Area forecast discussion
National Weather Service Billings Montana
708 PM MDT Tuesday may 21 2013
Update...
Updated the forecast to increase probability of precipitation and shower coverage across
the west this evening as shortwave energy and increasing upper
level diffluence help generate some weak convection. Expect the
showers and isolated thunderstorms to dissipate overnight with the
loss of daytime heating and as shortwave energy continues to move
away from that area.
Also expanded the potential for showers across the east a bit
farther west...to include areas such as Broadus and Miles City
this evening. Radar...satellite...and observation all support this
westward expansion. Anticipate that this area of rain showers will
be slowly pushed eastward overnight as upper level ridging begins
to build in from the west...ahead of the approaching upper level
low currently situated over the Pacific northwest. The rest of the
forecast is on track. Stc
&&
Short term...valid for Wednesday and Thursday...
Large upper low over the eastern Dakotas continues to impact our
far eastern zones this afternoon and will continue throughout the
night. Expect mostly cloudy skies along with a slight shower
chance from Custer and Powder River counties eastward.
Elsewhere...some clouds and an isolated shower will be possible
over the beartooth/Absaroka Mountains this evening with clear to
partly cloudy skies expected across our central areas.
Large upper low and trough currently moving onto the Pacific
northwest coast will move onshore during the day Wednesday. This
will provide a southerly and divergent flow aloft to our forecast
area Wednesday through Thursday. Numerous pieces of energy will
eject from this low beginning Wednesday afternoon into Thursday
night. At the same time...a strong low-level jet will develop
across our eastern third of the forecast area Wednesday night into
Thursday providing easterly surface winds to the entire area. Best
chances for showers and thunderstorms will be from about
Yellowstone County westward Wednesday afternoon into Thursday
night. Have raised probability of precipitation to likely for the beartooth/Absaroka
Mountains and foothills...as well as from about Reed Point west
and north Wednesday evening and night and will maintain high
chance probability of precipitation for Thursday from Billings westward.
Can't rule out severe thunderstorms Wednesday evening and again
Thursday. There will be good speed and directional shear...cape
and lapse rates across the central and western areas.
However...soundings show the area capped so thunderstorms would be
more elevated in nature resulting in more of a large hail threat.
Hooley
Long term...valid for Friday...Sat...sun...Mon...Tue...
Not many changes made to the extended period forecast...as
inherited forecast was in decent shape.
The period begins Friday morning with the region under the
influence of southwesterly flow aloft...primarily due to the
spinning low pressure system over the Pacific northwest.
By Saturday evening an easterly low level jet forms over the
eastern portion of Montana. This will help bring some moisture
and added instability to the region. Expect winds to be blowing
pretty good in parts of Fallon and Carter counties as this jet
strengthens by Sunday afternoon.
Due to the nature of the pattern aloft...coupled with the
presence of some moisture at the surface...cannot rule out the
potential for thunderstorm activity almost every day in the
period. Severity will depend on amount of dry air entrainment at
middle levels...especially during this upcoming weekend. Cape values
in the eastern zones will exceed 1000 j/kg at times...so this
needs to be monitored.
For the rest of the period...the region will continue to be under
the influence of SW flow aloft...before the main flow becomes more
zonal. Singer
&&
Aviation...
Rain showers will continue to bring MVFR/IFR conditions to areas
from kmls east through a good portion of tonight. The MVFR/IFR
potential will begin to diminish across the east late tonight
into early Wednesday morning.
An isolated shower or thunderstorm is possible through
late this evening near the Beartooth Mountains...which would
reduce visibilities and increase wind gust potential. Wednesday
afternoon...the potential for more widespread thunderstorm
activity increases west of Billings...including near klvm. Some of
the thunderstorms across the west Wednesday afternoon may be
strong.
Gusty east winds will weaken late tonight across the west...but will
increase across the entire region again by middle day Wednesday. Stc
&&
Preliminary point temp/pops...
Wednesday Thursday Friday Sat sun Monday Tuesday
-----------------------------------------------------------
bil 043/066 046/074 050/072 048/077 053/079 053/077 051/077
12/T 33/T 43/T 22/T 22/T 23/T 33/T
lvm 039/066 043/065 041/068 040/078 041/080 042/078 041/075
24/T 64/T 44/T 32/T 22/T 23/T 33/T
hdn 043/070 048/077 050/075 048/079 053/080 052/080 051/079
11/north 32/T 33/T 22/T 22/T 23/T 33/T
mls 042/065 046/072 051/077 051/079 057/082 058/079 054/079
31/north 12/west 23/T 22/T 23/T 33/T 33/T
4bq 040/065 046/074 052/079 050/081 055/085 052/081 052/081
31/north 11/north 13/T 22/T 23/T 33/T 33/T
bhk 039/061 042/066 048/074 050/073 056/077 056/077 052/076
41/north 11/north 13/T 22/T 33/T 33/T 33/T
shr 037/066 045/075 047/075 046/079 048/083 048/079 046/076
12/T 32/T 23/T 22/T 22/T 23/T 33/T
&&
Byz watches/warnings/advisories...
Montana...none.
Wyoming...none.
&&
$$
Weather.Gov/Billings
