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FXUS65 KTFX 280210 AFDTFX

Area Forecast Discussion National Weather Service Great Falls MT 810 PM MDT Sat Apr 27 2024

SYNOPSIS

Rain and mountain snow diminish later this evening, giving way to drier and breezy conditions for Sunday. The unsettled weather pattern resumes early next week with potentially colder and wetter systems moving through the Northern Rockies, especially towards the end of the work week.

UPDATE

Light precipitation persists across portions of Central and North- central Montana east of I-15, with additional, perhaps heavier precipitation developing along the MT-ID border. The latest forecast does an excellent job showcasing PoPs associated with this precipitation, which is forecast to begin diminishing early tomorrow morning. Given this, opted to only amend the hourly temperatures with the latest observations as the remainder of the forecast continues to describe the situation well. No further amendments were needed at this time. - Pierce

AVIATION
540 PM MDT Sat Apr 27 2024 (28/00Z TAF Period)

Light rain continues to spread northward across much of Central and North-central Montana this evening as a slow moving upper-level disturbance propagates from the Four Corners region and into the Central High Plains. Thunderstorm activity, albeit minimal, will be retained to portions of Southwest Montana, specifically near KEKS early in the period. Periods of erratic winds cannot be ruled out during this time. Widespread low-VFR/MVFR conditions will persist; however, cannot rule out some IFR conditions in any shower activity development. Given this, mountain obscuration is forecast throughout North-central, Central, and Southwest Montana through late Sunday morning. Otherwise, precipitation will prevail through the early morning hours; however, may linger across the mountains of Southwest Montana. Thereafter, periods of breezy to gusty winds are expected to develop across portions of North-central and Central Montana, impacting KCTB, KHVR, KGTF, KHLN, and KLWT after 14z Sunday. - Pierce

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

PREV DISCUSSION
/ISSUED 540 PM MDT Sat Apr 27 2024/

Moisture and shortwave energy within a southwesterly flow aloft has provided a cool and wet day for nearly all locations except the far eastern portions of Central/North-central Montana. The rainfall and abundant cloud cover have generally kept temperatures about 5 to 10 degrees lower than earlier forecasts, so the hourlies were adjusted through this evening to match current expectations of clouds and rain persisting for the remainder of the day. All winter weather highlights have been canned with diurnal heating and diminishing snowfall limiting winter weather impacts over the higher terrain of the southwest. The shortwave responsible for the wet conditions exits the region tonight with rain and mountain snow ending in a west to east fashion tonight.
Patchy overnight fog can't be ruled out for areas receiving precipitation this afternoon and evening, but lingering cloud cover and a shift to southwesterly winds over the the plains should limit both coverage and impacts. Drier and breezier weather is expected on Sunday, with the strongest winds approaching the 40 to 55 mph range along the Rocky Mountain Front.

Most ensembles feature a split trough moving onto the Pacific Northwest coast and impacting the Northern Rockies Monday through Wednesday. On Monday, precipitation will initially come in the form of lower elevation showers/isolated thunderstorms and mountain snow, mostly along the Continental Divide, while large scale ascent and moisture stream ahead of the approaching trough.
This system will have a better supply of colder air than previous ones with H700 temperatures running around -10 to -15C behind the cold front. this will result in snow levels falling to the valley floors Monday night into Tuesday morning and at least a brief period of accumulating snow over higher terrain. This quick hitting area of snow looks to bring the best chance for 4 + inches of snow to the Gallatin/Madison ranges. Other mountain areas, including the Central ranges and the mountains along the Continental Divide are currently looking at over a 50% chance for 2 inches of snow for the same period. Winter weather highlights may be needed in spots, especially if timing shifts later from Monday afternoon/evening to the overnight hours. This system will also bring periods of gusty winds, initially to Southwest Montana on Monday followed by the Rocky Mountain Front and the plains Monday night into Tuesday. Although wind exceedence probabilities support gusts over 40 mph, mostly along the Rocky Mountain Front and the north/south oriented southwest valleys, probabilities for gusts above 55 mph are running well under 50% for most locations.

The region will remain under the influence of the broad trough through Wednesday. Some ensembles featuring the northern closed circulation crossing the Continental Divide on Tuesday before slowing down and remaining over eastern Montana through early Thursday while the southern circulation moves southeastward along Montana/Idaho border. This solution favors overall colder and wetter conditions, particularly for the northerly upslope areas of Central/North-central Montana, where rainfall exceedence probabilities for a half inch of liquid precipitation are now running around 30%. This colder solution also has H700 temperatures around -10C, cold enough to support snowfall at all elevations, at least at night. At the very least, there is an expectation for wet and unsettled condtions with below average temperatures Monday night through Wednesday. Things warm and dry out some on Thursday, but the parade of Pacific weather systems continue heading into the next weekend favoring cooler and wetter conditions overall. - RCG

PRELIMINARY POINT TEMPS/POPS
GTF 37 60 39 55 / 100 0 0 60 CTB 33 57 36 54 / 80 0 0 10 HLN 38 62 38 55 / 80 10 10 80 BZN 36 59 35 57 / 90 40 30 90 WYS 33 49 28 47 / 90 60 20 90 DLN 34 56 35 54 / 70 10 10 80 HVR 41 66 38 62 / 90 10 0 30 LWT 37 58 36 56 / 80 10 20 90

TFX WATCHES/WARNINGS/ADVISORIES
None.

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