712
FXUS63 KGID 152234
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
534 PM CDT Sat Jun 15 2024

.KEY MESSAGES...

- Brief window for severe thunderstorm potential this afternoon
  and evening over mainly eastern portions of the forecast area.
  Large hail and damaging winds are the main concerns, but a
  tornado or two is possible, as well.

- 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.

&&

.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 /18Z TAFS THROUGH 18Z SUNDAY/...
Issued at 1250 PM CDT Sat Jun 15 2024

For KGRI/KEAR Airports:

Significant weather: Low level wind shear (LLWS) tonight.

Wind is the main concern this period as they`ll be strong this
afternoon at 15-20kt, gusting 25-30kt out of mainly the S. Sfc
winds back off some around sunset, but then LLWS will become a
concern 03-05Z thanks to 45-50kt low level jet. This should
veer/weaken by around 12Z. Winds on Sunday will be a bit lighter
out of the S-SW 10-15kt, gusting around 20kt.

Stratus will continue to lift and dissipate this afternoon,
becoming mainly FEW-SCT cumulus 4-6k ft. Can`t rule out a stray
shower or storm late this aftn and eve, but overall
chances/coverage too low to include at this time. Mostly clear
skies expected for the rest of the period.

&&

.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.

&&

$$

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