688
FXUS63 KOAX 102311
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
611 PM CDT Wed Jul 10 2024

.KEY MESSAGES...

- A few storms may produce hail and gusty winds this afternoon
  into this evening. Best chances are in southeast Nebraska and
  southwest Iowa.

- Most should remain dry through the weekend, but like many
  recent days, there could be some spotty showers and storms
  Thursday and Friday (5 to 10% chance).

- Dangerous heat is expected for much of the area this weekend
  into Monday, with heat index readings of 100 to 110 degrees
  likely. Sunday and Monday will be the hottest days.

&&

.DISCUSSION...
Issued at 233 PM CDT Wed Jul 10 2024

Mostly clear skies are obscured in parts of southwestern Iowa
with a shortwave helping to produce some agitated cumulus from
Seward County, NE to Montgomery County, IA. The area has gone
from an SPC category of "general thunder" to now "slight with
hatched hail", representing a two category jump in severe
weather threat. A WATCH has been posted from Lancaster County to
past the Kansas and Missouri state lines and far southern Iowa.
The primary change in the forecast was a slight increase in
expected BWD and steepening lapse rates with newer model runs.
The primary threat is 1-2" hailstones with a multicellular
storm mode. As the boundary layer cools this evening, the LL
lapse rates moderate and storms should weaken. The last of the
convection should be pushing into Missouri by midnight.

Have introduced patchy fog to the grids overnight in response to
the lack of winds and high dewpoints. Believe northeast Nebraska
has best chance of seeing the fog, but it could as far south as
I-80. Latest HREF suggests about a 50% chance of visibility
slipping below 5 miles along and north of I-80. With a high
summer sun angle, expect that fog to dissipate quickly on
Thursday morning.

While skies are expected to remain mostly cloud-free, we expect
them to remain milky with continued Canadian wildfire smoke
elevated across the area. The HRRR produces very little surface
smoke in it`s mid-day runs today, though at 3,000 feet the smoke
is considerably more dense and growing denser over the next 24
hours, especially for western Iowa. For all but those very
sensitive to smoke, it should act mostly as a sun filter.

Believe Thursday and Friday`s low POP chances deserved to be
pushed lower with deterministic models keeping things dry with
weak instability, little forcing, and paltry but noted cap in
place both afternoons.

Attention turns to the season`s hottest three day stretch so
far with high temps in the middle to upper 90s for three
consecutive days. Dewpoints, too, will be trending toward the
extreme. Have bumped up those supplied by the NBM.
Evapotranspiration from crops will help western Iowa`s
dewpoints to climb at least into the mid-70s: Hot and humid.

Sunday and Monday will be the hottest days with heat indices
managing 102 to 106 for most on Sunday and similar readings for
the southern half of the CWA for Monday as a cold front slips
through the area. As it stands, we`re shy of our excessive heat
warning criteria each afternoon but close to the 75F minimum
heat index suggested by NWS directives. The lower criteria
needed for a heat advisory may be met with forecast max heat
indices of 105+. As confidence grows heat headlines may need to
be issued, especially in the metro areas where concrete and
massive apartment buildings tend to hold the day`s heat much
later into the night.

20-30% PoPs have been introduced to the forecast for Monday
night (cold front) and Tuesday as the upper level ridging
breaks down and flow becomes zonal.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 556 PM CDT Wed Jul 10 2024

Scattered thunderstorms are ongoing across southeast Nebraska.
This activity is within the vicinity of KLNK, though
precipitation is expected to remain south. Lightning should
move out of the KLNK terminal area by the start of this TAF
period, but will monitor closely. There is also a very low
chance (10-15 percent) of a thunderstorm at KOFK between 01 and
03 UTC. These storms, currently around Sioux City, appear to be
weakening and odds are will not make it to KOFK. Convection
should remain south of KOMA. After 07 UTC, patchy fog (30 to 40
percent chance) is expected to develop across eastern Nebraska
and western Iowa. It does not appear to be a strong signal at
TAF sites, however if fog does develop visibilities down to 2
miles will be possible. Will monitor closely for inclusion into
TAFs tonight. Any fog that develops should be gone by 13 UTC.

&&

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

&&

$$

DISCUSSION...Nicolaisen
AVIATION...Darrah