Area forecast discussion
National Weather Service Omaha/valley NE
339 am CDT Sat may 18 2013
Short term...today through Monday night.
The focus for this portion of the forecast is severe weather
potential tonight and more so into Sunday and Sunday night.
Today and tonight...this period begins with upper level ridging
in place. A subsidence inversion in place from this ridge will
act to supress convection for much of the day. The trigger for
any convection will be a shortwave digging into the backside of
the ridge this evening into tonight. Given the lack of significant
forcing and enough heating (convective temperature is around 91 f) its
quite likely the atmosphere will remain capped into the early
evening hours.
The better opportunity for widespread convection is across
portions of western Nebraska/Kansas and Oklahoma where dry line
influences and strong day time heating will act to erode any
existing cap. This will be the activity we end up seeing tonight.
Decided to maintain going forecast and keep eastern Nebraska and
southwest Iowa dry through the day...then steadily push
thunderstorms chances east through the evening and overnight
hours. The main severe weather threats will be hail and wind as
outlined by the slight risk area from the Storm Prediction Center.
Sunday through Monday night...once again our area is outlined in
the slight risk area. This period brings with a much better
opportunity for severe weather. The main focus is a negatively
tilted upper level trough moving east through the region. Unlike
today and tonight there isn't a capping inversion to overcome and
convection will likely initiate early in the afternoon on Sunday.
Modified forecast soundings indicate modest instability available
and deep layer shear around 35 knots. As the upper level trough
and its surface reflection translate through the area...strong
thunderstorms and even supercells are expected to form. The
specific severe weather threats are large hail...possibly greater
than 2 inches...strong winds and even a few tornadoes can't be
ruled out.
Unsettled weather will continue through Monday night as the upper
level trough transforms into a closed low and slowly meanders north
and east. This warrants a continued mention of showers and
thunderstorms as well as cooler temperatures for Monday.
Long term...Tuesday through Saturday.
Closed upper low lingers over the area at the beginning of the
period for a continued chance of showers and thunderstorms before
moving east of the area on Thursday. Short wave ridge then develops
Thursday night into Friday as upper system digs over the western
Continental U.S. With increasing chance of showers and thunderstorms Friday
night into Saturday as upper energy ejects out of the western
trough. Temperatures look to remain seasonal through the period.
&&
Aviation...
06z tafs for kofk...koma and klnk.
Although the bulk of low level moisture spreading from southern
into northwestern Kansas should remain to the west-southwest of taf sites by Saturday
morning...there still appeared a chance lower ceilings could move
toward kofk Saturday morning. Thus a tempo group was maintained
for that site. Thunderstorms will likely increase across central
Nebraska late Saturday afternoon and spread toward kofk during the
evening. Activity could make it to koma and klnk Sat night...but
chances appeared too low to include mention before 19/06z.
&&
Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&
$$
Short term...Pearson
long term...fobert
aviation...chermok
