Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 241657

Area Forecast Discussion
National Weather Service Billings MT
1057 AM MDT Wed May 24 2017

Current water vapor imagery shows a low over Alberta with trof/pv
dropping into WA to NW MT. Pressures falling at a good clip along
our SW mountains with latest MSLP at 992.9mb at LVM. Rises noted
at 15Z at GTF-HLN-BTM, so a frontal passage is within a few hours
of Livingston. A fast-moving frontal passage will bring increased
winds across our cwa this afternoon. HRRR continues to produce
convection in our NW this morning, wrongly, but despite this poor
timing forecast would expect greatest coverage of showers/tstms in
our NE CWA this afternoon to early evening. Forecast has all of
this covered well. Not expecting a severe risk today, but frontal
and post-frontal winds with some convective assistance will need
to be watched. Messaging for wind looks good.

Have updated to raise pre-frontal gap winds at Livingston where
gusts currently are in the 40s. Westerly mid level flow will be
tapped into up at Harlowton when the front arrives, so expect a
dramatic increase in winds with gusts to 50 mph in our NW cwa by
midday. Have also raised pre-frontal west winds at Sheridan in the
early to mid afternoon. Forecast high temps already exceeded at
LVM and BIL, so have adjusted highs up today, per the existing
pre-frontal regime. Finally, as PV approaches from the NW,
believe there is enough mid level moisture (aided by snow melt) to
pop a few showers or weak tstms over our SW mountains/foothills
this afternoon and early have expanded pops a bit to
cover this.



.SHORT TERM...valid for Tdy and Thu...

A potent low pressure system over Canada and associated front
will continue to drop southeastward through the day today. We are
already seeing significant pressure falls east of the divide
which has brought wind gusts near 40 mph to the Livingston area
tonight. Southwest winds will continue to increase as we begin to
mix during the morning hours. Surface front will move through
around 2 PM in the Billings area with winds increasing
significantly in the afternoon hours, as we mix down some 40 to 50
mph winds from 700 mb. Although the guidance has trended more
into northern MT with the strongest core of winds during the
afternoon, the models are now keeping strong winds well in to the
night as the PV max pushes through the area above a well mixed
boundary layer. Therefore, we anticipate strong afternoon mixing
to bring 40 to 55 mph winds from Livingston north to Judith Gap
and east to Billings and Roundup during the afternoon, and 30 to
40 mph winds along the front axis as it slides through Sheridan
and eastern MT. Then a secondary wave of strong winds Between 7
and 11 PM is possible as the PV max moves through the area. Ahead
of the front isolated showers and thunderstorms will fire between
Noon and 3 PM in Treasure and Rosebud counties then push eastward
with increasing coverage through the afternoon. These showers and
thunderstorms will be capable of enhancing the surface winds by
ducting down strong winds aloft.

A lobe of energy cuts off over the northern Rockies which will
aid shower development into Thursday over the western foothills
and mountains. Temperatures will be about 10 to 15 degrees cooler
on Thursday with 60s expected across the region. Walsh

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

Extended forecast features three phases. First phase has upper low
over Saskatchewan and Manitoba with a wave slowly moving
underneath this low across southern Montana Friday. This brings a
threat for shower and thunderstorm activity with below normal
temperatures. Next phase has northerly flow pattern during the
weekend as upper low over north central US moves towards Great
Lakes. This transitions to lighter flow with ridging moving into
the western portion of the northern Rockies. Overall this pattern
for the weekend and beyond suppresses convection and keeps
temperatures cooler than normal initially with a warming trend
later in the period. borsum


VFR conditions will prevail through tonight. Isolated to scattered
thunderstorms will accompany a strong cold front through the area
today, exiting the area to the east early this evening. Local MVFR
conditions and strong wind gusts can be expected near any storms.
Ahead of the front southwest winds will gust to 45 kts at times,
shifting to the northwest behind the front. These gusty winds will
likely persist through late tonight and possibly into tomorrow
morning in some locations. Expect mountain wave activity along and
near the foothills, including KLVM and KSHR taf sites today.



    Tdy Thu     Fri     Sat     Sun     Mon     Tue
BIL 084 046/064 044/064 045/069 047/072 047/073 047/078
    2/T 11/N    23/T    22/T    11/B    11/B    11/U
LVM 074 041/060 036/060 038/067 040/071 039/073 040/076
    1/N 12/T    34/T    33/T    21/B    11/B    11/B
HDN 086 047/066 043/065 043/069 045/072 045/073 045/077
    3/T 21/N    12/W    23/T    22/T    11/B    11/U
MLS 082 046/065 043/067 045/069 046/070 046/072 045/076
    4/T 31/N    11/B    12/T    22/T    11/B    11/U
4BQ 083 045/064 041/064 042/067 044/068 044/070 043/073
    2/T 21/N    11/B    22/T    22/T    11/B    11/U
BHK 077 042/062 039/064 040/065 042/066 041/066 039/070
    4/T 61/N    11/B    12/T    22/T    11/B    11/U
SHR 086 041/061 039/058 039/062 042/065 041/068 040/073
    2/T 21/B    34/T    23/T    22/T    12/T    11/B




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