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162
FXUS63 KOAX 180331
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1031 PM CDT Mon Jun 17 2024

.KEY MESSAGES...

- Storm chances remain in the forecast for northeast Nebraska
  this this evening. A slight risk of severe storms exists.

- Strong and severe thunderstorms are expected Tuesday into
  Wednesday, along with locally heavy and possible flooding
  rains.

- Rain chances continue every day Thursday through Sunday.

&&

.DISCUSSION...
Issued at 220 PM CDT Mon Jun 17 2024

A stationary front remains draped across northeast Nebraska into
northwest Iowa this afternoon. North of the boundary, low clouds
have kept temperatures in the 60s and 70s, with winds from an
easterly direction. Expect boundary to begin moving northward
late this afternoon as heights increases slightly in advance of
large scale upper trough.

Tonight:

Upper level trough located across western U.S. syncs
with polar vortex progresses across central Canadian provinces.
The net result is a more pronounced H5 vort max ejecting
northeast into the northern plains Tuesday and Wednesday as a
100+kt H3 jet max rotates around base of western U.S. trough.
Large scale mass ascent increases late tonight with 50kt LLJ
aiding in low level moisture transport into the area. The
aforementoned stationary front, will lift northward into the
Dakotas and cold front-dryline retreats westward due to lowering
heights in the lee of the Rockies. The main focus of any
evening and nighttime thunderstorm development will be in
proximity to frontal system across western Nebraska and South
Dakota. The CAMS are split in advecting the remnants of any
convection that develops across western Nebraska into the
northwest part of the CWA late tonight. For consistency retained
some slight to low chance PoPs. Warming H7 temperatures should
limit the severe weather threat overnight. Also, there is a
10-15% chances of elevated convection developing with LLJ across
southeast Nebraska. Again, not anticipating any severe weather.


Tuesday:

H5 vort max continues its trek northeast and will allow surface
front to move southeastward across the CWA during the day.
Better kinematics will exists across northeast Nebraska and
northwest Iowa given orientitation of H2/H3 ULJ that will be
oriented across Wyoming, western Nebraska and western South
Dakota. Could see weak convection develop by late morning along
the front, but feel the severe threat as mid-level temperatures
look a little warm, in the mid- to upper teens. However, expect
lapse rates to increase with decreasing mid-level temperatures
through the afternoon. Combined with diabatic heating, the HREF
indicates CAPE will increase into the 2000-2500 J/Kg range, with
deterministic guidance even more unstable in the 3000-3500 J/Kg
range. Kinematics marginal across southeast Nebraska and
southwest Iowa, but 40-50kt bulk shear values northeast Nebraska
and northwest Iowa. CAMS are mostly consistent in developing a
linear convective system that looks reasonable given large scale
wind profile. There is better low level backing across northeast
Nebraska and northwest Iowa that will allow for some bowing
segments or quasi-linear segments in the line. The severe threat
will wane by early- mid-evening, but will have to monitor for
flash flood threat as convection continues to train. Convective
line will not move to far southeast as line becomes parallel
with upper level flow.

Wednesday and Thursday:

Upper vort max becomes sheared out across Great Lakes, but
remnants of cold front/mesoscale boundary will remain across
southeast Nebraska and southwest Iowa. Southwest flow aloft will
allow several weak disturbances to traverse the upper level
flow. Several rounds of convection expected to develop along the
boundary, mainly diabatically driven as main upper level
forcing will be north the area. With persistent moisture
transport, and upper level flow supporting training convection,
a flood or flash flood watch may be warranted. Decided to wait
on issuing to see how convection Tuesday evolves.

Friday through Sunday:

Upper level trough across western U.S. becomes more diffuse as
it disconnects with polar jet stream. The remnant move eastward
across the northern Plains Friday into Saturday. Overall, that
will cause stationary front across southern part of the CWA to
dissipate, with frontogenetical forcing evolving further north.
ensembles and deterministic models gradually move focus of
convection northward with focus now across northern CWA.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
-- Changed Discussion --
Issued at 1031 PM CDT Mon Jun 17 2024

VFR conditions overnight with low-level wind shear as the low-
level jet brings 50 to 55 kt winds just 1500 ft AGL out of the
south. These winds will weaken around 12-13Z right around the
time we see MVFR cigs start to spread across portions of eastern
Nebraska. it may not be a solid deck with a mix of cigs around
2500-3500 feet, so confidence is around 70% that terminals will
see a period of MVFR cigs. These cigs should lift to VFR by 18Z.

A front will bring storms to the area Tuesday evening starting
around 22-00Z, with lingering showers and storms possible
through the remainder of the TAF period. Winds will be shifting
to the north or northwest behind the front and weakening to
around 10 kt.
-- End Changed Discussion --

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.

&&

$$

DISCUSSION...Fortin
AVIATION...McCoy