Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 201607

Area Forecast Discussion...Updated
National Weather Service Billings MT
1007 AM MDT FRI MAY 20 2016

Weak returns were moving through parts of the central zones and
were shifting northward. This weak activity will shift north and
taper off this morning. Adjusted pops to trim back coverage this
morning over most of western and central zones for the late
morning hours.

Clouds were thick across all over the western and central zones
this morning, which could pose a problem for strong thunderstorm
development this afternoon. Clouds were breaking up over central
and northern Wyoming behind the passage of this mornings wave and
ahead of the next advancing wave moving through southwest Wyoming.
Models initiate convection off the east slopes around 20-21z and
then advance it north to northeast, approaching Billings anywhere
from 23-01z. Again, this will depend greatly on clouds breaking up
as the start time could be later if clouds hold in longer.
Projected shear is around 40kts over the western half of the area.
Surface dewpoints were around 50 with projected capes around
1000j/kg this afternoon. Should storms fire, they will be strong
to severe. That part of the forecast remains unchanged. TWH


.SHORT TERM...valid for Tdy and Sat...

Most of last evenings convection has weakened and moved north of
our CWA early this morning. Cold front has stalled near Rosebud
County and has generally become a north/south oriented stationary
boundary at this point. Today has potential for some strong storms
and even a few severe due to increased shear profiles, but as
usual things may not be quite that simple. Quick take is...if we
see enough sunshine this afternoon there is potential for stronger
thunderstorms than we saw Thursday.

Models are pointing to a nice easterly return flow in the lower
levels today. In the meantime, strong southerly flow will
continue over the region thanks to the nearly stationary upper
low parked over northern California and Oregon. This will set up a
well sheared vertical profile, especially across our western
zones. That easterly flow will help keep dewpoints up and as a
result model progs all agree mucape will be higher than Thursdays,
possibly reaching around 1250 j/kg in the Billings area. Some
things going against the threat of strong/severe thunderstorms...
we do have a weak wave expected to move across our western and
central zones this morning producing a few light showers or
sprinkles. Satellite imagery is also indicating a good deal of
cloud cover to our south which may end up across our area today.
These factors could limit our available energy.

My thinking at this time is cloud cover may limit mucape over
areas around the mountains west of Yellowstone County this
afternoon while at least some partial clearing is more likely over
our central zones behind the mornings short wave. Thus, Billings
may be in a decent place to see some strong thunderstorms right
toward evening. So while thunderstorms are more likely in western
zones...the stronger variety is more likely over our central
zones (Reed Point to Billings and Hardin) this evening. Most of
the action will then slip to the north and diminish overnight.

Saturday...that upper low to the west finally makes a move and
slides northeast across western Montana. This pushes a cold front
across our CWA again with pockets of potential energy lifting
south to north over the region. While isolated convection can be
expected over our entire area...models hint at a nice line of
convection developing along surface convergence over our far
eastern zones. This area could see a brief strong or severe storm
threat late Saturday. BT

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

Unsettled weather with showers and thunderstorms will be the
theme for the extended forecast.

Models were in general agreement in bringing an upper low east
along the MT/Canadian border on Sunday. Our area will be under a
westerly flow pattern with disturbances moving through, bringing
periods of scattered showers/thunderstorms. Model mixed layer
CAPE supported general (non-severe) thunderstorms across the area.
The best precipitation chances will be over and near the
mountains. Highs will range from near 60 west to the lower 70s

The departing low to the north of the area will leave cyclonic
flow with shortwave energy in its wake on Monday. Kept scattered
showers over most of the region with a slight chance of
thunderstorms. Energy continues to move across the area Tuesday
and Wed. with low chances of showers and thunderstorms. A split
trough will keep showers and thunderstorms in the forecast for
Thursday. There is a chance for more organized, steady rain especially
over southeastern MT late Thursday as the GFS/ECMWF show an upper
low tracking northeastward over South Dakota. Exact track of this
low will determine where the steady rain falls.

Temperatures will be near normal throughout the period. RMS/BT



Isolated to scattered showers and a few thunderstorms will affect
areas west and north of KBIL through 18z with possible MVFR
conditions. Chances for thunderstorms will increase over and west
of KBIL between 21Z and 00Z, and will continue through the evening.
MVFR/IFR or lower conditions will accompany the precipitation
along with possible wind gusts to 50 kt and hail. Isolated
thunderstorms are possible over the remainder of the area this
afternoon and evening. Chances for storms will decrease late
tonight. Mountain obscurations will increase this afternoon over
the Crazys, Beartooths and Absarokas and continue this evening.
The Northeast Bighorns will have localized to areas of
obscuration. Arthur



    Tdy Sat     Sun     Mon     Tue     Wed     Thu
BIL 074 052/077 048/067 045/067 045/067 047/072 048/072
    3/T 53/T    23/T    22/T    22/T    22/T    23/T
LVM 066 044/065 039/059 038/061 038/063 039/068 040/070
    7/T 54/T    25/T    34/T    44/T    43/T    33/T
HDN 078 049/082 046/071 042/069 042/069 044/073 045/074
    2/T 22/T    33/T    22/T    22/T    22/T    23/T
MLS 083 059/088 054/073 047/071 046/069 048/073 050/076
    2/T 23/T    53/T    22/T    22/T    22/T    22/T
4BQ 083 054/087 050/072 043/071 043/071 045/072 047/073
    2/T 23/T    63/T    22/T    22/T    22/T    23/T
BHK 079 052/082 051/072 043/070 041/069 043/070 045/072
    2/T 22/T    53/T    22/T    22/T    22/T    23/T
SHR 078 047/080 043/066 040/067 040/066 041/069 042/069
    2/T 22/T    33/T    23/T    32/T    22/T    24/T




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