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Area forecast discussion...updated 
National Weather Service Billings Montana
837 PM MDT sun Sep 21 2014

Update...
middle and high level clouds working their way into our region
tonight as upper trough lifts out of the Great Basin. I do not
anticipate any significant impacts from this system
overnight...but we could see some showers move into the beartooths
late...and into the big horns tomorrow morning. Some of the
activity in central Wyoming producing lightning...confirming the
instability models indicate with this system. Forecast is in good
shape and see no reason for any adjustments at this time. Bt

&&

Short term...valid for Monday and Tuesday...

Quiet weather today as we remain under the influence of strong
ridging aloft. Slow moving Great Basin low is lifting slowly north
and we will be seeing an increase in high cloud in our south over
the next several hours...along with some cumulus over the mountains upper
level ascent will increase over our SW late tonight and have
raised probability of precipitation prior to 12z as it looks as if showers will reach the
beartooth absarokas before sunrise. This rather weak low will
track west to east near the Montana/Wyoming border tomorrow. Forcing will
not be strong but an increase in precipitable waters to near an
inch along with some diurnal instability will be enough for
scattered showers during the day and into the evening
tomorrow...with greatest coverage in our south. With moisture
content anomalously high for late September...we could see some
locally heavy rain in any thunderstorms.

System will depart to the east tomorrow night into early Tuesday
as heights begin to build again from the west. Weak energy in SW
flow over our west may be enough for isolated/weak diurnal convection
over our western mountains on Tuesday...and have adjusted probability of precipitation slightly
for this...but otherwise most of the County Warning Area will be dry as the ridge
begins to build back in. Expect dry conditions Tuesday night.

Temperatures will be above normal the next two days as the weak low to
impact our region will not have any cooler air associated with it.
Cloud cover may hold temperatures back some tomorrow but we should see
70s to low 80s for highs. Most areas should see low to middle 80s on
Tuesday as heights rise into the 580s.

Jkl

Long term...valid for Wednesday...Thu...Fri...Sat...sun...

Models remain in good agreement Wednesday through early Friday
but diverge considerably by next weekend. Progression of large
upper low and trough continues to slow late this coming week as a
strong ridge of high pressure will be firmly situated over the
northern rockies Wednesday into early Friday. 850mb temperatures
look to be in the 25-27c range resulting in afternoon highs in the
middle 80s to around 90 degrees.

Both the GFS and European model (ecmwf) bring the trough across the Pacific
northwest on Friday shifting the ridge axis east into the
Dakotas. Models then diverge by Saturday as the GFS continues to
be about 48 hours faster than the European model (ecmwf) in bringing part of the
trough across our forecast area. The GFS splits the trough and
brings it through Saturday along with the possibility for showers
and thundestorms. However...the European model (ecmwf) closes off the upper low
over California and Nevada. The GFS then closes the low off over
Colorado Sunday while the European model (ecmwf) keeps it over Nevada. By
Monday...both models begin to open the low and shift it north into
eastern Wyoming and southeast Montana. As a result...forecaster
confidence remains low and made no changes to the forecast for
Friday through Sunday. At this point in time though...temperatures
do look to be cooler next weekend with readings in the 60s and
70s. Hooley
&&

Aviation...

Weak system lifting out of the Great Basin will bring scattered
showers and some thunderstorms to the region late tonight and Monday...
with greatest coverage in our south along the Montana/Wyoming border. VFR
will prevail through this evening...but showers could cause some
mountain obscurations before sunrise tomorrow. Expect local MVFR
conditions and occasional mountain obscurations on Monday over and
near the beartooth...absaroka and Big Horn Mountains. VFR should
prevail elsewhere. Jkl
&&

Preliminary point temp/pops...

Monday Tuesday Wednesday Thursday Friday Sat sun
-----------------------------------------------------------
bil 052/079 055/083 056/086 057/090 057/084 052/069 046/067
03/T 21/b 10/u 00/u 01/u 23/T 32/T
lvm 048/077 049/082 048/085 049/087 049/081 045/066 040/064
14/T 21/b 10/u 00/u 12/T 33/T 32/T
hdn 048/079 052/084 051/088 056/090 056/086 050/072 045/070
03/T 21/b 10/u 00/u 01/u 22/T 32/T
mls 049/083 054/085 055/089 058/091 058/087 053/073 049/071
01/u 21/b 10/u 00/u 01/u 12/T 32/T
4bq 049/082 054/083 052/088 057/091 057/087 055/073 050/071
03/T 31/b 10/u 00/u 01/u 12/T 32/T
bhk 044/079 050/081 050/085 054/087 054/086 055/073 049/070
01/u 21/b 10/u 00/u 01/u 11/b 22/T
shr 049/076 050/081 049/085 052/088 052/085 050/070 045/068
14/T 41/b 10/u 00/u 01/u 22/T 32/T

&&

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

&&

$$
Weather.Gov/Billings

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