Area forecast discussion
National Weather Service Cheyenne Wyoming
947 PM MDT Tuesday Jun 18 2013
Update...
issued at 946 PM MDT Tuesday Jun 18 2013
The thunderstorms over the County Warning Area continue to move east ahead of
the shortwave trough and were over the far East Part of the County Warning Area.
Meanwhile...a boundary over the far south part of the County Warning Area has
aided in the formation of additional thunderstorms from near kcys
to kibm late this evening. The activity in those areas should
slowly weaken and continue into early Wednesday morning. In a
recent update have made minor changes to the first period of the
forecast.
Update issued at 733 PM MDT Tuesday Jun 18 2013
Thunderstorms have been weakening over the Panhandle since 01z.
The activity continues to be pushed east ahead of a shortwave
trough. That feature should be east of the County Warning Area by 04z. Have kept
strong thunderstorms over mainly the East Part of the Panhandle
until that time. Otherwise...clearing will continue from west to
east over the County Warning Area. Made adjustments to the probability of precipitation for early tonight
and minor changes to the remainder of the forecast for tonight.
&&
Short term...(this evening through Thursday night)
issued at 230 PM MDT Tuesday Jun 18 2013
Forecast challenges deal with severe thunderstorm chances
today...followed by fire weather concerns through Friday. Please
refer to fire weather section below for fire weather details.
Currently...convection beginning to develop out west of the
Laramie range. Latest water vapor imagery showing a subtle
shortwave moving into southwestern Wyoming this afternoon...which
is most likely aiding in earlier development of thunderstorms out west. A
pretty moist atmosphere in place east of the Laramie range with
dewpoints in the upper 40s just east of the Laramie range here at
Cheyenne. Further east in the Panhandle...low to middle 50 dew points are
being reported. Latest Storm Prediction Center mesoanalysis showing convective available potential energy over extreme
southeastern Wyoming and southern Panhandle around 600-1000 j/kg
and convective inhibition at zero. Still capped some over the
northern Panhandle and Niobrara counties with roughly 50-75
j/kg...but this should erode away as temperatures continue to
climb this afternoon.
Thinking a repeat of yesterday convection wise...though could be more
widespread with the assistance of that little shortwave moving
through the area. Severe thunderstorms should move off the Laramie
range into the better environment to produce large hail and
damaging winds. Shortwave comes through eastern Wyoming by 00z
this afternoon. Latest hrrr composite reflectivity showing
individual cells developing over the Laramie range...then
congealing into a line near the Wyoming/Nebraska border after 00z.
Thunderstorms look to come to an end middle evening as the shortwave
moves east into western Nebraska after 03z or so. Upper ridge axis
shifts east as well...with west to southwest winds returning to
Carbon and Albany counties after midnight.
Wednesday looks like a very dry and windy day as 700mb winds
increase significantly. GFS showing these winds climbing to near
40kts west of the Laramie range. Good middle level warming as well
with 700mb temperatures climbing from +10c this afternoon to +16c
Wednesday afternoon. Leeside trough still hangs out over the
Panhandle Wednesday afternoon...so isolated to widely scattered
thunderstorms still a good bet out that way.
For Thursday...upper low currently off the Washington state coast
moves inland to the Idaho Panhandle. This will keep winds strong
over our County warning forecast area...but 700mb temperatures cool some...down to +10 to
+12c. So Thursday should be a little cooler over Wednesday by a
few degrees.
Long term...(friday through tuesday)
issued at 230 PM MDT Tuesday Jun 18 2013
Rex blocking pattern across western noam will break down early in
the period as the meandering pacnw closed low fills and moves out
onto the northern rockies/plains. The depth at which it does so will
be the main forecast challenge and will carry residual impacts to
sensible weather.
On Friday...upper low will swing from the Idaho Panhandle into
western Montana. 12z operational GFS and European model (ecmwf) are fairly similar
in its placement near the Idaho/Montana Stateline by early Saturday. Weak
instability across east central Wyoming and the northern Nebraska
Panhandle. So have confined convective chances there. This low
pressure area will swing through Montana during the day on
Saturday. The eastern plains should see another convective day on
Saturday as low level moisture deepens and backs up into the eastern
plains. This will result in cape values that will once again climb
above 2000 j/kg. Saturday looks to provide the best severe weather
potential through the period.
By Sunday and Monday...the upper low ejects from the Dakotas
northeast towards Hudson Bay. This should bring an end to
convective activity and begin to heighten fire weather concerns
for late in the weekend/early next week. Flow will become
increasingly southwesterly as well...which will aid in the
surfacing of gustier winds aloft.
700 mb temperatures will range between 13 and 15c through the upcoming
weekend and increase to 17c by Tuesday. High temperatures will
reach generally in the 80s and low 90s through the period...with
even some middle and potentially upper 90s out on the far eastern
plains by early next week.
&&
Aviation...(for the 06z tafs through 06z Wednesday evening)
issued at 947 PM MDT Tuesday Jun 18 2013
Thunderstorms will affect the far east and far south parts of
the County Warning Area through 08z. Some of storms will produce periods of MVFR
ceilings and visibilities in rain as well as wind gusts as high as
40 knots. Otherwise VFR conditions will be common through Friday.
West to southwest surface winds will gust as high as 40 knots
mainly during the daytime hours in areas along and west of the
Laramie range Wednesday through Friday.
&&
Fire weather...
issued at 230 PM MDT Tuesday Jun 18 2013
Elevated to locally critical fire weather conditions Wednesday
through Friday as high pressure moves off to the east and
southwest to west winds return to the area. Zones along and west
of the Laramie range look to see widespread winds of 20 to 30 miles per hour
sustained with gusts to 40 miles per hour beginning middle morning Wednesday
that will persist through Friday. Windiest time periods look to be
late morning through sunset. Afternoon humidities out west will
fall to 5 to 10 percent with poor overnight recoveries with these
strong winds. East of the Laramie range...winds will be less with
higher afternoon humidities. Since all zones are still reporting
fuels as not ready for rapid fire growth...no fire weather
headlines are forecast for tomorrow or Friday at this time.
&&
Cys watches/warnings/advisories...
Wyoming...none.
NE...none.
&&
$$
Update...Weiland
short term...claycomb
long term...Hahn
aviation...Weiland
fire weather...claycomb
