Area forecast discussion
National Weather Service Omaha/valley NE
1216 PM CDT Monday may 20 2013
Update...
forecast is generally on track for this afternoon. Surface-based
cape values are still expected into the 500-1000 j/kg range late
today in the southeast half of the County Warning Area...along with moderate
effective bulk shear around 40kt. A surface trough was noted in
central Nebraska...and rap forecast suggest this will be sweeping
across eastern Nebraska before 00z. So the combination of weak
instability with moderate shear and a focusing mechanism should
result in scattered showers and thunderstorms driven by afternoon
heating. Small hail and gusty winds are possible given lapse rates
approaching 8c in our far southeast and modest temperature-dew point
depressions.
Dergan
&&
Aviation...18z tafs for kofk...klnk and koma.
Generally VFR conditions are expected through Tuesday morning.
Scattered to broken cumulus near fl050 is forecast through the
afternoon. A few showers or isolated thunderstorms could develop
bringing MVFR conditions to some areas. However chances at taf
sites are rather slim. Precipitation should dissipate with the
setting sun...then ceilings near fl040 will overspread eastern
Nebraska from the north. Some MVFR ceilings are possible in northeast
Nebraska near kofk after 06z...but have left out of taf forecast
at the moment.
Dergan
&&
Previous discussion... /issued 323 am CDT Monday may 20 2013/
Discussion...
The upper level low currently centered over NE Nebraska and eastern South Dakota will
continue to be the main forecast issue through the short term.
Broad q-g forcing for ascent under the upper level low was
leading to scattered showers over central and NE Nebraska early this
morning. This should continue in NE Nebraska with most of the central and
southern County Warning Area dry this morning. Some sun is expected today over
this area of the County Warning Area /SW Iowa and southeast Nebraska/ that will steepen low
level lapse rates. Given the residual low level moisture in place
across this area and the cold middle level temperatures under the
upper level low...the atmosphere should become weakly unstable
this afternoon with around 400-600 j/kg of SBCAPE over the central
and southern County Warning Area. This should lead to scattered afternoon showers and
isolated thunderstorms across the forecast area. Severe weather generally seems
unlikely...but with the steep middle level lapse rates and moderate
shear some hail seems possible if sufficient heating can take
place through the morning. Otherwise the showers and isolated thunderstorms and rain
should diminish quickly this evening with the loss of daytime
heating. The setup for Tuesday isn't as favorable for afternoon
thunderstorms and rain as the low level residual moisture gets displaced to the east
as cold air advection moves through the forecast area behind a surface cold front on Monday night. This
will lead to seasonably cool temperatures for Tue/Wed. We may see
an isolated shower in the northern forecast area under the upper level low...but these
will be pretty isolated.
The low finally starts to shift east on Thursday with dry weather
returning...but this will only be for a short time as longer range
models are fairly consistent in bringing in a trough to the
western US with warm air advection type precipitation developing starting on Friday and
into next weekend. With the return flow temperatures will also be
returning to near normal as well.
Boustead
&&
Oax watches/warnings/advisories...
NE...none.
Iowa...none.
&&
$$
