Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 010451
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1050 PM MDT Sun Aug 31 2014

Updated Aviation

.UPDATE...
Current forecast overall looks in pretty good but did make some
minor changes to the chances of precipitation and sky cover. Also
restricted the mention of thunder for the rest of this evening to
near and southeast of a line from Bozeman to Monida Pass. Also
8 pm instability charts indicate that a thunderstorm would not be
out of the question across a portion of northcentral Montana. Also
changed the forecast for Wednesday near Glacier Park so see
updated discussion for that period below. Blank


&&

.AVIATION...
UPDATED 0500Z.
A few showers will linger overnight at KHVR and KLWT and have kept
VCSH in the TAF. Otherwise, drier conditions are expected elsewhere
tonight with scattered to broken cloud cover and some mountain
obscuration as moist northwest flow aloft persists. Breezy westerly
winds should taper at KCTB after midnight and forecast models hint
at the possibility of low clouds or fog, thus have added VCFG but
forecast confidence is low. Mainly dry and breezy conditions are
expected on Monday with the exception of an isolated mountain
shower. Overall, VFR conditions will be predominant through the
forecast period. MLV

&&

.PREV DISCUSSION...
/ISSUED 520 PM MDT Sun Aug 31 2014/

Sunday night through Tuesday...The broad upper level low pressure
trof that has been affecting the region for the past few days is
slowly moving east. Heights will rise slowly although the northwest
flow aloft will continue to be rather unsettled through the night.
The trend, however, is towards a more stable air mass. Flow aloft
will strengthen over the Rockies early Monday and spread east during
the day. Brisk winds will develop along the Rockies and adjacent
plains but remain well below warning criteria. The region will
remain dry Tuesday as a flat, high pressure ridge will be over
Montana ahead of the next low pressure system to the west. Temps
will remain a bit below normals Monday until warming again
Tuesday. Zelzer

Tuesday night through Sunday...12z deterministic guidance came into
better alignment regarding a broad trough sweeping across the
forecast area early Wednesday. As the trough and associated surface
cold front pass...precip chances will increase primarily over the
Hi-Line and Rocky Mountain Front where the best combination of
forcing for ascent and moisture will be located. Inherited
forecast precipitation amounts for the Glacier Park area looked
on the low side compared to those forecast by the models so
updated the forecast to increase them but did not go as high as
some models forecast. Inherited forecast snow levels of
around 7500 feet look OK so left them alone. Came up with snow
accumulations of around 2 to 4 inches above 8000 feet for the park
but some models were forecasting amounts of as much as near a
foot. Will need to watch this situation closely because should
snow levels drop lower and models continue to forecast snow
amounts of 6 inches to a foot a winter weather highlight might be
needed. By early Friday...trough axis shifts east of the forecast
area as mid/upper ridging builds in across the Pacific Northwest.
Did go ahead and lower PoPs from Thursday night through the
weekend given lack of moisture and broadscale forcing for ascent.
High temps Wed/Thurs will range from the mid 40s to around 50 over
the higher terrain to the low to mid 60s at lower elevations.
Temps begin to moderate back toward climo next weekend.
Blank/Foltz

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  48  70  48  76 /  20  10   0   0
CTB  47  68  46  72 /  20  10  10  10
HLN  47  71  47  79 /  10  10   0   0
BZN  42  66  42  77 /  20  10   0   0
WEY  33  58  32  65 /  30  20  10  10
DLN  44  66  42  76 /  20  10   0   0
HVR  48  74  49  77 /  30  10  10  10
LWT  47  67  47  75 /  20  10  10  10

&&

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

$$

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