Special Weather Statement, NWS Great Falls, MT

Area Forecast Discussion
National Weather Service Great Falls MT
600 PM MDT Mon Jun 26 2017

Aviation Section Updated

.SYNOPSIS...

Upper level high pressure ridge over the region will bring hot
conditions to Montana today. An upper level disturbance may kick off
a few thunderstorms this afternoon. Any storm that develops will be
capable of strong, gusty winds. Later tonight, a surface cold front
will sweep across the state with a better coverage of showers and
thunderstorms. The front will bring cooler temperatures with it on
Tuesday.

&&

.DISCUSSION...

Rest of today through Wednesday...Latest satellite imagery shows a
convectively-induced wave moving into western Montana at this time
with a second, stronger s/w back to the west, moving onto the NRN
CA/OR coast. Still think this lead wave should provide enough lift
for isolated storms through this evening, especially along/east of
the I-15 corridor and latest radar imagery suggests this is
underway as of 225 pm. Gusty/damaging winds look to be the main
threat (ie. 45-65 mph). There may be a brief lull in t-storm
activity this evening in the wake of the first wave, but the
coverage of thunderstorms should increase again tonight
associated with the 2nd and stronger wave mentioned above. It
will likely remain unstable through the night, but a gradual
decrease in instability and a lack of better shear should limit
the threat for any severe weather overnight.

In the wake of tonight's s/w, a cold front will drop south out of
Canada. The models are struggling with how unstable it will get
ahead of this front and this may largely depend on how much precip
falls tonight (ie. more precip could lead to more stable
conditions and vice-versa). Regardless, the threat of showers and
storms should continue through Tuesday afternoon. Of note, the
greatest instability/shear looks to be across far SW MT and is
where confidence is higher regarding the development of a few
stronger storms capable of gusty winds and hail. This same area
looks to be the focus on Wednesday as well. The overall severe
threat Tuesday and Wednesday looks somewhat lower due to a lack
of better shear. With the flow turning more northwesterly,
temperatures will trend much cooler Tuesday and Wednesday compared
to today. MARTIN

Wednesday Night through Sunday...An unsettled, northerly flow aloft
develops Wednesday night and Thursday associated with a closed upper
level low drifting through AB/SK. A cold front trailing behind this
system will lower temperatures into the low- to mid-70s on Thursday.
This pattern brings chances for scattered showers and thunderstorms,
although model guidance continues to differ on the timing and
spatial extent of this activity.  The latest forecast guidance has
slowed the departure of the upper low, with chances for isolated
light rain showers continuing Thursday night into Friday. Model
consensus suggests weak ridging through the weekend, providing
generally fair weather with temperatures near 80F and isolated
showers or thunderstorms possible. PN

&&

.AVIATION...
Updated 0000Z.
Scattered thunderstorms are moving through the eastern portions of
the region now. Main threat this evening will be gusty winds.
Another round should move in after 05z...and move northeast through
the area. A third round will move from north to south through the
region after 14Z Tue. Brief heavy rain main threat tomorrow. Brusda

&&

.FIRE WEATHER...
A Red Flag Warning remains in effect for zone 113 with modest
confidence that there will be critical fire weather conditions
into early this evening, primarily Blaine County. Gusty southeast
winds ahead of a surface low pressure system will combine with
minimum RH values in the teens and increasingly dry fuels in
eastern portions of Fire Weather Zone 113. In addition, isolated
thunderstorms moving through the area this evening could lead to
gusty and erratic winds. CC/MPJ/Martin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  61  77  50  77 /  30  40  10  10
CTB  57  76  48  75 /  20  20  10  10
HLN  61  79  52  78 /  50  40  10  10
BZN  53  76  47  75 /  30  80  20  20
WEY  44  69  38  66 /  40  70  30  40
DLN  54  73  47  73 /  40  60  20  10
HVR  62  80  52  81 /  40  40  10  10
LWT  59  75  48  75 /  40  60  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 8 PM MDT this evening Hill and Blaine
Counties.

&&

weather.gov/greatfalls

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