Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 192047
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
247 PM MDT Tue Aug 19 2014

.DISCUSSION...

Tonight...Isolated to scattered thunderstorms are expected this
afternoon and evening as Pacific moisture and weak surface front
move across the area. Most of this convection will stay confined
to higher terrain, however a few showers and storms may move over
the plains. Gusty winds and brief heavy rain may accompany some
stronger storms, however severe weather is not anticipated. Meanwhile,
a large-scale trough of low pressure will continue to deepen over
the Pacific Northwest and Northern Rockies. Weak shortwave energy
embedded within the trough will continue to keep a chance of
thunderstorms along the Continental Divide, though locations over
the plains should remain dry before the pattern changes on
Wednesday.

For Wednesday...expect a Canadian cold front to begin to push
southward into the region by late afternoon and through the
evening hours. There will be enough instability that scattered
thunderstorms should accompany the frontal passage. It does not
appear there will be enough instability for any severe storms at
this time. Afternoon highs will be near seasonal averages.

For Thursday...northerly surface winds...combined with cloud cover
and precip...will allow for much cooler temperatures to move into
the region. Afternoon highs will mostly be in the 60s over the
north and in the lower 70s over the southwest. The GFS/EC are the
most widespread with the precip on Thursday...with the NAM
confining the main area of precip to the mountains. With the
northerly upslope...the precip should generally be a bit more
widespread...thus prefer the GFS/EC models for now...and have
rather high pops over much of North Central and Central MT.
Overall precip amounts of 0.50 to 1.00 will be possible over much
of North Central and Central Montana from Wednesday evening
through Thursday. Brusda/MLV

Thursday Night through Tuesday...Medium range models remain in good
agreement that cooler and much wetter conditions will prevail late
this week and through much of the upcoming weekend. Objective
guidance temperatures from the GFS and ECMWF have trended cooler and
are in better agreement with the raw model solutions which are much
below seasonal averages through the weekend. Models also continue to
suggest that higher elevations of Glacier Park could see a mix of
rain and snow with minor accumulations possible, but at this time it
does not appear that any significant impacts should be expected.
Models solutions remain somewhat divergent for Sunday through
Monday but have reversed solutions with the ECMWF now keeping
troughing over the Northern Rockies while the GFS brings shortwave
ridging over the region on Monday. By Tuesday both models trend back
toward swinging another shortwave through Montana for another chance
of precipitation. Due to the uncertainty during this period I have
kept temperatures below seasonal averages with little change from
day to day and trended toward climatological PoPs. mpj

&&

.AVIATION...
UPDATED 1800Z.
Increasing west winds are expected across the north-central plains
this afternoon with gusts up to 20kts possible as a cold front
approaches. Isolated showers and thunderstorms are possible after
21z but confidence is low on thunderstorm coverage so have added
VCSH for most TAF locations and will continue to monitor. An
upper-level trough of low pressure and associated surface cold
front will begin to push into Montana tonight after 06z and winds
will shift north-northwest. A period of MVFR conditions are
possible at KCTB late tonight and Wednesday morning as moisture
and cooler air begin to push in behind the cold frontal passage.
Elsewhere, VFR conditions are expected over the next 24 hours. MLV

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  57  82  55  67 /  10  40  60  70
CTB  53  75  50  62 /  10  60  70  70
HLN  56  83  53  70 /  20  40  50  70
BZN  53  83  51  74 /  30  40  50  70
WEY  45  70  44  65 /  50  50  50  50
DLN  49  78  48  74 /  30  40  50  50
HVR  59  83  57  67 /  10  20  60  70
LWT  57  80  53  68 /  20  30  60  70

&&

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

$$

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