National Weather Service Raw Text Product

Displaying AFOS PIL: AFDLOT Received: 2018-06-29 11:02 UTC


899 
FXUS63 KLOT 291102
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
602 AM CDT Fri Jun 29 2018

.SHORT TERM...
254 AM CDT

Through Saturday...

Very hot and humid conditions are the main forecast story for at 
least Friday and Saturday across northern Illinois and northwest 
Indiana. Overall, no big changes in forecast thinking over the 
next couple days and guidance remains in good agreement suggesting
low to mid 90s for high temperatures. The official forecast errs 
on the warmer side of guidance as models tend to struggle with the
magnitude of these higher-end events. Moderate to strong MLCIN 
owing to 850/700mb temps of 23-25C and 14C, respectively, should 
keep skies mostly clear today with little concern for afternoon 
convection. 

Dew points on track to become quite oppressive across the region 
today. Early Thursday evening, dew points in the upper 70s to low 
80s were observed from the mid Missouri Valley southeast across 
the mid Mississippi Valley and guidance suggests this moisture 
axis will lift across northern Illinois and northwest Indiana 
today. Should be able to get a little higher even as the moisture
axis lifts into the corn belt. As with temperatures, staying on 
the high side of guidance for dew points. For the previous heat 
event last week, models across the board had a low bias with dew 
points. Given these factors, felt comfortable nudging dew points 
up a hair from previous forecast bringing more of the forecast 
area closer to the 80 mark outside the city. This yields heat 
indices of around 110F for the city of Chicago and portions of 
northwest Indiana, and into the 110-120 range farther west and 
southwest. 

Conditions don't change too terribly much for Saturday. The local 
area still lies under the thermal ridge and within the moisture 
axis, though the upper ridge axis does inch east away from the
area. As a result, soundings indicate only weak capping in place
during the afternoon hours. Forcing isn't readily apparent, 
though some models indicate convergence as winds over Lake 
Michigan try to turn a lake breeze. Couldn't rule out an isolated 
storm or two forming near the shores of Lake Michigan and moving 
over the lake if this were to occur, but more likely expect cap to
hold.

Will upgrade the remainder of the Excessive Heat Watch to and 
Excessive Heat Warning for Friday and Saturday.

Deubelbeiss

&&

.LONG TERM...
254 AM CDT

Sunday through Friday...

Confidence in the forecast details, especially with respect to the 
heat, begins to diminish by Sunday as weather could become more 
unsettled through the day. Upper ridge axis is progged to shift to
the East Coast Sunday while broad and shallow longwave trough 
spreads from the West Coast across the Great Plains. A lead 
shortwave trough and attendant surface cold front is progged to 
move across portions of the Upper Midwest on Sunday kicking off 
showers and thunderstorms. The cold front isn't expected to pass 
through the local area until Sunday night, but showers and 
thunderstorms will likely precede fropa adding uncertainty in the 
temperature forecast. Guidance ranges from mid 80s to mid 90s for
highs and will lean towards the middle of the spread given the 
uncertainty. If convection is able to hold off until late in the 
day, it's quite possible additional heat headlines will be needed 
through the day Sunday. In addition, the area could still 
experience moderate to strong instability Sunday with increasing 
shear expected as the shortwave trough approaches. Will have to 
keep an eye on the severe thunderstorm potential as we get closer.

Unsettled weather could continue throughout much of the upcoming 
week. Upper ridge will initially settle over the east coast with 
the local area falling on the western periphery of the ridge axis 
Monday. Temperatures briefly moderate in the mid 80s Monday behind
the front, but should see temps bounce back around or into the 
90s through the latter half of the week as a broad upper ridge 
builds from the Desert Southwest to the mid Atlantic Coast. 
Thermal ridge and effective cap remains just to our west through 
much of the upcoming week which could allow for scattered 
diurnally favored thunderstorms locally as MLCIN is eroded each 
afternoon. There isn't any notable synoptic scale forcing for 
ascent under the influence of the upper ridge, so will have to 
keep an eye out for smaller scale, lower amplitude features to get
a better handle on specific timing and coverage of these
thunderstorm chances.

Deubelbeiss

&&

.CLIMATE...

Record Temps

For the Chicago area...

Record High Max Temp
June 29: 97F (1954)
June 30: 99F (1913, 1953)

Record High Min Temp
June 29: 80F (1931)
June 30: 80F (1931)

For the Rockford area...

Record High Max Temp
June 29: 103F (1931)
June 30: 102F (1931)

Record High Min Temp
June 29: 75F (1931) 
June 30: 74F (1913, 1931)

&&

.AVIATION...
For the 12Z TAFs...

Concerns for the Chicago area TAFs are limited as a dome of heat
moves into the area.

South-southeast winds early this morning should quickly turn
south-southwest, with occasional gusts in the mid to upper teens 
by mid-late morning. Confidence in wind direction being 180 to 200
degrees today is high. The gusts should ease by early evening.
Aloft a low-level jet overnight will provide potential for RFD to
see low-level wind shear, with south-southwest winds around 40 kt
at only 1000 ft or so.

With full or close to full sun this afternoon, high heat will 
build in over the airfields, with heat index readings (combination
of temperature and dew point) of 105-115 forecast.

MTF

&&

.MARINE...
112 AM CDT

Southerly winds of 15 to 25 kt will prevail over the lake through
the weekend, with the exceptions being occasional gusts to 30 kt
this afternoon and evening across the north, where also a few
thunderstorms are possible midday that could temporarily shift 
winds westerly. Confidence in these are low though. Storms are 
again possible late Saturday night into Sunday,and across much of
the lake. For much of the weekend though, dry conditions are 
expected.

For the Illinois and Indiana nearshore, dry weather is likely for
much of the weekend. South to south-southwest winds will prevail.
On Sunday, these could be close to Small Craft Advisory criteria 
with gusts at or just over 20 kt presently forecast. With high 
pressure then expected later Monday through the holiday, lighter 
onshore flow is expected, especially across the Illinois 
nearshore.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Excessive Heat Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-
     ILZ022-ILZ023-ILZ032-ILZ033-ILZ039...11 AM Friday to 7 PM 
     Saturday.

IN...Excessive Heat Warning...INZ001-INZ002-INZ010-INZ011-INZ019...11 
     AM Friday to 7 PM Saturday.

LM...None.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO

899 
FXUS63 KLOT 291102
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
602 AM CDT Fri Jun 29 2018

.SHORT TERM...
254 AM CDT

Through Saturday...

Very hot and humid conditions are the main forecast story for at 
least Friday and Saturday across northern Illinois and northwest 
Indiana. Overall, no big changes in forecast thinking over the 
next couple days and guidance remains in good agreement suggesting
low to mid 90s for high temperatures. The official forecast errs 
on the warmer side of guidance as models tend to struggle with the
magnitude of these higher-end events. Moderate to strong MLCIN 
owing to 850/700mb temps of 23-25C and 14C, respectively, should 
keep skies mostly clear today with little concern for afternoon 
convection. 

Dew points on track to become quite oppressive across the region 
today. Early Thursday evening, dew points in the upper 70s to low 
80s were observed from the mid Missouri Valley southeast across 
the mid Mississippi Valley and guidance suggests this moisture 
axis will lift across northern Illinois and northwest Indiana 
today. Should be able to get a little higher even as the moisture
axis lifts into the corn belt. As with temperatures, staying on 
the high side of guidance for dew points. For the previous heat 
event last week, models across the board had a low bias with dew 
points. Given these factors, felt comfortable nudging dew points 
up a hair from previous forecast bringing more of the forecast 
area closer to the 80 mark outside the city. This yields heat 
indices of around 110F for the city of Chicago and portions of 
northwest Indiana, and into the 110-120 range farther west and 
southwest. 

Conditions don't change too terribly much for Saturday. The local 
area still lies under the thermal ridge and within the moisture 
axis, though the upper ridge axis does inch east away from the
area. As a result, soundings indicate only weak capping in place
during the afternoon hours. Forcing isn't readily apparent, 
though some models indicate convergence as winds over Lake 
Michigan try to turn a lake breeze. Couldn't rule out an isolated 
storm or two forming near the shores of Lake Michigan and moving 
over the lake if this were to occur, but more likely expect cap to
hold.

Will upgrade the remainder of the Excessive Heat Watch to and 
Excessive Heat Warning for Friday and Saturday.

Deubelbeiss

&&

.LONG TERM...
254 AM CDT

Sunday through Friday...

Confidence in the forecast details, especially with respect to the 
heat, begins to diminish by Sunday as weather could become more 
unsettled through the day. Upper ridge axis is progged to shift to
the East Coast Sunday while broad and shallow longwave trough 
spreads from the West Coast across the Great Plains. A lead 
shortwave trough and attendant surface cold front is progged to 
move across portions of the Upper Midwest on Sunday kicking off 
showers and thunderstorms. The cold front isn't expected to pass 
through the local area until Sunday night, but showers and 
thunderstorms will likely precede fropa adding uncertainty in the 
temperature forecast. Guidance ranges from mid 80s to mid 90s for
highs and will lean towards the middle of the spread given the 
uncertainty. If convection is able to hold off until late in the 
day, it's quite possible additional heat headlines will be needed 
through the day Sunday. In addition, the area could still 
experience moderate to strong instability Sunday with increasing 
shear expected as the shortwave trough approaches. Will have to 
keep an eye on the severe thunderstorm potential as we get closer.

Unsettled weather could continue throughout much of the upcoming 
week. Upper ridge will initially settle over the east coast with 
the local area falling on the western periphery of the ridge axis 
Monday. Temperatures briefly moderate in the mid 80s Monday behind
the front, but should see temps bounce back around or into the 
90s through the latter half of the week as a broad upper ridge 
builds from the Desert Southwest to the mid Atlantic Coast. 
Thermal ridge and effective cap remains just to our west through 
much of the upcoming week which could allow for scattered 
diurnally favored thunderstorms locally as MLCIN is eroded each 
afternoon. There isn't any notable synoptic scale forcing for 
ascent under the influence of the upper ridge, so will have to 
keep an eye out for smaller scale, lower amplitude features to get
a better handle on specific timing and coverage of these
thunderstorm chances.

Deubelbeiss

&&

.CLIMATE...

Record Temps

For the Chicago area...

Record High Max Temp
June 29: 97F (1954)
June 30: 99F (1913, 1953)

Record High Min Temp
June 29: 80F (1931)
June 30: 80F (1931)

For the Rockford area...

Record High Max Temp
June 29: 103F (1931)
June 30: 102F (1931)

Record High Min Temp
June 29: 75F (1931) 
June 30: 74F (1913, 1931)

&&

.AVIATION...
For the 12Z TAFs...

Concerns for the Chicago area TAFs are limited as a dome of heat
moves into the area.

South-southeast winds early this morning should quickly turn
south-southwest, with occasional gusts in the mid to upper teens 
by mid-late morning. Confidence in wind direction being 180 to 200
degrees today is high. The gusts should ease by early evening.
Aloft a low-level jet overnight will provide potential for RFD to
see low-level wind shear, with south-southwest winds around 40 kt
at only 1000 ft or so.

With full or close to full sun this afternoon, high heat will 
build in over the airfields, with heat index readings (combination
of temperature and dew point) of 105-115 forecast.

MTF

&&

.MARINE...
112 AM CDT

Southerly winds of 15 to 25 kt will prevail over the lake through
the weekend, with the exceptions being occasional gusts to 30 kt
this afternoon and evening across the north, where also a few
thunderstorms are possible midday that could temporarily shift 
winds westerly. Confidence in these are low though. Storms are 
again possible late Saturday night into Sunday,and across much of
the lake. For much of the weekend though, dry conditions are 
expected.

For the Illinois and Indiana nearshore, dry weather is likely for
much of the weekend. South to south-southwest winds will prevail.
On Sunday, these could be close to Small Craft Advisory criteria 
with gusts at or just over 20 kt presently forecast. With high 
pressure then expected later Monday through the holiday, lighter 
onshore flow is expected, especially across the Illinois 
nearshore.

MTF

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Excessive Heat Warning...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012-ILZ013-ILZ014-ILZ019-ILZ020-ILZ021-
     ILZ022-ILZ023-ILZ032-ILZ033-ILZ039...11 AM Friday to 7 PM 
     Saturday.

IN...Excessive Heat Warning...INZ001-INZ002-INZ010-INZ011-INZ019...11 
     AM Friday to 7 PM Saturday.

LM...None.
&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO