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000
FXUS63 KGID 251147
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
647 AM CDT Thu Apr 25 2024

.KEY MESSAGES...

- Elevated thunderstorms with marginally severe hail threat
  possible this morning near and south of the KS/NE state line.

- Next round of thunderstorms, which models are trending more
  intense with, expected to develop over and/or move into SW
  portions of the forecast area this evening, then continue NE
  overnight. Most widespread threat will be large hail, but
  damaging wind gusts and tornadoes will also be possible.

- Center of the upper low will only move slowly E/NE on Friday,
  which could keep the potential for renewed strong-severe
  thunderstorm development possible through the daytime. Areas N
  and E of the Tri-Cities appear most at risk.

- Expect a general lull in precipitation chances Friday night
  into at least the first half of the daytime Saturday.
  Thunderstorm chances will increase late Saturday afternoon
  into the evening, with more severe weather possible.

- Active weather continues into Sun, though details become more
  uncertain due to previous days` convection. Should finally dry
  out early next week as temperatures remain mild in the 70s/80s

&&

.DISCUSSION...
Issued at 415 AM CDT Thu Apr 25 2024

Very busy forecast this morning as there appears to be some
important trends in model data that would suggest greater risk
of severe, potentially significant, not only this evening, but
into Friday and possibly even Saturday, as well. Will take it
one round at a time below, then wrap up with total precipitation
expectations, and a brief look at general pattern next week.

Morning Thunderstorms...
Hi-res guidance has remained consistent in showing a NW to SE
band of elevated convection (which the EC has had virtually
every run for days) developing and expanding right through the
forecast area over the next few hours. If anything, model
guidance QPF has increased a bit, suggesting greater coverage
and perhaps more intense activity. Very steep mid level lapse
rates and effective shear magnitudes of 35-45kt will support the
potential for large hail, and perhaps even a few transient
elevated supercells, for areas mainly along and S of the NE/KS
state line through mid to late AM. However, model progged
MUCAPE has come in a bit lower than 24 hours ago which could
help limited the overall magnitude of the large hail threat. So
think nickel to half dollar size hail will be main concern. CAM
guidance remains consistent that brunt of organized activity
will shift SE into central/eastern KS for the aftn hours, though
can`t rule out some additional iso to widely scat showers or
weak storms at just about any today. More widespread sensible
weather this afternoon may turn out to be drizzle.

Thunderstorms This Evening-Overnight...
Will state up front that some of the recent CAM guidance has
trended towards initial development CLOSER to the SW fringes of
the forecast area, which means earlier arrival and thus
potentially more significant threat. 00Z/06Z HRRR runs would
fall into this camp, as well as some HREF members. Instead of
what appeared to be an after 03Z, and frankly more like after
06Z, timing has now trended more towards the 23Z-02Z time frame,
at least for areas like Furnas, Phillips, and Rooks Cos. Still
looks like timing for Tri-Cities will be well after sunset as
convective intensity begins a downward trend in intensity...just
not sure how QUICKLY the downward trend will ensue, however.
Probably most concerning with the most recent model runs is the
signal for scattered very intense supercells to develop near a
sfc triple point in GLDs forecast area, and remain at least
semi- discrete for longer as they quickly track NE into far SW
CWA during what is climatologically an uptick in probabilities
for tornadoes as LCLs lower and the low level jet ramps up. Any
particular scenario/evolution is far from certain, though, as AM
convection could both help and hurt later convection, and there
will be some mid level capping to contend with. The AM
convection will likely reinforce the warm front and serve as a
limit to the NEward extent of surface based t-storm and legit
tornado threat. Again, some of the guidance brings the triple
point slightly further N/NE by 00Z, which at least brings into
play the potential for a supercell tornado into a few of our far
SW zones. Models still have a tendency to "pinch off" the warm
sector S of the state line, and even Bunkers RM vectors would
take the supercells more N/NE and ACROSS the warm front and less
so eastward ALONG the warm front. So most plausible evolution
would be for convection bec increasingly elevated late evening
into the overnight and pose primarily a large hail threat (up to
around golf balls) considering continuation of steep lapse
rates (near or above 8 C/km), strong shear (50+kts) and moderate
instability. Main severe threat should conclude by ~3AM Fri.
Mesoanalysis will be key to communicating afternoon and evening
trends, but from what I`m seeing, one could make the argument
for expanding the Enhance Risk (level 3 of 5) into portions of
the forecast area SW of the Tri-Cities.

Scattered Thunderstorms Daytime Friday...
Believe there will be another decr/lull in convection Fri AM,
perhaps aided by advancing mid level dry slot. Both the sfc and
mid level low center are forecast to become stacked over the
Sandhills by 18Z. Mid-upper low will then take on increasingly
negative tilt as it moves NE into the Siouxland region Fri PM.
Arrival of the mid-level dry slot may contribute to some breaks
in the cloud cover and actually aid in some sfc-based
instability, perhaps as early as ~midday owing to close
proximity to pool of cold mid level temps. In fact, models now
indicate a lobe of near -20C at H5 tracking right through the
CWA during the daytime. Arrival of these cooler mid level temps
and strong ascent, in conjunction with aforementioned sfc
heating, could lead to rapid convective development as early as
16Z-18Z, roughly near the Hwy 281 corridor. Backed SErly sfc
flow beneath a northern punch of a strong mid level jet
(60-70kts at H5) will provide ample deep layer shear for
supercells, which when combined with low freezing levels and
steep lapse rates, could lead to some very large hail. High
ambient vorticity and backed sfc flow amidst 40-50kt of Srly
flow at H85 will lead to some tornado potential. Ultimately, the
threat for the GID CWA will come down to timing - the earlier
the development, the greater the risk/threat. Given it`s a
highly dynamic system, tend to favor earlier rather than later
development, thus why I think the potential for significant
severe weather may be incr for areas along/E of Hwy 281 Fri
aftn. Additional low-topped supercells directly beneath the mid
level cold core (high shear, lower CAPE) could also present an
isolated tornado threat, perhaps back as far NW as Ord. Overall,
this feels like it has some similarities to the event that
produced the highly photogenic Greeley County tornado last
spring which also produced due to early and further W dev. A
potential failure mode to this scenario would be for widespread
convection tonight to sweep E/NE, taking with it the primary
instability axis to our E. However, even if this occurs, hard to
completely remove the threat anytime there`s -20C above you at
H5 during the daytime hours. Should see a more distinct lull in
precipitation Fri evening through at least early Sat aftn.

Saturday PM into Sunday Thunderstorm Chances...
Already murky details in the short term become even murkier by
Sat, though it seems like there`s been a bit of a trend N and W
with the instability axis Sat aftn/eve, which could bring sfc-
based convection more into play for at least far E/SE zones.
This subtle trend is reflected in the latest SPC Day 3 Outlook
which brings a Slight Risk (level 2 of 5) into areas along and
SE of a line from Phillipsburg to York, and an Enhanced Risk
(level 3 of 5) right up to the Mitchell County line. By late
afternoon, expect a sfc low/triple point to set up somewhere
over central KS, with a stationary/warm front extending NE, and
a dry line extending to the S. In terms of significant severe
potential, the question will be how far W and N does the warm
sector, and associated risk for sfc-based supercells, become
established. Is the triple point back towards
Hays/Russell/Plainville...or is it more towards Salina and Great
Bend. Fairly small difference in the grand scheme of things, but
key to specific threats. NBM highs are now creeping into the
lower 80s far SE zones, further suggesting that NWward trend.
Within the warm sector, all modes of significant severe will be
fairly likely (Day 3 Enhanced is not thrown out like candy in a
parade) beginning late afternoon and continuing into the eve.
Further back to the NW, still think scat to widespread
convection will develop in these areas as heights fall and
ascent incr ahead of next strong shortwave disturbance. While
the threat for sfc-based supercells (and thus tornadoes) will be
lower in this area, threat for large hail will persist owing to
magnitude of the CAPE/shear/lapse rate parameter space.

Actual sfc/upper disturbance doesn`t kick through the Plains
until Sunday. Similar the Fri, there could be a significant
gradient in sensible weather from cool/cloudy NW to much warmer
and more unstable to the SE. Exactly where this zones sets up
remains pretty uncertain, but if anything, there`s been a wobble
to the NW in 00Z EC guidance. Mid level lapse rates should
finally see a significant decr to closer to 7 C/km, so
instability won`t be quite as large. Strong shear will still be
in place, though. Would like to see more model and run
continuity before really latching onto idea of continued severe
threat into Sun as conceptually speaking, seems most likely that
primary instability axis would favor areas to the SE near I-35.
Any wrap around showers should exit/end Sunday night.

Total Precipitation Amounts...
Deterministic QPF has edged higher, likely owing to greater
potential for stronger/deeper convection tonight and Sat
eve/night. Most areas still seem primed for a solid 0.75-1.5",
though it`s worth pointing out that a sharp drop-off in amounts
is not too far to the S/SW in central KS. Hopefully, this
doesn`t creep into Rooks/Osborne Counties. As always with
convection, there will be winners and losers. Still think with
locally higher amounts that flooding concerns are low since it`s
been dry as of late and there is time between each round.

Latest ensembles indicate mild temperatures for next week, and
mainly dry conditions for at least the early part of the week.
Various rain/storm chances return for mid to late week, but
signal for anything more specific is just too messy attm.

&&

.AVIATION /12Z TAFS THROUGH 12Z FRIDAY/...
Issued at 642 AM CDT Thu Apr 25 2024

Expect significant deteriorations to aviation conditions this
period, particularly during the day today.

Band of showers and thunderstorms will move in from the W over
the next couple of hrs. Appears greatest potential for strong
storms and perhaps some hail will remain S of the terminals.
This first wave should exit by mid to late AM, but in it`s wake,
models show quick lowering of CIGs to MVFR and even IFR by
around midday. Seems quite likely even further deterioration to
IFR or near LIFR will occur during the aftn or eve, and
possibly be accompanied by minor VSBY reductions and drizzle or
light rain showers. The next round of thunderstorms is forecast
to develop SW of the terminals late this afternoon or early
evening, then race NE to the I-80 corridor around 01Z-03Z.
Storms tonight could be severe with mainly a large hail threat.
IFR to LIFR CIGs will likely prevail overnight and into Fri AM.
Vast majority of the thunderstorm activity will move out by
around 09Z Fri. Confidence: Medium.

Winds will be on the incr out of the SE, becoming brzy within
the next couple of hours. Sustained winds of 15-20kt and gusts
of 30-35kt are likely for majority of the daytime hrs, and even
into tonight. May need some low level wind shear overnight, but
given the expected continued strong sfc winds, opted not too
include a marginal LLWS at this time. Winds will shift to the SW
then W on Friday and become even stronger. Confidence: High.

&&

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

&&

$$

DISCUSSION...Thies
AVIATION...Thies