Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 192330
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
530 PM MDT Sat Apr 19 2014

.DISCUSSION...

Today through Monday...Dry and breezy conditions today will be
followed by increasing clouds and an isolated mountain shower
tonight as a weak upper-level trough of low pressure moves across
the area. Though moisture is very limited with this disturbance, a
tightening pressure gradient will yield increasing winds along
the Rocky Mountain Front and adjacent plains. Winds along the
Rocky Mountain Front as well as eastern Glacier, Toole and Liberty
counties will have the strongest winds with wind gusts 60 to 65
mph beginning late tonight into Sunday afternoon. Have issued a
High Wind Warning for these areas beginning at 9pm this evening
through 6pm Sunday. The strongest period of winds will be Sunday
morning with a frontal passage. Breezy westerly winds are also
expected across the remainder of north-central Montana though high
winds greater than 57 mph are not anticipated. Winds will be
lighter across southwest Montana. No precipitation is expected in
the plains or valleys with this disturbance and only a slight
chance of precipitation is possible in the mountains. An upper-
level ridge of high pressure will build into the Treasure State
Sunday night and Monday with decreasing winds, dry conditions and
above average temperatures expected. This ridge will not last for
very long as a stronger storm system begins to move into the
Pacific Northwest on Monday. MLV

Monday night through Saturday...Large scale upper level trough
moves onto the west coast Monday night and progresses east into
the interior western US Tuesday, crossing the Rockies Tuesday
night/Wednesday. Models are in fair agreement through Tuesday
night with SW flow aloft ahead of the trough bringing warming to
the region on Tuesday before the initial shortwave and upper level
jet energy associated with the trough approach the Northern
Rockies late Tuesday afternoon. Inverted trough of low pressure at
the surface and cold front will shift east across the forecast
area Tuesday night in conjunction with good mid-upper level
forcing associated with the trough, bringing widespread
precipitation to most of the forecast area. Enough warming and
destabilization occurs Tuesday afternoon ahead of the trough for a
chance of thunderstorms late Tuesday afternoon and evening, mainly
over central and eastern portions of the forecast area. Models
then diverge with the evolution of the trough Wed/Thurs with GFS
model continuing to depict a closed/stacked system that slowly
drifts from eastern MT into the Dakotas, resulting in continued
wrap around precipitation and northerly/moist upslope flow through
at least Thursday morning, while the ECMWF model moves the system
through much quicker with drying and weak ridging moving over the
region late Wednesday through Thursday. With a downstream upper
level ridge over the central US/Canada depicted by both models, am
leaning toward a solution slower than the ECMWF but not as
wet/prolonged as the GFS and have maintained higher pops through
Wednesday evening with gradual drying Wednesday night/Thursday.
Cooler temperatures are expected Wednesday and Thursday as the
upper trough moves over the region with snow levels lowering to
around 5000-6000 ft Wednesday, then as low as around 4000 ft
Wednesday night. By Friday, models come back into agreement, at
least at the large scale, with weak upper level ridging shifting
east across the region before the next deep trough in the eastern
Pacific/Gulf of AK moves onto the west coast next weekend.
Hoenisch

&&

.AVIATION...
UPDATED 2330Z.
VFR conditions will prevail for the next 24 hours at all taf sites.
Winds will increase through the taf period as a weak cold front
pushes through the area. Gusts will generally range into the 30-40
kts range, with some gusts approaching 50kts at KCTB. Suk

&&

.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. Confidence remains high that most locations should see at
least a quarter of an inch of precipitation late Tuesday and Tuesday
night with central portions of the forecast area likely to see
around a half inch of precipitation during this period. Convective
nature of precipitation Tuesday evening could result in localized
heavier amounts. Confidence remains low however for additional
precipitation amounts Wednesday and Thursday due to model
differences. The threat for flooding will increase early next week
with increased snowmelt followed by widespread precipitation Tuesday
night. For Wednesday and Thursday, cooler temperatures and lower
snow levels should reduce runoff from snowmelt at higher elevations.
Hoenisch/Blank

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  41  59  34  68 /  10  10   0   0
CTB  37  57  30  66 /  10  10   0   0
HLN  39  61  37  70 /  10  10   0   0
BZN  34  62  32  70 /  20  10   0   0
WEY  33  55  30  60 /  20  10   0   0
DLN  35  61  34  70 /  10  10   0  10
HVR  41  65  31  70 /  10  20   0   0
LWT  38  58  32  65 /  10  10   0   0

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
HIGH WIND WARNING from 9 PM this evening to 6 PM MDT Sunday
Eastern Glacier...Liberty...Northern Rocky Mountain Front...
Southern Rocky Mountain Front...Toole.

&&

$$


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