Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 231807
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1150 AM MDT Sun Apr 23 2017

Aviation Section Updated.

.UPDATE...

A minor shortwave trough is crossing the continental divide this
morning, producing light rain along the Rocky Mountain Front and
adjacent plains as moisture ascends over cool, easterly surface
winds. The forecast was updated to shift the areas of rain further
north across North-central Montana. Expect this band of
precipitation to spread toward the east-northeast through early
afternoon north of a line from around Helena to Lewistown.
Areas of fog will persist under low ceilings amid the moist
easterly surface winds. Satellite imagery reveals clearing skies
over Southwest Montana, following an area of rain and snow that
had moved through the area earlier this morning. Short-term models
continue to destabilize this area under those clearing skies, so
the forecast continues to support isolated afternoon
thunderstorms. PN

&&

.AVIATION...
Updated 1750Z.

A widespread area of light rain with IFR or temporary LIFR continues
to move northeast from KGTF to KHVR this afternoon. Skies are partly
cloudy across southwest MT, but with showers expected to return
overnight. PN

&&

.PREV DISCUSSION...
/ISSUED 550 AM MDT Sun Apr 23 2017/

Today (Sunday) through Tuesday...an unsettled and "cool" pattern is
in store for most of the short term. Upper level ridging, which
brought calm and seasonable temperatures on Saturday, will
continue to break down during the day on Sunday as a shortwave
moves from the Pacific Coast and across the Intermountain West
into the morning hours on Monday. A weak front will begin to
traverse North Central and Southwest Montana during the late
morning and into the afternoon hours today, before stalling near
the Interstate 90 corridor across Southwest Montana. This front
and the approaching upper level shortwave, will bring the chance
for rain showers to the region today. A few thunderstorms are also
possible across Southwest Montana during the afternoon and into
the evening hours, as weak instability develops. Rain is then
expected to change over to snow tonight and into the morning hours
on Monday at elevations above 5500 feet, with a rain/snow mix as
low as 4500 feet and all rain below 4500 feet. Snow accumulations
over this time frame are expected to be light, with little to no
impacts expected to travel at this time. Zonal flow will then
become the predominate upper level feature through the remainder
of the short term, with weak embedded waves quickly racing east
within it. This will bring another chance for widespread light
accumulating precipitation Monday afternoon and into the day on
Tuesday, especially across Southwestern Montana where 0.25 to 0.50
inch of additional moisture on top of what falls today through
Monday morning is possible.

High temperatures through the short term period will be anywhere
from 5 to 10 degrees below normal for this time of the year, with
overnight lows running near normal (due to expansive cloud cover
limiting radiational cooling). - Moldan

Tuesday night through Sunday...Overall an unsettled weather pattern
will continue to reside over the region through much of the extended
period. With a deep upper level trof of low pressure over the area
until at least Friday, expect periods of rain/snow along with below
normal temperatures. The best chance for snow will be for elevations
above 5500 feet, but snow levels could lower to around 4000 feet
during the overnight/early morning hours. A few inches of snow are
possible in the mountains daily. Overall rainfall amounts for lower
elevations will generally average between 0.20 and 0.40 inches for
Wed thru Fri. In terms of pops, leaned towards the higher pop
solution of the National Blend, especially for Wed through Fri. By
next weekend, the upper level trof will start to move eastward a
bit, thus the chances for showers will be getting lower, and
temperatures will start to warm a touch, closer to seasonal normals.
Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  52  35  55  31 /  90  20  20  30
CTB  56  35  52  30 /  50  20  40  40
HLN  55  36  55  35 /  70  30  40  30
BZN  58  36  52  33 /  70  70  40  50
WEY  50  30  42  27 /  60  70  60  60
DLN  57  34  52  32 /  80  60  40  50
HVR  53  36  55  33 /  90  60  40  30
LWT  56  35  52  31 /  70  50  40  30

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



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