Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 131932
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
232 PM CDT SUN JUL 13 2014

.DISCUSSION...
245 AM CDT

TODAY THROUGH TONIGHT...
EARLY THIS MORNING THE CONVECTIVE LINE HAS CONTINUED TO PUSH FURTHER
SOUTH...LOCATED ALONG THE SOUTHERN FORECAST AREA STRETCHING
NORTHEAST AND CLIPPING A PORTION OF NORTHWEST INDIANA. THIS BOUNDARY
WILL SLOWLY SAG FURTHER SOUTH/EAST THROUGH THE MORNING HOURS. BEHIND
THE FEATURE...PRECIP HAS COME TO AN END AND THE BULK OF THE DAY IS
EXPECTED TO BE DRY FOR MUCH OF THE CWFA. THE EXCEPTION WILL BE THRU
THIS MORNING FOR THE SOUTHERN PORTIONS...ALTHOUGH IF THE BOUNDARY
CAN MAINTAIN A CURRENT FORWARD SPEED PRECIP MAY END JUST AFT
DAYBREAK.

THEN THE NEXT CHALLENGE WILL RESIDE WITH HOW WARM THE SFC WILL
BECOME. THE LACK OF A GRADIENT BEHIND THE INITIAL CONVECTIVE
BOUNDARY WILL AID IN KEEPING DEW PTS SLIGHTLY ELEVATED IN THE
MID/UPR 60S. SKIES SHUD BEGIN TO THIN BY MIDDAY...AND EXPECT HIGHS
TO PUSH BACK TO ARND 80 TO PSBLY THE LOW 80S.

A HANDFUL OF THE HI-RES SOLUTIONS SUGGEST THAT SOME STEEPENING IN
THE LAPSE RATES THIS AFTN COULD PAINT A FEW SHOWERS. THEN ONCE WE
LOSE THE DIURNAL COMPONENT...PRECIP WILL DIMINISH. OVERNIGHT LOWS
WILL LIKELY FALL INTO THE UPR 50S/LOW 60S.

MONDAY THROUGH TUESDAY...
ROBUST 500MB VORT/TROUGH WILL CONTINUE TO PIVOT SOUTHEAST ACROSS THE
UPPER MIDWEST TOWARDS THE GREAT LAKES REGION MON...WITH TEMPS
STEADILY COOLING ALOFT AND EVENTUALLY REACHING THE SFC. GUIDANCE
CONTINUES TO HINT THAT SOME WEAK INSTABILITY MAY DEVELOP...AND WITH
SOME BREAKS IN THE CLOUD COVER MARGINAL SFC INSTABILITY COULD
WARRANT AN ISOLATED THUNDERSTORM GENERALLY SOUTH OF I-80. TEMPS MON
WILL LINGER IN THE 70S. SOME HEIGHT RISES SHUD CREEP EAST INTO THE
AREA MON NGT AND BRING AN END TO THE ISOLATED CONVECTION...WITH SOME
BREAKS IN CLOUDS AND ALLOW TEMPS TO RADIATE INTO THE LOW 50S. IT IS
POSSIBLE THAT THE TRADITIONALLY COOL SPOTS COULD DIP INTO THE UPR
40S MON NGT.

WRAP AROUND MOISTURE WILL BE DIVING SOUTH/SOUTHEAST ACROSS WISC MON
NGT...AND SHUD CLIP THE NORTHEAST PORTIONS OF THE CWFA TUE MIDDAY
THRU EARLY EVE. THERE IS SOME DIFFERENCES IN THE LATEST SOLUTIONS
THAT ARE BEGINNING TO SUGGEST THE UPPER LEVEL TROUGH THAT ARRIVES
COULD REMAIN PROGRESSIVE...WHICH MAY ALLOW TEMPS TO BE A LITTLE
WARMER FOR TUE. HAVE NUDGED TEMPS UP A DEG TO ARND 70 TUE...AND IF
THE SOLUTIONS CONTINUE TO AGREE THAT A SLIGHTLY MORE PROGRESSIVE
TROUGH DOES OCCUR THEN TEMPS TUE COULD BE GENERALLY IN THE LOW 70S
AND PERHAPS END UP WITH A DRY DAY.

CONFIDENCE...HIGH.

WEDNESDAY THROUGH SATURDAY...
ENSEMBLES CONTINUE TO DEMONSTRATE HIGH CONFIDENCE IN THE EXTENDED
PERIODS WITH THE TROUGH AXIS LIFTING NORTHEAST BY THUR...AND FLOW
UPSTREAM BEGINNING TO BECOME FLAT. THERE IS SOME HINT THAT A WEAK
TROUGH MAY BEGIN TO DEVELOP OVER THE CANADIAN ROCKIES THUR/FRI...AND
ARRIVE OVER THE GREAT LAKES REGION LATER NEXT WEEKEND.

DESPITE THE STEADY LIFTING OF THE TROUGH AXIS...BROAD SFC RIDGING
WILL LINGER OVERHEAD THRU FRI BUT BE DRIFTING EAST BY THE WEEKEND.
GUIDANCE HAS BEEN CONSISTENT IN BRINGING A STEADY MODERATING TREND
AND A RETURN TO MORE SEASONAL AIR BY WEEKS END.

CONFIDENCE...HIGH.

BEACHLER

&&

.AVIATION...

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

* VERY SLIGHT CHANCE OF ISOLATED SHOWERS LATE THIS AFTERNOON AND
  EVENING.

* ANOTHER ROUND OF SHOWERS MAY IMPACT MDW LATE TONIGHT INTO MONDAY
  MORNING.

JEE

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

THE SURFACE LOW IS OVER NORTHEAST ONTARIO WITH A SURFACE TROUGH
LYING SOUTHWEST THROUGH THE MIDWEST. A COLD FRONT EXTENDS FROM
NORTHERN LAKE MICHIGAN THROUGH SOUTHWEST WI INTO IOWA WITH GUSTY
WEST WINDS TO ITS NORTH. THE FRONT WILL SLOWLY SHIFT SOUTHEAST
THROUGH THE AFTERNOON AND WE MAY SEE A FEW SHOWERS POP UP AHEAD OF
IT. THINKING THE BEST CHANCE FOR SHOWERS WILL BE AT RFD SO THEY
ARE THE ONLY SITE WITH THE MENTION OF PRECIP THIS AFTN. WINDS
WILL BECOME VERY LIGHT THIS EVENING AND OVERNIGHT. WINDS MAY ALSO
BECOME MORE NORTHERLY THAN CURRENTLY FORECAST...BUT SPEEDS WILL BE
5 KT OR LESS.

AN UPPER LEVEL WAVE MOVES THROUGH THE REGION LATE TONIGHT INTO
SUNDAY MORNING AND ANOTHER ROUND OF SHOWERS IS POSSIBLE MAINLY
SOUTH OF THE TERMINALS. GYY WILL HAVE THE BEST CHANCE OF RAIN
AND THE SHOWERS WILL BE CLOSE TO MDW. SOME MODELS SUGGEST THE
SHOWERS COULD IMPACT DPA AND ORD...BUT THINKING THE BEST CHANCE
WILL BE FOR MDW AND GYY. WINDS WILL THEN BE OUT OF THE WEST ARND
10 KT TOMORROW WITH VFR CONDITIONS EXPECTED.

JEE

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

* LOW CONFIDENCE IN SHRA THIS AFTN/EVE.

* MEDIUM CONFIDENCE IN VCSH AT MDW LATE TONIGHT INTO MONDAY
  MORNING...LOW CONFIDENCE IN HOW FAR NORTH SHOWERS WILL BE.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE

//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...

MONDAY NIGHT...VFR LIKELY.
TUESDAY...CHANCE OF SHRA. MAINLY VFR.
WEDNESDAY-FRIDAY...VFR LIKELY.
SATURDAY...SHRA/TSRA POSSIBLE.

KMD

&&

.MARINE...
227 PM CDT

A MORE EARLY FALL-LIKE PATTERN WILL BUILD INTO THE REGION EARLY
THIS WEEK AS STRONG LOW PRESSURE OVER JAMES BAY THIS AFTERNOON
DEEPENS AND MOVES NORTHEASTWARD. THIS WILL BRING SEVERAL FRONTAL
BOUNDARIES SOUTHWARD DOWN THE LAKE WITH THE FIRST MOVING THROUGH
THIS EVENING...WITH ANOTHER PASSING LATER TOMORROW. WESTERLY WINDS
WILL TURN MORE SOUTHERLY TONIGHT THEN WESTERLY MONDAY. STRONG
HIGH PRESSURE WILL BE MOVING SOUTHWARD INTO THE NORTHERN PLAINS
BEHIND THE NEXT PASSING COOL FRONT. THIS WILL BRING A FAIRLY
STRONG PRESSURE GRADIENT ACROSS THE LAKE MONDAY EVENING AND MONDAY
NIGHT IN CONJUNCTION WITH A PUSH OF MUCH COOLER AIR. THIS WILL
LIKELY SET UP THE FIRST UNSTABLE CONDITIONS WE HAVE SEEN OVER THE
LAKE IN QUITE A WHILE SUPPORTING THE MIXING OF STRONGER NORTHWEST
WIND GUSTS TO THE SURFACE. THE STRONGEST GRADIENT WILL BE ACROSS
THE SOUTHERN PART OF THE LAKE AND IT DOES APPEAR THAT 20 TO 25 KT
GUSTS WILL BE LIKELY INTO MONDAY NIGHT. THE PRESSURE GRADIENT
WEAKENS TUESDAY ALLOWING WINDS TO DIMINISH BEFORE THE HIGH BUILDS
OVERHEAD WEDNESDAY. THE INDIANA NEARSHORE WATERS MAY REACH SMALL
CRAFT CRITERIA FOR WINDS AND WAVES MONDAY EVENING AND MONDAY
NIGHT. BY WEDNESDAY...ONSHORE FLOW WILL LIKELY DEVELOP WITH LIGHT
SPEEDS WHICH MAY PERSIST INTO FRIDAY AT WHICH POINT THE BULK OF
THE HIGH WILL BE TO THE EAST. A STEADIER SOUTHERLY FLOW SHOULD TRY
TO SET UP NEXT WEEKEND BUT THE MAIN PRESSURE GRADIENT WILL STILL
BE TO THE WEST SO DAYTIME ONSHORE FLOW MAY CONTINUE SOUTH WHERE
THE PRESSURE GRADIENT LOOKS TO BE WEAKER.

ONE OTHER ITEM FOR MONDAY NIGHT IS THE POTENTIAL FOR WATERSPOUTS.
LATEST GUIDANCE SHOWS 850 MB TEMPS COOLING TO AROUND +4 OR +5 C
INTO THE OVERNIGHT HOURS LEADING TO A LAKE-850 DELTA T OF AROUND
+12 C. SOME OF THE LATEST FORECAST SOUNDINGS SHOW A PERIOD OF DEEP
INSTABILITY WITH EQUILIBRIUM LEVELS IN THE 20-25 KFT RANGE USING
TODAYS WATER TEMPS AT THE MID LAKE BUOYS. THESE CONDITIONS WOULD
BE ON THE LOWER END OF WATER SPOUT POTENTIAL SO WILL CONTINUE TO
MONITOR FOR NOW.

MDB

&&

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

$$

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