Sunrise 6:16 AM   Sunset 8:27 PM Moonrise 11:00 PM   Moonset 6:24 AM

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FXUS65 KTFX 260933 AFDTFX

Area Forecast Discussion National Weather Service Great Falls MT 333 AM MDT Fri Apr 26 2024

SYNOPSIS

Moisture increases across the area through early this weekend with rain and mountain snow showers becoming more widespread across the area by Saturday. Significant snow accumulations are expected across the highest elevations of southwest Montana through Saturday with some wet snow possible over some mountain passes.
After some drying late Sunday, the next series of weather systems from the Pacific move across the area early next week.

DISCUSSION

An active weather pattern is evolving for the area with broad upper level troughing in place across the western US and a leading wave lifting out into the central Plains states this morning while another moves onshore in the Pacific NW. The bulk of the energy moving onshore dives southeast into the Great Basin later today and tonight with a somewhat convoluted flow pattern developing to its north across MT as embedded moisture and weaker disturbances shift across the area in a developing easterly mid level flow later today through Saturday. Precipitation is ongoing early this morning across portions of SW MT where an embedded disturbance was located with another area of precipitation associated with an axis of moisture moving east into western MT. Deeper moisture and focus for precipitation will expand north from SW MT today with the western area of moisture gradually shifting to near the continental divide later today and tonight before moving east across the area Saturday night.
The absence of larger scale forcing will favor more persistent precipitation over the mountains of central and southwest MT with probabilities for one half inch precipitation amounts through Saturday ranging from around 50% across the central MT mountains to as much as 80% across the mountains of Gallatin and Madison counties.

Snow levels fluctuate around 7000ft through Saturday night with impactful snow accumulation mainly above this, but snow may fall as low as around 6500ft in times of more intense precipitation.
This primarily affects Big Hole and Targhee Passes with potential for snow accumulation on road surfaces but some periods of reduced visibility and slushy surfaces are also possible at other passes along the continental divide at 6500ft and above. Winter storm warnings and winter weather advisories are in effect through Saturday evening to highlight changing road conditions at pass levels and heavy snow primarily above pass levels.

Flow aloft turns back to westerly Sunday with moisture exiting to the east followed by a relatively dry period before the next series of systems from the Pacific arrive early next week. Cluster analysis reveals some notable differences still among the models, likely related to timing and specific track of shortwaves embedded within the broader trough and fast westerly flow that develops early next week. The first in this series of Pacific shortwaves arrives Monday with deterministic models now depicting a fairly vigorous Pacific cold front moving east across the area, though timing and moisture varies among the models. Probabilistic guidance currently gives a greater than 50% chance for wind gusts in excess of 55 mph along the Rocky Mtn Front and adjacent areas Monday with potential for more widespread strong wind gusts with a cold front.
Model differences amplify with additional waves and associated moisture moving through the area Tuesday and Wednesday with about one third of model ensembles depicting a somewhat further south track to energy which would result in higher precipitation amounts and cooler temperatures across northern portions of the forecast area. Hoenisch

AVIATION
5 1200 AM MDT Fri Apr 26 2024 (26/06Z TAF Period)

VFR conditions will persist across much of North-central and portions of Central Montana through the remainder of the evening and into the early morning hours. Light precipitation will begin affecting most terminals in central Montana after 26/16Z with periods of MVFR visibilities and MVFR/IFR ceilings possible heading into the afternoon.

Mountain snow across southwestern Montana has already started and will continue through the remainder of the TAF period. Periods of heavy mountain snow with mountain obscuration will be possible in the vicinity of KBZN and KEKS. At the terminals, light rain will persist through the period with reduced visibility and lowered cloud ceilings in MVFR/IFR conditions possible after 26/12Z.

-thor

Refer to weather.gov/zlc for more detailed regional aviation weather and hazard information.

PRELIMINARY POINT TEMPS/POPS
GTF 59 41 56 39 / 20 70 60 50 CTB 53 38 53 35 / 20 40 50 20 HLN 57 42 53 39 / 50 80 80 50 BZN 54 36 56 37 / 90 60 70 60 WYS 50 33 52 32 / 80 70 80 70 DLN 53 38 50 36 / 80 80 80 30 HVR 66 39 65 42 / 20 20 10 30 LWT 57 38 58 38 / 50 40 30 30

TFX WATCHES/WARNINGS/ADVISORIES
Winter Weather Advisory until 6 PM MDT Saturday for Elkhorn and Boulder Mountains-Ruby Mountains and Southern Beaverhead Mountains.

Winter Storm Warning until 6 PM MDT Saturday for Gallatin and Madison County Mountains and Centennial Mountains-Northwest Beaverhead County.

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