670
FXUS63 KGID 230027
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
727 PM CDT Wed May 22 2024

...Aviation Update...

.KEY MESSAGES...

- Can`t rule out an isolated shower/storm late tonight-early
  Thursday morning across southern portions of the forecast area
  (20 percent chance)...but most locations should have a quiet
  evening/night.

- Threat for thunderstorms increases late in the day Thursday-
  Thursday night (70-90 percent chances), with the potential for
  severe weather...most of the forecast area is included in the
  SPC Day 2 Enhanced Risk area.

- A few isolated storms are possible mid-late afternoon, but by
  far the better chances will be mid evening on into the
  overnight hours...mainly between 8PM-3AM. Wind gusts of at
  least 70 MPH looks to be the primary threat, but large hail up
  to the size of golf balls and brief spin-ups are not out of
  the question.

- Following a dry Friday, chances for thunderstorms return Sat-
  Mon, with the best chances looking to be Saturday evening
  through Sunday evening. Details regarding the potential for
  strong/severe storms (mainly Saturday) are uncertain at this
  time.

&&

.DISCUSSION...
Issued at 421 PM CDT Wed May 22 2024

Currently through tonight...

Been a pleasant day across the forecast area today...upper air
and satellite data show mainly westerly flow in place across
the Central Plains, set up under weak ridging between areas of
low pressure spinning over the western Great Lakes/Ontario and
over the Pacific NW. Satellite imagery also shows outside of a
bit of fair weather CU over northeastern portions of the area,
skies are sunny. At the surface, high pressure extending through
KS into MO, keeping winds westerly across the forecast
area...generally around 10 MPH, but there have been occasional
gusts closer to 20 MPH. A few locations may end up a couple
degrees short of expectations, but overall things have worked
out, with 3PM temps in the mid 60s to low 70s.

Looking at this evening into tonight, for most locations, it
should be a quiet period. Exception may be across southern
areas (near/south of the NE/KS state line), where some isolated
precipitation may develop, and have 20 percent chances going in
the forecast. Several models show at least spotty activity
sliding east after midnight through early-mid morning, driven by
subtle warm air advection/mid-level wave. Could end up being
little more than a few sprinkles...but some models do have the
potential for a hundred j/kg of CAPE to build north, so a few
thunderstorms (non-severe) are not out of the question. Winds
turn to the south with time tonight, as surface low pressure
moves onto the High Plains. Should see a few more clouds passing
through, overnight lows tonight are forecast to drop into the
low 50s.

Thursday and Friday...

Next widespread chance for thunderstorms and potential for
strong/severe storms returns to the area Thursday-Thursday
night. At 12Z Thursday, models show that upper level low
currently over the Pac NW having shifted east into the ID/WY
border region...and by 00Z shifts into the WY/SD border area,
with a southward extending trough axis. At the surface, during
the daytime hours winds across the forecast area look to remain
southerly...as low pressure remains over the High Plains. A
sharper dryline is expected to develop over western
KS/southwestern NE, with cold front getting pushed southeast by
the upper level system. Where exactly this cold front ends up by
late afternoon-early evening still has some
uncertainties...ranging anywhere from the western Sandhills to
knocking on the door of our western counties. The increased
southerly low level flow (wind speeds of 20-25 MPH and higher
gusts possible) pulls in warmer and more moist air into the
forecast are through the day...with forecast highs climbing into
the upper 70s to mid 80s. Currently expecting much of, if not
all, of the 12-00Z time frame on Thursday to be dry...but do
have a 20 percent chance of storms during the 21-00Z time frame,
as some models show the potential for isolated activity to
develop in or near southeastern portions of the forecast area
(most models keep this activity to our east). The better, more
widespread chances will come during the evening-overnight hours.
Thunderstorms are expected to develop along that approaching
surface cold front to our northwest, then transition into a more
solid line/MCS and push southeast through our forecast area.
Models showing MUCAPE values of at least 2500 J/kg ahead of
this complex to tap into, deeper layer shear of 30-40kts
possible, better upper forcing and an increasing low-level jet
(40+kts)...threat for severe weather is a concern...and much of
the area is included in the SPC Day 2 Enhanced Risk area. Wind
gusts of at least 70 MPH look to be the main concern with this
complex...but large hail and brief tornadic spin-ups are not
out of the question. And while this activity will also have the
potential for torrential rainfall rates, it should be
progressive enough to keep spots from accumulating significant
rainfall totals. Main time frame for severe weather looking to
generally be in the 8PM - 3AM.

Forecast for Friday and Friday night remains dry, as we sit
under generally zonal flow in the wake of this upper level
trough axis. Breezy northwesterly winds behind the cold front
passage are expected to continue on into the day on
Friday...tapering off closer to 10-15 MPH by late afternoon.
Should see plenty of sun during the day, with partly cloudy
skies overnight...afternoon highs are forecast to range from the
mid 60s in the north to lower 70s in the south.

Memorial Day Holiday weekend and on...

Each day of the upcoming holiday weekend and Memorial Day itself
continue to have precipitation chances in the forecast...with
the best chances currently Saturday evening through Sunday
evening (40-60 percent chances at various times). Models
showing continued generally zonal flow in the upper levels, with
a couple of shortwave disturbances pushing through the Central
Plains, driving those weekend precip chances. Chances on
Monday/Memorial Day are a little more iffy...weekend chances
look more widespread across the area, Monday may just be
clipping north-northeastern portions. Confidence in overall
timing/location of these systems isn`t overly high. Details
about potential for severe weather, which would mainly be
focused on Saturday, are not clear-cut...much will depend on how
much instability can work its way back north into the forecast
area (more solidly southerly flow doesn`t look to return until
Saturday morning). The slower the return, the less opportunity
for notable instability to be in place. Will just how the next
couple days trend. Forecast dries back out for Tuesday...and is
currently dry for Wednesday as well, but again, will see how
things trend with Wed.

As far as temperatures go, not looking at any big swings either
way Saturday through Wednesday. Forecast currently has mainly
70s Sat-Mon (confidence isn`t overly high in that due to the
precip chances)...with mid 70s-low 80s for Tuesday and low-mid
80s for Wed.

&&

.AVIATION /00Z TAFS THROUGH 00Z FRIDAY/...
Issued at 727 PM CDT Wed May 22 2024

- General overview for KGRI/KEAR:
This is a very high confidence period with regard to VFR
ceiling/visibility (mainly only passing high clouds tonight and
a scattered low-VFR deck Thursday daytime). It is also a high
confidence period with regard to dry/thunderstorm-free
conditions (barring a rogue passing sprinkle after sunrise
Thursday morning). That being said, and briefly peeking ahead,
there is a good chance of thunderstorms (possibly severe)
lurking for later Thursday evening...which will obviously be
addressed further in the subsequent 06Z/12Z TAFs.

As for THIS valid period, increasing southerly winds will be
the primary aviation issue, along with a period of marginally-
strong low level wind shear early Thursday morning (mainly KEAR).

- Wind details:
- Surface winds:
The very-lightest winds of the period are right away this
evening (generally variable direction at-or-below 6KT). By 06Z,
a steadier southerly component will be established, and during
the daytime hours Thursday speeds will quickly ramp up with
winds mid-morning onward averaging sustained 20-25KT/gusts
30+KT.

- Low level wind shear (LLWS):
Although kept a formal LLWS group out of KGRI due to falling
slightly short of TAF-inclusion criteria, the shear magnitude at
KEAR appeared just strong enough to introduce from 09-13Z. More
specifically, southerly winds within the lowest 1-2 K ft. AGL
will increase to around 40KT, resulting in around 30KT of mainly
speed shear between the surface and this level.

&&

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

&&

$$

DISCUSSION...ADP
AVIATION...Pfannkuch