Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 260450
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
1050 PM MDT Tue Apr 25 2017

.UPDATE...

Thunderstorms are now on a diminishing trend across the
CWA...however...we still have lingering showers as a result from a
sfc low across the southern half of the area and a broad scale
trough...with decent jet dynamics. As this sfc low pushes
south...upper level westerly flow kicks in and gives a brief dry
slot...and diminishing chances for showers for central portions
tonight into Wednesday morning...with some lingering chances for
rain and perhaps some low impact snow for northern and southern
portions. Another upper level trough then sets up across the area
Wednesday afternoon returning more chances for showers and
thunderstorms. Tommorrow`s instability and shear may not be as
high as today...but still sufficient to produce a few isolated
stronger storms with small hail...brief gusty winds...and heavy
rain. Anglin

&&

.AVIATION...
Updated 0450Z.

A very unsettled pattern continues across the region through the
current TAF cycle. One shortwave is moving out of the area at this
time and the associated shower activity should gradually diminish as
well, leaving behind SCT/BKN low clouds and mtn obscurations. MVFR
or lower CIGS will be possible overnight, especially KCTB/KGTF/KLWT.
At KCTB, low level moisture and light winds may allow IFR or lower
CIGS/VIS to develop with BR/FG. After a break in the shower activity
overnight, another round of SHRA/TSRA is expected WED afternoon as
yet another shortwave moves through. Once again, MVFR or lower
CIGS/VIS will be possible with any SHRA/TSRA activity. Small hail
and gusty winds may accompany any TS that develops. Martin

&&

.PREV DISCUSSION...
/ISSUED 304 PM MDT Tue Apr 25 2017/

Tonight through Thursday...Surface analysis this afternoon
reveals a trough aligned north-south broadly along I15. This
trough is associated with a stationary front, and is producing low
level converge and surface vorticity. This, combined with
divergent flow aloft associated with an approaching shortwave
trough is spawning numerous showers and thunderstorms across
N-central Montana. These showers will produce lightning, brief
heavy rain and small hail, along with a rapid drop in temperature.
One or two cold-air funnels may be possible in this environment.
All of this activity will advance west to east this evening along
with the upper level trough. Precipitation tapers overnight, but
only for a few hours as a surge of Pacific moisture spreads inland
on a westerly flow aloft. Showers initiate by late morning
Wednesday east of the Continental divide, then become
widespread/numerous while spreading east across the forecast area
through Wednesday night. Cool and unsettled weather follows on
Thursday, again with numerous rain and mountain snow showers.
Temperatures remain below seasonal averages through this mid-week
period, with snow levels dropping near to below 4000 feet.
Accumulating snow should remain above about 5500 feet. PN

Thursday night through Tuesday...An overall unsettled weather
pattern will reside over the region during the extended period.
Scattered/likely areas of precipitation are likely to continue
Thursday night through Monday, with the lowest chance for
precipitation being Sat/Saturday night. By Tuesday of next week,
the GFS model progs a fairly deep upper level trof of low pressure
to develop over the region, resulting in a fairly good spring
snowstorm over Central MT. However, it is too early to feel
confident in this storm at this time. Otherwise cool afternoon
temperatures on Thursday and Friday will warm a touch over the
weekend, only to cool a bit by next Tuesday. Brusda

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  33  53  36  47 /  70  60  60  60
CTB  30  49  34  44 /  70  70  70  70
HLN  35  54  37  50 /  40  60  60  50
BZN  33  52  34  46 /  50  80  80  60
WEY  26  40  27  37 /  50  90  90  70
DLN  33  51  32  46 /  30  80  80  50
HVR  32  53  35  49 /  40  50  50  60
LWT  30  50  33  43 /  50  70  70  70

&&

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

$$

weather.gov/greatfalls



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