294
FXUS63 KOAX 191909
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
209 PM CDT Thu Sep 19 2024

.KEY MESSAGES...

- Isolated strong to severe storms are possible (5-15% chance)
  this afternoon and evening in far southeast Nebraska and
  southwest Iowa. The main threats will be damaging winds and
  hail, though a tornado cannot be ruled out.

- Widespread rain will start Friday night and persist through
  the weekend, with the heaviest rainfall anticipated from
  Saturday night into Sunday (65-90%). Rainfall amounts of 1 to
  3 inches are expected.

- Above average temperatures, with highs in the 80s and low 90s,
  are expected to persist through Friday. Cooler conditions will
  arrive over the weekend and into next week, with highs
  dropping into the 60s and 70s.

&&

.DISCUSSION...
Issued at 159 PM CDT Thu Sep 19 2024

...TODAY AND TONIGHT...

The current upper level pattern consists of two separate low
pressure system bringing the bulk of our weather through the next
few days. A closed low currently spinning across southern
Saskatchewan/Manitoba is dropping a dryline across MN and trailing
cold front down into the central Plains. In the mid-MO Valley
vicinity, the surface cold front displays a northeast-to-
southwest orientation as it swipes through eastern NE/western
IA. This feature will be the focus of this evenings severe
weather potential. Another area of low pressure is currently
moving onshore near southern California before make a slow trek
northeast through the weekend.

As of 1:30 PM, surface analysis displays the approximate location of
the cold front from a line from York, NE to Tekamah, NE to Sioux
City, IA. Highs temperatures today will depend on the frontal
passage versus peak daytime heating. Behind the front, highs
are expected to peak in the mid-80s with the low 90s possible
ahead of the front. The location of the front will also come
into play for tonight`s severe weather potential. Convective
initiation is expected along and just ahead of the front early
this evening. Current guidance is displaying the front passing
through much of the area before CI occurs. The most likely
scenario will be a brief period of severe weather in our far
southeast NE and southwest IA counties before pushing southeast.
Afternoon destabilization is expected to bring 2000-2500 J/kg
of SBCAPE ahead of the front along with 35 kts of 0-6 km shear.
An initial supercell storm structure is expected before upscale
growth takes over. The primary hazards will be damaging wind
gusts (50-65 mph) and hail (up to 1.5"). Enough low-level
hodograph curvature is present for 50-125 m2/s2 of 0-1 km SRH,
bringing the potential for a brief tornado or tow. Overall,
confidence is high in convection occurring this evening with the
big question regarding if these storms will mature within our
CWA or not. Watching the location of the front in the following
few hours will be the key determining factor. SPC has a marginal
risk for severe weather along the mid-MO River Valley with a
slight risk just to its east.

...FRIDAY...

Friday looks to be another warm day with mostly dry conditions as we
sit on the top of a flattening ridge centered over central TX/OK.
Highs are expected to top out in the upper 80s/low 90s, about
10-12 degrees above the climatological average for mid
September. We could see some fog development in extreme
southwest Iowa Friday morning, though winds of 10-15 kts above
the surface should keep any fog restricted to patchy coverage.
Skies will remain mostly clear before high clouds push in from
the south during the late afternoon. A long weekend of rainfall
will kickoff late Friday night into Saturday morning. A chance
of light scattered showers will push in along and south of
Interstate 80 after 7 PM (15% chance), but the better
precipitation chances looks to hold off until the 10 PM to
midnight time frame. During this time, moisture transport begins to
impinge areas south of Interstate 80 and will likely kick off a
round of scattered showers and storms. These storms will push
north through the overnight hours (PoPs 30-45%), likely
remaining scattered in coverage.

...SATURDAY AND BEYOND...

A gloomy and rainy weekend is ahead. The aforementioned western
CONUS low will continue to deepen and trek towards the Four Corners
region by the start of the weekend. This feature will spin up a
surface low near western KS before tracking northeast. Initially,
spotty coverage of showers and storms will be in place on Saturday.
This could lead to a few breaks in the cloud cover and modest
destabilization. If this were to occur, we could see a few stronger
storms Saturday evening. High temperatures have also increased a bit
to the low- to mid-80s due to the decrease in expected cloud cover
and precipitation coverage.

A cold front is expected to push through Saturday evening, bringing
more widespread rainfall chances (PoPs 65-90%). Continued moisture
transport ahead of the deepening system will help to usher in
PWAT values of 1.5-1.8", above the climatological 90th
percentile for mid September. The heaviest rainfall is expected
Saturday night into Sunday morning before tapering off Sunday
afternoon/evening. The frontal passage and increased cloud cover
on Sunday is expected to bring highs into the low- to mid-60s
on Sunday. A fitting day for the Autumn equinox. Expected
rainfall totals through the weekend are in the 1-3" range for
much of the area. Locally heavy rainfall could bring pockets of
totals near 4". The axis of the heaviest QPF has shifted a bit
south, towards the IA/MO/NE border. This brings decreased totals
to northeast NE (0.5-1.5") and the highest totals to southeast
NE and southwest IA. An additional shift to the north could
change these totals, but recent guidance has continued to trend
towards this southern option. WPC has much of the area in a
marginal risk for excessive rainfall on Saturday & Sunday.

The aforementioned surface low is expected to track east/northeast
across KS/MO through Sunday. Currently, most ECMWF and GEFS ensemble
members keep the warm sector to our south. A northward shift of this
track could bring severe weather potential to the area on Sunday.
However, guidance has again trended towards the southern option.

PoPs will take a step back on Monday with a chance of seeing some
patchy afternoon sun. Highs are expected in the 60s on Monday. A
shortwave feature will push an additional cold front through the
area Tuesday evening, though the best chance of precipitation
remains to our west for now. Highs will continue in the 70s through
the remainder of the work week. The autumn lovers will have to
savor these days as the CPCs 8-14 day temperature outlook is
leaning above normal. Precipitation totals are also leaning
below normal for this time frame.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1208 PM CDT Thu Sep 19 2024

VFR conditions are favored throughout the forecast period. A
cold front sweeping through the area has southwesterly winds
ahead of the front with a clockwise shift to northwesterly
behind the front. The front has already passed KOFK and is
expected to pass KLNK by 20-22Z and KOMA by 23-00Z. Winds above
12 kts will continue into the afternoon and calm by 22-00Z.
Thunderstorms are possible along the front this evening, though
the front will likely be past the TAF sites beforehand. There is
a 10% chance of these storms impacting KOMA.

&&

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

&&

$$

DISCUSSION...Wood
AVIATION...Wood