Area Forecast Discussion
Issued by NWS Great Falls, MT

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867
FXUS65 KTFX 220253
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
853 PM MDT Wed Jun 21 2017

.UPDATE...

Evening updated has been published. Previous forecast is holding
strong, so only minor adjustments were made to POPs and Sky Cover
to account for recent radar and satellite trends. With regards to
POPS, added 10% POPs further south across portions of Pondera,
Chouteau, and Southern Blaine counties. These POPs were added due
to current radar trends, however, given Great Falls evening
sounding which depicted very dry air throughout the atmospheric
column, am only anticipating sprinkles out of these showers.
Otherwise, scattered showers and even an isolated thunderstorm
will be possible along the Hi-Line before the midnight hour. Also,
adjusted sky cover up a bit across the Hi-Line to account for on-
going satellite trends and recent short term guidance. - Moldan

&&

.SYNOPSIS...

Breezy and generally dry conditions are expected for this evening.
There will be a slight chance of a few thunderstorms across the
Hi-Line of Montana through sunset. Overnight tonight will see dry
and less breezy conditons. Thursday will be cooler with more
breezy conditions. A few showers are also possible across northern
portions.

&&

.AVIATION...
Updated 0040Z.

VFR conditions will continue through at least Thursday. Energy in
the west-northwest flow aloft will keep scattered to broken mid
clouds with a chance of showers along the Hi-Line through around
08Z. Lingering gusty westerly winds will also gradually decrease
overnight. A stronger disturbance with an associated weak cold front
will move south over the forecast area from 15Z through 21Z,
increasing winds and shifting them more northwesterly. A surge of
moisture behind this front will also bring increasing mid level
clouds, along with a chance of showers/thunderstorms for the Hi-Line
once again.  Coulston

&&

.PREV DISCUSSION...
/ISSUED 640 PM MDT Wed Jun 21 2017/

Today through Thursday...A pseudo warm front has developed along
the Hi-Line this afternoon...and is starting to develop a cumulus
cloud field. This area will need to be monitored this afternoon
and evening as a weak wave from an upper low in Canada clips the
northern portions of the state...and meets weak instability...and
abundant amount of shear in the prime exit region of the upper
jet. Any thunderstorm development will be isolated to widely
scattered...with gusty to isolated strong winds being the main
threat...given inverted-v soundings and the high based nature of
the storms. Confidence is still low for thunderstorm
development...as most storms are still expected to remain in
Canada. The remainder of the area should stay dry and mostly clear
today. Some gusty winds have developed from a passing boundary
earlier today...and could remain gusty into the late evening
hours. Winds and thunderstorms then diminish tonight. Thursday
will see more gusty winds and cooler temperatures as a weak cold
front drops south out of Canada. A few isolated to widely
scattered showers are also possible...mainly along the Hi- Line
and Rocky Mountain Front. Instability looks weaker yet on
Thursday...but cannot rule out an isolated thunderstorm as a
result of the weak front. Anglin

Thursday night through Tuesday...An unseasonably strong SFC high
then builds in Thursday night with below normal temps expected
under clear skies/light winds. MT will remain on the western
periphery of a large scale upper level trough late this week into
early this weekend. Shortwave and upper level jet energy moving
through cyclonic NW flow aloft will support at least a slight
chance of showers Friday and Friday night. Best chance looks to be
along the Northern Rocky Mtn Front/Glacier Park vicinity late
Friday as the next surge of surface high pressure nosing south
from AB creates a period of N/NE upslope flow late Friday, which
then translates east across N-central MT Friday night into
Saturday morning. Airmass dries Saturday and Sunday as the upper
trough moves off to the east. Surface high pressure center drifts
east across MT Saturday with morning low temps around 10 degrees
below seasonal averages Saturday morning and possibly again Sunday
morning. Upper ridge amplifying along the West Coast late this
weekend shifts inland and across region early next week for more
significant warming, though this appears to be brief with the next
Pacific trough moving onshore Tuesday or Wednesday. There is
still a great deal of uncertainty by this point with the inland
progression of the trough, but somewhat cooler conditions with at
least a chance for precipitation looks to develop following the
progression of the ridge axis east of the region. Martin/Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  79  46  68  42 /   0   0  10  10
CTB  74  43  64  41 /  10  20  10  30
HLN  82  49  71  45 /   0   0   0   0
BZN  83  44  72  40 /   0   0   0   0
WEY  76  40  68  34 /   0  10   0   0
DLN  80  43  72  41 /   0   0   0   0
HVR  79  47  67  44 /  20  30  20  10
LWT  77  45  65  40 /  10   0   0  10

&&

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

$$

weather.gov/greatfalls



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