textproduct: Great Falls

KEY MESSAGES

- Strong winds that peaked overnight across north-central and central Montana will begin to subside this morning.

- A longer duration and more widespread wind event begins late tonight with with the most extensive and potentially damaging winds affecting the area through the day Wednesday.

- An energetic Pacific frontal system crossing the region Wednesday brings some locally intense rain or snow showers with more impactful snowfall limited to northern portions of the continental divide.

DISCUSSION

- Meteorological Overview:

A fast westerly flow aloft continues across the Northern Rockies and MT with one embedded shortwave and mid-level jet streak exiting to the east this morning before a sharper shortwave and stronger wind maximum moves onshore today and across the area Wednesday. Gusts in excess of 60 mph have been fairly widespread across N-central MT overnight as the initial wind maximum translated east across the area. The risk for gusts in excess of 60 mph across across N-central MT will gradually subside from west to east this morning as mid level flow decreases and the surface pressure gradient relaxes by early this afternoon.

A relatively benign period of weather is expected this afternoon and evening with temperatures just slightly cooler today but still well above seasonal averages. An impactful Pacific frontal system and dynamic shortwave trough are on track to sweep across the area Wednesday with continued support for an exceptionally widespread and potentially damaging wind event for the area. 700MB winds are progged to exceed 60kts across most of the forecast area with a wide coverage 75-85kts across much of central/N-central MT. Strong cooling aloft will allow this momentum to transfer down to the surface across much of the area resulting in multiple hours of gusts exceeding 50-60 mph with 60-80 mph peak gusts across north- central MT.

In addition, a surge of Pacific moisture will accompany the frontal system with snow increasing along northern puritans of the continental divide tonight. Snow levels sharply lower along the divide early Wednesday morning as the front passes with impactful snow and winds affecting Marias Pass into Wednesday afternoon. Instability and moisture surges east across north-central and southwest MT with the frontal passage Wednesday morning with enough instability for locally intense showers. Precipitation may quickly change to snow or graupel with these showers beneath the rapid cooling aloft, resulting in brief instances of lower visibility along with the onset of strong gusty winds. There is even a small risk for isolated thunder with the frontal passage early Wednesday, with probabilities as high as 20-30% across southwest MT. Hoenisch

- Forecast Confidence & Scenarios:

Aside from the unusually widespread coverage of strong winds on Wednesday one thing that makes this wind event different and holds the potential for increasing impacts to the area is the expected duration of strong wind speeds/gusts on Wednesday. Relatively deep (for winter) atmospheric mixing behind the front will maintain strong winds for multiple hours late Wednesday morning through the afternoon. The longer duration may increase the likelihood of damage vs the typically shorter (1-3 hr duration) of peak winds.

The potential for blowing dust will also need to monitored. Recent moisture and lack of the usual drying associated with wind events in this area may mitigate this. However, the anticipated longer duration of this event and recent mild temperatures could still make some soils or dry lake/alkali flats available to lift locally. Hoenisch

AVIATION

16/12Z TAF Period

VFR conditions prevail through tonight. Mountain wave turbulence and instances of low level wind shear may decrease some later today before increasing again tonight. Hoenisch

PRELIMINARY POINT TEMPS/POPS

GTF 56 40 51 25 / 10 20 60 0 CTB 47 33 44 18 / 10 40 40 0 HLN 52 35 48 27 / 10 40 90 0 BZN 55 36 51 23 / 20 10 90 0 WYS 38 30 40 12 / 10 60 100 10 DLN 54 36 47 23 / 10 30 90 0 HVR 45 30 45 8 / 10 30 50 20 LWT 49 35 48 18 / 10 10 60 10

TFX WATCHES/WARNINGS/ADVISORIES

High Wind Warning until 11 AM MST this morning for Bears Paw Mountains and Southern Blaine-Cascade County below 5000ft- Eastern Pondera and Eastern Teton-Fergus County below 4500ft- Hill County-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Madison River Valley-Northern Blaine County- Snowy and Judith Mountains-Upper Blackfoot and MacDonald Pass- Western and Central Chouteau County.

High Wind Warning from 3 AM Wednesday to midnight MST Wednesday night for Bears Paw Mountains and Southern Blaine-Beaverhead and Western Madison below 6000ft-Big Belt, Bridger and Castle Mountains-Canyon Ferry Area-Cascade County below 5000ft-East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera-Eastern Pondera and Eastern Teton-Eastern Toole and Liberty-Elkhorn and Boulder Mountains-Fergus County below 4500ft- Gallatin Valley-Gallatin and Madison County Mountains and Centennial Mountains-Gates of the Mountains-Helena Valley-Hill County-Judith Basin County and Judith Gap-Little Belt and Highwood Mountains-Madison River Valley-Meagher County Valleys- Missouri Headwaters-Northern Blaine County-Northern High Plains- Northwest Beaverhead County-Ruby Mountains and Southern Beaverhead Mountains-Snowy and Judith Mountains-Southern High Plains-Southern Rocky Mountain Front-Upper Blackfoot and MacDonald Pass-Western and Central Chouteau County.

Winter Storm Warning from 8 PM this evening to 11 PM MST Wednesday for East Glacier Park Region-Southern Rocky Mountain Front.

High Wind Warning until 8 AM MST this morning for East Glacier Park Region-Eastern Glacier, Western Toole, and Central Pondera- Eastern Toole and Liberty-Northern High Plains-Southern High Plains-Southern Rocky Mountain Front.