Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 240323

Area Forecast Discussion
National Weather Service Great Falls MT
923 PM MDT TUE AUG 23 2016

Partly to mostly cloudy skies cover the majority of the central
and Hiline counties this eve, with mostly clear skies over
southwest MT. Latest radar imagery is picking up some very light
rainshowers from western Teton County down to the Big/Little Belt
Mtns. With water vapor satellite imagery showing some drier air
heading our way from western MT, forecast models have reduced
precip chances over the central plains for tonight, but we`ll
keep 25 to 40 percent chance along the Rocky Mtn Front. Whatever
rain does occur should be quite light...only a trace to few
hundredths of an inch at most. Waranauskas



Gusty northwest winds will decrease somewhat overnight as a low
pressure system exits the area. However, a slow moving disturbance
in the wake of this system will continue to spread low to mid level
cloudiness south through the forecast area. VFR ceilings are
generally expected across the area, but the northerly upslope flow
will likely bring occasional MVFR to IFR ceilings with isolated to
scattered showers between 06Z and 18Z, mainly over the plains of
North Central Montana. The airmass will become weakly unstable after
18Z, bringing a chance of thunderstorms to far Southwest Montana
(including KBZN).


/ISSUED 455 PM MDT TUE AUG 23 2016/

Tonight through Thursday...A closed upper level low over
Saskatchewan will move slowly east and leave Central and
Southwest Montana underneath unsettled northwest flow aloft. Weak
disturbances will rotate around the low and a weak cold front
associated with one of these disturbances will cross the Canadian
border this evening and push into the southwest zones by morning.
This will provide some additional moisture for showers during the
day. The extreme southwest zones will become weakly unstable
during the afternoon and this area could also see isolated
thunderstorm development Wednesday afternoon. Conditions will dry
Thursday and the chance of showers will decrease although the
extreme southwest zones will once again become slightly unstable
and a thunderstorm cannot be ruled out. The cooler air mass will
keep temperatures well below normals Wednesday but temperatures
will already begin to trend upwards again by Thursday.

Thursday night through Tuesday...Tonight it appears that the
medium range models have been reset and have come into good
agreement for Thursday night through Sunday. Period will start
off with an upper level positive-tilt trough whose axis stretches
from southwest Montana northeastward into Saskatchewan. This
feature digs southward overnight then sweeps eastward across
Montana and into the Dakotas by Saturday morning. Montana will be
left beneath an initially northwesterly flow aloft that gradually
backs to the southwest over the weekend period. GFS and ECMWF
each attempt to carve out a low pressure trough along the British
Columbia coast but, as usual, disagree on strength and timing. As
a result, each indicate southwest flow aloft over the region
Monday and Tuesday. However, the flow aloft in the ECMWF
indicates cyclonic flow, while the GFS has an anti-cyclonic

Fortunately, the overall trend for sensible weather across
Montana remains relatively unchanged from that of previous
forecast periods. Thursday night and Friday should see variable
cloud cover along with isolated showers/thunderstorms beneath the
influence of the upper level trough. Temperatures warm back up
above seasonal averages for the weekend with mostly dry
conditions and mostly clear to partly cloudy skies prevailing.
Forecast for early next week is somewhat uncertain but I have
kept temperatures relatively stable and generally in agreement
with those of the weekend with a slight chance for
showers/thunderstorms being introduced under the assumption that
southwest flow aloft over the region will be slightly unstable.


GTF  47  65  42  69 /  20  20  10  10
CTB  47  64  42  67 /  20  20  10  20
HLN  51  65  45  70 /  20  20  10  10
BZN  46  68  41  70 /  10  20  20  20
WEY  37  62  34  63 /  10  20  20  20
DLN  43  66  40  69 /  10  20  20  10
HVR  50  67  46  72 /  20  20  10  10
LWT  48  63  43  67 /  20  20  20  10



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