A light snow event: Feb 2-4, 2003

2/3/03 – 6Z (midnight) Small storm passes to the SE, cold front to the NW +

NWS Forecasts, 4am (9Z) Feb 4 BLACK HAWK-BREMER-GRUNDY-MARSHALL-STORY-TAMA- INCLUDING THE CITIES OF...AMES...MARSHALLTOWN... WATERLOO/CEDAR FALLS 352 AM CST MON FEB WINTER WEATHER ADVISORY FOR THIS AFTERNOON AND THIS EVENING....TODAY...CLOUDY WITH A CHANCE OF FREEZING DRIZZLE OR DRIZZLE THIS MORNING...THEN WIDESPREAD SNOW THIS AFTERNOON. ACCUMULATION 1 TO 2 INCHES. TURNING COLDER. BRISK. TEMPERATURES FALLING INTO THE UPPER 20S. NORTH WINDS 15 TO 25 MPH...GUSTING TO 30 MPH FROM LATE MORNING ON. CHANCE OF PRECIPITATION 80 PERCENT..TONIGHT...WIDESPREAD SNOW EARLY...THEN PARTLY CLOUDY. ACCUMULATION 1 TO 3 INCHES. BRISK WITH BLOWING AND DRIFTING SNOW. LOW IN THE MID TEENS. NORTHWEST WINDS 15 TO 25 MPH...GUSTING TO 30 MPH. CHANCE OF SNOW 80 PERCENT..TUESDAY...PARTLY SUNNY. HIGH NEAR 20. NORTHWEST WINDS 10 TO 20 MPH. DALLAS-MADISON-POLK-WARREN- INCLUDING THE CITIES OF...DES MOINES...INDIANOLA 352 AM CST MON FEB WINTER WEATHER ADVISORY FOR THIS AFTERNOON AND THIS EVENING....TODAY...CLOUDY WITH A CHANCE OF FREEZING DRIZZLE OR DRIZZLE THIS MORNING...THEN WIDESPREAD SNOW THIS AFTERNOON. ACCUMULATION 1 TO 2 INCHES. TURNING COLDER. WINDY. TEMPERATURES FALLING INTO THE UPPER 20S. NORTH WINDS 15 TO 25 MPH...GUSTING TO 35 MPH FROM LATE MORNING ON. CHANCE OF PRECIPITATION 80 PERCENT..TONIGHT...WIDESPREAD SNOW EARLY...THEN MOSTLY CLOUDY WITH SCATTERED FLURRIES FROM LATE EVENING ON. TOTAL ACCUMULATION...1 TO 3 INCHES. BRISK WITH BLOWING AND DRIFTING SNOW. LOW IN THE MID TEENS. NORTHWEST WINDS 15 TO 25 MPH...GUSTING TO 30 MPH. CHANCE OF SNOW 80 PERCENT..TUESDAY...PARTLY SUNNY. HIGH IN THE LOWER 20S. NORTHWEST WINDS 10 TO 20 MPH.

RWFS Forecast 9Z – 3 Feb 2003 RUN

RWFS – predicted storm totals QPF (inches) Snowfall (inches)

Forecast at Ames (reprocessed) PRETREAT w/110 brine– 17Z (11am)

Forecast at Des Moines (rep.) PRETREAT w/110 brine – 17Z (11am)

The event – 2/3/03, 12-15Z AMW: 1 o C, OVC DSM: 2 o C, OVC AMW: 1 o C, OVC DSM: 1 o C, OVC + +

The event – 2/3/03, 18-21Z AMW: 1 o C, OVC DSM: 1 o C, OVC AMW: -2 o C, +SN DSM: -1 o C, SN + +

The event – 2/4/03, 0-3Z AMW: -5 o C, BLSN DSM: -5 o C, BLSN AMW: -9 o C, “UP” DSM: -8 o C, BLSN + +

A closer look – important features

Forecast vs. Observed 2/3/03 – 9Z RUN QPF SNOW

Temperature forecast: Ames noon 6pm mid 6am noon 6pm

Treatment comparison: Ames 6am noon 6pm mid 6am noon

Temperature forecast: Des Moines noon 6pm mid 6am noon 6pm

Treatment comparison: Des Moines 6am noon 6pm mid 6am noon

Light Event Summary RWFS forecast –Temperature: Fine during event, rapid cooling after SN –Precipitation: location, timing, amount, type All reasonable Treatment –Reasonable given forecast –Matched reality well, except for… Late plowing & salting due to roads icing over & BLSN Lessons –Use a “whole storm” perspective for rec. treatments –Method to handle or alert for blowing snow treatments Wind speed, direction – local knowledge is key for treatment