Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 202334
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
535 PM MDT Sat Sep 20 2014

UPDATED AVIATION SECTION

.DISCUSSION...

Tonight through Monday...Forecast area will remain under the
influence of an upper level ridge tonight and Sunday for mostly
clear and dry conditions. Temperatures for tonight and Sunday will
remain above seasonal averages and winds will be generally light
as they gradually veer around to the south-southeast. Increasing
uncertainty in the forecast develops Sunday evening as an upper
level closed low, currently over the Central California coast,
drifts northeast and approaches the Yellowstone region. Latest
models weaken this feature into an open trough as it approaches
Southwest Montana Sunday night, then shear it eastward on
Monday. Biggest question will be how far north will scattered
showers and thunderstorms associated with the upper low move.
Morning model runs suggest that isolated precipitation could move
as far north as the Little Belt Mountains by Monday afternoon.
Stability parameters indicate that isolated thunderstorms may even
form over mountainous areas as far north as Glacier Park. Have
therefore tweaked forecast pops for Monday a bit higher in the
north. However, it should be noted, that the likelihood for any
strong to severe storms appears low at this time. mpj

Monday Night through Saturday...Remnants of the weakening cut-off
low drift away to the east as an upper level ridge begins to
amplify over the Intermountain west. This will result in fair and
warmer conditions through early Thursday. The upper ridge axis
moves east of the region on Thursday as heights begin to fall
ahead of a broad synoptic trof advancing through the Pacific
Northwest. Isolated showers and thunderstorms will begin to
develop Thursday evening with decreasing stability over the higher
terrain of western and southwest Montana.

Models maintain overall good consistency through Friday. The GFS
moves the trof axis a bit faster than the ECMWF. Ensemble means and
extended guidance from NWS WPC tends to favor the GFS guidance for
the end of the forecast period. In general the forecast reflects
temperatures returning to seasonal averages with above average
chances for precipitation.
Nutter

&&

.AVIATION...
UPDATED 2335Z.
High pressure will persist over the area providing dry and stable
conditions. Skies will be clear with light surface winds. VFR
conditions prevail.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  46  77  50  83 /   0   0   0  10
CTB  42  76  44  83 /   0   0   0  10
HLN  46  80  50  83 /   0   0  10  20
BZN  41  76  46  78 /   0   0  20  30
WEY  34  72  39  64 /   0  10  50  50
DLN  45  78  51  77 /   0  10  30  40
HVR  43  79  45  83 /   0   0   0  10
LWT  45  75  48  82 /   0   0  10  20

&&

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

$$

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