Verification of the RWFS(Road Weather Forecast System)

Ben C. Bernstein

Jamie Wolff, Seth Linden

NCAR/RAP

Boulder, CO

Purpose and Presentations• Take a close look at key aspects

– Quality, performance…

• Case studies– What did the forecasts look like before events

• Heavy event: 2/15/03• Light event: 2/4/03

– How did the case evolve• Key factors

– Recommended vs actual treatments (two I-35 segments)

• Bulk statistics– Individual sites and all Iowa sites combined– Weather parameters– Road temperature

• Thanks to IA DOT & CTRE – data collection

Road Segments

A heavy snow event:Feb 14-16, 2003

2/14/03 – 6Z (midnight)A classic storm was setting up…

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NWS Forecasts, 4am (9Z) Feb 14IAZ047>050-061-062-142157-

BOONE-JASPER-MARSHALL-POWESHIEK-STORY-TAMA-

INCLUDING THE CITIES OF...AMES...BOONE...GRINNELL...MARSHALLTOWN... NEWTON

357 AM CST FRI FEB 14 2003

...WINTER STORM WARNING FOR TODAY AND TONIGHT...

.TODAY...WIDESPREAD FREEZING RAIN...SNOW...OR SLEET. ACCUMULATION 2 TO 3 INCHES. TEMPERATURES STEADY IN THE UPPER 20S. EAST WINDS 10 TO 20 MPH. CHANCE OF PRECIPITATION 90 PERCENT.

.TONIGHT...WIDESPREAD SNOW. TOTAL ACCUMULATION 4 TO 6 INCHES. BRISK WITH BLOWING AND DRIFTING SNOW. LOW IN THE MID TEENS. NORTHEAST WINDS 15 TO 25 MPH...GUSTING TO 30 MPH. CHANCE OF SNOW 80 PERCENT.

.SATURDAY...CLOUDY WITH A CHANCE OF SNOW. HIGH IN THE LOWER 20S. NORTHEAST WINDS 10 TO 20 MPH. CHANCE OF SNOW 50 PERCENT.

.SATURDAY NIGHT...PARTLY CLOUDY. LOW NEAR 10.

IAZ044-057>060-142157-

AUDUBON-CRAWFORD-DALLAS-GUTHRIE-POLK-

INCLUDING THE CITIES OF...DENISON...DES MOINES

357 AM CST FRI FEB 14 2003

...WINTER STORM WARNING FOR TODAY AND TONIGHT...

.TODAY...WIDESPREAD FREEZING RAIN...RAIN...OR SLEET. ACCUMULATION 1 TO 2 INCHES. HIGH IN THE LOWER 30S. EAST WINDS 10 TO 20 MPH. CHANCE OF PRECIPITATION 90 PERCENT.

.TONIGHT...WIDESPREAD SNOW. TOTAL ACCUMULATION...4 TO 7 INCHES. BRISK WITH BLOWING AND DRIFTING SNOW. LOW IN THE MID TEENS. NORTHEAST WINDS 15 TO 25 MPH...GUSTING TO 30 MPH. CHANCE OF SNOW 80 PERCENT.

.SATURDAY...CLOUDY WITH A CHANCE OF SNOW. HIGH IN THE LOWER 20S. NORTHEAST WINDS 10 TO 20 MPH. CHANCE OF SNOW 50 PERCENT.

.SATURDAY NIGHT...PARTLY CLOUDY. LOW NEAR 10 ABOVE.

RWFS Forecast3Z – 14 Feb 2003 RUN

RWFS – predicted storm totals

QPF (inches) Snowfall (inches)

Storm totals – much of QPF expected to fall as freezing rain

Forecast at Ames (reprocessed)

Forecast at Des Moines (rep.)

The event – 2/14/03, 6am-12pm

AMW: -1oC, BKN

DSM: 0oC, OVC

AMW: 0oC, OVC

DSM: 2oC, -RA

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2/14/03, 11a.m. (17Z)Changes: NWS & RWFS

DES MOINES IA-HENDERSON IL-HENRY IA-JEFFERSON IA-KEOKUK IA-LOUISA IA-

MERCER IL-WARREN IL-WASHINGTON IA-

INCLUDING THE CITIES OF...ALEDO...BURLINGTON...FAIRFIELD...MONMOUTH...

MOUNT PLEASANT...OQUAWKA...SIGOURNEY...WAPELLO...WASHINGTON

1137 AM CST FRI FEB 14 2003

UPDATED TO ADJUST TIMING OF WATCH AND MAKE TWEAKS TO PCPN/TEMPS

...WINTER STORM WARNING LATE THIS AFTERNOON THROUGH SATURDAY...

.THIS AFTERNOON...OCCASIONAL LIGHT RAIN OR DRIZZLE...POSSIBLY MIXED WITH SLEET. PRECIPITATION CHANGING TO ALL SNOW LATE. HIGH IN THE UPPER 30S. EAST WIND 10 TO 20 MPH. CHANCE OF PRECIPITATION 80 PERCENT.

.TONIGHT...SNOW AND BLOWING SNOW. ACCUMULATIONS 3 TO 5 INCHES. WINDY WITH A NORTHEAST WIND 20 TO 30 MPH. LOW IN THE LOWER 20S. CHANCE OF SNOW 90 PERCENT.

.SATURDAY...SNOW TAPERING TO FLURRIES. CONTINUED WINDY WITH BLOWING SNOW. TOTAL ACCUMULATIONS...5 TO 9 INCHES. TEMPERATURES STEADY IN THE MID 20S. NORTHEAST WIND 20 TO 30 MPH...DIMINISHING TO 15 TO 25 MPH. CHANCE OF SNOW 80 PERCENT.

BOONE-MARSHALL-STORY-TAMA-

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

350 PM CST FRI FEB 14 2003

...WINTER STORM WARNING FOR TONIGHT...

.TONIGHT...FREEZING RAIN...RAIN...OR SLEET THIS EVENING…THEN CHANGING TO ALL SNOW...HEAVY AT TIMES. TOTAL ACCUMULATION...4 TO 8

INCHES. WINDY WITH BLOWING AND DRIFTING SNOW. LOW IN THE MID TEENS. NORTHEAST WINDS 15 TO 30 MPH...GUSTING TO 40 MPH.

.SATURDAY...CLOUDY WITH A CHANCE OF SNOW. BRISK. HIGH IN THE LOWER 20S. NORTHEAST WINDS 15 TO 25 MPH...GUSTING TO 30 MPH. CHANCE OF SNOW

50 PERCENT.

The event – 2/14/03, 6pm-12am

AMW: 0oC, OVC

DSM: 1oC, -RA

AMW: -3oC, -SN

DSM: -2oC, +SN

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The event – 2/15/03, 6am-12pm

AMW: -6oC, -SN

DSM: -6oC, +SN

AMW: -7oC, -SN

DSM: -7oC, -SN

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The event – 2/16/03, 6pm

AMW: -7oC, BKN, SNE1803

DSM: -7oC, OVC, SNE2030

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A closer look – important features

Forecast vs. Observed 2/14/03 – 3Z RUN

QPF

SNOW

10.9

Temperature forecast: Ames

-12

-10

-8

-6

-4

-2

0

2

4

3 5 7 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 15 17 19 21 23 1

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 6pm

-20

-15

-10

-5

0

5

10

3 5 7 9 11 13 15 17 19 21 23 1 3 5 7 9 11 13 15 17 19 21 23 1

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

Temperature forecast: Des Moines

noon 6pm mid 6am noon 6pm

Treatment comparison: Des Moines

6am noon 6pm mid 6am noon 6pm

Heavy Event Summary• RWFS forecast

– Temperature: CRITICAL– Precipitation: location, timing, amount– PRECIPITATION TYPE– Improved later on 2/14, ditto for others

• Treatment– Reasonable given forecast– Matched reality?

• Lessons– Value of COND probability info for precipitation type– Forward error correction (TEMP)