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046
FXUS63 KOAX 031711
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1211 PM CDT Fri May 3 2024

.KEY MESSAGES...

- Dense fog this morning for much of southwest Iowa and parts
  of southeast Nebraska is expected to clear around or shortly
  after 8 AM.

- Thunderstorms are expected this evening into the overnight
  hours south of a line from Columbus to Shelby with a 5 to 10%
  chance of damaging hail and wind.

- There is another chance of severe thunderstorms (15 to 30
  percent chance) Monday afternoon and evening.

&&

.DISCUSSION...
Issued at 416 AM CDT Fri May 3 2024

Today into Tonight:

Water vapor imagery this morning shows a broad trough over the
northwest quadrant of the CONUS while a handful of storm
clusters travel eastward underneath the southwesterly flow from
Texas to the northeastern US. A recent surface map shows the
main surface low of the mature cyclone centered over far
northwestern Minnesota with its main influence on the local area
being a weak ridge of high pressure allowing surface
temperatures to cool efficiently and for calm winds, resulting
in areas of fog in southwest Iowa and southeast Nebraska.
Shortly after sunrise, expect fog to dissipate and for winds to
reestablish out of the southeast and increase in speed, with
gusts of 20 to 25 mph during the afternoon hours. Highs are
expected to climb into the low-to-mid 70s, with an approaching
cold front expected to bring our next chance of storms late this
evening.

By the early evening hours, short-term models are in good agreement
that convection will organize along a cold front extending from just
southeast of the Nebraska Panhandle northeastward into north-central
Nebraska. These storms along the cold front are expected to continue
eastward in a QLCS form, passing through the forecast area from 9 PM
to 6 AM. With 30 to 40 kt wind shear values expected alongside
sufficient ML and MUCAPE around 1500-2000 J/kg in the pre-frontal
region, portions of these storm will have the potential to be strong
to severe. The timing of storm arrival will oppose storm potential,
with nocturnal stability seeming to limit CAM-forecasted wind gust.
Nonetheless, steeper lapse rates near the KS/NE border and enhanced
surface moisture will give southeast Nebraska the best shot at
seeing damaging hail and winds. A lower-end chance of seeing strong
to severe storms does extend northward to a line from Columbus to
Shelby, but potential will be limited by worse surface moisture and
as a result lower instability.

Saturday and Beyond:

By Saturday morning, we`ll be left with northwesterly winds and a
break in the action as a weak ridge builds ahead of the next deep
system. Highs take a hit both days into the 60s, but they should be
an overall nice couple of days. The next focus of the forecast
period comes Monday, when a high-amplitude and negatively-tilting
trough pivots eastward from the Rockies, shooting a cutoff low
northeastward just to the north of the forecast area. With it strong
frontal passage will be dragged eastward with steep lapse rates,
strong moisture transport, and strong deep-layer shear that
will result in another round of strong to severe storms. Long-
range model hodographs certainly have enough low-level
curvature to entertain a tornado risk, but the orientation of
the front and how negatively tilted it will become will have a
great deal to say regarding storms` ability to stay discrete or
not. Fortunately this round of storms will mark the last for
what looks to be the remainder of the work week with increasing
chances for moisture returning next weekend and highs in the
upper 60s.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
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Issued at 1207 PM CDT Fri May 3 2024

VFR conditions this afternoon with some high clouds over
northeastern Nebraska and winds out of the southeast. We`ll see
a line of thunderstorms move across eastern Nebraska overnight
tonight along a cold front with winds shifting to northwesterly
behind the line of storms. I have given a good estimate of
timing for storm arrivals at each of the terminals but this
timing may need to be adjusted as we see the complex develop
this evening and we get a better idea of timing. Models are
fairly confident in MVFR cigs developing behind the line of
storms with a shield of light rain. Cigs could lower as low as
700 feet, but more confident in MVFR cigs at this time. Will see
how models trend ahead of the next TAF package to see if we need
to change post-frontal cigs to IFR (20 percent chance at this
time). Expect low cigs to break out by Saturday afternoon.
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&&

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

$$

DISCUSSION...Petersen
AVIATION...McCoy