956
FXUS63 KOAX 201111
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
611 AM CDT Mon May 20 2024

.KEY MESSAGES...

- More strong to severe storms will be possible this evening
  through the overnight hours. Biggest threats will be damaging
  winds, hail, and flash flooding.

- A cold front will move through midday Tuesday bringing another
  round of strong to severe storms, with large hail, damaging
  winds, and a tornado or two also possible.

- After a break on Wednesday, additional rounds of thunderstorms
  will be possible starting Thursday night. Timing and
  potential for severe weather is unclear at this time.

&&

.DISCUSSION...
Issued at 318 AM CDT Mon May 20 2024

Today - Tonight:

Storms moved out of the area last night, leaving behind a stable
boundary layer in its wake. Temperatures are in the 60s and
winds are nearly calm across the area this morning. Through the
rest of this morning we`ll watch as a frontal boundary currently
draped across northwest Nebraska through central South Dakota
sinks southeast toward our area in eastern Nebraska and stalls
somewhere around Columbus to Sioux City. During the day today
we`ll see a resurgence of warm, moist air to the south of this
boundary with highs in the low 80s and dew points in the mid-
to-upper 60s, while areas northwest of this boundary see highs
only in the upper 70s and dew points in the upper 50s to low
60s.

The CAMs still have some spread in what will play out this
afternoon, though the environment does seem fairly set. The
HRRR, which has a tendency to over-mix the environment kicks off
convection around 5 to 7 PM right along the boundary and we see
significant convection blow up and train along the boundary
sinking south down through the I-80 corridor. This would likely
be a high-end flash flooding scenario that would occur through
the overnight hours. The HRRR really is the only CAM that shows
this scenario, though. The rest of the CAMs are more sparse with
storms that develop along the boundary during the evening. We
see more significant storms develop to our west over the
Nebraska panhandle which develops into a strong MCS that tracks
east across the state. This MCS makes it to our area around 1 to
3 AM tonight with a damaging wind and heavy rain/flash flooding
threat.

Tuesday - Tuesday Night:

Whichever scenario plays out tonight will set us up for the
arrival of the surface low on Tuesday. This round of storms may
be our best chance for more discrete surface-based supercells
with a tornado threat as well as damaging winds and large hail.
With spread in the timing and track of the surface low, this
will affect how long or short of a window we have for severe
weather late Tuesday morning through early afternoon. Right now
I`d hedge on a window from 10 AM to 2 PM.

Behind the front we`ll see a second trough bring additional low
chances for showers Tuesday night, but drier northerly flow
in place will make showers fairly sparse with very little
accumulating rain expected.

Wednesday - Sunday:

High pressure builds into the Central Plains on Wednesday giving
us a break in the chances for showers and storms. We continue to
see an active upper-level pattern in place across the CONUS,
however, with additional shortwaves moving from the west along
the broad upper-level trough across the western 2/3rds of the
US.

The next system will bring a cold front through associated with
a cold front moving across the Dakotas Thursday night into
Friday morning. Right now severe potential with this system
looks fairly low, especially with the overnight timing which
will limit surface-based instability. A lot is still up-in-the-
air with the details for this system, however.

There appears to be another system on its tail coming up from
the southwest which could bring a better chance for severe
weather, but again, details are still very uncertain at this
time for Friday-Saturday. We keep shower and storm chances in
the forecast for Sunday as well due to the active storm pattern
and uncertainty in timing for these systems.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 553 AM CDT Mon May 20 2024

A discrete area of fog over northeast Nebraska is bringing MVFR
visibilities this morning before returning to VFR conditions
shortly after sunrise. Model guidance is bringing a few
rain showers to southeast Nebraska between 15-20Z, confidence is
low in this impacting KOMA or KLNK. A warm front draped from
west to east across east-central Nebraska this morning will be
a dividing line for wind directions. Calm southwesterly winds
will be present south of the boundary with north to
northeasterly winds north of it.

Strong to severe thunderstorms will be present this evening
with low confidence in the timing and widespread extent of
coverage. HRRR guidance is displaying storms firing along the
warm front in the 04-10Z timeframe while other guidance displays
a more delayed scenario. Each terminal should expect a period of
showers and thunderstorms overnight with the exact timing
details to be worked out with future TAF issuances.


&&

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

&&

$$

DISCUSSION...McCoy
AVIATION...Wood