Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 200213

Area Forecast Discussion...Updated
National Weather Service Billings MT
813 PM MDT Tue Sep 19 2017

Widely scattered showers across our CWA this evening. These should
be gradually tapering off overnight as primary forcing aloft
shifts east. Another round is due in tomorrow, mainly affecting
the mountains and nearby lower elevations.

Main change for this update package was to pull trigger on a wind
advisory for some of our western foothill zones for tomorrow.
Local probability tools and BufKit soundings support strong mix
down winds through gap locations. We will run this from 3 AM to 9
PM to give it some room as transition season can sometimes
surprise us. Main impacts are expected to be along I-90 in the
Livingston vicinity. There may be some decent gusts on Highway 191
from Big timber to Judith Gap as well as showers move through
tomorrow afternoon. BT


.SHORT TERM...valid for Wed and Thu...

As the jet is starting to push farther east, the area is starting
to loose the lift. There will continue to be scattered showers
across the area as the remaining energy moves through the area.
There have been a few lightning strikes around Livingston this
afternoon, so have kept the mention of thunderstorms this
evening. Overnight expect winds around Livingston to increase and
by morning on Wednesday could see gusts approaching 55 mph. Local
guidance continues to show a 60 to 70 percent chance of seeing
gusts to 58 mph, but given that this is not a pure gap flow event
rather a mix down event, may not be able to achieve high enough
winds for an advisory. The gradient will be aligned with the
terrain, along with the winds aloft ,so the potential is still
there. Going into Thursday, energy will start to move into the
area from the next through moving into the West Coast. The area
will see temperatures will be cooler, in the 50s, and rain chances
will be spreading from west to east through the day. Reimer

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

Persistent troughing continues in the extended period over the
western half of the CONUS.

The apex of the upper level jet will work its way into south
central Montana by Friday. The divergent exit region of this jet
will serve as the focal point of widespread precipitation...snow
in the higher terrain and rain across the plains...through

At the mid levels, several vort maxes will work their way into
central Wyoming and into SE Montana setting up a nice deformation
zone...Friday and Saturday. To give an idea of how much rain
will be with this system, GEFS plumes for KBIL are showing mean
values at just above 1.5 inches. Not every locale will get that
much, but those values are pretty impressive considering how dry
the region has been for the past several months.

The rain chances will diminish by Sunday, with the jet axis moving

Temperatures will remain cooler over the weekend for the entire
CWA. Highs will struggle to make it out of the mid 50s until early
next week. Singer



Expect generally VFR conditions to prevail. Scattered showers and
an isolated thunderstorm are still possible this evening and could
produce some localized MVFR conditions. Expect winds around KLVM
to increase overnight, and by 12z gusts to be up to 45 kts are
possible. Breezy conditions are possible around K6S0 and KBIL as
well Wednesday. Reimer/AAG



    Wed     Thu     Fri     Sat     Sun     Mon     Tue
BIL 041/065 044/055 039/045 036/045 035/049 036/054 039/056
    21/N    23/W    76/W    46/W    43/W    21/B    12/W
LVM 037/056 037/051 034/043 031/045 030/048 030/051 034/054
    34/W    65/W    66/W    34/W    22/W    21/B    22/W
HDN 039/068 043/058 039/050 037/049 037/051 035/055 037/059
    41/N    22/W    76/W    45/W    44/W    22/W    12/W
MLS 041/067 044/061 041/052 038/052 037/051 037/055 037/060
    20/B    12/W    55/W    33/W    44/W    31/B    12/W
4BQ 038/069 045/062 040/052 038/050 037/046 036/051 035/058
    10/U    11/E    34/W    34/W    54/W    31/B    12/W
BHK 039/067 044/065 041/055 038/053 038/051 036/054 035/059
    10/N    01/E    34/W    34/W    44/W    31/B    12/W
SHR 035/067 042/057 036/048 033/045 032/045 030/049 031/054
    10/U    13/W    65/W    55/W    54/W    32/W    12/W


MT...Wind Advisory in effect from 3 AM to 9 PM MDT Wednesday FOR
      ZONES 65-66.


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