Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 191741
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
1141 AM MDT Tue Aug 19 2014

.UPDATE...

Current forecast is on track this morning so did not make any
changes to the forecast. An isolated thunderstorm is possible in
higher terrain along the Continental Divide this afternoon and
evening, however severe weather is not anticipated. MLV

&&

.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

&&

.PREV DISCUSSION...
/ISSUED 540 AM MDT Tue Aug 19 2014/
Today through Thursday...Today should be the last very warm day
for most locations for quite awhile...as a change in the weather
pattern will start to occur by Wednesday evening.

For today...an upper level ridge of high pressure will begin to
move eastward away from the region. This will allow for a warm
southerly flow to develop over the region...with afternoon highs
mostly ranging from the upper 80s to lower 90s. Again there will
be a small chance for a passing thunderstorm...mainly south of a
line from Dillon to Bozeman and up in the Glacier Park region.

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 on the warm side...but with
increasing cloud cover they should not be as warm as Tuesday.

For Thursday...the biggest change is the northerly surface
winds...combined with cloud cover and precip...will allow for much
cooler temperatures to move into the region a day earlier than
previously thought. Thus 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 0.40 to 0.70 will be possible over much
of North Central and Central Montana from Wednesday evening
through Thursday. Brusda

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

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  89  57  82  55 /  10  10  40  60
CTB  84  53  75  50 /  10  10  60  70
HLN  90  56  83  53 /  10  10  40  50
BZN  89  53  83  51 /  20  30  40  50
WEY  77  45  70  44 /  30  40  50  50
DLN  85  49  78  48 /  20  20  40  50
HVR  92  59  83  57 /  10  10  40  50
LWT  88  57  80  53 /  20  20  40  60

&&

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

$$

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