Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/08/19

Area Forecast Discussion

National Weather Service Hastings NE

 721 PM CDT Sun Apr 7 2019

...Aviation Update...

.SHORT TERM...(This evening through Monday)
Issued at 351 PM CDT Sun Apr 7 2019

Aloft: Aircraft obs and RAP dynamic tropopause analyses show low-
amplitude flow over the CONUS. A trof extended from MN-TX with
modest ridges over the Ern and Wrn USA. Low-amplitude will remain
over the CONUS thru Mon with WNW flow over the Cntrl Plns...but
the Wrn ridge will amplify a bit as a trof approaches the W coast.

Surface: A very wk cool front moved thru this AM. The 850 mb
thermal trof was already E of the CWA. A small area of wk high
pres was building into NEB/KS. A wk low was forming over MT. The
high will depart to the S while this low crosses ND tonight. As
this occurs... the associated wk cool front will drop into Wrn
NEB. This front will cross the CWA tomorrow with a small area of
wk high pres moving in after 17Z.

Tonight: A bit of thin cirrostratus and possibly a few altocu
will move thru...but overall mostly clr. Another very mild night.
Lows should be in the 30s in early Apr...but instead they`ll be in
the 40s.

Mon: Another mostly sunny/very warm day. A bit brzy...espcly over
the SW 1/3 of the CWA. Can`t rule out some near-critical fire wx
down in Rooks county. RH is currently fcst around 25%.

.LONG TERM...(Monday night through Sunday)
Issued at 351 PM CDT Sun Apr 7 2019

Aloft: The Wrn ridge will move E and crest over the Cntrl Plns
Tue as a deep trof moves into the Wrn USA from the Pac. This trof
will cont E Tue night and be over CO/NM Wed. This trof will induce
lee cyclogenesis with a low forming and deepening right over the
CWA Wed night. Clustering of the global mdls suggest this low will
move into Wrn KS 00Z/Thu and then head ENE into Ern Neb by
00Z/Fri. This low will depart the rgn and head to LkSup Fri with
cyclonic WNW flow here. Meanwhile...another shrtwv trof is fcst to
dive down the back side of the newly established Wrn USA longwave
trof. As this trof heads thru the Desert SW Sat...a shrtwv ridge
will move thru here. There is quite a bit of spread btwn the NCEP
and international deterministic mdl suites. The GEFS mean supports
the slower EC/GEM solutions. It conts to look like the Desert SW
trof will probably head E into the Srn Plns Sun...vs heading NE
into the Cntrl Plns.

Surface: The wk cool front that moves thru Mon will become
stationary from NW-SE acrs NEB/KS. The temp grad will strengthen
acrs that front Tue as lee cyclogenesis ensues over Ern CO. Mdls
cont to fcst this front to sink S Tue night...forcing the lee low
S and favoring a track acrs KS. The last 5 EC runs have been
further S into KS. The GEM runs the furthest N near I-80 with the
GFS/GFS-FV3 runs in between near the state line or Nrn KS. While
there are minor timing/location diffs btwn the EC/GFS runs...they
all come together close to OMA by 12Z/Thu. So even the GFS runs
(while not as hvy as the EC) support accumulating snow. The deep
sub-985 low will occlude over Ern NEB Thu. High pres will slide
into the area Fri-Sat as the low heads to the GtLks. The next low
should form well SE of the area next Sun.

Temps: Contd way warmer than normal Tue. Wed there is tremendous
uncertainy with the front bisecting the CWA. There will probably
be a 25-30F temp gradient from N-S. Thu much colder than normal.
Fri-Sat will also be considerably cooler than normal...espcly
where substantial snow falls. Sun temps should return close to
normal.

As for sensible wx with the upcoming storm...

Little has changed from our prvs thinking. There will probably be
little or no precip in the warm sector while it is over/near the
CWA...as it will be capped by an uncontaminated EML that will be
advected off the Desert SW and wrapped into this system. Some
elevated shwrs/tstms will probably develop N of I-80 Tue night
into Wed AM. Right now we do have a chance of shwrs/tstms expanded
acrs the entire CWA during the day Wed. This is probably
overdone. If the NAM/GFS are right...there is a slight chance that
some isolated shwrs/tstms could occur over the SE 1/2 of the CWA
at the triple pt where the dryline intersects the sagging cold
front. The NAM/GFS scenario would also result in significant fire
danger and probably Red Flag Warnings behind the dryline.

If the EC verifies...fire wx won`t be a concern and warm sector
tstms probably won`t either.

A large shield of stratiform precip will evolve on the cold side
of the front...and as the low moves by the deformation zone is
expected to move in from NW-SE Wed night into Thu. Rain will move
in and change to snow...and the snow could be hvy.

The occlusion over Ern NEB depicted by the last 5 EC runs is
disconcerting because it packs the isobars. EC and GFS 850 mb
winds are fcst 50-55 kt. That would produce blzd conds with
significant blowing/drifting.

The Thu AM commute is looking rough!

Snow: we will probably not see accums in our CWA as high as the
Sandhills...but believe we could still see a swath of 3-6" bounded
by an area of 1-3". Drifts 3-5 ft high will be possible given the
expected strength of the winds.

Suggest keeping a close eye on the fcst and be prepared to alter
plans and take necessary precautions.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Monday)
Issued at 720 PM CDT Sun Apr 7 2019

General overview:
High confidence in VFR ceiling/visibility through the period,
withonly limited high level cloud cover at worst. That leaves at-
times breezy and directional-shifting winds as the main
issue...read on for more details.

Winds:
The lightest winds of the period will occur right away this
evening, as a passing ridge axis promotes a light/variable regime.
Then late tonight, a light-but-steady south-southwest breeze will
kick in. During the daylight hours Sunday, a passing surface
trough will promote steadily shifting and increasing breezes, with
direction transitioning to northwesterly and sustained speeds
increasing to around 15KT/gusts to around 20KT. The overall-
strongest breezes should focus 15-22Z, before sustained speeds
ease down closer to 11KT by the last 1-2 hours of the period.

On one final note, there are hints of some marginal low level
wind shear (LLWS) mainly during the 09-15Z time frame.
However, with the shear magnitude currently expected to average
under 30KT, and with any possible LLWS concerns well beyond these
first 6 hours, will defer to next TAF issuance to take another
look for possible inclusion.

&&

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

$$

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



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 626 PM CDT Sun Apr 7 2019

.SHORT TERM...
259 PM CDT

Through Monday night...

Weather forecast concerns continue to focus on the potential for
another period of scattered showers and thunderstorms late this
afternoon.

Over the past hour additional shower development has onset across
western portions of IL in advance of an approaching mid-level
disturbance. While thunderstorms will also be possible with this
activity as it shifts eastward across northern IL late this
afternoon, aircraft AMDAR soundings out of MDW indicate rather
poor mid-level lapse rates to support more than a couple rumbles
of thunder. For this reason it appears that the threat for strong
storms in the area will remain low, with only a gusty wind and
small hail threat. Expect the activity to remain scattered late
this afternoon through very early evening before waning. Another
quick moving disturbance could produce a few additional light
showers later this evening, but that should be about it.

The main story then becomes the nice weather expected on Monday.
Dry and mainly sunny conditions will set up our first day of the
calendar year in the low to mid 70s. It is important to note that
areas right along the lake front may experience a lake breeze late
in the morning through early afternoon. As a result, temperatures
may remain cool along the lake front for the first part of the
afternoon. However, later in the afternoon west-southwesterly
winds are expected to increase across the area in response to a
strengthening pressure gradient associated with an area of low
pressure shifting eastward into Lower Michigan. This should result
in the lake breeze being pushed back offshore by late afternoon.
Because of this, high temperatures along the lakeshore may also
get to around 70, but it may not be until late in the afternoon.

A cold front will then shift southward across the area Monday
night. This should result in cooler weather for Tuesday.

KJB

&&

.LONG TERM...
323 PM CDT

Tuesday night through Sunday...

The spring time weather roller-coaster will be in full swing over
the coming week. The main focus is on a strong mid-week system that
will bring multiple rounds of precip and periods of windy conditions.

Tuesday: Relatively quiet weather is expected through at least
Tuesday evening with the area on the SW flank of broad upper-trough
over eastern Canada. With surface high pressure building in from the
west, gusty NW winds to around 20 mph are expected for the
afternoon. These winds will support decent mixing into fairly dry
air above the boundary layer and support min RH values of 30-35%,
with the potential for a decent area to even drop into the upper 20%
range.

Late Tuesday night through Wednesday night: Lee cyclogenesis will be
ongoing over eastern Colorado Tuesday night with a NW to SE oriented
low-level baroclinic zone settling just SW of the CWA. Broad and
weak low-level isentropic ascent will support a developing ribbon of
precip across the north half of the CWA toward daybreak Wednesday,
with the precip band slowly lifting NE through the day. The
combination of thermal profiles aloft and cold NE flow off Lake
Michigan support precip mixing with or beginning as all snow across
the far NE CWA. Diurnal heating will allow precip to become all rain
by mid-morning Wednesday. Overall, Wednesday will be a blustery and
damp day with highs in the 40s and E/NE winds gusting 25 to possibly
30 mph. By Wednesday night, stout WAA will take hold and push the
CWA into the warm sector of the approaching system. Associated WAA-
forced precip may remain north of the CWA through the night, but
have continued to keep chance PoPs north of I-80 given uncertainty
of how quickly the warm sector builds in the CWA.

Thursday and Thursday night: By late morning, the area should be
fully in the warm sector of the approaching system, with the low
achieving maximum intensity over eastern NE/KS prior to daybreak. The
associated occlusion/cold front will shift across the area Thursday
afternoon and evening. This sets the stage for a conditional severe
weather day across northern IL. While shear will be more than
enough, with the potential for a rather windy day, instability may
be the limiting factor as plenty of mid-level cloud cover is
expected through the day. Either way, a period of showers and
thunderstorms are expected along the front during the afternoon into
early evening. Also, if enough daytime mixing occurs, S to SW gusts
to 40 mph will be possible in the afternoon, especially south.
Behind the front, SW winds gusting to 30 mph will usher in a notably
cooler air mass.

Friday: CAA within deep cyclonic flow combined with lingering low-
level moisture will support at least a slight chance of showers
through the day. Surface wet-bulb temps may even allow for some
morning showers to be a mix of rain/snow. Expect another blustery
day with temps in the 40s and SW/W winds gusting in to 30 mph.

Friday night through Sunday: Quiet and seasonably cool weather is
expected next weekend with high pressure drifting across the Great
Lakes region. However, the southern CWA may be clipped by a low
pressure system tracking NE through the Ohio Valley late Sunday.

Kluber

&&

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

Convection should be east of the terminals by the 00z effective
time of the TAFs, except for a small chance of an isolated cell in
vicinity of GYY through 0030z or so. Otherwise, look for west
winds to perhaps be a bit gusty to start the TAFs, but any
gustiness should abate with sunset. Winds will veer to northwest
early Monday morning before backing to southwest again during the
afternoon. Could see a short window of modest gusts late Monday
afternoon prior to sunset. Another cold front will move across the
terminals Monday evening with a wind shift to northwest expected,
though precip chances appear quite low with this front at this
time.

- Izzi

&&

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

$$

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