Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 080438

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1138 PM CDT Fri May 7 2021

...Updated Aviation Forecast Discussion...

Issued at 335 PM CDT Fri May 7 2021

.Tonight through Sunday:

A shortwave trough which moved onto the west coast this morning
will progress east into the Rockies tonight before ejecting into
the central plains on Saturday afternoon into Saturday night. In
the low levels, a surface low is forecast to deepen over eastern
CO tonight before developing into central KS by Saturday evening.
There are still model differences on the track of the surface low
and associated warm front, which is forecast to lift north toward
the NE-KS border on Saturday afternoon. And, the specific
positioning of the warm front will be a major determinant in
whether a surface-based, severe storm threat develops over
southeast NE.

Based on latest model data, a reasonable-worst-case scenario
would be a more northern low track with the warm front moving into
southeast NE. Forecast parameter space is supportive of
supercells capable of large hail and perhaps a few tornadoes in
the vicinity of the warm front where moisture and low-level shear
are maximized. Convection would subsequently grow upscale into a
convective system with increasing threats for damaging winds and
flash flooding.

The most-probable scenario is a more southern low track with the
warm sector and associated surface-based storm risk remaining in
KS. However, sufficient MUCAPE (owing largely to very steep mid-
level lapse rates) and vertical shear will exist to support large
hail with the strongest storms over southeast NE and southwest IA
during the evening hours. A risk for localized flash flooding
would still exist under this scenario, namely over portions of
southeast NE.

From a broader perspective, strengthening warm/moist advections
along a nocturnally strengthening low-level jet will support an
increasing chance of showers late tonight into Saturday morning.
Showers and thunderstorms are expected increase in coverage and
intensity on Saturday evening as large-scale forcing overspreads
the region from the west. Showers and a few thunderstorms are
expected to continue overnight into mid morning on Sunday before
dissipating from west to east across the area from late morning
into afternoon.

We are forecasting highest storm-total rainfall amounts of
1.0-1.5" over portions of east-central and southeast NE into
southwest IA. However, it`s important to note that localized 2-4"
totals are possible, especially in corridors where
training/backbuilding storms occur. And, that situation could
lead to localized flooding.

Highs on Saturday will range from the 50s across the northern half
of our area to mid 60s to around 70 near the KS border, depending
on how far north the warm front makes it.

Low temperatures on Sunday night could dip into the mid 30s over
northeast NE and west-central IA with some frost possible.

.Monday through Wednesday:

The 12z global models suggest that mid-level troughing will
persist over the central part of the nation during the first half
of the upcoming work week. That will support the continuation of
below-normal high temperatures and some precipitation chances,
especially by about mid week.

.Thursday and Friday:

The models are in relatively good agreement in depicting mid-level
height rises over the central U.S. by late in the work week. That
would translate to warmer temperatures.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1138 PM CDT Fri May 7 2021

Main forecast concern is shower and storm chances by late
afternoon/early evening Saturday. Questions remain on how far
north any thunderstorm threat will be, but latest short term
guidance suggests both KLNK and KOMA will have some thunderstorms
in the area by 00Z or shortly thereafter. Expect rain to be on the
heavier side, so IFR conditions would be possible at times.
Greatest severe weather threat looks like it will remain just
south of KLNK, but can`t rule out some stronger storms capable of
hail and perhaps stronger wind gusts. Will include VCTS mention at
KLNK and KOMA for now, with future forecasts likely to narrow
down timing.

Otherwise, ceilings will gradually become lower through the
period, eventually reaching low VFR or high MVFR Saturday morning.
Could see a band of light scattered showers slide through early
Saturday morning, but confidence is low on any direct impact to a
TAF site. Otherwise, expect east/southeast winds gusting in the 20
to 30 kt range by the early morning hours before becoming more
northeasterly Saturday evening.




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