288
FXUS63 KOAX 140543
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1243 AM CDT Wed Aug 14 2024

.KEY MESSAGES...

- There is a 60-80% chance of thunderstorms tonight into early
  Wednesday. Greatest threat will be localized flooding, but
  hail and damaging winds will also be possible (5-15%).

- Severe storms are possible Wednesday afternoon and evening
  (10-20% chance). Large hail, damaging winds, and localized
  heavy rain and flooding will be the primary hazards.

- Continued small shower and storm chances will persist into the
  Thursday (15-20% chance), but the overall trend will be
  toward drier, seasonably warm weather over the weekend.

&&

.DISCUSSION...
Issued at 1243 AM CDT Wed Aug 14 2024

Storm development was well underway in southeast NE as of 12:30
AM with low level moisture transport pointing into the area.
Farther west a strong to severe bowing segment was producing 60+
mph winds across southwest into south-central NE. Latest CAMs
continue to suggest this bow will eventually push east-northeast
and somewhat weaken through the early morning hours. However,
wondering if it won`t stay a little farther south than guidance
indicates and follow the MUCAPE gradient progged to set up
across southeast NE (roughly near and south of Omaha). Still,
the primary upper level forcing does look to take more of a
northeasterly track. Guessing the answer will be somewhere in
the middle. Either way, the elevated instability along with
fairly strong 0-3 km shear should yield a continued threat of
severe weather...moreso wind with the bow, but maybe some large
hail with any initially discrete storms ahead of the bow on the
nose of the low level jet. In addition, heavy rain and localized
flooding will be possible with these storms just given the
orientation of ongoing storms and potential for repeat rounds.
Also, if heavy rain falls on the narrow band of 1-2" that fell 2
nights ago from the Omaha metro toward Red Oak, IA, impacts
could increase. When all is said and done, thinking there should
be a decent band of of 1-2 inches with localized 3+ inch
amounts. The question will be just exactly where it sets up.

Most precip with the overnight MCS should pass off to our east
by mid-morning, but clouds and perhaps a few light showers could
linger into the afternoon ahead of a surface low pushing
northeast out of KS. The exact track of the surface low and
resultant clearing of clouds will play a large role in severe
weather potential for the afternoon and evening. Latest guidance
continues to suggest we see some clearing in the southern 2-3
rows of counties in southeast NE and far southwest IA by early
afternoon, with HREF mean SBCAPE values in the 2500-3000 J/kg
range. While deep layer shear could be somewhat limited (around
30 kts of 0-6 km), low level shear will increase in the evening
as the low level jet strengthens. This will result in decent low
level hodograph curvature and yield some tornado threat to go
along with the threat for damaging winds and large hail. In
addition, while storms do look like they`ll be fairly
progressive, the environment is set up pretty well for efficient
rain-producing storms with precipitable water values near or
over 2 inches and warm cloud depths nearing 4 km. Should we get
any degree of training storms or if they move over areas that
received recent heavy rainfall, flooding could develop. Timing
of the greatest threat currently looks to be roughly 5 PM to
midnight.

Precip should exit to the east by early Thursday morning
immediately followed by a cold front and then additional weak
shortwave energy during the afternoon. Guidance suggests some at
least some decent elevated instability could be in place as the
shortwave moves through along with 30-40 kts of 0-6 km shear.
This could lead to a few additional stronger to isolated severe
storms (5-10% chance), but higher chances should remain to our
east ahead of the cold front where there will be much more
instability. By Friday morning, a cutoff low is progged to
develop over MN/WI/the Great Lakes with guidance in good
agreement that associated precip on the back side remains just
to our northeast (though wouldn`t completely rule out a few
sprinkles Friday). We`ll remain under northwest flow aloft while
upper level ridging amplifies just to our west. Do expect an
overall drier pattern heading into the weekend, though guidance
does show a few weak bits of shortwave energy sliding through
the eastern side of the ridge, bringing us at least some small
periodic precip chances (10-20%) through the weekend and into
early next week. Otherwise, high temperatures should remain
pretty steady in the 80s.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1129 PM CDT Tue Aug 13 2024

A line of thunderstorms currently ongoing across southeast
Nebraska will move into northeast Nebraska (KOFK), east-central
Nebraska (KOMA) and southwest Iowa tonight after 07Z. These
storms will have the potential for heavy rain, wind gusts up to
60 knots, and hail up to the size of quarters. As of now, the
highest chances for thunderstorms appears to be just north of
KLNK, so have refrained from a TEMPO TSRA group for now. There
is still a 30 to 40 percent chance of thunderstorms in Lincoln,
so will monitor to see if TAFs need to be amended to include
this. Otherwise, a deck of low stratus has developed across
eastern Nebraska and southwest Iowa (all TAF sites). Ceilings
are lower than what current guidance has suggested, so have
manually brought ceilings down in the TAFs. A scattered deck of
IFR ceilings is expected to build in tonight. Have kept these
out of TAFs for now, but if observations shows more robust IFR
cloud cover moving into terminal areas, will amend the TAFs
accordingly. Lastly, there will be another chance for scattered
strong to severe thunderstorms (KLNK and KOMA) tomorrow evening.
Have denoted the more likely time frame to see precipitation
with a SHRA FM group. After the round of thunderstorms tonight,
will likely have a TEMPO TSRA group included in the KLNK and
KOMA TAFs to start narrowing down the timing for this second
round of storms.

&&

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

&&

$$

DISCUSSION...CA
AVIATION...Darrah