522
FXUS63 KOAX 171036
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
536 AM CDT Sat May 17 2025

.KEY MESSAGES...

- Pleasant today with decreasing winds this afternoon and high
  temperatures mostly in the upper 60s to mid 70s.

- Shower and storm chances Sunday into Wednesday. The highest
  potential for severe weather will be Sunday and Monday,
  primarily in southeast Nebraska and southwest Iowa (15-30%
  chance).

- With potential for repeated rounds of thunderstorms, flooding
  could become a concern at times.

&&

.DISCUSSION...
Issued at 335 AM CDT Sat May 17 2025

Early morning water vapor imagery showed the cutoff low responsible
for our recent winds and severe weather to our east spinning over
WI/upper MI. Northwest winds on the back side in our area remained a
little breezy overnight, with gusts as of 3 AM mostly in the 20
to 30 mph range. This was also keeping temperatures on the cool
side, with readings in the mid 40s to lower 50s.

The winds will gradually taper off through the day as surface high
pressure builds in and relaxes the pressure gradient. This will also
bring abundant sunshine by the afternoon with temperatures topping
out mostly in the upper 60s to mid 70s.

Attention then turns to shower and storm chances Sunday through
Tuesday, with potential for severe storms at times. A trough
currently off the Pacific Northwest coast will dig into the Desert
Southwest tonight and start to push eastward on Sunday, spinning up
a surface low east of the Rockies. A warm front will extend east
from the surface low and push northward through KS during the day
and possibly reach the NE/KS border by Sunday evening. Near and just
south of the front, expect surface dewpoints in the lower to mid 60s
with 1500-2500 J/kg of SBCAPE. The big question will be just how far
north this warm front can make it during the day before strong
moisture transport starts pointing into the area and storms develop.
Latest guidance, especially CAMs, have trended toward keeping the
primary instability plume south of the NE/KS border through much of
the evening. Still, looks like we should get some decent elevated
instability with steep mid-level lapse rates into our area, along
with plenty of deep layer shear to yield an organized severe weather
threat, with the primary threat being large hail and smaller, but
nonzero chances for damaging winds and tornadoes. In addition, heavy
rain/flooding could become an issue given the strong moisture
transport pointing into a boundary and potential for repeat rounds
of efficient rain producing thunderstorms (precipitable water near
1.5" and warm cloud depths around 3500 m). Should the warm front
make it farther north on Sunday, our severe weather threat would
substantially increase, as wind profiles are rather impressive, with
large curvature in the low levels. Think this is pretty unlikely
though, as there should be substantial storm development near the
boundary by the afternoon which should help slow northward progress.

There will be additional severe weather chances on Monday, though
still lots of questions on smaller scale details that day as well.
In general, expect the primary moisture/instability to push
northeast, though our destabilization could be limited by ongoing
showers and storms (or at the very least, cloud cover) Monday
morning. Still, guidance is in decent agreement that we`ll see a
narrow plume of lower to mid 60s dewpoints and 2000-3000 J/kg of
SBCAPE edging into portions of southeast NE and/or southwest IA.
Deep layer shear remains impressive and sufficient for supercells,
though the strongest low level shear looks to primarily remain
northeast of the instability. Still, there could be a very narrow
corridor of overlap right along the warm front and just northeast of
the ejecting surface low to yield a tornado threat. And while the
strongest moisture transport will be pointing to our east, there
should be plenty working to get storms to go with the ejecting
shortwave energy/surface low and enhanced convergence near a triple
point. So once again, lots of details to be worked out, but it seems
like Monday is a better bet for surface-based storms in our area.

Showers and perhaps a few thunderstorms will continue on Tuesday as
the primary large scale trough/cutoff low finally swings through the
area. Guidance is in pretty good agreement that instability will be
well off to our southeast, so barring a big slowdown in the overall
pattern, our severe weather threat looks quite low on Tuesday. In
addition to the continued precip, the trough will also be bringing
a cooldown, with high temperatures in the mid 50s to mid 60s.

A few light showers could linger into Wednesday on the back side of
the departing low, with highs remaining in the upper 50s to lower
60s. By the time all the precip moves out, there is potential for
some areas to have received 2-3" of rainfall (20-30% chance per EPS
guidance and 30-50% per GEFS), but given all the questions on how
smaller scale details will play out, confidence in rainfall amounts
for a given location is rather low.

Surface high pressure and upper level ridging will then start to
build in for Thursday bringing temperatures back into the 70s with
dry weather during the day. By the evening/early Friday, guidance
hints at a weak shortwave/boundary pushing through, giving us our
next chance of rain (20-30%), but currently it doesn`t look too
impactful.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 536 AM CDT Sat May 17 2025

MVFR ceilings could linger for a few hours this morning, but
should scatter out/exit by 15Z giving way to VFR conditions with
passing mid to high clouds. Northwest winds will gust 18 to 22
kts early in the period, but speeds will come down this
afternoon with direction becoming more northerly to
northeasterly.

&&

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

&&

$$

DISCUSSION...CA
AVIATION...CA