Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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557 FXUS65 KTFX 181951 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 151 PM MDT Wed Sep 18 2024 .SYNOPSIS... This afternoon through tonight there will be rain showers across most of North-central, Central, and Southwestern Montana. The rain showers will end in Southwestern Montana this evening and from west to east across North-central and Central Montana by Thursday morning. Thursday it will warm up and be dry during most of the day. Unsettled weather returns to close out the work week continuing through the weekend. Early next week widespread precipitation looks to return to North-central, Central, and Southwestern Montana. && .DISCUSSION... Rest of Today... There is a surface low over Petroleum County that will track east this afternoon before moving north out of Montana by midnight tonight. This is bringing precipitation to much of North- central, Central, and Southwestern Montana this afternoon. The heaviest precipitation will be in Hill, Blaine, Choteau, Fergus, and Judith Basin Counties. The precipitation will end by early Thursday morning from west to east across North-central and Central Montana. The precipitation will end in Southwestern Montana by 6 pm tonight. There is a 40 - 80% chance for greater than a half inch of rain in Hill, Blaine, Choteau, Judith Basin, and Fergus Counties through midnight tonight. There is a 50% chance for an inch of rain or greater through midnight tonight from Havre to Fort Benton to southern Fergus County to northeastern Blaine County. For the other areas that are east of the I-15 Corridor there is a 20 - 50% chance for a tenth of an inch of rain or greater through midnight tonight. For more hydrology information see the HYDROLOGY section below. Due to the rain and clouds temperatures across North-central, Central, and Southwestern Montana will struggle to get to 60 degrees this afternoon. Due to a strong surface pressure gradient and an upper- level jet it will be windy across the plains of North-central Montana this afternoon through tonight. There is a 90% chance for wind gusts of 55 mph or greater in Fergus and Judith Basin Counties through midnight tonight. There is also a 70% chance for sustained winds of 40 mph or greater in Fergus and Judith Basin Counties through midnight tonight. As a result a High Wind Warning remains in effect for Fergus County and Judith Basin County below 5000 feet through midnight tonight. Thursday through Saturday... On Thursday an upper-level ridge moves over North-central, Central, and Southwestern Montana. As result due to clearing skies, thursday morning there is a 50% chance for fog to form in the West Yellowstone area. The upper-level ridge will warm up temperatures to around seasonal averages and bring dry conditions to the area for the day on Thursday. Between midnight and 6 AM Thursday there is 30 - 60% chance for a quarter inch of rain in Hill, Blaine, Choteau, Judith Basin, and Fergus Counties. On Friday a weak upper-level trough moves above North-central, Central, and Southwestern Montana. This will bring isolated showers to the area with slightly cooler temperatures. On Friday there is a 5 to 30% chance for a tenth of an inch of rain or greater across North- central, Central, and Southwestern Montana. On Saturday the upper- level trough remains over North-central, Central, and Southwestern Montana. This will cool temperatures down to a few degrees below seasonal averages. There will also be an isolated rain shower across North-central, Central, and Southwestern Montana. On Saturday there is a 5 - 10% chance for a tenth of an inch of rain or greater across the area. Sunday through next Wednesday... On Sunday an upper-level ridge moves over North-central, Central, and Southwestern Montana. Then an upper-level shortwave will move through the flow. This will bring a 5 - 10% chance for rain to North-central, Central, and Southwestern Montana. On Monday clusters indicate that there will be zonal flow over North-central, Central, and Southwestern Montana. This will keep unsettled weather in place for the area. On Tuesday and next Wednesday ensemble clusters and deterministic models begin to diverge. One scenario is for zonal flow to remain over North- central, Central, and Southwestern Montana. This keeps the unsettled weather in place for the area. Another scenario is for an upper- level ridge to move over North-central, Central, and Southwestern Montana. This would warm up temperatures and bring dry and calm conditions to the area. The third and final scenario is for an upper-level trough to begin to move over North-central, Central, and Southwestern Montana. This would bring cooler temperatures and widespread precipitation to the area. -IG && .AVIATION... 18/18Z TAF Period Widespread rain will continue through the remainder of the day on Wednesday as a notable weather system continues to affect North Central and Southwestern Montana. Currently, a band of moderate to heavy rain was along a line extending north of KGTF and then east to KLWT, and this band is not expected to move much through 0z or so. Expect IFR to LIFR conditions in and near this band, particularly at KLWT. Outside of this band, expect gusty winds but generally better cigs and vis, with occasional -RA brining cigs below 025 and vis under 6sm. Rain will taper off overnight, though some pockets of fog may develop at various airports, though confidence is not high enough to mention in the TAFs quite yet. Ludwig Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .HYDROLOGY... Moderate to heavy rain will continue to pivot through the Plains and island mountain ranges of North Central Montana through the remainder of the afternoon and evening. As this moderate to heavy rain continues, watch for areas of minor flooding and rockslides, especially in low lying areas and steep terrain. River flooding is not expected to be a major concern, however, as rivers remain seasonally low with adequate capacity to absorb the extra runoff. Ludwig && .PRELIMINARY POINT TEMPS/POPS... GTF 47 73 48 70 / 40 0 0 0 CTB 46 71 45 64 / 10 0 0 30 HLN 47 74 48 73 / 10 0 0 0 BZN 40 71 42 73 / 30 0 0 10 WYS 29 60 31 64 / 40 10 0 10 DLN 39 68 41 69 / 10 0 0 0 HVR 47 72 47 67 / 90 0 0 10 LWT 45 68 45 67 / 90 0 0 10 && .TFX WATCHES/WARNINGS/ADVISORIES... Flood Watch through late tonight for Bears Paw Mountains and Southern Blaine-Fergus County below 4500ft-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Snowy and Judith Mountains. High Wind Warning until midnight MDT tonight for Fergus County below 4500ft-Judith Basin County and Judith Gap-Snowy and Judith Mountains. Flash Flood Watch until 6 PM MDT this evening for Big Belt, Bridger and Castle Mountains. && $$ http://www.weather.gov/greatfalls