450
FXUS63 KGID 160508
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1208 AM CDT Thu May 16 2024

.KEY MESSAGES...

- In the very short term (next 5-6 hours or so): Marginal Risk
  for a few severe storms is the primary concern...mainly a
  hail/wind threat. Could even see a few strong/possibly severe
  storms outside (west of) the official SPC Marginal Risk.

- Late tonight through Saturday evening, our forecast remains
  dry area-wide...with the main stories through that time frame
  being a decent warm-up (widespread 80s especially Friday) and
  a return to breezy/windy conditions (out of the south
  Fri/north Sat). Prior to that, Thursday`s weather looks
  spectacular!

- Unsettled weather returns perhaps as early as later Saturday
  night, but more so Sunday-Monday. Although we are not yet
  officially "outlooked" for severe storms by SPC, latest model
  data (along with CSU machine-learning probabilities) certainly
  suggest these are our next potential "day(s) of interest".

- On a "side note": although many folks have probably assumed
  this already, it`s becoming increasingly-apparent in model
  data that any chance of a "sneaky" late-season frost/freeze
  is looking increasingly-minuscule (probably 5% chance at
  most), with the very coldest nights through the end of May
  currently looking to drop no lower than 40s.

&&

.DISCUSSION...
Issued at 413 PM CDT Wed May 15 2024

-- PRIMARY CHANGES TO THIS 7-DAY FORECAST VERSUS THE PREVIOUS
 ONE (issued Wed AM):

- In the shorter term:
Minor upward nudges to high temps Thurs-Fri, with wind speeds
(mainly gusts) boosted about 5 MPH higher for Friday (southerly
gusts easily 20-25+ MPH especially Nebraska zones).

- In the longer term:
Rain/thunderstorm chances (Pops) were raised a bit for Sunday
(as mentioned above, possibly our next shot at severe storms).


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

- CURRENT/RECENT WEATHER SCENE AS OF 3 PM:
Overall, no big surprises to speak of. As I type, isolated to
scattered showers and a few weak thunderstorms are roaming
various parts of our coverage area (CWA), but have (thus far)
showed no strong push toward going severe. Over the course of
the day, spotty rainfall has generally drifted from west to east
across much of the area, prompting considerable mid-high level
cloud cover and muting a temperature rise, although some
increased breaks in the cloud cover should allow most areas to
eventually top out somewhere in the 68-74 range.

In the big picture of the mid-upper levels, water vapor imagery
and short term model data clearly depict a moderately-strong,
progressive shortwave trough passing eastward along an axis
centered from Nebraska up into the Dakotas. At the surface, a
fairly weak (1008 millibar) low is centered over the SD/MN
border area, with a weak cold front trailing south-southwestward
which has effectively cleared all but our extreme southeastern
CWA. As a result, winds in most of our CWA are currently out of
the west to northwest around 10 MPH.


- LATE THIS AFTERNOON-OVERNIGHT:
Obviously spotty severe storm potential is our main concern.

Starting with some general thoughts:
1) Fully agree with SPC keeping our risk category as Marginal
(level 1 of 5). Although the potential is certainly there for a
few severe storms (and even some transient supercell structures)
given widespread mixed-layer CAPE 500-1500 J/kg and respectable
(but not overly-strong) deep layer wind shear of 30-40KT), the
widespread clouds/weak convection so far today have "junked up"
the environment somewhat, as evidenced by mid-level lapse rates
(700-500 millibar layer) only 6-7 C/km, which will keep
instability/CAPE profiles on the "skinnier" side and in theory
limit the potential for hail much larger than quarter size. In
addition, low level shear is (and will remain abysmal),
rendering any tornado threat extremely low (barring some kind of
"mesoscale accident"). Clearly our CWA is on the northern
fringes of a more-concerning severe threat to our south (see
Enhanced Risk) along/south of the KS/OK border.

2) That being said, here at the local level we honestly wouldn`t
have minded seeing the Marginal expanded west to include more of
our western CWA, as latest higher-res models (HRRR/NAMnest)
suggest that the threat for spotty severe probably exists
almost anywhere in our CWA (not just the southeast half where
the "official" Marginal is assigned).

Attempting to decipher some more specific expectations:
As the late afternoon-evening wears on, the upper trough axis
will gradually pass overhead, largely coincident with the peak
heating cycle. Per higher-res models, we will continue to see at
least isolated/scattered redevelopment of showers/storms,
including a fresh batch that will likely enter our western
counties mainly after 5 PM. Coverage of any thunderstorms
(including weak ones) will probably remain fairly spotty, let
alone truly severe activity, but again will have to monitor
closely for at least marginally-severe hail/wind gusts here or
there.

With no low level jet in play whatsoever this evening, severe
storm potential is primarily instability-driven, and strongly
tied to afternoon-early evening heating. As a result, any severe
storm threat that might materialize should really fade by 9-10
PM. In fact, our official forecast has storm chances ending
altogether by 10 PM within about our northwest half, and
eventually vacating even our far southeast zones by no later
than the 12-2 AM time frame.

Once showers/storms move out:
The late overnight hours should be dry/uneventful, with skies
clearing to at least some degree (especially north half) while
more clouds (mainly higher level) hang on south. Although
probably cannot rule out some late night/early morning patchy
fog especially in our southeast 1/3, have held out of official
forecast for now as: 1) light north-northwest breezes should
prove unfavorable for widespread fog development...2) higher-res
visibility progs from HRRR/RAP keep main fog potential at least
slightly south-southeast of our CWA. Lastly, nudged low temps
down very slightly for tonight, ranging from mid-upper 40s
northwest, to around 50 central, to mid 50s far southeast.


- THURSDAY DAYTIME-NIGHT:
In the wake of our departing disturbance, we will reside under
uneventful west-northwest flow...leaving high confidence in a
dry and seasonably-pleasant 24 hours. Under no worse than mostly
sunny to partly cloudy skies, this will truly be a day to enjoy!
For one, it will be our last truly light wind day for a while,
with sustained speeds only averaging 5-10 MPH (mainly out of a
west-northwesterly direction). High temps were nudged upward
slightly, with most of the CWA now aimed 76-78. During the
evening-overnight hours, winds will flip around to southerly and
average 5-15 MPH. This will help hold low temps up about 2-5
degrees warmer than tonight, with most of the CWA aimed 50-54.


- FRIDAY-FRIDAY NIGHT:
High confidence in a dry forecast continues, as we remain under
benign, quasi-zonal (west-east) flow aloft, although a vigorous
shortwave trough will arrive into the western Dakotas late
Friday night. The main story for us will be a breezier and
warmer day, with with southerly wind speeds and temps nudged
upward from previous. In fact, Friday looks to be the overall-
warmest day of the next 7 for most of our CWA, with highs
currently aimed 82-85 most places. Daytime winds will be
overall-strongest in our Nebraska zones (sustained 10-20
MPH/gusts 15-25 MPH). Southerly breezes will stick around into
the night, keeping up the trend of overnight lows being a little
bit warmer than the night before (most places aimed 55-59).


- SATURDAY-SATURDAY NIGHT:
The aforementioned Northern Plains upper trough will remain to
our north as it heads into the Upper Great Lakes region.
Although suppose a passing sprinkle/high-based shower cannot be
ruled out, have kept the daytime-evening forecast dry, with the
main feature being a noticeable cold frontal passage (at least
wind-wise) during the day, marked by sustained north winds
15-20+ MPH/gusts 20-30 MPH. Temperature-wise, this front is not
overly-strong, as although highs were lowered very slightly, we
still are calling for mid-upper 70s central/northwest, to low
80s south-southeast. Late Sat night/early Sun AM, a weak wave
approaching from the southwest could spark our next thunderstorm
chances (probably not severe yet).


- SUNDAY-MONDAY:
Not going to go into great detail here, but as mentioned at the
top, these are likely our next days of concern for possible
severe storms (and more widespread thunderstorm activity in
general). Aloft, both the ECMWF/GFS filter weak/low amplitude
disturbances into our region in persistent west-southwesterly
flow aloft, As a warm front lifts north and instability builds
back in, Sunday afternoon-evening have early hints of being
active, with perhaps a bit of a break late Sun night-Monday AM
before another round of storms develops Mon afternoon-overnight.
(although instability levels are more in question for Monday
depending on how far south a cold front and/or outflow
boundaries from Sunday`s activity sinks). Temp-wise, both days
are currently projected into the upper 70s-low 80s most spots.


- TUESDAY-WEDNESDAY:
Our official forecast continues persistent, mainly low-end
(20-30%) PoPs during this time, but raw model data suggest that
Tuesday would likely be more active again as another upper wave
passes through, with Wednesday perhaps more likely to be dry in
its wake. Of course, these details are plenty murky at this Day
6-7 range. Temp-wise, there are hints of a slight cool-down, and
highs are aimed mainly low-mid 70s most places (upper 70s mainly
in KS zones).

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1204 AM CDT Thu May 16 2024

Dry weather with VFR conditions are forecast for this TAF
period, though will keep a close eye on those pre-dawn hours,
not totally out of the question for some patchy fog to develop
as cloud cover diminishes and winds stay light. Expect some fair
weather CU to develop midday/afternoon, but ceilings look to
stay VFR. Winds are on the light/variable side through much of
the morning, becoming more westerly late morning-midday and
staying that way through the afternoon. Speeds looking to top
out around 10-15 MPH. This evening winds are expected to turn
more southerly.

&&

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

&&

$$

DISCUSSION...Pfannkuch
AVIATION...ADP