Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 202317

Area Forecast Discussion
National Weather Service Omaha/Valley NE
617 PM CDT Sun Oct 20 2019

...Updated for 00Z Aviation Forecast Discussion...

Issued at 230 PM CDT Sun Oct 20 2019

Tonight into Monday night:

An intense deep-layer cyclone over southwest SD as of early
afternoon will reach southeast SD/northwest IA by Monday morning
before continuing into eastern MN/western WI by Monday night.
Current plan-view VWP data indicate that a dynamically driven
40-50+ kt low-level jet is present ahead of the synoptic cyclone,
which is contributing to the gradual moistening of the warm
sector air mass over the central Plains. That moisture increase
coupled with a meridional swath of clearing skies along the
surface cold is supporting a narrow axis of weak instability this
afternoon across central NE.

Latest convection-allowing model data is suggestive that a forced
band of low-topped convection will materialize by mid to late
afternoon along the surface front (and within the weak-instability
axis) to the immediate west of our area. That activity will
subsequently shift east through eastern NE and western IA during
the late afternoon and evening hours. Both vertical shear and
forcing for ascent will be quite strong. However, the primary
factor limiting a more robust severe-weather threat appears to be
the marginality of the surface-based instability. That being
said, low CAPE-high shear setups are notoriously difficult to
assess as often the amount of CAPE that is necessary to support
sustained, surface-based storms is only a couple hundred J/kg. So,
even minor errors in model estimates of CAPE can lead to
mis-diagnosis. So, given the dynamic nature of this synoptic
system, it`s entirely possible that there could be a strong to
briefly severe storm embedded within the expected convective band.
While gusty winds and hail are the primary hazards, a brief
tornado is also possible.

On Monday morning, the surface cold front will surge through the
area with northwest winds increasing markedly, especially during
the afternoon. Gusts of 45-55 mph will be possible. Wrap-around
showers will spread east/southeast across the northern half of our
area. An embedded thunderstorm can`t be ruled out owing to the
steep lapse rates. High temperatures will range from upper 40s
north to mid 50s south.

The gusty northwest winds will continue Monday night with the
showery precipitation ending.

Tuesday and Wednesday:

The strong synoptic system over the Great Lakes will lift
northeast ahead of the next mid-level trough amplifying across the
northern Rockies. In the low levels, a weak surface low will pass
to our immediate north Tuesday night and Wednesday morning with a
small chance of light precipitation across our northern counties
during that time. A cold front will trail that surface low, moving
through our area on Wednesday. Highs on Tuesday and Wednesday will
be from the mid 50s to lower 60s.


A brief shot of cooler air will overspread the mid MO Valley in
response to the amplification of another mid-level trough over the
upper MS Valley. Highs will be in the 40s with a small chance of
light precipitation over southeast NE and southwest IA.

Friday to Sunday:

A split-flow, upper-air pattern is forecast to develop with the
primary feature of interest being a mid-level low initially over
the southern Plains which will eject northeast into the Ozarks
next weekend. Currently, it appears any precipitation associated
with that weather system will remain to our south with generally
dry conditions expected. Highs on Friday and Saturday will be in
the 50s and 60s. By Sunday, the passage of a cold front could lead
to cooler readings.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 615 PM CDT Sun Oct 20 2019

Expect scattered SHRA and TSRA to affect the TAF sites this
evening - with MVFR or lower conditions expected in the heavier
precipitation. Then it appears that any low clouds will scatter
out with mainly VFR conditions 06Z-12Z. Low level moisture
should then wrap back into eastern Nebraska from the northwest
Monday morning with MVFR ceilings after 12Z. Winds will decrease
a bit for the overnight, then will shift to west or northwest and
increase late tonight through Monday. Gusts over 35 knots possible
Monday afternoon, especially at KLNK and KOFK.




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