Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 250315
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
915 PM MDT Thu Apr 24 2014

.UPDATE...
Current forecast is on track...with just a few
adjustments...mainly to pops. Showers are gradually moving east or
dissipating over North Central MT this evening...thus pops have
generally be removed in this region. A few scattered showers will
pass through Southwest MT...so pops have mainly been left alone in
this region. Temperatures look on track...with just a minor
adjustment in the West Yellowstone area.

Otherwise...the main concern will be the upcoming storm system to
affect the region this weekend. Most models indicate a fairly good
chance for rain over Southwest MT on Friday afternoon...spreading
northward into North Central MT by Friday evening. Rainfall
amounts of 0.25 to 0.50 inches will be possible with this first
event. Then things get fairly tricky for Saturday through
Sunday...as the NAM model is fairly dry...the GFS has precip but
not significant amounts...and the EC is fairly wet. Thus there is
quite a bit of uncertainty on precip amounts for Sat thru
Sunday...and right now it looks to be more of a high pop/low QPF
event for our area...with the heavier precip generally falling out
over Eastern MT. Continue to monitor updates over the next few
days on this developing storm over the weekend. Brusda

&&

.AVIATION...
UPDATED 2323Z.
A weak upper level shortwave will move east of the region this
evening and showers over central Montana will diminish. An upper
level low pressure trof over the Eastern Pacific will move over the
West Coast by Friday morning. Moisture ahead of this system will
move across the Rockies during the day and scattered showers will
develop across central Montana by afternoon. MFR conditions are
possible near showers and over mountains. Elsewhere, VFR conditions
will prevail through the next 24 hours.

&&

.PREV DISCUSSION...
/ISSUED 525 PM MDT Thu Apr 24 2014/
Tonight through Saturday...Increasing clouds with a chance of
showers this afternoon as upper level energy and Pacific moisture
move across the region. Conditions dry up overnight before a
large low pressure system digs into the Western US Friday and
Saturday. Flow aloft turns to the SW ahead of the trough on Friday
with moisture and instability increasing by Friday afternoon. The
first showers and possibly a few isolated thunderstorms develop
over SW MT Friday afternoon, evolving into more widespread
precipitation across Central and North Central Montana Friday
night. A brief period of little activity is expected Saturday
morning before a second wave moves through the region later on
Saturday. Many locations look to get around hone half inch of
liquid with higher terrain and Southwest Montana maybe getting an
inch of liquid, some in the form of overnight snow. Temperatures
remain warm Friday but will cool Saturday. Winds will be breezy,
starting out westerly Friday before shifting easterly Saturday.

Saturday night through Thursday...Medium range models are in good
agreement for the early portion of the forecast period. Southern
portion of an upper level trough over the western USA is expected to
move slowly east-northeast Saturday night through Monday night and
gradually forms a cutoff low over the Great Plains. However, the
northern portion of this trough remains anchored along the British
Columbia coast forming a negative tilt trough that keeps the
Northern Rockies in an unsettled northwesterly flow aloft. This
pattern is expected to keep temperatures generally near seasonable
averages with showers lingering over the forecast area. Have updated
the forecast to increase pops for Saturday night and Sunday then
kept isolated to scattered pops in place through Tuesday. By Tuesday
night models begin to inch the closed low further east and build a
positive tilt ridge into the Northern Rockies. This is similar to
what was shown by the ECMWF for early to mid week last night but
models are now showing more of a dry northeast flow transitioning
into a better likelihood for western Montana to come under the
influence of the ridge axis. Have gone with a somewhat drier
forecast for Tuesday night through Thursday with model guidance in
better agreement in a slow warming trend. mpj

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  35  58  38  52 /   0  60  90  80
CTB  32  57  34  48 /   0  20  90 100
HLN  37  56  37  55 /  20  70  80  60
BZN  35  60  35  54 /  20  70  70  80
WEY  28  49  31  45 /  40  80  60  70
DLN  36  55  36  50 /  30  70  60  60
HVR  34  63  39  57 /   0  10  70  90
LWT  33  57  37  52 /  10  60  90  70

&&

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

&&

$$

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