327
FXUS63 KOAX 190451
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1151 PM CDT Wed Jun 18 2025

.KEY MESSAGES...

- Showers and storms (30-50% chance) continue across far eastern
  portions of the forecast area this afternoon before tapering
  off this evening.

- Conditional risk of showers and storms exists Thursday evening
  into early Friday morning, with PoPs currently less than 15%.
  A Marginal Risk of severe weather exists along and north of
  I-80.

- First dangerous heat event of the year for the forecast area expected
  from Friday through Sunday. An Extreme Heat Watch is in
  effect from 10 am Friday through 9 pm Sunday.

&&

.DISCUSSION...
Issued at 322 PM CDT Wed Jun 18 2025

.SHORT TERM.../Today through Thursday Night/

KOAX radar imagery has been tracking areas of showers and
thunderstorms this afternoon mainly across extreme eastern Nebraska
into western Iowa. Much of this activity appears to be driven by a
ribbon of vorticity extending from a 500 mb shortwave seen over
eastern South Dakota/western Minnesota. The mid level wave will
phase with a more potent shortwave over eastern Missouri this
afternoon and evening which will result in some increase in shower
and storm activity as hinted at by the various CAMs, primarily over
western Iowa where PoPs peak at around 40-50%. Mesoanalysis shows
some SBCAPE of 1500 to 2000 J/kg, but with some cloud cover evident
across western Iowa, current thinking is that we may not tap into
this energy source. Effective bulk shear remains rather weak as
well, generally less than 20 kts, so not really expecting to see
severe weather with this activity. Highs today will be in the upper
70s to low 80s with cloud cover decreasing toward the evening hours.
Lows tonight will be in the upper 50s to low 60s.

500 mb wave will eject to the northeast toward the Great Lakes area
late tonight into Thursday. Ridging will build into a large portion
of the Central and Northern Plains during the day, and coupled with
increasing low level southwesterly flow resulting in warm air
advection, will see highs reach the low 90s. Dew points in the low
60s will result in uncomfortable conditions outside. NWS HeatRisk
products show a moderate risk of heat related impacts expected for a
large swath of eastern Nebraska and portions of western Iowa. People
who plan to be outdoors tomorrow should take necessary precautions
to avoid heat related illnesses.

A few weak disturbances try to make their way through the 500 mb
ridge Thursday evening. This may provide some forcing to generate a
few isolated showers and storms. At this time, CAMs seem to have
quite a bit of spread in showing where (if any) convection may
develop with some models like the NAMnest and NSSL WRF indicating
portions of northeast Nebraska seeing some storms after 00z, while
the HiRes ARW and FV3 keep activity over in the GID county warning
area. Convection that is able to form appears to fizzle out by the
time it enters the forecast area. Meanwhile, the 12z HRRR seems to
not generate any convection at all interestingly enough until just
after the short term period associated with some convergence along
the nose of an 850 mb LLJ, mainly northeast of the forecast area.
Current thinking is that an elevated warm layer should help inhibit
convection, and large scale kinematics don`t appear too great
either, more than likely due to the height rises observed with the
ridge. If a storm is able to form, it could potentially become
severe with hail and strong winds, given the presence of an unstable
air mass coupled with sufficient shear available. This has resulted
in the Storm Prediction Center issuing a marginal risk of severe
weather, primarily north of Interstate 80. Given the large amount of
uncertainty with regards to placement of convection for this
forecast package, have opted to have unmentionable PoPs (<15%)
primarily north of Interstate 80. Expect further refinements to PoPs
from the midshift forecaster as we get more CAM guidance.

.LONG TERM.../Friday through Tuesday/

Thermal ridging will continue to amplify and strengthen across the
Central and Northern Plains from Friday through Sunday, with
impressive 1000-500 mb thicknesses reaching around 590dam to maybe
even 600dam. With increasing dew points/moisture expected for Friday
into the weekend, our first dangerous heat event appears almost
certain for this period. As has been the trend seen per past
forecast shifts, newest NBM run came in with slightly warmer high
temperatures for Friday through Sunday (upper 90s to low 100s F). In
collaboration with neighboring WFOs, have gone ahead and issued an
Extreme Heat Watch for the entire CWA from 15z Friday through 2z
Monday as heat indices reach the 100 to 105F range, even potentially
touching the 110F mark. Expect to see this headline converted to
either a Heat Advisory or Extreme Heat Warning within the next few
forecast packages. NWS HeatRisk guidance shows a major risk of heat
related impacts across a large portion of the forecast area for
Friday, while Saturday and Sunday show portions of eastern Nebraska
reaching the extreme category risk of heat related impacts. Those
with any outdoor plans during this period should make sure to stay
hydrated and, if possible, try to avoid being outdoors to reduce
likelihood of heat related illnesses.

The upper level ridge will try to limit and suppress our chances of
convection through at least Sunday morning. A more potent longwave
trough over the western CONUS will begin to move eastward into the
Northern and Central Plains by Sunday evening. PoPs will thus return
Sunday evening through Tuesday as several waves within the longwave
trough eject northeastward toward Nebraska and Iowa. Much of the
severe weather machine learning guidance displays at least a 5%
chance for some strong to severe storms during this period.
Regardless, expect a wet start to the upcoming work week, especially
late Monday and Tuesday where NBM PoPs are at 50-80%, mainly along
and north of Interstate 80. The good news is that these rain chances
will drive temperatures down a bit for Monday (highs of mid 80s
north to mid 90s south) and Tuesday (highs of mid 70s to low 90s in
the far south).

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1122 PM CDT Wed Jun 18 2025

VFR conditions are expected to prevail through the period.
Patchy fog may develop across parts of portions of eastern
Nebraska and southwest Iowa by early Thursday morning, but is
not expected to impact the TAF sites at this time. Winds will
remain light, out of the southwest, becoming more southerly
after 18Z Thursday and increasing to 12+ kts.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Extreme Heat Watch from Friday morning through Sunday evening
     for NEZ011-012-015>018-030>034-042>045-050>053-065>068-
     078-088>093.
IA...Extreme Heat Watch from Friday morning through Sunday evening
     for IAZ043-055-056-069-079-080-090-091.

&&

$$

DISCUSSION...Castillo
AVIATION...KG