699
FXUS63 KOAX 161720
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1220 PM CDT Wed Apr 16 2025

.KEY MESSAGES...

- Very high fire danger expected today with south winds gusting
  25 to 30 mph.

- Increasing amounts of near surface smoke through mid-morning
  today due to seasonal burning across the Kansas Flint Hills.
  Additional smoke may move in by late afternoon depending how
  many fires are going in the area.

- There is a 30-50% chance of storms late tonight into early
  Thursday. A few storms could be severe in southeast
  NE/southwest IA (5-15% chance) with hail and gusty winds the
  primary threats.

- There is an additional severe weather threat late Thursday
  afternoon into the evening (15-30% chance, mainly 5-10 PM).
  The primary threat will be large hail, but a few damaging wind
  gusts are also possible and a tornado cannot be ruled out.

- Shower and storm chances return to the region Sunday into
  Monday, though confidence is low in exact timing/placement of
  the heaviest rain.

&&

.DISCUSSION...
Issued at 341 AM CDT Wed Apr 16 2025

Pretty quiet across the region early this morning as an upper level
ridge axis was approaching and we remained on the western periphery
of a surface ridge. To our west, surface low pressure was starting
to organize east of the Rockies leading to a tightening pressure
gradient and strengthening southerly flow. As a result, we had a
fairly large temperature difference from west to east across the
area as of 3 AM, with breezier western areas still in the mid
40s to lower 50s and calmer portions of southwest IA in the mid
30s. Otherwise, as those southerly winds continue to pick up
near-surface smoke from fires to our south is progged to move
into the area and lead to decreasing air quality through mid-
morning. An air quality alert remains in effect for eastern NE.

The main story for today will be very high fire danger as the
aforementioned southerly winds pick up further, with gusts of 25
to 30 mph, temperatures back in the mid 70s to lower 80s, and
RH falling into the lower to mid 20s. Model soundings do show
some potential for occasional higher gusts with 30 kts at the
top of the mixed layer, but those stronger winds aloft are
progged to exit the area by late morning/early afternoon, so any
resulting stronger gusts are not currently expected to coincide
with the lowest RH values. Should also note that the latest
HRRR guidance suggests near surface smoke could return to
portions of southeast NE into southwest IA by late this
afternoon/early evening, but it will depend on how many fires
are going to our south.

Attention then turns to shower and storm chances by midnight or
shortly after as some weak shortwave energy starts to push in and
low level moisture transport strengthens and points into the area.
Latest guidance suggests a decent environment for severe hail with
MUCAPE in the 1000-2000 J/kg range and 45-55 kts of deep layer shear
across southeast NE into southwest IA. While many CAMs keep much of
the storm development confined to KS, given the moisture transport
pointing into the area and the shortwave energy moving directly
through the area, find it hard to believe we won`t get at least some
thunderstorm development in the early morning hours Thursday.

Most guidance suggests any storms that do develop push east of the
area by 7-8 AM. However, we`ll see another chance of strong to
severe storms by late Thursday afternoon into the evening, though
unfortunately there remains a decent amount of model spread
regarding some of the key features. The general setup is that a
surface low will push eastward along or just south of the NE/KS
border as some additional shortwave energy pushes through.
Meanwhile, a surface cold front will be pushing in from the
northwest while a dryline bulges into southeast NE. Ahead of these
features, strong southerly flow will continue to usher in warmer air
and more moisture, with temperatures topping out in the in the 80s
and dewpoints getting into the mid 50s to lower 60s. This should
once again lead to at least 1000-2000 J/kg of MUCAPE in the area.
Vertical shear profiles are fairly impressive, with good low-level
hodograph curvature and 50-60 kts of deep layer shear, certainly
good enough for supercells to develop as the cold front moves in.
Now for the uncertainty. The biggest questions are:

1) How quickly will the cold front push in?

Faster solutions will lead to less time for moisture/instability to
build prior to storm initiation. The HRRR had been trending
toward a faster frontal passage, but now the 16.06Z run has
slowed it back down. Overall, guidance continues to have quite a
bit of spread here.

2) How much will we mix out during the day?

Part of this will have to do with how quickly morning
convection/clouds exit the area. There will be a pretty stout EML in
place which will keep things capped through much of the afternoon
(possibly into the evening). However, some guidance suggests we mix
enough to erode most of that cap and get some surface based storms.
If this happens, damaging winds will be possible along with an
outside shot at tornado given the low level hodograph curvature, but
this scenario would also likely feature fairly high LCLs/cloud
bases which would limit that tornado threat.

In addition, there are questions about the timing/track of the
surface low which will have an impact on low level wind fields/shear
and convergence that will allow storms to develop (especially if we
erode the cap).

So with all that said, the most likely scenario seems to be we get a
few supercells by 4-5 PM as the cold front pushes into southeast NE
and southwest IA, with the main threat being large hail (possibly
larger than 2" in diameter) and perhaps a few pockets of damaging
winds. Given the strong deep layer shear, storms should be fairly
organized and long-lived and could produce some fairly long swaths
of hail. At this time, the tornado threat looks pretty conditional
and on the lower side (SPC outlook has a 2% contour), but it`s still
something worth keeping an eye on. Should also mention that this
does not look like a widespread rain. There could be a few stripes
of 0.25-0.50"+ with any supercells, but they could also be
accompanied by large hail. Areas outside of these stripes would
likely only get a few hundredths, if anything.

The severe weather threat should exit by 10 PM with perhaps a few
lingering light showers in northeast NE into Friday morning as
additional weak shortwave energy slides through. Behind the front
we`ll be much cooler on Friday, with highs in the 50s to lower 60s.

Heading into the weekend, the big question will be the timing and
track of an ejecting trough and associated surface low that`s
progged to develop over TX and push northeast through the Plains.
There is still A LOT of spread in the track of this low and
associated precipitation. EPS guidance consensus favors a track over
the NE/KS/IA/MO border area which would give us a fairly widespread
swath of 0.25-0.75", but individual members range from eastern NE to
the IL/IN border. On the other hand, GEFS is generally much farther
east, with many members completely shutting us out on precip (though
there are a few members that are more in line with what EPS shows).
So bottom line, our best chances for widespread rain will be
sometime Saturday night through early Monday (currently a 30-60%
chance), but overall forecast confidence in this period remains
quite low.

Behind that system, we`ll see some mid-level height rises and a
return of southerly flow which should allow us to warm back up into
the mid 60s to mid 70s following the upper 50s to lower 60s over the
weekend. We`ll also see a continued train of weak bits of shortwave
energy bringing occasional shower and storm chances, though
confidence in timing and track of any one of these is rather low,
with model consensus giving a persistent 20-30% chance from Tuesday
morning onward.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1217 PM CDT Wed Apr 16 2025

VFR conditions through the early TAF period, but MVFR ceilings
develop at KLNK/KOMA by 13z. Otherwise, southerly winds at 16-30
knots at TAF issuance. We lose the wind gusts by 00-01z, and
then LLWS develops 05-12z with winds at 2000` from the southwest
at 40-45 knots. There is a 20% chance of showers at KLKN/KOMA
overnight, but too low to mention in the TAF, and it very well
could remain south of those locations. KLNK would have the best
probability for any precipitation. And any thunderstorms look
to remain farther south near the NE/KS border and south.

&&

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

&&

$$

DISCUSSION...CA
AVIATION...DeWald