Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 292317
AFDTFX

Area Forecast Discussion
National Weather Service Great Falls MT
516 PM MDT Thu Sep 29 2016

AVIATION SECTION UPDATED

.DISCUSSION...

Tonight through Saturday...Water vapor satellite imagery reveals
mid- to upper-level moisture moving north into portions of central
and southwest Montana. Short term guidance consistently introduces a
subtle shortwave trough that produces scattered showers and
isolated thunderstorms over southwest Montana this evening.
Forecast soundings indicate a dry boundary layer, so expect little
if any precipitation reaching the ground, but small hail and brief
heavy rain cannot be ruled out in a few isolated cells. Any
convective activity dissipates overnight. Remnants of a low- level
temperature inversion remain in place over north- central MT where
areas of fog are possible once again along the Milk River valley.
Height falls over the PacNW on Friday along with downslope
southwesterly surface winds will introduce greater instability.
Hence, scattered showers and thunderstorms are expected over the
western and southwest mountains Friday evening. This recent period
of warmer weather ends on Saturday afternoon as a cold front
crosses the Continental Divide. Widespread precipitation is
expected across much of central MT as the front moves through.
Total rainfall amounts Saturday afternoon and evening will be
limited to around 0.1 to 0.25 inches as the system moves through
rather quickly. PN

Saturday night through Thursday...Weather in the medium range period
continues to be dominated by the movement and subsequent development
of an upper level trough. This feature starts out as a closed low
off the Washington coast. Both medium range models have trended
toward developing this system into an open trough over the western
USA with bulk of energy associated with the system moving as far
south as the Four Corners region. As a result, models continue to
trend toward warmer (but still chilly) temperatures with the bulk of
expected precipitation trending towards Eastern Montana. There still
appears to be a good chance for showers through North Central and
Southwest Montana for much of the forecast period; but, if models
continue to trend this way, it is quite possible that any chances
for significant wetting rains may need to be dropped from the
forecast in the coming days. mpj

&&

.AVIATION...Updated 2315Z.

The air mass is weakly unstable and unsettled southwest flow aloft
is bringing moisture over Southwest Montana. Isolated showers and
thunderstorms will diminish quickly by 03z. The air mass will become
weakly unstable again Friday afternoon and a slight chance of
showers or thunderstorms will develop across Southwest Montana. VFR
conditions will prevail through the next 24 hours.

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  49  80  51  74 /  10  10  20  60
CTB  45  75  49  64 /  10  20  30  50
HLN  51  79  49  72 /  20  20  30  60
BZN  49  78  49  75 /  10  10  20  30
WEY  41  67  40  63 /  30  20  10  40
DLN  48  76  46  68 /  30  20  30  50
HVR  49  78  52  80 /   0   0  10  30
LWT  53  77  53  76 /  10  10  10  30

&&

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

$$

weather.gov/greatfalls



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