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Area forecast discussion 
National Weather Service Billings Montana
244 PM MDT Tuesday Sep 1 2015

Short term...valid for Wednesday and Thursday...

Previous forecast was in good shape and have made only minor
adjustments for the afternoon package. Upper low off the British Columbia coast
on water vapor imagery this afternoon will rotate slowly southeast
through the period...as a strong jet moves around the base of the
low to the east side of the system. Airmass will remain dry in this
SW flow aloft until Thursday when the flow aloft becomes more southerly
and advects monsoonal moisture into the area. Thus kept a dry
forecast through Thursday morning...then continued the low probability of precipitation over
the far west including the mountains Thursday afternoon. Jet
divergence...shortwave energy and moisture will be on the increase
Thursday night in a Post-frontal regime which will bring more
widespread...but low...chances of precipitation to the region.
Steep lapse rates supported keeping thunder in the forecast. The
models were not in good agreement regarding how much quantitative precipitation forecast the
region would receive Thursday night.

Meanwhile...on Wednesday...models still showed hot and dry conditions
across the area. Kmls will approach their record high of 100
degrees. Humidities will fall into the teens with a bit higher
values in the mountains. A surface low will settle over central to
east parts of the area in the afternoon ahead of a cold front
dropping down from the north. In general...models showed a decent
pressure gradient over the far western zones. Looking at a
combination of model time-heights and soundings...it appeared the
best mixing would be over the far western zones...then mixing
would decrease from west to east...due to the proximity of the surface
low. The highest wind gusts to possibly 40 miles per hour or higher will be
over klvm into Wheatland County. Expect gusty winds over higher
elevations as well. Placement and timing of the rfw looks fine for
now.

The cold front will move through the area Wednesday night through early
Thursday ushering in cooler conditions and chances for precipitation
Thursday night as mentioned above. The far S and southeast zones look to
remain warm and dry on Thursday as the Post-frontal airmass does not
reach these areas. It will be breezy in these areas...but not
windy enough to support red flag conditions. Arthur

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

Still much uncertainty resides in passage of an upper level low
over Montana. Some solutions remain very slow and would keep cool
temperatures in the region throughout the weekend...the
Euro...while others are slow initially but then kick out the upper
trough very quickly...the GFS/Canadian. With so much
uncertainty...forecast specifics at this time are not clear.
However...all the models do agree that at some point this weekend
we should see one or two cool and cloudy days

The period begins with a weak frontal boundary in place over the
region. As upper level energy increases in the backing
flow surface low should become well established over the Dakotas.
This will help move the rest of the front through the entire
forecast area. Cooler northeast flow should develop as a result
of the surface trough to our east. Most locations west of Billings
will see good rain chances as better forcing aloft rotates
through the trough to the west. Some middle-level capping...due to a
dry slot...could keep conditions drier and warmer over the east.

For Saturday the GFS indicates better shower thunderstorm chances
as it is much less aggressive with the upper level dry slot.
Meanwhile the Euro and Canadian keep very isolated shower/tstorm
chances out east and areas west of Billings wetter. Seeing as the
most recent Euro moved closer to the Canadian will not be
aggressive with probability of precipitation. Locations west of Billings should be fairly
cool while eastern locations will be seasonable under the dry
slot.

The upper level low should begin to tighten and as it deepens
the surface low to our east...wrap around moisture and good
dynamics aloft should bring higher rain chances for nearly the
entire area. However...with a fairly pronounced dry slot aloft
temperatures and rain chances will be highly dependent on where
the eventual upper low wraps up. After the system moves out
sometime Monday zonal flow and seasonable conditions should
return. Dobbs
&&

Aviation...

Some gusty west and west-northwest are impacting area terminals
as daytime heating mixes higher winds to the surface. Expect winds
at all terminals except klvm to calm around 00z. Klvm will remain
elevated near 15 knots.
&&

Preliminary point temp/pops...

Wednesday Thursday Friday Sat sun Monday Tuesday
-----------------------------------------------------------
bil 061/093 058/078 051/070 049/065 048/062 045/072 046/078
00/u 11/b 22/T 34/T 55/T 31/u 11/u
lvm 053/089 050/077 045/068 043/065 044/059 039/072 040/078
10/north 12/T 34/T 45/T 55/T 31/u 11/u
hdn 057/097 056/083 051/074 050/070 049/066 044/074 045/080
00/b 01/b 22/T 34/T 44/T 31/u 11/u
mls 059/099 060/086 056/075 053/071 051/071 044/071 045/078
00/u 00/b 22/T 45/T 55/T 42/T 11/u
4bq 058/099 058/091 056/079 054/073 053/074 048/071 048/078
00/u 01/b 22/T 35/T 55/T 42/T 11/u
bhk 057/098 058/091 056/077 053/071 052/072 044/069 044/075
00/u 00/b 12/T 45/T 55/T 42/T 11/u
shr 054/096 055/088 050/077 048/073 047/069 041/073 042/079
10/u 01/b 22/T 34/T 44/T 21/u 11/u

&&

Byz watches/warnings/advisories...
Montana...red flag warning in effect from noon Wednesday to midnight
MDT Wednesday night for zones 28-34-39>41-56-63>68.
Wyoming...none.

&&

$$
Weather.Gov/Billings

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