Severe Thunderstorm Warning 1, NWS Billings, MT

Area Forecast Discussion
National Weather Service Billings MT
250 PM MDT FRI MAY 20 2016

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

Convection has been slow to materialize today with cloud cover
sticking around into the early afternoon. Clouds have held
temperatures down into the mid 60s over central zones. Sheridan
county and eastern Montana zones have gotten more sunshine and
have thus warmed into the 70s. Cape has been building despite the
cloud cover with values rising to around 1000j/kg available.
Effective bulk shear has increased to around 45kts from Billings
westward. Jet energy was pushing northward from northern Utah and
has kicked off some showers over Idaho. Shortwave energy does not
look overly strong coming out of southwest Wyoming, and the jet
rounding the western trough is pointed toward western Montana with
a glancing blow over our western zones. Forcing does not look
tremendously strong, but there was upslope flow and some moisture
convergence along with frontogenesis along the slopes that should
be able to fire a few storms, given the clouds get out of the way
fast enough. Clouds have been breaking up over Wyoming, but
filling back in with a little sunshine. All of this leaves a lot
of questions over the potential severe for this afternoon and
evening. High resolution models were pointing to a late ignition
off the mountains and foothills, with storms becoming strong due
to the environment and heading northeast toward Billings early
this evening.

Drier air will work in tonight and effectively taper convection
off quite a bit. Surface low pressure moves into central Montana
Saturday afternoon and will turn winds to the west over central
and western zones. This will dry the low levels out some and allow
dewpoints to fall into the lower 40s. The east will be very warm
with 850mb temperatures reaching 25c. Highs in the mid to upper
80s are expected with increasing southeast winds. Winds will gust
near 45mph around Baker while keeping dewpoints up. Surface
convergence around the low along with height falls will generate
thunderstorms. Storms could be severe over the east from Miles
City to Broadus eastward. Strong shear and capes around 2000j/kg
will lead to a threat for large hail and damaging wind, along with
an isolated tornado possible. Central and western zones will be
much more stable and drier with limited convection. The ECMWF does
keep instability over the western half of the area Saturday
afternoon and thus develops convection, so will maintain isolated
to scattered pops.

The western upper trough broadens quite a bit on Sunday with the
strong piece of energy cutting off a low over southern Canada.
This will put the area in downslope flow for drier weather. Much
cooler air will spill over the area with 850mb temperatures
falling to around 15c. Highs will be limited to the mid 60s to
lower 70s. TWH

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

Very little change to the going extended forecast which continues
to feature unsettled weather. Upper low currently situated over
the Pacific NW, will be situated just north of the Canadian border
through Tuesday while weakening. Cyclonic flow over the forecast
area will give way to unsettled SW flow. The low will dissipate as
it shifts E on Wed., leaving the area under general troughiness.
Westerly flow will prevail over the region into Tue. with some
moisture and instability. This pattern will favor isolated
afternoon and evening showers and thunderstorms. Westerly flow
becomes light on Wednesday. Will continue the scattered showers
and thunderstorms across the region. Temperatures will be near
normal through Wednesday.

Models continued a troughy unsettled pattern Thu. and Fri., but
disagreed in the pattern details. Kept isolated to scattered
showers and storms in the forecast with not much change in
temperatures. Arthur

&&

.AVIATION...

Showers and thunderstorms will gradually fill in from KBIL west
late this afternoon and evening. Isolated to scattered showers and
storms will occur elsewhere. MVFR/IFR or lower conditions will
accompany the precipitation along with possible wind gusts to 50
kt and hail. A few showers will continue overnight into Sat.
morning west and north of KBIL. Thunderstorms will increase across
the area Sat. afternoon. Some storms may be severe with large hail
and wind gusts to 50 kt from Rosebud County east. MVFR/IFR or
lower conditions will accompany the thunderstorms. Mountain
obscurations will be widespread over the Crazys, Beartooths and
Absarokas this afternoon, otherwise expect localized to areas of
obscuration through Saturday. Arthur

&&

.PRELIMINARY POINT TEMP/POPS...

    Sat     Sun     Mon     Tue     Wed     Thu     Fri
-----------------------------------------------------------
BIL 054/077 048/068 045/068 044/068 046/070 048/071 049/072
    53/T    33/T    22/T    22/T    23/T    33/T    32/T
LVM 045/065 041/060 038/061 038/062 039/066 040/067 041/068
    54/T    25/T    34/T    44/T    43/T    33/T    33/T
HDN 052/082 046/072 042/071 042/070 044/072 046/073 047/074
    22/T    33/T    22/T    22/T    23/T    33/T    32/T
MLS 060/087 054/074 047/072 046/071 048/073 050/075 051/076
    23/T    53/T    22/T    21/B    23/T    33/T    33/T
4BQ 056/087 050/072 043/072 043/072 045/071 046/073 046/073
    23/T    53/T    22/T    22/T    23/T    34/T    43/T
BHK 055/082 051/072 043/071 042/071 043/070 045/072 045/073
    22/T    53/T    22/T    22/T    23/T    34/T    43/T
SHR 047/080 043/067 040/068 040/067 042/069 042/069 043/069
    22/T    33/T    23/T    33/T    33/T    33/T    33/T

&&

.BYZ WATCHES/WARNINGS/ADVISORIES...
MT...None.
WY...None.

&&

weather.gov/billings

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE BILLINGS MT
300 PM MDT FRI MAY 20 2016

MTZ028>042-056>058-063>068-WYZ098-099-211200-
SOUTHERN WHEATLAND-MUSSELSHELL-TREASURE-NORTHERN ROSEBUD-CUSTER-
FALLON-NORTHERN STILLWATER-YELLOWSTONE-POWDER RIVER-CARTER-
SOUTHERN BIG HORN-EASTERN CARBON-NORTHERN PARK-
NORTHERN SWEET GRASS-GOLDEN VALLEY-RED LODGE FOOTHILLS-
NORTHERN BIG HORN-SOUTHERN ROSEBUD-JUDITH GAP-PARADISE VALLEY-
LIVINGSTON AREA-BEARTOOTH FOOTHILLS-ABSAROKA/BEARTOOTH MOUNTAINS-
CRAZY MOUNTAINS-NORTHEAST BIGHORN MOUNTAINS-SHERIDAN FOOTHILLS-
300 PM MDT FRI MAY 20 2016

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL
MONTANA...SOUTH CENTRAL MONTANA...SOUTHEAST MONTANA AND NORTH
CENTRAL WYOMING.

.DAY ONE...THIS AFTERNOON AND TONIGHT

THERE IS A POTENTIAL FOR SOME STRONG THUNDERSTORMS LATER THIS
AFTERNOON AND THIS EVENING...MAINLY ALONG AND WEST OF A ROUNDUP TO
BILLINGS LINE. THE MAIN THREATS ARE HAIL AND LIGHTNING. PLEASE
KEEP AN EYE ON THE SKY AND HEAD TO SHELTER IF THREATENING WEATHER
APPROACHES.

.DAYS TWO THROUGH SEVEN...SATURDAY THROUGH THURSDAY

FOR SATURDAY...THE THREAT FOR STRONG TO SEVERE THUNDERSTORMS
SHIFTS TO EASTERN MONTANA AND NORTHEAST WYOMING...MAINLY EAST OF A
FORSYTH TO SHERIDAN LINE. THE MAIN THREATS THERE WILL BE LARGE
HAIL...DAMAGING WINDS AND TORRENTIAL RAINFALL. BE PREPARED TO TAKE
ACTION SHOULD A STORM APPROACH.

ONE MORE THING...SHOWERS AND THUNDERSTORMS WILL COMBINE WITH
ONGOING MOUNTAIN SNOW MELT TO CAUSE AREA RIVERS AND STREAMS TO
RISE THIS WEEKEND. ALTHOUGH FLOODING IS NOT EXPECTED AT THIS
TIME...PLEASE BE MINDFUL OF RISING WATER LEVELS AND FASTER FLOWS.

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