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Area forecast discussion 
National Weather Service Billings Montana
304 PM MDT Wednesday Sep 2 2015

Short term...valid for Thursday and Friday...

Cold front was through khvr and kgtf at 20z...per temperatures in
the 70s/80s...wind shift and pressure rises. It was hot and dry
ahead of the front over the forecast area with temperatures
climbing through the 90s from kbil east...and through the 80s west of
kbil. Winds were increasing over central and western parts of the
area...and klvm has been hitting red flag criteria with gusts over
40 miles per hour. Will keep the rfw going through midnight MDT. A few dry
thunderstorms have developed east of kbil this afternoon. Will watch
trends with these storms and add them to the evening pop grids if
needed.

The front will push south-southeast through most of the area tonight. WRF/GFS
developed some quantitative precipitation forecast over the western mountains overnight...but
relative humidity profiles looked too dry for precipitation so
will keep forecast dry. The front will stall out over southeast Montana/NE Wyoming
on Thursday as a surface low moves SW along the boundary into this
area. Weak shortwaves will move through the area in SW flow
aloft...but airmass continued to look mainly dry. Given the
increasing quantitative precipitation forecast trends in the models however...did expand the
western probability of precipitation a bit further east. Temperatures will range from the 70s
west to the 90s southeast near the front. Relative humidities near the front
will be in the teens...but winds are not expected to be strong so
fire weather is not a concern.

Models showed moisture increasing across the area Thursday night and
then shifting north on Friday. A strong wave is expected to skirt the east
Montana border on Friday...otherwise weak waves will continue moving
through the flow. NE low-level winds Thursday night will become east on
Friday...and models indicated some cape and shear on Friday afternoon
and evening...especially over the east. Kept southeast Montana dry Thursday night
based on drier air over this area...otherwise continued low probability of precipitation
across the area. Had southern areas dry on Friday morning then
brought low probability of precipitation back into this area Friday afternoon as the instability
should fuel thunderstorms. Friday will be cooler with highs in the
70s and 80s. Upper low/trough will be over or/north California Friday night. Jet
divergence...isentropic lift and low-level east flow will bring a
chance of precipitation to the entire area. Arthur

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

Latest models showing better agreement but the European model (ecmwf) is trending
to be quicker than with previous runs...bringing the movement of a
trough with a cutoff circulation passing from southwest Montana to
northeast Montana on Sunday now earlier than the GFS... supported
by GFS ensemble guidance which still has strong spread Saturday
and Sunday.

Moisture deepens in low level easterly flow and by late Saturday
and into Sunday afternoon supports scattered shower and
thunderstorm activity. The upper low moving across the area
maximizes lapse rates aloft but is more optimally timed for
diurnal heating cycle in the GFS. There are still good chances
for rainfall but the northward track of the upper low compared to
some previous model solutions does limit confidence. This is
emphasized in model trends which are not forcing wrap around
precipitation into southern Montana and northern Wyoming as
strongly. This suggests that by Sunday afternoon precipitation chances
should be ending.

By Monday models generally agree on dry SW flow transitioning to
zonal on Tuesday with a warming trend in temperatures continuing
to Wednesday. Mrowell

&&

Aviation...

VFR conditions will prevail this afternoon and tonight. Isolated
high based dry thunderstorms will be possible from Rosebud County
east into this evening. Any of these storms could produce locally
strong wind gusts. South to southwest winds over western areas
will gust 30 to 40kts ahead of a cold front that will slowly work
across the forecast area tonight. Isolated showers and
thunderstorms are possible behind the front...mainly after
06z. Chambers
&&

Preliminary point temp/pops...

Thursday Friday Sat sun Monday Tuesday Wednesday
-----------------------------------------------------------
bil 059/080 053/072 054/074 049/065 043/071 045/072 046/074
11/b 22/T 35/T 66/T 31/u 11/b 11/b
lvm 052/080 046/072 046/073 040/063 036/072 038/073 038/076
12/T 34/T 45/T 55/T 31/b 11/b 11/b
hdn 057/085 053/077 053/079 049/069 043/073 044/075 044/076
01/b 22/T 34/T 55/T 31/u 11/u 11/b
mls 061/089 059/077 059/082 053/069 044/069 045/071 045/074
11/b 22/T 44/T 55/T 42/west 11/b 11/b
4bq 059/094 059/081 058/085 054/072 046/071 048/072 048/074
00/b 12/T 34/T 44/T 21/u 11/b 11/b
bhk 059/093 059/081 057/075 053/071 045/068 043/070 045/072
01/b 22/T 44/T 55/T 22/west 11/b 11/b
shr 055/091 052/080 051/083 047/071 039/072 040/074 042/074
01/b 22/T 34/T 44/T 21/u 11/u 11/u

&&

Byz watches/warnings/advisories...
Montana...red flag warning in effect until midnight MDT tonight for
zones 28-34-39>41-56-63>68.
Wyoming...none.

&&

$$
Weather.Gov/Billings

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