textproduct: Glasgow

DISCUSSION

KEY MESSAGES:

1) Widespread west winds ranging from 30 to 40 mph, gusting to 50 to 60 mph are expected tonight and Tuesday.

2) A wintry mix combined with cold ground temperatures is expected to lead to icy surfaces, leading to difficult walking and driving conditions. Sharply falling temperatures Tuesday evening could make conditions more hazardous.

3) The next winter storm may approach Tuesday night through Thursday with an initial wintry mix, changing to snow. Some places may see significant snowfall accumulation.

WEATHER PATTERN OVERVIEW:

There are several operational challenges in the forecast this go around. First, the decision was made to upgrade the High Wind Watch to a High Wind Warning. Included all of NE Montana between 11pm this evening through 5pm Tuesday. Strong cold air advection behind the next clipper system should help mix down the stronger winds, especially for higher elevations. HREF ensemble max wind gusts show widespread 50 to 60 mph gust outcomes during the period shifting from west to east. This is consistent with where 850mb wind maxima evolve - near 50 kts in the west this evening to between 50-60 kts in the east by Tuesday afternoon. Snow cover can complicate mixing, especially in the valleys. From an impact standpoint however, there is not much difference between falling just shy or just over exact criteria. Bottom line: expect west winds 30 to 40 mph with gusts between 50 and 60 mph at times to be fairly widespread. For context, both HREF and NBM show 50-70%+ probabilities for gusts over 50 mph for large portions of the CWA, with HREF a bit more pronounced.

Second, a complex weather maker will bring the next round of precipitation to the region spreading from west to east tonight into Tuesday. Temperatures are mild enough to support mainly rain with some snow and freezing rain. Road temperatures across NE Montana are near or below freezing across the board. Given evaporation from the strong winds, icing may begin to accumulate even if precipitation occurs mostly as rain and/or if a little snow melt adds to wet surfaces. Over time, the combination of the cold ground and wintry mix is expected to lead to slippery surfaces and difficult walking and driving conditions. Tuesday evening, temperatures are expected to sharply fall into the teens and 20s, which could exacerbate the icy conditions. Most of the precipitation will be over with by the afternoon, but the impacts will continue beyond into the overnight and the next system will be approaching quickly - so this end time provides some flexibility to future shifts.

Tuesday night through Thursday will feature low pressure bringing an initial wintry mix which may include freezing rain, shifting to snow. Ensemble guidance shows the potential for several inches of snow to stack up, if not more in some places. Thus, this could be a meaningful event for NE Montana, especially if snow accumulates over pre-existing icy surfaces.

In short, cold and active weather are most likely for the second half of the week.

FORECAST CONFIDENCE & DEVIATIONS:

Given the anomalous system approaching, winds were nudged toward NBM90 with 75% weighting for the tonight and Tuesday period. Given where model 700mb and 850mb winds are at, confidence is high on very windy conditions developing across the area even if confidence is more moderated toward reaching exact high wind criteria.

Confidence is more moderate on precipitation type and amount for tonight and Tuesday given the complex weather system moving in, but given the potential for impacts, have nudged toward headline decisions to help guide messaging.

Confidence is growing on a significant meaningful winter storm toward the middle of the week with a wintry mix changing to snow for at least portions of the CWA.

AVIATION

LAST UPDATED: 0945Z

FLIGHT CAT: IFR - VFR

DISCUSSION: Complex weather with patchy fog, low stratus at times, and a wintry mix tonight and Tuesday will lead to low ceilings and a reduction in visibility at times. Look for icing concerns from mixed precipitation tonight into Tuesday.

WIND: West at 10 to 20 kts, gusting to 30 kts today and tonight. Winds will generally look to increase by Tuesday morning.

GGW WATCHES/WARNINGS/ADVISORIES

High Wind Warning from 11 PM this evening to 5 PM MST Tuesday for Central and Southeast Phillips-Central and Southern Valley- Daniels-Dawson-Eastern Roosevelt-Garfield-McCone-Northern Phillips-Northern Valley-Petroleum-Prairie-Richland-Sheridan- Southwest Phillips-Western Roosevelt-Wibaux.

Winter Weather Advisory from 11 PM this evening to 2 PM MST Tuesday for Central and Southeast Phillips-Central and Southern Valley-Daniels-Dawson-Eastern Roosevelt-Garfield-McCone-Northern Phillips-Northern Valley-Petroleum-Prairie-Richland-Sheridan- Southwest Phillips-Western Roosevelt-Wibaux.