Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 250943

Area Forecast Discussion
National Weather Service Billings MT
343 AM MDT Tue Apr 25 2017

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

A closed upper low was positioned over north central Wyoming this
morning and was drifting slowly toward northeast Wyoming. Jet
divergence and strong 850-700MB frontogenesis was producing an
area of precipitation over southern Montana and northern Wyoming.
Precipitation has changed over to snow at Sheridan with visibility
being reduced to less than a mile at times. Occasional moderate
snow can be expected early today. Webcams showing some
accumulation starting to show up in the grass with some slush
cover getting on the roads as of 3 AM. Snow accumulations will
likely slow down some after sunrise and thus will keep the
Advisory in place and not jump to a Warning at this time.
Locations closer to the slopes may indeed have pockets of warning
criteria snow totals, but this will be elevation dependent. The
biggest impact on travel and visibility will be along and south of
a Lodge Grass to Ashland to Broadus to south of Ekalaka line.
Locations such as Biddle, Ridge and Alzada will likely have the
biggest snow totals, along with higher hills and the higher
elevations of the Bighorn foothills.

Snow has developed over the western foothills too with snow
reported at Livingston to Red Lodge. Webcams show mainly wet roads
despite the snowfall. High resolution models have this area of
snowfall decreasing quickly this morning, so will not issue an
Advisory at this time. Existing forecast for Monday night into
early Tuesday was for 1-3 inches of snow in these locations and
that looks good at this point. KBLX radar was showing the main
band of rain and snow has drifted south and west of Billings and
this is consistent with latest model trends. Will linger PoPs
across all of south central Montana this morning, with the higher
PoPs being over the south.

Precipitation will taper off this afternoon as the upper low
fills and drifts toward western South Dakota. Raised PoPs a little
more over southeast Montana as the tapering off process has been
slowed by the models. Will be a chilly day today with wet ground
and cloud cover. Lowered high temperatures a few degrees. The west
will have clouds break up first later this morning and early this
afternoon, and this may allow for more showers to develop this
afternoon. Enough instability present for isolated thunder, but
confined this to the far west.

The next wave of energy streams into the forecast area Wednesday
and Wednesday night. Have raised PoPs for the west as the focus
seems to be over the mountains and foothills. Will be another shot
of mountain snowfall with lower elevation rain. May see some
lower elevation snow accumulation Wednesday night over the
foothills but models were projecting 850MB temperatures at 3C and
higher, so this may be limited. Will have to monitor this closely
with the next few model runs as the ECMWF was a bit colder with
850mb temperatures, having them falling to around 1C. TWH

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

Thursday and Friday should be cool with upper trough dropping
southeastward over Montana. This upper trough has some Q-vector
convergence associated with it over the western and central zones
on Thursday, so think that numerous showers are likely for those
areas on Thursday. Lower level trough axis looks to stall
somewhere over south central or SE MT Thursday night. The low-
level convergence found near this trough could then focus
precipitation for Thursday night, although showers are still
possible across southern MT and north central WY due to large-
scale cyclonic flow. Upper troughing continues on Friday, so more
showers are possible due to disturbances propagating through the
flow and instability from cool air aloft. High temperatures
should be in the 40s during the Thu.-Fri. timeframe.

This upper trough should produce more mountain snow with
potentially some foothill snow but accumulation rates will be slow
and daytime melting could occur below 6000 feet. So, winter
impacts may be limited. The amount of precipitation will
cumulatively cause sloppy conditions for non paved roads and will
continue to increase the amount of moisture in the ground and in
the snowpack so streams and rivers will remain at elevated levels
for this time of year.

Upper flow turns northwesterly for Saturday and Sunday. This
pattern favors an overall drier environment than what we have
experienced/should experience early this week and again later this
week. A few showers are still possible over the weekend, but they
should be scattered. High temperatures should return to the 50s.

Another large upper trough looks to move over Montana next Monday,
but models differed on the track of this system. Regardless of the
exact track, showers are possible again next Monday. RMS/TWH


IFR should continue at most TAF sites this morning due to low
clouds and precipitation. Conditions should improve to MVFR and
then VFR over southern MT this afternoon as storm system moves
away from the region. Conditions should improve at SHR later in
the day, closer to 00z Wed. Mountains will be obscured today.


    Tdy Wed     Thu     Fri     Sat     Sun     Mon
BIL 043 033/057 037/047 036/046 034/052 036/059 041/059
    5/O 32/W    57/W    55/W    22/W    11/B    33/W
LVM 046 031/054 035/047 030/046 028/051 030/056 035/056
    7/T 46/T    76/W    34/W    32/W    12/W    33/W
HDN 043 031/058 036/049 036/049 035/054 035/060 040/061
    5/O 22/W    46/W    45/W    22/W    11/B    33/W
MLS 043 028/055 034/053 037/051 036/055 036/061 041/061
    1/C 01/B    23/W    54/W    21/B    11/U    33/W
4BQ 037 022/048 029/048 034/047 032/050 032/058 038/060
    8/O 11/B    23/W    54/W    32/W    11/U    33/W
BHK 038 023/050 026/052 029/051 030/053 032/058 035/058
    1/C 10/B    11/B    22/W    21/B    11/U    33/W
SHR 036 025/050 033/044 033/042 031/047 029/053 036/056
    +/O 22/W    46/W    55/W    32/W    11/B    34/W


MT...Winter Weather Advisory in effect until 6 PM MDT this evening
      FOR ZONES 36>38-58.
     Winter Storm Warning in effect until 6 PM MDT this evening
      FOR ZONE 67.
WY...Winter Weather Advisory in effect until 6 PM MDT this evening
      FOR ZONES 98-99.


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