impactful winter storm late tonight wednesday morning...evening •relative humidity ......

Impactful Winter Storm

Late Tonight–Wednesday Morning

Situation Briefing

Monday, September 7, 2020

Bill Mokry, Meteorologist

National Weather Service

Chris Jones, Meteorologist

National Weather Serviceweather.gov/cheyenneNWSCheyenne

Main Points

• Red Flag Warnings in effect until this evening

• Relative Humidity10-15%

• West-northwest wind 20 to 30 mph with gusts around 40 mph

• Sharp wind shift occurring between 5 and 7 PM along theI-80 corridor

Red Flag Warnings in Effect into early Monday evening

Cheyenne , WYWEATHER FORECAST OFFICE

weather.gov/cheyenne9/7/2020 3:02 PM

Zones 277, 278, 279Until 8 PM

Main Points

• Winter Storm Warningstonight and Tuesday, lingering until 6 AM Wed overSE Wyoming and the Nebraska Panhandle

• Winter Weather Advisories tonight and Tuesday, lingering until 6 AM Wed overSE Wyoming and the Nebraska Panhandle

• Freeze Warnings in effect 10 PM Tuesday –9 AM Wednesday

• High Wind WarningJackson Valley in effect 9 PM Mon to 9 AM Tue

Impactful Winter Storm Late Tonight – Early Wednesday



Main Points (continued)

• What we do know:

• Potent winter storm and sub-freezing temperatures will affect Most of

Wyoming and northern Nebraska Panhandle

• Potential Impacts: • Heavy snowfall over a significant portion of elevations over 5500 feet

• Rain/Snow mix below 4000 feet, transitioning late evening/overnight

• Blowing snow with strong winds creating areas of limited visibility and in some cases damaging downsloping wind (Jackson Valley and Sweetwater County)

• Sub-freezing temperatures to allow for frozen accretion on surfaces and the end of the effective growing season

• Hazardous driving conditions likely

• Localized power outages and downed tree limbs possible




Main Points Cont.

• What we don’t know: • Exactly where the heaviest snow will fall

• There is still some uncertainty

• How quickly snow rates will overtake surface temperatures and start accumulating




Precipitation Transition Timing

Cheyenne, WY

Laramie, WY

Rawlins, WY

Douglas, WY

Chadron, NE

Alliance, NE

Scottsbluff, NE

Sidney, NE

Mix

SnowHeavy Snow

Rain

Precipitation will start as rain this evening and transition to snow late tonight through Tuesday morning. The Nebraska Panhandle will be the last to transition from rain to snow, occurring early- to mid-morning on Tuesday from northwest to southeast.


1-3”

1-3”

9/7/2020 3:02 PM

Overview

• Winter Weather Headlines in effect tonight and Tuesday, lingering until 6 AM Wednesday over southeast Wyoming and the Nebraska Panhandle

• Freeze Warnings in effect 10 PM Tuesday – 9 AM Wednesday

• High Wind WarningJackson Valley in effect9 PM Mon to 9 AM Tue




Overview

Potential Impacts: • Heavy snowfall over a significant portion of elevations over 5500 feet

• Rain/Snow mix below 4000 feet transitioning late evening/overnight

• Blowing snow with strong winds creating areas of limited visibility

• Sub-freezing temperatures to allow for frozen accretion on surfaces and end of effective growing season, certainly by Wednesday morning

• Hazardous driving conditions likely

• Localized power outages and downed tree limbs possible

What We Do Not Know: • Exactly where the heaviest snow will fall - some uncertainty still remains

• How quickly snow rates will overtake surface temps and start accumulating




Impactful Winter Storm Monday Night –Wednesday Morning

NWS Cheyenne, Wyoming

weather.gov/cheyenneNWSCheyenne

National Weather Service Cheyenne

1-800-269-6220 (toll free)

307-772-2468weather.gov/cheyenne

NWSCheyenne

impactful winter storm late tonight wednesday morning...evening •relative humidity ......

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