Weather Service Report

FXUS65 KBYZ 201210

Area Forecast Discussion...Updated
National Weather Service Billings MT 
510 AM MST Fri Jan 20 2017


Issued freezing rain advisory for large section of central CWA
through 10 AM this morning. MDOT reporting freezing rain and black
ice in I-90 from east of Billings to Crow Agency, and we suspect
it goes all way down into Sheridan County Wyoming near Ranchester. 
Chances are I-94 will be impacted by this as well next couple of
hours as precipitation band hitting this area hard. Most of
precipitation is east of Billings, even a little on bridges and
overpasses will create some black ice and dangerous travel this
morning. Felt it was prudent to issue advisory for the morning
commute. Precipitation may dwindle by mid morning...but linger in
our southeast. BT


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

Band of precipitation affecting our CWA this morning is situated 
north to south, generally from the Big Horns to Musselshell and
Northern Rosebud Counties. We have not had any reports so far
other than light rain or drizzle within this band. Temps in the
east and even at Sheridan dropped well below freezing, but as
clouds moved in readings have risen dramatically preventing
freezing precipitation from depositing on sidewalks or streets. 
For instance, Sheridan was down to 25 degrees, but warmed to 37
degrees as clouds moved in. Temps are much colder a little east of
the cloud cover (teens to lower 20s), so there is a risk of seeing
some freezing precipitation right on the edge of the precipitation
band before temps warm up. However, the warm layer aloft is
shallow on progged soundings. So its possible rain changes to snow 
over much of the CWA by sunrise. Bottom line, we do not feel the
need for any type of winter weather advisory this morning, but our
media partners may want to mention the possibility of isolated
slick roads and bridges. 

The precipitation is slowly working east and downslope flow off
the higher terrain appears to be quickly drying out our western
zones. So have lowered PoP's in the west for the morning and
afternoon. The band of precipitation is linked to the 500 MB
jet and associated differential vorticity. Much of this forcing
weakens later today as jet maximum slides north, but some
remaining low level upslope and convergence may have precipitation
linger in the east into the evening. 

Saturday, 500 MB ridging occurs over our region ahead of the next
approaching trough. Wind fields look weak so there will not be
much mixing. Temperatures will be around normal. Some Pacific moisture
moves into the mountains as the upper winds back to the southwest.
So some low PoP's for the west facing slopes seems appropriate for
Saturday night. BT

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

Large upper trof pushes into the west coast over the weekend. As
southern stream of the jet enhances over the southwestern part of
the country a lobe of low pressure develops over Wyoming and
pushes eastward into the Dakotas. Although the upper-level pattern
is agreed upon fairly well by the GFS and ECMWF, the qpf pattern 
is quite different. ECMWF keeps precip confined mainly to extreme 
southern Montana and Wyoming with most of the snow south of 
Billings. GFS is much more bullish with upslope flow bringing 
several inces of snow into Billings. For now have gone with a 
blended solution, which brings an inch or so up to south central 
Montana with several inches in northern Wyoming and southern 
Montana. Snow tapers of Tuesday as amplified ridging begins to 
move in from the west. Expecting generally dry conditions through 
the end of the week with temps near to slightly below climo. Walsh



Conditions already improving at LVM and BIL with vis and cigs
expected to remain VFR now that -RASN has begun to move east of
the area. -RASN will impact MLS and SHR through the afternoon 
hours with vis/cig reductions to MVFR/IFR possible. Walsh



    Tdy Sat     Sun     Mon     Tue     Wed     Thu     
BIL 037 018/032 021/032 016/027 016/026 012/024 012/026
    5/W 10/U    01/B    12/S    53/S    22/S    11/U
LVM 039 014/036 022/039 018/034 012/028 009/027 010/028
    2/J 11/B    21/B    24/S    42/S    22/S    11/B
HDN 035 011/029 009/030 006/025 010/024 004/022 003/024
    8/W 10/U    01/B    11/B    54/S    22/S    21/U
MLS 036 019/030 014/028 006/023 009/022 007/021 005/022
    3/W 21/E    01/U    11/B    33/S    22/S    21/B
4BQ 036 016/032 014/032 005/027 009/025 006/023 005/025
    3/W 31/B    00/U    11/B    54/S    22/S    21/B
BHK 034 021/031 014/027 005/024 010/022 008/021 006/022
    1/B 22/J    21/B    11/B    32/S    22/S    21/E
SHR 035 010/032 009/033 008/029 009/024 003/023 003/026
    5/J 20/U    01/B    12/S    75/S    22/S    21/B


MT...Freezing Rain Advisory in effect until 10 AM MST this morning
      FOR ZONES 30-35-38-57-58.
WY...Freezing Rain Advisory in effect until 10 AM MST this morning
      FOR ZONE 99.



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