Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 182339
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
535 PM MDT Fri Apr 18 2014

UPDATED AVIATION SECTION

.DISCUSSION...

Today through Sunday...Isolated showers and thunderstorms will
continue this afternoon as an upper-level trough continues to move
over the Treasure State. Some showers may continue brief heavy
rain, gusty winds over 40 mph and graupel. These showers and
thunderstorms will diminish after sunset with loss of daytime
instability. Strong westerly winds will persist along the Rocky
Mountain Front and adjacent plains with wind gusts up to 60 mph
and a High Wind Warning remains in effect until Midnight. Drier
and warmer conditions are expected on Saturday as an upper- level
ridge of high pressure builds into the Northern Rockies. The ridge
will quickly shift east by Saturday night as the next upper- level
trough approaches. Another period of strong and gusty westerly
winds are expected along the Rocky Mountain Front with a slight
chance for showers across north- central and southwest Montana.
Any precipitation will be light with less than one-tenth of an
inch of liquid expected. As for winds, confidence is low on the
potential for high winds exceeding 57 mph, however will continue
to monitor for possible high wind highlights. Temperatures will
climb above seasonal averages on Saturday and lower a few degrees
to near seasonal averages on Sunday in the wake of the upper-
level disturbance. MLV

Sunday night through Friday...Models are in decent agreement into
Tuesday but then significant differences show up. An upper ridge
will result in Sunday night being dry and quite likely Monday as
well. A strong upper trough off the west coast Monday will move
into the west coast states Tuesday with moisture increasing over
the area in the southwest flow aloft. Expect scattered showers to
develop over southwest Montana and spread to central Montana by
afternoon. There will also be a threat of thunderstorms.
Precipitation will increase Tuesday night. Will continue with the
inherited forecast which had chances of precipitation ranging from
70 pct to 100 pct over a good portion of the forecast area. Models
really begin to diverge by Wednesday. The GFS is dry over most of
the forecast area and in particular over the plains. The ECMWF and
GEM models continue with precipitation over the entire forecast
area. On Thursday the GFS and GEM models have precipitation over
the forecast area associated with an upper low over the Dakotas.
On the other hand the ECMWF has an upper ridge over western
Montana with dry conditions except for possibly the western
mountains and southwest Montana. Due to model differences have
stuck close to the inherited chances of precipitation which show a
gradual decrease. Still expect unseasonably mild temperatures
Monday and Tuesday before cooling sets in the wake of a cold front
Tuesday night. Blank

&&

.AVIATION...
UPDATED 2335Z.
Strong and gusty westerly winds will gradually decrease across north
central and southwest Montana mainly from 03Z through 07Z. Gusts
will mostly range from 35 kt to 45 kt, but gusts in excess of 45 kt
are still possible along the Rocky Mountain Front and along the
Canadian border, mainly through 03Z. Winds will then mostly range
from between 5 and 15 kt after 07Z. Otherwise, scattered to broken
mid level clouds will persist through around 06Z with a few showers
possible, then skies will become mostly clear. Westerly winds will
increase again after 18Z Saturday, but they will not be nearly as
strong as those today.
Coulston

&&

.HYDROLOGY...
Expect increased snow melt Monday through Tuesday as
snow levels range from 7000 to 8000 feet in the north to 8000 to
9000 feet in the south. As for precipitation from Tuesday night
through Thursday afternoon have high confidence that most
locations should see at least a quarter of an inch of
precipitation but some models are showing small areas receiving as
much as 1.5 inches to 2.5 inches during that time frame. Of course
with the model differences confidence in precipitation details is
very low at this point. The threat for flooding will increase with
increased snowmelt followed by increased precipitation. For
Wednesday and Thursday with the cooler temperatures snow levels
should drop to near or below 6500 feet. Blank

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  31  65  40  59 /  10   0  20  20
CTB  29  61  36  56 /  20   0  10  10
HLN  34  68  39  62 /  10   0  20  10
BZN  28  68  33  63 /  10   0  20  10
WEY  24  56  33  56 /  30   0  20  10
DLN  29  67  34  62 /  10   0  10  10
HVR  31  64  38  64 /  20   0  20  20
LWT  27  63  35  58 /  10   0  20  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING until Midnight MDT tonight Eastern Glacier...
Northern Rocky Mountain Front...Southern Rocky Mountain Front...
Toole.

&&

$$


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