Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 021802
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
102 PM CDT SAT MAY 2 2015

.SHORT TERM...
325 AM CDT

THROUGH SUNDAY...

HIGH PRESSURE IS OVER THE REGION AND IT WILL CONTINUE TO SLOWLY
SHIFT SOUTHEAST THROUGH TONIGHT. FLOW IS ZONAL ALOFT WITH A WEAK
SHORTWAVE MOVING OVER THE REGION LATE TONIGHT. SO FOR TODAY
EXPECTING MOSTLY SUNNY SKIES...SOUTHWEST WINDS...AND A LAKE BREEZE
THAT HUGS THE IMMEDIATE SHORE. RAISED TEMPS QUITE A BIT BASED ON
CLIMATE DATA SO THAT ALL AREAS ARE IN THE UPPER 70S AND A FEW
SITES LIKE RFD AND PONTIAC REACH OR GET CLOSE TO 80. THINKING
THERE WILL NOT BE MUCH LAKE COOLING AS LONG AS THE LAKE BREEZE
BEHAVES AND DOES NOT PUSH INLAND. ALSO BANKING ON CLOUD COVER TO
DECREASE THIS AFTERNOON ALLOWING FOR AMPLE WARMING. HAVE MEDIUM-
HIGH CONFIDENCE IN HIGH TEMPS TODAY AND IF WE GET MORE SUN COULD
SEE MORE SITES REACHING 80 TODAY.

DECIDED TO KEEP A VERY SLIGHT CHANCE FOR THUNDERSTORMS ALONG AND
WEST OF I-39 FROM MIDNIGHT INTO VERY EARLY SUNDAY MORNING.  HAVE
VERY LOW CONFIDENCE IN THUNDERSTORMS WHICH IS WHY I CAPPED POPS IN
THE LOW SLIGHT CHANCE RANGE.  FORECAST SOUNDINGS LOOK ON THE DRY
SIDE BUT THE SHORTWAVE MAY PROVIDE ENOUGH FORCING FOR A FEW ELEVATED
THUNDERSTORMS.

THE UPPER LEVEL FLOW BECOMES ZONAL AGAIN SUNDAY WHILE A SURFACE LOW
PUSHES NORTH OVER HUDSON BAY. THE LOWS COLD FRONT REMAINS TO OUR
WEST OVER THE UPPER MIDWEST...WHICH MEANS WILL BE IN THE LOWS WARM
SECTOR. WAA LOOKS TO BE VERY STRONG WITH SOUTHWEST WINDS GUSTING TO
30 MPH. THE BIG QUESTION FOR SUNDAY IS CLOUD COVER. DECIDED TO RAISE
MAX TEMPS A BIT SO JUST ABOUT ALL AREAS SEE 80 DEGREES...BUT IF
CLOUD COVER IS LESS COULD EASILY SEE MANY LOCATIONS GETTING INTO THE
LOW-MID 80S. ON THE OTHER HAND...IF CLOUD COVER IS GREATER...80S MAY
BE A STRETCH.

JEE

&&

.LONG TERM...
325 AM CDT

SUNDAY NIGHT THROUGH FRIDAY...

THE UPPER LEVEL ZONAL FLOW GIVES WAY TO A RIDGE THAT HANGS AROUND
THROUGH LATE NEXT WEEK. THE SFC PATTERN IS BUSIER THOUGH. THE VORT
STREAMER AND TROUGH ASSOCIATED WITH THE APPROACHING COLD FRONT
SWING THROUGH EARLY MONDAY MORNING BUT WE SHOULD START TO SEE THE
PRECIP AHEAD OF THE FRONT AS EARLY AS SUNDAY EVENING. HAVE MEDIUM
CONFIDENCE IN HOW QUICKLY THE PRECIP MOVES IN AS GUIDANCE DIFFERS
WITH THE SPEED OF THE FRONT AND PRECIP. AM EXPECTING WIDESPREAD
THUNDERSTORMS AS LAPSE RATES ALOFT ARE RATHER STEEP RESULTING IN A
FEW HUNDRED JOULES OF ELEVATED CAPE. PWAT VALUES WILL BE ABOVE
NORMAL AT 1.0-1.3 INCHES SO THE THUNDERSTORMS MAY PRODUCE
SIGNIFICANT RAINFALL.

MONDAY LOOKS STORMY AS THE VORT STREAMER CONTINUES TO MOVE THROUGH.
PWAT VALUES INCREASE TO AROUND 1.5 INCHES AND EXPECTING AROUND A
HALF INCH OF PRECIP ALONG THE IL/WI STATE LINE AND 0.25-0.4 INCHES
ALONG AND SOUTH OF I-80. LOCALLY HIGHER TOTALS ARE POSSIBLE UNDER
THUNDERSTORMS.  HIGH TEMPS WILL VARY FROM AROUND 70 ALONG THE IL/WI
STATE LINE AND LAKE FRONT TO THE MID 70S ALONG AND SOUTH OF I-80.

THE COLD FRONT STALLS OUT MONDAY EVENING AND THE MODELS DISAGREE ON
WHERE THE FRONT WILL END UP. THE GFS HAS THE FRONT OVER THE IL/WI
STATE LINE...THE NAM HAS IT ROUGHLY ALONG I-80...AND THE ECMWF HAS
IT OVER THE SOUTHERN BORDER OF MY CWA.  DECIDED TO GO WITH THE
MIDDLE OF THE ROAD APPROACH ALONG I-80 AND HAVE LIKELY POPS IN FOR
MONDAY NIGHT AND TUESDAY. EXPECTING CONVECTION TO FESTER ALONG THE
FRONT WHEREVER IT SETS UP SO FELT CONFIDENT ENOUGH TO SAY WE WILL
SEE THUNDERSTORMS DURING THIS PERIOD.  AROUND ANOTHER HALF INCH OF
PRECIP IS EXPECTED...ONCE AGAIN WITH LOCALLY HIGHER AMOUNTS UNDER
THUNDERSTORMS.  HIGHS ON TUESDAY REFLECT THE LOCATION OF THE FRONT
AS IT WILL BE COOLER NORTH OF THE FRONT AND WARMER TO THE SOUTH.

THE FRONT LIFTS NORTH AS A WARM FRONT WEDNESDAY MORNING. CAPPED POPS
IN THE LOW CHANCE RANGE BECAUSE IF THE FRONT LIFTS QUICKER THERE IS
A CHANCE WE MAY ONLY SEE ISOLATED THUNDERSTORMS IN THE WARM SECTOR.
SOUNDINGS DO NOT FEATURE MUCH FORCING NOR CAPE...BUT THERE IS ENOUGH
CAPE TO SUPPORT THE IDEA OF ANYTHING THAT DOES GO WILL HAVE THUNDER
AND LIGHTNING.  CLOUD COVER IS THE OTHER FACTOR WEDNESDAY AS IF IT
IS MOSTLY SUNNY...MY CURRENT HIGH TEMPS IN THE LOW TO MID 80S AWAY
FROM THE LAKE WILL BE MUCH TOO CONSERVATIVE AND WE COULD EASILY SEE
MID 80S AND MAYBE A COUPLE OF UPPER 80S.

LATE NEXT WEEK ALSO LOOKS WARM AND PERHAPS STORMY ESPECIALLY FRIDAY
AS THE NEXT LOW PASSES OVER LAKE SUPERIOR AND ITS COLD FRONT MOVES
THROUGH THE CWA.  THURSDAY LOOKS SIMILAR TO WEDNESDAY WHERE HIGH
TEMPS DEPEND ON CLOUD COVER. RAISED TEMPS BY A FEW DEGREES INTO THE
LOW TO MID 80S...BUT SLIGHTLY COOLER AIR MOVES IN FRIDAY WITH HIGHS
AROUND 80.

JEE

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* POSSIBLE LAKE BREEZE LATE THIS AFTERNOON.

RODRIGUEZ

//DISCUSSION...UPDATED 18Z...

VFR CONDITIONS WITH SOUTHWEST WINDS EARLY THIS AFTERNOON WILL
LIKELY CONTINUE FOR THE REMAINDER OF THE AFTERNOON. SOUTHWEST
SPEEDS SHOULD BE HIGH ENOUGH TO KEEP THE LAKE BREEZE EAST OF THE
TERMINALS TODAY. HOWEVER...AM MONITORING THE LOW POTENTIAL FOR IT
TO REACH ORD/MDW/GYY LATER THIS AFTERNOON. VFR CONDITIONS WILL
REMAIN FOR THE REMAINDER OF THE FORECAST PERIOD BUT WITH AN
INCREASE IN MID/HIGH CLOUDS LATER TONIGHT INTO SUNDAY MORNING.
PRECIP WELL WEST OF THE TERMINALS AT THIS TIME MAY MOVE EAST
ACROSS THE AREA LATE TONIGHT. IF THIS OCCURS...IT WILL BE LIGHT
AND WITHOUT THUNDER.

RODRIGUEZ


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* HIGH CONFIDENCE WITH VFR CONDITIONS.

* LOW CONFIDENCE WITH LAKE BREEZE POTENTIAL.

RODRIGUEZ

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...SHRA AND EMBEDDED TSRA LIKELY AFTER MIDNIGHT.
               SOUTHWEST WINDS.
MONDAY...PERIODS OF SHRA/TSRA PROBABLE. WINDS BECOMING NORTHEAST.
TUESDAY-WEDNESDAY...CHANCE OF TSRA. EAST TO SOUTHEAST WINDS.
THURSDAY-FRIDAY...CHANCE OF TSRA. SOUTH WINDS.

MTF

&&

.MARINE...
135 AM CDT

THE PRESSURE GRADIENT OVER THE LAKE WILL STRENGTHEN THROUGH THE
NEXT TWO DAYS AS HIGH PRESSURE MOVES TO THE SOUTHEAST U.S. AND A
COLD FRONT ADVANCES EAST ACROSS THE UPPER MIDWEST. SOUTHERLY WINDS
WILL INCREASE ACROSS THE OPEN WATER TODAY...WHILE ILLINOIS AND
INDIANA NEARSHORE AREAS ARE STILL FAVORED TO TURN AT LEAST A
PARTIAL ONSHORE COMPONENT. ON SUNDAY...OFFSHORE FLOW INTO THOSE
NEARSHORE ZONES WILL LIKELY BE AT A STRONG ENOUGH MAGNITUDE TO
WARRANT A SMALL CRAFT ADVISORY.

THE LOW PRESSURE DRIVING THE APPROACHING FRONT WILL ADVANCE
EASTWARD WELL NORTH OF THE REGION ON SUNDAY NIGHT...MEANING ITS
TRAILING FRONT WILL BEGIN TO SLOW AS IT MOVES SOUTHWARD DOWN THE
LAKE LATE THAT NIGHT AND INTO MONDAY. THIS FEATURE IS EXPECTED TO
STALL JUST SOUTH OF THE LAKE MONDAY NIGHT WITH NORTHERLY WINDS
BEHIND IT THEN BECOMING EASTERLY INTO TUESDAY. THEN THE BOUNDARY
WILL DEVELOP NORTH DURING THE MIDDLE OF THE WEEK WITH SOUTHERLY
WINDS INCREASING IN SPEED THROUGH THE LATTER PART OF THE WEEK.

MTF

&&

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

$$

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