Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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060 FXUS65 KTFX 261527 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 927 AM MDT Sun May 26 2024 .UPDATE... Satellite imagery this morning shows a compact shortwave disturbance (vort center) tracking east just north of the MT/AB border. Enhanced wind speeds aloft to the south of this feature as well as a moderate surface pressure gradient to the SW of a low/trough straddling the AB/SK border will maintain breezy to windy conditions across most of the forecast area through this afternoon. Isolated showers associated with the Canadian disturbance will become more numerous across the Hi-line area this afternoon with a few isolated thunderstorms possible across mainly Hill/Blaine counties (20-30% along US-2 to 40% near the SK border). CAPE and shear are relatively low (<500J/Kg; <25Kts) so expect cells to be short-lived and weak, though low freezing levels should support some very small hail in some cells. There could also be a brief period of favorable conditions for cold air funnels early this afternoon, primarily across Hill and Blaine counties. Hoenisch && .SYNOPSIS... Today it will breezy and mostly sunny for all but the Hi- Line where there will be showers and thunderstorms this afternoon and evening. There will be gusty winds along the Rocky Mountain Front Today and Wednesday. Monday through Tuesday it will warm up with thunderstorm chances Tuesday afternoon and evening. Wednesday through Friday there will be an upper-level trough in place that will cool down temperatures and bring showers and thunderstorms to the area. && .AVIATION... 26/12Z TAF Period VFR conditions are expected through at least 27/12Z across North Central (KCTB, KHVR), Central (KLWT, KGTF, KHLN), and Southwest (KBZN, KEKS, KWYS) Montana, unless otherwise noted. The more widespread concern for this forecast period is the wind. A weak shortwave trough moving east along the Canadian border will increase the westerly winds aloft over the area through around 03Z, causing mountain wave turbulence. There will also be widespread low level wind shear over North Central and Central Montana until around 15Z, then gusty winds should translate down to the surface over the area. Winds will mostly gust between 25 and 35 kt, likely exceeding 45 kt gusts along the Rocky Mountain Front. Winds should decrease after 03Z as the shortwave exits the area. Otherwise, areas of lingering mid- and high-level cloudiness over the area will mostly be cleared out by 18Z. However, patchy fog may still form in the valleys of Southwest Montana between now and then, potentially causing periods of MVFR/IFR visibility. -Coulston Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 545 AM MDT Sun May 26 2024/ Today through Memorial Day... This morning in the Gallatin Valley and portions of far Southwestern Montana fog could form after skies clear. Some model soundings and probabilistic guidance show the potential for this fog while others do not. Only for isolated locations in those areas fog has the potential to reduce visibility down to a half mile or less. Today an upper-level ridge begins to move into the area above North-central, Central, and Southwestern Montana. Ahead of this ridge there is an upper-level shortwave that will move across the Hi-Line this afternoon and evening bringing rain showers and thunderstorms. For everywhere else outside of the West Yellowstone area it will be mostly sunny and slightly cooler than seasonal averages. Due to a moderately strong surface gradient there will gusty winds primarily along the Rocky Mountain front Today. Along the Rocky Mountain Front there is a 70 - 90% chance for wind gusts exceeding 55 mph Today. Along the plains adjacent to the Rocky Mountian Front there is 30 - 50% chance for wind gusts exceeding 55 mph Today. Elsewhere across portion of North- central and Central Montana there is 40 - 70% chance for wind gusts exceeding 47 mph Today. On Memorial Day the upper-level ridge remains in place over North-central, Central, and Southwestern Montana. Memorial Day will be sunny and dry across the area with about seasonal average temperatures. Tuesday through Wednesday... On Tuesday the upper-level ridge remains in place over North-central, Central, and Southwestern Montana and so temperatures will continue the warming trend. On Tuesday across North-central Montana there is a 95% chance for temperatures 80 or greater in the Golden Triangle Region of Central and North-central Montana (Cut Bank to Great Falls to Havre) and the Helena and Gallatin Valleys. Tuesday late afternoon through Wednesday morning a cold front begins to move east across North- central, Central, and Southwestern Montana. This combined with southwest flow aloft will cause the atmosphere to become unstable. This will result in the potential for thunderstorms some of which could be severe. These thunderstorms have the potential to occur Tuesday late afternoon through the evening. At this time it appears unlikely that there will be widespread severe thunderstorms on Tuesday. On Tuesday there is a 10 - 30% chance for locations across North-central, Central, and Southwestern Montana receiving a tenth of inch of rain or greater. Monitor the forecast for updates. On Wednesday an upper-level trough associated with the cold front begins to move over North-central, Central, and Southwestern Montana. This will bring cooler temperatures and rain to most of the area on Wednesday. Along and south of the Highway 200 Corridor in Central Montana there is 30 - 50% chance for a half inch of rain or greater on Wednesday. Other locations of North-central, Central, and Southwestern Montana have a 20 - 40% chance for seeing a quarter inch of rain or more on Wednesday. On Wednesday due to strong flow aloft and a strong surface pressure gradient there is a 60 - 80% chance for wind gusts exceeding 55 mph along the Rocky Mountain Front. Along the plains adjacent to the Rocky Mountian Front there is a 65% chance for wind gusts exceeding 47 mph on Wednesday. Wednesday afternoon and early evening along with the rain there is the potential for thunderstorms some of which could be severe. Continue to monitor the forecast for details. Thursday through next Sunday... On Thursday the upper-level trough remains in place over North-central, Central, and Southwestern Montana. Showers and thunderstorms are possible across the area on Thursday. The thunderstorms will not be severe. On Thursday there is a 20 - 40% chance for locations across North-central, Central, and Southwestern Montana receiving a tenth of an inch of rain (total liquid for mountain locations) or more. On Thursday for the mountains of North-central, Central and Southwestern Montana there is 40 - 60% chance for receiving a tenth of an inch of snow or more. On Friday clusters indicate that an upper-level trough remains in place over North-central, Central, and Southwestern Montana which will keep unsettled weather in place for the area on Friday. On Saturday two clusters (66% of ensemble members) have an upper-level ridge in place over North-central, Central, and Southwestern Montana. The other two clusters (44% of ensemble members) have the upper-level trough remain in place over the area on Saturday. This indicates uncertainty in the weather for Saturday at this time. Next Sunday three clusters (80% of ensemble members) have an upper-level ridge over North-central, Central, and Southwestern Montana. Next Sunday one cluster (20% of ensemble members) has the upper-level trough remaining over the area. This indicates that by Sunday the weather pattern will most likely change to have warm and calm weather for North-central, Central, and Southwestern Montana. -IG && .PRELIMINARY POINT TEMPS/POPS... GTF 62 40 72 45 / 10 0 0 0 CTB 60 39 70 42 / 10 0 0 0 HLN 65 44 75 48 / 0 0 0 0 BZN 64 37 71 41 / 10 0 0 0 WYS 55 32 65 35 / 20 10 0 0 DLN 62 37 72 41 / 0 0 0 0 HVR 65 42 73 45 / 50 20 0 0 LWT 59 37 66 43 / 10 10 0 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls