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FXUS63 KOAX 190820
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
320 AM CDT Sun May 19 2024

.KEY MESSAGES...

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- Several rounds of strong to severe thunderstorms will be
  possible across our region today through Tuesday afternoon.
  All modes of severe weather including flash flooding will be
  possible.

- There will be another chance for thunderstorms Thursday night
  or Friday.
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&&

.DISCUSSION...
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Issued at 320 AM CDT Sun May 19 2024

Today and Tonight:

A MCS has taken shape across western Kansas up through central
Nebraska this morning associated with an upper-level shortwave
that will continue northeast into eastern Nebraska by 7 AM this
morning, brining this complex of storms through our area. With
surface dew points in the 40s out ahead of this system and a
stable boundary layer in place, these storms will remain
elevated as they move across our area, which should limit any
severe potential. While we could see a few wind gusts up to 40
to 50 mph, the bigger threat will likely be locally heavy
rainfall which could cause flash flooding.

CAMs show this storm complex exiting our area around noon, but
we see additional showers and storms develop behind this
complex, acting to delay environmental recovery this afternoon
across most of our area. What we will be watching closely is the
northward advancement of the warm front out of Kansas. Models
differ on how far north the warm front gets, and it will likely
depend on how much shower and storm activity we see across our
area. There is a greater chance of sufficient surface-based
instability for severe storms developing along and south of this
warm front during the afternoon, and higher confidence this warm
front gets at least to the Missouri state line but could get as
far north as I-80.

Severe storm potential will start to increase around 4 PM with
the northward advancement of the warm front as we`ll start to
see stronger discrete storms develop in the warm-sector south of
the warm front. I think our best chance for severe weather will
be with the QLCS feature that starts to develop over Central
Kansas during the late afternoon and moves into southeast
Nebraska this evening. This will be around a 4-hr window from
around 6 PM to 12 AM. During this time period, we see a broad
region with 60 to 80% chance of greater than 1500 J/kg of SBCAPE
and 200 m2/s2 of 0-3 km SRH. This indicates a primed environment
with ample instability and shear for strong to severe storms.
QLCS storm mode indicates the greatest threat will likely be
damaging winds with hail also possible. We`ll want to watch
closely along the warm front, though, as LCL heights get lower
near the warm front and we see higher 0-1 km SRH as well. The
warm front could provide an anchor for low-level vorticity which
could increase the tornado threat locally.

Monday - Monday Night:

Once these storms exit the area tonight, CAMs show a
break in the shower activity while the NAM and GFS show the
potential for a few lingering showers into Monday morning. In
any case, the severe weather threat will be over and our
attention turns to the next shortwave that will eject out ahead
of the trough over the Southwest region. We see a stationary
boundary set up bisecting our area near I-80. Another MCS
appears likely to develop and ride north of this stationary
boundary producing heavy rainfall Monday night into early
Tuesday with a risk for flash flooding across northeast
Nebraska.

South of the stationary boundary we`ll have more destabilized
environment but low-level shear will be lacking during the day
on Monday. Tuesday night we`ll see the shortwave arrive
associated with the MCS to the north which will provide stronger
forcing for ascent and additional low-level shear which will
increase the potential for severe storms. The only question will
be how well the boundary layer can decouple ahead of storm
development which could limit tornado potential. Hail and
damaging winds seem like the biggest threats at this time.
Best timing for severe weather will probably be 7 PM to
midnight.

Tuesday - Tuesday Night:

Tuesday we see the first upper-level trough move through,
bringing the surface low northeast along that stationary frontal
boundary bisecting our area. By Tuesday morning we`ll see the
surface low already over our area bringing the cold front
through with the air mass ahead of the cold front destabilizing
quickly. Storms will initialize along the cold front in eastern
Nebraska by 10 AM and crossing into Iowa and out of our area by
noon. The Storm Prediction Center has us under an Enhanced
(level 3 out of 5) risk for severe storms during this window
with a 30% chance for severe storms for our southwestern Iowa
counties. It will be a short window as storms will initiate in
our area but move quickly off to the east. Once the cold front
moves through, we may have a few showers linger behind the
front, but winds will shift to northerly and it will feel cooler
during the afternoon into the evening.

Wednesday - Saturday:

Going into the latter half of the week, we find ourselves north
of the storm track as the broad upper-level trough expands
eastward into the Central US. Wednesday we get a bit of a break
in the storms as a surface high moves in behind the cold front.
Temperatures will be a bit on the cooler side with highs in the
low 70s. Meanwhile, we watch out to the west as additional
trough activity reloads, getting ready to move in to our area
Thursday night or Friday. There is still quite a bit of model
spread on timing of the late-week system with precip chances
Thursday through Saturday to encompass this uncertainty. Can`t
rule out another chance for severe weather at this time as CIPS
and CSU Machine Learning does show some signals for potential
for far southeast Nebraska, though the greater potential does
appear to stay to our south over Kansas. We`ll want to monitor
this time frame just in case.
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&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1138 PM CDT Sat May 18 2024

Latest model data suggest that the small MCS currently along
the CO-KS border will advance northeast, reaching the terminal
locations in the 11-12z timeframe. The showers and thunderstorms
may only last a couple hours at KOMA and KLNK, but could linger
into early Sunday afternoon at KOFK. Another round of
thunderstorms is possible at the terminal locations later Sunday
afternoon into evening; however, confidence in storm coverage
and specific timing is too low to include in the forecasts at
this time. VFR conditions are likely to prevail through the
forecast period. A possible exception is if a stronger storm
were to move over the terminal location.

Light north winds will switch to east or southeast overnight
before increasing to 12-15 kt with higher gusts by mid morning
or early afternoon.

&&

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

&&

$$

DISCUSSION...McCoy
AVIATION...Mead