Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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822 FXUS65 KTFX 290605 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1205 AM MDT Tue May 29 2024 ...Updated Aviation Section... .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. && .UPDATE... Scattered thunderstorms and rain showers continue to move northeast from Southwest to North Central Montana this evening and through the overnight hours. Only minor adjustment needed to the probability of precipitation for the next 4 to 6 hours as the shower activity continues based on current surface observations and latest high resolution model guidance. The rest of the forecast is doing well and on track for tonight into tomorrow. Webb && .AVIATION... 29/06Z TAF Period VFR conditions will prevail for the KHLN, KGTF, KCTB, and KHVR terminals for this TAF period. At the KBZN, KEKS, KWYS, and KLWT terminals there is a 50% chance for thunderstorms to occur and reduce visibility to MVFR levels Wednesday afternoon and evening. Wednesday afternoon at the KBZN, KEKS, KWYS, and KLWT terminals ceilings will be reduced to MVFR levels. At the KBZN, KEKS, KWYS, and KLWT terminals there will be rain showers Wednesday afternoon and evening due to a front moving the area. At the KLWT and KWYS terminals winds will gust up to 22 kts Wednesday afternoon and evening. At the KBZN, KEKS, and KWYS terminals there is 20% chance for showers and thunderstorms during the first 6 hours of this TAF period. At the KHVR and KGTF terminals for the first 3 hours of this TAF period there is a 20% chance for thunderstorms. At the KGTF and KHVR terminals there is 50% chance for rain showers Wednesday morning. At the KHLN and KCTB terminals for the first three hours of this TAF period there is a 50% chance for thunderstorms around those terminals. For the KHLN and KCTB terminals there is 20% chance for showers and thunderstorms from 3 AM to 6 AM Wednesday morning. At the KHLN terminal there is a 50% chance for rain showers the rest of Wednesday morning. During thunderstorms there will be gusty and erratic winds. At the KGTF and KHVR terminals winds will gust up to 25 kts from the middle of this TAF period through the end. At the KCTB terminal during the middle of this TAF period through the end winds will gust up to 38 kts. At the KHLN terminal from the middle of the TAF period through the end winds will gust up to 29 kts. There will be mountain obscuration during this TAF period. During the middle and end of this TAF period there will be mountain wave turbulence. -IG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 541 PM MDT Tue May 28 2024/ 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 && .PRELIMINARY POINT TEMPS/POPS... GTF 52 65 41 62 / 50 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 / 50 90 50 10 WYS 42 59 30 53 / 40 90 60 10 DLN 46 62 33 60 / 70 80 20 0 HVR 54 67 41 63 / 60 50 10 50 LWT 49 62 36 57 / 20 90 30 20 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls