Wind Advisory 3, NWS Missoula, MT

001 
WWUS75 KMSO 232015
NPWMSO

URGENT - WEATHER MESSAGE
National Weather Service Missoula MT
115 PM MST Sun Feb 23 2020

IDZ009-010-232115-
/O.CAN.KMSO.WI.Y.0003.200224T0200Z-200224T0900Z/
Western Lemhi County-Eastern Lemhi County-
115 PM MST Sun Feb 23 2020

...WIND ADVISORY HAS BEEN UPGRADED TO A WINTER WEATHER ADVISORY
BEGINNING LATE THIS AFTERNOON...

$$

Area Forecast Discussion
National Weather Service Missoula MT
243 PM MST Sat Feb 22 2020

.DISCUSSION...

Warm high pressure and an increasingly high sun angle will continue
to erode away valley temperature inversions today and Sunday. Low
elevation snow pack and lack of surface winds are the main reason
that some valleys (e.g., Missoula Valley) have been slow to warm
above freezing this afternoon.

Most valley temperature inversions will break by midday Sunday, as
clouds increase and strong cold front approaches the Northern
Rockies. Winds are projected to become a bit gusty by Sunday
afternoon, particularly over high terrain (gusting 20 to 30 mph).
Anticipate the surface cold front to pass through the region between
early Sunday afternoon (northwest Montana) through Sunday evening
(southwest Montana). Model guidances suggest that there will be a
significant blast of snow along the cold front, with up to 2 inches
snow accumulation within a few hours of frontal passage. The most
impressive accumulations and travel impact from this snow event will
be found over area mountain passes, where 3-6 inches are expected
between Sunday afternoon and midday Monday. Despite a slightly lower
travel impact from snow anticipated at valley elevations, a delayed
cold front would mean that any snow that falls would be able to
develop into ice after sunset. Southwest Montana appears most at
risk of a flash freeze scenario, however the confidence in this
forecast caveat is currently a bit low.

Following the cold front, there is a chance that banded snow
features could develop across west central Montana Sunday late
evening and continuing into Monday morning. Any banded snow features
that develop would be capable of a quick 1-2 inch accumulation,
however this is any low confidence feature of the current forecast.

Mountain snow showers will linger Monday night through Tuesday
morning, as upper level flow shifts from northwest to northerly.
Temperatures will remain seasonably cool through Tuesday.

Midweek through early Saturday across the Northern Rockies will be
mostly under the influence of warm high pressure. The warmth of this
next high pressure event should be enough to warm area valleys to a
greater extent than the current high pressure (mainly due to loss of
valley snow pack and an increasingly high sun angle).

Beginning next weekend and continue through at least the middle of
the following week, model guidances have been consistent in
depicting an extended period of snow across the region (e.g., the
next storm cycle). The biggest question in the extended forecast
that needs to be answered is how much cold air will be available for
snow in low/middle elevation valleys? It appears that travel impacts
due to snow accumulation will be present at least the mountain
passes and possibly for some high/middle elevation valleys.

&&

.AVIATION... VFR conditions through overnight Saturday with clouds
building over west facing terrain this afternoon. After 23/10z,
snow showers in the vicinity of KGPI, as well as aerodromes west
and north of KGPI, have a increasing chance of snow showers. As
Sunday progresses, higher terrain will continue have obscurations
due to snow showers. Then after 24/00z, a cold front will pass
through all terminals, bringing a brief period of moderate snow.

&&

.MSO WATCHES/WARNINGS/ADVISORIES...
MT...Winter Weather Advisory from 2 PM Sunday to 11 AM MST Monday
     West Glacier Region.

ID...None.
&&