Area Forecast Discussion
Issued by NWS Great Falls, MT

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FXUS65 KTFX 172054
AFDTFX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GREAT FALLS MT
254 PM MDT Sun Aug 17 2014

.DISCUSSION...

Tonight through Tuesday...Upper low over southern Saskatchewan
continues to move slowly east. Wrap-around circulation also
continuing to bring some moisture and instability to the Hi-Line
where isolated thunderstorms will develop from now through early
evening. CAPE values approaching 1000 J/kg across northern Montana
but bulk shear numbers are about nonexistent indicating brief
heavy rain and gusty winds the greatest threat from any storms.
Convective activity ends after midnight. Monday will be dry except
for southwest Montana where a return of monsoonal moisture will
help spawn isolated afternoon thunderstorms. Increasing southwest
flow aloft ahead of an approaching upper trof will allow
thunderstorms to develop again on Tuesday with storms becoming
more widespread in coverage. Temperatures will be above seasonal
averages to start the week.

Tuesday Night through Sunday...Medium range models continue to
indicate that a significant change in the weather can be anticipated
by mid to late week. Period will start out with a weak trough
extending from the Yukon southward along the West Coast to Central
California. A strengthening upper level jet will help to carve out a
deeper and broader trough over the Pacific Northwest and Northern
Rocky Mountains through the end of the week for an increasing chance
of showers and thunderstorms Wednesday and Thursday. By Friday there
is good agreement that a Canadian cold front will push southward
through Montana setting up northerly surface winds for upslope flow
and a good chance of widespread precipitation. Models bring the
coolest temperatures into North Central Montana Friday and Saturday
with high temperatures expected to be only in the 60s over the
plains and there is a distinct possibility that even cooler high
temperatures may materialize. Higher elevations of Glacier Park may
even see snow mixed in with the rain early Saturday morning. Model
consensus disappears by Sunday with the ECMWF accelerating the upper
trough eastward while the GFS holds it back over the Northern
Rockies. Will continue cool temperatures with PoPs remaining above
seasonal averages for now. mpj

&&

.AVIATION...
UPDATED 1752Z.
A NW flow brought a slight increase in low and mid-level moisture
into north-central Montana this morning. Isolated SHRA and TS can be
expected through 03z. VFR conditions will prevail but MVFR/IFR
possible in brief showers/storms. A BKN stratus deck will persist
north and east of a KHLN-KBZN line into Monday morning. Uttech

&&

.PRELIMINARY POINT TEMPS/POPS...
GTF  55  86  56  88 /  20  10  10  20
CTB  54  85  55  84 /  30  10  10  20
HLN  54  88  56  88 /  10  10  10  20
BZN  51  86  53  87 /  10  20  10  20
WEY  38  76  44  74 /  10  20  20  20
DLN  49  84  49  83 /  10  20  10  20
HVR  57  88  59  91 /  30  10  10  20
LWT  54  84  56  88 /  20  20  10  20

&&

.TFX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

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