565
FXUS63 KOAX 182327
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
627 PM CDT Fri Jul 18 2025

.KEY MESSAGES...

- A 50 to 60% chance for storms exists along our northern and eastern
  service area, with 30 to 40% chances areawide late tonight
  into early Saturday morning. Storms may be strong to severe,
  mainly north of a line from Platte to Shelby counties.

- Another round of storms (20-30% chance) may develop Saturday afternoon
  and evening, with chances peaking early Sunday morning (30-
  50%). Some of these storms could be strong to severe. Flood
  potential will also increase.

- Active pattern continues into next week with some low end
  chances for evening and nighttime storms (15-30%). Dangerous
  heat will also return for much of next week.

&&

.DISCUSSION...
Issued at 319 PM CDT Fri Jul 18 2025

.SHORT TERM.../Today through Saturday Night/

H5 zonal flow continues across much of Nebraska and Iowa this
afternoon, with a subtle shortwave seen across the Nebraska
Panhandle region. This wave has resulted in a 1010 mb sfc low
developing in the Panhandle area, with the warm front now draped
across portions of eastern Nebraska. Low level moisture advection
has kept the pesky stratus deck across the forecast area this
afternoon, but do see a few peaks of sunshine. The clouds should
mostly thin out by the late afternoon and early evening as the sfc
low keeps moving to the east northeast. Aided by H8 warm air
advection, should see highs today reach the mid to upper 80s across
most of the CWA, with western Iowa slightly cooler in the low 80s.

Our main concern for the short term forecast period is the threat
for severe weather. As the warm front races to the north today, low
level moisture advection will usher in low to mid 70s dew points,
and coupled with midlevel lapse rates of 7 to 8 deg C/km, will most
likely have an unstable airmass across much of the forecast area
with MUCAPE around 1,500 to 2,500 J/kg. BUFKIT soundings seem to
suggest capping remaining in place for much of the afternoon and
evening hours, so if convection can develop late this evening, it
will likely be rooted aloft. 0-6 km bulk shear looks favorable,
primarily over northeast Nebraska at 35 to 40 kts by this evening.
Forcing still seems to be rather weak in the midlevels as weak
height rises are observed at H5. Forcing will largely by driven by
any low level convergence along boundaries and also by a 25-30 kt
LLJ at H8 which overspreads much of OAX this evening.

Lots of questions remain though regarding the placement of
convection, and if it will even spread into our forecast area. If we
take a look at the 12z run of the HRRR, it ignites convection along
the boundary in southeast South Dakota after 00z, with much of it
either grazing far northern and eastern portions of the forecast
area as it moves east southeast. A separate area of convection also
develops along the cold front over north central Nebraska, but
quickly dissipates as it moves into northeast Nebraska. The Hi Res
ARW and NAM Nest seem to somewhat agree with this solution, although
they tend to keep the convection along the cold front a bit more
organized and track it just along our western border. The NSSL WRF
and HiRes FV3 seem to be the most aggressive, developing discrete
supercells early this evening across southeast South Dakota before
congealing into an MCS and tracking east southeast into the Missouri
River Valley. The SPC currently has a slight risk of severe weather,
mainly along and north of a line from Platte to Shelby counties. The
main hazards with this convection appear to be damaging wind gusts
and some hail, but certainly can`t rule out a brief tornado if any
supercells are able to develop and remain discrete before upscale
growth.

Given the myriad of solutions, have kept a general 30 to 40% chance
of PoPs across much of the forecast area from 4z to 10z, with 50 to
60% chances mainly along the northern and eastern edges of our
service area. Lows tonight will be in the mid 60s to low 70s.

Showers and storms will exit the forecast area by mid morning on
Saturday. A few of the CAMs suggest some lingering storms across
northeast Nebraska in the late morning hours, so have added some
light PoP mentions (15%) here. Highs for Saturday will be in the low
to mid 80s north of I-80, and in the low to mid 90s south of I-80.
Another shortwave will eject from the west toward central Nebraska
on Saturday, with showers and storms forecast to redevelop in the
afternoon across central Nebraska and track to the east in the
evening hours (20-30% chance, peaking at 30 to 50% by late Saturday
night into early Sunday). These storms could be strong to severe,
but much of the severe potential will be dependent on how much
destabilization can occur. 0-6 km bulk shear does seem to be a lot
more favorable for severe storm development, with values at 40 to 50
kts. For now, the SPC has a marginal risk of severe weather across
our service area, with higher chances of severe weather mainly to
the west and east of the forecast area.

Heavy rainfall and flooding will be of concern in the short term
forecast period given we`ll see successive rounds of storms. HREF
PWAT values suggest anywhere from 1.8 to 2 inches of water available
in the atmospheric column Friday night, with slightly higher amounts
for Saturday night into Sunday. Coupled with favorable warm cloud
depths, should expect to see warm rain processes prevail. Storm
total QPF from Friday to early Sunday suggests anywhere from a half
inch of QPF across portions of northeast Nebraska, with up to an
inch across west central Iowa. A slight risk for excessive rainfall
has been issued for this evening and overnight across our far
northeast and east, and again for Saturday, this time across east
central Nebraska and much of western Iowa.

.LONG TERM.../Sunday through Thursday/

Lingering PoPs will exit the forecast area by Sunday afternoon. H5
pattern will keep a quasi-zonal flow across the Northern Plains
through at least Sunday, with another shortwave skirting through.
This results in a 15 to 30% chance for PoPs across the forecast area
Sunday evening into Monday morning. A few of these storms could be
strong, with the SPC having issued a marginal risk of severe weather
for the forecast area.

The H5 zonal pattern will break down late Sunday evening as ridging
across the southern and southeast US amplifies. This will result in
more of a southwesterly flow closer to home, with several shortwaves
forecast to ride this flow. This leads to at least some low end 15-
30% chances for evening and nighttime storms through at least
Thursday. Some machine learning guidance suggests at least a low end
severe chance with this activity. Will need to keep an eye on flood
potential during this period, especially given that issues could
arise if storms track across areas that have received heavy rainfall
from earlier storms.

Dangerous heat will return to the forecast area from Sunday through
Thursday. NBM currently forecasts heat indices in the upper 90s to
low 100s during this period, especially along and south of I-80.
Monday through Wednesday could see heat indices reach up to 110 at
times, mainly across southwest Iowa. Heat headlines appear likely
during this timeframe, so those with any outdoor plans for next week
should continue to pay attention to the forecast should any be
issued and prepare to take necessary precautions to avoid heat
related illnesses.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 627 PM CDT Fri Jul 18 2025

Main concern for this TAF period will be convective trends
through Saturday. Models have been too aggressive with
convective development early this evening, but generally
expecting storms to develop over eastern SD and far northeastern
NE late evening, then progress southeast late tonight into
Saturday morning. Highest chance for TS appears to be at OMA
early Saturday morning, with OFK and LNK likely a bit too far
west. A front will stall in the vicinity of I-80 Saturday, which
may allow additional TS to develop along it Saturday afternoon
and evening. Overall, forecast confidence is low with this TAF
set given the myriad of differing model solutions.

Generally VFR conditions are expected, but some MVFR cigs are
possible late tonight and Saturday morning, especially at OFK.

&&

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

&&

$$

DISCUSSION...Castillo
AVIATION...Borghoff