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564
FXUS63 KOAX 181958
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
258 PM CDT Tue Jun 18 2024

.KEY MESSAGES...

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- Strong to severe thunderstorms through around 8 PM today.
  Widespread rain is expected, with some local areas potentially
  receiving 3+ inches.

- Rain chances continue every day through Saturday, especially
  across northern parts of the area. Severe storms are unlikely
  though.

- Temperatures will be much cooler on Wednesday, but warming
  back up by the end of the week.
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&&

.DISCUSSION...
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Issued at 229 PM CDT Tue Jun 18 2024

At 2 PM, the cold front extended from near Sioux City to
Columbus to Hastings. This front continues to progress east
across northeast NE, but has stalled a bit over south central
NE. Thunderstorms have developed along the entire front, and are
expected to intensify and organize a bit in the next few hours.
MLCAPE in advance of the front is greater than 2000 J/kg with
limited inhibition and effective shear only around 30 kts.
Immediately behind the front, the deep layer shear including the
northwesterly surface winds and a stronger belt of
southwesterly flow at 500 hPa, is a fair amount stronger.
Individual cell motion within the line will be nearly parallel
to the front, and thus expect a majority of the updrafts to
become elevated over and slightly behind the frontal boundary
over time...especially as storms develop more organized
downdrafts to push it quicker to the east at the surface.
Assuming slightly elevated updrafts, especially as the evening
progresses, believe that true effective shear will struggle to
be strong enough to influence the updrafts into persistent
mesocyclones. If this is the end result, then large hail would
struggle to be much of a hazard aside from the initial onset of
stronger updrafts, especially with ample seeding from nearby
updrafts and a rather warm airmass aloft. Post-frontal updrafts
would also limit the overall tornado potential (although see
note a few lines below). Rather, the primary severe weather
hazard would likely be areas of 55-70 mph wind gusts where the
stronger updrafts can develop in close proximity, produce an
organized conglomerated downdraft cold pool, and push it to the
east northeast in the higher CAPE environments. This may become
a bit more of a hazard during the time frame in early evening
when low level winds increase but instability remains in place.
And, if these bowing segments develop during the early evening
with increasing low level wind shear, a mesovortex tornado or
two could become possible. This currently appears to be a lower
end potential, but non-zero. Finally, with front-parallel flow
and a slow moving boundary amidst a very moist environment with
ample low level moisture transport, heavy rain and isolated
flash flooding will be possible. It seems that rainfall rates in
the strongest storms could approach 2 inches per hour...so if a
couple of stronger updrafts can train over the same areas before
the cold pool organizes and pushes east quicker, those area the
areas where flash flooding will become possible with local
amounts greater than 3" possible.

To recap, expect a few storms to produce rain capable of flash
flooding and wind gusts of 55-70 mph. Large hail and tornadoes
are unlikely...but the threat is non-zero.

By 8 PM or so, most of the stronger storms should push east of
the area and/or weaken, but off and on showers and thunderstorms
will continue across a large part of the area, and will probably
see an increase in coverage late tonight into early Wednesday.
Expect a few showers or a storm around the region on Wednesday
but most of the day will be dry. Then overnight, expect another
complex of non-severe thunderstorms to develop and move into the
area early Thursday morning. Non-severe thunderstorm chances
continue intermittently through Saturday, although the greatest
chances do shift north to the Dakotas. By Saturday, a front
pushes through with decreasing storm chances thereafter
(although the environment does seem to re-build its instability
profile so if a subtle system is capable of developing storms,
might need to watch for a bit of severe potential).
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&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1246 PM CDT Tue Jun 18 2024

Primary focus this TAF issuance is on timing and intensity of
thunderstorms. Have attempted to focus the greatest potential
into a 2 hour window. It appears that the window for stronger
storms, while around 2 hours long, may come in off-and-on
greater intensity so maintained a tempo for the lowest
conditions. After storms, there are questions about if/when/how
long MVFR ceilings may persist. Especially at LNK/OMA, could
have some MVFR or briefly IFR ceilings over the course of
several hours, but feel that VFR is more likely for a majority
of the time so have been a bit conservative with ceiling heights
at this time.

&&

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

&&

$$

DISCUSSION...Barjenbruch
AVIATION...Barjenbruch