Severe Thunderstorm Warning 103, NWS Hastings, NE

AREA FORECAST DISCUSSION
National Weather Service Hastings NE
714 PM CDT Thu Jul 2 2020

.UPDATE...
Issued at 710 PM CDT Thu Jul 2 2020

Have increased PoPs to likely for tonight over the S/W due to
latest radar trends.

Latest SPC Mesoanalysis places 4000-4500 J/kg of MLCAPE over SW/W
portions of the CWA, with effective deep layer shear rather weak
at 25-30kt. Convection over SW NE/NE CO has grown upscale into an
organized/mature QLCS with a general motion to the ESE around
30kt. This would place arrival time to Furnas Co area around
0030-0100Z. This activity has generated a significant cold pool
(air temps in low to mid 60s under/behind line of tstms) and
several 50-70mph gusts have been reported...including 74mph just W
of KMCK. Given the weak deep layer shear, linear mode, organized
cold-pool...fairly high confidence that the greatest threat will
be strong-dmg winds of 50-70mph. Question is how long this will
last? While expect a gradual weakening trend, the current trends
suggest a svr threat will probably exist for at least areas from
Elwood to Stockton...with E extent of svr risk possibly as far E
as EAR to HJH. 0-3km shear vectors as well as Corfidi vectors
turning more SE-SSE suggests this activity should turn a bit as
this activity spreads E toward 04Z-05Z. Diurnal decr in
instability should help tstms gradually decr toward 06Z. Like the
general idea of both the HRRR and HRRREXP, though both are 1-2hr
too slow.

Reference SPC MD #1086 for latest thoughts on potential new watch.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 500 PM CDT Thu Jul 2 2020

Covering the first first 5 periods/60 hours in this section, by
far the main challenge are VERY tricky-to-forecast
rain/thunderstorm chances (PoPs), while confidence is considerably
higher in other elements such as high/low temperatures and winds.
To be very honest, these type of "summery" weather patterns with
subtle forcing aloft drive this forecaster nuts, because although
we "know" that most areas will be dry most of the time, there is
just enough potential for storms to mainly either roll in from
the west off the High Plains and/or form "randomly" overnight
along little low-mid level convergence zones (mainly rooted
between 850-700 millibars), that we just have to keep various low
PoPs in the forecast. Some of these low chances will certainly not
come to fruition, but others likely will.

As for severe thunderstorm potential:
By far our main concern (and the one that carries any kind of
modest-confidence at all) comes right away this evening-tonight,
as the potential exists not only for spotty/more isolated activity
almost anywhere, but also for possibly a more organized storm
complex/mesoscale convective system (MCS) rolling in from the
west. SPC currently has mainly western portions of our CWA
assigned a Marginal to Slight Risk of severe, and if anything,
kind of wish they would have more of our central counties in the
Marginal as they had in the previous outlook, as a severe threat
could easily extend to at least Highway 281 later if models such
as the HRRR/NAMNest are onto anything.

Briefly looking at the current/recent weather scene as of 430 PM:
Overall, it's been a dry day CWA-wide once the somewhat-unexpected
early morning showers/storms in our far southeast zones faded
away. Aloft, large-scale ridging dominates, but subtle embedded
waves along with upslope low-level flow to our west has really
ignited quite a bit of convection (some severe) to our west in the
CO/KS/NE border area. At the surface, east-southeast breezes of
generally 10-15 MPH with some higher gusts to around 20 MPH or
slightly higher have prevailed today. High temps have topped out
mainly upper 80s-low 90s.

In the interest of time, will finish this section with some
abbreviated comments on the next 5 night/day periods...

This evening-overnight:
See our latest Hazardous Weather Outlook (HWOGID) for our general
expectations, but while the entire area will be prone to at least
spotty convection at some point, our biggest concern will be with
whether a more organized MCS will roll in from the west sometime
after 7-8 PM. Worst-case scenario is a corridor of damaging winds
of 70+ MPH, but with relatively weak ambient shear, this will
depend more on how organized of an eastward-surging cold pool that
storms to our west can form. Even late in the night, would not be
surprised to see "random" showers/storms bubble up along mid-level
boundaries (much as what happened in our southeast this morning).
Low temps mid 60s west to around 70 east.

Friday daytime:
While confidence is high that most areas will be dry most of the
day, lingering activity from the overnight hours (likely non-
severe) could occur at least into the morning mainly within the
eastern half of the CWA, and have this covered with low PoPs. For
the afternoon, took a small chance and removed PoPs, calling for
dry conditions as any storm development should remain well to our
west. Otherwise, very similar to today temp-wise, with highs
mainly a few degrees either side of 90. Breezes also similar,
generally 10-15 MPH from the southeast with some higher gusts.

Friday night:
Although am not expecting nearly the potential for possible storms
that tonight holds (especially those rolling in from the west),
felt it was prudent to at least carry some basic slight chances
given continued subtle forcing overnight. Likely dry for most
areas though. Low temps upper 60s to around 70.

Saturday daytime (Independence Day):
Like today was and tomorrow should be, confidence is fairly high
that the vast majority of the CWA remains dry, with simply another
warm day with highs upper 80s-low 90s and slightly-breezy
southeast winds. That being said, this is just far enough out in
time that it falls into the time frame where our "default" multi-
model blend is more "in control" of the forecast, and because it
insists on some small rain chances being around, we continue to
call for low-confidence slight chances most areas.

Saturday evening-night:
Much like the daytime period, most raw model data leans toward a
dry evening-night for outdoor activities. However, especially our
far western counties could see some potential for evening storms
TRYING to drift in from the west. For now, will run with some
slightly toned-down Pops from the default multi-model blend, with
mainly 30 percent chances west and only 20s (slights) east. Low
temps aimed mid-upper 60s.

.LONG TERM...(Sunday daytime through Thursday)
Issued at 500 PM CDT Thu Jul 2 2020

General overview of this 5-day period:
Carrying the same theme of from the short term above, there is
certainly more confidence regarding temperatures through this time
frame than in "exact" rain/thunderstorm chances (PoPs). To put it
bluntly, this is just a very "murky" weather pattern when it comes
to having any great confidence in PoPs. In the mid-upper levels,
we spend the vast majority of this time frame in a fairly weakly-
forced, "typical" mid-summer weather pattern, as we reside south
of the main upper jet axis that generally resides from the western
through north-central CONUS. Thanks to the predominant ridging,
mid level temps will be warm enough on most afternoons to likely
prevent convection from firing in the absence of stronger forcing.
That being said, we will certainly be prone to occasional
storms/complexes wandering in from the west during especially the
evening, along with very subtle low-mid level warm air advection-
induced activity (mainly rooted 850-700 millibars) during the
overnight and perhaps morning hours on some days.

Precipitation/thunderstorm chances:
Needless to say, this forecast is simply littered with low
confidence thunderstorm chances, affecting at least portions of
the CWA each and every day and night. While the vast majority of
night and especially days will likely remain dry, these small
(mainly 30 percent or less) PoPs clearly outline the uncertainty
in the forecast. Obviously we will attempt to refine
(increase/decrease) these POPs as periods move into the shorter-
term range, but for now we just have to live with them all. As for
severe storm chances, they are certainly not zero, especially
given what will likely be appreciable instability much of the
time, but given overall weak shear, it will difficult to forecast
organized storm potential very far in advance. However, could
certaintly foresee at least a few Marginal/Slight risk setups
during this time.

Temperature overview:
Certainly, there is higher confidence here. Although the presence
of pesky clouds and/or storm outflow could easily throw things off
by 5+ degrees on a few days/nights, certainly the majority of
these 5 days looks to feature highs between the upper 80s-mid 90s
(some upper 90s more favored southwest), and overnight lows
between the mid 60s and low 70s. In other words, a seasonably-hot,
but not overly-hot weather pattern (not the type that would
require formal Heat Advisories).

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Saturday)
Issued at 640 PM CDT Thu Jul 2 2020

Significant wx: Potential storms/outflow this eve, MVFR cigs near
dawn

Tonight: VFR to potentially MVFR. Generally low confidence period
due to unknown track of storms off to the W. At the minimum, will
get BKN to OVC cirrus, but depending on the track, both terminals
may get side swiped by the convection, with generally better chcs
just off to the S. Given uncertainties in track, kept VCTS for
now, but did indicate a likely switch in wind dir 03Z-05Z to SW
or W, due to outflow from this convection, as well as bring in
some low cigs that could potentially be MVFR. Short term models
exit/weaken the convection around 06Z. Can't completely rule out
additional elevated convection late overnight, but too low of
potential to include attm. Finally, some models indicate BKN MVFR
cigs near dawn for GRI, with maybe even lower cigs and patchy MVFR
fog poss as well. Again, though, this is low confidence as will
depend on convective trends.

Fri: MVFR to VFR. Any low cigs should scatter and lift by mid-
morning...leaving VFR conditions and occasional mid to high clds.
Winds will be SE 6-10kt. Confidence: Medium.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&

UPDATE...Thies
SHORT TERM...Pfannkuch
LONG TERM...Pfannkuch
AVIATION...Thies