985
FXUS63 KGID 171053
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
553 AM CDT Mon Jun 17 2024

.KEY MESSAGES...

- Another day, another VERY UNCERTAIN risk for possible severe
  thunderstorms mainly in the 5 PM-midnight time frame, as it
  will be another "battle" between very warm air aloft (serving
  as a cap) and high instability. IF we end up with a later-day
  severe threat, it would mainly favor Nebraska areas west of an
  Alma-Kearney-Fullerton line.

- Although hot again this afternoon across most of our area
  (especially south), heat index readings are expected to be
  peak SLIGHTLY lower than yesterday, with most of our Nebraska
  area topping out 95-99 and any possible low-100s most favored
  in our KS zones (but still short of official Advisory
  criteria).

- This afternoon and especially this evening-overnight will be
  unusually-windy by mid-June standards, sustained southerly
  speeds commonly 25-35 MPH/gusts up to around 45 MPH.

- A seasonably-strong cold front will arrive Tuesday and stall
  out near our southern fringes through Wednesday before lifting
  back north. The net result will be the potential for several
  rounds of rain/thunderstorms across the region, with not only
  at least a narrow zone of severe storm potential mainly Tues
  afternoon-evening, but also a wider swath of perhaps at least
  2-4" of rain across much of our area over the course of these
  36-48 hours (at least localized flooding possible).

- High confidence that Wednesday is the coolest day of the week,
  with widespread clouds/rain holding most places down in the
  60s-70s for highs.

- Thursday-Sunday: Although not as overall-rainy as Tues-Wed
  will be, intermittent, lower-confidence chances for
  rain/thunderstorms continue almost every day or night for at
  least parts of our area, with at least occasional/limited
  chances for strong to severe storms and localized heavy rain.

&&

.DISCUSSION...
Issued at 552 AM CDT Mon Jun 17 2024

-- Up front "admin note": Given a very complex short term
 forecast with multiple pesky concerns/uncertainties, will keep
 the main part of this discussion focused ONLY on these next 48
 hours (through Tues night).


-- SHORTER TERM FORECAST OVERVIEW/HIGHLIGHTS (through Tues
 night):

-- CURRENT/RECENT WEATHER SCENE AS OF 5 AM:
On a very positive note (and as suspected as a definite
possibility here in last few discussions), most of our coverage
area (CWA) was "saved" from a severe thunderstorm threat Sun
afternoon-evening as a strong cap (warm air aloft) held firm.
Although we had one radar-indicated marginally-severe storm in
Phelps/Harlan counties, it quickly died with nightfall, and the
vast majority of stronger overnight and ongoing activity has
concentrated at least slightly north of our CWA within the exit
region of a strong 40-50 KT low level jet (evident at 850
millibars).

That being said, a fairly expansive outflow boundary has settled
considerably farther south into our CWA than expected even 6
hours ago...marked by northerly/easterly winds that have worked
southward through roughly the I-80 corridor (this will make
especially hour-to-hour temperature/wind forecasting this
morning VERY tricky).

Precip-wise, a smattering of isolated-scattered, high-based
showers/thunderstorms (rooted well above the surface) are
affecting parts of mainly our western/northern CWA at this
time, with especially the northern activity in/near Nance County
being aided by the low level jet lifting air upward over the
top of lower-level outflow. None of this activity is
particularly intense (nor is it expected to be), but occasional
wind gusts into 40-50 MPH have occurred near storms.

Temperature-wise, the pesky outflow boundary down to near I-80
has dropped much of our northern CWA unexpectedly far down into
the 60s this morning, but unseasonably-warm readings in the 70s
counties are present especially Highway 6 southward into KS
where southerly breezes still prevail (the jury is still out
regarding whether or not Grand Island/Hastings will set new
record warm low temps for today...as it all depends on the
aforementioned outflow (see separate CLIMATE section below for
details).


-- TODAY-TONIGHT:
Will admit up front that confidence in how today plays out is
(if anything) a bit lower than even 12 hours ago, especially in
the temperature-wind department this morning, as depending on
how slowly/quickly southerly winds become re-established,
especially parts of our northern half may not get as hot as
expected today (stay tuned for potentially noticeable
adjustments to hourly and possibly even daily high temps in
later forecasts).

But, focusing on the basic expectations by topic:
- Isolated to scattered (and most likely non-severe)
  showers/storms will continue to develop/stream overhead
  through much of this morning, but should gradually diminish
  fade away with time as the low level jet weakens.

- Other than perhaps some rogue sprinkles/very spotty showers,
  the vast majority of our CWA is probably looking at a dry
  afternoon-evening.

- However, like yesterday, it will be another battle between
  warm air aloft (mid level/700 millibar temps even warmer than
  yesterday...at least 13-15C), and healthy instability/mixed-
  layer CAPE expected tor each at least 2500-3500 J/kg by peak
  heating.

- Based on how yesterday turned out, feel that UNLESS outflow
  boundaries from this morning linger around longer than
  expected and provide a focus for late afternoon-evening storm
  development, it is quite possible that our ENTIRE CWA will
  remain capped, with the main potential for severe storms
  focusing at least slightly off to our west-through-northwest
  where surface moisture convergence might be a bit more
  focused.

- However, IF anything is able to break through the cap within
  our northern/western CWA late this afternoon-evening, it could
  quickly become severe, capable of producing large hail to at
  least golf ball size, damaging winds 60+ MPH and MAYBE a brief
  tornado, but this would depend on a mesoscale boundary being
  present. One limiting factor would be fairly weak deep layer
  shear of only 20-30KT. Currently expect the post-midnight
  hours to be dry with activity focusing well to our north by
  that time.

- In summary regarding storm potential: Feel that the SPC
  Slight/Marginal risk areas are probably plenty generous into
  our CWA, and should be viewed as very CONDITIONAL (much like
  yesterday).

- Temperature-wise, assuming skies clear sufficiently in time
  and southerly flow is able to re-establish northward across
  the CWA, high temps should reach at least the low-mid 90s most
  areas (upper 90s most favored in KS). Fortunately, heat index
  values should hold below 100 today most areas (possibly
  reaching 100 or very slightly higher in KS), but falling short
  of Advisory criteria. Assuming no "surprise" outflow
  influences, low temps tonight should hold up in the 70s area-
  wide.

- This afternoon-tonight, deepening low pressure to our west
  will induce increasing southerly winds area-wide (unusually
  strong for mid-June). Sustained southerly winds commonly
  25-35 MPH/gusts up to around 45 MPH and would not be surprised
  if a rogue 50+ MPH gust happened overnight especially in our
  west.


- TUESDAY-TUESDAY NIGHT:
The main basic story is that a well-anticipated cold front will
gradually pass through the CWA from north to south during the
day, likely stalling near our far southern/southeast edges by
late afternoon. There is some uncertainty into exactly how fast
this front moves in, which also leads to resultant uncertainty
in temps/location of best storm chances.

- Rain/thunderstorm potential:
The morning could feature the first spotty, elevated (and likely
weak showers/storms) just behind the front. However, by mid-late
afternoon (peak heating), a narrow line of strong to severe
storms is expected, with higher-res models currently focusing
this activity within the southeastern 1/3 of our CWA. This would
mainly be a hail/wind/heavy rain threat.

Then during the evening-overnight hours, concerns will increase
for a POSSIBLE more widespread heavy rain event, as pronounced,
west-southwest to east-southeast corridor of convergence
develops in the 850-700 millibar layer (north of the surface
front). While NOT EVERYBODY will see truly heavy rain, could
envision at least a 50-mile corridor of our CWA picking up a
widespread 2-4" of rain, and this will need closely monitored
for possible flooding concerns (WPC has our entire CWA under a
"strongly worded" Slight Risk for excessive rainfall).

- Temperatures/winds:
Could easily see some areas end up 5+ degrees cooler/warmer
depending on exact frontal timing, but for now have daytime
highs aimed from low 80s far north/west-central, to mid 80s
central, to upper 80s-low 90s far southeast. No matter what, at
least slightly cooler than today all areas. Low temps Tues night
should bottom out at least 10-15 degrees cooler than Monday
night (most areas mid 50s to lower 60).

The north winds behind the front Tues daytime do not look
overly-strong (gusts probably 20-30 MPH...not as strong as the
southerlies out ahead of it).

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 114 AM CDT Mon Jun 17 2024

For KGRI/KEAR Airports:
- General overview:
Although there are small chances (mainly 10-20%) for a few
passing showers/thunderstorms both at some point this morning
and perhaps again Monday evening, odds favor an overall-dry
period and confidence is overall very high in VFR
ceiling/visibility throughout. That leaves moderately-strong
southerly surface winds and even stronger low-level winds as by
far the main concern (including two separate low level wind
shear/LLWS groups).

- Ceiling/visibility/rain and thunderstorm potential details:
Particularly between 10-17Z, there is a chance that a few
showers/likely weak thunderstorms will pass through, but with
overall-probability of occurrence and expected impacts fairly
low, will only include a generic "vicinity shower" (VCSH)
through part of this time frame for now. Although a few to
scattered lower-level VFR clouds are possible at times,
confidence is overall-high in VFR ceiling/visibility throughout.

- Winds:
- Surface winds:
By mid-June standards, this will be a fairly windy period.
Assuming no unexpected influences from convective outflow
boundaries, speeds will prevail southerly throughout, with
sustained speeds commonly 15-25KT/gusts 25-35KT.

- Low level wind shear (LLWS):
There are two separate periods of TAF-worthy LLWS during the
period, even despite the surface winds being plenty breezy
themselves.

1) Right away this morning through around 14Z, southwesterly
winds within roughly the lowest 2K ft. AGL will top out around
50KT, promoting roughly 30-35KT of shear magnitude between the
surface and this level.

2) This evening (02Z onward), if anything an even stronger
southerly low level jet will kick in, with speeds within roughly
the lowest 1,500 ft. AGL accelerating to around 55KT, causing
fairly strong shear magnitude at least 35-40KT between the
surface and this level.

&&

.CLIMATE...
Issued at 552 AM CDT Mon Jun 17 2024

-- Regarding possible RECORD WARM LOW TEMPS on Monday
(June 17th):

Overnight temperatures both this morning (Monday AM) and again
Tuesday AM will end up being quite warm, with many places
especially south of I-80 holding up well into the 70s. Depending
on how far south an outflow boundary manages to drift this
morning, potential June 17th records for warmest low
temperature COULD be threatened at Grand Island/Hastings
airports (the 2 sites for which we issue formal Record Event
Reports/RERs).

Please note that NO records are expected to be set on Tuesday
the 18th, as despite very warm early morning lows, a cold front
arriving during the day and evening should easily drop temps
safely below record territory by midnight that night.


- GRAND ISLAND
                   Record Warm Low      Latest Forecast
Monday June 17th     74 (1906)               74
                                       (but could abruptly
                                        be cooler if outflow
                                        boundary passes through)


- HASTINGS
                   Record Warm Low      Latest Forecast
Monday June 17th  72 (2020/2014/1946)        74


NOTE/REMINDER: in order for a new record warm low/minimum
temperature to become official it has to "survive" the entire
24-hour calendar day (in other words, it is not always based
solely on the early-AM low temp).

&&

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

&&

$$

DISCUSSION...Pfannkuch
AVIATION...Pfannkuch
CLIMATE...Pfannkuch