367
FXUS63 KGID 172350
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
650 PM CDT Fri May 17 2024

.KEY MESSAGES...

- Although a rogue, high-based shower or a few passing sprinkles
  cannot be totally ruled out in VERY limited spots late this
  afternoon into Sat AM, for sure the vast majority of our
  coverage area (CWA) will stay dry/storm-free until late Sat
  night-early AM.

- Particularly late Sat night through Tues, we enter a very
  unsettled pattern with several chances for
  showers/thunderstorms, some of which will likely be
  severe...particularly Sunday-Monday...although we want to
  make it very clear that DETAILS ARE STILL MURKY.

- Additional, intermittent shower/thunderstorm chances exist
  Wed-Fri, but overall these chances appear to be less
  widespread/spotty than Sun-Tues, and with an overall-lower
  severe risk (especially Wed).

- Temperature-wise: certainly nothing out of the ordinary by
  mid-late May standards, with highs most days somewhere between
  the upper 60s-low 80s, and lows most nights somewhere between
  the upper 40s-low 60s.

&&

.DISCUSSION...
Issued at 445 PM CDT Fri May 17 2024

-- PRIMARY CHANGES TO THIS 7-DAY FORECAST PACKAGE VERSUS THE
 PREVIOUS ONE ISSUED FRI AM:

Nothing major of note, but at least in the shorter term:
- nudged up winds (mainly gusts) a few MPH mainly for Sat AM
  behind the cold front (gusts around 30 MPH likely for at least
  a few hours).
- Delayed any mentionable (15+ percent) chances for
  thunderstorms Saturday night to AFTER midnight based on
  consensus of most models (including HREF)


-- 7-DAY FORECAST OVERVIEW/HIGHLIGHTS (heavily focused on the
 first 3 days):

- CURRENT/RECENT WEATHER SCENE AS OF 4 PM:
Overall, today has turned out very much as expected. Although
this will indeed likely end up being the warmest day most places
will see for at least the next week, if anything official highs
are on track to fall JUST short of this forecaster`s
expectations from this morning in some spots, with most places
likely topping out 85-89, and a few places mainly in our far
western counties most favored to tag 90. As expected, it`s been
a very breezy to somewhat-windy day, with southerly speeds
commonly sustained 15-25 MPH/gusts 25-35 MPH (overall stronger
in Nebraska zones than KS). Skies have been very sunny, except
for a smattering of high-based cumulus along a weak surface
trough axis in our far western counties. In the big picture
aloft, water vapor satellite and short term model data confirm
rather benign west-northwesterly flow aloft, as we are well
downstream from a vigorous shortwave trough churning eastward
across western MT.

- LATE THIS AFTERNOON-OVERNIGHT:
This forecaster is "100% confident that at least 98% of our CWA
remains void of rain"...especially of the measurable variety.
That being said, there is a very low chance (probably 5-10%)
that a rogue/high-based shower/non-severe thunderstorm MIGHT try
popping up mainly in our extreme northern zones between 5-9 PM
(corresponding to just after peak heating). However forcing is
meager and the best lower-level convergence looks to focus up
closer to the SD border, so have left our official forecast
dry/storm-free for now.

Otherwise tonight, aloft the aforementioned MT disturbance will
drive east into ND by sunrise. Our area will remain plenty far
south/removed from this for any truly active weather, but at the
very least a batch of mid-level clouds will drift in from the
west, with an outside chance that a few very late night-early AM
sprinkles could also try falling. However, with any such
activity so high-based and meager in nature, felt it was not
"ruining" our going dry forecast for. At the surface, the vast
majority of the night will feature continued steady southerly
breezes, with sustained speeds staying up 10-15+ MPH. However,
toward sunrise the leading edges of a cold front will enter far
northern/western zones, turning direction northwesterly. Low
temps tonight will hold up at least 3-8 degrees warmer than last
night most areas, with most places aimed 58-62.

- SATURDAY DAYTIME-EVENING (through midnight):
Unless some rogue sprinkles do indeed graze our southeast zones
between sunrise and mid-morning, this should remain a dry time
frame with departing mid level clouds giving way to abundant
sunshine. By far the main feature will be a period of breezy to
moderately-windy conditions behind the passing cold front, with
the leading edges of this front through all but our far
southeast counties by 10 AM, and through all areas by Noon. In
the wake of the front, north winds will be sustained at least
15-20 MPH/gust 25-30 MPH for at least a few hours. However,
speeds will steadily diminish in the afternoon while slowly
turning more northeasterly, making for what will honestly be
another rather pleasant mid-late afternoon time frame. Temp-
wise, this front is rather weak, and while most areas will be
5-10 degrees cooler than today, highs are still aimed into the
upper 70s-low 80s in our Nebraska zones, and low-mid 80s KS.
During the late afternoon-evening, some storms (possibly
strong) could try to fire along the cold front to our south-
southeast, but any such activity should remain 50+ miles south-
southeast of our domain.

- LATE SAT NIGHT-SUNDAY MORNING:
This is where things abruptly turn more active. As the first in
a series of low amplitude disturbances arrives in west-southwest
flow aloft, low level moisture will return northward as a
southerly low-level jet ramps up. Confidence is fairly high that
at least scattered (if not more widespread) thunderstorms will
blossom between midnight and sunrise, and track from west to
east across parts of our area, although exact north vs. south
placement is somewhat in question. While this activity should be
elevated, enough elevated instability/CAPE and sufficient shear
should exist to promote a few strong to marginally-severe storm,
mainly with a hail (to around quarter size) and brief heavy rain
threat (damaging winds less likely given time of day). The
majority of this activity should "clear" our eastern zones by
mid-late Sunday morning.

- SUNDAY AFTERNOON-EVENING:
This is where A LOT OF QUESTION MARKS BEGIN. The real million
dollar question is: will our airmass destabilize sufficiently to
to realize potentially robust late afternoon-evening storm
development (which if so could easily be severe), or will the
morning activity and or also lingering cloud cover really hold
down instability and "mute" our severe threat? These things are
yet to be pinned down, but for what it`s worth the latest 18Z
NAMNest would target our KS zones more so than our Neb zones for
a severe threat. The bottom line: nearly our entire CWA is under
a Slight Risk (level 2 of 5) from SPC for good reason, with
perhaps both a morning and late afternoon-severe threat on the
table. In other departments, for some of the same reasons above
(possible lingering clouds), confidence in high temps for Sunday
is not overly-high, and if anything have nudged most placed down
slightly, now aimed mainly upper 70s to around 80 in Neb, and
better odds for widespread 80s in KS.

- MONDAY-MONDAY NIGHT:
As if Sunday doesn`t still hold enough uncertainty regarding a
severe threat, the uncertainty only grows for Monday. Sticking
to only GENERAL model trends, it appears much of the daytime
hours could be fairly quiet/dry as we reside "in between" the
parade of low amplitude upper waves, but with the evening-
overnight hours holding another uptick in convection and
possible severe potential. That being said, it is starting to
look like most of our CWA (except may KS zones) will likely
remain north of the main west-east frontal boundary and
resultant highest instability (especially low-level
instability), which could also mute our severe threat somewhat
here (although large hail/heavy rain north of the boundary could
still be very well on the table). A lot to sort out here, but
cannot disagree with the SPC Day 4 severe risk area for now.

- TUESDAY-WEDNESDAY:
While fairly widespread rain and mainly weaker thunderstorm
activity could linger into especially Tues daytime, the general
expectation per latest ECMWF/GFS is that MOST of this time frame
will be overall-drier and less active as instability gets
shunted south. In fact, Wed looks to be the overall-coolest day
of the week with highs only upper 60s-low 70s most areas, and
also the least likely day of the week to carry a severe storm
threat (as supported by CSU Machine Learning progs).

- THURSDAY-FRIDAY:
By this time, primary models start to diverge even on the bigger
picture aloft, with the latest ECMWF a bit faster than GFS
bringing in another wave around Thurs night-Fri. For now, our
forecast simply continues to carry various, low-confidence
chances in intermittent showers/storms.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 648 PM CDT Fri May 17 2024

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

Tonight: VFR expected thru the night. Main concern will be incr
LLWS around 03-04Z in response to developing 45-50kt LLJ. The
LLJ will start off Srly, but then veer to SWrly just ahead of a
cold front. Sfc winds will also veer, though a bit slower than
just above the sfc. A wind shift from SW to NW will occur with a
cold front very near daybreak, and this will mark the end of the
LLWS as the primary LLJ is shunted E. Confidence: High.

Saturday: Sfc winds will quickly shift from SW to NW Sat AM and
bec brzy with gusts for at least a few hrs around 25-30kt.
Lighter N-NNE winds arrive for the afternoon. Not expecting much
for cloud cover, though a brief (~1-2hr) period of MVFR CIGs
can`t be ruled out immediately behind the cold front. Otherwise,
any clouds will be of the high level variety. Confidence: High.

&&

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

&&

$$

DISCUSSION...Pfannkuch
AVIATION...Thies