Scientific Forecaster Discussion
fxus63 koax 192318
Area forecast discussion
National Weather Service Omaha/valley NE
618 PM CDT Thu Sep 19 2019
Short term...(tonight through sunday)
issued at 330 PM CDT Thu Sep 19 2019
Forecast concerns in the short term will be the next chance for
rain/heavy rainfall...severe potential Friday night into
Severe storms erupted over a small area near Cortland, Hickman,
Lincoln and Eagle, NE Wednesday evening. Concurrently, additional
storms began to develop north of the front in an area from
Clarkson toward Walthill with further development northward toward
Wayne and Norfolk. These storms blossomed across northeast
Nebraska into western Iowa and were anchored there in an area of
thickness diffluence. The storms then dropped southeast. The Flood
Watch area covered a decent part of the heavy rain area, however
not quite far enough to the northwest. A large area of 1 to 3
inches covered the northeast half of the forecast area with 3-5"+
area. 6 inches near Fort Calhoun was the highest, although a
social media report of 5.50" inches of rain before it overflowed
could also be close. Here at the National Weather Service office, we had 1...
had 2.05", Lincoln 0.01" and Norfolk 0.81".
Visible satellite shows the outflow boundary had pushed into Kansas.
Surface metars had general south flow across the forecast area at
20z. Temperatures were in the 80s with dewpoints in the 60s and
70s. Some convection persisted in north central into northeast
Nebraska with an area of h7 warm air advection/pocket of moisture.
The shortwave that facilitated the storms overnight and this morning
was over Minnesota/ern Iowa at midday. The h5 trough from Montana/Nevada will
shift slightly to the east tonight into Wyoming Friday. This trough
will continue to lift northeast into the Dakotas Saturday. This
southwest flow aloft pattern keeps the forecast area under in the
high precipitable water air and vulnerable to storms. The lack of
focus will mean more isolated/scattered coverage.
Tonight, the warm air advection/increasing 35kt low level jet
will tend to take the storms over northeast Nebraska northward.
Will maintain a isolated pops this evening for small areas in
eastern neb/wrn Iowa. A shortwave trough over western Kansas will swing
northeast through Friday morning and forecast soundings show
isolated elevated convection possible. Friday afternoon, a
stronger shortwave over Arizona/nm is forecast to lift northeast.
Heating could allow isolated surface based storms to develop. The
marginal and slight risks for severe weather are generally farther
west closer to the upper trough, however instability will be
moderate with steep low level lapse rates, but shear is lacking.
Friday night into Saturday, synoptic lift increases and see
thunderstorms develop in waves. Across parts of northeast
Nebraska into western Iowa with the initial lift, then along the
front. Some heavy rainfall and strong to severe storms are
possible ahead of and with the front. The high pwat values appear
to get shunted toward Kansas and Missouri Saturday. The surface
front stalls near the Kansas/Missouri border, thus until this deep
moisture gets scoured out, storms and heavy rain will remain a
Above normal highs continue in the 80s for Friday and Saturday,
but are closer to normal Sunday.
Long term...(sunday night through thursday)
issued at 330 PM CDT Thu Sep 19 2019
By Sunday, the trough is pushing through the area with mid level
ridging and dry weather for Monday. A shortwave Monday night will
return thunderstorms to parts of central Nebraska and across the
forecast area into Tuesday. The strength of the flow Wednesday is
zonal enough void of waves, where it should be mainly dry
Wednesday. Monday through Thursday though, there are still some
big differences in how the trough/h5 over the southwest U.S. Is
handled. Temperatures remain above normal Mon-Wed.
Aviation...(for the 00z tafs through 00z Friday evening)
issued at 609 PM CDT Thu Sep 19 2019
VFR conditions expected through the fcst pd.