Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 210455

1050 PM MDT Wed Aug 20 2014


Update forthcoming. Have made minor adjustments to the PoP grids for
the remainder of the evening. Thunderstorm coverage has decreased
and will continue to do so through midnight. The surface cold front
continues to push south and showers will increase again in areal
coverage behind the frontal passage, with the cold front likely
reaching the Great Falls area between 11 pm and midnight. Very wet
and unsettled pattern still on track for the area the next several
days. Temperatures tonight look on track.


Scattered -SHRA continue to move through parts of central MT this
evening ahead of an approaching upper-level trough and surface cold
front. At 0430Z the front was just north of KGTF and is expected to
make slow progress southward through the overnight period.
Precipitation should become more isolated after 06Z but then
redevelop behind the front vcnty KCTB/KHVR around 09-10Z, with the
coverage of showers expanding south toward KGTF/KHLN/KLWT on Thurs
morning.  Ceilings should generally remain VFR tonight, with some
brief MVFR conditions possible under any moderate showers. As the
rain develops tomorrow morning, ceilings will gradually trend
downward to 3000-5000 ft, with better chance for MVFR ceilings from
midday onward as rain becomes more widespread.


.PREV DISCUSSION...Issued 253 PM MDT Wed Aug 20 2014

Tonight through Friday...A deepening upper-level trough of low
pressure will bring a period of widespread, prolonged
precipitation across the area beginning late tonight through
Friday. The Canadian surface cold front remains north of the
International Border and is expected to cross the border between 5
pm and 8 pm this evening. Instability and Pacific moisture ahead
of the front will lead to scattered showers and thunderstorms this
afternoon and evening. Some thunderstorms could produce gusty
winds up to 30 mph, small hail and heavy rain. This activity will
diminish after sunset before steadier rainfall develops behind
the frontal passage. The first period of rainfall will occur late
tonight into Thursday morning, then there should be a break from
midday Thursday through Thursday evening before the next round of
widespread precipitation occurs Thursday night into Friday. The
airmass will cool further Thursday night with snow levels lowering
to around 8000 feet in Glacier National Park. The coolest period
will be Friday night into Saturday morning as snow levels lower to
6500 feet in Glacier National Park. Total precipitation through
Friday will be near one inch, however an additional inch of
precipitation is possible through Sunday morning. High
temperatures will be 20 to 30 degrees below seasonal averages with
highs in the 60s Thursday and Friday. MLV

Friday Night through Wednesday...Medium range models are in good
agreement that wetter and much cooler conditions will prevail
through the weekend. Objective guidance temperatures continue to
trend cooler keeping high temperatures in the 50s and 60s Saturday
and Sunday. Overnight lows will be cold enough to support minor snow
accumulations over the highest elevations of Glacier Park, but it
does not appear that any significant impacts should be expected.
Models are in better agreement for the Monday through Wednesday
period with upper level troughing remaining over the Northern
Rockies through Tuesday. Unsettled conditions will keep isolated to
scattered showers and thunderstorms in the forecast but temperatures
are expected to warm back toward the 70s. By Wednesday the trough
will finally progress eastward allowing shortwave ridging to build
over Montana and temperatures to trend back toward seasonal
averages. mpj


GTF  55  66  51  64 /  80  80  60  90
CTB  51  58  47  57 /  80  80  60  90
HLN  54  72  51  67 /  70  80  60  90
BZN  50  73  49  70 /  50  80  60  70
WEY  43  63  42  59 /  50  50  50  40
DLN  47  73  45  66 /  50  50  50  70
HVR  57  66  53  67 /  80  80  60  80
LWT  54  65  50  61 /  70  70  60  80




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