it’s not 40”, but still my biggest storm (25.2”)

January 14, 200420th WAF & 16th NWP Conference/AMS Annual Meeting

Ed Szoke

Performance of Various Operational and Experimental Numerical Forecasts for the

March 2003 Colorado Snowstorm

Ed Szoke* Brent Shaw* and Paul SchultzNOAA Forecast Systems Lab

Boulder, [email protected]

Dave Barjenbruch Boulder WFO

*In collaboration with the Cooperative Institute for Research in the Atmosphere (CIRA), Colorado State University, Fort Collins, Colorado


Ed Szoke

It’s not 40”, but still my biggest storm (25.2”)


Ed Szoke

Impressive snow in the foothills...87.5” at 9000 feet in Coal Creek Canyon southwest of Boulder


Ed Szoke

The snow was quite heavy with lots of broken limbs and roof collapses


Ed Szoke

It’s not 40”, but still my biggest storm (25.2”)


Ed Szoke


Ed Szoke

Ski area snow reports

Loveland Ski Area...at Continental Divide on I70


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I70….closed for over 2 days


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The widespread snowfall boosted mountain snowpack to normal


Ed Szoke

• There are MANY interesting aspects of this massive storm

• Longer range (8-15 days) model forecasts indicated potential

240 h forecast from the GFS run initialized at 0000 UTC on 8 March and valid 0000 UTC on 18 March


Ed Szoke

• Longer range (8-15 days) model forecasts indicating potential

• Drifting to poorer forecasts in the mid-range

GFS 132 h forecast initialized 0000 UTC on 13 March and valid 1200 UTC on 18 March. This forecast produces a major storm in the Midwest but very little snow for the Front Range of Colorado.


Ed Szoke

Use of GFS and Canadian ensemble forecasts as well as multi-model “ensembles” to make a better forecast. GFS ensemble shown below for same 132h forecast.


Ed Szoke

Then quite good NWP forecasts in the < 2-3 day range. This Eta 84h forecast issued 1200 UTC Fri/14 Mar and valid 0000 UTC Tue/18 Mar is quite good.

500 mb height, vorticity and wind

Surface pressure, thickness, and precip


Ed Szoke

Outline

• Then quite good NWP forecasts in the < 2-3 day range

• Including impressive 5+ ft. model forecasts for the foothills

• Excellent 1-1.5 day NWS snowfall forecasts for historic event

• Included forecast of 3-8 ft. of snow for the foothills

• Smaller scale details…including the “Lyons snow hole”


Ed Szoke

Smaller scale details…including the “Lyons snow hole”


Ed Szoke

Outline...continued

• A significant forecasting aspect of the storm was rain versus snow at the lower elevations where most of the population is located

• Although a Winter Storm Warning was issued for the Front Range cities as early as Sunday (valid from Monday night into Wednesday)...there were conflicting signals as late as Monday evening about when (if?) the rain would change to snow!

• The operational models (Eta, RUC) were indicating that temperatures would be too warm for snow perhaps until late Tuesday

• However, it was noted that actual surface temperatures were colder then forecast or even analyzed by the models (at 00z/18 Mar)

• The focus of the rest of this talk will be on this issue and examining the 0000 UTC/18 March analyses and forecasts


Ed Szoke

But first...a quick overview of the storm. 500 mb analysis at 0000 UTC/18 Mar


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500 mb analysis for 1200 UTC on Tue/18 March


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500 mb analysis for 0000 UTC on Wed/19 March


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Focus on the 0000 UTC/18 March time period

• Critical forecast issue was when the rain would change to snow.

• First a look at some observations


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1800 UTC/17 March IR image and surface observations

Most of the precipitation is north of CO with a surface low taking shape over se CO.


Ed Szoke

1800 UTC/17 March radar and surface observations

Mild conditions along the Front Range with some light rain. Quite warm over eastern CO. Main precip area is in WY with cooling conditions there.


Ed Szoke


Mi


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Ed Szoke


Still raining along most of the Front Range but barrier jet that had been forming to the north producing strong northerly flow down the Front Range and advecting colder air southward from se WY.


Ed Szoke


Precipitation has changed to snow with several inches of accumulation in many areas along the Front Range.


Ed Szoke




Ed Szoke

Composite radar with obs at 21z 17 Mar

Convection becoming widespread on the Plains


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Eta cross-section of RH (image), wind, theta, T, 18h forecast valid 06z 18 Mar

Still has the nly winds along the Front Range.Interesting reverse flow w of the Divide…does this effectively raise the mtn height and coupled with the very moist and deep ely flow help yield the S++ west of the Divide?


Ed Szoke

Comparison of radar and obs at 00z 18 Mar with Eta forecast


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Closeup reveals the wind is captured well but temps too warm


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Similar problem with the 6h forecast from the 18 UTC Eta


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Closeup of 18z run.


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Eta analysis of surface T and wind with radar for 00z 18 Mar

Even the analysis misses the colder temps near the Front Range.


Ed Szoke

Closeup of the 00z analysis of the Eta run


Ed Szoke

00z/18 Mar Eta 6h forecast of surface T, wind and pcpn with radar for 06z 18 Mar

The warmer temps near the Front Range in the analysis carry over through 6h.


Ed Szoke

Closeup….


Ed Szoke

00z/18 Mar LAPS analysis of surface T and wind with radar for 00z 18 Mar

The LAPS analysis did do a good job, so in theory a fine scale model initialized with this analysis should do better.


Ed Szoke

Closeup of the 00z/18 Mar LAPS analysis


Ed Szoke

Composite radar with obs at 12z 18 Mar

it’s not 40”, but still my biggest storm (25.2”)

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