219
FXUS63 KGID 160637
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
137 AM CDT Sun Jun 16 2024

...Aviation Update...

.KEY MESSAGES...

- Main concern shifts to heat for Sunday and Monday with highs
  well into the 90s and heat indices 100-105F in spots. There
  will at least be some wind for "relief" - gusting up to 40 MPH
  on Monday.

- Record-warm LOW TEMPERATURES possible for Monday (June 17) at
  Grand Island/Hastings airports (see separate CLIMATE section
  below).

- Thunderstorm chances Sun-Mon are low and isolated, but better
  chances for frequent rounds of storms arrives for the Tue-Thu
  time frame. Some storms could be strong to severe, but the
  main hazard may shift to heavy rain and localized flooding.

&&

.UPDATE...
Issued at 658 PM CDT Sat Jun 15 2024

***The Tornado Watch is CANCELLED for south central Nebraska as
 of 7PM.***

Visible satellite trends show a distinct decrease in agitated
cumulus over the past hour, and the upper level shortwave
responsible for the current convection continues to lift E/NE.
An isolated storm may redevelop prior to sunset (~20% chance),
but additional severe weather is not expected. Thunderstorms
currently over the High Plains are forecast to dissipate as they
shift east after sunset, thanks to increasing convective
inhibition.

&&

.DISCUSSION...
Issued at 515 PM CDT Sat Jun 15 2024

Rest of today into tonight:
A weak surface boundary, reinforced by last night/early AM
convection, and currently residing from roughly Grand Island to
Hebron, will continue to shift E/NE through the remainder of the
daytime hours. The first storm developed around 20Z in Mitchell
Co, likely in an area of reduced CINH on nose of very steep low
level lapse rate plume (as evidenced by multiple severe wind
gusts with convection in central KS), and has quickly shifted
NE. This storm has shown signs of organization and potential
hail core, at times, but several negative factors to deep severe
convection are working against it: poor mid level lapse rates
(~6.5 C/km), weak 0-6km bulk shear (~25kt), and poor mid to
upper level storm relative flow. This basically just leaves the
strong instability (MLCAPE 2000-3000 J/kg) and low level
helicity (0-3km SRH 200-300 M2/S2) as ingredients favorable to
severe wx. Furthermore, what weak mid-level troughing remains is
quickly shifting E/NE with subtle height rises expected for
central/western zones through the evening. Thus, the window for
severe weather in the E will be limited to next few hrs (perhaps
even less). Unsure if we`ll get anything to fill the gap between
BVN and HJH along the retreating boundary and within axis of
strong instability as sfc convergence seems weaker. If we do,
large hail up to around 1.25-1.5" (limited by the weak shear and
poor lapse rates), damaging wet microburst, and perhaps a
tornado would be the main threats. At least iso convection is
trying to develop along another instability gradient along Hwy
183/283 corridors in Phillips and Rooks Counties, but upper
support is even worse out there. Additional convection over the
NE Panhandle within deep mixing and along sfc trough will likely
weaken by the time it arrives in our area due to capping.

Sunday - Monday:
Main story will be heat, though a non-zero chance for an
isolated storm exists in parts of the area, as well. A cold
front will attempt to push into the area Sun AM, but likely
stall out and even lift back to the N/NW as a warm front during
the afternoon. It will become hot S of the front thanks to
breezy Srly winds, deep mixing and mostly sunny skies. In fact,
areas near/S of the state line could push triple digits on air
temps. Humidity will decr some compared to today owing to the
deeper mixing, but still be enough to produce some heat indices
100-105F. Opted against an advisory on this shift as this heat
event appears somewhat marginal for us given we well into June
now, its fairly short-lived at 2, maybe 3, days, and we have
wind during the hottest temps. Speaking of wind, rather unusual
strong gradient winds by June standards are forecast for Monday
in which gusts may reach 40-45 MPH. Fortunately many areas saw a
nice rainfall Fri night as things are going to dry out quickly
with that kind of heat/wind and strong sunshine. Some model
guidance hints at iso storm development near a sfc low/triple
point in far W zones Sun aftn, within area of intense mixing
that may erode an otherwise seasonably strong cap. If
convection indeed forms, its likely going to take every bit of
heating and sfc convergence as the broader mid to upper level
pattern will be pretty hostile. Moderate to strong instability
and modest deep layer shear support a conditional risk of severe
hail/wind, and this is handled well in the SPC Day 2 outlook.
Convective chances appear even more isolated/conditional on Mon
given very warm mid level temps 15-17C and the primary sfc front
even a bit further N.

Rest of the forecast:
Not a lot has changed to overall thinking during this period as
ridging intensifies over the NE CONUS and a trough works its way
through the Great Basin/N Rockies and into the N Plains Mon
night into Tue. This will result in SW upper flow and a plethora
of weak perturbations, along with cooler mid level temps and
weaker capping. In addition, models continue to show a
persistent plume of moisture with tropical origins/source
wrapping around the eastern ridge in a "ring of fire" type
effect. The N Plains trough will help to force a frontal zone
into the region either later on Tue or into Wed and combine with
the aforementioned factors to produce repeated rounds of
convection for much of the second half of the work week. Severe
weather potential is pretty uncertain, locally, as we`ll be on
the SE fringes of stronger mid/upper level flow/shear. More
confidently, however, will be the risk for heavy rainfall and at
least localized flooding. PWATs consistently AOA 1.5" (1.5 to 2
standard deviations above normal), deep layer flow potentially
parallel to sfc front/low level baroclinic zone, and multiple
rounds is a setup that will almost always present increased risk
of flooding in mid to late June. With that said, details will be
important, so too soon to go into even modestly specific amounts
or local areas of concern. Temperatures will depend on
rain/clouds and sfc front position, but in general will be quite
a bit cooler than early week. Ensembles have been hitting on Wed
being particularly cool in the upper 60s to 70s for most of our
Neb zones. Increasingly zonal upper flow could keep the active
weather going into next weekend before perhaps some ridging
returns around the 23rd or 24th.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 135 AM CDT Sun Jun 16 2024

For KGRI/KEAR Airports:
- General overview:
Confidence is overall-high in VFR ceiling/visibility and also
rain/thunderstorm-free conditions through the period, although
there is admittedly a very small chance for a brief
shower/thunderstorm both early this morning, and then again late
afternoon-evening (deemed around 10% or less). However, the main
story of the period will be winds, and in particular two
separate periods of low level wind shear (LLWS)...the latter
more intense than the former.

- Ceiling/visibility/rain and thunderstorm potential details:
Confidence is very high in VFR ceiling/visibility through the
period, with perhaps a scattered lower-VFR cumulus field
developing during the daytime hours, but otherwise any clouds
mainly near-to-above 10K ft. As for shower/thunderstorm
potential, odds appear to strongly favor the entire period
staying dry (90% chance). However, there is also an outside
chance that a shower/weak storm could pass through early this
morning, and a similar outside chance that a stronger
thunderstorm could flare up late this afternoon-evening.
However, with both of these chances deemed to only be around
10%, and with better chances for the later afternoon-evening
storms to focus at least slightly off to the north, will forego
any formal inclusion of rain/thunderstorm chances.

- Winds:
- Surface winds:
Although a bit breezy/gusty at times, overall surface winds will
not be a significant issue. The majority of the period (but
especially the first and final several hours will feature a
prevailing southeast/southerly direction, with sustained speeds
commonly 10-15KT and gusts into the 20-25KT range. However,
particularly between 13-18Z, direction could honestly be quite
variable as a weak front stalls in the area before lifting back
north.

- Low level wind shear (LLWS):
There are two distinct periods of mentionable LLWS during the
period, with the second one overall-stronger than the first:

1) Right away this morning through around 13Z, southwesterly
winds within roughly the 1,500 ft. AGL will top out around 45KT,
creating roughly 30-35KT of shear magnitude between the surface
and this level.

2) This evening (02Z onward), a very strong southerly low level
jet will kick in, with speeds within roughly the lowest 1.500
ft. AGL accelerating to around 50KT, creating fairly strong
shear magnitude around 40KT between the surface and this level.

&&

.CLIMATE...
Issued at 530 PM CDT Sat Jun 15 2024

-- Regarding possible RECORD WARM LOW TEMPS on Monday
(June 17th):

Both Sunday night-Monday morning and Monday night-Tues morning
are expected to remain very warm, with most of our CWA not
dropping below the low-mid 70s. As a result, calendar day
(midnight-to-midnight) records for warmest low temperature could
be threatened at Grand Island/Hastings airports (the 2 sites
for which we issue formal Record Event Reports/RERs).

Any such records are most likely to be threatened on Monday the
17th, because a cold front arriving Tuesday the 18th is currently
expected to drop temps safely below record territory by midnight
that night.

- GRAND ISLAND
                   Record Warm Low      Latest Forecast
Monday June 17th     74 (1906)               73


- HASTINGS
                   Record Warm Low      Latest Forecast
Monday June 17th  72 (2020/2014/1946)        73


NOTE/REMINDER: in order for a new record warm low/minimum
temperature to become official it has to "survive" the entire
24-hour calendar day (in other words, it is not always based
solely on the early-AM low temp).

&&

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

&&

$$

UPDATE...Thies
DISCUSSION...Thies
AVIATION...Pfannkuch
CLIMATE...Pfannkuch