751
FXUS63 KGID 161206
AFDGID

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

...Aviation Update...

.KEY MESSAGES...

- Like yesterday, the late afternoon-evening hours hold VERY
  CONDITIONAL potential for popping off up to a few severe
  storms (kind of an "all or nothing" scenario depending on
  whether or not the cap can hold). Main threat would be our
  northern/western counties.

- Both today and Monday will be plenty hot, with actual high
  temperatures well into the 90s most places and flirting with
  100 especially in parts of KS. However, factoring in
  humidity, wind speeds etc., today is likely the worst of the
  two days, with widespread peak heat index of 100-104 across
  especially the southeast 2/3rd of our coverage area (CWA). In
  other words, JUST short of official Advisory criteria.

- Overnight lows also quite warm these next 2 nights (most areas
  dropping no lower than low-mid 70s). Potential record- warm
  lows (through the full calendar day) could be in play at
  Grand Island/Hastings airports on Monday (June 17). See
  separate CLIMATE section below for details.

- Monday afternoon-night will be quite windy by mid-June
  standards, with sustained southerly speeds commonly 25-35 MPH
  and gusts up to around 45 MPH.

- Rain/thunderstorm chances Mon-Sat: each and every day/night
  forecast period features at least small/iffy chances somewhere
  in our area, but by far the highest chances for the most
  WIDESPREAD activity looks to focus between Tues afternoon-Wed
  night as a cold front enters and stalls over our region (at
  least limited chances for both severe storms and heavy
  rains/localized flooding).

&&

.DISCUSSION...
Issued at 550 AM CDT Sun Jun 16 2024

-- PRIMARY CHANGES TO THIS 7-DAY FORECAST PACKAGE VERSUS THE
 PREVIOUS ONE (issued Sat afternoon):

- Honestly, no changes of major significance. While confidence
  is lower-than-average regarding thunderstorm chances (or lack
  thereof?) these next few days, confidence is high in various
  other aspects including: the heat today-Monday, seasonably-
  strong winds Monday afternoon-night, decent rain chances Tues-
  Wed and that Wed should be the overall-coolest day of the
  week.


-- 7-DAY FORECAST OVERVIEW/HIGHLIGHTS (heavily focused on the
 first 48 hours):

- CURRENT/RECENT WEATHER SITUATION AS OF 5 AM:
Briefly looking back at yesterday afternoon-early evening: our
CWA indeed got fairly lucky in terms of potential severe storm
threat. While we did issue a couple of Severe Thunderstorm
Warnings for mainly the Thayer County area (and a few other
semi-strong storms developed in our KS zones), as was expected,
the VAST MAJORITY of severe storms (and even some tornadic
activity) focused mainly slightly east-northeast of our CWA
within the OAX coverage area (our area largely spared by being
JUST behind the passing mid level trough axis by peak heating).

Turning to the current and more recent weather scene, since
nightfall last evening we had a few weak storms brush into both
our extreme southeast (Thayer County) and also our extreme
west-northwest (Dawson/Valley counties), but this activity has
long since moved out (east) or dissipated (west), leaving us dry
CWA-wide at this time under mainly clear skies.

In the mid-upper levels, water vapor imagery and short term
model data reveal the since-departed mid level shortwave trough
axis centered from IA to eastern KS, with our CWA under subtle
ridging in its wake. At the surface, the main feature on the
regional map is a roughly 998 millibar low pressure center over
the eastern Dakotas, with a trough axis/weak cold front trailing
southwestward from this low through north central/western NE.
However, our entire CWA remains in the warm sector to the
south-southeast of this boundary, with early-AM breezes
generally 10-20 MPH out of the south (some higher gusts
especially east). These breezes, in tandem with dewpoints well
into the 60s, has low temps on track to bottom out between 66-70
most areas.


- TODAY-TONIGHT:
We are truly dealing with two primary concerns...one of one
high-confidence (near-Advisory level heat) and one of lower
confidence (will any spotty storms...possibly severe...form
later this afternoon-evening?).

In the big picture of the mid-upper levels, our flow aloft will
turn more west-southwesterly as various/subtle disturbances kick
into our region well-downstream from a larger-scale trough over
the far northwest CONUS. Compared to yesterday (and perhaps a
big factor later today), mid-level temps have warmed a bit, with
700 millibar readings now 12-14C over most of our CWA. At the
surface, the situation is a touch complex today, as the
aforementioned trough axis/weak cold front currently just to
our northwest will work southward into especially the northern
1/3 of our CWA today, before stalling out this afternoon ROUGHLY
near I-80 and then lifting back north this afternoon as a warm
front. This will result in a varied wind regime today, with
breezier south winds prevailing in our southern zones today
(gusts at least 25-30 MPH especially in KS), while lighter
breezes prevail especially in our north from a variety of
directions (including northerly/easterly) as the front stalls
out. Temperature-wise, the vast majority of our CWA should soar
into the mid-upper 90s (with 100 possible mainly in KS), but the
presence of the stalling front should keep roughly our
northwest 1/4 (mainly north of a Lexington-Fullerton line) a bit
cooler in the upper 80s-low 90s. However, some areas near the
boundary could also see the highest humidity levels with
dewpoints most favored to be in the upper 60s to around 70 at
peak heating. The net result will be widespread heat index
readings of upper 90s to around 104 across most of the
southeastern 3/4ths of our CWA. This puts us VERY close to
official Advisory criteria, but for many of the same reasons
given by previous forecaster (and also the fact we`ve already
had a few pretty hot days recently so this is not a "totally
new" thing this season), have opted against issuing one.

Turning to thunderstorm potential, this is admittedly a
frustrating, type of "all or nothing" forecast. Leaning on
higher-res CAM models as usual in the very short term, on one
hand recent HRRR runs have the capping (warm air aloft) winning
out and keeping our entire CWA storm-free through the evening.
However, other models including the often-over-aggressive
NAMNest (but also deterministic NAM/GFS/ECMWF runs) suggest that
at least isolated/spotty storms could erupt along the
aforementioned surface front anytime from around 4 PM into the
evening. A perusal of both plan-view and forecast sounding data
reveals that this will clearly be one our first truly "huge
instability/CAPE days" of the year, with considerable mixed-
layer CAPE around 4000 J/kg possible near the front during peak
heating. The bottom line is that IF the cap is breached a few
storms could become severe quickly, with the saving grace that
deep-layer shear appears to be fairly weak (20-30KT). Even so,
given that much instability, hail to at least golf ball size and
some damaging winds cannot be ruled out. Overall agree with SPC
on keeping it "only" a Marginal Risk categorically (level 1 of
5) especially given the conditional nature of the threat, but
IF storms go it could get active quickly.

No matter what does/doesn`t happen late this afternoon-evening,
especially post-midnight the vast majority of active/possibly
severe convection should focus at least slightly north of our
CWA into northern NE/southern SD within the exit region of a
powerful low level jet. That being said, at least spotty/weak
elevated convection could from within this low level jet axis
especially within our western zones and am carrying some low
chances/PoPs to cover this.


- MONDAY-MONDAY NIGHT:
Although at least spotty/weak elevated showers/storms cannot be
ruled out especially during the morning, compared to today,
there is overall-less concern about potentially severe storms
developing overhead during the later afternoon-evening, as that
focus should clearly reside to our north as the surface front
will have surged north of our entire CWA by then. Even so, will
carry some slight chances for storms mainly far north in the
evening, just in case. Overall though, the big stories Monday-
Monday night will be more heat, but this time with more
wind...in fact quite a bit of wind by mid-June standards. Actual
high temps will be fairly similar to today most areas solidly
90s), but with dewpoints expected to "mix out" a bit more, heat
index readings should MOSTLY top out slightly under 100 degrees.
Wind-wise, have nudged up wind speed for the afternoon-overnight
hours, with sustained southerlies of 25-35 MPH and gusts of
40-45 MPH looking increasingly likely as seasonably-strong low
pressure deepens to around 990 millibars over western NE.


- TUES-TUES NIGHT:
Various models are in excellent agreement that a decent cold
front will arrive during the day, turning winds northerly and
beginning a cool-down, and also likely sparking at least a
narrow corridor of afternoon storms along the front. Tues
evening-overnight, more widespread convection will likely
blossom across the area as forcing increases north of the
surface boundary, with at least limited severe storm potential
in play (SPC Marginal Risk) along with heavy rainfall/localized
flooding potential (currently a WPC Slight Risk for excessive
rain).


- WED-THURS:
Healthy rain chances continue especially Wed-Wed night, as Wed
clearly looks to be the coolest day of the week and has trended
a few degrees cooler yet (highs most places aimed mid 60s to
upper 70s). However, winds turn southerly again Thurs and allow
another warm up to begin (highs mainly 80s).


- FRI-SAT:
Admittedly spent VERY little effort looking at these days, but
a quick glance at latest ECMWF/GFS suggests Friday should be
mainly dry and breezy from the south (highs well into 80s to
around 90 again), with a possible disturbance bringing back
increasing storm chances for Sat and probably more so Sat night.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 705 AM CDT Sun Jun 16 2024

For KGRI/KEAR Airports:
- General overview:
Confidence is medium-high in VFR ceiling/visibility and also
rain/thunderstorm-free conditions through the period, although
there is at least some concern (low probability...around 20%)
that a robust/perhaps severe storm could rapidly develop in the
general area late this afternoon-evening near a weak surface
boundary (this bears close watching). However, of high
confidence is that the the main story of the period will be
winds, and in particular separate periods of low level wind
shear (LLWS)...the latter more intense than the former.

- Ceiling/visibility/rain and thunderstorm potential details:
Confidence is high in VFR ceiling/visibility through the period,
with perhaps a scattered lower-VFR cumulus field developing this
afternoon, but otherwise any clouds mainly near-to-above 10K ft.
As for shower/thunderstorm potential, odds still appear to favor
the entire period staying dry (80-90% chance). However, in the
slight chance (10-20%) that thunderstorms DO manage to develop
late this afternoon (mainly after 21Z), they could quickly
intensify in the vicinity of the terminals (probably favoring
KEAR more so than KGRI), so short-term trends bear close
watching. Considered introducing a low-confidence VCTS to mainly
KEAR with these TAFS, but with any possible thunderstorm threat
beyond the first 6 hours opted to hold off and let later
issuances assess further.

- Winds:
- Surface winds:
Much of the period will be fairly breezy, but particularly right
away this morning (mainly KGRI) and then again later this
afternoon into tonight at both sites. While direction will
prevail southerly to southeasterly the vast majority of the
time, the presence of a stalling front will probably result in
variable directions at times especially between 14-20Z (but also
lighter speeds). The overall-strongest speeds will focus later
this evening-overnight (sustained 15+KT/gusts around 25KT).

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

1) Right away this morning through around 14Z, southwesterly
winds within roughly the 1,500 ft. AGL will continue around 40KT,
creating marginally TAF-worthy shear magnitude around 30KT
between the surface and this level.

2) This evening-overnight (starting 03Z but really ramping up by
06Z), 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 550 AM CDT Sun Jun 16 2024

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

Both tonight-Monday morning and Monday night-Tues morning are
expected to remain very warm, with most of our CWA not dropping
any cooler than 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,
because a cold front arriving Tuesday 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)               71


- 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...Pfannkuch
AVIATION...Pfannkuch
CLIMATE...Pfannkuch