Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 051740

1040 AM MST Thu Mar 5 2015

Updated Aviation Discussion


Today...High pressure aloft will keep the airmass warm and dry.
Updated to raise max temps several degrees across most of the
central and northern zones. Current forecast looks on track. Zelzer


High pressure over the interior Western US will remain stationary,
keeping a dry and stable NW flow aloft over the region through
Friday. A weak weather disturbance moving through the NW flow aloft
will spread scattered to broken clouds at or above 12000 ft MSL
across the region today and tonight. Southwest winds with gusts to
30 kts can be expected during the period at KCTB and KGTF. Gusts of
35 kts to 45 kts with local gusts to 55 kts can be expected over
ridgetops and along the immediate Rocky Mountain Front. Hoenisch


/ISSUED 450 AM MST Thu Mar 5 2015/
Today through Saturday...Most active weather element the next few
days will be downslope winds along the east slopes of the Rocky
Mountains. It is possible winds could approach high wind criteria
through favored canyons and passes due to tight surface pressure
gradients but mid and upper level winds do not appear favorable for
any type of downslope windstorm activity at this time.

Otherwise, forecast area under eastern extent of upper level high
pressure ridge currently centered over Pacific Northwest coast,
with a surface lee side trough along the Rocky Mountain Front.
As mentioned above, pattern should bring increasing westerly
winds over the next few days along with a warming trend back above
seasonable averages. Variable cloudiness anticipated through the
end of the week as small weather disturbances embedded in the flow
track across the area. Little in the way of precipitation expected,
however, with the exception of the very highest peaks of the
Continental Divide, mainly in and around Glacier Park.

Saturday Night through Thursday...Dry conditions with well-above
normal temperatures expected for Sun through Tues as broad high
pressure ridge along the West Coast drifts eastward toward the
Great Basin and Northern Rockies. Latest model runs indicate we`ll
likely see spring-like upper 50s to low 60s at lower elevations on
Mon/Tues, but generally stay below record-high range (mostly mid
60s to low 70s).

From late Tues onward, the forecast is quite challenging with
several widely varying solutions possible, each with some support
from various model analysis tools. Most notably, the GFS model is
sticking to its call for a strong Canadian shortwave trof to bring
sharply colder temps and widespread, low accumulation snowfall for
most of our region (lower snow chances over the eastern Hiline)
from Tues night through Thurs morning. Meanwhile, the ECMWF model,
though it now indicates weaker the ridging over MT than seen in
yesterday`s run, remains considerably warmer and drier than the
GFS through Wed night. The models` disparate solutions are most
telling in the significant differences in their thickness values,
which are on the order of 200-250 meters. This translates to a
20-30 degree difference in predicted temperatures on Wed for the
Hiline and central counties (teens and 20s (GFS) vs 40s and 50s
(EC)). Also, if the GFS pans out, we could see strong winds for
the Rocky Mtn Front and adjacent plains for Tues/Wed.

The varying solutions continue into Thurs, with the GFS pushing
the Canadian shortwave into southeast MT with clearing/dry
conditions for our region. The EC brings a weak upper-level trof
from the Pacific with some light rain and rain/snow mix for most
of the region through Thurs night. Given the wide differences,
current forecast grids try to find some sort of compromise until
the favored solution becomes more clear in later model runs. Have
introduced some slight chances for mixed rain/snow showers over
most of the forecast area for Wed aftn through Thurs morning, with
cooler temps (30s and 40s) along/north of a Lincoln-Great Falls-
Lewistown line, with the southwest counties remaining in the upper
40s and low-mid 50s both days. Waranauskas


GTF  49  30  50  29 /   0   0   0  10
CTB  47  30  49  28 /   0   0   0  10
HLN  51  29  54  32 /   0   0   0  10
BZN  45  21  51  25 /   0   0   0  10
WEY  36   9  41  13 /   0   0  10  10
DLN  48  24  52  28 /   0   0   0  10
HVR  46  27  50  24 /   0   0   0  10
LWT  43  28  48  26 /   0   0   0  10



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