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000
FXUS65 KTFX 161154
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
550 AM MDT Thu May 16 2013

Updated Aviation

.DISCUSSION...

Today through Saturday...Satellite indicates a broad upper level
trof approaching the West Coast. This will move over the West Coast
by late afternoon. As the trof approaches, moisture will increase
and the airmass will become slightly unstable. Isolated
thunderstorms are possible, especially across Southwest Montana, but
the forecasted soundings do not show any levels with strong
instability and mainly showery activity is expected. The airmass
will continue to moisten tonight, and Southwest Montana will be
close to saturation at low levels, so POPs will increase
significantly through the night. The trof will be over the Pacific
Northwest Friday although most of the dynamics will be well to the
south. This will put the zones underneath a long fetch of moist
southwest flow aloft and the wet conditions will continue. The
chance of precip will decrease further to the north along with lower
rainfall amounts. By Saturday, the upper level trof will have a
negative tilt with only very slow movement east. The models once
again try to develop very weak instability. And again, the best
chance for thunderstorms is over extreme Southwest Montana.
Temperatures will trend downwards through the period, dropping below
normals Friday and Saturday. Zelzer

SATURDAY NIGHT THROUGH THURSDAY...FAIRLY GOOD MODEL AGREEMENT
THROUGH THE PERIOD. EXPECT AN UNSETTLED WEATHER PATTERN AS THE BROAD
UPPER TROUGH...ALREADY IN PLACE...MOVES EASTWARD. ON TUESDAY WEAK
RIDGING BUILDS INTO THE AREA. THE ECMWF HAS THE RIDGE BUILDING A
LITTLE STRONGER NORTH INTO MONTANA...BUT THE RIDGING IS SHORT LIVED.
BY TUESDAY NIGHT THE AREA HAS DIFFLUENT FLOW WHILE BETWEEN SYSTEMS.
BY WEDNESDAY MORNING THE CWA WILL START TO FEEL THE EFFECTS OF THE
LOW IN THE PAC NW. AS FAR AS PRECIPITATION GOES...MODEL SOUNDINGS
CONTINUE TO SHOW DEEP MOISTURE THROUGH MONDAY MORNING...BUT NOT AS
MUCH INSTABILITY. MOST OF PRECIPITATION WILL FALL AS RAIN WITH THE
EXCEPTION OF THE HIGHEST OF ELEVATIONS. THIS WEEKEND`S SYSTEM WILL
BRING MUCH NEEDED RAINFALL OVER MUCH OF THE STATE...WITH ADDITIONAL
CHANCES BY THE END OF NEXT WEEK. MERCER

.HYDROLOGY...
Increased releases out of Gibson Reservoir are causing rises along
the Sun River and the higher flows are expected to continue at
least through this week. At this time, these rises are not
expected to exceed flood stage. Elsewhere, cooler temperatures will
moderate the melting of the snowpack. However, the increased chance
of precipitation will also increase the chance for further
rises in rivers and streams across much of north central and
southwest Montana through the upcoming weekend.

&&

.AVIATION...
UPDATED 1150Z.
A broad trough will continue to push into the area today causing
conditions to deteriorate over parts of the area. KHLN has
already seen some light rain showers with lower ceilings this
morning. Expect ceilings to continue to lower throughout the
afternoon over most locations. VFR conditions should
prevail...however...it is possible to see MVFR conditions over some
terminals. Expect lower ceilings and showers at most of the TAF
sites for the next 24 hours. Mercer

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  64  45  61  44 /  50  50  70  50
CTB  64  42  63  41 /  40  40  50  40
HLN  65  46  63  45 /  60  60  80  60
BZN  66  42  62  41 /  80  70  80  70
WEY  61  43  56  39 /  70  60  70  70
DLN  63  43  59  41 /  70  70  80  80
HVR  71  47  68  46 /  50  60  60  40
LWT  64  46  59  43 /  80  70  70  70

&&

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

$$


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