# Presentation: 675310

- Storm Prediction Center
- Winter Weather Operations

**Peter Banacos**
**NOAA/NWS/NCEP/SPC**
**WDTB Winter Weather Workshop**
**10 October 2002**

## Winter Weather Program Overview

- Program began winter 1997-98
- The SPC writes mesoscale discussions:  concise, technical products containing specific, event driven guidance for hazardous winter weather events affecting areas within the continental U.S.
- A component of NCEP’s “seamless suite” of forecast and guidance products

## ‘SEAMLESS SUITE’ OF PRODUCTS

**CPC**: Seasonal outlooks, U.S. Hazards Assessment discussion and graphic (3-14 days)
**HPC**: Heavy snow/icing discussion, graphical outlooks (6-54 hr period)
**SPC**: Mesoscale discussions with graphic (0-9 hr period, up to 3 hour lead time prior to onset of forecast conditions)

- WINTER WEATHER

## Winter weather MD content

- Discussion of precipitation amounts/rates, initiation and cessation of heavy winter precipitation, and mesoscale trends of winter weather hazard down to the county-scale.

## Guidelines for Winter Weather Mesoscale Discussion Issuance

- 1”/hr snowfall rates lasting 2+ hours (< 4kft)
- 2”/hr snowfall rates lasting 2+ hours (4-8 kft)
- Freezing rain greater than 0.05”/ 3 hrs
- Blizzard conditions (e.g. winds 35+ mph and visibility 1⁄4 or less in snow and/or blowing snow
- Significant trends in precipitation type or mesoscale organization (forecaster judgment)
- Climatologically rare events (forecaster judgment)

## Accessing Mesoscale Discussions

- AWIPS ID:       **SPCSWOMCD**
- Internet:      _[www.spc.noaa.gov/products](http://www.spc.noaa.gov/products)_

## Mesoscale Discussions via the Web

- includes graphic and text product for each issuance...

## Winter Weather MD Format

- Generally 2 paragraphs (15-20 AWIPS lines). First paragraph provides _what_, _when_, and _where_ of the forecast.
- Second paragraph explains _why_ (i.e. physical processes responsible for production of heavy snow or mixed winter precipitation)
- Internet graphic depicting the mesoscale discussion area (graphic lat/lon points are now also included on text product)

## Mesoscale Discussions in 2001

- (84.2%)

- Combined Total: 2334

- (11.1%)

- (4.7%)

## SPC Winter Weather Discussions in 2001

- 167 	Heavy Snow
- 46 	Freezing Rain
- 42 	Precipitation Trends / Mixed Winter 	Precipitation
- 4 	Blizzard Conditions

## Jan-Apr 1999 Winter MD Coverage Graphic

**Jan-Apr 1999 Winter MD ****Coverage Graphic**

## Operational Data Sources/Uses

- Detailed, subjectively analyzed meso-surface and isobaric charts (keep current with observational trends), combined with objective computer generated diagnostic fields.
- Satellite imagery (deformation zones, baroclinic leafs, cloud top cooling, dry slots!, etc.)
- Radar imagery: national mosaics and individual radar sites (“bright banding”, precipitation banding)

## Operational Data Sources/Uses (cont.)

-  Profiler and VAD wind data (temperature advection, jets, trough and ridge axes, potential for banding, seeder/feeder mechanisms)
-  Observational and model rawinsondes (precipitation type, sufficiency of moisture)
-  Lightning data (heavy, convective snowfall)

## Operational Data Sources/Uses (cont.)

-  Operational and experimental NWP output (PTAX output)
-  Water temperatures (marine influence on precipitation type near coastal areas, anticipation of coastal fronts)
-  Lake temperatures (lake-effect snow intensity, precipitation type)

## MD Examples for Four Scenarios

-  Banded Precipitation
-  Lake Effect Snowfall
-  Orographic Snowfall
-  Mixed Precipitation

## Mesoscale Banding Example (Graphic/1st Paragraph)

- VALID January 6th 2053-0300z
- HEAVY SNOWFALL WILL DEVELOP NEWD INTO MUCH OF NRN PA AND SCENTRAL NY THROUGH 07/00Z... BEFORE DEVELOPING INTO INTERIOR PORTIONS OF SERN/ECENTRAL NY...WRN MA AND SRN VT BETWEEN 07/00Z AND 07/03Z. SNOWFALL RATES FROM 1 TO 2 INCH/HR WILL BE POSSIBLE.

- Pinpoint timing and location of mesoscale banding resulting in heavy snowfall.

## Mesoscale Banding Example (cont.)

- HEAVY SNOWFALL CURRENTLY OCCURING OVER PORTIONS OF WV/SRN PA WILL CONTINUE TO DEVELOP NEWD IN REGION OF STRONG DEEP LAYER UVM. **GREATEST CONTRIBUTION TO MESOSCALE FORCING FOR ORGANIZED BANDS OF HEAVY SNOW WILL CONTINUE TO BE STRONG FRONTOGENETICAL LIFT AT MID LEVELS IN REGION OF FAVORABLE DENDRITIC SNOW GROWTH LAYER****.** PORTIONS OF NCENTRAL/NERN PA...SCENTRAL/SERN NY WILL SEE THE GREATEST THREAT FOR HEAVY SNOW BETWEEN 06/21Z AND 07/02Z. ACROSS INTERIOR SERN NY/WRN MA AND SRN VT STRONG WAA WILL CONTINUE TO WORK TO SATURATE THE SFC-850 MB LAYER THROUGH THE EARLY EVENING HOURS. HEAVY SNOWFALL WILL BEGIN TO DEVELOP NEWD INTO THIS REGION BETWEEN 07/00Z AND 07/03Z...ONCE LOW LEVELS BECOME SATURATED. **GREATEST THREAT FOR HEAVY SNOWFALL WITH HRLY RATES FROM 1-2 INCHES WILL EXIST WHERE STRONGEST FRONTOGENETICAL FORCING IN THE 750 TO 650 MB LAYER IS MAXIMIZED ALONG AND 50 MILES EITHER SIDE OF AN AXIS FROM UNV TO BGM TO ALB THROUGH 07/02Z.** SOME CONVECTIVE SNOWFALL WILL BE POSSIBLE ALONG THE ERN EDGE OF THE DISCUSSION AREA THIS EVENING FROM NERN PA NEWD INTO WRN MA...ALONG REGION OF 6 TO 6.5 DEG C/KM MID LEVEL LAPSE RATES/STRONGEST WAA. SNOWFALL RATES IN CONVECTIVE SNOWBURTS MAY APPROACH 2 INCH/HR.
- ..CROSBIE.. 01/06/02

## Mesoscale Banding Example (cont.)

## Snowfall Accumulations 

**Snowfall Accumulations**** **

## Lake Effect Snow Example

- VALID December 29th,2001 : 1626-2200z
- THE SINGLE INTENSE SNOW BAND OFF LAKE ONTARIO WILL OCCASIONALLY PRODUCE SNOW RATES OF 1-3 IN/HR THROUGH THIS AFTERNOON **ACROSS JEFFERSON...LEWIS...AND NRN HERKIMER COUNTIES IN NY**. **THE BAND WILL DRIFT SLOWLY NWD THIS AFTERNOON...AND THEN MOVE SWD INTO NRN OSWEGO COUNTY BETWEEN 21-00Z.**

- Highlight changes in location and intensity of snow bands.

## Lake Effect Snow Example (cont.)

**SLIGHT BACKING OF LOW-LEVEL FLOW IS EXPECTED THROUGH MID-AFTERNOON AS A WEAK SHORTWAVE TROUGH MOVES EWD ACROSS ERN LAKE ERIE AND LAKE ONTARIO**...DRIFTING MIDDLE OF 10NM SNOW BAND NWD NEAR OR JUST NORTH OF ART. SNOW INTENSITIES MAY VARY WITHIN THE BAND AS MODEST DIRECTIONAL SHEAR/VORT MAX MOVES ACROSS ERN LAKE ONTARIO THIS AFTERNOON. THE 12Z RUC AND ETA SHOW THAT THE MEAN LOW-LEVEL WIND VEERS BETWEEN 29/21-30/00Z AS SHORTWAVE PASSES...RESULTING IN BAND MOVING SWD TOWARD NRN OSWEGO COUNTY BY EARLY EVENING AND LIKELY BECOMING BETTER ORGANIZED.
**THERMODYNAMIC CONDITIONS CONTINUE FAVORABLE FOR SINGLE BAND ORGANIZATION WITH SFC-850MB TEMPERATURE DIFFERENCES AROUND 20C AND SFC-700MB DIFFERENCES NEAR 30C. OWING TO THE SHORTWAVE AND WEAK BACKGROUND UVV...ETA MODEL SOUNDINGS INDICATE LOW-LEVEL INVERSION WILL REMAIN WEAK AND LOCATED AT A HIGH LEVEL...NEAR 9500 FT**. WITH A DEEP UNSTABLE LAYER AND NEARLY UNIDIRECTIONAL WIND PROFILE...SNOW RATES WILL REMAIN HIGH AND LOCALLY UP TO 3 IN/HR.
- ..BANACOS.. 12/29/01

## Orographic Snowfall Example

- VALID: January 21st 0436-1200z
- SNOWFALL RATES EXPECTED TO INCREASE TO 1-2 INCHES PER HOUR WITH THE APPROACH OF...AND ALONG A PACIFIC COLD FRONT MOVING THROUGH WRN ORE BETWEEN 06-12Z.  **SNOW LEVELS WILL FALL WITH THE PASSAGE OF THE FRONT WITH STEADY SNOW THEN CHANGING TO CONVECTIVE SHOWERS.  SNOW LEVELS OVER ERN MARION AND EXTREME WRN JEFFERSON COUNTIES INITIALLY AROUND 3500 FEET EXPECTED TO FALL TO 2500 FEET BY 09Z**.  SNOW LEVELS OVER EXTREME ERN DOUGLAS AND NWRN KLAMATH COUNTIES EXPECTED TO REMAIN AROUND 4000-4500 FEET THROUGH 09Z...AND THEN FALL TO 2500-3000 FEET BY 12Z.

- Timing of heavy snow with changes in snow levels noted.

## Orographic snowfall (cont.)

**WATER VAPOR IMAGERY SHOWS A PACIFIC COLD FRONT EXTENDING FROM NWRN WA TO OFFSHORE AT 42 N 132 W**.  THIS FRONT WILL CONTINUE TO TRACK TO THE SE AT 40-50 KT...MOVING INTO THE NRN ORE CASCADES AROUND 06Z AND THEN THROUGH THE CENTRAL ORE CASCADES BETWEEN 09-12Z.  STRONG ONSHORE FLOW HAS ALLOWED SNOW LEVELS TO REMAIN NEARLY STEADY OR RISE THIS EVENING IN ADVANCE OF THE FRONT TO 3500-4500 FEET.  00Z SOUNDINGS ALONG THE WA/ORE COAST SHOW DEEP MOISTURE WITH A FETCH OFMOISTURE EXTENDING OFFSHORE PER WATER VAPOR IMAGERY.  AS THE FRONT/UPPER TROUGH MOVES THROUGH WRN ORE...UVVS WILL INCREASE...ESPECIALLY ALONG THE FRONT.  **THE COMBINATION OF THE FRONTAL LIFT...UPPER DYNAMICS... FAVORABLE UPSLOPE AND DEEP MOISTURE WILL ENHANCE THE SNOWFALL RATES BETWEEN 06-12Z.**
- ..PETERS.. 01/21/02

## Mixed Precipitation Example

- A MIXTURE OF SNOW...SLEET AND FREEZING RAIN WILL SPREAD EWD INTO
-                    THIS REGION OVER THE NEXT FEW HOURS.  PRECIPITATION WILL LIKELY
-                    START AS SNOW OR SLEET...BUT MAY CHANGE OVER TO FREEZING RAIN
-                    ACROSS FAR NERN AR...THE MO BOOTHEEL...WRN KY...FAR NWRN TN.
-                    PRECIPITATION RATES SHOULD EXCEED .05"/HR IN THE HEAVIER
-                    SHOWERS...AS IS OCCURING ACROSS N-CENTRAL/NWRN AR ATTM.
-                    A LARGE AREA OF MODERATE TO OCCASIONALLY HEAVY RAIN CONTINUES TO
-                    SPREAD ACROSS CENTRAL AR ALONG NOSE OF 35-45 KT SWLY LLJ.  WAA IS
-                    ALSO MAINTAINING A BROADER AREA OF LIGHT TO MODERATE SNOW/SLEET/
-                    FREEZING RAIN FROM NERN OK ACROSS THE OZARKS.  THOUGH SURFACE
-                    TEMPERATURES ARE JUST ABOVE FREEZING ATTM INTO THE MID MS RIVER
-                    VALLEY...WET BULB READINGS NEAR OR BELOW FREEZING FROM FAR NERN
-                    AR/SERN MO NWD INDICATE SUB-FREEZING SURFACE TEMPERATURES SHOULD
-                    DEVELOP ONCE THE HEAVIER PRECIPITATION BEGINS DURING THE NEXT HOUR
-                    OR TWO.  IN ADDITION...THE 00Z LZK SOUNDING INDICATED A WARM LAYER
-                    CENTERED NEAR H85 WITH A MAX TEMP OVER 6C.  THIS WILL CONTINUE TO
-                    OVERRIDE NEAR FREEZING SURFACE TEMPERATURES IMMEDIATELY TO THE
-                    NORTH AND NORTHEAST AND MAINTAIN A THREAT OF FREEZING RAIN AND
-                    SLEET /NORTH OF A JBR TO DYR LINE/.  CONVECTIVELY FAVORABLE
-                    ENVIRONMENT WITH NEAR NEUTRAL INSTABILITY FROM H7 TO H5 MAY ENHANCE
-                    THE PRECIPITATION RATES.  FORECAST SOUNDINGS SUGGEST MUCH OF THE
-                    PRECIPITATION WILL REMAIN SNOW AND SLEET NORTH OF AR/THE MO
-                    BOOTHEEL...WITH SNOWFALL RATES UP TO 0.5-1.0"/HR.
-                    ..EVANS.. 01/19/02

- VALID January 19th 0303-0700z
- A MIXTURE OF SNOW...SLEET AND FREEZING RAIN WILL SPREAD EWD INTO THIS REGION OVER THE NEXT FEW HOURS.  PRECIPITATION WILL LIKELY START AS SNOW OR SLEET...BUT MAY **CHANGE OVER TO FREEZING RAIN ACROSS FAR NERN AR...THE MO BOOTHEEL...WRN KY...FAR NWRN TN. PRECIPITATION RATES SHOULD EXCEED .05"/HR IN THE HEAVIER SHOWERS**...AS IS OCCURING ACROSS N-CENTRAL/NWRN AR ATTM.

- Delineate mixed condensate regions and intensity of precipitation.

## Mixed Precipitation Example

- A LARGE AREA OF MODERATE TO OCCASIONALLY HEAVY RAIN CONTINUES TO SPREAD ACROSS CENTRAL AR ALONG **NOSE OF 35-45 KT SWLY LLJ**.  WAA IS ALSO MAINTAINING A BROADER AREA OF LIGHT TO MODERATE SNOW/SLEET/ FREEZING RAIN FROM NERN OK ACROSS THE OZARKS.  THOUGH SURFACE  TEMPERATURES ARE JUST ABOVE FREEZING ATTM INTO THE MID MS RIVER VALLEY...**WET BULB READINGS NEAR OR BELOW FREEZING FROM FAR NERN AR/SERN MO NWD INDICATE SUB-FREEZING SURFACE TEMPERATURES SHOULD DEVELOP ONCE THE HEAVIER PRECIPITATION BEGINS DURING THE NEXT HOUR OR TWO**.  IN ADDITION...THE 00Z LZK SOUNDING INDICATED A WARM LAYER CENTERED NEAR H85 WITH A MAX TEMP OVER 6C.  THIS WILL CONTINUE TO OVERRIDE NEAR FREEZING SURFACE TEMPERATURES IMMEDIATELY TO THE NORTH AND NORTHEAST AND **MAINTAIN A THREAT OF FREEZING RAIN AND SLEET /NORTH OF A JBR TO DYR LINE**/.  CONVECTIVELY FAVORABLE ENVIRONMENT WITH NEAR NEUTRAL INSTABILITY FROM H7 TO H5 MAY ENHANCETHE PRECIPITATION RATES.  FORECAST SOUNDINGS SUGGEST MUCH OF THE PRECIPITATION WILL REMAIN SNOW AND SLEET NORTH OF AR/THE MO BOOTHEEL...WITH SNOWFALL RATES UP TO 0.5-1.0"/HR.
- ..EVANS.. 01/19/02

## SPC/NSSL CollaborationOn Winter Weather Topics

-  COMET Precipitation Type (PTAX) Experiment
- (NSSL, SPC, HPC)
-  Daily Weather Briefings (Monday through Friday)
-  SPC Winter Weather Workshops each fall (attendees include WFO Norman forecasters, NSSL researchers)
-  Other collaborative research efforts between SPC forecasters and NSSL researchers:
- e.g., Kain, John S., Stephen M. Goss, Michael E. Baldwin, 2000: _The Melting Effect as a Factor in Precipitation-Type Forecasting._ *Weather and Forecasting*: Vol. 15, No. 6, pp. 700–714.

## Summary

-  The SPC provides short-term winter weather guidance in support of public, aviation, and other commerce interests in the form of mesoscale discussions down to the county-scale or portions of CWAs.
-  These discussions fit within NCEP’s “seamless product suite” covering a range of spatial and temporal scales.
-  The SPC has a relatively new, but scientifically sound winter weather program. Improvement will continue with additional experience, training, and continued research.