Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 231810
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
110 PM CDT SAT JUL 23 2016

.UPDATE...
Issued at 949 AM CDT Sat Jul 23 2016

Some early thoughts regarding the rest of the daytime hours:

1) Although the day is young and there is plenty of time for
things to really climb fast with a few hours of sun, am starting
to wonder if maybe our high temps for today could be at least 2-4
degrees overdone (not that anybody would complain about that
though!). Not only is there considerable coverage of mid level
clouds here at mid-morning, but 500 millibar RH progs from models
such as the NAM/RAP suggest that a respectable coverage of these
clouds could continue into at least the early-mid afternoon. Will
refrain from making "big" changes at this time, but just something
to keep in mind for later forecast updates. Even if highs do fall
a bit short of expectations, currently have no intentions of
letting go of Excessive Heat Warning until at least mid-late
afternoon, and it might very well ride to it`s "natural"
expiration at 7 PM.

2) Related to section 1 above, it appears that a smattering of
passing showers/possibly weak thunderstorms could continue flaring
up here and there for several more hours, possibly well into the
afternoon. This elevated, rather weak activity is likely rooted
way up around 12,000 ft/650 millibars per forecast soundings
(above a formidable capping inversion to lower-based parcels),
and seems to be tied to a southwest-northeast oriented zone of
fairly persistent mid level convergence. As for potentially more
robust/severe and lower-based storms later today/this evening,
shorter term models such as the RAP/HRRR and even the latest 12z
NAM are showing little if any of this development, implying it may
be very isolated at best. If anything, our far southwestern CWA
may have the overall-best chance of popping a few vigorous late-
day storms near the invading cold front given the overall-hotter
and more deeply-mixed boundary layer in that area. Latest 09z SREF
calibrated severe probs are sure not very supportive of severe
storms for our CWA this afternoon/tonight, instead focusing much
higher chances within the official SPC Slight/Enhanced areas well
to our northeast. That being said, with the low-level cold front
moving in later in the day, one can "never say never" on at least
isolated severe development, and thus cannot discount the current
SPC Marginal Risk for essentially our entire CWA.

&&

.SHORT TERM...(Today and tonight)
Issued at 347 AM CDT Sat Jul 23 2016

Another hot day is forecast today before a cold frontal boundary
crosses our region this evening and tonight. The pattern aloft
featured a series of shortwave troughs translating across the
Central and Northern Plains states which were breaking down the
upper ridge axis and shunting it south to the Southern Plains, and
bringing more zonal flow to our region. Convection initiated along
the high plains during the evening hours and this activity was
gradually working eastward early this morning and expect some hit
or miss activity to linger into the first part of today.

Temperatures are tricky given the varying cloud cover from the
remnant convection however mid level temperatures remain very toasty
near 30C ahead of an approaching cold frontal boundary moving
through western Nebraska during the afternoon. Still looking for
temperatures to top out well into the 90s to over 100 degrees and
combined with high dewpoints primarily in the 70s, afternoon heat
indices in the 100 to 107 degree range are expected and the
current heat headline remains in effect through early evening.

Another round of showers and thunderstorms are possible this evening
and tonight as the cold frontal boundary crosses our cwa. Convective
models are not impressive on coverage of convection but cannot rule
out the chance along the baroclinic zone. If storms can go, a strong
to severe storm may occur with damaging winds and large hail the
primary hazards.

.LONG TERM...(Sunday through Friday)
Issued at 347 AM CDT Sat Jul 23 2016

Primary forecast concern through the long term lies with
thunderstorm chances.

At the start of the period Sunday morning, models continue to show
upper level zonal flow in place across the region, set up between
elongated high pressure across the southern CONUS and a low pressure
system moving into Ontario. At the surface, a cold front continues
to shift south, pushed by that northern system, and at 12Z looks to
be draped near the NE/KS state line. Models continue to vary with
how much/if any precipitation is ongoing Sunday morning, so while
PoPs are still in the forecast, they remain low. Through the day,
the surface front sags a bit further south, ending up near I-70,
before stalling as it loses its upper level push. With this front
around, though overall forcing is on the weak side, can`t completely
rule out preciptiation, and have 20-30% chances continuing into
Sunday night/Monday morning. Possible that should additional storms
form, some could be on the strong side, but at this point the
overall threat of severe weather is on the low side. Main story for
Sunday however will be the noticeable change in temperatures, with
the CWA sitting on the northern side of that front. East-northeast
winds are expected through the day, around 10-15 MPH. Highs will be
closer to normal for this time of year, and are expected to top out
in the mid 80s in the north to lower/mid 90s in the south.

As we get into the work week, overall confidence in precipitation
chances remains low. Outside of there being good chances in much of
the day Monday being dry, chances remain in the forecast through the
period. Upper level high pressure over the southern CONUS tries to
reamplify and ends up getting reorganized over the desert SW, but
never can build too far north with a train of disturbances moving
through. The next best chances look to come Tuesday night into
Wednesday with a stronger wave, but can`t totally rule out any day
beyond that. Have 50% chances in Tues Night-Wed morning, with 20-40%
following. Temperatures start the week out near normal in the upper
80s/near 90, but with the waves/precip chances moving through during
the rest of the week, highs by Friday in the lower/mid 80s are
possible.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Sunday afternoon)
Issued at 109 PM CDT Sat Jul 23 2016

Confidence remains fairly high in VFR ceiling/visibility through
the period, despite what could be a "decent" amount of mid level
cloud cover at times. The main uncertainty remains whether or not
at least a brief passing shower/thunderstorm could occur at some
point, but at this point have deemed the probability of convection
directly affecting the terminals to be around 15 percent or less,
and thus cannot even justify a "vicinity" mention at this point.
This will need closely monitored, however. One other possible
issue could be low level wind shear (LLWS) late tonight, somewhat
oddly in this case due to increasing north-northeast winds
between the surface and roughly 1500 ft behind a passing cold
front. However, given that this looks fairly brief/marginal and
will occur beyond the first 12 hours, have opted to defer to later
TAFs to potentially include this. As for surface winds, a
prevailing southerly direction this afternoon will give way to a
period of fairly/light variable breezes this evening as cold front
approaches, before a prevailing north-northeast direction arrives
later tonight into Sunday morning, but with sustained speeds
averaging under 12kt.

&&

.GID Watches/Warnings/Advisories...
NE...Excessive Heat Warning until 7 PM CDT this evening for
     NEZ039>041-046>049-060>064-072>077-082>087.

KS...Excessive Heat Warning until 7 PM CDT this evening for
     KSZ005>007-017>019.

&&

$$

UPDATE...Pfannkuch
SHORT TERM...Fay
LONG TERM...ADP
AVIATION...Pfannkuch


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