Areal Flood Warning 21, NWS Omaha, NE

Area Forecast Discussion
National Weather Service Omaha/Valley NE
335 PM CDT Mon Oct 8 2018

.SHORT TERM...(Tonight through Thursday)
Issued at 335 PM CDT Mon Oct 8 2018

A prominent mid to upper-level low over the Four Corners region
will evolve into an open wave tonight before a sizable piece of it
ejects into the central Plains on Tuesday, in tandem with a 50-60
kt mid-level jet streak. In the low levels, 19z mesoanalysis
places the primary baroclinic zone from south-central KS north-
northeast to along a Beatrice-Omaha-Harlan, IA line. A weak wave
along that boundary over northeast KS is expected to develop
through southeast NE and southwest IA late this afternoon into
evening.

Forcing associated with the mesolow/frontal wave coupled with a
gradually warming and moistening boundary layer east/southeast of
the front has yielded a steady increase in convective coverage
and intensity over southeast NE early this afternoon. While lapse
rates are poor, weak instability combined with a modestly sheared
and vertically veering wind profile may be sufficient to support
an isolated severe storm or two with a risk for locally strong
wind gusts and/or a brief tornado. The location of the surface
front will also likely delineate the preferred corridor of
heaviest rainfall.

The ongoing convection across southeast NE may serve to displace
the effective surface boundary into the far southeast part of our
area tonight with the best heavy-rainfall potential on the
immediate cool side. On Tuesday, a deepening surface low
associated with the ejecting mid-level wave mentioned above may
support the west/northwest movement of the front back into a
larger part of our area, prior to the cyclone passage to our east
Tuesday night.

The net result as it relates to rainfall is a southeastward shift
in the heavy-rain axis with an additional two to three inches
still expected from tonight through Tuesday night. In addition to
the flooding potential, there will be a risk for isolated strong
to severe storms immediately ahead of the surface low track from
far southeast NE into southwest IA Tuesday afternoon and evening.

Precipitation is expected to shift east of the area late Tuesday
night into Wednesday morning in concert with the strong synoptic
system lifting into the upper Midwest. Behind the associated cold
front, a cooler and drier continental air mass will overspread the
mid MO Valley with high temperatures in the 40s to lower 50s on
Wed and Thu.

.LONG TERM...(Thursday night through Monday)
Issued at 335 PM CDT Mon Oct 8 2018

Latest model guidance continues to indicate the next precipitation
potential late Thursday night into Friday morning in association
with a fast-moving short-wave trough tracking through the mid MO
Valley. The models have trended a bit warmer with that system,
though it does appear that a rain-snow mix is possible for a short
period of time over parts of northeast NE. By next weekend, the
models begin to diverge on the evolution of the large-scale
pattern. There is some signal that a strong cyclone will move
through the central and southern Plains, bringing another chance
of precipitation to our area with a continuation of below-normal
temperatures.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1226 PM CDT Mon Oct 8 2018

Expect mainly IFR and some LIFR conditions to continue through
the period, with periods of showers, light rain or drizzle. A few
thunderstorms will be possible, mainly at KLNK and KOMA this
afternoon. Some higher ceilings will again be possible briefly,
but do not expect these to be representative of prevailing
conditions. Visibilities will be quite variable.

&&

.HYDROLOGY...
Issued at 335 PM CDT Mon Oct 8 2018

Thus far, precipitation amounts have been less than forecast.
However, given the uptick in convection over southeast NE, and the
anticipated, synoptically driven precipitation band on Tuesday, we
still expect a swath of two to four+ inch storm totals. As
mentioned above, we have trended to the southeast with the axis of
highest QPF. As that translates to flooding, we still expect
additional flooding on the MO River given it's larger basin and
antecedent high stage. With regard to other rivers and creeks in
our area, the stage forecasts are still largely based on QPF.
Those forecasts will likely be adjusted as observed rainfall
amounts over the next 12 to 24 hours are input in the hydrologic
model.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Flood Watch through Wednesday morning for NEZ015-018-031>034-
     042>045-050>053-065>068-078-088>093.

IA...Flood Watch through Wednesday morning for IAZ043-055-056-069-079-
     080-090-091.

&&

SHORT TERM...Mead
LONG TERM...Mead
AVIATION...KG
HYDROLOGY...Mead

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