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000
FXUS65 KTFX 121111
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
510 AM MDT Wed Mar 12 2014

Updated Aviation Discussion

.DISCUSSION...

Today through Friday...Water vapor indicates a good high pressure
ridge building although with some moisture moving over the top. A
good surface pressure gradient remains along the Rockies but the
only site pushing windy conditions is Deep Creek. Winds aloft are
not giving much support and these brisk winds should weaken during
the day. A shortwave will approach the Rockies Wednesday night.
Although the main dynamics will be over Southwest Montana, moisture
is scarce and the main effect will be breezy winds along the Rockies
and adjacent plains...but winds will weaken Thursday as the
shortwave moves past the zones. The associated cold front will bring
some slightly cooler air south across the border and max temps will
be moderated a bit. The upper level ridge will rebuild quickly
Thursday but another weak shortwave will again approach the Rockies
by late Friday but will be far enough west to only be affecting the
western mountains. This will make it a bit breezy again along the
Rockies and adjacent plains as the shortwave approaches. Zelzer

Friday night through Wednesday...Medium range weather models remain
in fair agreement through this weekend but continue to have problems
beginning early next week. A shortwave sliding SE downstream of a
building upper level ridge along the west coast will move quickly
through MT Friday night through Saturday morning, bringing a chance
of showers to most of the forecast area as well as cooler, but still
near seasonal, temps on Saturday. Quick movement of this system will
keep precipitation amounts fairly low. Snow levels will lower enough
Friday night for any precipitation to be in the form of snow by
Saturday morning, though accumulations will generally be limited to
the mtns, where up to 2 inches may fall. The upper level ridge along
the west coast builds in quickly behind the departing shortwave
Saturday afternoon and shifts east across the Northern Rockies and
MT Sunday, providing a period of dry and much warmer conditions on
Sunday. The ridge begins to flatten late Sunday through Sunday night
and westerly flow aloft strengthens. This in combination with
strengthening surface pressure gradients will likely produce windy
conditions by Sunday evening over much of north-central MT with the
potential for strong winds along the Rocky Mtn Front and adjacent
Plains through Sunday night. ECMWF model digs a stronger trough from
the eastern Pacific into the western US Mon/Tues, while the GFS
brings a much weaker trough across the region. Will lean slightly
toward the ECMWF solution as it has been somewhat more consistent
over the past few runs vs the GFS, though both models continue to
have a large spread among there ensemble members leading to
generally low confidence. Hoenisch

&&

.AVIATION...
UPDATED 1100Z.
VFR conditions will prevail through tonight as high pressure over
the northern Rockies maintains dry conditions under a NW flow aloft.
A period of broken high clouds will move SE across the region this
morning, otherwise cloud-cover will be scattered. Breezy west to
southwest winds will continue over the north-central MT plains with
lighter surface winds in the valleys of SW MT. Hoenisch

&&

.HYDROLOGY...
A few hydrologic highlights remain in effect for portions of
North Central and Southwest Montana. However...warmer air will
begin to move back into the region later this week and into the
weekend...increasing the snow melt. Small stream flooding is
likely to continue over a portion of the region for the next
several days. Additionally...even though overnight lows are
expected to fall near/slightly below freezing over the next few
nights...snow melt runoff will likely slow up a bit during the
overnight hours...but not completely stop.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  51  30  50  29 /   0   0  10  10
CTB  49  28  46  27 /   0   0  10   0
HLN  49  25  50  28 /   0   0  10   0
BZN  44  21  48  23 /   0   0  10  10
WEY  39  10  41  10 /   0   0  10   0
DLN  45  21  47  24 /   0   0   0  10
HVR  54  27  50  26 /   0   0  10  10
LWT  49  30  48  28 /   0   0  10  10

&&

.TFX WATCHES/WARNINGS/ADVISORIES...

URBAN and SMALL STREAM FLOOD ADVISORY until 115 PM MDT Wednesday for
Jefferson County.

URBAN and SMALL STREAM FLOOD ADVISORY until 200 PM MDT Wednesday for
Glacier and Pondera counties.

URBAN and SMALL STREAM FLOOD ADVISORY until 930 PM MDT Wednesday for
Lewis and Clark County.

&&

$$


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