Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 252120
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
420 PM CDT SAT JUN 25 2016

.SHORT TERM...(This evening and tonight)
Issued at 419 PM CDT Sat Jun 25 2016

This first section focuses solely on these next 12-15 hours
through tonight, and the associated possibility (likelihood?) of
seeing at least a few severe storms/locally heavy rainfall
primarily within the southeast 1/2 to 1/3 of the CWA.

Have been examining/pondering our severe weather chances for this
afternoon/tonight for the past several hours, and quite frankly,
confidence is gradually waning versus 6-8 hours ago in both the
areas coverage and likelihood of more than a few marginally severe
storms, which if they were to occur would mainly be during the 6
PM-midnight time frame. That being said, certainly cannot "pull
the plug" on the possibility of a few severe storms just yet,
especially within roughly about the southeast 1/4 of the CWA.

Taking a brief look at the current scene as of 4 PM, the primary
mid/upper disturbance of note is a powerful closed low churning
along the ND/Canada border, with a much weaker/more subtle
trailing to its south into the local Central Plains area. At the
surface, a fairly well-defined (in the wind field) but also
somewhat weak (in the temperature/thermal field) cold front
roughly bisects the CWA from southwest-northeast at this time,
with northerly breezes behind it and southerly-to-westerly breezes
ahead of it. To state the obvious, although quite a bit of clouds
were expected today, if anything it has been cloudier than
expected, thanks in part to numerous weak mid level showers
developing above a capping inversion. High temps have at least
touched 90 in KS zones, but have struggled to reach 80 far
north/northwest and the mid-80s central.

Looking ahead forecast-wise...

Late this afternoon/evening (pre-midnight):
Although things continue to slowly destabilize, the extensive
clouds are keeping the lower-level capping in place fairly solidly
thus far, especially given mid level temps still as high as 12-13C
per meso-analysis. That being said, at least filtered sun
especially near our KS zones is helping foster generally 1000-2000
J/kg mixed-layer CAPE which could be realized within the next few
hours. Although still fairly weak, deep layer shear is expected to
increase to generally 30-40 knots into this evening, fostering an
environment supportive of potentially widespread storm development
mainly along and a few counties behind the surface front, a few of
which could be severe. The longer it takes for strong/severe
convection to develop, the more of the central/northwestern CWA
may be spared, with the main focus being within the southeastern
1/4, and probably especially KS zones. Could see a few brief
supercells structures, but mainly looks like multicell convection
with potential for hail to around ping pongs/winds to around 60
MPH. Locally heavy rain in excess of 2+ inches cannot be ruled
out, especially if storms start to congegrate/train within the
frontal zone given precipitable water values averaging up to
around 1.8 inches in the southeast.

Late tonight(post-midnight):
The vast majority of convection should be concentrated near/south
of the NE/KS border by this time, as forcing aloft and the low-
level frontal zone continues to shunt off to the south and east.
Could still see a few strong storms ongoing late into the night
along with locally heavy rainfall, but would be surprised to see
much of a severe threat by then. That being said, latest RAP13
keeps respectable elevated instability of around 1000 J/kg hanging
around/stalling out within our southern zones even late tonight,
so any lingering storms will bear watching.

.MID TERM...(Sunday daytime through Tuesday daytime)
Issued at 419 PM CDT Sat Jun 25 2016

This section addresses the 60-hour "mid term" period between
tonight`s storm chances and the seemingly decent storm
chances/coverage from Tuesday night-Wednesday night (addressed
below).

Clearly the main focus continues to be at least limited chances
for storms and possibly even some possibility of severe weather
(especially Monday afternoon/evening). That being said, confidence
in the development/coverage of convection during these 60 hours is
not overly-high, and as a result, PoPs have been kept at no higher
than 30 percent for the time being. Temperature-wise, both
Sunday/Monday are currently expected to feature similar,
slightly-above normal highs in the upper 80s/low 90s range (for
most areas), before a slight "cool-down" into mainly the low-mid
80s occurs for Tuesday. In the mid-upper levels, the predominant
pattern is one of quasi-zonal flow aloft for Sunday, which
gradually transitions to more northwesterly for Monday-Tuesday as
the Central Plains resides along the eastern periphery of a
mid/upper ridge axis setting up over the Southern Rockies/Four
Corners area.

Will attempt a few brief details for each of these 5 day/night
forecast periods:

Sunday daytime:
Came very close to leaving the entire CWA void of mentionable
PoPs, as the vast majority of the area should be looking at a dry
and warm day with increasing sunshine and generally easterly winds
behind the departing system from tonight, and as the main cold
front stalls out and starts returning back northward. However,
this front and the associated elevated instability axis stalls out
just close enough to the southern edge of the CWA, that along with
some hints from a few (not all) models, decided to play it safe
and re-introduce a low-confidence slight PoP to North Central
Kansas zones. Not expecting anything severe, but should this
occur, it could either be a continuation of lingering activity
from tonight, new development or both.

Sunday night:
Although it might not last in later forecasts, decided to keep
this period dry CWA-wide for at least one more forecast cycle as
forcing looks fairly minimal. That being said, the latest models
are hinting that at least isolated convection could at least flirt
with, if not infiltrate, mainly far southern and western portions
of the CWA, so this will need watched closely.

Monday/Monday night:
While the morning daytime hours should largely be dry, we will
need to keep an eye on the afternoon/evening hours for what could
be our next severe weather threat. In the mid-upper levels, deep-
layer shear strengthens a bit as the mean flow aloft becomes more
northwesterly, and with seasonably cooler temperatures aloft, it
may not take much of a shortwave aloft to get storms going. The
latest NAM/ECMWF is especially aggressive with afternoon storm
development (potentially severe) but the latest GFS not quite as
much so. For being only 2 days out, plenty of uncertainty here,
but the SPC Day 3 Marginal/Slight risk outlook appears warranted.

Tuesday daytime:
In theory this is largely a dry/storm-free day before the
seemingly much better storm chances move in Tuesday night. That
being said, will maintain a slight PoP in roughly the northwestern
half of the CWA for now. Slightly cooler temps expected as
slightly cooler air circulates clockwise on southeast winds from a
surface high centered over the MN/IA area.

.LONG TERM...(Tuesday night through Saturday)
Issued at 419 PM CDT Sat Jun 25 2016

This section focuses on the "long term" period (Days 4-7) for
which the forecast is primarily derived from a default
multi-model blend, with only limited forecaster modification.

Not a lot of time to delve into much regarding this 4-day period,
but to make a long story short, several more chances for
showers/thunderstorms and maybe some severe weather/heavy rainfall
continues. Each and every one of these day/night periods contains
at least a slight chance of precip somewhere within the CWA, as
low PoPs have now been introduced to the previously "dry"
Thursday/Thursday night time frame. Temperature-wise, the big
news here is what should be a slight, much-awaited cool-down for
many. Although it may somewhat depend on precipitation/widespread
clouds materializing, only have highs aimed into the upper 70s in
most areas Wednesday/low 80s Tuesday, before rebounding to near-
normal highs mid-upper 80s Friday/Saturday.

As highlighted by previous night shift forecaster, our primary
window of opportunity for the most widespread thunderstorm
activity appears to focus during the Tuesday night-Wednesday night
time frame, as both the ECMWF/GFS continue to suggest the
potential for organized MCS development. This possibility is
supported by seasonably-strong northwest flow aloft and fairly
cool mid level temperatures, which could easily allow one or more
thunderstorm complexes to roll through. Am normally not very
comfortable advertising 60+ percent "likely" pops out this far in
the forecast, but previous forecast already had them, and the
latest models suggest not backing off for now.

Beyond Wednesday night, confidence in the precip details through
the last few days of the official forecast is quite low, but with
the same west-northwest flow pattern persisting, it is just
impossible to rule out at least a slight chance of convection in
any given period. Plenty of details to sort out here with time.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Sunday afternoon)
Issued at 1248 PM CDT Sat Jun 25 2016

Overview:
Confidence is fairly high that VFR ceiling/visibility
will prevail through the period, with the main caveat consisting
of the possibility a few strong to perhaps severe thunderstorms
affecting the terminals this afternoon/early this evening.
Otherwise, surface wind direction will shift in the wake of a
passing cold front.

Ceiling/visibility:
Plenty of mid-high level clouds will hang around especially
through the first half of the period, but VFR ceiling should
prevail unless a brief heavy thunderstorm does in fact pass
through. This possibility would be handled in future
amendments/TEMPO groups.

Precipitation/thunderstorms:
Although confidence in occurrence is not yet high enough to
justify a prevailing or TEMPO group, have maintained a generic
"vicinity thunderstorm" (VCTS) mention from 20z-00z, and there is
even the possibility of a brief severe storm with strong
winds/hail. It`s not out of the question that a few showers/storms
could linger slightly beyond 00z, but will keep this out for now.

Surface winds:
Taking any possible thunderstorm outflow effects out of the
equation, the expectation is for winds to veer from
southerly/westerly right off the bat to northerly by mid-afternoon
as a weakening cold front passes. A generally light northerly to
light/variable regime will prevail overnight before turning more
easterly Sunday morning. Although sustained speeds could exceed
12kt both behind the front and in association with any storms,
speeds should average less than this the majority of the period.

&&

.GID Watches/Warnings/Advisories...
NE...None.
KS...None.
&&

$$

SHORT TERM...Pfannkuch
LONG TERM...Pfannkuch
AVIATION...Pfannkuch



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