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Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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492 FXUS65 KTFX 161500 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 900 AM MDT Fri Aug 16 2024 .SYNOPSIS... A lingering disturbance will keep scattered showers and thunderstorms over North Central Montana today, but fewer storms expected over Southwest Montana. High pressure aloft will bring warmer and drier conditions for Saturday, but a southwest flow aloft will then bring chances for showers and thunderstorms each day next week. && .UPDATE... Dense fog in the West Yellowstone area is beginning to diminish and will clear up over the course of the next hour. Haze from wildfires remains along the High-Line and in Fergus county this morning and will affect those areas through the day today. Showers and thunderstorms will affect most of North-central, Central, and Southwestern Montana today. For the update high temperatures across the plains of North- central and Central Montana were increased to better match current observations. Sky grids were adjusted to better match current satellite imagery trends. Pops in Hill, Blaine, Choteau, and Fergus Counties were increased this morning to better match current radar trends. The rest of the forecast is on track. -IG && .AVIATION... 16/12Z TAF Period Scattered showers and perhaps a rumble of thunder or two will impact the Hi-Line terminals through 16/18Z. Patchy dense fog will continue over some southwest valleys including KWYS through 16/16Z. Smoke and haze from regional wildfires may compromise diurnal slantwise visibility for many locations, with some periods of MVFR or near MVFR visibility restrictions for KHVR and KLWT. Another disturbance advances northeastward into the region this afternoon and evening for more scattered showers and thunderstorms and associated brief downpours, gusty winds, and lightning. Once again some of this activity will persist into the overnight hours tonight. Light winds are generally expected outside of showers and thunderstorms. - RCG Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 547 AM MDT Fri Aug 16 2024/ Key Points: - Another round of scattered showers and thunderstorms this afternoon and evening, some with gusty winds and heavy downpours - Near to slightly above normal temperatures for much of next week with chances of thunderstorms each day Today through Saturday... The most immediate concern this morning will be the potential for areas of fog and low clouds to form in the valleys of Southwest and Central Montana, as well as on the Rocky Mountain Front, where showers and thunderstorms persisted until around midnight. Am not anticipating dense fog conditions at this time, but will monitor the situation. Otherwise, a slow-moving shortwave trough over North Central Montana will continue scattered showers and thunderstorms there into this evening; farther south, isolated showers and thunderstorms are forecast to develop over Central and Southwest Montana this afternoon. The scattered storms to the north will have precipitable water values of 1 to 2 standard deviations above normal, making brief heavy downpours a possibility with wind gusts up to 40 mph. However, the storms to the south will not have as much moisture to draw from, and downdraft instability values are forecast to be a bit higher there, so there is less of a potential for heavy downpours, but gusts could reach 50 mph at times, similar to those on Thursday. Overall, though, wind shear should be fairly weak, so severe storms are not expected. Weak high pressure aloft is then forecast to move in overnight and into Saturday, which should help dry out and warm up the forecast area. Slightly below normal temperatures today should warm to near seasonal averages on Saturday. Sunday through next Friday... Ensemble model forecast clusters tend to be in agreement in developing a fairly stagnant weather pattern for much of this period. The axis of a strong high pressure ridge will extend from the Southern Great Plains north into Eastern Montana, which should keep temperatures generally 5 to 10 degrees warmer than normal. However, a deep low pressure trough off the Pacific Coast will maintain an unstable southwesterly flow aloft with a tap into Pacific and monsoonal moisture, keeping at least a chance of showers and thunderstorms for each day, with some storm potentially becoming strong. As of the latest model runs, the highest chance for showers and storms will be on Monday. Model blend guidance indicates a lowering of temperatures a bit late next week, with the potential for the low pressure to start pushing the ridge slightly east. -Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 82 53 85 55 / 40 20 0 0 CTB 75 47 81 52 / 70 30 0 10 HLN 82 54 88 57 / 50 20 0 0 BZN 83 47 88 54 / 30 30 0 0 WYS 72 38 80 44 / 10 10 0 20 DLN 77 46 83 52 / 30 20 0 10 HVR 85 55 87 59 / 40 60 0 0 LWT 81 49 84 56 / 50 30 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls