178
FXUS63 KOAX 262322
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
622 PM CDT Fri Jul 26 2024

.KEY MESSAGES...

- There will be a lower chance (25 to 40 percent) of
  thunderstorms Sunday evening. A few of these storms may be on
  the stronger side with gusty winds the primary hazard.

- Another system will bring chances for storms (20 to 35
  percent) Tuesday and Wednesday evenings.

- Temperatures are expected to warm into the middle of next
  week, with Wednesday looking to be the hottest day of the
  forecast. The highest heat indices are expected across
  southeast Nebraska.

&&

.DISCUSSION...
Issued at 253 PM CDT Fri Jul 26 2024

     Today and Tomorrow...

A high-amplitude positively tilted ridge continues to persist
across much of the western and central CONUS. This will keep
skies clear and temperatures warm for the rest of the day. Hazy
conditions are expected to persist today into tomorrow as
residual smoke from wildfires in the Pacific Northwest and
western Canada continues to linger.

Tomorrow, a weakening mid-level disturbance will drift
northeast into the central Mississippi River Valley. PVA on the
north side of this system in combination with CAPE around 1500
J/kg will bring a very low end chance (10 to 20 percent) for a
stray shower or thunderstorm south of I-80. Any convection that
can initiate tomorrow afternoon will be diurnally driven, and as
such will weaken and should dissipate shortly after sundown.

     Sunday and Monday...

There is fairly good consensus amongst short term guidance in a
weak low-amplitude disturbance ejecting out into the central and
northern Plains Sunday afternoon. At the surface, a low-pressure
system will develop in the vicinity of the Black Hills and track
east-southeast through the evening hours into southeast South
Dakota. South of the pressure center, a dryline will extend
south through central Nebraska, with surface dew points in the
upper 60s and low 70s to the east of the boundary. By late
afternoon, isolated thunderstorms (25 to 40 percent chance of
rain) are expected to initiate along the dryline and move to the
east. These storms will likely have high LCLs, ranging from 1000
to 2000 feet. Low relative humidities in the boundary layer
suggest that strong gusty winds will be the most likely hazard
with these storms. The higher end gusts may range from 50 to 60
miles per hour, though any severe wind that does occur should
remain very isolated at best. Thunderstorms will weaken as they
move west and after sundown, with the strongest storms
anticipated west of the Missouri River.

Monday morning, a weak cold front will push south across the
region. Moisture pooling along the front in conjunction with
evapotranspiration will mitigate any cooling effect this will
have, with the only noticeable change being a shift of wind
direction from south to north. Furthermore, subsidence on the
backside of the front may help bring smoke aloft to the
surface, slightly reducing visibilities and air quality for a
few hours after frontal passage. Winds are expected to become
southerly again Monday night as a surface high pressure moves
south and east of the area.

     Tuesday and Wednesday...

Medium range guidance suggests that the high-amplitude ridge
over the western and central CONUS will breakdown over the
Plains, resulting in more zonal flow aloft. Embedded in this
broader scale flow, embedded low-amplitude perturbations will
traverse the northern CONUS. Though the exact timing and
intensity of these disturbances is still uncertain, there is
increasing agreement among models in low-end (20 to 30 percent)
chances for thunderstorms Tuesday and Wednesday in the afternoon
and early overnight hours. Tuesday, the primary mitigating
factor to any thunderstorm development will be a strong capping
inversion over the region. Wednesday, height falls due to a more
robust disturbance will help erode this cap. However, the
surface front may push south and east of the area before any
convection can develop. As such, will continue to monitor trends
the next few days. If thunderstorms are able to develop either
of these days in our area, some may be on the stronger side
with gusty winds and small hail as the primary hazards.

These two days are also projected to be the warmest days of the
forecast period as of now. Afternoon highs will range from the
mid 90s (north of I-80 and east of US-77) to near 100 degrees
(southeast Nebraska and Knox County). As such, heat indices
will likely range from 100 to 110 both days later in the
afternoon. However, there are several caveats to this. First,
new wildfires out west may reintroduce smoke into our area which
would keep temperatures a degree or two cooler than what we`re
currently forecasting. Because these fires are new, there is
some uncertainty in model guidance as to how much smoke will be
generated and where this smoke will be transported. Also, if
convection either day is able to develop, precip from these
storms would locally bring down afternoon highs by several
degrees.

     Thursday and Friday...

Ridging will build out west by the end of next week with the
return of northwesterly flow aloft over our area. At the
surface, a high pressure is expected to move south into the
northern Plains and Midwest from Canada. As such, temperatures
are expected to cool down somewhat, with afternoon highs ranging
from the upper 80s further north to the mid 90s near the Kansas
border.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 622 PM CDT Fri Jul 26 2024

VFR ceilings through the TAF period.

Isolated convection across southeast Nebraska has dissipated,
though cannot rule out additional storms while daylight
persists. Activity appears to be associated with low level
diabatic forcing and H7 frontogenesis. Activity has remained
south and east of TAF sites, and don`t plan to include.
Otherwise, hazy skies persist early this evening across the
forecast area with mainly high level smoke circulating around
mid- level ridge axis. Area ASOS depicting visibilities 6 to 9
SM with HZ currently, thus some particulate trapped near ground.
Decoupling will allow MVFR-low VFR visibility to persist during
the overnight hours. Short- term ensembles gradually dissipate
smoke concentration through early afternoon Saturday.

As a mid-level disturbance lifts northward from lower Arkansas
River Valley into lower Missouri Valley, there are small chances
(10-15%) of isolated convection after 20Z Saturday, but will
leave out of TAF for now.


&&

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

&&

$$

DISCUSSION...Darrah
AVIATION...Fortin