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978
FXUS63 KOAX 051145
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
645 AM CDT Sun May 5 2024

.KEY MESSAGES...

- Slightly warmer and dry today, with highs in the upper 60s.

- Potentially strong storms are expected Monday afternoon,
  primarily from 4 to 10 PM as a line of storms moves thought
  the area. Damaging wind, hail, and an embedded tornado are
  possible.

- Light showers and a few rumbles of thunder linger through the
  end of the work week, with drier conditions and highs in the
  70s returning for the weekend.

&&

.DISCUSSION...
Issued at 353 AM CDT Sun May 5 2024

Today:

Water vapor imagery this morning features an eye-catching and deep
trough entering the far western CONUS, with a broad arm of mid-level
moisture and ascent stretching from Arizona northward into
Idaho/western Montana, while the weakening shortwave exiting to the
north of the Great Lakes region continues to leave the far eastern
CONUS with continued cloudcover. Looking at a recent surface
analysis, the aforementioned trough is carrying with it a frontal
zone an impressive distance east past the Pacific Coast into eastern
Nevada, where many other systems see theirs washed out. Drilling
down to the forecast area, surface high pressure is seated near Fort
Dodge, Iowa with weak winds at the surface extending well into
eastern Nebraska. Clear skies above have aided nocturnal cooling to
help develop very patchy fog despite relatively dewpoints in
the upper 30s to low 40s, primarily in river valleys. By
sunrise, any leftover fog should dissipate, and leave
southeasterly winds in place alongside sunny skies. Highs are
expected to reach into the upper 60s, with areas of northeast
Nebraska seeing gusts to 20-25 mph before diminishing around
sunset. Warm southerly flow should keep overnight lows from
getting to cool, preventing another foggy morning (patchy or
not).

Monday:

The primary focus of the forecast period continues to be the strong
storm system that will make its way to the forecast area Monday. In
the mid/upper levels, the aforementioned trough out west will have
translated eastward, becoming negatively-tilted as it prepares to
eject into the Central Plains. As it is arriving, a strong pressure
gradient and overall mass response will develop, resulting in strong
moisture transport and gusty winds that develop early Monday across
much of central and western Nebraska and spreads eastward throughout
the morning. Wind gusts in the 35 to 45 mph range will be possible
out of the southeast, while dewpoints of just over 60 degrees spread
northward to the NE/SD border by the afternoon. Ample shear and
sufficient instability supportive of severe storms will be present,
with all forms of severe weather expected to be present.

As far as additional details go for Monday`s severe potential,
initial runs of the extended CAMs during the afternoon hours
continue to jive with an arrival time to eastern Nebraska in the 3-4
PM time range. Low-level shear vectors continue to combine with the
strong forcing for ascent to quickly grow any convection upscale
into a long bowing structure, that will move eastward across the
area before exiting to the east by 10 PM. Areas with the highest
surface moisture in southeast Nebraska continue to show the
greatest potential for severe weather, which is reflected by the
Enhanced Risk from the SPC (with the rest of the forecast area
in a Slight Risk). One sticking point that could make the
afternoon more tricky would be the presence of a convergent zone
joining warm air advection out ahead of the main front that
could kick start scattered shower and storm activity early.
This activity would then interact with the bow/QLCS, and locally
enhance tornadic potential as the prefrontal cells are
ingested. Nonetheless, continued attention is due as we approach
Monday afternoon (though the strongest of the storms will stay
well to the south of the forecast area).

Tuesday and Beyond:

With Monday`s storm system in the rear view mirror, the main
mid/upper trough is expected to cut off and drift northward, with a
center near the MT/ND border region. A strong zonal to slightly
southwesterly mid/upper jet will be settled over the area and will
provide no shortage of shortwaves and embedded impulses that will
keep light showers and a few rumbles of thunder in to the forecast
for the remainder of the week. Highs will take a slight hit and fall
into the 60s for much of the remaining work week before highs return
to the 70s for Saturday and Sunday. By that point the influence from
the Monday system will have finally left the area in favor of
increasing heights and northwesterly flow as a couple of days settle
in for the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
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Issued at 645 AM CDT Sun May 5 2024

Patchy IFR and MVFR fog is occurring across the area this
morning, but so far all three TAF sites are maintaining VFR
visibilities. There`s a 15 to 20% chance that MVFR mist could
develop at KOMA, but will leave out for now.

VFR conditions will prevail through the first twelve hours of
the TAF period. Ceilings will decrease in the 06/03-06z
timeframe into lower VFR levels, FL040-060. Low level moisture
will surge northward during the overnight hours, further
decreasing ceilings into MVFR category at all three TAF sites.

Light and variable to light southeast winds of less than 10
knots will prevail through the morning. By early afternoon,
southeast winds 10 to 15 knots will prevail with gusts 20 to 25
knots.
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&&

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

&&

$$

DISCUSSION...Petersen
AVIATION...Fortin