Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 250925
AFDBYZ

Area Forecast Discussion
National Weather Service Billings MT
325 AM MDT THU AUG 25 2016

.SHORT TERM...valid for Tdy and Fri...

An unseasonably cool upper trough was swinging through the
northern Rockies/Plains this morning. Shortwave activity, combined
with upslope flow, produced scattered showers over the mountains
and near the foothills on Wednesday. Flow backs today and becomes
more downslope, and low level upslope will not be near as strong
as yesterday. Also, MUcape was progged lower today with 700mb a
bit warmer this afternoon. Weak shortwave energy does moves
through southern Montana today, but everything in place looks less
compared to yesterday. Will keep PoPs in similar locations to
yesterday, but not expecting convection to be as deep with less in
coverage too. Will confine PoPs to along the terrain. HRRR was
actually dry for all but Sheridan county today. The NSSL WRF did
initiate convection over the mountains, so will keep that idea in
place. Tempeatures today will be a tad warmer as mid levels turn
weakly downslope. Surface high pressure currently sitting over the
forecast area, does not move much today, so winds will be much
weaker.

A reinforcing shot of energy swings into the forecast area late
tonight and early Friday. This will provide increasing
instability, especially over southeast zones. Scattered showers
and isolated thunderstorms will develop during the afternoon and
evening. Have raised PoPs for central and east to account for
this. 700mb downslope flow will increase with this trough, and
thus expect temperatures to be a few degrees warmer. TWH

.LONG TERM...valid for Sat...Sun...Mon...Tue...Wed...

Made only a few changes to the extended forecast which begins
on Saturday. Noted the GFS/GEFS showed good agreement through the
period, whereas the ECMWF ensembles showed less confidence through
the period. The deterministic GFS/ECMWF were not in great
agreement through much of the period.

On Sat., a NW flow becomes more zonal through the day. Despite
some energy crossing the area, the airmass appears dry so have
gone with a dry forecast, except had a slight chance of
precipitation above 8000` in the Beartooths/Absarokas based on GFS
time-heights. Zonal flow and building heights take over the region
through Sun. night keeping the forecast dry. 700 mb temperatures
move up to +12 degrees c on Sun., bringing temperatures back to
around 90 degrees.

Model differences emerge on Mon., when the GFS tries to turn the
flow aloft SW and the ECMWF maintains weak ridging. Both models
have Pacific troughing on Tue., but the GFS has a split trough
resulting in ridging over western MT, while the ECMWF has the
ridge axis further E. Despite these differences, the airmass was
very warm and dry on both models, so had no precipitation in the
forecast, and temperatures in the mid 80s to around 90. Both
models had some form of SW flow over the area for the rest of the
period, but varied in how they handled energy ejecting out of the
Pacific trough into the area. Continued low PoPs, mainly over the
mountains during this time. Arthur

&&

.AVIATION...

Expect VFR conditions across the area today through this
evening, with localized mountain obscurations in showers and
thunderstorms. There will be a slight chance of showers over and
near the Crazy and NE Bighorn mountains late tonight, as well as
over far SE MT. Localized MVFR conditions are possible, along with
mountain obscurations. Arthur

&&

.PRELIMINARY POINT TEMP/POPS...

    Tdy Fri     Sat     Sun     Mon     Tue     Wed
-------------------------------------------------------
BIL 070 050/074 050/085 056/090 056/088 057/086 057/087
    0/B 13/T    21/B    01/U    11/U    11/U    11/B
LVM 069 041/072 043/083 049/089 049/088 050/086 049/086
    1/B 13/T    11/B    11/U    11/U    11/U    11/B
HDN 073 048/076 047/086 055/091 055/090 056/089 056/089
    0/B 13/T    31/U    00/U    11/U    11/U    11/B
MLS 073 051/076 051/085 057/093 058/090 058/088 058/089
    0/B 13/T    31/U    00/U    11/U    11/B    11/B
4BQ 070 049/073 049/084 055/091 057/091 058/089 058/090
    1/B 24/T    31/U    00/U    00/U    11/U    11/B
BHK 070 047/073 048/081 053/089 055/089 056/086 056/085
    0/B 13/T    31/U    10/U    11/U    11/U    11/B
SHR 070 045/072 045/084 052/090 052/089 053/088 053/089
    2/T 23/T    31/U    11/U    11/U    11/U    11/B

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

$$
weather.gov/billings



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