Area Forecast Discussion
Issued by NWS Hastings, NE

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525
FXUS63 KGID 301822
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
122 PM CDT SAT JUL 30 2016

.SHORT TERM...(Today and tonight)
Issued at 402 AM CDT Sat Jul 30 2016

Difficulty continues to lie with timing and chances of precipitation.

Today will be a day of transition as the upper level flow becomes
more zonal as the subtropical high begins to build. Temperatures
today will be close to 5 degrees warmer and dewpoints perhaps a few
degrees warmer as well, compared to yesterday.

Although we do have some showers/thunderstorms kicking up in our
north/westerly this morning as a subtle perturbation slips by, it
appears that slight ridging aloft may give us a relative lull by late
morning early afternoon, but I`m not confident enough to pull pops
completely for mid-day with our given conditions in lower levels.
With increased instability and moderate bulk shear in the 40 kt
range, I would not be surprised to see a severe thunderstorm or two
pop up by late afternoon and heading into the evening, and this
looks especially true for areas southwest of the tri-cities.

Our best shot at rain should come overnight tonight as the low-level
jet strengthens and provides support for thunderstorm activity,
especially focused in our southeast. I could see some stronger
updrafts producing some decent sized hail, so severe weather could
occur for pretty much most of the night.

For temperatures, sky cover, and dewpoints, etc., I made very small
changes. I did increase chances of rain late tonight after midnight
due to the strengthening low-level jet.

.LONG TERM...(Sunday through Friday)
Issued at 402 AM CDT Sat Jul 30 2016

Aloft: Heights will rise next week with a subtropical high
developing over the Srn Plains...and overtaking the Srn 2/3 of the
CONUS. The Westerlies will retreat to the US-Can border. Overall...
the mean position of the ridge will be over the Nrn Plains...with
trofs over the NE and NW. Two systems will force cool fronts S into
the fcst area. The first is a low that will form today over British
Columbia. This low will head into Cntrl Canada and stall. The second
will be the low currently over the Gulf of AK. This low will move
into the Pac NW Tue and weaken as it moves thru the Nrn Plains ridge
...temporarily lowering heights.

Surface: A weak warm front will be lifting thru the fcst area Sun...
as low pres heads into Cntrl Canada and its trailing cool front
advances thru the NW USA. This cool front will cont E...slowly
crossing most of the fcst area late Mon night into Tue. It will
temporarily stall over KS and then lift back to the N as a warm
front Wed...with low pres forming over MT and ejecting into Canada.
The cool front associated with this low should cross the fcst area
Thu before stalling along the KS-OK border Fri and then dissipating
Sat. Weak high pres will build in Fri...then shift E of the region
Sat.

Some details...

Temps: the main trend will be upward thru Wed...back into the 90s
and probably some low 100s over parts of N-cntrl KS. Temps then drop
Thu with frontal passage before beginning another warming trend into
next weekend.

Rain: the next best chance will be with the front Thu per the EC QPF
probabilities and deterministic global models. Before that...
anything will be very isolated.

Sun: Sct tstms will probably be on-going at daybreak over Ern
Neb/KS. The Wrn fringe of this activity could be affecting parts of
the fcst area E of Hwy 281 thru mid-morning...but it should be all E
of the fcst area by noon at the latest.

Mon-Tue: Heat cranks up again. Can`t rule out an isolated storm or
two meandering in from the high plains...but don`t count on it.
Advection of the EML over the region combined with subsidence aloft
should keep the fcst area mostly capped.

Temps could be hotter Mon than what we`ve advertised. GFS/NAM cross
sections suggest a fair amt of clouds.

Thu: if the last 3 EC runs are right...this could be a very
productive front rainwise. They are fcstg a SW-NE oriented 100 kt
jet streak just ahead of the trof axis...putting the front and Cntrl
Plains in the favorable RRQ. Slow movement of the front will also be
a plus.

The ridge will resurge back into the region next week behind the
departing trof. This should cap most of the fcst area once again.

&&

.AVIATION...(For the 18Z KGRI/KEAR TAFS through 18Z Sunday afternoon)
Issued at 122 PM CDT Sat Jul 30 2016

Will state up front: beyond the first 6-9 hours, this is
definitely a lower-than-average confidence forecast with regard to
ceiling/visibility and thunderstorm chances, so stay tuned for
potentially significant changes/updates in later scheduled
issuances/amendments.

Confidence is in fact rather high in VFR and storm-free conditions
through at least these first 6 hours this afternoon with breezes
generally near/below 12kt from the southeast. Then later this
evening and especially overnight, there are increasing chances for
storms in the area, but because models are still rather
inconsistent on timing and location will only advertise a generic
"vicinity" (VCTS) from 03-09z, which would be the most favored
time frame. IF in fact storms do affect the terminals, severe
weather with hail, strong winds and heavy rain are possible.
Beyond the 09z time frame, the general model consensus is that
convection should be focusing more to the east of KGRI/KEAR. Then
the million dollar question is whether sub-VFR ceiling/visibility
might form in low stratus and/or fog. Despite model guidance
insisting on potentially IFR or worse conditions, am not willing
to go quite this pessimistic yet given that convection in the area
often "muddies" the potential for the lowest aviation categories,
especially if low-level breezes stay up a bit. For now will aim
for a "middle ground" approach with MVFR ceiling/visibility
focused from 09z-15z, but please note that conditions "could" be
worse than this if some of the current model guidance is in fact
onto something. Last but not least, there is also the potential
for a period of low level wind shear (LLWS) tonight mainly between
03z-09z, but with some of the latest guidance showing fairly
marginal shear values mainly just below 30kt, will keep this out
for now and let later issuances re-assess.

&&

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

$$

SHORT TERM...Heinlein
LONG TERM...Kelley
AVIATION...Pfannkuch



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