High Wind in Montana, May 6, 2020

Area Forecast Discussion
National Weather Service Great Falls MT
1007 AM MDT Wed May 6 2020

.SYNOPSIS...

A wet spring storm will bring fairly widespread lower elevation
rain and mountain snow to much of the region later this afternoon
through Thursday afternoon. Expect somewhat cooler than normal
conditions, with occasional shower chances, to continue into early
next week.

&&

.UPDATE...

Satellite imagery this morning shows a compact but potent and
vertically stacked trough across the NW US with rain across
eastern OR/WA state moving into the Northern Rockies. A secondary
disturbance to its east is spreading increasing cloud-cover into
central and SW MT with a few embedded very light showers in this
area likely to increase some through early this afternoon. Main
precipitation event is still largely on track as the low
progresses east into MT this evening and overnight. By this
afternoon, decreasing stability and favorable upper level lifting
mechanisms ahead of the trough will support the development of
a few thunderstorms, possibly as far north as north-central MT.
As the airmass moistens up considerably later today, the main
threat from these storms will be locally heavy rain, but strong
winds are also a possibility going into this evening. Hoenisch

&&

.AVIATION...
Updated 547 AM MDT Wed May 6 2020 (06/12Z TAF Period)

Strong Pacific weather system continues to approach the area with
high and mid level clouds increasing through the morning. VFR
conditons expected through at least 18Z when showers and gusty
westerly winds spread eastward across the area with some potential
for scattered thunderstorms. Widespread low clouds and light to
moderate rainfall develops across much of the forecast area after
00Z Thursday for IFR/MVFR conditions with areas/periods of LIFR
conditions in heavier showers. After 06Z, many terminals will see a
mixture of rain and snow although the snow is currently expected to
melt rather than accumulate. mpj

NOTE: Amendments not scheduled for Ennis (KEKS) due to ongoing
runway closure.

&&

.PREV DISCUSSION...
/ISSUED 547 AM MDT Wed May 6 2020/

Today through Thursday night...The well advertised spring storm is
just moving into the Pacific Northwest this morning as high clouds
ahead of this system stream into the western half of Montana.
Showers along with a few thunderstorms will develop ahead of a cold
front and move through the region this afternoon and evening,
bringing the potential for brief heavy rain and gusty winds. The
most vigorous showers/storms will occur over the southwest. Then
the showers will evolve into a general rain event overnight tonight
into Thursday for the lower elevations Central and North Central
Montana, with snow expected for the mountains. Some precipitation is
also expected in Southwest Montana, but heavier amounts and the
largest impacts will take place over the northern half of the CWA.
Most short term models are in good agreement that an inverted
surface trough will extend to the north-northwest from the parent
low during this period. The bulk of precipitation will be associated
with this trough as it moves through Montana. The current forecast
has shifted the area of the heaviest liquid precipitation amounts(.5
to 1 inch) to the eastern half of Central/North-central Montana and
along the northern portion of the Continental Divide. Accumulating
snow is expected for elevations above 5000 to 5500 ft of Glacier
Park, The Little Belts, and Big Snowy Mountains, with amounts
ranging from 4 to 9 inches. Kept the Winter Weather Advisories for
the Marias Pass area and higher elevations on the Northern Rocky
Mountain Front and the Kings Hill Pass area of the Little Belts.
This is mainly due to accumulating and blowing snow impacts on those
mountain passes, as gusty west winds will remain in place in the
wake of a cold front Wednesday night into Thursday morning.

Friday through next Wednesday...Unsettled conditions and cool
temperatures will linger over Montana through the weekend and into
early next week. There is good agreement between the diagnostic
models and most of the ensembles that a highly amplified, but
narrow, upper level ridge will build over the West Coast of the USA
and extend as far north as the Yukon through the weekend. This
system will act to amplify any disturbances moving southward along
the eastern periphery of the ridge. As a result, models suggest that
several amplified shortwave troughs will sweep southward through
Montana during the Sunday through Tuesday period. The National Blend
of Models (NBM) appears to have embraced this solution so have used
the latest NBM forecast for this period wholesale with not local
edits made to the national solution.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  67  37  57  36 /  70  70  80  10
CTB  62  38  58  37 /  60  70  50  10
HLN  68  37  55  35 /  70  40  30  10
BZN  70  31  52  31 /  70  60  30  10
WYS  62  23  49  23 /  50  50  20   0
DLN  66  31  51  32 /  50  20  10   0
HVR  70  40  65  41 /  30  80  40  10
LWT  64  32  50  33 /  30 100  80  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 9 PM this evening to noon MDT
Thursday above 5500 feet for Cascade...Judith Basin...Meagher.

Winter Weather Advisory from 9 PM this evening to 9 AM MDT
Thursday above 5000 feet for Northern Rocky Mountain Front.

&&

http://www.weather.gov/greatfalls