Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 300852

Area Forecast Discussion
National Weather Service Billings MT
252 AM MDT Thu Mar 30 2017

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

Satellite imagery shows dynamic upper trof along the Pacific coast
digging toward the northern Great Basin. This will be the main
feature of interest over the next two days as it eventually
evolves into a cut off low near the 4-corners. In the SW flow
ahead of this trof, a shortwave lifting thru the northern Great
Basin is producing a rather large area of ascent/pcpn in central/
eastern ID.

Frontogenesis in our western cwa will increase over the next
several hours, allowing pcpn to develop, by sunrise in our west
and spreading east thereafter. High res models seem to have a good
handle on this scenario, and have raised morning pops. During the
afternoon it looks as if we will see a period of subsidence
across our western cwa behind this initial wave as it tracks E/NE
and as western trof continues to dig. So, believe we will see a
break in the synoptically forced pcpn late this afternoon into the
evening. That being said, with a moist boundary layer and low
convective temps, we should see low-topped showers develop rather
easily. Have adjusted pops thru the day to account for these

By tonight, as low continues to drop south, we will see increasing
enhancement along our southern foothills as upslope winds deepen
to above mountain top level. Weak synoptic ascent will be provided
by northern portion of split trof as it moves across the northern
Rockies tonight and Friday, but bulk of pcpn will be along our
north aspects. Pcpn will taper off from W to E Friday night as
northern PV shifts east and subsidence spread in from the west,
with the upper low well to our south.

This system is too warm for any wintry impacts other than over our
southern mountains mainly above 6000 feet. Lower elevations will
see just rain, totaling 0.10-0.75 inches total per a model
consensus, least in our far east and highest closer to the
foothills. North aspects of the Beartooth/Absarokas and Bighorns
should see an inch or more of pcpn, yielding a foot or more of
snow over the high country. Will make no changes to the winter
storm warnings in effect for these areas. Analysis of wet bulb
zero heights on the GFS suggest a mix with wet snow is still
possible as low as Red Lodge and Story by early Friday morning.
This will need to be watched, but right now see no reason to
expect anything more than an inch or two of slushy snow at these
foothills locations, tops.

Temps will be cooler but definitely not cold the next couple days.
Expect 50s to lower 60s today, warmest east. Areas along the
foothills will likely not get out of the 40s on Friday.


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

The extended period will feature a progressive flow with periods
of unsettled weather. The ensembles and deterministic models
showed a good deal of spread concerning the main system of the
extended on Sunday night/Monday. Otherwise there were many
differences in the details in timing of shortwaves and placement
of QPF throughout the period, so confidence was not overly high
for this period.

A bit of a trowal hangs back over the SE zones from the Fri. night
system on Saturday. Thus had some low morning PoPs over SE MT and
Sheridan County on Saturday. A zonal flow moves in with shortwaves
in the flow into Sunday. Using model blends resulted in some
isolated PoPs Sat. night and Sunday. There was good agreement on
temperatures with upper 50s to lower 60s expected each day.

Upper trough digs SE through the Pacific NW Sun. night, with a
cutoff low developing over the E ID/W WY border on Monday. PoPs
affect mainly areas S and W of KBIL Sun. night. Decent
precipitation amounts, around a third of an inch, are possible
over many areas on Monday. A mix of rain and snow is possible over
western areas and Sheridan County Sun. night as 850 mb
temperatures approach zero degrees C. The main upper low passes to
the S Mon. night and shifts E on Tuesday. Precipitation will
shift E Mon. night. The ECMWF holds onto precipitation over the SE
through Tue., while the GFS moves it out. With 850 mb
temperatures around zero degrees C, rain and snow would be likely
Mon. night into Tuesday. SE MT would have 1 to 2 inches of
precipitation if the ECMWF pans out. There is much uncertainty
with the details of this system, so it bears watching.

Drier weather is in store for Wed. and Wed. night as an upper
ridge moves over the area. The GFS brings energy into the ridge on
Thursday with a chance of precipitation in the western mountains.



Rain will overspread the area from W to E through the day. The
rain will bring MVFR/IFR conditions, along with widespread
mountain obscurations in rain and snow. Chances for rain continue
tonight, with the best chances from KBIL S and W. MVFR/IFR
conditions will continue with LIFR in some locations. The
mountains will remain obscured. Arthur



    Tdy Fri     Sat     Sun     Mon     Tue     Wed
BIL 054 041/050 034/061 043/061 040/050 033/050 032/056
    9/R 77/R    21/U    11/B    36/R    62/O    11/B
LVM 051 034/049 029/059 036/058 033/047 029/049 029/055
    +/R 88/O    20/U    12/T    45/O    42/O    11/B
HDN 057 040/052 034/062 040/063 037/053 033/051 031/058
    8/R 76/R    41/B    11/B    36/R    63/O    11/B
MLS 060 042/056 037/062 043/063 039/056 036/053 032/059
    6/R 55/R    31/B    11/N    24/R    53/R    11/B
4BQ 061 040/053 037/058 040/061 037/055 035/048 030/054
    4/R 55/R    42/W    11/B    25/R    65/O    21/B
BHK 062 040/055 036/060 040/061 035/056 033/048 029/054
    3/R 52/R    31/B    11/N    15/R    65/O    21/B
SHR 056 038/046 032/057 035/058 035/050 032/046 028/053
    4/R 89/R    71/B    12/W    36/R    64/O    11/B


MT...Winter Storm Warning in effect until midnight MDT Friday
      night FOR ZONE 67.
WY...Winter Storm Warning in effect from 6 AM this morning to 6 AM
      MDT Saturday FOR ZONE 98.


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