Severe Thunderstorm Warning 33, NWS Hastings, NE

Area Forecast Discussion
National Weather Service Hastings NE
1236 AM CDT Tue Apr 16 2024

.KEY MESSAGES...

- Thunderstorms develop and move through the area tonight. A few
  storms are possible as early as 6pm, but the main timeframe is
  expected to be 10pm to 4am.

- Tornadoes, very large hail, and damaging winds are all
  possible. And this threat continues well into the overnight.

- Additional rain and thunderstorms are expected Tuesday,
  especially across Nebraska, but the main severe risk will
  shift east of us.

- Turning cooler through the week and into the weekend, with off
  and on precipitation chances.

&&

.UPDATE...
Issued at 909 PM CDT Mon Apr 15 2024

- Various notes regarding the overnight severe weather threat:

1) A legitimate severe storm threat with all hazards possible
(large hail, damaging winds, a few tornadoes) most definitely
STILL EXISTS for the vast majority of our coverage area (CWA)
overnight, and recently issued Tornado Watch 113 is currently
valid until 3 AM for all of our KS counties along with our NE
counties along/south of I-80 and along/west of Highway 281.
Further overnight expansion of this Watch (or perhaps a new
Watch) is quite possible.

2) Potential development several hours ago (that prompted the
since cancelled/replaced Severe T-storm Watch for 4 of our
west-northwestern most counties) ended up tracking well-
northwest of our CWA, with capping keeping any other convection
at bay locally.

3) This always was expected to be a MAINLY OVERNIGHT (aka late)
"main show" for our CWA, which is actually a bit unusual for so
early in the convective season. Above all else, folks need to
remain unusually vigilant and have a way to receive Warnings at
a time of night that may be more common in June than April.

4) Going into some basics of the meteorology/expectations:
- The recently-developed showers/weak thunderstorms in our
  southeast counties are not of significant concern for a severe
  threat (they are elevated), but will be watched closely.

- As the large-scale Pacific cold front intercepts the well-
  defined dryline in western KS/NE and large-scale ascent
  increases ahead of the vigorous closed upper low shifting
  across central CO, rapid/intense storm development is likely
  mainly 10 PM-Midnight within or just south of our far western
  and southwestern CWA (particularly near/west of Hwy 183).

- Initial storms could quickly become supercells, and at least
  briefly maintain some isolation (this would be the peak time
  of large hail threat). However, especially by around/after 1
  AM, storm mode will likely become quite "messy", with clusters
  or line segments racing north-northeast across the majority of
  our CWA (but with the most intense activity probably favoring
  the southern and eastern halves of it).

- As things trend "messier" in storm mode, the large hail threat
  would likely decrease, but as long as storms remain surface-
  based, a damaging wind and QLCS tornado threat (meaning
  tornadoes embedded within kinks in the line or along any
  breaks in a line) would remain a threat, especially given
  strong low level (0-1km) shear ramping up to 30-40KT.

- Latest hi-res models (including HRRR) suggest our severe storm
  threat should vacate our eastern CWA by the 5-7 AM time frame
  (again unusually late at night/early in the morning for our
  area!).

- Briefly touching on TUESDAY DAYTIME (after 7 AM):
Although the MAIN severe weather threat should clearly be to our
east, there will likely be enough residual instability under the
heart of the closed upper low as it tracks directly overhead to
prompt a few strong to MAYBE marginally-severe storms with
mainly a hail threat (up to around 1" size), especially early-
mid afternoon. This, however, is not a "sure thing" as we are
overall-far more concerned with the upcoming overnight.

&&

.DISCUSSION...
Issued at 330 PM CDT Mon Apr 15 2024

Returning moisture and diurnal heating ahead of an upper low has
pushed MLCAPE values as high as 3000J/kg in southwestern
portions of the area. Latest satellite shows cumulus development
stretching from near North Platte down to near Beloit.
This cumulus doesn't seem to be developing quickly, and there
is still some uncertainty on when this will develop. The HRRR
keeps our entire area convection-free until almost midnight, but
the NAMnest shows convective development within the next 1-2
hours.

Regardless, the expectation is that this first round of
thunderstorms (wherever they develop) will be primarily a hail
threat with steep midlevel lapse rates and relatively limited
low-level shear.

Around sunset, increasing low level shear and helicity will lead
to increasing tornado threat, and better forcing arriving from
the west should allow for additional thunderstorms to develop
overhead or just to our southwest late this evening (after
10pm). This activity will then move through the area into the
late overnight, with continued threats for damaging hail, wind
and tornadoes. The tornado threat will likely be greatest along
the southern extent of the cluster/line.

Storms push to our east Tuesday morning, but additional showers
and thunderstorms are expected to develop as the upper low moves
through the area. Instability will be much more limited on
Tuesday, so severe weather is unlikely.

Winds will turn to the northwest behind the low Tuesday evening
into the overnight, and gusts of 40-50 MPH are expected.

Another shortwave will bring us another chance for precipitation
Wednesday night into Thursday morning (along with a shot of
cooler air). This should be primarily rain (and some weak
thunderstorms), but a mix of rain/snow is possible Thursday
morning as surface temperatures fall into the 30s.

A upper low over Manitoba will keep us in a cooler pattern
into next weekend, with spotty precipitation chances each day.
Subfreezing temperatures appear likely Saturday night.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1232 AM CDT Tue Apr 16 2024

MVFR conditions are expected this evening and through the day
tomorrow. A storm system moving through the region will bring
chances for thunderstorms, a few of which could be strong to
severe before sunrise. Expect the possibility for some
reductions to visibility, gusty winds, and sudden windshifts due
to outflow in the vicinity of thunderstorms.

Heading into the late morning/early afternoon, there remains a
chance for some showers, with possibly an isolated rumble of
thunder in the vicinity of the terminals. Winds will transition
to the southwest in the late morning/early afternoon, shifting
to the west by 23Z. Winds of 15-25kts with gusts as high as
40kts will be possible during this time.  Showers/storms clear
out tomorrow afternoon/evening, with winds becoming
northwesterly.

&&

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

&&

UPDATE...Pfannkuch
DISCUSSION...Mangels
AVIATION...Wekesser

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