Area Forecast Discussion
Issued by NWS Great Falls, MT
Issued by NWS Great Falls, MT
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716 FXUS65 KTFX 220543 AFDTFX Area Forecast Discussion National Weather Service Great Falls MT 1143 PM MDT Sat Sep 21 2024 UPDATED AVIATION SECTION .SYNOPSIS... High temperatures will warm to near normal on Sunday and Monday before climbing well above normal for the remainder of the upcoming work week. Overall dry conditions are expected for much of the upcoming week; however, an isolated shower or two can`t be ruled out from Sunday afternoon through Sunday night as a fast moving disturbance moves over the Northern Rockies. && .UPDATE... No changes made with this evening`s update aside from refreshing the hourly temperatures and increasing the coverage of fog a bit. Ludwig && .AVIATION... 22/06Z TAF Period VFR conditions are forecast to continue across North Central (KCTB, KHVR), Central (KLWT, KGTF, KHLN), and Southwest (KBZN, KEKS, KWYS) Montana through at least 23/06Z. Mainly high cloudiness will move over the area in the west-northwest flow aloft through around 16Z. Patchy fog may form in some Southwest and Central Montana valleys, but the high cloudiness will keep the probability low for significantly reduced visibility at any of those terminals. As the flow aloft increases after 16Z, the potential for mountain wave turbulence increases as well. A chinook arch of mid level cloudiness will also likely form from north to south over the area; any precipitation that falls out of the clouds will likely not reach the ground. Westerly downslope winds will become gusty after 16Z as well, with the areas of potential 30+ kt gusts being limited to along and west of a KCTB-KGTF line. -Coulston Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information. && .PREV DISCUSSION... /ISSUED 540 PM MDT Sat Sep 21 2024/ Rest of today through Sunday...transient ridging moving over the Northern Rockies through late(early) Sunday morning(afternoon) will continue to bring dry and overall quiet conditions to Southwest through North Central Montana. Light and variable winds, with the exception of the eastern slopes of the Rocky Mountain Front, through the overnight hours tonight will once again allow temperatures to fall into the 20s to 30s; with the coldest temperatures occurring in the cold prone valleys of Southwest and Central Montana. Increasing cross barrier flow on the upstream side of the transient ridge and an increasing surface pressure gradient along the Continental Divide and Central Montana mountains will lead to breezy and gusty winds for areas along the Rocky Mountain Front and MT Hwy 200 corridor for the afternoon and evening hours on Sunday. While high winds are not expected across these areas over this timeframe, latest NBM probabilities do support a 15-30% chance for wind gusts in excess of 45 mph between Cut Bank and Marias Pass. These downsloping winds, and overall increasing winds elsewhere, will help to push high temperature on Sunday near to slightly above normal. A fast moving shortwave over British Columbia Sunday afternoon will then dive southeast and over the Northern Rockies through Sunday night, potentially bringing an isolated shower or two to areas along and north of the I-90 corridor. - Moldan Monday... The shortwave trough with its associated Pacific cold front is forecast to move through the forecast area on Monday. However, forecast models continue to weaken this fast-moving disturbance, which will limit the 20 to 30 percent chance for measurable precipitation to the mountains. Breezy westerly downsloping winds with the passage of the system will also hinder precipitation development over the plains. Temperatures are only forecast to cool down to near or slightly below normal. Tuesday through next Saturday... Ensemble model cluster analysis continues to agree with bringing an amplified high pressure ridge back into the area on Tuesday with an increasing southwest flow aloft on Wednesday. This will keep the area dry as temperatures warm to between 10 and 15 degrees above normal by Wednesday with breezy southwest winds; some plains areas will have a 30 to 50 percent chance of exceeding 85 degrees on Wednesday. The cluster analysis starts to differ after Wednesday, as 60 percent of the clusters agree on keeping the area under the influence of the ridge, while 40 percent want to start breaking the ridge down. Regardless, moisture is fairly limited, so even a persistent southwesterly flow aloft will keep the area dry, but the NBM starts a gradual cooling of temperatures. The next chance for a widespread chance of precipitation does not move in until Friday night into Saturday as temperatures approach seasonal averages once again. -Coulston && .PRELIMINARY POINT TEMPS/POPS... GTF 39 74 48 72 / 0 0 10 0 CTB 36 68 45 69 / 0 10 10 0 HLN 38 74 52 72 / 0 0 10 0 BZN 32 71 45 69 / 0 0 10 10 WYS 23 64 33 62 / 0 0 10 10 DLN 32 71 43 67 / 0 0 10 0 HVR 33 71 49 70 / 0 0 20 0 LWT 35 70 47 65 / 0 0 10 0 && .TFX WATCHES/WARNINGS/ADVISORIES... None. && $$ http://www.weather.gov/greatfalls