Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 280255

Area Forecast Discussion...Updated
National Weather Service Billings MT
855 PM MDT FRI MAY 27 2016

Upper trough over the pacific northwest was dropping into western
Montana with increasing diffluent flow. This pattern generated
quite a few showers and thunderstorms over southern Montana and
north central Wyoming this evening. Locally heavy rain was
reported in almost every shower, with up to half inch hail in the
stronger thunderstorms. The activity has weakened a great deal
over the last couple of hours, but the radar was still being
painted with a few showers. Have trimmed pops back over parts of
the western and central zones. Tops of convection over the west
was so low that the radar was shooting right over it, hard to get
a feel for activity west of Columbus. High resolution models
dissipate the activity overnight. The GFS lingers showers from
Livingston to Judith Gap into the early overnight hours, so kept
scattered pops in place for locations west of Billings. TWH


.SHORT TERM...valid for Sat and Sun...

Showers and thunderstorms were developing over the western forecast
area this afternoon. Other showers were forming over the NE
Bighorns and SE MT. The showers and storms were forming in an
unstable airmass with CAPES of 500 to 1000 j/kg. There was no
shear present. Pacific jet will dive SE into W MT tonight bringing
divergence from the left-front quadrant to the area. The lift will
move N of the area late. Weak vorticity will affect the western
and central zones tonight and instability will weaken with time.
Precipitable waters on the order of a half inch to /0.75/ inches
over the area will move east during the night. Expect some storms
to contain heavy rainfall due to slow storm movement and briefly
high precipitable waters. Freezing level around 6000` AGL will
support the potential for small hail. The new NSSL WRF did not
cluster storms around KBIL like the 00Z run showed...but did have
some storms moving through the Billings area around 23Z-00Z. So
had high chance to likely PoPs central to W this evening, with a
slight chance for showers SE. Then, had chance pops W of Custer
and Powder River Counties overnight.

Some vorticity will rotate NE through the area on Sat. around a
Pacific upper low, before a westerly flow overtakes the region
Sat. evening. Models showed some CAPE over the far eastern zones
on Sat. along a cold front moving out of the area. Shear continues
to be weak. Expect thunderstorms along the departing cold front so
had highest PoPs in the afternoon over the far E. Otherwise, had a
slight chance of morning showers, with a low chance of
thunderstorms central and W in the afternoon. Highs will be
slightly below normal.

West flow aloft will be over the region Sat. night through Sunday.
Some weak energy will reach the area Sun. afternoon. Airmass dries
out late Sat. night through Sunday. Sunday looked warm with highs
well into the 70s. Pacific trough approaches the area Sun. night
sending energy into the region. Given increasing shear and decent
CAPES over SE MT, went with showers and thunderstorms through the
night. Arthur

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

Thoughts from the midshift remain consistent with the 12z runs.
Models struggling with consistency for Monday- Tuesday storm
system. Latest Canadian and GFS models drop a stronger wrapped up
system from the Pacific NW through the area during this period,
while the ECMWF is faster bringing the energy across as an open
wave and keeps main area of dynamics well north of the area along
the Canadian border. Given the differences in the models have kept
chance pops going and will await better consistency before making
adjustments for this period. Models come to better agreement with
strengthening ridge of high pressure developing mid to late week
and continuing into next weekend. This will trend drier and warmer
heading through the end of the week. Chambers/Borsum



Scattered showers and thunderstorms currently noted on radar
across the region. Primary impacts to aviation will be light rain
at LVM with VCSH and RA potential at all sites through the night.
Most of the shower activity will clear out by 09Z with
west/northwest winds below 15 knots expected at all terminals.



    Sat     Sun     Mon     Tue     Wed     Thu     Fri
BIL 047/068 046/076 050/068 045/063 044/069 047/078 053/079
    42/T    11/U    25/T    34/T    42/T    11/U    11/B
LVM 040/063 039/071 043/063 041/060 039/069 044/076 049/079
    62/T    21/U    34/T    43/T    32/T    11/B    11/B
HDN 047/070 045/078 050/071 044/063 042/069 046/080 052/082
    52/T    10/U    24/T    34/T    43/T    11/U    11/U
MLS 051/072 049/078 054/073 048/065 045/068 047/079 054/082
    12/T    11/U    34/T    44/T    43/T    21/U    11/U
4BQ 046/071 045/078 050/075 045/065 042/068 044/078 051/082
    14/T    11/B    23/T    33/T    33/T    21/U    11/U
BHK 046/071 044/076 049/072 044/063 040/065 042/075 048/078
    15/T    21/U    25/T    44/T    43/T    21/U    11/U
SHR 042/068 041/075 046/070 042/061 039/067 042/077 048/081
    32/T    11/U    25/T    34/T    43/T    11/U    11/B




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