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FXUS65 KTFX 201149 AFDTFX

Area Forecast Discussion National Weather Service Great Falls MT 549 AM MDT Mon May 20 2024

Aviation Section Update

SYNOPSIS

Today, low elevation rain, and some mountain rain snow impacts our region. Temperatures warm today and tomorrow, before cooling, mid week. Afternoon and evening thunderstorms develop and move across portions of north central, central and southwest Montana, for the next few days. An active weather pattern favors periods of rain snow, through the week.

DISCUSSION

Note: The forecast area for the National Weather Service Great Falls Weather Forecast Office includes, north central, central and southwest, Montana.

Today...Temperatures are on a gentle warming trend. An upper level trof progresses across the region. Low elevation rain and some mountain rain/snow impacts the region. The greatest amount of impactful snow accumulation is forecast to occur across Raynolds Pass and US 191 near Big Sky, where there is a 70% chance of up to 3 inches of snow accumulation. Considering that we're approaching the end of May, and people, especially those who may be visitors to The Treasure State, may be surprised to encounter some slushy and slippery stretches of roadway, I've issued a Public Information Statement for this area. Generally, any snow that falls is wet and heavy and falling on mostly warm road surface temperatures. Thunderstorm activity is forecast to develop and move across the region. The greatest impact from these storms is forecast to be strong and erratic gusty winds.

Tuesday through next Monday...A weak upper level ridge enters the region, Tuesday, and low elevation high temperatures are forecast to range around normal, with highs ranging from the upper 50s to the mid to upper 60s. General afternoon and evening thunderstorms develop and pass through our region into the mid week period. For the remainder of this forecast period, periods of low elevation rain and mountain rain/snow are forecast. The greatest impacts are forecast to occur mid week, when there is a 40% to 70% chance that some of our mountains will receive 4 to 9 inches of snow at and above pass level, during the 24 hour period from Wednesday evening through Thursday afternoon. For this reason, I've issued Winter Weather Watches for these areas. We continue to monitor and will adjust Watches, Warnings and Advisories, as is appropriate. As the week progresses, the active weather pattern continues, with daily periods of precipitation forecast. Please, see the HYDROLOGY section below for more information in reference to potential flooding impacts.
- Fogleman

AVIATION
20/12Z TAF Period

Note: The NWS Great Falls Weather Forecast Office manages the following TAFs: KCTB, KHVR, KGTF, KLWT, KHLN, KBZN, KEKS and KWYS.

At the onset of this TAF period, low visibility in mist, along with a low cloud deck, push KCTB into IFR conditions, intermittently.
This issue resolves by 20/14Z. Otherwise, periods of MVFR conditions, due to rain/snow and mist and with low ceiling, are forecast at all airfields. Mountain obscuration is forecast.
Afternoon/evening thunderstorms develop and move through the region.
Generally, winds are forecast light to breezy. Gusty winds to 25KT develop across southwest Montana, courtesy of northerly winds flowing through north-south oriented mountain valleys.
- Fogleman

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

HYDROLOGY

A flood watch has been issued for the Kings Hill, Monarch and Neihart areas from Wednesday night into Friday. There is a 50 percent chance of 1 inch of liquid from this event in this area.
There is a 10 percent chance of 2 inches of liquid. Some of the precipitation will fall as snow, especially for elevations above 7000 feet, which will help, but for areas lower than 7000 feet, impacts could develop fairly quickly given how saturated the soil is and how full the creeks/streams are currently in this region.

At this time, other areas of North Central and Southwest MT should be able to handle the expected rainfall, but there is the potential that additional flood statements might be needed. Brusda

PRELIMINARY POINT TEMPS/POPS
GTF 58 35 64 41 / 30 20 30 10 CTB 56 34 62 40 / 60 30 30 10 HLN 60 39 66 43 / 50 30 30 10 BZN 55 32 61 37 / 60 40 40 10 WYS 50 28 52 29 / 60 50 50 20 DLN 53 32 59 38 / 50 40 20 10 HVR 59 37 64 41 / 30 20 20 20 LWT 54 32 59 37 / 60 20 50 20

TFX WATCHES/WARNINGS/ADVISORIES
Winter Storm Watch from Wednesday evening through Thursday morning for Elkhorn and Boulder Mountains-Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Southern Rocky Mountain Front.

Flood Watch from Wednesday evening through Friday morning for Little Belt and Highwood Mountains.

Winter Storm Watch from Wednesday evening through Thursday afternoon for Gallatin and Madison County Mountains and Centennial Mountains.

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