763
FXUS63 KOAX 200818
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
318 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 /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1141 PM CDT Sun May 19 2024

Considerable uncertainty exists this forecast period,
specifically in regard to the timing of shower and thunderstorm
development at the terminal locations. Several runs of the HRRR
have indicated the development of showers and thunderstorms in
the vicinity of KLNK and KOMA in the 14-17z timeframe. However,
other model solutions do not indicate that scenario. As such,
no precipitation be included in the forecast at that time.
About that same time, there is some model signal for periods of
MVFR ceilings at the terminal locations. While VFR conditions
will be maintained, observational trends will have to be
monitored. Finally, it does appear that thunderstorms will
become increasingly likely after 20/00z, and subsequent
forecasts will likely include that potential once details become
more clear.

&&

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

&&

$$

DISCUSSION...McCoy
AVIATION...Mead