798
FXUS63 KGID 241738
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
1238 PM CDT Wed Apr 24 2024

.KEY MESSAGES...

- Active pattern develops late tonight/early Thu AM and
  continues into the weekend. There is a Slight Risk (level 2 of
  5) for severe thunderstorms along and S of I-80 on Thu/Thu
  night, with a Marginal Risk (level 1 of 5) elsewhere.

- Lesser, but non-zero, chances for severe thunderstorms
  continues for mainly far E/SE portions of the forecast area
  Fri aftn and Sat eve/night.

- Ensemble output continues to suggest widespread, appreciable
  moisture is likely over the next several days. Latest EPS
  remains consistent from 24hrs ago with 25th-50th percentile
  amounts averaging 0.75-1.5".

- Friday will be windy out of the W/SW and there`s a 50-70%
  chance for gusts of at least 40 MPH. Fortunately, relative
  humidity looks to remain high enough to preclude a significant
  fire weather concern.

- After 60s/70s each day today through Saturday, cooler 50s/60s
  with wrap-around rain showers are expected on Sunday. We`ll
  dry out and warm up for the first half of next week.

&&

.DISCUSSION...
Issued at 515 AM CDT Wed Apr 24 2024

Heading into an active next few days, so quite a bit to discuss.
Overall, no major changes with this forecast, and appears
forecast confidence in some of the finer details is at least
trending in the right direction towards to moderate-high.

Today...
Will keep this brief as this is the calmest period of the next
several. Likely dealing with at least patchy frost in the usual
cold spots over the far W and N with current temps in the mid
30s. These are also areas that don`t typically see their last
frost worthy temps until early to mid May...so overall impacts
are probably pretty minor. Expect the band of light showers over
far SW zones to make little to no northward progress this AM,
before gradually fading after sunrise. Kept some mention of
sprinkles going through the daytime for most spots given incr
mid level cloud cover, but probabilities for anything measurable
are around or less than 10%. SErly winds will incr this aftn,
esp W of Hwy 281, but the clouds will hold temps back a bit from
peak potential...generally upper 60s to lower 70s. Mainly dry
conditions look to persist through the eve hrs.

Late tonight - early Thu severe potential...
The first window for potentially strong-severe storms will come
late tonight, but moreso in the early AM hrs of Thu; let`s say
from around 3AM to 10AM. This will come on the nose of an
increasing and veering low level jet (and associated theta-e
advection) and in conjunction with at least one or two low
amplitude perturbations embedded within 40-50kt SWrly H5 flow
ahead of a deepening trough in the Four Corners region. Exact
location of potential convective development remains a bit
uncertain, likely owing to minor, but important, differences in
structure of low level jet and placement of best convergence.
Nonetheless, EC has been very consistent with the idea that
elevated convection develops after 06Z in a NW to SE arc from
around MCK to ICT. 06Z HRRR and other members of the 00Z HREF
(sans the NAMnest) depict a similar, albeit weaker, scenario. If
convection can develop, it will likely be rooted between H85-H7
and be able to take advantage of very steep mid level lapse
rates (in excess of 8 C/km) and at least 35-45kt of effective
deep layer shear. Various MUCAPE progs have trended a bit higher
and prefer the 00Z HREF/06Z HRRR/03Z RAP idea that initial
values around 1K J/kg will quickly incr to ~2K J/kg by 15Z Thu.
Assuming convective indeed develops, believe this parameter
space is conducive to elevated supercells with large hail,
potentially up to golf ball size the main threat.

Thursday afternoon-evening...
The initial round of thunderstorms should weaken and/or shift
SE of the area by midday as the LLJ temporarily veers and
weakens. Additional elevated convection chances through the rest
of the daytime are low, but non-zero. Tend to think the primary
sensible weather for Thu aftn/eve will be cloudy, cool and
breezy with either drizzle or light rain showers. This is
evident by forecast soundings showing fairly classic drizzle
setup - saturated lowest 3-5K ft, persistent weak-moderate lift
within warm air advection, and stout mid level temp inversion.
Furthermore, the AM convection will likely only reinforce and
suppress the primary sfc warm front from making substantial
northward progress and keep it well SW/S of the CWA.
Accordingly, highs have trended cooler to mostly low- mid 60s.

Thursday night...
The next round of strong-severe thunderstorm potential looks to
come Thu night, either from 1) activity moving off the triple
point/dry line from W KS and growing upscale with strengthening
low level jet, possibly enhanced by the Pacific cold front
overtaking the dry line, or 2) from new development within
strengthening ascent associated with NEward ejection of
negatively tilted mid- upper level trough. With that said, exact
evolution is a bit uncertain as scenario 1 or 2, or a
combination of the two, seem equally plausible and each have
their pros and cons. Overall timing being late overnight during
late April argues against anything really robust and models seem
to be in decent agreement showing that any sfc based
instability only moves into some of our KS zones and only in a
narrow corridor. On the other hand, continued steep lapse rates
will keep at least moderate instability in play all night, and
it is a fairly robust shortwave trough. Overall timing of the
threat looks to be similar to the event from earlier this month
on the 15th/16th in that it`s largely near and after midnight. A
notable difference, though, is that the preceding low
stratus/drizzle likely precludes a significant northward surge
or establishment of steep low level lapse rates and sfc based
instability. Thus, tend to think large hail would be the main
threat (up to around golf ball size), with perhaps more of a
wind and iso tornado threat in north central KS, esp. if a
linear system develops.

Daytime Friday...
Majority of deep/strong convection is expected to race E/NE of
the area by dawn Fri AM as the mid level dry slot begins to
move in. Stacked low pressure over central Nebraska will likely
keep at least iso- scat shwrs/weak storms within environment of
low level wrap- around moisture and steep mid level lapse rates
going for areas near/N of the state line through much of the
daytime hours. As the sfc low deepens and wraps up, expect
strong SW/W winds by the aftn hrs. Latest EPS gives majority of
the forecast area a 50-70% chance for wind gusts of at least 40
MPH. Fortunately, the wrap around low level moisture should keep
all but maybe Rooks and Osborne Counties from seeing a
significant drop in RHs and incr in fire weather concerns.

Friday night through Sunday...
Appears Fri night through late Sat aftn will be a period of
mainly dry conditions with the area sandwiched between two
systems. This should make Sat the pick day of the weekend as
highs reach the upper 60s to upper 70s amidst mostly sub-25 MPH
wind. Rain and thunderstorm chances will ramp up Sat eve and esp
overnight as another mid level disturbance ejects NE through the
Plains. Main low level baroclinic zone and instability axis
should set up further SE with this wave, so think brunt of
severe risk will focus roughly along I-35 corridor. Could see
enough instability (mostly elevated) lag further to the NW
closer to the mid level low to keep a marginal hail threat going
for mainly SE half of the forecast area, but mid level lapse
rates should be quite a bit lower than Thu. Sun looks to be a
bit of a repeat of Fri in that there will be plentiful cloud
cover, wrap around moisture, and cool temps. Wind gusts don`t
look to be quite as strong. Latest WPC guidance and EPS output
are in alignment that majority of the area should receive around
0.75-1.5" of total moisture over the next few days. High end of
the range (and perhaps locally even higher amounts) will tend to
favor the Hwy 81 corridor, while SW zones should tend to be in
the lower end of the range.

Expect a calmer pattern for at least first part of next week,
along with a trend toward warmer temps in the 70s and 80s.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1232 PM CDT Wed Apr 24 2024

Winds will remain out of the southeast with some gusts up to
around 20 knots likely this afternoon. Low ceilings are likely by
15z with wind shear possible around that same time. Showers are
also possible beginning at 06z.

&&

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

&&

$$

DISCUSSION...Thies
AVIATION...Schuldt