Area Forecast Discussion
Issued by NWS Great Falls, MT

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118
FXUS65 KTFX 200924
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
324 AM MDT Tue Jun 20 2017

.SYNOPSIS...

A weakening upper level ridge of high pressure over the region
will result in very warm conditions today with increasing winds as
a Pacific cold front moves across the region this afternoon and
evening. A few showers and thunderstorms are possible today,
mainly over southwest Montana with some of the thunderstorm
activity late this afternoon potentially producing strong gusty
winds and hail.

&&

.DISCUSSION...

.Today through Wednesday night...
Low amplitude upper level ridge progressing east across the Northern
Rockies and MT early this morning with embedded mid level
moisture/instability resulting in a few early morning
showers/isolated thunderstorms tracking into central MT. These
should dissipate this morning, but models poor handling of these
features overnight leads to somewhat lower than average
confidence in moisture/precipitation placement later today.
Somewhat greater cloud-cover than previously anticipated moving
across the region today, but still expect the warmest temperatures
of the week today with many locations reaching the upper 80s.
Still expect convection to be rather isolated this afternoon and
primarily focused over SW MT, but with somewhat better moisture
evident upstream of the region early this morning can`t rule out
an isolated storm or two further north across the forecast area as
well. Greatest instability/CAPE will be focused across SW MT this
afternoon with moderate wind shear also present for some
potential for an isolated strong to severe storm with main threat
being strong winds, though hail is also possible if any of these
storms could be maintained despite very strong winds aloft. Late
this afternoon and evening the surface trough/Pacific front
shifts into eastern MT with widespread breezy to gusty west winds
spreading across the forecast area. Weak surface high pressure and
cooler airmass move into the region from the NW late tonight
through Wednesday with afternoon temperatures about 10 degrees
cooler. Drier conditions will prevail Wednesday with breezy west
to northwest winds likely Wednesday afternoon. Hoenisch

Thursday through Monday...The main issue during this period is the
evolution of an upper level trough that is forecast to get carved
out across a large portion of the US. The models generally agree on
the trough, but it is with the individual shortwaves within the
larger trough that they are struggling with. Regardless of
timing/location, this pattern favors cold fronts dropping south out
of Canada, each with a brief cooldown and possibly some showers.

Still, though, significantly impactful weather is not expected at
this time. It is worth noting, however, that recent runs of the EC
and CMC have hinted at a more widespread precip event for a part of
the area with one of the frontal passages later this week. But, all
of the models have generally backed off this idea for now. Still
worth continuing to keep an eye on model trends regarding this
potential. The only other item of interest is the potential of below
to well below normal lows Friday night with the potential of an
unseasonably strong SFC high building in. Martin


&&

.AVIATION...
Updated 0425Z.

VFR conditions will continue at least through Tuesday evening. A
broad high pressure ridge will keep a brisk westerly flow aloft with
scattered to broken mid/high level clouds over most of the area,
especially along the Hi-Line. After 18Z, a weak disturbance in the
flow will bring increasing westerly winds to the area, along with a
chance of isolated showers and thunderstorms south of Interstate 90
(including KEKS). The main threat from these storms will be strong
wind gusts in excess of 35 kt due to very warm and dry air at the
surface. Storms, clouds, and winds should decrease after 02Z
as the airmass begins to stabilize.
Coulston

&&

.FIRE WEATHER...

Fire weather concerns will be elevated this afternoon as
temperatures warm to the mid to upper 80s at lower elevations
with relative humidity falling to around 20 to 30 percent.
Strengthening westerly flow aloft and deep afternoon mixing will
promote gusty west winds late this afternoon, continuing into the
evening period along the Rocky Mtn front and adjacent plains.
Cooler temperatures are expected Wednesday, although dry and
breezy conditions will continue. Fire weather highlights are not
anticipated at this time due to fuel conditions near peak
greenness across much of the area, though the warm/dry and windy
conditions will likely accelerate the drying & curing process,
particularly across far-eastern portions of north-central MT,
where recent precipitation has not been as abundant. Hoenisch

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  86  55  75  45 /  10   0   0   0
CTB  84  49  71  41 /  10   0   0  10
HLN  88  57  79  48 /  20   0   0   0
BZN  89  55  80  42 /  20  20   0   0
WEY  81  47  77  37 /  40  20   0   0
DLN  86  54  79  43 /  20  10   0   0
HVR  91  55  77  45 /  10  10   0  10
LWT  87  54  75  44 /  10  10   0   0

&&

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

$$

weather.gov/greatfalls



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