846
FXUS63 KOAX 130830
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
330 AM CDT Tue Aug 13 2024

.KEY MESSAGES...

- There is a 60-80% chance of thunderstorms tonight into early
  Wednesday. A few could be strong to severe in southeast
  Nebraska and southwest Iowa (5-15% chance) with localized
  flooding, hail, and gusty winds the primary hazards.

- Additional strong to 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
  weekend (20% chance), but the overall trend will be toward
  drier weather.

- Today will be the last day of widespread below average
  temperatures (highs in the 70s). Highs in the 80s return for
  most on Wednesday and continue area-wide through the weekend
  into early next week.

&&

.DISCUSSION...
Issued at 330 AM CDT Tue Aug 13 2024

Early morning analysis showed mean upper level ridging pushing
into the area from the west, though a fairly potent shortwave
trough was sliding east-northeast through KS leading to a
complex of strong thunderstorms. The northern edge of these
storms is progged to cross into southeast NE by around 6-7 AM,
though guidance is in pretty good agreement that anything strong
should stay just south of the NE/KS border. Otherwise, fog and
stratus was building into the area with patchy visibility under
1 mile as of 3 AM. Will keep an eye on trends for a potential
dense fog advisory to match neighbors to our southeast, but
latest HREF guidance suggests generally a 20-40% chance for
sub-1/4-mile visibility. Clouds will linger through much of the
day with perhaps a few sprinkles at times, though could see a
few breaks by this afternoon. Temperatures are expected to top
out in the mid 70s to perhaps right around 80 where we get any
said breaks.

Attention then turns to storm chances this evening and
overnight as another shortwave trough (currently over the Four
Corners region) approaches. At the surface, a low will eject
eastward into KS while an attendant warm front will edge
northward, but should stay in KS. However, southerly low level
flow will strengthen, with strong moisture transport riding over
the surface front and pointing into southeast NE. As a result,
expect storm development in the area this evening, as early as
10 PM, but more likely just after. Questions still remain on
just how far north/south they develop, but wherever it happens,
instability should be sufficient for a few stronger storms,
though shear will be fairly limited suggesting the threat of
large hail and damaging winds will remain somewhat low (5-10%).
Perhaps more concerning will be the threat of heavy rain and
flooding, especially given trends in some CAMs which depict some
potential for training thunderstorms. In addition, guidance
suggests precipitable water values approaching 2" with warm
cloud depths over 4 km, meaning any storms that do develop will
be efficient rain- producers, with nearly every HREF member
producing a band of 1-2" somewhere in the area. Particularly
notable are the 13.00Z and 13.06Z runs of the HRRR which place
several inches of rain very near or right over the 1-2" band of
rain we received Sunday night into Monday (stretched from around
Omaha/Fremont toward Red Oak and Villisca). At this point,
these solutions are outliers and seem unlikely. Still, will
definitely want to watch trends...if something like that were to
pan out, impactful flooding would be likely.

Most of this precip should exit by 8-9 AM on Wednesday, though
cloud cover and perhaps a few light showers could linger through
a good chunk of the day. Meanwhile, the surface low and warm
front in KS look to eventually push northeastward into our area
with model consensus suggesting the warm sector reaches
southeast NE and southwest IA with clouds clearing. This could
lead to a severe weather setup in that area, though there are
still differences in exact track of the low (and any clearing),
which will play a large role in said severe weather threat.
Within the warm sector, expect ample moisture and instability
with dewpoints in the 70s and MUCAPE values approaching 3000
J/kg. Deep layer shear looks somewhat limited (25-30 kts in the
0-6 km layer), but a strengthening low level jet and being in
vicinity of the surface low could yield enough low-level
hodograph curvature for at least a low-end tornado threat.
Otherwise the main threats will be large hail and damaging
winds, along with heavy rain and localized flooding, especially
should these storms overlap with any areas that received heavy
rain the previous night(s).

Some of these showers and storms are expected to linger into
Thursday morning before yet another shortwave trough approaches
along with a surface "cold" front. Depending on exact timing of
the front, there could be sufficient instability in place ahead
of it for another strong to severe storm threat Thursday
afternoon and evening, mainly near and east of the Missouri
River. That said, it`s a fairly low confidence forecast and
there`s a lot to work out with the storm chances before then.

By Friday, a cutoff low is progged to develop somewhere over
MN/WI/the Great Lakes, with associated precip on the back side
remaining just to our east. However, guidance is in decent
agreement that we`ll see continued weak bits of shortwave energy
sliding southeast through the area into the weekend, bringing
low-end precip chances, though expect more dry time than wet.

Finally, temperature-wise, today should be the final cooler-
than- average day for most of the area. By Wednesday, expect
widespread 80s to perhaps 90 degrees in areas that clear out
(though northeast NE could stick in the upper 70s). Beyond that,
expect area-wide highs in the 80s through the weekend and into
early next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1205 AM CDT Tue Aug 13 2024

Current satellite trends indicate an expansion of IFR and MVFR
ceilings westward, as low level moist isentropic ascent
increases across the area. Deterioration of ceilings is expected
sooner than previous forecast based on satellite and
observational data trends, with LIFR ceilings FL002-005 by
07-08 UTC. In tandem visibilities are expected to diminish to
between 1/2 to 3/4SM by 10z and persist through 13z before
diurnal mixing allows visibilities to improve into MVFR range by
mid-morning. As for ceilings, deterministic and ensembles keep
LIFR ceilings at all three TAF sites through 14-15 utc.
Improving ceilings expected by midday as a drier air 850-700mb
may erode depth of cloud layer, and for now have improved
ceilings into low VFR category between 19-20 utc.

There are low chances (15-30%) of showers affecting KLNK 11-13
UTC that could further diminish visibilities to below 1/2SM.

&&

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

&&

$$

DISCUSSION...CA
AVIATION...Fortin