# Presentation: 424359

## Forecasting Significant Weather Events: Comparing Your System to Climatology 

*By*
*Richard H. Grumm*
*National Weather Service*
*State College PA 16803*
*and *
*Robert Hart*
*The Pennsylvania State University*
*V_1.3 8 August 2002*

## Introduction

**What is a significant weather event?**
***Definition***
***methodology (you want to do this too?)***
**How to anticipate significant  events:**
***a word about return periods***
***display concepts***
**Types of events and parameters**
***different events appear to be impacted by***
***winds ***
***moisture***
***thermal and height anomalies***
***winter storm examples/application***

## Significant weather events

**Definition:** *a significant weather event is considered to be an event where the fields, such as the height, wind, moisture, or thermal fields depart significantly from* ***normal***, representing “rare activity”. The latter is based on known ***return periods***.
**Normal:** *fields depart less then ~1.5 standard deviations from the 30-year mean*.
**Notes:** *some ****event types**** are more sensitive to anomalous winds, moisture, or thermal anomalies.*
*NOTE:  The impact on population, financial loses are not directly accounted for here!  Purely objective.*

## Historic weather events

**Historic events**: *a unique type of significant weather event where total tropospheric anomaly of four primary variables (****MTOTAL****) departs more than 4.5 standard deviations from normal.*
***Only 5 such events since 1948 in E. North America***
***MTOTAL = ******Total Atmospheric Anomaly***
***Explained in Methods section***

## Significant QPF events

**Definition:** *a QPF event is considered to be event where the the rainfall amounts exceeds 2 standard deviations from normal*, representing “*unusual activity*”
**Key parameters (VARS):**
- 850 hPa winds- the low-level jet concept
- 700 and 850 hPa specific humidity-moisture for rainfall
- Precipitible water anomalies
- anomalous upper-level lows destabilize and relate to convergence patterns/jets.

## Method

**Climatological Data:**
- NCEP re-analysis Data 1948-2001*.
- Fixed 30 year POR 1961-1990 from re-analysis data
*21 day running means and*
*standard deviations*
*stored in netCDF files by parameter.*
*365 entries with mean and standard deviation*
*March 2002 computed terrain correct Precipitible water climatology*
**Model data acquisition**
- operational NCEP model grids
- locally generated models
- case data via Liz Page (COMET)

## Method-II

**Displays using GRaDS**
- show parameters forecast as standard contours
- display the departures of these parameters from the 30 year means, displayed as the number of standard deviations from normal, called the ***Standardized Anomaly***.
**Real-time model data and anomalies:**
- MRF-ensembles (http://eyewall.met.psu.edu/ensembles)
- SREF-ensembles (http://eyewall.met.psu.edu/SREF)
- Eta (http://eyewall.met.psu.edu/eta)
- AVN (http://eyewall.met.psu.edu/avn)
**Cases **
*climatological data only*
*Model forecasts with anomalies*

## Computing Departures

**Compute**
- deviations from daily normal by variable, and level
**N**
- vertically integrated deviations from normal of each variable
***MMOIST, MTEMP, MHEIGHT, MWIND***
*Displays of Climatological and forecast fields*
*verse 30-year Climatology*
*expressed in terms of standard deviations from normal*
*may be positive or negative (MTOTAL uses absolute value).*

## Ndeparture of a variable at a level in standard deviations from normal

***N =  (var******Z******-mean) /variability***
*	**where *
*	**	**var     = (HGT, TMP, etc) **single field*
*	**	**Z        = pressure level (**surface, or mandatory level**)*
*	**      **mean    = daily mean for location *
*variability      = 1 standard deviation measure*
*	**	*

## Mtropospheric mass-average mean departure of a parameter

***M =  ************z ************ABS****** ******(N******MAX******))/n***
*	****where ***
*          ****N****      = departure of variable at some level.*
*	**	****Z  ****      = is summed over levels (ie 1000-200)*
*	**	**var     = single variable (height, temperature, moisture, u-wind or v-wind)*
*	**	****Max****  can be over a specific domain or point. It can also be a large negative departure!*

## MTOTALthe sum of all M’s

***MTOTAL = (M******temp******+ M******hgt******+M******q****** M******wind ******)/4***
***	******where**** *
*	**	****levels****        = 1000 to 200 hPa*
*	**	****M        ****   = Absolute value each Maximum N*
*	**	**4   for the four equally weighted variables in this example.*

## Return PeriodsMTOTAL only (average of the integrated sum of u,v,T,q anomalies)

## Variable Return Periods500 hPa heights 

**Variable Return Periods*****500 hPa heights***** **

## Variable Return Periods850 hPa temperatures 

## Moisture returns850 specific humidity 

## Variable Return Periods850 hPa temperatures and 500 hPa heights 

## Variable Return PeriodsM by variable 

## Moisture returns850 specific humidity 

## Moisture returns at a Point850 specific humidity near State College 

## Winter Storm Event Types

- The biggest events over eastern North America
*http://eyewall.met.psu.edu/rankings/*
- Snow storms
- Some recent events of note
*NWA Article June 2001: Nov 1992 Storm *
*The big blow 9-10 March 2002*
- Other

## Record Eastern US Events25N-50N/95W-65W

**Hart and Grumm MWR Sept 2001**
**Events:**
- determined strictly by anomalies and no human interventions
*hurricanes were eliminated for data resolution reasons*
- stratified by top of all time, by variables, and by Month
- searched for studies on big events in WAF/MWR/NWA-Digest/QJRMS/Weather/Weatherwise/StormData
**Events on line:**
- _[http://eyewall.met.psu.edu/rankings/](http://eyewall.met.psu.edu/rankings/)_
**Updated monthly, as necessary**

## Top 20 Eventsnote many were worthy of research

**Top 20 Events*****note many were worthy of research***

**From:  Hart and Grumm MWR Sept 2001**

## MTEMP

**M****TEMP**

**M****HEIGHT**

**M****MOIST**

## The singular event0000 UTC 9 Jan 1956

## #2 1200 UTC 15 Jan 1995

## #3 The Storm of the Century

## #4Minnesota Blizzard

## #5Major Northeast Icestorm

## #2 November EventAppalachian Snow storm

## #3 February EventRecord mid-winter Warmth

## Historic Heavy Event Types

**Snow storms**
**Thermal events**
*Arctic outbreaks*
*record heat events*
**Severe weather events**
*tornadic event signatures*
*derecho signatures*
**flood events**
*cut-off lows*
*east-west fronts*
*sharp cold fronts **(**Narrow cold frontal rainbands)*

## Applications

**Know the Climatology of event types**
*signatures of associated anomalies*
*patterns of associated anomalies*
**Apply this to model data**
- select model fields relative to departures
- allows one to see when models are forecasting
*big snow storms*
*big rain storms*
*heat waves*
- models show great skill in this with some caveats

## Heavy snow Model Applicationwe are talking winter here!

**30 December East Coast snow storm**
*NYC biggest December snow in 40 years*
***applying Climatological Fields to model forecasts****!*
**Model forecast a significant/record event**
*Eta did have a track and depth error*
*but signal of a big storm was clearly evident*
**Signals:**
*anomalous low (height and mslp)*
*anomalous easterlies*
*warm surge in warm sector*

## Slide 34

## Twins?  Steadfast AVN forecasts

## Slide 36

## Slide 37

## 30 December Snow case

**Models showed**
*showed sharp and strong easterly jet anomaly*
*these anomalies are often associated with significant QPF events see Preprint AMS-QPF Sym. Jan 2001.*
- showed anomalous surface cyclone and upper level low
- suggested a potentially significant storm for the date.
**Comparison to Kocin and Uccellini Events**
*Grumm and Hart 2001 WAF*

## Slide 39

## Snow storm findings

**East Coast and Midwest**
- distinct signatures of features
*study in Michigan*
*study in State College and Mid-Atlantic with Wakefield *
- Some key features:
*anomalous 850 hPa jet*
*anomalous surface, 850, 700, and 500 cyclone*
*thermal anomalies*
**Kocin and Uccellini**
- there storms typically were in the MTOTAL 2 range
- the super storm was an exceptional event

## Winter Wind Events

**10 November 1998 record storm**
*$40 million in damage IL,IA,KY,MI,MN and WI*
*large are winds >= 50kts*
*not a top-ten November event!*
*But had a signal*
**9 March 2002**
- the big blow
- winter storm with strong winds
- killed people in Chicago on Saturday 9 March

## Slide 42

## Slide 43

## Slide 44

## Slide 45

## Winter Wind Events

**10 November 1998 record storm**
*$40 million in damage IL,IA,KY,MI,MN and WI*
*large are winds >= 50kts*
*not a top-ten November event!*
*But had a signal*
**9 March 2002**
*the “big blow” & the State College WalMart Storm*
*winter storm with strong winds*
*killed people in Chicago on Saturday 9 March*
*incredible LLJ jet with +V wind anomaly*

## Slide 47

## Slide 48

## Slide 49

## Conclusion

**We defined a significant weather event**
*based on number of standard deviations from normal*
**We learned to anticipate significant  events:**
***~N**** of 2 is normal for any given parameter*
*~N of 0 is very rare*
**There are different types of events**
*parameters seem to impact different events differently*
*snowstorm events*
*need easterly jet*
*deep low*

## Conclusion

**There are different types of events**
*parameters seem to impact different events differently*
*snowstorm event*
*need easterly jet*
*deep low*
*winter wind storms*
*need not be big MTOTAL events*
*deep low and deep upper level lows*
*anomalous winds (Big MWIND)*
*Other points:*
*some recent success forecasting heavy rains and identifying heavy rain types (See WAF conference preprints 2002).*

## Learning More

**These data are free thanks to NCEP/NCAR**
*design study of event types*
*look for parameters that affect your area*
*determine anomalies associated with event types*
*climatological netCDF files are available***.**
**There is a lot to be done**
*we touched the tip of the iceberg*
*we did not look in the western US*
*great opportunity*
*We learned to anticipate significant  events:*
**Jump start your study:**

## Jump start your study

**Method with Indiana and Michigan**
**identify your events**
**make flat file:**
**00Z24JAN2000**
**12Z24JAN2000**
**12Z30DEC2000**
**email to richard.grumm@noaa.gov**
**perl script to make images**
**anomaly output for databases**
**if you find cool stuff, get the 60 GB dbms.**

## References

- Hart, R.E and R.H. Grumm 2001: Using normalized Climatological anomalies to rank synoptic-scale events. * MWR*,**129**,2426-2442**.**
- Grumm,R.H, and R.E. Hart, 2001:Standardized Anomalies Applied to Significant Cold Season Weather Events: Preliminary Findings. *Wea.Fore*.,**16**,736-754.
- Grumm, R.H., and R. Hart, 2001: Anticipating heavy rainfall events: Forecast aspects. Preprints, *Symposium on Precipitation Extremes: Prediction, Impacts, and Responses*, Albuquerque, NM, Amer. Meteor. Soc., 66-70.
- Hart, R., and R.H. Grumm, 2001: Anticipating heavy rainfall events: Climatological aspects. Preprints, *Symp. on Precipitation Extremes: Prediction, Impacts, and Responses*, Albuquerque, NM, Amer. Meteor. Soc., 271-274.
- Iacopelli,A.J. and J.A. Knox, 2002: Mesoscale dynamics of the record-breaking 10 November 1998 Mid-Latitude cyclone: A satellite-based case study.  NWA Digest,**25**,33-41.
- Grumm, RH, R. Hart, N.W. Junker and Lance F. Bosart, 2002: Can possible heavy rainfall events be identified by comparing various parameters to the climatological norms? Preprints, *19th Conf. On Wea. Anal and Fore. San Antonio, TX*, NM, Amer. Meteor. Soc., XXX-YYY.