Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 210534
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1130 PM MDT Fri Apr 20 2018

...Aviation Section Updated...

.UPDATE...

No significant changes to the forecast this evening with an upper
level ridge of high pressure traversing the area for continued
dry conditions with. Surface winds increase along the east slopes
of the Rockies late tonight and latest model guidance continues
to support high wind potential along the Rocky Mtn Front and east
to the Cut Bank area tomorrow afternoon. Hoenisch

&&

.SYNOPSIS...
The upper level ridge currently over the region will move eastward
tonight. A fast moving Pacific cold front will move through the
region on Saturday, producing strong winds over the front range of
the Rockies and adjacent Plains. Temperatures will cool off a touch
on Sunday, as a another fast moving spring storm moves into
Southwest MT by late Sunday afternoon. Expect widespread rain and
snow over Central and Southwest MT Sunday night and Monday, before
warmer and drier air returns to the region by the middle portion of
next week.

&&

.AVIATION...
Updated 0530Z.

Upper level ridging will push east of the Northern Rockies tonight
as a compact shortwave quickly moves from the Pacific Northwest and
into Southern Alberta by Saturday evening. The main impacts that
this disturbance will have on the terminals of North Central and
Southwest Montana will be a period increasing high clouds during the
mid/late morning hours through the afternoon, in addition to strong
winds, especially during the afternoon hours across North Central
Montana. Winds gusts in excess of 50kts will be possible this
afternoon along the Rocky Mountain Front and over the immediate
plains east of the Front, especially at the KCTB terminal. Frequent
wind gusts in excess of/near 35kts are then expected at the KHVR,
KGTF, and KHLN terminals this afternooon. - Moldan

&&

.HYDROLOGY...
Updated 300 PM Friday
Areal flood warnings continue for Toole, Liberty, Hill and Blaine
counties.

Areal flood advisories continue for Glacier and Pondera counties.

Numerous point flood warnings continue for the Milk River
and its tributaries across Hill and Blaine counties where additional
snowmelt and inflow from upstream tributaries will maintain flooding
through the next several days.

All flooding over North Central MT will be slow to diminish over the
next few days, as snowpack from Southern Canada begins to melt, and
the runoff works its way southward into MT, particularly from the
Cypress Hills area. Thus Blaine County will be the hardest impact
area, with flooding expected to continue through all of next week.

A storm system will bring rain/snow to Southwest MT Sunday night
through Monday. Some of the heavier precipitation amounts of 0.40 to
0.60 inches will be possible over portions of Southwest and Central
MT. Brusda

&&

.PREV DISCUSSION...
/ISSUED 530 PM MDT Fri Apr 20 2018/
Tonight and Saturday...Mostly clear conditions and generally light
winds persist into this evening but the next upper level wave will
approach the region on Saturday. Models remain in good agreement
that downslope pressure gradients will tighten up along the Rocky
Mountain Front (RMF) and that mid-high level winds will increase
significantly by Saturday afternoon. Have continued the High Wind
Watch for the RMF and for Glacier County but have opted to not
expand or upgrade this highlight in order to give the overnight
shift at least one more good batch of model runs to make a final
decision on this event. Temperatures will remain seasonably warm
across most of the forecast area on Saturday, with the exception
being the far northwest zones which should see passage of a surface
cold front by early-mid afternoon. mpj

Saturday night through Friday...Winds decline quickly Saturday
night, with dry but somewhat cooler temperatures on Sunday. The
next shortwave trough develops Sunday night, producing chances for
precipitation across southwest Montana. Global ensemble forecasts
have been consistent in producing moderate precipitation.
However, recent forecasts from the NAM and SREF models present a
weaker wave and much drier solutions. Continued a high likelihood
for moderate precipitation based on GFS/ECMWF continuity in
solutions. Precipitation amounts Sunday night through Monday could
exceed 0.5 inches over portions of Southwest Montana. Snow levels
could fall below 6000 feet, with a few inches of wet snow
possible at and above mountain passes. Since this scenario would
present rain and mountain snow, it does not appear to create an
immediate flooding concern. However, snow accumulations at pass
level in southern portions of central Montana as well as across
southwest Montana suggest that a Winter Weather Advisory may be
required.

A broad and high amplitude ridge builds over the region starting
next Tuesday, and persisting through the week ahead. Temperatures
will trend above average, with freezing (melting) levels possibly
climbing above 9k feet and focusing new attention to mid-
elevation snowmelt runoff.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  39  63  32  57 /   0   0   0   0
CTB  37  54  30  53 /   0  10   0   0
HLN  39  63  36  61 /   0   0   0   0
BZN  34  64  33  61 /   0   0  10  10
WEY  19  52  27  53 /   0   0   0   0
DLN  35  63  31  60 /   0   0   0  10
HVR  36  64  32  55 /   0  20  10   0
LWT  37  64  32  56 /   0   0  10   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
High Wind Watch from Saturday morning through Saturday evening
Eastern Glacier...Northern Rocky Mountain Front...Southern Rocky
Mountain Front.

Flood highlights continue for portions of North Central MT.

&&

$$

http://www.weather.gov/greatfalls



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