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… +

NWS Forecasts, 4am (9Z) Feb 14 IAZ047> BOONE-JASPER-MARSHALL-POWESHIEK-STORY-TAMA- INCLUDING THE CITIES OF...AMES...BOONE...GRINNELL...MARSHALLTOWN... NEWTON 357 AM CST FRI FEB 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. IAZ > AUDUBON-CRAWFORD-DALLAS-GUTHRIE-POLK- INCLUDING THE CITIES OF...DENISON...DES MOINES 357 AM CST FRI FEB 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 Forecast 3Z – 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: -1 o C, BKN DSM: 0 o C, OVC AMW: 0 o C, OVC DSM: 2 o C, -RA + +

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 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 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: 0 o C, OVC DSM: 1 o C, -RA AMW: -3 o C, -SN DSM: -2 o C, +SN + +

The event – 2/15/03, 6am-12pm AMW: -6 o C, -SN DSM: -6 o C, +SN AMW: -7 o C, -SN DSM: -7 o C, -SN + +

The event – 2/16/03, 6pm AMW: -7 o C, BKN, SNE1803 DSM: -7 o C, OVC, SNE2030 +

A closer look – important features

Forecast vs. Observed 2/14/03 – 3Z RUN QPF SNOW 10.9

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

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

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)