textproduct: Great Falls

KEY MESSAGES

- This afternoon it will be hot and windy across North-central, Central, and Southwestern Montana.

- Rain showers will affect North-central Montana this evening and bring gusty to strong winds.

- This weekend it will be cooler with light mountain snow along the Rocky Mountain Front.

DISCUSSION

- Meteorological Overview:

This afternoon an upper-level trough, associated with a Pacific Cold Front, with strong southerly flow approaches Montana. Due to a strong surface pressure gradient and strong low-level and mid-level winds it will be windy this afternoon across North-central, Central, and Southwestern Montana. The Pacific Cold Front will move through the area this afternoon/evening. This will bring strong winds to the Rocky Mountain Front and plains west of I-15 this evening though early Saturday morning. As the cold front moves through North- central Montana, rain showers have the potential to bring gusty to strong winds. Tonight light snow will affect the Rocky Mountain Front. See the Forecast Confidence & Scenarios Section for details.

On Saturday the upper-level trough remains over North-central, Central, and Southwestern Montana. This combined with the cold front will bring cold temperatures (slightly below seasonal averages) to the area. Saturday morning snow will linger along the Rocky Mountain Front and it will be mostly dry elsewhere. On Sunday an upper-level ridge begins to build in over North-central, Central, and Southwestern Montana. This will keep cool temperatures over the area with mostly dry weather. On Monday a weak upper-level trough moves over the area. This will allow temperatures to warm up some with isolated showers around. On Tuesday an upper-level ridge briefly builds in over the area. This will allow warm temperatures to remain with dry weather. Tuesday night into Wednesday the upper-level ridge breaks down. This will bring strong winds to North-central Montana. On Wednesday and Thursday there will be zonal flow over North- central, Central, and Southwestern Montana. This will bring breezy, warm, and dry conditions to the area on Wednesday and Thursday. For details for Friday through next weekend see the Forecast Confidence and Scenarios section. -IG

- Forecast Confidence & Scenarios:

Along the Rocky Mountain and plains west of I-15 there is greater than an 80% chance for wind gusts of 55 mph or greater this evening through tomorrow morning. Since hi-res models suggested that strong winds could last until noon tomorrow, the High Wind Warning for those areas was extended until noon tomorrow. In the Sweet Grass Hills there is greater than an 80% chance for wind gusts of 55 mph or greater from this evening through early tomorrow morning. However since this is a localized area a High Wind Warning was not issued for this area. The HREF (Hi-res ensemble forecast) showed strong 850 mb winds greater than 40 kts over the bears paw mountains associated with the cold front. As a result a High Wind Warning was issued for the Bears Paw Mountains from 8 PM tonight through 6 AM tomorrow morning.

Tonight across the golden triangle region associated with the cold front a line of showers will move through. At least isolated portions of the line have at least a low chance to produce wind gusts in excess of 58 mph (severe wind gusts). Tonight along the northern Rocky Mountain Front there is at least a 80% chance for greater than a tenth of an inch of snow. Tonight along the higher peaks of the northern Rocky Mountain Front (the eastern portion of Glacier National Park) there is a greater than a 60% chance for an inch of snow.

Next Friday through next Sunday some of the models and ensembles are predicting a snowfall event. Two of the four clusters which represents around 50% of the ensemble members have an upper-level trough over Montana next Friday through next Sunday. This scenario would bring well-below seasonal averages for temperatures with the potential for both lower-elevation and mountain snow next Friday through next Sunday. These two clusters differ on how strong and how far east the upper-level trough is. A stronger trough centered over Montana would bring more snow and colder temperatures than a trough that is less strong and/or further east. The other two clusters which represents the other 50% of ensemble membership have a upper-level ridge over North-central, Central, and Southwestern Montana next Friday through next Sunday. This will bring above seasonal average temperatures with dry weather to the area next Friday through next Sunday. -IG

AVIATION

25/18z TAF Period.

Southwest surface winds and high level clouds increase this afternoon in advance of an approaching Pacific cold Front. The front will move west to east through the forecast area roughly between 25/22 and 26/06Z. This will bring gusty westerly winds and mountain wave activity, strongest along the Rocky Mountain Front and adjacent high plains, with gusts exceeding 50 kts at times.

Isolated shower and thunderstorm activity will accompany the frontal passage for northern areas and may also enhance the winds, at least on a temporary basis. Winds begin to decrease Saturday morning, although diurnal mixing will maintain 25 to 35 kt winds throughout the day, especially over the plains.

Otherwise, general VFR conditions will prevail outside of mountain obscuration along the Rocky Mountain Front tonight and smoky/hazy skies from prescribed burns between Lincoln and Helena this afternoon. - RCG

PRELIMINARY POINT TEMPS/POPS

GTF 45 63 38 63 / 30 0 0 0 CTB 42 56 33 59 / 20 0 0 0 HLN 43 64 40 65 / 20 0 0 0 BZN 41 65 39 65 / 10 0 0 10 WYS 35 59 34 64 / 0 0 10 10 DLN 39 65 40 65 / 20 0 0 10 HVR 46 65 37 67 / 20 0 0 0 LWT 43 66 37 65 / 20 0 0 0

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning from 5 PM this afternoon to noon MDT Saturday for Eastern Glacier, Western Toole, and Central Pondera-Northern High Plains-Southern High Plains.

High Wind Warning from 8 PM this evening to 6 AM MDT Saturday for Bears Paw Mountains and Southern Blaine.