Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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025 FXUS65 KTFX 232019 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 219 PM MDT Thu May 23 2024 .SYNOPSIS... Unsettled conditions will continue through the end of the work week and weekend, with temperatures running below normal and chances for showers, thunderstorms, and at times mountain snow. && .DISCUSSION... Rest of today through tonight...upper level disturbance over North Central Wyoming and its associated surface low over Western South Dakota will continue to slide east and away from the Northern Rockies through the evening hours tonight. This will lead to decreasing precipitation across Southwest Montana through the remainder of the afternoon hours, with additional snow accumulations of 1-2" and isolated amounts approaching 4" across the remaining Winter Storm Warnings for the Bridger, Gallatin, and Madison Ranges. Clear skies during the early morning hours over the plains of Southern Alberta, North Central Montana, and northern portions of Central Montana allowed temperatures to warm into the 50s, which combined with unstable northwesterly flow aloft and an embedded wave tracking southeast through the flow has allowed scattered showers and isolated thunderstorms to develop. These showers and storms will track slowly east through the overnight hours tonight, bringing brief periods of heavy rain and the potential for small hail. A brief cold air funnel can not also be ruled out given H500 temperatures approaching -25C and the presence of existing vorticity associated with the longwave trough and secondary closed (H500) over Alberta and Saskatchewan. Should any cold air funnel form they would be brief and pose no danger to the public or infrastructure. - Moldan Tomorrow through Memorial Day is favored by ensemble model guidance to continue to see unsettled weather conditions through the Memorial Day weekend in terms of scattered rain showers and thunderstorms. Tomorrow is favored along the Hi-Line down to Great Falls and Lewistown for scattered thunderstorms as an upper level shortwave is forecasted to move across North Central Montana tomorrow afternoon and quickly depart our area (Fergus and Blaine Counties) by Saturday night. Then, models are favoring another upper level trough to move in for Saturday and Sunday across Southwest and North Central Montana with more coverage of rain shower and thunderstorm activity. Sunday afternoon and early evening can be periodically breezy with wind gusts as high as 40 mph across the Hi-Plains region as our upper level trough begins to depart to our east. Primary concerns for thunderstorm development this weekend is going to be lightning, heavy downpours, small hail size, and gusty erratic winds. Temperatures this weekend are also going to remain unseasonably cool with highs in the 50s and 60s and lows in the 30s (20s in mountainous terrain). Monday into Tuesday morning, upper level ridging is favored by latest ensemble model guidance to build back into the region and bring dry conditions with warm afternoon temperatures. Latest National Blend of Models 4.2 Probabilistic data suggests high temperatures reaching over 80 degrees for Tuesday is high (>75 percent) for locations from Great Falls to Havre down to Helena. Wednesday afternoon and evening into the end of next week, ensemble model guidance is still uncertain on the exact path of upper level troughing across our region. Upper level troughing could come down from Canada and bring more unsettled weather conditions to our region or it could remain to our north. What is currently favored is a cold front from the Pacific Northwest to move across our region Wednesday and Thursday bringing temperatures back to near normal (60s and low 70s) for the end of May. Webb && .AVIATION... 23/18Z TAF Period Upper level disturbance responsible for widespread rain and/or snow across Central and Southwest Montana this morning will continue to slowly pull away from the Northern Rockies through early this evening, with precipitation falling at the KBZN, KEKS, and KWYS terminals through 23/22z to 24/01z. Precipitation at these terminals is expected to transition to predominately rain or a rain/snow mix this afternoon; however, periods of snow will be possible in the heavier bursts of precipitation. These periods of snow will lead to reduced CIGS/VIS to VLIFR to IFR, with the rain or rain/snow periods being predominately MVFR. Elsewhere, MVFR to VFR conditions are expected throughout the TAF period, with showers and thunderstorms developing this afternoon and persisting through the overnight hours over the plains of North Central Montana. These showers and thunderstorms will predominately impact the KCTB and KHVR terminals. - Moldan Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PRELIMINARY POINT TEMPS/POPS... GTF 39 63 40 65 / 30 30 10 60 CTB 39 60 37 62 / 70 50 10 40 HLN 37 65 42 64 / 10 20 10 70 BZN 26 62 36 62 / 10 20 10 70 WYS 23 54 30 52 / 10 10 10 80 DLN 27 61 36 58 / 10 10 20 70 HVR 42 63 39 69 / 60 60 10 50 LWT 33 60 37 62 / 10 40 10 80 && .TFX WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 6 PM MDT this evening for Big Belt, Bridger and Castle Mountains-Gallatin and Madison County Mountains and Centennial Mountains. && $$ http://www.weather.gov/greatfalls