-- Discussion containing changed information from previous version are highlighted. --
573
FXUS63 KOAX 150510
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1210 AM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Widespread thunderstorms are expected tonight. While most of
  the area will receive less than an inch of rain, a few
  locations might see 2 inches or more, which could lead to
  localized flooding. A few damaging wind gusts are also
  possible, mainly west of a Norfolk to David City to Beatrice
  line.

- Rain will end Saturday morning, but scattered strong to severe
  storms will develop between 3 and 11 PM, especially south of
  a Columbus to Sioux City line. Large hail, damaging wind,
  heavy rain, and one or two tornadoes will be possible with the
  strongest storms.

- Daily storm chances exist at least somewhere in our coverage
  area every day from Sunday night through next week. While
  details are fuzzy, each round of storms will have potential
  for some severe weather and heavy rain.

- Very hot temperatures expected Sunday and Monday with
  afternoon heat index values approaching 105 on Sunday, and
  greater than 100 again on Monday.

&&

.DISCUSSION...
Issued at 134 PM CDT Fri Jun 14 2024

Friday has been generally pleasant, warm, and with a drier
airmass in place than the past few days, owing to yesterdays
frontal passage and a bit of cool dry advection. The weather
pattern aloft features a bit of a ridge into the northern Plains
with broad troughing building into the western CONUS, unsettled
weather in the central and northern High Plains with lead short
wave energy crossing the Rockies, and a compact but potent
short wave trough drifting northeast over the heart of the Four
Corners region. Looking around the region, some light rain
showers are crossing north central NE, and may put a few
sprinkles down in northeast NE through this evening. Farther
west, there is quite a bit of thunderstorm development in
western NE down into the Colorado front range. Lee surface low
pressure centered near Cheyenne, and also in southeast CO are
helping to drive convergence and moisture advection into these
regions. There also appears to be a warm front extending
southeast of the CYS low, and a slightly elevated, slightly more
diffuse boundary into north central and northeast Kansas where a
gradient from clear skies to shallow cumulus field illustrates
a change in boundary layer conditions.

By this evening into tonight, the western thunderstorm activity
will conglomerate into a sizable convective system and march
east across Nebraska and into Iowa. Generally speaking, the low
level wind fields favor propagation to the east northeast, but
the instability fields favor a southeastward build by the time
it reaches eastern NE. These conflicting fields, and a general
reduction in available instability with eastward progression
into the local area, is not particularly favorable for severe
weather. That said, any northeastward propagating bowing
segments could produce locally strong winds, as well as any
bowing segments in the better MUCAPE axis over southeast
Nebraska. Another interesting thing to watch tonight is heavy
rain potential. Moisture transport is impressive in the local
area with precipitable water approaching 2 inches. At this time,
the MCS looks to be progressive which will limit overall rain
totals. However, if the southern portion of the line should take
on a rearward propagating component into the LLJ, there could
be a transition into heavy rain production especially over
southern parts of the forecast area. As of now, this is a low
probability scenario, but something to be aware of. The main MCS
should be departing the forecast area by 9 AM or so, although
there could be some elevated development in the wake convergence
zone.

Saturday`s severe convective weather potential is an interesting
case. The morning convection timing and track will greatly
influence the late day setup depending on ability for the
atmosphere to recharge and also in the location of outflow
boundaries. The Four Corners trough will be slowly moving across
eastern NE during the afternoon and early evening hours,
becoming more compact over time and weakening. This will
influence the deep layer shear profiles substantially in time
and location as the mid level wind speed enhancements are small
and subtle, but sufficient to enhance the shear profile such
that it could produce a few good supercells. The low level shear
profile is really the more impressive side of things, so if the
environment can organize a supercell...especially near the
outflow boundary...storm intensity could escalate quickly withe
very large hail and some tornado potential. It does seem that
long-lived supercells would be more challenging to come by, but
again...the devil will be in the mesoscale details. Currently,
anticipate the greatest severe weather potential to be southeast
of a Columbus to Sioux City line, and focused between 3-10 PM.
Once again, given the orientation of the forcing parallel to mid
level winds, in conjunction with quality moisture, could see
some heavy rain or flash flooding.

By Sunday, the northern stream trough becomes dominant, pulling
the front north. This will focus the best strong/severe storm
parameter space over our far northwest regions. There does
appear to be a good chance for initiation in north central NE or
southern SD where convergence is maximized along the front at
peak heating. If this occurs on the Nebraska side, it would be
amid a favorable CAPE/Shear space to promote a cluster of strong
to severe storms moving into northeast NE, as well as some
training and heavy rain potential.

Sunday into Monday will also be quite hot as that front lifts
north and the warm/moist advection returns to the area.
Dewpoints in the 70s and temperatures in the mid to upper 90s
will bring the heat index to 100 and above for both days,
especially over the southern half of the forecast area. HeatRisk
will be elevated and this 2 day event early in the year appears
favorable for an increase in heat related illnesses across the
region.

Thunderstorm chances from Monday through next week continue
almost daily. Trying to pin down the specifics of storm mode and
timing amidst so many convective remnants is a brutal challenge.
At this time, believe it`s safe to say that almost any one of
these rounds of storms will have severe potential as the
boundary layer will be warm with quality deep moisture, and
persistent southwesterly flow will recharge the mid level
instability profile. Tuesday through Friday also appears
increasingly favorable for multiple rounds of heavy rain and
increasing flash flood potential. The synoptic front will be
oriented largely parallel with the mid and upper level flow
while the environment will have ample moisture. But again, the
details of MCS timing and outflow boundaries will play a large
role in this.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
-- Changed Discussion --
Issued at 1210 AM CDT Sat Jun 15 2024

A line of strong to isolated severe storms will track through
the area early in the period with TS lasting for about 2 hours
at a given spot with some showers lingering behind. Expect MVFR
to IFR conditions with 30-40 kt gusts as the storms pass
through, followed by some MVFR to IFR ceilings once the showers
exit, most likely at OFK and LNK. Guidance still suggests some
additional spotty storms could form behind the showers from
around 11 to 14Z, but confidence is low in those hitting a TAF
site (highest chances at LNK and OMA).

Additional strong to severe storms are expected to develop
Saturday afternoon/evening as early as 20-21Z, but confidence in
exact timing and placement is too low to include at this time.
Highest chances are at LNK and OMA, but some hints that storms
could remain south of all sites. Otherwise, outside of storms,
expect southeast winds through the period, with gusts of 20-30
kts for most of the period.
-- End Changed Discussion --

&&

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

&&

$$

DISCUSSION...Barjenbruch
AVIATION...CA