Scientific Forecaster Discussion
fxus63 koax 190455
Area forecast discussion
National Weather Service Omaha/valley NE
1155 PM CDT Wed Sep 18 2019
Short term...(tonight through saturday)
issued at 340 PM CDT Wed Sep 18 2019
Forecast concerns in the short term will be to assess the flood
potential each day with multiple rounds of thunderstorms possible
into next week.
The mid tropospheric pattern has a shortwave that moved through
the upper Midwest and brought a cold front into the area. The
storms overnight were more widespread up toward sux, however did
fill in southwestward as expected toward Omaha into western Iowa.
The front has pushed to south of tqe/fet/jyr. In the warm sector,
surface winds are from the south at 8 to 18 mph with some
stronger gusts. Temperatures were the 80s to lower 90s. There is
quite a bit of variability due to the lingering cloud cover and
precipitation. North of the cold front...temperatures have dropped
back into the 70s with dewpoints in the 50s.
Visible satellite and radar show an uptick in the Post-frontal
thunderstorm development from Boone toward Sioux City with cumulus
along the front and some lingering showers moving out of southwest
Tonight, the front will remain in place or may sag slightly south
with the storms as the shortwave over Wyoming and a weak ripple
farther northeast lift north and east. Several ingredients are in
place with the high precipitable water values of 1.5 to 2 inches,
pooling of moisture along and ahead of the h85 front and
continued warm air advection in the steep lapse rate environment.
The negatives are that the upper level divergence is more subtle
locally and better to the east and the low level jet is mostly 25
to 30kts and thus more subtle.
Over the last two weeks, about 70 percent of the area has seen
normal to below normal rainfall, however there are about a dozen of
our counties that have parts of their counties that have had 2 to 5
inches of above normal rainfall during that period. We currently
have flood warnings for minor to moderate flooding from Decatur
to Rulo. A Flood Watch has been issued to heighten awareness of
related to thunderstorm development/potential locally heavy rain
and increased flood risk should heavy rain develop with ongoing
flooding, crops are mature will lead to more runoff, impacts due
to local levee failures and flood gates being closed etc.
Some warm air advection lingers into Thursday afternoon and the
surface front begins to wash out/lift north Thursday night. The
low level jet strengthens across central Nebraska. At this time we
do not have storms mentioned, however should there be a little
more forcing, could see some isolate storms develop.
The large trough over Montana/Wyoming results in broad synoptic lift with
thunderstorms returning to the forecast Friday . Storms become
likely Friday night in northeast Nebraska and parts of western
Iowa into Saturday morning. Will need to further assess severe
potential. The cold front sweeps east Saturday.
Above normal highs in the 70s and 80s through Saturday.
Long term...(saturday night through wednesday)
issued at 340 PM CDT Wed Sep 18 2019
The cold front may stall over parts of the southern forecast area
Saturday night with thunderstorms lingering. There is not good
agreement for Monday night into Tuesday/Wednesday as the GFS has a
much stronger/wetter/more phased evolution of the closed low in
the southwest U.S.
Aviation...(for the 06z tafs through 06z Thursday night)
issued at 1135 PM CDT Wed Sep 18 2019
Areal coverage of thunderstorms and rain over eastern NE is gradually increasing in
areal coverage over. Expect storms invof ksux to begin migrating
south along the MO river Vly and push into koma/klnk sometime
around 19/09-10z. Activity should be moving out then by mid
NE...Flood Watch through Thursday afternoon for nez034-045-052-053-
Iowa...Flood Watch through Thursday afternoon for iaz043-055-056-069-