Tornado Warning 18, NWS Omaha, NE

Area Forecast Discussion
National Weather Service Omaha/Valley NE
325 PM CDT Mon May 19 2025

.KEY MESSAGES...

- Showers and storms (40-80% chance) develop this afternoon and
  evening across the forecast area. Storms may be severe with
  large hail, damaging winds, heavy rain/flash flooding, and a
  tornado or two.

- Showers and storms may linger into Tuesday (15-30% chance)
  over northeast Nebraska/western Iowa, and again Wednesday.

- Pleasant weather is in store for Thursday, with precip chances
  returning Friday through Sunday (20-40%).

&&

.DISCUSSION...
Issued at 307 PM CDT Mon May 19 2025

.SHORT TERM.../Today through Tuesday Night/

GOES-19 satellite imagery shows an area of stratus across
northeast Nebraska extending into western Iowa this afternoon
with clearing now evident across portions of southeast Nebraska.
19z RAP sfc analysis shows the main sfc low based over south
central Nebraska and north central Kansas with the main warm
front now draped over southeast Nebraska.

Our main attention in the immediate short term continues to be the
severe threat for the afternoon/evening hours today. Forcing for
ascent will increase throughout the day as a 500 mb left exit region
of a jet streak sits on top of the forecast area. The 998 mb sfc low
is forecast to continue tracking east northeast, continuing to lift
the warm front and warm sector over southeast Nebraska/southwest
Iowa helping bring in anywhere from 65F to maybe even 70F dew
points. Steepening 700-500 mb lapse rates with 1,500 to 3,000 J/kg
of MLCAPE and the additional moisture is resulting in an unstable
airmass with little to no capping seen in areas where clearing is
evident. 0-6 km bulk shear values show around 50 to 60 kts
indicating supercells would be the most favored convective type
initially, particularly in areas ahead of the sfc cold
front/dry line and in the warm sector where the shear vector is
more perpendicular to the frontal boundary. Hodographs do show
decent low level curvature with latest KOAX VWP data showing
0-1 km SRH between 100-200 m^2/s^2. SRH looks to be particularly
higher over southwest Iowa per model guidance, and the best 0-1
km bulk shear still appears to be mainly to the east northeast
of where the instability axis is seen.

On to the CAMs...convective evolution admittedly is somewhat messy,
but the majority of CAMs have been keying in on two areas for storm
initiation around 20-21z: primarily along the southeast
Nebraska/northeast Kansas border where a cluster of supercells
develop and track northeast and eventually congeal into an MCS
feature over southwest Iowa, and a broken line of storms along a
boundary over northeast and east central Nebraska. This broken line
of convection eventually pushes eastward but seems to dissipate by
the 03-05z timeframe as it nears the Missouri River area.

It is also worth noting that CAMs also indicate convection
developing mainly in the open warm sector over the western
Missouri/extreme northeast Kansas area this afternoon and evening.
KEAX radar has already started to pick up on this activity as of
1940z. This activity could potentially hinder and limit available
instability for storms developing in southeast Nebraska. For now,
have introduced two main areas of 60 to 80% PoPs to account for the
two main areas of convective initiation with widespread 40-50% PoPs
for the rest of the forecast area this evening as storms congeal
together.

For these reasons, the Storm Prediction Center highlights a
large portion of our forecast area in a slight risk of severe
weather, with an enhanced risk including far southeast Nebraska.
The main hazards expected with any convection that develops
continue to be large hail and damaging winds, with a tornado
also possible.

Heavy rain and isolated flash flooding will also be of concern
as the Weather Prediction Center highlights a slight risk of
excessive rainfall across far southeast Nebraska and southwest
Iowa, with a marginal risk encompassing the area just outside of
the slight risk. Warm cloud depths continue to be around that
3,500 meter range with PWATs anywhere from 1.5 to 1.75 inches at
times this evening and overnight. Repeated passage of storms
coupled with last night's rainfall may result in flooding
issues.

Showers and thunderstorms may linger (15-30% PoPs) throughout the
day Tuesday mainly over northeast Nebraska and western Iowa as we'll
still be under the influence of the 500 mb circulation and cyclonic
flow. Highs Tuesday will be in the low 50s north to mid 60s near the
Nebraska/Kansas border under cloudy skies.

.LONG TERM.../Wednesday through Sunday/

Lingering ribbon of vorticity from the 500 mb circulation may
trigger a few scattered showers and storms (15-30% PoPs) again over
northeast Nebraska/far western Iowa Wednesday, but not expecting a
whole lot from this activity. Otherwise, Thursday appears to be a
fairly nice day with highs in the 60s although somewhat breezy with
northwesterly winds.

As we head toward Friday and the end of the work week, will see some
more 500 mb waves swing through and generate some forcing for
scattered showers and storms (20-40% chance per NBM guidance).
Several of the severe weather machine learning algorithms show at
least some low end chance for severe, but with these systems still
being several days out, a lot could change. Temperatures will remain
in the mid 60s to low 70s to end the week.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1223 PM CDT Mon May 19 2025

A busy TAF period is in store, initially with low ceilings ranging
from MVFR to LIFR while areas of drizzle and mist reduce
visibilities into the MVFR/IFR range at and around KOFK. The
bank of clouds is expected to stick around, only clearing out of
Lincoln for a short period of time this evening before filling
back in overnight. Potentially strong storms are expected to
develop as well, affect each of the TAF sites for short period
of time, bringing strong winds and hail where the strongest ones
track. Winds should stay out of the southeast at KOMA/KLNK
through a good chunk of the overnight while KOFK sits on the
other side of the wind shift that eventually begins sweeping
eastward after 10z tomorrow morning.

Thunderstorm Timing Today:

KOFK: 19-22Z
KOMA: 23-01z
KLNK: 22-00z

&&

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

&&

DISCUSSION...Castillo
AVIATION...Petersen

Hazardous Weather Outlook
National Weather Service Omaha/Valley NE
333 PM CDT Mon May 19 2025

IAZ043-055-056-069-079-080-090-091-NEZ011-012-015>018-030>034-
042>045-050>053-065>068-078-088>093-201045-
Monona-Harrison-Shelby-Pottawattamie-Mills-Montgomery-Fremont-
Page-Knox-Cedar-Thurston-Antelope-Pierce-Wayne-Boone-Madison-
Stanton-Cuming-Burt-Platte-Colfax-Dodge-Washington-Butler-
Saunders-Douglas-Sarpy-Seward-Lancaster-Cass-Otoe-Saline-
Jefferson-Gage-Johnson-Nemaha-Pawnee-Richardson-
333 PM CDT Mon May 19 2025

This Hazardous Weather Outlook is for portions of southwest
Iowa...west central Iowa...east central Nebraska...northeast
Nebraska and southeast Nebraska.

.DAY ONE...Tonight and Tuesday

Showers and thunderstorms remain possible this afternoon and
evening (40-80% chance). Severe weather is possible over
southeast Nebraska and southwest Iowa where the main threats are
large hail, damaging winds, localized flash flooding, and
tornadoes.

Showers and storms may linger into Tuesday over northeast Nebraska
and western Iowa, but not expecting these to be severe.

.DAYS TWO THROUGH SEVEN...Tuesday night through Monday

Showers and storms return for Friday through Sunday. The severe
threat will be better determined in the coming days.

.SPOTTER INFORMATION STATEMENT...

Spotters may be needed this afternoon and evening.

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