Several bands of heavy rain may cause flash flooding in the Mid-South. A potent storm will bring strong winds and critical fire weather threats into the Southwest, and damaging Santa Ana winds to southern California. Heavy mountain snow will linger across the North and Central Rockies and Inter-Mountain West. A Wintery mix is also possible in the Appalachians and portions of the Northeast. Read More >
Overview
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The onset of a high impact wind event began on Tuesday January 12th, 2021, when a typical brand of strong winds descended over the normally wind prone Rocky Mountain Front and adjoining areas. Widespread anomalously strong winds then swept through much of Montana on the following day as a vigorous Pacific weather system and its attendant cold front moved east through the Northern Rockies into the plains. Great Falls (76 mph), Helena (80 mph), and Havre (78 mph) all set wind speed records for the month of January. The winds were not only abnormally strong but they persisted longer than what is usually experienced, with some locations seeing frequent severe wind gusts (58 mph or greater) for six hours or more. The impacts were felt throughout North-central and Southwest Montana and included, road closures due to areas of dense blowing dust, semi-trailer roll overs, power outages, and property damage. |
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Photos & Video:
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| A large tree tumbled in the strong winds at the Helena Civic Center. Image Credit: Erin Yost via Twitter | The strong winds caused blowing dust along interstate 15 near Valier. Image Credit: Nathan St. Goddard via Twitter | A Semi-trailer flipped in the strong winds. Image Credit : Nathan St. Goddard via Twitter | Wind damage near Lewistown. Image Credit : Jaime Jackson via Twitter |
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| A grassfire broke out near Highwood, MT during the peak of the high wind event. Image Credit : Belt Rural Volunteer Fire Department via Facebook | Strong winds cause roof damage in the Havre area. Credit Northwestern Energy via Twitter | Areas of dense blowing dust were observed in the Gibson Flats area south of Great Falls. Credit: Tony Bynum via Twitter |
Wind Reports
Click here for a list of peak wind gusts by county |
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| Regional peak wind gusts for January 13th, 2021 | Peak wind gust map for January 13, 2021 |
Environment
Increased westerly flow aloft (Figure 1) and a tightening pressure gradient (Figure 2) developed ahead of an approaching Pacific trough and brought typically strong winds to the Rocky Mountain Front on Tuesday January 12th, 2021. The winds strengthened and became more widespread on the following day as the trough axis and associated 70 to 100 kt 700 mb jet max (Figure 3) moved through the state. These mountain top winds were ranked close to the 99th percentile when compared to the 30 year climatological average. A Pacific cold frontal passage (Figure 4) helped transfer these winds to the surface and cold air advection (Figure 6) and surface pressure rises (Figure 5) on the subsident side of the trough maintained higher wind speeds for much of the day.
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| Figure 1: Storm Prediction Analysis Mid-level (500 mb) Winds January 12th, 2021 3 pm to 11pm mst | Figure 2: Storm Prediction Analysis Surface Pressure and Wind January 12th, 2021 5 pm to 11pm mst | Figure 3: Mountain Top (700 mb) Winds January 13th, 2021 5am to 5pm mst |
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| Figure 4: Weather Prediction Center Surface Analysis January 13th, 2021 5 am to 5 pm mst | Figure 5: Storm Prediction Center Surface Pressure Change January 13th, 2021 5 am to 5 pm mst | Figure 6: Mountain Top (700 mb) Temperature January 13th, 2021 5 am to 5pm mst |
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