808
FXUS63 KGID 182335
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
635 PM CDT Sat May 18 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms move in late tonight and
  continue into Sun AM. Most likely non-severe, but small hail
  and gusty winds will be possible in strongest cores.

- Off and on thunderstorms are expected Sun PM through Tue,
  some of which could be strong to severe and pose risks for all
  severe hazards. However, confidence on details is only low to
  medium as each round will have significant impact on
  subsequent rounds` severity, timing, and placement.

- Cold front sweeps through the area and brings somewhat cooler
  and less active weather for Tue night into Thu.

- Temperatures most days will peak in the 70s-80s, though mainly
  mid 60s-70s are expected Tue-Wed. Lows will be mainly 50s-
  60s, except for cooler 40s Tue/Wed nights.

&&

.DISCUSSION...
Issued at 208 PM CDT Sat May 18 2024

Expect increasingly pleasant conditions late this aftn and into the
evening as wind speeds gradually decr and temps remain mild. Short
term CAMs are in pretty good agreement that elevated convection will
develop over the central High Plains 03-06Z as 45kt LLJ noses into
the region, then shift E/NE into our area 06-09Z. Peak MUCAPE will
increase to around 1500-2000 J/kg for parcels lifted from H7-H8
amidst steep mid level lapse rates. However, the bulk of the veering
in the wind profile is below the MUCAPE layer, so effective shear is
rather marginal at mainly 25-30kt. This could yield some "pulsey"
elevated hailers, generally of the low-end variety (penny to half
dollar size), and perhaps some gusty winds around 40-50 MPH. Recent
HRRR runs and HREF seem to focus the majority of the activity along
and S of the Platte River, which is a bit of southward shift from
where previous forecast placed the highest PoPs. Seems probable (60-
70%) that at least scattered activity will persist into the mid to
late AM hrs Sunday as the LLJ slowly veers and weakens, though the
lingering activity will probably have a lesser hail risk.

Pattern recognition and general model guidance would suggest a dry
period, or at least a lull in coverage/intensity, from around midday
Sunday through AT LEAST mid aftn. Thereafter, details for
additional convection become quite a bit more murky owing to
uncertainties left by the earlier round, such as location of
outflow boundaries, cloud cover that will affect ability to
destabilize, and quality/depth of BL moisture. The overall upper
pattern will feature only modest height falls, but most
guidance has several weak disturbances in moderately fast SWrly
mid-upper flow, and the AM round may actually help to suppress
the strongest mid level capping to our S. As it stands now,
there appears to be two scenarios of convective potential:

1) Seems plausible that enough recovery will occur to allow for
a narrow window of sfc based development along lingering
outflow boundary that will probably be located somewhere between
the NE/KS border and I-70 corridor around 22Z-02Z. After that,
cooling BL will probably become capped along this boundary in
the absence of stronger forcing. It is a highly conditional, and
probably isolated, threat...but if something does pop up, it
will likely be supercellular with all modes of severe possible -
including tornadoes - given tendency for backed low level flow
and perhaps some pooling moisture. Worth noting, however, that
forecast soundings suggest moisture quality/depth will not be
great during the late aftn/early eve period and subject to
mixing out - so would really need some pooling and backed flow
to get low enough LCLs for tors. Greatest risk would likely be
large to very large hail given very steep mid level lapse rates
and bulk shear values of 40-50kt in the presence of clockwise
curved hodographs, along with damaging wind gusts.

2) The other scenario - which is more probable and likely more
impactful because of coverage - will be for tstms to develop along a
N-S corridor along the High Plains from the NE Panhandle southward
to TX/OK Panhandles within warm/hot, deeply mixed environment with
little to no capping and beneath slightly stronger height falls.
This activity would have a tendency to become outflow dominate given
inverted-V thermodynamic profiles and more forward propagating due
straighter hodographs. Since it`s developing further W, this threat
would likely be a bit later, generally after 00Z, but severe will
still be a risk as this activity will actually be moving into pool
of greater instability, and LLJ again increases to 40-50+kt. Would
tend to favor W/S zones the most, but if a mature MCV develops then
local dynamical forcing could overcome incr capping after 03Z to
persist the severe threat longer and further E. Heavy rain is
not a concern attm given isolated/conditional nature of scenario
1, and likely progressive nature of scenario 2.

Thunderstorms remain possible into Monday, and the entire area is
outlooked in either a Marginal or Slight Risk of severe weather
(levels 1 and 2 on a scale of 5) on SPC Day 3 outlook. As there are
uncertainties on Sun due to earlier convection, the uncertainties
are even higher on Monday. In general, upper troughing still resides
to the W and we`ll remain in diffluent (but kinda weak) SWrly upper
flow. At least one or two upper waves will likely be ejecting NE out
of the broader trough, which could enhance the upper flow late in
the day and moreso into Mon night. Sfc mass fields suggest a triple
point over central KS, with previous outflow boundaries possibly
augmenting and/or narrowing the primary instability axis to the E of
this triple point and southward trailing dry line. I have a tendency
to doubt we`ll have much sfc-based activity in our CWA prior to
sunset as mid level temps appear to be 1-2 deg warmer, though
mesoscale details will be important. Would think the later arrival
of upper support would favor activity moving off the High Plains
after sunset and/or new development ahead of possible northward
moving warm front in response to incr LLJ. This would provide more
of a wind/hail threat and lesser of a tornado threat, but again,
plenty of details to work out.

Trough moves through on Tuesday, and timing will be key for severe
weather chances in our area. At this time, appears it will be just
fast enough to keep primary risk to our E/SE, but any slowing trend
and our chcs will incr. Continued cloud cover and shwr chcs behind
departing system amidst NWrly low level flow will likely keep temps
considerably colder in the 60s, esp N/W of the Tri-Cities. Flow
turns more zonal late in the week and into the start of the holiday
weekend, which should support seasonable temperatures and off and on
pcpn chances.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 625 PM CDT Sat May 18 2024

A cluster of showers and thunderstorms is expected to move
through central Nebraska early Sunday morning, with near-term
models showing additional scattered showers and storms redevelop
later Sunday morning.

In addition to the thunderstorms, ceilings could dip to MVFR
Sunday morning. The probability for this occurring is a bit
higher at EAR compared to GRI.

Another round of stronger thunderstorms is possible Sunday
evening, just beyond this TAF period.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...None.
KS...None.

&&

$$

DISCUSSION...Thies
AVIATION...Mangels