Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 182322
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
522 PM MDT Mon Aug 18 2014

.DISCUSSION...

Tonight through Wednesday...Airmass beginning to become a bit
unstable as satellite imagery showing cumulus fields developing
across the area. Monsoonal moisture also working its way across
southwest Montana with isolated thunderstorms now developing along
the Montana-Idaho border where CAPE values are running between 500
and 1000 J/kg. As has been the case the past several days, bulk
shear numbers are virtually nonexistent so severe thunderstorm
development is not anticipated. An area of elevated CAPE values
also exists along the Rocky Mountain Front and an isolated
thunderstorm is also possible there. Convective activity should
end by midnight. Tuesday looks to be a repeat of today with
isolated thunderstorms over the high country of southwest Montana.
The weather pattern faces a significant change on Wednesday as a
cold front moves across the area during the afternoon. Showers and
thunderstorms will become widespread during the afternoon and
evening. Temperatures will remain above seasonal averages Tuesday
but drop below seasonal averages Wednesday as a cooling trend
commences.

Wednesday Night through Monday...Models continue to trend toward a
significant change in the weather later this week. An upper level
jet will carve out a broad trough over the Northern Rockies for an
increasing chance of showers and thunderstorms Wednesday night and
Thursday. Models also continue to suggest that there will be a good
chance for widespread precipitation across North Central Montana by
Friday so have continued to trend PoPs higher for late this week.
Temperatures are expected to fall below seasonal averages with the
coolest temperatures anticipated for Friday and Saturday. Higher
elevations of Glacier Park may see snow mixed in with the rain early
Saturday morning but widespread accumulations are not anticipated.
Models diverge Sunday and Monday with the ECMWF continuing to
accelerate the upper trough eastward while the GFS holds it back
over the Northern Rockies. Will continue cool temperatures with PoPs
remaining above seasonal averages for now. mpj

&&

.AVIATION...
UPDATED 2322Z.
Weak high pressure aloft will generally keep the air mass warm and
dry. A slight chance for showers or thunderstorms development is
expected over Southwest Montana Tuesday afternoon but areas north
should be free from any convection. VFR conditions will prevail
through the next 24 hours.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  88  57  81 /   0  10  10  40
CTB  57  84  54  74 /  10  10  10  60
HLN  57  89  57  84 /   0  10  10  40
BZN  53  87  54  83 /  10  20  30  40
WEY  43  74  46  69 /  20  20  40  40
DLN  51  82  50  80 /  10  20  20  40
HVR  59  91  60  82 /   0   0  10  40
LWT  57  88  58  81 /   0  10  20  40

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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