Climatology notes for June

Looking at 850mb, 500mb, and 200 mb average charts for June (see
<http://bocachica.arc.nasa.gov/HAVE/Climo>) we see the following: an
anticylone poking into the northern Gulf of Mexico leading to persistent
low level south-southeasterly flow;

and weak westerlies at 500 mb and 200 mb in a fairly zonal pattern.
Notably, the summer anticylone has yet to develop at the upper levels.
What this means is that the Houston area is more likely to be affected
by synoptic waves than later in the summer. Day to day variability in
the low level winds is significant, but the direction (see the RH model
loop links at <http://bocachica.arc.nasa.gov/HAVE/Forecasting.html>) is
pretty much confined to the southerly to easterly quadrant.

Cloud climatologies (both HIRS, which is depicted on the web site, and
ISCCP) suggest about 50% cloud amount, which is slightly less than in
October in the same region. The Houston area and the Gulf are actually
in a minimum region between maxima in the southeastern US and the
Mexican Sierra Madre Occidental. Opaque cloud incidence (where the 20km
by 20km HIRS pixels are essentially completely covered) are only about
15%. At high altitudes (say clouds above 200 mb) the US, the Gulf, and
Mexico are in an overall maximum region. Most of these are fairly thin
clouds and might represent outflow from the extensive convective
activity that is more prevalent north of Houston, over Florida and the
southeastern US, and over the Mexican Sierra Madre.

Year-to-year variation in the nature of the cloudiness is significant,
based on a comparison of 2004 and 2002 (see satellite loop links in
<http://bocachica.arc.nasa.gov/HAVE/Forecasting.html>). During 2004
early June, what appears to be a moisture surge from the south coupled
with midlatitude wave influence results in several days of extensive
convection and cloudiness. The last 10 days of the month are quite
convective and cloudy as what appears to be a stationary front sits over
the Houston area leading to extensive convection (instead of further
north where it usually sits). In contrast, 2002 is much more benign.

Implications for validation goals:

OMI:

Probably the most severe weather constraint is for OMI, where reasonably
clear skies over the Houston area are important (if I understand this
correctly). I don\'t know if it is important that we capture a situation
where clean air is coming off the Gulf, and subsequently polluted by
Houston industries (as opposed to more southerly flows where pollution
from Mexico may add to the mix). I would say that, even in a bad year
(like 2004) we have enough flights over a long enough period to be able
to find at least one day where the OMI validation goal of somewhat clear
(scattered clouds) skies over Houston with appropriate winds can be
found. I assume that high thin clouds (which occur relatively frequently
in the summer here) are not a serious problem.

TES:

I would like to look at some visible loops over the Gulf, but based on
our experience in October, and the relative magnitudes of cloud cover in
October and June (from ISCCP), clear skies over a TES spot should be
attainable.

MLS:

Because the midlatitude jet is closer to us than in July, we may be able
to sample variations in CO carried across from Asia by the midlatitude
jet -- emphasis on "may." During INTEX-A, such CO enhancements were
typically in the northern US or further north. The GEOS-CHem model
seemed to be pretty good at predicting these situations. We may have
more ready access to MOZART -- I don\'t remember how good that model was
at forecasting this). Enhanced upper tropospheric ozone associated with
a history of lightning generated NO was also forecast by GEOS-CHEM and
observed during INTEX-A. A simple trajectory lightning history also
simulated (qualitatively) the regions of enhanced ozone. UT pollution
from convection can be forecast, though imperfectly (I think the Langley
RAQMS people were most interested in this). Simple trajectory convective
influence calculations can show where the most recent convection to
affect an air mass was located.

HRDLS:

HRDLS wants regions of gradients in the tropopause (based on the figures
in the presentation). June is certainly better than July, but the mean
position of strongest tropopause gradient is certainly well north of
Houston at this time (see <http://bocachica.arc.nasa.gov/HAVE/Climo> and
click on the trop link). I have yet to look at PV loops, which would be
an indication of the likelihood of getting to a region of strong PV
gradient. Based on the analysis loops showing 925mb wind, 925 RH, and
500mb height, the jet does swing south often enough to offer
opportunities (go to
<http://bocachica.arc.nasa.gov/HAVE/Forecasting.html> and click on RH
model loops).

Operations:

Thunderstorms are the major constraint on operations that I see. In the
past four years, the number of thunderstorm days during June was between
7 and 15. I have not been able to establish any real diurnal pattern to
the coldest clouds, and I suspect that the diurnal variation on this is
minimal. Based on the satellite loops, thunderstorms are related more to
synoptic wave patterns than a diurnal variation. Longer term
climatologies put the number of thunderstorm days at 6. Rain of some
kind can be expected 4.5 to 12 days during June, but over .1" can be
expected on only 3.8 days during June (mean). There is a diurnal peak in
rain incidence from noon to 6PM local time. A key statistic for us is
that cloud cover less than .3 can be expected at noon only 2.3 days
during June (19 days at midnight, so this has a big diurnal component.