Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 06/06/20

Area Forecast Discussion

National Weather Service Louisville KY

 911 PM EDT Fri Jun 5 2020

.Forecast Update...
Issued at 910 PM EDT Fri Jun 5 2020

Have some high clouds moving into our counties west of I-65 this
hour, but otherwise a quiet evening across the region. Still some
signs that we could see some patchy fog overnight, with low
temperatures within a few degrees of afternoon crossover
temperatures. Best focus from high-res models places the best
chances south of the I-64 corridor, so have a few spots with "areas
of fog". Will send out a zone update shortly, to add in those areas
of fog and to make slight adjustments to low temperatures based on
current trends.

&&

.Short Term...(This evening through Saturday)
Issued at 259 PM EDT Fri Jun 5 2020

Things are quiet across the CWA at this hour, and expect them to
stay that way through the afternoon and evening. That being said,
there are couple of subtle things to watch through the evening.
First off, an outflow boundary from the morning MCS over MO/AR/TN is
pushing into our western CWA at this hour, and you can see some
subtle enhancement to the cu field as this occurs. There is some
moderate instability around 2000-2500 J/KG of CAPE to work with,
however a notable warm layer between 850-700 mb is keeping things
suppressed. Taking a look at AMDAR soundings and lifting a 90/69
(worst case scenario) surface parcel still wouldn`t be able to
overcome that layer. So, think we will stay dry as CAMs suggest, but
will continue to monitor in case something does pop.

Otherwise, expect a quiet evening with patchy fog developing mainly
over our west, south, and east CWA. Most of southern IN and north
central KY should see less fog. Expect it could be dense in spots,
but there does appear to be a batch of some upper level clouds
overnight, which could be a limiting factor for some more widespread
dense fog formation. So, won`t do anything further than mention
patchy fog for now. Lows drop into the upper 60s and low 70s tonight.

A weak frontal boundary will approach and drop through the region
tomorrow. The trend in data has really backed off pops for tomorrow,
however given the amount of instability and at least some weak
surface convergence possible along the wind shift boundary wanted to
leave at least 20 pops in south of the Ohio River. If a storm is
able to pop, it could be quite robust given some strong instability
and decent mid level lapse rates. The overall environment would
still be a pulse type environment if a storm were to develop. At
this point, it looks like most locations, if not all, will stay dry.
SPC did keep general thunder over our southern half of the CWA,
which is where we expect the best potential. Highs tomorrow reach
the 86 to 91 degree range.

.Long Term...(Saturday night through Friday)
Issued at 309 PM EDT Fri Jun 5 2020

Fair weather is expected during the second half of the weekend and
heading into Monday. Mid and upper level ridging builds over the
Great Lakes and Ohio Valley during this period. Saturday night and
Sunday will feature northerly and northeasterly sfc winds following
the Sat fropa. Low level thicknesses continue to support a decent
temp gradient on Sunday. Morning lows should range from around 60 in
southern IN and the northern Bluegrass to the upper 60s near the TN
border. Highs Sunday afternoon will likewise range through the 80s.

The heat builds on Monday, and many areas in central and southern KY
could see their first 90 degree day of the season. Monday night into
Tuesday, Cristobal is likely to be a Tropical Depression moving from
Arkansas to Missouri. Latest NHC track continues with a NNE movement
up through east-central Missouri on Tuesday. Went with isolated to
chance PoPs Tue for showers/storms, highest PoPs west of I-65.

Tuesday night through Wednesday, Cristobal makes the extratropical
transition and gets absorbed into a central CONUS trough. The
notable eastern CONUS ridge during the early to mid week period
continues to support a track generally up the MS River Valley and
eventually the western Great Lakes. At this point, therefore, the
flooding potential seems low. The merged system continues to race NE
into Canada, with a cold front sweeping through the Ohio Valley in
the Wednesday-Wednesday night time frame. A round of convection
looks likely, with cooler air arriving late week.

&&

.Aviation...(00Z TAF Issuance)
Issued at 730 PM EDT Fri Jun 5 2020

We did mix in some drier air to the terminal sites this afternoon,
but not convinced we won`t see some vsby restrictions. Trended the
sites a little better, though did keep in IFR chances at KBWG around
daybreak, where the signal is just a little better to see brief
conditions. Otherwise, we will see light and variable winds tonight.
A weak cool front will drop southward Saturday, bringing more
northerly winds. Isolated showers/storms may form along this front
in the afternoon, but coverage/confidence is too low to include in
this forecast.


&&

.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&

$$

Update...RJS
Short Term...BJS
Long Term...EBW
Aviation...RJS



Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 624 PM CDT Fri Jun 5 2020

.SHORT TERM...
254 PM CDT

Through Saturday night...

Isolated severe risk through early evening:

The convective potential this afternoon-evening continues to
be uncertain, and if thunderstorms occur, coverage is expected to
be low/isolated to perhaps widely scattered. There remains a
conditional strong to severe thunderstorm risk, covered well by
SPC`s Marginal (level 1) Risk. Expansive convective blow-off
cirrus has been shrouding the region, though temperatures have
been able to warm into the mid to upper 80s. A recent aircraft
sounding out of MDW indicates a lingering cap to surface based
convection there, though SPC/RAP Mesoanalysis suggests cap is
eroding from the northwest. Lake breeze boundary is stalled out
from the Cook County North Shore area to the eastern portion of
Lake County.

Potential scenario for convective initiation (CI) this afternoon
into the evening is similar to earlier posted update. It will be
tied to low level frontal convergence, enhanced by lake breeze
convergence, likely with an emphasis on the lake breeze/cold front
inflection. Visible satellite imagery shows most congested
cumulus near the lake breeze in southeast Wisconsin and far
northeast Illinois and there was an attempted shower near Kenosha
around 2pm. Farther upstream, cumulus field not all that
impressive looking and winds have already turned northwesterly in
the northwest portion of the CWA with a pre-frontal wind shift. It
appears true frontal boundary stretches from near the MS River to
southwest Wisconsin.

MLCAPE values may top out in the 1500-2500 j/kg range as
suggested by recent mesoanalysis, which is more than sufficient
given northwesterly deep layer shear of 30-40 kt. Biggest
question mark continues to be the coverage of thunderstorms, if
any, ahead of the front. 12z sounding from Aberdeen SD sampled
exceedingly dry air in the 700-500 mb layer and model forecasts
suggest this is in the process of being advected overhead. Lack
of large scale mid and upper level forcing and relying solely on
frontal convergence also adds to the uncertainty. The mid-level
dry air entrainment could be tough for incipient updrafts to
overcome and mature into thunderstorms, which may have been the
case with attempted CI over southeast WI.

Dew points have also mixed out a bit over portions of the Chicago
metro, though this is not uniformly the case. It is apparent that
some of the more aggressive 12z CAM solutions, namely the 3km
NAMNest and NSSL WRF, will be overdone with dew points along the
front, which helps explain their more concerning depiction. The
above limiting factors in mind, am still concerned that a couple
storms may be able to overcome the dry air entrainment,
particularly in the vicinity of the lake breeze/cold front
inflection through early evening where convergence will be
maximized. *If* a storm or two should tap into the favorable
parameter space on the instability, shear, mid-level lapse rate
spectrum, there is a concern for an isolated robust severe storm.
Main threats if a storm does become severe would be damaging
downburst winds given steep low level lapse rates and plenty of
DCAPE from aforementioned dry air aloft. In addition, with
favorable shear vector orientation to cold front, any supercells
would also have a large hail threat.

Recent HRRR runs have been steadfast in little/no development with
the front, with the aforementioned WRF based guidance on the other
end of the spectrum. The latest observational trends seem to point
toward coverage being low at most, but still don`t want rule out
the possibility of a thunderstorm or two getting going. Will need
to monitor satellite and radar trends closely. With all the
uncertainty described, kept PoPs capped at 20% to 30%. The storm
motions should be 30-40 mph off to the southeast, so while any
thunderstorm would certainly produce brief heavy downpours, not
expecting a flash flood threat. If convection occurs, it will sag
south and gradually dissipate with diurnal stabilization by the
mid to late evening near and south of the Kankakee River. Timing
for isolated severe risk could be as early as 3-4pm in the far
north to 8-9pm south of I-80.

Skies will clear out tonight behind the front as the cooler and
drier/less humid air mass advects in for the weekend. After a
relatively cool start to the day, Saturday will be a pleasant
early summer day with plenty of sunshine despite 500 mb heights
from mid-level ridging over the central CONUS typically being
supportive of warmer readings. This will be due to expansive high
pressure taking on backdoor characteristics as is centers over the
Great Lakes. Dew points are likely to drop to the 40s to around 50
Saturday afternoon, which will make it comfortable for outdoor
activities. Highs will top out in the lower to mid 80s well inland
(warmest south) and 70s downwind of Lake Michigan, with mid to
upper 60s lakeside due to steady northeast winds. It appears that
the magnitude of the northerly winds will be just shy of producing
waves more concerning from a dangerous waves and currents
perspective at the beach. Saturday night will feature lows in the
50s area wide, and can`t rule out an isolated upper 40s reading in
far northern Illinois.

Castro

&&

.LONG TERM...
303 PM CDT

Sunday through Friday...

Sunday through Monday night: The southwest extent of high pressure
drifting across the northern Great Lakes will remain across the area
during this time as a pronounced mid/upper ridge builds eastward.
With 850 hPa temps surging into the 20-22C range Sunday night into
Monday, afternoon highs Monday are expected to reach the low 90s for
all but the immediate lakeshore of northeast Illinois. With
dewpoints in the upper 50s and low 60s under a decent amount of
sunshine, some localized readings tapping into the mid 90s cannot be
ruled out. With the less humid conditions, heat index values should
remain capped at values near the air temperature.

Tuesday through Wednesday: Focus remains on local impacts from
Tropical Storm Cristobal currently drifting north off the Yucatan
Peninsula. Atmospheric Rex blocking from the aforementioned
mid/upper ridge over the area Sunday into Monday creates some
forecast challenges with regards to Crisotbal`s movement through mid-
week, but the overall forecast is for a broad and deep trough over
the western CONUS this weekend to nudge the ridge eastward and pick
up Cristobal`s remnants on Tuesday. Guidance has been fairly
consistent on this overall evolution, though placement and timing
have varied enough due to phasing issues to preclude too much
specificity in the forecast at this time. Consensus guidance brings
the remnants northward just west of the Mississippi River through
Tuesday morning before a northeast shift across the western Great
Lakes Tuesday night. With it will come a tropical air mass with
PWATs in excess of 2" and potentially strong winds in response to an
anomalously deep surface low. While current indications are for the
heaviest associated rains to remain just west of the CWA late
Tuesday afternoon into Tuesday night, the CWA is well within the
ensemble envelope of solutions to potentially fall within the axis
of heaviest rain. Those with forecast sensitive interests Tuesday
into Wednesday should continue to monitor the latest forecast
through the weekend.

Thursday through Friday: The western trough will deamplify to some
extent while gradually lifting northeast into eastern Canada during
this time. Most of this period should be dry with the exception of
scattered precip along a potential cold front dropping south into
the area on Friday.

Kluber

&&

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

624 PM...Only forecast concern this period are the winds.

There remains a small chance for an isolated thunderstorm this
evening ahead of a cold front moving into northern IL. Nothing has
developed so far and much of the short term guidance keeps the
area dry this evening and no precip mention with this forecast.

Winds are slowly turning northwesterly across northern IL and will
likely become more northerly this evening...possibly turning to
the north/northeast at ord/mdw but confidence is low. Winds should
settle back on a light north/northwest direction overnight and
winds will then turn northeasterly Saturday morning. Speeds should
increase into the 10-12kt range and its possible some gusts into
the upper teen kt range may develop late morning into the
afternoon. cms

&&

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

$$

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