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Area forecast discussion 
National Weather Service Billings Montana
332 PM MDT Thursday Sep 18 2014

Short term...valid for Friday and Sat...

Scattered to numerous showers and thunderstorms will occur tonight
and isolated strong or even severe storms are possible through the
middle evening hours.

As of middle afternoon...there have been enough breaks in cloud cover
to enable temperatures in the 70s f behind the earlier showers and
thus MLCAPE values have risen to 500-1000 j/kg in southwestern and
south central Montana per rap-based Storm Prediction Center mesoanalysis data. Height falls
have contributed to several storms from the Idaho Panhandle to around
Livingston as of 21 UTC. We expect further expansion of that storm
activity as it propagates east-northeast across the area and so we
are carrying likely probability of precipitation across south central Montana and north central
Wyoming this evening. Recent hrrr runs appear to match this idea and so
we leaned toward its solutions to build the evening forecast. Some
risk of strong or even marginally severe storms exists with 0-6-km
bulk shear around 40 knots. Well-organized...persistent cells with 50
dbz heights over 25 thousand feet above ground level and/or base velocities of 50
knots or better at heights under 2000 feet above ground level may need severe thunder-
storm warnings...though we need to stress that will be an isolated
occurrence at most. A chance of showers and weak storms will exist
over the area after midnight too...but mainly in southeastern Montana.

A drier northwest flow aloft will take over Friday and by Sat heights
aloft will be rising steadily as a ridge develops over the region.
We are now advertising a dry forecast in most areas Friday except for
the mountains and in far southeastern Montana in the morning as none of
the 12 UTC guidance simulated any precipitation and soundings from
those models showed stable profiles with a middle-level inversion. We
expect highs near 80 f Friday in a well-mixed air mass and in the 70s
f Sat with lighter winds in a more shallow boundary layer. Schultz

Long term...valid for sun...Mon...Tue...Wed...Thu...

Relatively warm...Low-Key weather is expected for much of the long
term forecast period and we accordingly leaned on the consensus of
12 UTC guidance to build the gridded forecast database. We do have
a chance of showers and storms in play across north central Wyoming and
parts of southern Montana Sun night through Tuesday in respect to potential
for a weak upper-level low meandering across Wyoming. Guidance has been
trending a bit north with that feature and an in-house set of MOS-
based pop data supported low-end precipitation chances during that
time frame. However...the track of the low is questionable because
it will be undercutting mean ridging aloft which itself looks like
it will move eastward with time as a trough becomes established in
the Pacific northwest by late in the week. A warming trend will be
in place with warm air advection ahead of that trough. Schultz

&&

Aviation...

Scattered showers and thunderstorms continue across much of the
region this afternoon...and are expected to continue into
tonight. MVFR to IFR conditions can be expected with the
thunderstorms. Obscuration over area mountains will continue into
tonight. Showers and thunderstorms are expected to clear from west
to east early Friday morning. Aag

&&

Preliminary point temp/pops...

Friday Sat sun Monday Tuesday Wednesday Thursday
-----------------------------------------------------------
bil 059/080 052/075 049/076 053/075 054/077 054/078 054/079
61/b 10/u 00/u 12/T 22/T 11/u 12/T
lvm 051/078 043/077 043/076 047/077 049/078 048/079 049/079
61/north 10/u 00/u 12/T 22/T 21/b 22/T
hdn 058/082 050/077 045/078 052/078 052/078 052/080 052/081
61/b 10/u 00/u 12/T 22/T 11/u 12/T
mls 061/082 051/075 045/076 052/078 054/076 053/079 053/081
42/T 00/u 00/u 01/u 12/T 21/u 11/b
4bq 061/082 051/076 046/076 053/076 054/075 052/079 052/082
42/T 10/u 00/u 12/T 22/T 21/u 11/u
bhk 060/080 049/074 041/073 047/076 051/072 049/076 050/078
32/T 10/u 00/u 01/u 12/T 21/u 11/b
shr 058/080 048/076 045/077 051/073 049/075 049/078 050/080
62/T 20/u 00/u 22/T 22/T 21/u 11/b

&&

Byz watches/warnings/advisories...
Montana...none.
Wyoming...none.

&&

$$
Weather.Gov/Billings

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