Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 282048

Area Forecast Discussion
National Weather Service Great Falls MT
248 PM MDT Fri Oct 28 2016


Tonight through Sunday...Mid- to upper-level high pressure ridging
will persist over much of the CWA through the period. However, a
weather disturbance centered just northeast of San Francisco Bay at
time of writing will undercut the ridge as the disturbance continues
moving northeastward to eastern ID and vicinity by early Saturday.
This disturbance should then move east-southeastward to IA by early
Sunday before advancing farther east-southeastward thereafter.
Elsewhere, a shortwave trough offshore the Pac NW should move
northeastward to southeast BC and vicinity by early Sunday before
nearing northern MB by early Monday, as it rides along the periphery
of the aforementioned ridge. Finally, another Pacific disturbance
should reach the Pac NW coast by early Monday.

The aforementioned weather pattern will cause skies to trend partly
to mostly cloudy throughout the period. Periods of precipitation
will continue into Saturday morning in Southwest MT and portions of
Central MT, before giving way to just a few lingering showers in the
afternoon. Here, additional liquid precipitation amounts should
reach a few hundredths to a tenth of an inch near and south of a
Helena to Grass Range line. Farther south, many places near and
south of a Martinsdale to Dillon line should receive an additional
tenth to six tenths of an inch of liquid through Saturday afternoon,
with the highest amounts likely occurring in the mountains. Then,
late Saturday evening through Sunday, expect a separate round of
scattered precipitation over the CWA, especially along/near the
Continental Divide and over/near the mountains of Southwest and
Central MT. In addition, weak mixed layer CIN and mixed layer CAPE
near 250-350 J/kg may allow some isolated thunderstorms to occur
Sunday afternoon near and especially south of a Helena to Grass
Range line. Snow levels should average near 7000 feet MSL in North-
Central MT and near 8500 feet MSL in Southwest MT. Thus, little, if
any snow accumulation is expected along mountain passes.

Lows tonight will reach the 30`s in most places, while Saturday`s
highs will mainly reach the upper 40`s to mid 50`s. After Saturday
night lows mainly in the mid 30`s to lower 40`s, highs on Sunday are
expected to reach the 50`s. While lows will be about 10 degrees
above normal, highs will be near-normal. Jaszka

Sunday Night through Friday...A broad and weakening Pacific trough
crosses the forecast area Sunday night through Monday afternoon. The
best chances for precipitation with this system will be over the
mountain areas and across much of southwest MT where 0.25 to 0.5"
are indicated, with some isolated higher totals. Snow levels drop to
around 5500 to 6500 feet by Monday morning. 6-10 inches of snow may
be possible on the higher peaks of southwest MT, but do not expect
snow related impacts on area passes.  Precipitation will taper and
move away to the east Monday evening, with a few mainly mountain
snow showers lingering. Temperatures for Halloween will be in the
mid 40s for most lower elevation locations, with possible fog in
southwest valleys. Another weak disturbance passes quickly Tuesday
afternoon, producing a few mountain showers. Gusty southwest winds on
Wednesday will push temperatures slightly warmer. Large scale
ridging over western portions of the central plains keeps drier
weather in the forecast Wednesday through Friday, but cannot rule
out a few showers as weak shortwave cruise over the ridge to our
north. PN


.AVIATION...Updated 1745Z.

Several weather elements in play this aftn. First, moist southwest
flow aloft will continue to bring widespread moisture, creating VFR,
mid-level ceilings across southwest and parts of central MT into
this evening. Meanwhile, area of -RA near KLWT is associated with
weak trough that is heading into eastern MT; precip should taper off
in next hour or so, with ceiling height increasing. Finally, low-
level northwest flow has pushed IFR cloud deck in to KHVR area.  May
see some improvement in ceilings there with aftn mixing.

By tonight, a low pressure system will move across central ID and
bring sufficient moisture for scattered areas of -RA and MVFR/IFR
conditions over southwest MT, including KEKS/KBZN.  Further north,
main impact will be IFR ceilings (except KHLN remaining VFR) as
broad, low-level upslope flow develops over most of central MT and
continues into Sat morning.


GTF  36  53  42  58 /  10  10  20  20
CTB  31  47  36  53 /  10  10  40  20
HLN  37  54  38  57 /  20  10  20  30
BZN  41  53  39  58 /  80  70  20  40
WEY  41  46  35  50 /  90  80  20  60
DLN  39  55  39  56 /  70  50  20  30
HVR  36  50  35  56 /  10  10  10  20
LWT  36  50  40  59 /  10  10  20  30



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