Area Forecast Discussion
Issued by NWS Great Falls, MT

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411
FXUS65 KTFX 211120
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
520 AM MDT Wed Apr 21 2021

...AVIATION SECTION UPDATED...

.SYNOPSIS...

Expect mainly clear and dry conditions expected today into
tonight, with temperatures peaking near seasonal averages. Clouds
will be on the increase starting early tomorrow morning as the
next potent cold front brings another shot of colder conditions,
gusty winds, and some snow to the area. Accumulations at lower
elevations should be on the light side, but some mountains and
foothills could pick up several inches of snow. An active weather
pattern is likely to continue through at least the weekend.

&&

.DISCUSSION...
Today through Friday...
A shortwave upper-level ridge builds southeast across the region
today, bringing mainly clear and dry conditions. Temperatures on
Wednesday should rebound back to near seasonal averages for most
of the area but this will be short-lived before another frontal
system brings cooling again on Thursday.

The next upper level trough digs south through western Canada
tonight, with a shortwave disturbance dropping south into the
Northern Rockies tomorrow. A potent surface cold front crosses the
border early Thursday morning, and likely crosses most of north-
central Montana by around midday. Models remain consistent with
a shift to northerly winds, which could be quite gusty, with an
area of precipitation following behind the front. Precipitation
will linger through Thursday night, especially south of the Hi-
Line through the Big Hole, Madison, and Gallatin Valleys of
Southwest Montana. Precip should wind down by midday Friday as the
base of the upper trough should slide southeast of the CWA during
the morning hours. The greatest precip amounts still look to be
focused along an arc from the Rocky Mtn Front east along and just
north of the Little Belts and Big Snowys, where 0.25"-0.50" liquid
amounts are expected. Lesser amounts are forecast for the Hi-Line
east of Browning, and for far southern parts of the forecast
area.

Precipitation type will likely again see a quick transition
from rain to snow for most areas on Thursday with snow for most
areas by Thursday evening. Snow accumulation may be difficult at
lower elevations Thursday afternoon but will become more likely
Thursday evening/overnight as air and surface temperatures fall
below freezing. Snow totals up to 3 inches are expected for lower
elevations across north-central MT. We currently have 3 to 7
inches forecast for the Little Belts, Big Snowys, and Rocky Mtn
Front, and adjacent foothills, including Marias, Rogers, and Kings
Hill Passes. Mountains around Helena and White Sulphur Springs
and points south may see several inches of snow, but lower
elevations in the southern half of the forecast area are likely to
see fairly minimal snowfall. Again, the above forecast snow
amounts are mainly for grassy areas, with road temps at the start
of the event likely leading to a fair amount of initial melting on
roads, similar to the most recent event. -Kredensor/Hoenisch

Friday night through next Wednesday...
Brief shortwave ridging aloft should allow for mostly dry but
continued cloudy and cool conditions for Friday night into early
Saturday. But as soon as the crest of this ridge crosses the
Northern Rockies Saturday afternoon, moisture and resulting precip
are forecast to spill east of the Divide. It will remain overall
cool and unsettled early next week as a 500mb cut-off comes ashore
the Pac NW on Sunday, then finally works its way over to Montana
by Tuesday as it gets absorbed back into the general storm track.
The overall active weather pattern for this weekend and early
next week appears to have moderate to high confidence levels, and
confidence in individual disturbances and periods of precip are
also increasing, so likely POPs were allowed at times, especially
along the Divide and in central and Southwest Montana. There
seems to be some agreement among the operational models for some
ridging by the middle of next week. However, looking at ensemble
data shows that these deterministic models are generally on the
higher side of the guidance envelope, with ensemble means and the
spread skewed to the low side of these models. Thus the mid-week
forecast may need to be cooled off a bit depending on how fast the
ridging builds into the region. -Kredensor

&&

.AVIATION...
520 AM MDT Wed Apr 21 2021 (21/12Z TAF period)

VFR conditions are expected through the TAF period. Some gusty S-SW
winds are expected over north-central MT this afternoon. A cold
front likely starts to work into north-central MT by 12z Thurs.
Aside from a shift to gusty NW`ly winds and a chance for lowering
clouds and a shower at the end of the period, no other aviation
impacts are expected in the next 24 hours. -Kredensor

Refer to weather.gov/zlc for more detailed regional aviation
weather and hazard information.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  30  41  22 /   0   0  60  60
CTB  58  31  36  21 /   0  10  70  30
HLN  57  31  47  28 /   0   0  40  60
BZN  53  24  53  28 /   0   0  20  70
WYS  50  12  46  20 /   0   0  10  40
DLN  53  25  54  29 /   0   0  10  40
HVR  58  30  45  25 /   0   0  30  30
LWT  50  26  46  23 /   0   0  30  80

&&

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

$$

http://www.weather.gov/greatfalls



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