Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 08/14/19

Area Forecast Discussion

National Weather Service Hastings NE

 641 PM CDT Tue Aug 13 2019

.SHORT TERM...(This evening through Wednesday)
Issued at 334 PM CDT Tue Aug 13 2019

Aloft: RAP tropopause analyses and aircraft wind data show low-
amplitude zonal flow over the CONUS with a flat/suppressed
subtropical high along the LA/TX coast. A wk shrtwv trof was
making its way thru the Nrn Rckys. This trof will cont E tonight
passing just N of the CWA. In its wake...the flow will veer to the
WNW tomorrow.

Surface: Very wk high pres was over NEB. 1011 mb low pres was
over MN with a cool front extending W along the SD-NEB border into
MT. This high will disappear while the cool front slips S thru
the CWA tonight. Nrn Plns high pres behind the front will quickly
drop S into NEB tomorrow.

700 mb WAA/FGEN in the RRQ of a 60 kt upr-lvl jet streak resulted
in a persistent area of shwrs and a cpl tstms this morning over
the Sandhills. Some of the light shwrs moved acrs S-cntrl NEB this
morning...along and N of Hwy 6. They have long since dissipated
leaving sunny skies.

Rest of this afternoon: Sunny but incrsg thick cirrus blow-off
from svr tstms in SW NEB.

Tonight: Mostly cldy as significant anvil blow-off from tstms to
the W streams over the CWA. A slight chance of a shwr/tstms...
primarily W and S of the Tri-Cities. Lows a little below
normal...in the 60s except upr 50s Valley/Greeley counties.

Upslope flow and convergence in the lee trof was resulting in svr
tstms firing over SE NEB. CAMs are indicating these storms will
congeal and grow upscale into an MCS that propagates SSE into Wrn
KS. There is a chance the Ern fringe of these tstms could clip the
SW part of the CWA...from Cambridge-Phillipsburg-Plainville.
Can`t completely rule out a svr tstm...but odds favor them
remaining just W-SW of the CWA.

There are a cpl mdls that suggest a few tstms could dvlp along
the NEB-KS border or down in N-cntrl KS toward dawn. Kept a 20 POP
in the fcst to cover this. It`s far from certain.

Wed: Some uncertainty but believe it will probably play out as
dcrsg clds during the morning...espcly over S-cntrl NEB. Overall
should average mostly sunny and dry. Did keep a 20 POP just in
case something rogue pops up as suggested by a cpl mdls.

Wed will be the coolest day of the wk with temps svrl degs below
normal (78-84F over S-cntrl NEB/80-87F over N-cntrl KS).

.LONG TERM...(Wednesday night through Tuesday)
Issued at 334 PM CDT Tue Aug 13 2019

Aloft: The last 2 runs of the global mdls GFS-FV3/EC/CMC/UKMET
have come into much better agreement vs 24-36 hrs ago yielding
greater fcst confidence. Low-amplitude WNW flow will remain over
NEB/KS thru Sun. From Thu night thru Sat...svrl shrtwv trofs are
fcst to cross the rgn which will turn the WNW flow cyclonic. The
strongest of these trofs is slated to move thru Sat. As that trof
departs to the E...heights will rise Sun-Tue as the subtropical
high over NM expands.

Surface: These days will alternate with very weak cool frontal
passages followed by high pres the next day. Wk cool fronts are
fcst to cross the CWA Thu night...Sat and Tue.

Temps: Averaging slightly cooler than normal.

Rain/Tstms: Lots of uncertainty due to typical weak summer
forcing. Isold or sct tstms will be possible thru Sat night. Some
storms could be svr at times.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Wednesday)
Issued at 640 PM CDT Tue Aug 13 2019

Overall a fairly quiet forecast is expected with some caveats. 1.
There is a small chance for thunderstorms during the
overnight/early morning hours. Otherwise the best chance for
storms is during the afternoon/evening Wednesday. Due to the small
chance for storms, have left the mention out of the TAFs at this
time. Winds are light and generally northerly, that being said
brings caveat 2. A wake low has formed in the trailing stratus of
the MCS in northern Kansas and a 60 mph wind was reported at KLXN
about 6pm Tuesday night. KEAR has some gusts to 15 mph and winds
are out of the south. Winds will be light and northerly for much
of the forecast.

&&

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

$$

SHORT TERM...Kelley
LONG TERM...Kelley
AVIATION...Billings Wright



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 706 PM CDT Tue Aug 13 2019

.SHORT TERM...
259 PM CDT

Through Tonight...

Main concern is the threat for any lightning with scattered
showers through early to mid evening. A weak short-wave over
Wisconsin noted on W/V imagery and from higher coverage of showers
over central and southern Wisconsin will progress southeast
through the evening. The strongest forcing will brush us just to
the north but there will be some minor mid-level height falls into
the evening. As was earlier alluded to, overall modest forcing
will interact with the lingering moist air mass over the region to
produce widely scattered showers. A lake breeze pushing inland
will help aid in focus with enhanced low level convergence, and
there have already been a few brief showers in this axis.

Big question continues to be occurrence of any lightning with the
convection. Recent AMDAR soundings from MDW continue to show very
weak mid-level lapse rates and high freezing levels of 15.5-16kft
AGL, owing to warm mid-level temps centered at 600 mb. It`s
uncertain whether any cores will be able to overcome the weak
lapse rate environment to grow tall enough for lightning
generation. Observational trends over Wisconsin have indicated
most of the activity struggling to produce lightning, with one
robust sustained storm able to do so over the past couple hours.
This is despite effective shear of about 40 kt, highlighting the
deleterious effects of the weak lapse rates and resulting limited
instability. Will continue to carry slight/isolated thunder
chances, with thinking that most of the activity is lightning-
less, and a few isolated storms. Highest scattered shower coverage
should be north of I-80 in Illinois late this afternoon through
early evening. Severe weather is not expected, though can`t
completely rule out a rogue storm capable of brief gusty winds, as
wind shear will increase some over the next few hours. Main
threats will be localized downpours, and lightning with any
thunderstorm. The showers will gradually drift southeast and
likely diminish in coverage through the mid-late evening, with
lightning becoming even less likely.

Overnight into early Wednesday, the lingering moist air mass over
the area (65-70 dew points) this afternoon may be conducive to
patchy fog development outside of Chicago. It appears that we`ll
hold onto some cloud cover, likely precluding much of a dense fog
risk despite winds going light/calm. However, pockets of clearing
could yield spotty sharper visibility reductions in favored
outlying low lying areas. While isolated showers can`t be ruled
out overnight, it appears most areas should stay dry after the
evening activity winds down. The next wave approaching from the
northwest could bring some isolated showers toward portions of
north central and far northern Illinois toward sunrise.

Castro

&&

.LONG TERM...
202 PM CDT

Wednesday through Tuesday...

Any lingering patchy fog should lift and scatter out through the mid-
morning on Wednesday. Some spotty showers will be possible to start
the day as the southern periphery of a rather stout shortwave--
currently pivoting into west-central Minnesota--dips into southern
Wisconsin. The associated forcing for ascent shows up pretty well as
a nice ribbon of upglide near 300 K. We`ll cap PoPs at 20% with this
morning activity, but coverage may end up being a bit higher.
Additional shower activity may continue to develop through the
morning and into the afternoon hours in the vicinity of an inverted
trough axis which looks to stretch from near Rockford to Rensselaer
and on an additional lake-enhanced backdoor boundary which is slated
to slosh westward into the region through Wednesday morning. This
boundary may bring in just enough drier low-level air to begin to
shut off precipitation chances near the lake during the afternoon.
While 500 mb temperatures will cool to around -10 C tomorrow, a
fairly prominent layer of warmer air in the 700-600 mb layer may
ultimately curtail electrification potential, and we`ve limited
thunderstorm chances to 20% or less area-wide as a result.

While we`re showing generally dry conditions Wednesday night and
into Thursday, a low potential for showers will linger through this
period as we`ll remain in a fairly moist airmass with numerous
subtle little cols present in the low-level flow. It`s just at this
point the precip chances seem to be at a relative minimum during
this period.

The main message as we head into the end of the week and the
upcoming weekend is a mainly dry forecast, likely punctuated by at
least episodic chances for showers and thunderstorms. Unfortunately,
the upper air pattern will certainly not lend itself to a high
degree of predictability. A fairly amplified Rex Block/Dipole
blocking pattern has set up across the East Pacific and through the
Gulf of Alaska, with numerous mid-level perturbations set to crest
the associated ridge axis and drop into fast, confluent flow into
this weekend. Trying to time any of these disturbances with any
confidence will likely remain a big challenge, and it`s not
surprising to see such a high degree of variability in the
extended model guidance.

The first such disturbance may approach the region on Friday or
Friday night. Precipitation chances will increase as a result. There
may actually be a potential for some strong or even severe
convection with this wave due to fast mid-level flow, but the
potential for robust moisture return appears limited ahead of this
feature. Another disturbance may encroach on the region over the
weekend. We`ll keep slight chance to chance PoPs going through the
end of the forecast as a result.

Carlaw

&&

.AVIATION...
For the 00Z TAFs...

Small cluster of showers/storms will continue to drop
south/southeast across the terminals over the next 1-2 hours.
However, at this point, expect only MDW and GYY to be impacted by
these storms. There are some isolated light showers approaching
the RFD area at this time, and these could move across the
terminal. Don`t anticipate any vis restriction or thunder at RFD
at this time. Dry conditions then expected for much of the period.
with the exception of some possible scattered showery development
Wednesday afternoon. North northeast winds this evening will
become more light and variable tonight, and then once again become
northeast Wednesday afternoon.

Rodriguez

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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