Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 230919

Area Forecast Discussion
National Weather Service Billings MT
319 AM MDT Fri Sep 23 2016

.SHORT TERM...valid for Tdy and Sat...

Upper low was positioned over eastern Nevada early this morning.
Strong upper divergent flow was producing bands of convection over
northern Utah, eastern Idaho and western Wyoming. This activity
was releasing northward into Montana. The forecast area had one
batch of showers swing through during the night, with another
batch quickly moving up from central Wyoming. High resolution
models have actually had a good hold of this short term event,
with the second convectively driven area swinging through during
the very early morning hours. Have raise morning PoPs to account
for this. Models want to provide a lull in the activity for the
mid to late morning, into the early afternoon.

Strong divergent flow then pulls into southern Montana this
afternoon as the upper low moves into southwest Wyoming. There is
good consensus on this. This will create another round of
convection developing over northern Wyoming, moving northward into
the forecast area. This area of precipitation will be mainly
confined to south central zones into parts of the southeast and
continue into Saturday morning. As the upper low pulls into
southeast Montana, the precipitation shield wraps around this low
and gradually pushes across southeast Montana during the day
Saturday. Both the GFS and ECMWF keep the heaviest precipitation
with the wrap around east of Billings. Still looking at the
potential for over an inch of rainfall today through Saturday,
especially just east of Billings.

As far as snow is concerned, the system was pretty warm yet with
locations over the Beartooths still in the 40s with rainfall. The
cold air holds off until this evening as 700mb temperatures fall
below 0c then. 700mb temperatures fall to -3c tonight and Saturday
as the low wraps up and sends warp around precipitation into
locations from Billings to Sheridan. The Beartooths will be west
of the heaviest QPF locations during the cold push of air, but the
Bighorns will get a direct shot. Have raised QPF amounts for the
Bighorns as the GFS was hitting that location hard in the wrap
around flow. The ECMWF had the highest QPF east of the Bighorns
but close enough to warrant a concern as the cold air arrives.
Have raised snow amounts for the Bighorns and decided to issue a
Winter Weather Advisory for tonight through Saturday. Would expect
4-10 inches of snow by the time it tapers off Saturday evening.

Need to talk about winds on Saturday. GFS was coming in very
aggressive with 850mb winds over the east with 55kts showing up
over southeast Montana Saturday afternoon. The surface reflection
of the upper low will move into eastern Montana during the
afternoon and produce a tight gradient. At this point, believe
there will be too much ascent to realize all the wind at 850mb but
certainly enough there with the gradient to produce wind gusts to
50mph. Have raised winds and will need to monitor closely. If the
ascent weakens, these winds will have the potential to surface and
could then see higher gusts than 50mph. Will continue to monitor
the latest model runs on this. TWH

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

Extended forecast period looks pretty quiet for the most
part...with upper level high pressure in control over the region
through the bulk of the period...resulting in mainly dry

Expect to see a warming trend through mid week...with highs
climbing back above seasonal normal. Did raise highs for Tuesday
and Wednesday into the upper 70s for ridge axis
crosses the region...and mid 70s Wednesday as ridge flattens. Flow
aloft turns southwest Wednesday night...bringing some slight
chances of precipitation to the mountains again. Weak energy
continue to stream into the mountains through Thursday...keeping
isold pops for the high terrain. A stronger wave...with a bit
more progged into the area Thursday night and
Friday...with bring another shot of showers across much of the
area. Cooler...below the upper 60s are
expected for Thursday and Friday. AAG



Periods of rain continue across the area this morning
through Saturday. Conditions will vary from IFR and
lower with heavier rain...fog and stratus. Embedded thunderstorms
are possible with the rain through this afternoon. The mountains
will be mostly obscured through the period. AAG



    Tdy Sat     Sun     Mon     Tue     Wed     Thu
BIL 058 048/058 043/065 045/072 048/077 051/073 048/069
    6/T 87/W    31/B    01/U    11/U    11/U    11/B
LVM 054 043/056 037/065 042/073 045/077 046/074 045/069
    6/T 84/W    21/U    01/U    11/U    11/U    11/B
HDN 062 047/057 042/064 042/071 045/077 048/074 047/071
    7/T 88/W    31/B    11/U    11/U    11/U    11/B
MLS 063 050/056 043/063 042/070 045/075 050/074 049/071
    7/T 89/W    51/N    11/U    11/U    11/U    11/U
4BQ 069 049/055 042/062 040/069 044/075 048/076 049/074
    6/T 67/W    41/N    01/U    11/U    11/U    11/U
BHK 061 049/056 042/059 039/065 041/071 046/072 047/071
    7/T 78/W    51/N    11/U    11/U    11/U    11/U
SHR 065 046/055 041/061 041/070 042/076 045/075 046/073
    6/T 87/W    31/B    11/U    11/U    11/U    11/B


WY...Winter Weather Advisory in effect from 6 PM this evening to 6
      PM MDT Saturday FOR ZONE 98.


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