002
FXUS63 KOAX 172357
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
657 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 /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 632 PM CDT Mon Jun 17 2024

VFR conditions this evening with potential storms near the
Nebraska-South Dakota border late tonight. The Low-Level Jet
will ramp up around 02-03Z leading to low-level wind shear
developing at KOFK as winds around 1500-1800 feet increase to
50-55 kt. Winds aloft should be slightly weaker at KLNK and
KOMA, only around 45 to 48 kt, and with surface winds staying up
around 20 to 25 kt gusting to 30 kt overnight, we should stay
just under the threshold of 30 kt for LLWS in the TAFs. If winds
weaken at the surface or look stronger aloft we may need an
amendment to add LLWS to the TAFs at KLNK and KOMA as well.
Wind shear should diminish with the low-level jet around 12-13Z
Tuesday morning. The next concern will be the potential for MVFR
cigs to spread across the area around 13-14Z Tuesday morning
from the south. Models are less certain in whether cigs will be
around 2500 or 3500 feet, so confidence is only around 60% at
this time, but have kept them in the TAFs from earlier. In any
case, we should see these cigs improve by around 18Z lifting to
around 3500-4000 feet and becoming more broken or scattered.

A front will move across the area tomorrow evening bringing
storms through during the late afternoon-evening hours. While we
are still not confident in timing, I did give a window with our
best guess at timing for storms for KOFK and KLNK, with KOMA
seeing storms right around 00Z at the end of the TAF period.
This window may shift by an hour or two as we get closer, but
it should be fairly representative.


&&

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

&&

$$

DISCUSSION...Fortin
AVIATION...McCoy