Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 220238

Area Forecast Discussion...Updated
National Weather Service Billings MT
838 PM MDT Fri Apr 21 2017


Diffluent flow aloft with isentropic ascent at the lower levels
continues to produce precipitation across most of the central
zones this evening. Thunderstorms developed east of the main
stratiform precipitation shield this afternoon where there was
better surface heating, and have persisted into the evening.
Thunderstorms should continue to decrease over the next couple of
hours as instability wanes. Precipitation will gradually diminish
across the area overnight, consolidating towards the Bighorn
Mountains and associated foothills. Have updated pops and winds to
current trends. Winter Weather Advisory for the northeastern
Bighorn Mountains still looks in good shape so will allow it to
continue. Some of the SNOTELs are reporting snow amounts of 6 to 8
inches so far. Otherwise, the rest of the forecast remains on
track and the previous forecast discussion and an updated aviation
discussion are below. STP


.SHORT TERM...valid for Sat and Sun...

Will continue to see an area of substantial precipitation over
central areas through the evening hours as low level isentropic
ascent persists under diffluent pattern aloft. Hi-res models
continue to paint the axis of heaviest precipitation from the Bull
Mountains south through Billings and into the Bighorn Mountains,
with an additional quarter to half inch of precipitation before it
tapers off late tonight. On the eastern boundary of this
precipitation in an area of differential heating radar and
satellite are showing scattered convection getting going. Added
mention of isolated thunderstorms to the forecast through mid
evening to cover this. Any storms will be weak but some
graupel/small hail will be possible with them. SNOTEL reports in
the Bighorn Mountains showing 4 to 6 inch accumulations in the Big
Goose and Little Goose headwater areas, but the rest of the area
only a couple of inches so far. Will keep the Winter Weather
Advisory going tonight with an additional 6 to 8 inches expected
through tomorrow morning.

System works its way south of the area tomorrow morning with some
lingering fog across the area. Saturday afternoon looks very
pleasant with ridging aloft and temperatures around 60 degrees.

More Pacific energy slides into the area for Sunday. Temperatures
warm into the mid 60s ahead of this energy, with precipitation
chances increasing west to east during the afternoon and evening
hours. There is enough CAPE and upper energy to support a few
afternoon/evening thunderstorms across western and central zones.
Precipitation amounts with this system will be hampered just a bit
by downslope winds and fast flow aloft, under a quarter of an inch
for heaviest amounts forecast through Monday afternoon. This is a
warmer system than the current one with mountain snow accumulations
looking light. Chambers

.LONG TERM...valid for Mon...Tue...Wed...Thu...Fri...

Long term periods still appear to be dominated by a progressive
pattern with periods of showers and daytime temperatures
generally below seasonal norms.

Zonal flow with a good strong tap of Pacific moisture and
occasional shortwaves starts our next work week, eventually
followed by a stronger trough around Wednesday which looks to
induce decent height falls and push even cooler air into the
region for the last part of the work week. The models diverge on
details late in the week, but generally keep a very unsettled and
cool pattern over our region that is also generally cyclonic in
nature and thus prone to producing precipitation across the
region. So cool and wet remains the outlook for much of next week.
As for thunderstorms, the best bet appears to be late Tuesday and
perhaps some thunder again Wednesday. BT



Showers from Rosebud County west and over Sheridan County will
gradually end from N to S overnight. MVFR conditions are possible
in the showers. There will be areas of obscuration over the Crazy,
Beartooth and Absaroka mountains, with widespread obscurations
over the NE Bighorns. Patchy fog is possible over the area late
tonight into early Saturday. VFR is expected over the area on
Saturday, but MVFR ceilings could linger over KMLS and KSHR. Arthur



    Sat     Sun     Mon     Tue     Wed     Thu     Fri
BIL 039/060 041/063 043/057 040/056 040/055 038/053 037/053
    92/R    13/T    43/W    44/T    35/W    43/W    33/W
LVM 031/059 038/057 037/054 034/054 035/052 033/051 033/051
    41/U    26/T    64/W    54/T    45/W    43/W    43/W
HDN 040/061 039/066 043/060 040/058 039/058 038/054 037/055
    93/R    03/T    43/W    34/T    25/W    44/W    33/W
MLS 042/061 042/064 044/058 041/057 040/057 039/053 038/055
    42/R    02/R    33/W    34/T    35/W    44/W    33/W
4BQ 039/061 039/067 044/059 040/055 038/054 037/052 036/053
    42/R    01/B    33/W    45/T    25/W    45/W    34/W
BHK 037/061 037/059 038/055 034/053 035/052 034/051 033/053
    11/B    11/B    33/W    23/T    24/W    54/W    33/W
SHR 036/057 037/065 040/056 038/054 037/053 036/049 035/050
    93/O    02/T    43/W    44/T    35/W    44/W    34/W


WY...Winter Weather Advisory in effect until 6 AM MDT Saturday FOR
      ZONE 98.


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