Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 140953
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
353 AM MDT Mon Aug 14 2017

.SYNOPSIS...

Scattered showers and storms are possible today and tonight
across Southwest Montana, with isolated showers and storms
possible along the Hi Line during the afternoon and evening
hours. Some gusty winds are possible with any stronger shower and
storm that develops this afternoon and evening over both Southwest
Montana and the Hi Line. Temperatures over the next 48 hours are
expected to remain below normal, with generally light winds.

&&

.DISCUSSION...

Today through Wednesday...broadscale troughing, will transition to
near zonal/slightly northwesterly flow over the North Rockies and
Northern High Plains. For today and tonight, H500 jet max moving
across Eastern Idaho and Northwestern Wyoming this morning, will
transition east/northeast into Southeastern Montana/Northeastern
Wyoming by the early morning hours on Tuesday. In addition to this
H500 feature, a weaker jet max rounding the trough axis over
Southern BC this morning, will slide east southeast into the
Northern Rockies by this evening. The aforementioned synoptic setup,
should allow for scattered showers and thunderstorms over
Southwestern Montana, and at least some isolated showers/storms
across the Hi-Line today and tonight. By Tuesday, the H500 flow will
become nearly zonal as a wide trough axis slides east across the
North Rockies. H500 temperature will cool throughout the day to near
-15C by the afternoon hours, with southwesterly flow at H700. The
combination of steepening lapse rates from diurnal heating and
"moistening" southwest flow, will bring a chance for precipitation
across Southwest and into portions of Central Montana for the day on
Tuesday.

Zonal flow throughout the H700 to H500 layer then develops by
Tuesday evening, persisting through the day on Wednesday. This
pattern will/should bring quiet conditions to most if not all of
Southwest and North Central Montana. Breezy conditions are possible
during the afternoon hours on Wednesday along the North Rocky
Mountain and onto adjacent plains due to downsloping effects, with
some gusts approaching 25 to near 40 mph (mainly over the higher
ridgetops/mid-slopes). These downsloping winds combined with daytime
mixing and temperatures in the mid to upper 80s, will cause relative
humidity values to fall below 20 percent across all of North Central
and Central Montana.

Temperatures are expected to remain below normal over the next 48
hours, with values returning to near normal by Wednesday. - Moldan

Wednesday Night through Sunday...We stay in a generally zonal upper-
level flow aloft as we get into the second half of the week. A
passing disturbance may ignite some isolated showers or storms and a
wind shift to northwesterly over the north-central plains Thursday.
We return to a weak ridging pattern aloft Friday but then the region
may come under the influence of increasingly weak upper level
troughing over the Pacific Northwest, which may help to increase
southwest (downslope) winds across the region, which may result in
elevated fire weather conditions. CC

&&

.AVIATION...
Updated 0415Z.

VFR conditions are expected over the next 24 hours. Clouds and any
lingering showers/storms in the KHVR and KLWT areas will continue to
decrease from west to east through 09Z as the cold front exits the
area. However, a weak disturbance will bring showers to far
southwest Montana (KBZN, KEKS) between 09Z and 15Z. Weak instability
will redevelop along the Hi-Line (KHVR) and in far southwest Montana
(KBZN, KEKS) after 18Z, so have continued the chance of showers
(KHVR) and thunderstorms (KBZN, KEKS) between 21Z and 03Z.
Coulston

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  77  47  79  49 /  10  10  10  10
CTB  76  44  77  46 /  20  20  10  10
HLN  78  51  81  51 /  10  10  10  10
BZN  76  46  78  47 /  70  20  20  20
WEY  63  39  67  37 /  50  50  40  30
DLN  74  46  77  46 /  40  30  20  10
HVR  79  51  80  50 /  20  20  10  10
LWT  74  49  76  49 /  10  10  20  10

&&

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

$$

weather.gov/greatfalls


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