Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 240946

Area Forecast Discussion
National Weather Service Billings MT
346 AM MDT TUE MAY 24 2016

.SHORT TERM...valid for Tdy and Wed...

Upper low over southern Saskatchewan will continue to wobble
along the Montana/Canadian border today. The related cyclonic
flow and unstable atmosphere induced over us by its position
will continue to produce isolated to scattered showers...mainly
over our western zones this morning. Some thunder is possible but
not likely as forcing is just glancing our CWA at this point.

A more significant player for our weather today is short wave
energy within the mean southwesterly flow to our south. This
energy is still progged to track across Wyoming and the southeast
corner of Montana late today through tonight. Proggs also continue
to indicate a switch of westerly to easterly flow at the surface
by midday across our southern zones ahead of this wave. This will
increase directional shear and start to advect higher dewpoints
into southeast Montana. WRF NSSL projects MUCAPE along the lines
of 500-750 j/kg along the Montana and northeast Wyoming border
late today, but I feel like even that may be a bit overdone given
current dewpoints in upper 20s to low 30s and limited period of
easterly flow before disturbance reaches area. SPC has moved their
marginal risk as far west as Hardin and north to Hysham and
Forsyth. This probably prudent, but we feel the better chance of
any strong storms is across Sheridan and Powder River Counties
where best MUCAPE and updraft helicity are expected late
today/early evening as short wave tracks across. At any rate, we
are not anticipating more than a few strong cells. Rain and
embedded thunderstorms will continue across east zones overnight.
Have further nudged up POPs in the east.

Cooler and more stable conditions will exist at least initially
in our east Wednesday once early morning wave departs. However,
upper trof and cool air aloft will remain over the region through
Wednesday night. Thus, mainly afternoon and evening showers/tstms
are in store once again. Not expecting any severe weather thru the
short term period, but cannot rule out some small hail given the
seasonably low wet bulb zero heights. Temps the next couple of
days will remain near or slightly below normal with highs in the
60s to lower 70s. BT

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

Upper shortwave trough axis should cross the region during the
day on Thursday. This shortwave should help to destabilize the
atmosphere enough to generate scattered showers and thunderstorms.
Low-level flow should be west/northwesterly, which means that
dewpoints and instability will be limited. Because of low
instability, severe weather is not expected on Thursday. Behind
the trough axis, a period of shortwave ridging builds in for
Thursday night. This ridging should give most of the area a mostly
quiet/dry night...except perhaps for the western zones where
cyclonic flow could produce a few showers there toward sunrise

Large upper low slowly moves eastward over the Pacific NW Friday-
Monday, with several shortwaves rotating around it. These
shortwaves should produce showers and storms at times Fri-Mon.
Low-level easterly flow is progged for Saturday afternoon-evening
which should help raise surface moisture. The low-level moisture
combined with large-scale ascent and decent 0-6 km shear could
produce some strong storms mainly for the central/eastern zones
Sat afternoon- evening. By Sunday, low-level flow turns
northwesterly for most of the area, which is generally a more
stable environment for us, resulting in a few showers and just
general t-storms for much of the CWA. Low-level southeasterly flow
could hang on a bit longer in southeast MT Sunday morning,
possibly generating a few strong storms there.

For next Monday, 00z ECMWF brings upper low farther east, over our
western zones, with a vigorous shortwave that produces perhaps a
steadier rain for the area. The GFS keeps the upper low farther
west, giving our area a warmer and more convective solution. Too
early for details...but at this time at least part of Memorial Day
could be wet.  RMS/BT


A few showers are occurring over southern MT this morning.
Scattered showers should continue today and tonight.  Showers are
likely near KSHR and southeast of KBIL after 00z Wed.
Thunderstorms are possible this afternoon and evening. Low clouds
are possible near KLVM and KBIL this morning, but CIGs should be
MVFR or higher. Mountains will be obscured at times today and
tonight. RMS/BT



    Tdy Wed     Thu     Fri     Sat     Sun     Mon
BIL 066 047/065 046/068 046/070 047/067 047/069 046/066
    2/T 44/T    33/T    24/T    44/T    43/T    33/T
LVM 061 039/063 041/065 041/064 040/061 040/064 040/061
    4/T 35/T    34/T    35/T    54/T    43/T    33/T
HDN 071 046/067 044/071 045/072 047/069 046/071 046/068
    2/T 64/T    33/T    24/T    44/T    43/T    33/T
MLS 072 050/067 048/070 050/073 052/073 051/072 049/070
    2/W 76/T    13/T    23/T    34/T    43/T    33/T
4BQ 074 047/065 043/071 046/073 048/073 047/073 047/070
    2/T 75/T    13/T    22/T    24/T    43/T    33/T
BHK 073 046/063 043/069 045/072 046/073 048/072 045/068
    2/W 88/T    23/T    22/T    23/T    33/T    33/T
SHR 070 043/063 041/067 042/070 044/068 044/069 043/066
    3/T 64/T    34/T    34/T    44/T    43/T    33/T




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