EF0 tornado, Beecher, Illinois, June 9, 2017

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
302 PM CDT Fri Jun 9 2017

.SHORT TERM...
257 PM CDT

Through Saturday...

For the remainder of the afternoon, the main forecast concern will
focus on a lake breeze pushing inland from Lake Michigan and the
effect on temperatures, wind direction and the chances for a. Any
shower or thunderstorm development.  Latest radar imagery indicates
that the lake breeze boundary is accelerating southwestward through
Lake and Cook Counties in nern IL and is about to move inland into
nwrn IN as well.  Winds are shifting to nely behind the lake breeze
and temperatures are dropping off rapidly as the lake-cooled air
spreads inland.  Ahead of the lake breeze, under ample sunshine and
dewpoints a little lower than previously anticipated, temperatures
have been able to rise a bit faster and higher, with many areas
approaching or hitting 90F.  However, following the lake breeze
passage, lakefront locations have seen temperatures dropping off
into the upper 60s in a short time.  There is some concern for the
development of shra/tsra along the lake breeze through early this
evening.  There is also some concern for isold-sct shra/tsra
developing this afternoon and evening away from the lake breeze as
well.  Low pressure is moving from southern Lake Michigan into swrn
Lower Michigan with a trailing cold front through nrn IL/srn WI and
then curves northwest to deepening low pressure over the Dakotas.
Latest sfc analysis shows very little evidence of the synoptic
boundary, with the exception of a weak pressure trough and some
enhanced moisture pooling invof the boundary. A wind shift and
frontal convergence is more pronounced through srn MN/nrn IA and
toward the low center.  With only very weak sfc forcing, there
should be enough moisture and instability to generate isold-sct
shra/tsra over nrn IL/nwrn IN this afternoon and into early evening.
 Since any convective activity would be diurnally enhanced rather
than dynamically driven, expect any shra/tsra potential to diminish
with sunset.  Severe weather is unlikely, though a brief heavy
shower, isold wind gust to 40 mph and lightning is possible.

Conditions should become relatively quiet overnight, with winds
diminishing and much of the diurnally cu dissipating.  Mostly clear
skies with lows dropping into into the lower to middle 60s.

Saturday will see the warming trend continue, with strengthening
swly winds as the pressure gradient strengthens between the
deepening low moving into the upper Mississippi Valley and high
pressure sitting over the sern CONUS.  Latest guidance suggests that
winds gusty winds to 30 mph or so developing by late morning.  Warm,
moist advection will strengthen as well under the swly flow, with
dewpoints increasing as flow become more directly sourced from the
Gulf of Mexico.  Also, temperatures will likely be a little higher
than Friday as upper ridging builds across the Middle and Upper
Mississippi Valley.  Widespread highs in the low 90s are likely
tomorrow with dewpoints rising into the upper 50s to lower 60s. Even
though temperatures and low level moisture will be on the increase,
the environment will be fairly stable, so any pcpn is unlikely.

&&

.LONG TERM...
257 PM CDT

Saturday night through Friday...

Heat will continue to be the focus through midweek as a fairly
low amplitude ridge remains positioned across much of the central
and eastern parts of the U.S. Expect conditions to be pretty
similar Sunday through Tuesday overall. South to southwesterly
flow will be rather strong leading to breezy conditions,
especially Sunday and Monday. The atmosphere will not be overly
moist with dewpoints peaking in the low to mid 60s with forecast
soundings suggesting that they could mix a little lower each
afternoon. At the same time, the stiff southwest breezes will help
propel temps into the 90-95 degree range each day. Accounting or
all of the above expect heat index values within a few degrees of
the actual temperature Sunday and be in the mid to upper 90s
Monday and Tuesday as dewpoints creep up. Overnight lows will only
fall to around 70 degrees with lower 70s across much of the
Chicago metro and mid 70s in the heart of the metro.

Precipitation chances will remain to the north and west of the
area through Tuesday. The large upper low off the Pacific
Northwest will have moved into the northern Rockies into mid week
and will amplify the ridge axis over the upper Mississippi River
Valley as well as start to push it eastward. Precipitation chances
look to return some time Wednesday as the progression occurs with
temperatures moderating as well. From there, the overall pattern
looks to become more active as the flow briefly becomes more
zonal before an upper trough potentially develops over the central
U.S next weekend.

MDB

&&

.CLIMATE...
300 PM CDT

Expecting a string of consecutive 90+ degree days this weekend and
into next week. While the current forecast does not have high
temperatures reaching record highs, Monday and Tuesday may be
only a couple of degrees away from record high temps, especially
at Rockford. Below are the Chicago and Rockford record high
temperatures for Saturday through Monday.

                      Chicago         Rockford
Saturday June 10th    98 1911         98 1933
Sunday   June 11th    97 1954/1933    98 1933/1911
Monday   June 12th    97 1956         95 1956
Tuesday  June 13th    95 1956/1954    94 1987/1976/1956/1921

NWS Chicago

&&

.AVIATION...
For the 18Z TAFs...

TAF concerns:

...Timing of wind shift associated with lake breeze development.
...Timing and coverage of showers and thunderstorms this
   afternoon and evening.
...Gusty southwest winds on Saturday.

Weak low pressure over sern Lake Michigan continues to slowly move
east to over Lower Michigan this afternoon, with a diffuse, nearly
stationary frontal boundary extending west invof the IL/WI
border. The boundary then extends northwest to deepening low
pressure over the nrn plains as a warm front. Latest sfc analysis
indicates that the boundary is very diffuse with little sfc
convergence and the only significant indicator of its' presence
is dewpoint pooling over nrn IL/srn WI. Latest radar imagery shows
the lake breeze boundary pushing inland over far nern IL and sern
WI and slowly moving inland. Still waiting for the lake breeze to
make landfall into into nern IL/nwrn IN from PWK south through
nwrn IN. Latest high res model guidance still wants to push the
lake breeze through ORD/MDW/GYY and have maintained the trend of
the going forecast, but confidence in the timing of the wind shift
associated with the lake breeze is lowering with time.

The next concern is timing and coverage of shra/tsra chances this
afternoon and into this evening. Current thinking is that the most
favored location for any convective development will be along the
lake breeze and the synoptic warm front. While the actual synoptic
front is initially very diffuse, most of the guidance would
suggest that sfc convergence along the boundary will increase
through the late afternoon and into the evening, especially as the
lake breeze merges with the synoptic front. The coincidence of the
moisture pooling along and north of the weak boundary and the
weak sfc convergence is sufficient to maintain the vcts mention in
the TAFS, but confidence is low as to the timing of convective
initiation and coverage. Any convective activity should have a
strong diurnal component given the weak forcing, so would
anticipate that any shra/tsra would diminish with sunset and the
remainder of the night should be relatively quiet, with
diminishing winds and dry/VFR conditions.

For tomorrow, main concern will be winds. The sfc low initially
over the nrn plains should continue to deepen and track to the
northeast. Combined with a large area of high pressure over the
sern CONUS which is expected to only very slowly build to the
east, expect a strengthening swly pressure gradient to develop
across the region. Sustained winds should approach 20 kt through
the morning and through the afternoon. Deep layer mixing under
ample sunshine should allow deep mixing with gusts of 30 kt likely
from late morning until sunset tomorrow. Otherwise, conditions
should remain dry and VFR tomorrow.

&&

.MARINE...
257 PM CDT

Surface low pressure of 29.8 inches is moving
east and will reach Lake Ontario at around 29.9 inches Saturday
morning. High pressure of 30.0 inches is stretched from the Ohio
Valley to the Arklatex region and will move east and merge
with high pressure off the Carolina coast. Strong low pressure of
around 29.2 inches will move from southern Manitoba to northern
Quebec Saturday and Saturday night bringing the potential for a
period of south to southwest gales to central and northern Lake
Michigan Saturday afternoon and evening. Areas to the south will
see breezy but sub gale conditions but strong enough winds to
warrant a small craft advisory for the nearshore waters. Another
weaker low pressure system will move northeast across upper
Michigan later Sunday. Another low pressure system will then move
into the northern plains setting up a warm front across northern
Lake Michigan mid week turning winds southeast to east across
northern sections. A cool front then passes some time later
Wednesday or early Thursday turning winds southwest and eventually
westerly late in the week.

MDB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement...ILZ006-ILZ014...noon Saturday to 4 AM
     Sunday.

IN...Beach Hazards Statement...INZ001-INZ002...noon Saturday to 4 AM
     Sunday.

LM...Small Craft Advisory...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...noon Saturday to 4 AM Sunday.

&&

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Hazardous Weather Outlook...CORRECTED
National Weather Service Chicago/Romeoville IL
356 PM CDT Fri Jun 9 2017

ILZ003>006-008-010>014-019>023-032-033-039-INZ001-002-010-011-019-
102100-
Winnebago-Boone-McHenry-Lake Illinois-Ogle-Lee-De Kalb-Kane-
DuPage-Cook-La Salle-Kendall-Grundy-Will-Kankakee-Livingston-
Iroquois-Ford-Lake Indiana-Porter-Newton-Jasper-Benton-
356 PM CDT Fri Jun 9 2017 /456 PM EDT Fri Jun 9 2017/

THIS HAZARDOUS WEATHER OUTLOOK IS FOR NORTH CENTRAL ILLINOIS...
NORTHEAST ILLINOIS AND NORTHWEST INDIANA.

.DAY ONE...Tonight.

WEATHER HAZARDS EXPECTED:
  Limited Thunderstorm Risk.

DISCUSSION:

Widely scattered thunderstorms will continue till about mid
evening over portions of northern Illinois and northwestern
Indiana. While severe weather is unlikely... storms will produce
cloud to ground lightning strikes... brief heavy rain... and gusty
winds possibly as high as 50 mph.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Saturday...
  Limited Non Thunderstorm Wind Risk.
  Elevated Fire Weather Risk.
Tuesday Night...
  Limited Thunderstorm Risk.
Wednesday...
  Elevated Thunderstorm Risk.
Thursday...
  Limited Thunderstorm Risk.

DISCUSSION:

A period of early season hot weather is forecast from Saturday
through at least the middle of next week. Temperatures are likely
to climb into the lower to middle 90s each day with night time
low temperatures remaining in the lower to mid 70s in urban and
suburban areas. Max heat indices during the period are expected to
generally remain just below 100 degrees.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be necessary through tonight.

GENERAL STORM MOTION OF THE DAY:

Moving toward the southeast at 30 mph.

&&

LMZ740>745-102100-
Winthrop Harbor to Wilmette Harbor-
Wilmette Harbor to Northerly Island-
Northerly Island to Calumet Harbor-Calumet Harbor to Gary-
Gary to Burns Harbor-Burns Harbor to Michigan City-
356 PM CDT Fri Jun 9 2017

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE ILLINOIS NEARSHORE
WATERS OF LAKE MICHIGAN AND THE INDIANA NEARSHORE WATERS OF LAKE
MICHIGAN.

.DAY ONE...Tonight.

  Limited Thunderstorm Risk.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Saturday and Sunday...
  Hazardous Conditions for Small Craft are likely.
Tuesday night through Thursday...
  Limited Thunderstorm Risk.

&&

LMZ080-261-362-364-366-563-565-567-669-671-673-675-777-779-868-
870-872-874-876-878-102100-
Lake Michigan from Michigan City IN to St. Joseph MI 5 NM
offshore to Mid Lake-
Lake Michigan from Seul Choix Point to Rock Island Passage 5 NM
offshore to Mid Lake-
Lake Michigan South of a line from Seul Choix Point to the
Mackinac Bridge and north of a line from Charlevoix MI to South
Fox Island 5 NM offshore-
Lake Michigan from Charlevoix to Point Betsie MI 5 NM offshore to
Mid Lake-
Lake Michigan from Point Betsie to Manistee MI 5 NM offshore to
Mid Lake-
Lake Michigan from Rock Island Passage to Sturgeon Bay WI-
Lake Michigan from Sturgeon Bay to Two Rivers WI 5 NM offshore to
Mid Lake-
Lake Michigan from Two Rivers to Sheboygan WI 5 NM offshore to
Mid Lake-
Lake Michigan from Sheboygan to Port Washington WI 5 NM offshore
to Mid Lake-
Lake Michigan from Port Washington to North Point Light WI 5 NM
offshore to Mid Lake-
Lake Michigan from North Point Light to Wind Point WI 5 NM
offshore to Mid Lake-
Lake Michigan from Wind Point WI to Winthrop Harbor IL 5 NM
offshore to Mid Lake-
Lake Michigan from Winthrop Harbor to Wilmette Harbor IL 5 NM
offshore to Mid Lake-
Lake Michigan from Wilmette Harbor IL to Michigan City IN 5 NM
offshore to Mid Lake-
Lake Michigan from Pentwater to Manistee MI 5 NM offshore to Mid
Lake-
Lake Michigan from Whitehall to Pentwater MI 5 NM offshore to Mid
Lake-
Lake Michigan from Grand Haven to Whitehall MI 5 NM offshore to
Mid Lake-
Lake Michigan from Holland to Grand Haven MI 5 NM offshore to Mid
Lake-
Lake Michigan from South Haven to Holland MI 5 NM offshore to Mid
Lake-
Lake Michigan from St. Joseph to South Haven MI 5 NM offshore to
Mid Lake-
356 PM CDT Fri Jun 9 2017

THIS HAZARDOUS WEATHER OUTLOOK IS FOR THE OPEN WATERS OF LAKE
MICHIGAN.

.DAY ONE...Tonight.

There is a small chance of thunderstorms over far southern Lake
Michigan this evening.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday.

Periods of thunderstorms are possible Sunday and Sunday night...
and again Monday night and Wednesday over the north half of the
lake.

Gales are possible Saturday and Saturday night across the north
half.

&&

Ed F

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