Area Forecast Discussion
Issued by NWS Billings, MT

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FXUS65 KBYZ 231551

Area Forecast Discussion
National Weather Service Billings MT
951 AM MDT MON MAY 23 2016

Water vapor imagery shows upper low over southwestern Saskatchewan
with cyclonic flow across MT. Ascent and showers are focused over
western and north central parts of the state this morning, but we
are seeing increasing cloud cover and some light showers spread
into our west/northwest as moisture continues to wrap around the
slow-moving upper low. Combination of modest synoptic ascent,
diurnal destabilization and some mid level frontogenesis will
bring increasing showers to mainly our west and central parts
later today into this evening. Surface dew pts are quite low and
CAPES will be only 200-400 j/kg, but this should be enough for
isold tstms. Wet bulb zero heights around 5 kft suggest some small
hail is a possibility with any heavier showers, and our western
mountains will see some high elevation snowfall. For the update
this morning have expanded scattered pops east to include Billings
and Forsyth late this afternoon and evening. High temps today will
range from only the 50s in our west to lower 70s in our east. JKL


.SHORT TERM...valid for Tdy and Tue...

We will primarily be under the influence of an upper low today
situated over southern Saskatchewan. Thus, westerly flow aloft
will prevail and keep moisture limited across the region. There is
a spoke of vorticity progged to rotate around the upper low into
north central Montana this afternoon. This combined with decent
lapse rates from the cold 500mb temps aloft will produce isolated
to widely scattered showers and thunderstorms to move out from
the western higher terrain into our CWA. This convection should be
relatively average due to limited dynamics, and die off with

Tuesday is a little different animal. Upper low over Canada
weakens and southern branch of overall broadscale trough across
the west is primary influence. Southwesterly flow will thus
prevail over our region and send some short wave energy across the
central rockies late Tuesday afternoon/evening. Progs currently
have some timing differences, but generally suggest short wave
induced convection will move through north central Wyoming and
into southeast Montana in the evening/overnight hours. There is a
possibility of weak easterly surface flow developing in in this
area as well with surface low development over central Wyoming. So
some increase in moisture and shear seems a reasonable assessment.
Thus, an isolated storm or two in the evening could be a little
stronger than average with some hail and heavy rain.

Will make some adjustments to POP`s based on this.

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

On Wednesday, several shortwaves are progged to move across the
region in weak westerly/southwesterly flow. These should produce
scattered showers and thunderstorms. In our southeastern CWA
(mainly Carter County), mixed layer CAPE approaches 1000 J/kg and
0-6 km shear approaches 40 kt Wed. afternoon-evening, so an
isolated severe thunderstorm is possible there. For much of the
rest of south-central MT, CAPE and shear are weaker, indicating
that general (but not severe) thunderstorms are possible.

For Thursday-Friday, several more weak disturbances should move
over the region, sparking scattered showers and thunderstorms. CAPE
and shear look to remain low enough to prevent storms from
becoming severe at this point.

Saturday-Sunday...ECMWF and GFS agree that an upper low should be
over the western U.S...although they differ on the location of the
low. 00z ECMWF deterministic run brings the low close to the CWA,
providing good synoptic-scale lift and low-level southeasterly
flow. This pattern could produce a stormy scenario for our
region. 00z ECMWF ensemble mean generally supports the
deterministic run. The 00z GFS deterministic run and ensemble mean
hold the low back farther to the west, keeping the better dynamics
and associated precipitation west of the CWA at least on Sunday.
So, the potential is there for more organized thunderstorm
activity next weekend, but confidence is limited at this time due
to model differences. RMS/BT


Mid to high level clouds were moving in from the northwest this
morning associated with an upper low off to the north and an
approaching weak front. Scattered showers and isolated
thunderstorms will form across the west late this morning/early
afternoon and spread eastward to much of south-central Montana by
mid-late afternoon. Most of the shower and thunderstorm activity
should end by 06z Tuesday. Mountain obscurations are possible
near any showers/thunderstorms. Winds will remain gusty at KLVM
through the day. STP



    Tdy Tue     Wed     Thu     Fri     Sat     Sun
BIL 066 043/066 047/067 047/070 048/069 048/071 049/074
    3/T 32/T    34/T    33/T    33/T    32/T    33/T
LVM 059 037/062 041/064 040/066 041/064 040/066 042/069
    4/T 44/T    34/T    33/T    34/T    44/T    43/T
HDN 069 040/071 045/069 046/072 046/072 048/073 047/077
    2/T 22/T    34/T    33/T    33/T    32/T    33/T
MLS 070 046/072 051/071 050/073 050/074 052/075 052/079
    2/T 21/B    44/T    33/T    33/T    32/T    23/T
4BQ 071 042/073 047/071 046/072 046/073 048/074 048/078
    2/T 22/T    45/T    33/T    33/T    32/T    23/T
BHK 070 042/073 047/069 046/071 046/073 048/073 047/076
    1/U 21/B    55/T    33/T    32/T    22/T    22/T
SHR 067 039/068 043/066 043/068 042/069 044/070 044/075
    2/T 23/T    44/T    33/T    33/T    32/T    33/T




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