159
FXUS63 KOAX 132324
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
624 PM CDT Tue Aug 13 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 322 PM CDT Tue Aug 13 2024

We have another cloud day today, with temperatures only peaking
in the mid-to-upper 70s this afternoon. Clouds will slowly try
to clear, with the best chance for clearing being over northeast
Nebraska. There is an axis of moisture along a convergence
boundary stretching from Seward southeast to Falls City which
will make clouds difficult to clear with low (15-20%) chances
for light rain through this afternoon along this boundary. We
will see clouds try and clear along this boundary later this
afternoon, but will want to continue to monitor its location as
it likely will become a focus for overnight storms and potential
heavy rainfall (training storms).

CAMs have been trending farther north for the potential axis of
heavy rainfall, bringing it into northeast Nebraska. Our "best
guess" for placement is probably somewhere between I-80 north
through around Yankton, SD. Within this axis we`ll probably see
swaths of 1 to 2 inches of rainfall with locally higher amounts
possible if storms consistently train over one area.

The dynamics of this system show a shortwave trough moving
through, triggering storm development in a region with strong
moisture advection from the low-level jet. This region will see
vertical motions enhanced by an area of strong divergence aloft
associated with the curvature of the Jet Stream. This is a
nearly ideal scenario for heavy rainfall production, with the
only limiting factor being the orientation of the LLJ isn`t
completely perpendicular to the surface boundary. This could
help the system be more progressive in nature with less storm
training, but locally heavy rainfall will still be possible.
Timing for this system is looking to be later, with storms
moving into our area generally after midnight continuing through
around 10 AM Wednesday.

Depending on how long it takes for the rain to clear, we will
likely see cloud cover hang around again through much of the day
again on Wednesday. We might see clouds clear across far
southeast Nebraska southwest Iowa, where temperatures could
reach near 90 degrees tomorrow afternoon. Areas that remain
under cloud cover most of the day likely won`t see high
temperatures get out of the upper 70s to low 80s.

Wednesday Severe Weather:
Daytime conditions on Wednesday will play a big part in how well
our environment can charge ahead of another shortwave that will
move through Wednesday afternoon and evening. The best severe
weather potential will likely be limited to southeast
Nebraska/southwest Iowa where we see some clearing and
temperatures get into the upper 80s to near 90 during the
afternoon. The environment will be too stable to the north where
cloud cover is slow to clear.

We do see a dry line move across southeast Nebraska which will
provide the lifting mechanism for storms to develop in a region
with ample moisture ahead of the boundary and dew points in the
upper 60s to low 70s. With ample instability and moisture in
place, the next thing to look at is shear. Model soundings in
southeast Nebraska show weak 0-1km shear, but strong 0-3km SRH
indicating the potential for strong, rotating updrafts. Because
the 0-1km shear is low and LCL heights are up around 1000
meters or higher, tornadoes won`t be a big risk for tomorrow
afternoon/evening, but do remain possible. The bigger threats
will be damaging winds and large hail. Hail size will be
dependent on the amount of instability we can achieve, with the
potential for up to 2" hail possible. Severe weather should
mostly clear the area by midnight.

Thursday - Friday:
We`ll see a trend toward warmer temperatures going into the
weekend as we finally see the cloud cover clearing by Thursday
afternoon, and mostly clear skies on Friday. Temperatures should
get up into the mid-to-upper 80s each afternoon. We could see a
couple showers/storms develop Thursday afternoon as well as
ridging starts to build into eastern Nebraska. This boundary
could kick off a few storms, but chances are around 15-20%. Our
southern counties could get clipped by an MCS moving across
eastern Kansas into western Missouri Friday night, but severe
potential is low.

Saturday - Monday:

We`ll remain seasonably warm through the weekend with highs in
the mid-to-upper 80s. There is some uncertainty in the dry
forecast for this weekend as the latest GFS not included in the
latest NBM forecast from this morning does show the potential
for an MCS developing and moving through Saturday night into
early Sunday, but it appears to be an outlier at this time with
other models showing high pressure centered over the region.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 611 PM CDT Tue Aug 13 2024

Scattered thunderstorms are expected to move into east-central
and northeast Nebraska (KOFK and KOMA) after 06Z. An additional
area of thunderstorm development is likely, extending from
east-central Nebraska into northwest Missouri in the same time
frame (KOMA). The highest chances for thunderstorms appear to be
just north of KLNK, so have refrained from including a TEMPO
TSRA group in those TAFs for now. But there is still a chance
(30 to 40 percent) that KLNK will see TSRA conditions in the
terminal area between 07Z and 11Z. Surrounding this convection,
a low-level cloud deck is expected to develop at all TAF sites.
Current guidance suggests the overcast/broken clouds will remain
at VFR/MVFR heights. However, guidance has resolved a scattered
deck of IFR cloud cover. This is likely underdone to a certain
extent, so have included IFR ceilings in the KOFK and KOMA TAFs.
Have kept IFR conditions out of KLNK for now for similar
reasoning as keeping TSRA conditions out. At the end and just
beyond this TAF forecast period, there will be the potential for
scattered strong to severe thunderstorms (primarily around KLNK
and KOMA). Hazards with these storms include 60 knot winds and
hail up to 2 inches. Expect these storms to be included in
future TAF issuances.

&&

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

&&

$$

DISCUSSION...McCoy
AVIATION...Darrah