Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 180941

Area Forecast Discussion
National Weather Service Billings MT
341 AM MDT Tue Oct 18 2016

.SHORT TERM...valid for Tdy and Wed...

Strong zonal jet stream to the south of the area buckles,
deepening trof over the area this afternoon and tonight. This will
increase instability over the area for isolated to scattered
showers across western into central areas...mainly west of
Billings. Downslope flow should be enough to keep lower elevation
precipitation amounts low. As the trof deepens it also pulls down
a weak cold front from the north...turning surface winds to the
north late in the day into tonight. High temperatures today will
be mainly in the 50s.

Precipitation chances increase tonight with some jet enhanced
divergence sliding into the area from the west along with
increased QG forcing as the back edge of the trof approaches. Weak
upslope will add additional lift in the north/east facing
foothills. Keeping precipitation chances in the 30 to 40 percent
range for the lower elevations overnight into the day
Wednesday...with likely or better across the mountains.
Temperatures will be cold enough for a mix of rain/snow in the
lower elevations overnight into Wednesday morning. Mountains above
6000 feet could see several inches of snow accumulation,
especially in the south/west facing slopes around Cooke City. With
substantial cloud cover and showers in the area, Wednesday
temperatures will hold in the low to mid 50s. Chambers

.LONG TERM...valid for Thu...Fri...Sat...Sun...Mon...

Extended models were showing the same general pattern
they have been showing over the last several nights. There were a
few differences between the GFS/ECMWF beginning on Saturday, and
have used the CONSALL guidance to manage the PoPs during these

A shortwave ridge over the region on Thursday will shift E Thu.
night. The models brought some Pacific moisture into the western
mountains on Thu., but not enough to warrant PoPs. More moisture
and weak energy moves through the area Thu. night. Downslope flow
will keep areas in the lee of the mountains dry, but could not
rule out a slight chance of precipitation over the western
mountains and over areas E of KBIL. Lee troughing sets up over the
area through Thu. night which will increase gap flow. At this
point, the pressure gradient did not look strong enough to support
Advisory strength winds. Mixing will remain below 700 mb Thu.,
resulting in highs in the mid and upper 50s.

The upper ridge rebounds over the area on Friday and persists into
Saturday. However, the GFS brought a shortwave through the region
Fri. night and Saturday, and brought a weak cold front through the
area on Saturday. Models varied in their moisture depictions but
were generally dry. Temperatures will reach the 60s on Fri., but
were more uncertain for Saturday. Model blends had highs in the
low to mid 60s. The ridge strengthens over the area again into
Monday and models were dry except for moisture over the SW
mountains on Monday. Thus had mountain PoPs for Mon., and used a
model blend for temperatures due to model differences in the
temperature profiles. A more active WSW flow overtakes the area
Mon. night and Tuesday. Used a model blend for PoPs resulting in
slight chances over portions of the region. Arthur



VFR will prevail over the area today and tonight. Some showers
are possible around KLVM this afternoon, and from KBIL W and S
tonight. The showers may produce localized MVFR conditions. Areas
of mountain obscuration over the Beartooths/Absarokas this
morning, will become widespread this afternoon through tonight.
Expect areas of mountain obscuration over the NE Bighorns this
afternoon and widespread obscurations tonight. There will be areas
of obscuration over the Crazys through tonight. Arthur



    Tdy Wed     Thu     Fri     Sat     Sun     Mon
BIL 057 039/054 035/058 043/064 041/062 039/061 042/061
    1/B 32/W    01/B    10/B    10/B    11/B    11/B
LVM 052 033/048 033/056 040/060 039/061 036/061 039/060
    3/W 33/W    01/N    21/N    11/B    11/U    12/W
HDN 059 037/055 032/060 040/066 039/064 038/062 039/063
    0/B 23/W    11/B    10/B    10/B    11/U    01/B
MLS 058 036/054 034/060 041/064 040/062 037/061 038/061
    1/B 12/W    10/U    20/B    11/B    11/U    01/B
4BQ 060 036/052 032/061 040/066 038/065 037/065 039/067
    1/U 13/W    10/U    20/B    00/U    11/U    01/B
BHK 056 032/051 031/058 038/062 037/062 035/059 036/062
    1/B 11/B    10/U    20/B    11/N    11/U    01/B
SHR 056 033/050 027/059 036/065 036/065 034/064 038/065
    2/W 33/W    10/B    10/U    00/U    11/U    01/B




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