265
FXUS63 KOAX 081701
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1201 PM CDT Wed May 8 2024

.KEY MESSAGES...

- Marginal risk of severe thunderstorms today and this evening
  in northeast Nebraska and western Iowa

- Some storms today and this evening could be strong to severe,
  capable of producing hail, damaging winds and funnel clouds

- Forecast for Friday through early Sunday is mostly dry. Chance
  of showers and thunderstorms returns Sunday afternoon and
  lingers into early next week.

- Warmer temperatures expected Sunday into Tuesday.

&&

.DISCUSSION...
Issued at 439 AM CDT Wed May 8 2024

.Today...

A band of showers continues to move northeast across the
forecast area this morning, associated with moist isentropic
lift along the 305-310K, prompted by increasing large scale
ascent in advance of H5 closed low digging southward into the
central plains. Drier air below 5K AGL is limiting measurable
precipitation. Better focus moves east of forecast area by mid-
morning, thus expect a lull in precipitation by then.

Upper level low begins to move east along the Nebraska-South
Dakota border by mid-day, sharpening the large scale wind field,
with bulk shear values of 40-70kt by midday. Lapse rates will
increase as cold core and vort lobe from upper low moves across
the area. In tandem, low level theta-e increases,which will
lead to SB/MUCAPE near 1000 J/Kg northeast Nebraska and western
Iowa, and about 1200 J/kg extreme southeast Nebraska. An
inverted trough will be oriented from southwest Iowa, across
extreme northeast Nebraska into southeast South Dakota,
providing adequate surface convergence to allow for scattered
thunderstorm development. Given proximity to upper low,
increased stretching and low-level shear, present an environment
conducive for funnels and/or possibly a tornado or two,
especially storms interacting with inverted trough across
extreme northeast Nebraska and northwest Iowa. Further south,
across southeast Nebraska, proximity to main surface low could
aid in low level convergence for storms, but tornado or funnel
threat in this area is not expected.

Threat of severe weather will diminish by early evening as vort
lobe moves east of the area, leading to subsidence across the
region. A few more showers could develop during the overnight
hours as another disturbances ripples through broad cyclonic
flow aloft.

Temperatures today will be similar to those seen yesterday.
Overnight lows will be in the 45 to 50 degree range.

.Thursday...

Area remains on the cyclonic shear side of broad, latitudinal
trough that stretches from North Atlantic to western U.S.
Mid-level isentropic convergence will help to sustain band of
showers and possibly isolated thunderstorms, especially during
the daytime when diabatic effects will aid in destabilization.
Precipitation coverage and chances will wane Thursday evening,
as upper trough axis moves south and east of the area, and
increases large scale subsidence.

Clouds, evaporative cooling and low level cold advection will
keep temperatures about 5 to 10 degrees cooler, with highs only
in the 60s. Lows will be in the 40s.

.Friday through Saturday...

Large scale subsidence will keep precipitation chances slim, and
will allow for temperatures to rebound into the 70s for highs.
Sharpening trough across the eastern U.S. pushes a backdoor cold
front into the area for Saturday. In cooling associated would
affect Iowa moreso than Nebraska, with downslope warming
mitigated low level cool air advection.

.Sunday through Tuesday...

Temperatures will increase as upper level ridging builds, with
high temperatures climbing into the 80s. An open H5 wave will
progress from the 4-corners area across the southern plains
Sunday and Monday, and bring another chance of showers and
thunderstorms. The surface pattern doesn`t suggest a threat of
severe weather, as better mass responsive will be south of the
area.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1154 AM CDT Wed May 8 2024

The surface wind field across eastern Nebraska and western Iowa
remains complex given two surface low-pressures in close
proximity to one another. At this time, the northeast Nebraska
low appears to dominate the surface flow at all TAF sites, so
have written TAFs given these current observations. As such,
winds will veer with time, ultimately becoming north-
northwesterly by the end of the forecast period. Scattered
showers and thunderstorms are expected to develop across
portions of northeast Nebraska and western Iowa by 20Z. Some of
these storms may be on the stronger side with winds gusting to
60 mph and hail up to an inch. These storms are largely expected
to remain northeast of TAF sites.

Tomorrow, scattered showers are expected to develop across the
region at the end or shortly after the end of this TAF period.
Will provide more detail regarding these in a subsequent TAF
issuance.

&&

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

&&

$$

DISCUSSION...Fortin
AVIATION...Darrah