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 4BLACK HAWK-BREMER-GRUNDY-MARSHALL-STORY-TAMA-

INCLUDING THE CITIES OF...AMES...MARSHALLTOWN...

WATERLOO/CEDAR FALLS

352 AM CST MON FEB 3 2003

...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 3 2003

...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 Forecast9Z – 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: 1oC, OVC

DSM: 2oC, OVC

AMW: 1oC, OVC

DSM: 1oC, OVC

+

+

The event – 2/3/03, 18-21Z

AMW: 1oC, OVC

DSM: 1oC, OVC

AMW: -2oC, +SN

DSM: -1oC, SN

+

+

The event – 2/4/03, 0-3Z

AMW: -5oC, BLSN

DSM: -5oC, BLSN

AMW: -9oC, “UP”

DSM: -8oC, BLSN

+

+

A closer look – important features

Forecast vs. Observed 2/3/03 – 9Z RUN

QPF

SNOW

Temperature forecast: Ames

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6

6 8 10 12 14 16 18 20 22 0 2 4 6 8 10 12 14 16 18 20 22 0 2 4

Time (UTC)

Tem

p (

°C)

METAR w/o FSL

METAR w/ FSL

AMW_METAR_OB

Precip Type

RWIS w/o FSL

RWIS w/ FSL

AMW_RWIS_OB

noon 6pm mid 6am noon 6pm

Treatment comparison: Ames

6am noon 6pm mid 6am noon

Temperature forecast: Des Moines

-16

-14

-12

-10

-8

-6

-4

-2

0

2

4

6 8 10 12 14 16 18 20 22 0 2 4 6 8 10 12 14 16 18 20 22 0 2 4

Time (UTC)

Tem

p (

°C)

METAR w/o FSL

METAR w/ FSL

DSM_METAR_OB

Precip Type

RWIS w/o FSL

RWIS w/ FSL

DSM_RWIS_OB

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