteristics of orographic blocking of a rotating continuously stratified quid as revealed in a simple model problem retaining full nonlinear and transient effects hydrostatic dynamics is assumed and the obstacle is taken to be an infinitely long ridge with height h x the key questions treated are the strength of the upstream deceleration of cross mountain flow and the length scale over which the decelerated region extends by means of scale analysis the controlling parameters are found to be the rossby number ro u fl and the froude number fr nhm u where u is the speed of the oncoming flow f is the coriolis parameter l the mountain half width n the brunt vaisala frequency and hm is the maximum mountain height the scale analysis also

observations and scale analysis of coastal wind jets abstract blocking of onshore flow by coastal mountains was observed south of vancouver island british columbia by the noaa p 3 aircraft on 1 december 1993 winds increased from 10 m s 1 offshore to 15 m s 1 nearshore and became more parallel to shore in the blocked region which had a vertical scale of 500 m and an offshore scale of 40 50 km these length scale and velocity increases are comparable to theory the flow was semigeostrophic with the coast being hydrodynamically steep that is the coast acts like a wall and the alongshore momentum balance is ageostrophic this is shown by the nondimensional slope parameter the burger number b hmn flm being greater than 1 where hm and lm are the height and half width of the mountain n is the stability frequency and f is the coriolis parameter the height scale is given by setting the local froude number equal to 1 that is hl u n 500 m where u is the onshore component of velocity this scale is appropriate when hl is less than the mountain height

the transition of the hurricane frederic boundary layer wind field from the open gulf of mexico to landfall abstract numerous aircraft ship buoy and land nation data were composited with respect to the center of hurricane frederic for two time periods a 24 h period corresponding to the storm s position in the open gulf of mexico on 12 september 1979 and an 8 h period corresponding to the landfall of frederic near 0400 gmt on 13 september comparison of wind analyses for the two periods indicated a rotation of maximum inflow angles from the southeast to northeast quadrants and a strong frictional decrease of wind speed over land them and other features of the landfall analysis were compared with a model landfall study by moss and jones 1978 the landfall composite wind field was compared with the fujita damage vector analysis to determine the damage time interval and mean wind speed range damage vector directions were found to be well correlated with the surface streamlines with the most severe damage being associated with frederic s northern eyewall ten meter level wind speed data over water vo and

multiple precipitation mechanisms over mountains observed by airborne doppler radar during map iop5 abstract this study uses airborne doppler radar measurements from the special observing period of the mesoscale alpine programme map to document the detailed airflow and precipitation structure over the mountainous regions near the border of northeastern italy and slovenia as a cold frontal system moved eastward and encountered the eastern alps on 4 october 1999 during map iop5 in contrast to previously documented map cases the environmental conditions associated with this case are characterized by a deep layer of strong convective instability in the lower troposphere and by a cold northeasterly continental flow coming down from the mountains the so called bora wind along the southeastern alps over the study region there are two primary mountain barriers the julian alps oriented roughly west east with a peak mountain height of 2500 m and a significant variation in terrain height along its length and the other the dinaric alps a relatively lower mountain range oriented northwest southeast

multiscale mountain waves influencing a major orographic precipitation event abstract this study combines high resolution mesoscale model simulations and comprehensive airborne doppler radar observations to identify kinematic structures influencing the production and mesoscale distribution of precipitation and microphysical processes during a period of heavy prefrontal orographic rainfall over the cascade mountains of oregon on 13 14 december 2001 during the second phase of the improvement of microphysical parameterization through observational verification experiment improve 2 field program airborne based radar detection of precipitation from well upstream of the cascades to the lee allows a depiction of terrain induced wave motions in unprecedented detail two distinct scales of mesoscale wave like air motions are identified 1 a vertically propagating mountain wave anchored to the cascade crest associated with strong midlevel zonal i e cross barrier flow and 2 smaller scale 20 km horizontal wavelength undulations over the windward foothills triggered by interaction

two dimensional simulation of orographic effects on mesoscale boundary layer convection in this paper orographic effects on mesoscale boundary layer convection are studied through a series of idealized numerical experiments it is found that hills tend to weaken convective activity at their summits under higher background winds whilst strong updraughts can be observed at the summits or slightly downwind of the peaks under light wind conditions these can be associated with so called convective cores when the background winds are strong the effects of the hill length on the results are only significant when the height of the hill reaches 500 m the combined effect of a sensible heating maximum on the hill summit and baroclinic tendencies due to the elevated heating is a tendency to produce a convective core under reasonably light wind conditions under higher wind conditions the strong ascents and descents on both sides of the hill as well as the lee wave dynamics seem to pose a more important impact on the convective features than the thermal forcing of the hill a richardson number balance has been proposed to explain these two kinds of response finally under stronger wind conditions the convective available potential energy cape is small at the summit and reaches its maximum value in the lee of the hill while under light wind conditions the air parcels at the summit have more buoyancy and the cape downwind of the top of the hill is slightly larger than that elsewhere copyright 2002 royal meteorological society

atmospheric factors governing banded orographic convection abstract the three dimensional structure of shallow orographic convection is investigated through simulations performed with a cloud resolving numerical model in moist flows that overcome a given topographic barrier to form statically unstable cap clouds the organization of the convection depends on both the atmospheric structure and the mechanism by which the convection is initiated convection initiated by background thermal fluctuations embedded in the flow over a smooth mountain without any small scale topographic features tends to be cellular and disorganized except that shear parallel bands may form in flows with strong unidirectional vertical shear the development of well organized bands is favored when there is weak static instability inside the cloud and when the dry air surrounding the cloud is strongly stable these bands move with the flow and distribute their cumulative precipitation evenly over the mountain upslope similar shear parallel bands also develop in flows where convection is

effects of moist froude number and cape on a conditionally unstable flow over a mesoscale mountain ridge abstract in this study idealized simulations are performed for a conditionally unstable flow over a two dimensional mountain ridge in order to investigate the propagation and types of cloud precipitation systems controlled by the unsaturated moist froude number fw and the convective available potential energy cape a two dimensional moist flow regime diagram based on fw and cape is proposed for a conditionally unstable flow passing over a two dimensional mesoscale mountain ridge the characteristics of these flow regimes are 1 regime i flow with an upstream propagating convective system and an early slowly moving convective system over the mountain 2 regime ii flow with a long lasting orographic convective system over the mountain peak upslope or lee slope 3 regime iii flow with an orographic convective or mixed convective and stratiform precipitation system over the mountain and a downstream propagating convective system and 4 regime iv flow with an orographic stratiform precipitatio

sensitivities of orographic precipitation to terrain geometry and upstream conditions in idealized simulations abstractthis study examines how variations in relatively simple terrain geometries influence orographic precipitation and its spatial patterns of sensitivity to small changes in upstream conditions an idealized three dimensional model is used to simulate a moist flow impinging upon three alpine scale terrain shapes a straight ridge a concave ridge and a convex ridge a variety of simulations are conducted to investigate the sensitivity of precipitation patterns to ridge length and upstream thermodynamic and wind conditions for an impinging flow with a nondimensional mountain height of approximately unity it is found that for the straight and convex ridges the flow response is mostly linear for the conditions examined here and passes over the obstacles with little lateral deflection the concave ridge however exhibits strengthened flow deceleration wave breaking in the lee and flow confluence between the ridge arms the concave ridge also generates substantially more precipitation than the other

radar observations of intense orographic precipitation associated with typhoon xangsane 2000 abstract with measurements from two ground based doppler radars located in northern taiwan this study documents the detailed aspects of intense orographic precipitation associated with typhoon xangsane 2000 as it moved northward immediately off the eastern coast of taiwan bringing strong low level northeasterly to north northeasterly winds impinging on the mountainous northern coast with relatively good persistent coverage of radar echoes on both inland and upstream regions this particular event provides a unique description of the orographic precipitation and its relationship with orographic geometry strong upstream oncoming flow and the precipitation inherently associated with typhoon circulations in this case the heaviest precipitation was observed to occur primarily over two coastal mountain barriers mount da tun dt and the nangang keelung range nkr barrier dt is an approximately 3d mountain barrier and the nkr adjacent to the southeast of dt is a relatively lower narrower 2d moun

diagnosed characteristics of precipitation systems over taiwan during the may june 1987 tamex abstract characteristics of mei yu precipitating cloud systems over taiwan during the may june 1987 taiwan area mesoscale experiment tamex have been studied using sounding surface precipitation and radar data vertical motion has been computed over the island at 6 h intervals from 13 may to 15 june using a modification of the kinematic method that takes into account the mountainous lower boundary within a four station sounding polygon two primary characteristics of the precipitation have been found first the major rainfall event were linked to the passage of midlatitude disturbances and typically consisted of both deep convective and stratiform components deep convection was primarily prefrontal or frontal while the stratiform precipitation was postfrontal presumably in association with overrunning and orographic lifting second there was a pronounced diurnal variability in the rainfall vertical motion heating q1 and moistening q2 profiles have been used to define the character of the pr

formation of the convective lines off the mountainous coast of southeastern taiwan a case study of 3 january 2004 abstract convective lines frequently occurring off the mountainous coast of southeastern taiwan under weakly synoptically forced weather conditions are one of the most well known mesoscale phenomena in taiwan these lines usually develop close to the coast but frequently can also be observed well offshore while nearshore lines are better understood the formative processes of the offshore lines remain unclear the main objective of this study is to use various available observations e g doppler radar surface and sounding observations quikscat and ncep data collected over southeastern taiwan to investigate a specially chosen case on 3 january 2004 in an attempt to identify possible mechanisms leading to the formation of the offshore lines the studied line was formed 50 60 km away from the southeastern coast of taiwan and oriented south southwest to north northeast and approximately parallel to the coast detailed analyses of the event indicated that the formation of the line did not appear direc

triple doppler radar analysis of the heavy rain event observed in the lago maggiore region during map iop 2b this paper presents analyses of data collected with three ground based doppler radars during the mesoscale alpine programme map intensive observation period iop 2b from 1900 utc 19 september until 1100 utc 20 september 1999 during this period the synoptic situation was characterized by the propagation of a deep upper tropospheric trough towards the alps as often observed when heavy precipitation occurs on the southern slopes of the alpine massif a frontal cloud system with embedded convective cells passed over northern italy in association with the trough moving rapidly eastwards ahead of the advancing cold front a strong south to south easterly low level flow impinged on the mountains near lago maggiore and produced copious amounts of rain 200mm at several locations an analysis of three dimensional radar derived wind and precipitation fields shows that the most intense precipitation occurred where and when the easterly component of the low to mid level flow was the strongest with however a preferential location on the southern slopes of the alps this phenomenon can be explained by enhanced confluence between the main southerly flow and an intensifying easterly flow and or more favourable orientation of the moist inflow perpendicular to the mountain slopes in addition the propagation of convective cells from the po valley toward the alps led to enhanced precipitation over the mountainous area taking advantage of the approximately two dimensional character of the event the different terms of the water budget are calculated for a series of 25 successive vertical cross sections to analyse the transformation of atmospheric moisture into surface rainfall copyright 2003 royal meteorological society

dual doppler derived profiles of the southwesterly flow associated with southwest and ordinary typhoons off the southwestern coast of taiwan abstractthis study used ground based dual doppler observations to explore an understanding of kinematic characteristics of the southwesterly flow associated with the southwest sw and ordinary or typhoons immediately off the southwestern coast of taiwan the sw or typhoon stated herein is referred to as a typhoon with without an obvious combination of its outer circulations and the summer southwesterly monsoon active over the south china sea six typhoon events mindulle 2004 kalmaegi 2008 morakot 2009 talim 2005 jangmi 2008 and fungwong 2008 were chosen for analysis the first latter three listed belong to the family of the sw or typhoons the vertical profiles generated from hourly synthesized winds for these typhoons indicate that intense orographic rainfall tended to occur during the prevalence of the west southwesterly wsw flow that was more perpendicular to the south north orientation of the topography in southern taiwan a unique consistent feature of the wsw flow as

investigation of orographic precipitation over an isolated three dimensional complex topography with a dense gauge network radar observations and upslope model abstractthis study uses a dense rain gauge network radar observations and an upslope model to document the detailed aspects of precipitation over da tun mountain dt of northern taiwan under pre

mechanisms of intense alpine rainfall abstract numerical studies by the authors and others of the 1994 piedmont flood show that the orographically modified flow was a critical element for the production of extraordinary rainfall to uncover the precise mechanism of orographic rainfall occurring in full physics mm5 simulations of the 1994 piedmont flood the authors carried out simulations with the same real data initial and boundary conditions but with the real orography replaced by an idealized one with excellent agreement between real and idealized orography on the rainfall rate versus time in the piedmont area analysis of the idealized orography simulation provides a clear picture of the model s mechanism of orographically induced rainfall as noted in previous studies of the 1994 piedmont case a moist saturated airflow has a reduced effective static stability and tends to flow over the mountains while an unsaturated airstream is stable and tries to flow around toward the left in the northern hemisphere in the 1994 piedmont case t

radar observations of the diurnally forced offshore convective lines along the southeastern coast of taiwan this study documents offshore convective lines along the southeastern coast of taiwan a frequent but poorly understood mesoscale phenomenon that influences coastal weather during the taiwan mei yu season doppler radar and surface observations were gathered from a specially chosen period 11 15 may 1998 when the offshore convective lines were active off the southeastern coast of taiwan these observations were used to show the basic character structure and possible formative processes of offshore convective lines the synoptic environment accompanying these events was found to be relatively undisturbed and featured uniformly prevailing southerly south southeasterly winds in the boundary layer with southwesterlies westerlies aloft examination of radar data during the study period indicates that the lines generally occurred 10 30 km offshore and were characterized by an elongated narrow zone 5 10 km wide of heavy precipitation the lines were oriented roughly parallel to the coastline and generally did not move significantly the intensity of the radar reflectivity associated with the lines exhibited a marked diurnal variation and was closely related to the coastal offshore flow developing at night detailed analyses of an event on 14 15 may 1998 further show the important physical link between the offshore flow and the development of the line the offshore line was found to be located near and immediately ahead of the seaward extent of the offshore flow particularly a very narrow zone 2 km of low level heavy precipitation 40 45 dbz coincided with regions of strong updrafts and convergence where the prevailing southerly onshore flow encountered the cool offshore flow nearshore this offshore flow induced convergence given a stable thermodynamic condition in the lowest 1 km in the inflow region was a crucial low level forcing that provided lifting to trigger moist deep convection in this case the line s precipitation tilt eastward was confined primarily to the warmer inflow side rather than feeding the offshore flow to the west of the line no consistent upshear tilt of updrafts throughout the storm layer was observed which is consistent with the presence of a strong westerly shear in the line s environment both of these observations explain a relatively strong weak modification of low level onshore offshore flow by precipitation additionally a combination of surface and doppler radar observations indicates that the leading edge of the offshore flow moved seaward very slowly at 0 7 m s 1 and possessed a frontal character with notable discontinuities in near surface wind and temperature instead of pressure and dewpoint temperature

orographic effects on precipitating clouds 1 precipitation over and near mountains is not caused by topography but rather occurs when storms of a type that can occur anywhere deep convection fronts tropical cyclones form near or move over complex terrain deep convective systems occurring near mountains are affected by channeling of airflow near mountains capping of moist boundary layers by flow subsiding from higher terrain and triggering to break the cap when low level flow encounters hills near the bases of major mountain ranges mesoscale convective systems are triggered by nocturnal downslope flows and by diurnally triggered disturbances propagating away from mountain ranges the stratiform regions of mesoscale convective systems are enhanced by upslope flow when they move over mountains in frontal cloud systems the poleward flow of warm sector air ahead of the system may rise easily over terrain and a maximum of precipitating cloud occurs over the first rise of terrain and rainfall is maximum on ridges and minimum in valleys if the low level air ahead of the system is stable blocking or damming occurs shear between a blocked layer and unblocked moist air above favors turbulent overturning which can accelerate precipitation fallout in tropical cyclones the tangential winds encountering a mountain range produce a gravity wave response and greatly enhanced upslope flow depending on the height of the mountain the maximum rain may occur on either the windward or leeward side when the capped boundary layer of the eye of a tropical cyclone passes over a mountain the cap may be broken with intense convection resulting

determination of stress parameters for eight well recorded earthquakes in eastern north america we determined the stress parameter for the eight earthquakes stud ied by atkinson and boore 2006 using an updated dataset and a revised point source stochastic model that captures the effect of a finite fault we consider four geometrical spreading functions ranging from 1 r at all distances to two or three part functions the values are sensitive to the rate of geometrical spreading at close distances with 1 r 1 3 spreading implying much higher than models with 1 r spreading the important difference in ground motions of most engineering con cern however arises not from whether the geometrical spreading is 1 r 1 3 or 1 r at close distances but from whether a region of flat or increasing geometrical spreading at intermediate distances is present as long as is constrained by data that are largely at distances of 100 km 800 km the simple 1 r model fits the sparse data for the eight events as well as do more complex models determined from larger datasets where the larger datasets were used in our previous ground motion predic tion equations this suggests that uncertainty in attenuation rates is an important com ponent of epistemic uncertainty in ground motion modeling for the attenuation model used by atkinson and boore 2006 the average value of from the point source model ranges from 180 bars to 250 bars depending on whether or not the stress parameter from the 1988 saguenay earthquake is included in the average we also find that for a given earthquake is sensitive to its moment magnitude m with a change of 0 1 magnitude units producing a factor of 1 3 change in the derived

further sensitivities of orographic precipitation to terrain geometry in idealized simulations abstractthis study examines how variations to the nondimensional mountain height and the horizontal aspect ratio of a straight ridge and a concave ridge influence orographic precipitation an idealized three dimensional model is used to simulate a moist flow impinging upon these two ridges with 0 66 2 0 and 1 0 8 0 the concave ridge generates substantially more precipitation than the straight ridge via an established precipitation enhancing funneling mechanism near the ridge vertex when the flow is unblocked based on previous work it was hypothesized that when the approaching flow becomes blocked the strength of the precipitation enhancement by the concave ridge relative to the straight ridge becomes negligible this study reveals that if is sufficiently large to induce flow reversal on the windward slope then a secondary circulation develops that is strengthened by the concave ridge with a subsequent enhancement of precipitation it is also shown that the competing effects of the ridg

distribution and mechanisms of orographic precipitation associated with typhoon morakot 2009 abstractusing a combination of doppler radar observations and rain gauge data this study documents detailed aspects of the orographic precipitation associated with typhoon morakot 2009 rainfall distribution over underlying topographical features and possible physical mechanisms responsible for the observed orographic enhancement are explored the study region constitutes an approximately two dimensional south north oriented orographic barrier with higher wider lower narrower terrain features in its northern southern portions i e the northern and southern barriers upstream conditions were characterized by abundant typhoon background precipitation embedded within strong nearly saturated westerly to west southwesterly oncoming flow the observations show that a wide area of topographically enhanced precipitation and the rainfall maxima were confined to the windward slopes of the northern barrier whereas the strongest rainfall tended to occur near and or slightly downstream of the mountain c

the addition of heat to a stratified airstream with application to the dynamics of orographic rain summary the response of a stratified airstream to combined thermal and orographic forcing is investigated theoretically using the linearized hydrostatic equations of motion the magnitude of the heating aloft is computed from observed rainfall rates the elevated heating is shown to produce vertically propagating waves whose amplitude relative to the mountain waves is determined by the parameter gqb cptuanh symbols appendix i for typical wind speeds and rainfall rates the thermally generated waves will equal or exceed the orographically generated waves these waves produce large vertical variations in the wave momentum flux at the levels where heat is being added and alter or even reverse the mountain drag in hydrostatic flow the phase relationship between the heating rate and the induced vertical displacements is found unexpectedly to be negative in the vicinity of the heating air parcels are displaced downwards this result can be explained by wave propagation ideas but not by parcel arguments this helps to explain why mountain wave amplitudes are sometimes reduced in moist atmospheres the broad heat induced descent may act to limit the amount of condensation precipitation occurring in a stable middle level orographic cloud other types of orographic precipitation involving embedded convection in stratus layers low level feeder clouds or deep cumulus convection may not be adversely effected by the heat induced descent

the climatology of small scale orographic precipitation over the olympic mountains patterns and processes the climatology of small scale patterns of mountain precipitation is poorly constrained yet important for applications ranging from natural hazard assessment to understanding the geologic evolution of mountain ranges synthesizing four rainy seasons of high resolution precipitation observations and mesoscale model output from the penn state ncar mm5 reveals a persistent small scale pattern of precipitation over the 10 km wide 800 m high ridges and valleys of the western olympic mountains washington state usa this pattern is characterized by a 50 70 excess accumulation over the ridge crests relative to the adjacent valleys in the annual mean while the model shows excellent skill in simulating these patterns at seasonal time scales major errors exist for individual storms investigation of a range of storm events has revealed the following mechanism for the climatological pattern regions of enhanced condensation of cloud water are produced by ascent in stable flow over the windward slopes of major ridges synoptically generated precipitation grows by collection within these clouds leading to enhanced precipitation which is advected by the prevailing winds instances of atypical patterns of precipitation suggest that under certain conditions during periods with a low freezing level or convective cells fundamental changes in small scale patterns may occur however case studies and composite analysis suggest that departures from the pattern of ridge top enhancement are rare the basic patterns and processes appear robust to changes in temperature winds and background rainfall rates copyright 2008 royal meteorological society

precipitation over concave terrain abstract many topographic barriers are comprised of a series of concave or convex ridges that modulate the intensity and distribution of precipitation over mountainous areas in this model based idealized study stratiform precipitation associated with stratified moist airflow past idealized concave ridges is investigated with a focus on windward blocking flow confluence and the associated precipitation enhancement it is found that flow confluence and precipitation enhancement by a concave ridge are controlled by the nondimensional ridge height m m nmhm u where nm is the moist buoyancy frequency hm is the maximum ridge height and u is the wind speed based on which three dynamical regimes can be defined in the linear regime m 0 4 a flow confluence zone is present over the upwind slope of the ridge vertex where precipitation is significantly enhanced the precipitation enhancement is due to the additional updraft driven by the horizontal flow convergence with a considerable contribution fr

small scale precipitation elements in midlatitude cyclones crossing the california sierra nevada abstractradar data in some frontal systems passing over the sierra nevada of california show large variance on scales of 10 km the most prominent features are a few kilometers in scale and are similar to small scale precipitation cells embedded in fronts seen over other mountain ranges other frontal systems crossing the sierras are characterized by more uniform air motions updrafts in large variance storms have characteristics of shear induced turbulence although buoyant instability may also contribute large variance storms occur under stronger upstream winds and vertically integrated cross and along barrier moisture fluxes rain gauges indicate that large variance storms have precipitation greater than smaller variance storms stronger horizontal moisture fluxes may provide greater mean upslope condensation rates however it is hypothesized that accelerated microphysical processes are needed to most efficiently convert the condensate into precipitation that falls out on the lower slopes before be