426
FXUS63 KOAX 182255
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
555 PM CDT Wed Sep 18 2024

.KEY MESSAGES...

- There is a 20-30% chance of storms late this afternoon into
  the evening, with a 5-15% chance of severe storms. Hail and
  damaging winds will be the primary threats, but a tornado
  cannot be ruled out (2% chance).

- Additional isolated severe storms will be possible (5% chance)
  in far southeast NE and far southwest IA Thursday afternoon
  and evening.

- Widespread rainfall will begin Friday night and continue
  through the weekend. The heaviest rainfall is expected
  Saturday night into Sunday (60 to 80%). Rainfall totals of 1.5
  to 3" inches are expected.

- Above average temperatures (highs in the 80s/low 90s) are
  expected to continue through Friday. Temperatures will cool
  this weekend into next week with highs in the 60s and 70s.

&&

.DISCUSSION...
Issued at 238 PM CDT Wed Sep 18 2024

     TODAY AND TONIGHT...

The current upper level pattern depicts three areas of low pressure
across the CONUS. The features are located in NC/SC, the ND/MT/SK
vicinity and CA. Much of the region resides in southwesterly flow
aloft as the ND/MT/SK low impinges the area. Clouds breaking up will
lead to a breezy afternoon with highs in the mid 80s. The
aforementioned area of low pressure in ND/MT/SK will drag a
surface front through the area, bringing a risk for strong to
severe storms. Isolated to scattered storms are expected to
initiate ahead of the surface front late this afternoon into the
evening. The environment will encompass modest mid- and low-
level lapse rates (6- 6.5 C/km), 1250-2000 J/kg of SBCAPE and
30-35 kts of 0-6 km shear. The primary hazards will be damaging wind
gusts up to 60 mph and hail up to 1". A brief tornado or two
can`t be ruled out, primarily in northeast Nebraska, as low-
level hodograph curvature is sufficient enough for 50-100 m2/s2
of 0-1 km SRH. SPC has northeast Nebraska in a slight risk for
severe weather while the remainder of the area resides in a
marginal risk. Due to the isolated/scattered nature of this
event, PoPs remain in the 20 to 30% range this evening. Aside
from the strong to severe storms, we can expect another
overnight period of scattered showers and storms thanks to the
recurring moisture transport across eastern NE/western IA.
Showers should gradually push east and decay into the morning
hours. PoPs of 15 to 20% continue through the overnight period.

     THURSDAY...

Morning scattered showers and storms will push east into western
Iowa by sunrise Thursday morning (PoPs 20-30%). The clouds will
break way for the warmest day of the week for much of the area. The
ND/MT/SK low will slide northeast into southern Manitoba, dropping a
northeast-to-southwest orientated cold front across the area. This
front will begin to slide across northeast NE and northwest IA by
the afternoon, keeping highs limited to the mid 80s behind the
front. Ahead of the front, highs are expected to climb just above
90 degrees, a solid 10-13 degrees above the climatological
average for mid September.

The aforementioned trailing cold front will bring another chance for
strong to severe storms Thursday evening. The front is expected to
be somewhere in the western IA/southeast NE vicinity by the
time of convective initiation in the late afternoon/evening.
This location could shift a bit west if the front slows.
Instability ahead of the front is expected to be in the
1500-2500 J/kg range coupled with 30-35 kts of 0-6 km bulk
shear. Enough low-level hodograph curvature is present once
again for a brief tornado or two, though it will primarily be a
hail (up to 1") and damaging wind (50-60 mph) hazard. PoPs
remain in the 15 to 25% range for western IA/southeast NE before
pushing off to the east into the late evening. SPC has extreme
eastern NE and western IA in a marginal risk for severe weather.

     FRIDAY AND BEYOND...

Friday looks to be the last day with well-above average temperatures
as a mostly clear day brings highs in the upper 80s/low 90s. The
aforementioned low over the western CONUS will slowly trek towards
the Four Corners region by the start of the weekend. This will spin
up a surface low near the western KS/NE border before
progressing northeast through the weekend. Chances for showers
and storms move into the area late Friday night into Saturday
morning. The onset timing will depend on the speed of the
aforementioned low reaching the region. Model guidance has
continued to trend slower on its arrival. Much of Friday evening
is expected to remain dry before moisture transport ramps up
between 10 PM and midnight. Scattered showers and storms will
likely develop during this time frame before increasing in
coverage overnight. PoPs increase from 30 to 60% overnight.

Widespread precipitation is expected to continue through the weekend
with PoPs peaking in the 65 to 80% range Saturday night into the
first half of Sunday. This is coupled with PWAT values of 1.5 to
1.75", exceeding the climatological 90th percentile for late
September. Total QPF through the weekend is expected in the 1.5-3"
range. WPC has much of the area in a marginal risk for excessive
rainfall both Saturday and Sunday, leaving a risk for locally heavy
rainfall. This hazard will be enhanced if we can gather enough
instability for some heavier showers and storms. PoPs will taper off
late Sunday into Monday (20 to 40%). Severe weather potential
through the weekend remains a bit uncertain. Instability remains on
the lower end, maxing out around 500 J/kg of SBCAPE in response to
the continued thick cloud cover and showers. Sunday could be a day
of interest depending on the track of the surface low across the
area. However, there is still plenty of time to work these details
out.

The other point of interest in the long range forecast is the drop
in temperatures this weekend. Highs are expected to drop into the
low 80s on Saturday and upper 60s/low 70s on Sunday and Monday.
Highs in the 70s are expected to continue into the first half of
next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 553 PM CDT Wed Sep 18 2024

VFR conditions through the period. LLWS will be possible at
KOFK/KLNK 08-12z with winds at 2000` from 190-200 degrees at
35-40 knots. There could also be spotty thunderstorms at KLNK
01-03z, and again 06-08z. And then spotty thunderstorms could
occur at KOMA 07-11z.

&&

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

&&

$$

DISCUSSION...Wood
AVIATION...DeWald