Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 272355
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
555 PM MDT FRI MAY 27 2016

...Aviation Section Updated...

.DISCUSSION...

Tonight through Sunday...Water vapor pix show a low pressure trof
moving over the Rockies. The airmass has become slightly unstable
and radar shows isolated convective activity across most of the CWA.
A surface cold front is moving through the region...wind shift is
already into Eastern Montana...and cooler, drier air is moving in
from the west. However, convection will linger into the evening
across the southwest and eastern zones. The airmass will become
slightly unstable again Saturday and Sunday afternoons across
portions of Southwest Montana but the change to drier air will keep
most of the region dry through Sunday. West winds aloft will bring
stronger winds across the slopes of the Rockies and adjacent plains
Saturday and Sunday afternoon although, in general, winds will
remain light. Temperatures will remain below seasonal normals behind
the cold front but trend slowly upwards towards seasonal normals by
Sunday. Zelzer

Sunday night through Friday...The period starts with a fairly potent
shortwave trough digging SE into the Pac NW. At this time, the
models still differ on the exact evolution of this feature. The
GFS/CMC/GEFS are stronger and more moist while the ECMWF/ECMWF
ensembles keep the wave open/weaker and more progressive with less
moisture. For now, planning to keep with previous forecasts and WPC
and lean towards the more progressive/slightly drier solution seen
in the ECMWF. Regardless of model choice, it appears that the axis
of heaviest precipitation with this system through Monday will be
across the eastern half of our CWA (ie. along and east of a Bozeman
to Havre line). In this area, the potential exists for up to an inch
of QPF for some locations, even if the drier solutions pan out.
Hydrology-wise, it will be something to keep an eye on given recent
rainfall in that area, especially for small streams/creeks, such as
Clear Creek. With Monday`s system, snow levels look to drop down
into the 7-8k ft range, but could drop a bit lower if the shortwave
slows down/closes off.

Once the Memorial Day system moves out, the models are in decent
agreement with building an upper level ridge across the western US,
something we haven`t seen in awhile. This should bring a period of
warmer/drier conditions. Of note, though, the GFS isn`t quite as
strong with the ridge and actually brings a few weak shortwaves
through the area. Will keep low chance pops in later next week, but
at this time it looks like the best chance of seeing a shower or
storm will be across the higher terrain. Martin
&&

.AVIATION...
UPDATED 2355Z.

A cold front continues to slowly progress ENE across the area at
this time. Scattered SHRA/TSRA associated with the front will
continue to lift slowly ENE through this evening as well. Occasional
MVFR VIS/CIGS and mtn obscurations will be possible as the showers
move through, mainly in the vicinity of KLWT/KHVR. The coverage of
SHRA may increase some from KLWT to KHVR tonight along and just
behind the front with a continued threat of MVFR CIGS/VIS and
mountain obscurations. The coverage of SHRA will gradually decrease
from west to east after 06z/SAT with improving VIS/CIGS. SHRA may
redevelop across SW MT on SAT, but for now, confidence isn`t high
enough to put SHRA at KBZN. In the wake of the front, gusty winds
are likely across north-central MT SAT afternoon. Martin

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  40  62  41  69 /  40  10  10  10
CTB  37  60  39  65 /  10  10  10  10
HLN  41  63  42  70 /  40  10  10  20
BZN  39  62  39  71 /  60  30  10  10
WEY  33  53  32  60 /  60  40  20  10
DLN  37  61  38  68 /  70  30  10  10
HVR  45  65  42  70 /  70  20  10  10
LWT  42  62  41  68 /  80  30  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

weather.gov/greatfalls



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