Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 180251

Area Forecast Discussion
National Weather Service Billings MT
851 PM MDT Wed May 17 2017

Widespread precipitation continues across our west/south, in
diffluent region of slow-moving upper low over southeast ID. Rain
amounts have exceeded an inch at Billings and 1.5 inches at
Livingston, the latter being a record for the day. Heaviest precip
has shifted W/SW of Billings in upslope areas. Snow has been
falling at Livingston, but with temps in the mid 30s it has not
been sticking yet. Temps have fallen to the lower 30s and snow is
beginning to stick at Red Lodge per area web cams. Will make no
changes to the winter wx advisory in effect for the Beartooth and
Red Lodge foothills as wet snow will continue to fall into
tomorrow. Mountains are receiving heavy snowfall, of course, and
winter storm warnings continue above 6000 ft.

Recent web cams over Bozeman Pass suggest difficult travel
conditions on I-90 west of Livingston. Temperatures at Livingston
will fall to the lower 30s this evening and this should allow for
a little wet snow accumulation tonight, though likely not as much
as at Red Lodge and Nye, and a shift to easterly winds will
moderate temps once the backdoor front arrives. Easterly upslope
flow will also continue to favor the Livingston area for
precipitation through the night. With all of this in mind, will
add Livingston to the foothills winter weather advisory.

For Billings, we are past the heaviest rain, but periods of
lighter rain will continue til late tonight or tomorrow morning
before tapering off completely. Upslope areas will see precip a
bit longer. The combination of upper low/ascent drifting further
southeast and low level dry advection from the NE will allow
precip to taper off across our cwa tomorrow.

Have adjusted pops per current activity and expected trends



.SHORT TERM...valid for Thu and Fri...

Significant event unfolding as expected with moderate band of
rainfall developing along inverted surface trough across our
central and western zones. Some thunderstorms also scattered over
southern portion of CWA with some small hail reported in Sheridan.
Have only made some slight adjustments to placement of categorical
PoP`s for this package. The one decision we had to make was with
regard to the foothills. Our basic tools were not putting much if
any snowfall in Nye or Red Lodge, but cross sections show freezing
levels dropping to around 5000 ft in this area later tonight give
or take. Copious moisture and deep upslope concern us. We have
thus issued a Snow Advisory from 6 PM to Noon Thursday for the
Beartooth and Red Lodge Foothills. There is a potential for heavy
wet snow here so impacts are more tree damage and power outages
than slick roads (roads may be slushy or with ponding water by
morning we believe).

The other concern is the potential for flooding. We have one
spotter in Golden Valley who has been under heavier precipitation
all day. Our radar precip had him with 2.6 inches, but his actual
ground truth is more like 1.00 to 1.5. (the difference likely due
to bright banding). We feel the ground can handle most of what has
fallen so far, though there will likely be areas of minor flooding
in poor drainage/low lying areas by evening. We continue to be in
a monitoring mode as far as flooding goes.

Precipitation is still expected to taper off tomorrow. BT

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

The gist of the extended forecast remains unchanged with chances
for showers and thunderstorms each day. Models and ensembles were
in good agreement with the overall synoptic pattern until later in
the period.

NW flow will be over the region on Saturday as a shortwave
approaches from the NW. The wave will move through the region
through Sunday. Another wave will move S into the area by early
Monday and trailing energy will move S through the area on
Tuesday. Models disagreed about Wednesday with the GFS maintaining
northerly flow over the area and the ECMWF building a shortwave
ridge into the region. Kept PoPs over the western zones through
Sat. night near the shortwave. Spread PoPs further E over the area
on Sunday as the wave passes S of the area. Energy moving S into
the region will bring a chance of precipitation to the area on
Monday. Tuesday will be drier in the wake of the Mon. wave. Went
near climatological PoPs Wed. due to model differences.

Used model blends for temperatures through the period due to
differences between the model temperature profiles. High
temperatures will be mainly in the 60s. Arthur



Widespread rain/snow will continue to bring poor flight conditions
through the night to areas from KBIL west to K3HT/KLVM and south
to KSHR. MVFR to local LIFR conditions expected, and mountains
will remain obscured. Slow-moving storm system will drift
southeastward, allowing for drier air and improvement to VFR
across most of the forecast area Thursday afternoon. KMLS and KBHK
will remain unaffected by precip from this system, but could see
local MVFR cigs late tonight and tomorrow morning. JKL



    Thu     Fri     Sat     Sun     Mon     Tue     Wed
BIL 041/053 037/060 040/065 045/068 046/066 043/069 046/073
    +4/R    11/B    02/T    23/T    33/T    22/W    12/T
LVM 034/048 031/058 036/063 038/065 040/064 038/069 039/070
    +7/O    11/B    12/T    23/T    33/T    21/B    23/T
HDN 042/056 038/061 037/066 042/070 045/067 042/069 044/074
    73/R    11/B    11/B    12/T    33/T    32/W    12/T
MLS 040/059 040/061 038/064 044/072 046/067 043/069 045/073
    10/B    01/B    11/U    01/B    22/T    22/W    22/T
4BQ 038/057 038/055 035/061 040/070 043/065 042/066 042/069
    21/E    13/W    21/B    02/T    33/T    32/W    22/T
BHK 034/057 035/057 034/058 037/068 042/063 040/065 041/068
    00/B    01/B    12/T    11/B    33/T    32/T    22/T
SHR 038/047 034/051 033/059 038/064 041/060 038/063 039/067
    +8/R    33/W    21/B    23/T    33/T    32/T    22/T


MT...Winter Weather Advisory in effect until noon MDT Thursday FOR
      ZONES 56-65-66.
     Winter Storm Warning in effect until 6 PM MDT Thursday FOR
      ZONES 67-68.
WY...Winter Storm Warning in effect until 6 PM MDT Thursday FOR
      ZONE 98.


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