FXUS65 KTFX 282052 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 252 PM MDT Tue May 28 2024 .SYNOPSIS... Showers and thunderstorms continue today with some isolated severe gusts possible primarily across west Central/North Central, and Southwestern Montana. By Wednesday afternoon, precipitation spreads east to eastern Central/North-Central and Southwest Montana. Gusty winds are possible along the Rocky Mountain Front Wednesday. By Thursday, precipitation shifts north to North-Central Montana. Warmer and drier weather returns for Friday and Saturday. && .DISCUSSION... Tonight Through Tomorrow Morning Current satellite shows cumulus clouds and a few showers popping up along Southwest MT, the Continental Divide. The upper level shortwave and a cold front will continue to initiate afternoon showers and thunderstorms. The Storm Prediction Center has the Inverness to Bozeman corridor and west in a Marginal Risk for some isolated severe wind gusts(5%). Mesoscale analysis shows instability building in (up to 1,000 J/kg of CAPE). This along with deep inverted V's vertical profile soundings support an isolated severe wind gust(58mph) threat. Small hail can also accompany any stronger storm. Another impact we will watch for is for higher mountain snowpack run off with heavier precipitation from thunderstorms along the Continental Divide. Precipitable water(PWAT) along the higher end amounts from models of 0.7-0.8" indicate there can be some heavier rainfall with showers/storms. The Weather Prediction Center has the Continental Divide in a Marginal Risk for excessive rainfall. Meaning, there's a 5%-15% of exceeding flash flood guidance through early Wednesday morning. However, there's a 20-40% of the immediate eastern slopes of the Rocky Mountains receiving a half inch of precipitation. This should keep runoff impacts limited but something we will continue to monitor. Storms wind down as the sun sets tonight, but showers continue to be scattered to widespread along the cold front through Wednesday morning. Wednesday With the upper level trough still in the region and the cold front propagating east across the CWA, there will be redevelopment of widespread precipitation Wednesday afternoon. The bulk of the heavier precipitation will mostly be from southwest Madison County to Lewistown line and to the southeast. Although the thunderstorm risk will be lower tomorrow afternoon, precipitation concerns still linger. The Weather Prediction Center has a Marginal Risk for excessive rainfall(5-15% of exceeding flash flood guidance)along that corridor. Probabilities are showing a 10-20% of precipitation amounts exceeding 1" for the Madison/Gallatin Counties and Big Snowy mountains. Warmer rain falling on the snowpack can melt snow and increase surface run off. Since models keep higher end precipitation amount to 1" of QPF and impacts on rivers don't look to be widespread, I am holding off on Hydrology highlights for now. However, we will continue to monitor the situation. Look in the HYDROLOGY section for more information. In addition to precipitation on Wednesday, gusty conditions are possible along the Rocky Mountain Front. 700mb winds between 30-45kts and a pressure gradient force sets up along the Rocky Mountain Front Wednesday through Thursday morning. Probabilistic guidance shows most of the gusty winds stay along the immediate eastern slopes of the Rocky Mountain Front. Locations along the adjacent plains of the Northern Rocky Front through Cut Bank have a 40-60% of exceeding 55mph (High Wind Warning Criteria). Since the threat of winds reaching High Wind Warning criteria is more isolated, I have hold off of any wind highlights for now. Thursday through Friday As the upper level trough propagates eastwards Thursday, we transition into northwest flow aloft. An upper level disturbance tries to clip North Central MT/Central MT mountains on Thursday, bringing lower end, light precipitation chances. Probabilistic guidance shows a 20-40% of those locations receiving at least a tenth of an inch of precipitation. By Friday, dry and warmer weather moves in, moving temperatures up close to seasonable averages. -Wilson Saturday through next Tuesday... On Saturday a weak upper-level ridge moves over North-central, Central, and Southwestern Montana. This will warm up temperatures and keep most of North-central and Central Montana dry with some precipitation chances for Southwestern Montana. On Sunday cluster analysis shows that an upper-level ridge remains over North-central, Central, and Southwestern Montana which will allow temperatures to warm up on Sunday. On Monday cluster analysis keeps the upper-level ridge over the area. Two of the clusters have a very strong ridge over North-central, Central, and Southwestern Montana. This could cause hot temperatures for the area. This will need to continue to be monitored. Next Tuesday three clusters (81% of ensemble members) keep the upper-level ridge over North-central, Central, and Southwestern Montana. The other cluster (19% of ensemble members) shows an upper-level trough beginning to move over Montana. This indicates that the weather pattern has the potential to change for the middle of next week. -IG && .AVIATION... 28/18Z TAF Period VFR conditions are expected to prevail across North Central and Southwestern Montana this afternoon ahead of the development of a few showers and thunderstorms this evening, with the threat area generally being along and west of a line from KHVR to KGTF to KHLN to KEKS. Given the relatively dry air at the surface, watch for strong downdrafts and strong outflow winds that produce turbulence near the surface. Showers will weaken and move south and east overnight and tomorrow, resulting in a few additional rain showers and thunderstorms across the area on Wednesday. Ludwig Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... Showers and thunderstorms today and tomorrow may bring heavier bursts of precipitation. Today, the main focus is along the Continental Divide and tomorrow, it shifts to across Central, North Central, and Southwest Montana. Rain falling on warm winter snowpack can increase the melting of snow and runoff from the mountains. River hydrographs indicate rivers should be able to handle the increased runoff. However, we can't rule out the potential of a few localized areas along smaller streams and creeks for increased flow and minor flooding, especially near the Madison and Gallatin Mountains. We will continue to monitor the situation for possible flood highlights. -Wilson && .PRELIMINARY POINT TEMPS/POPS... GTF 52 65 41 62 / 40 60 0 20 CTB 48 60 38 60 / 80 30 10 20 HLN 52 64 41 63 / 60 50 10 10 BZN 46 59 34 59 / 30 90 50 10 WYS 42 59 30 53 / 30 90 60 10 DLN 46 62 33 60 / 60 80 20 0 HVR 54 67 41 63 / 20 50 10 50 LWT 49 62 36 57 / 20 90 30 20 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls