Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 121425
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
925 AM CDT SAT JUL 12 2014

.DISCUSSION...
316 AM CDT

TODAY THROUGH TONIGHT...
MAIN FOCUS FOR TODAY CONTINUES TO REVOLVE AROUND CONVECTIVE
TIMING/COVERAGE AND INTENSITY. EARLY THIS MORNING AN AREA OF SHOWERS
WAS BEGINNING TO DEVELOP OVER THE CENTRAL/SOUTHERN PORTIONS OF THE
FORECAST AREA...MAINLY ASSOCIATED WITH WARM AIR ADVECTION. DEW PTS
WERE NUDGING UP TO THE MID 60S...WITH THE EXPECTED 70 DEG DEW PTS
JUST SOUTH/SOUTHWEST OF THE CWFA. PWAT VALUES LATER TDY ARE STILL
PROGGED TO NEAR 2"...AND THE LCL ARW8KM IS SUGGESTING THAT A FEW
POCKETS OF JUST OVER 2" PWAT VALUES FOR PORTIONS OF THE AREA SOUTH
OF I-80 LATE THIS AFTN/EARLY EVE. TEMPS TODAY WILL BE A
CHALLENGE...AS IF ANY BREAKS IN THE CLOUDS CAN OCCUR TEMPS COULD
NUDGE UP A FEW DEGREES. AT THIS TIME WILL MAINTAIN TEMPS IN THE LOW
TO NEAR MID 80S. WITH THE HIGH AMOUNT OF MOISTURE IN PARCELS...IT
WILL BE DIFFICULT FOR TEMPS TO SOAR AND LIKELY BE A SLOW DIURNAL
CURVE TDY. CONFIDENCE OF ANY BREAKS IN THE CLOUDS LOOKS
MINIMAL...AND MAY QUICKLY FILL BACK-IN.

THERE REMAINS A CONCERN ABOUT STRONG TO POSSIBLY SEVERE STORMS. THE
SPC CONTINUES TO HAVE THE ENTIRE FORECAST AREA OUTLOOKED FOR A
SLIGHT RISK OF SEVERE STORMS IN THE DAY 1. THE FOCUS FOR ACTIVITY
CONTINUES TO BE ALONG MOIST BOUNDARY THAT WILL EXTEND FROM CENTRAL
IOWA EAST THROUGH NORTHERN IL/NORTHWEST IN. GUIDANCE SOUNDINGS WOULD
SUGGEST RATHER UNIFORM WIND AT 30-40KTS...HOWEVER THIS IS ALL AHEAD
OF THE POTENT TROUGH THAT WILL BE STARTING TO DIG INTO THE UPPER
MIDWEST THIS EVENING. EXPECT AN MCS TO DEVELOP AND COULD BE SLOW
MOVING ACROSS THE REGION THIS EVENING.

THE PRESENCE OF A WARM LYR ALOFT WILL LIKELY
CAP THE CONVECTIVE COVERAGE UNTIL 21Z...THEN SHUD STEADILY DISSOLVE.
SO THE FOCUS FOR TIMING APPEARS TO BE MORE THIS EVENING INTO THE
OVERNIGHT HOURS. SEVERAL WEAK PIECES OF VORTICITY ARE PROGGED TO
SLIDE ALONG THE MOIST BOUNDARY AS IT SLOWLY SAGS SOUTH/SOUTHEAST
OVERNIGHT. THUS IT IS POSSIBLE SOME TRAINING OF STORMS MAY
OCCUR...AND GIVEN THE ANOMALOUSLY MOIST ENVIRONMENT FLOODING
CONCERNS COULD BE AN ISSUE.

LATE TONIGHT INTO EARLY SUN MORNING...THE BOUNDARY IS PROGGED TO BE
SLOWLY SLIDING SOUTHEAST ACROSS THE FORECAST AREA. GUIDANCE APPEARS
TO HAVE BEEN SLIGHTLY MORE PROGRESSIVE...AND COULD BRING AN END TO
THE CONVECTION A FEW HOURS AFT MIDNIGHT FOR THE NORTHWEST CWFA.

SUNDAY THROUGH MONDAY...
GUIDANCE HAS BEEN TRENDING DRY FOR MUCH OF THE DAY SUN...WITH WEAK
DIFFLUENCE NEAR THE SFC COVERING WISC/NORTHERN IL. LCL ARW8KM HAS
ALSO BEEN TRENDING DRY WITH THE LATEST CYCLES...SO CONFIDENCE HAS
INCREASED AND WILL LEVERAGE THIS WITH A DRY FORECAST SUN. THE
EXCEPTION WILL BE THE SOUTHERN CWFA WHERE THE BOUNDARY WILL STILL BE
RATHER CLOSE. THERMAL TEMPS WOULD STILL BE SUPPORTIVE OF A WARM
AFTN...SO HAVE HELD ONTO TEMPS IN THE LOW 80S SUN.

THE WEAK SFC RIDGE SHUD HOLD ACROSS THE REGION THRU THE EVE
HOURS...THEN BEGIN TO WEAKEN WITH THE MAIN FRONTAL BOUNDARY
APPROACHING FROM THE NORTHWEST EARLY MON. 500MB VORT WILL BE DIGGING
INTO THE UPPER MIDWEST EARLY MON. THE COMBINATION OF COOLER AIR
ALOFT AND SOME THIN CLOUD COVER MON MORNING WILL ALLOW LAPSE RATES
TO STEEPEN AND ADD THE POTENTIAL FOR ISOLATED STORM MON. SFC TEMPS
MON WILL BE STARTING THE COOL DOWN WITH HIGHS GENERALLY IN THE
LOW/MID 70S.

CONFIDENCE...MEDIUM/HIGH.

TUESDAY THROUGH FRIDAY...
ENSEMBLES CONTINUE TO DEMONSTRATE HIGH CONFIDENCE WITH MINIMAL
SPREAD AMONGST MEMBERS FOR THE BULK OF THE EXTENDED FORECAST
PERIODS. POTENT 500MB VORT WILL ARRIVE OVER THE GREAT LAKES
TUE...AND PRODUCE AN UNSEASONABLY COOL DAY WITH HIGHS STRUGGLING TO
WARM BEYOND THE 60S AS THE 850MB THERMAL TROUGH IS PROGGED AT 4 TO 6
DEG C. FORTUNATELY WITH BROAD SFC RIDGING ARRIVING TUE NGT AND
EXPECTED TO PERSIST THRU THE END OF THE WEEK...TEMPS WILL STEADILY
WARM INTO THE 70S.

CONFIDENCE...HIGH.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* MODERATE TO HEAVY SHOWERS AND SOME EMBEDDED TSRA MOVING THROUGH
  TIL AROUND 1530/16Z OR SO. HEAVIEST MAY SKIRT ORD JUST TO THE
  SOUTH.

* MVFR CIGS/VSBY IN RAIN IMPROVES TO VFR BY LATE MORNING. BRIEF
  SUB 1SM VSBY POSSIBLE AT MDW.

* WINDS SHOULD SHIFT WEST WITH APPROACHING LINE OF
  SHRA/TSRA...THEN MAY BECOME VARIABLE OR EVEN NORTHEAST AND LIGHT
  FOR A SHORT PERIOD AS RAIN ENDS.

* LOW CHANCES FOR SHRA/TSRA THIS AFTERNOON BUT BEST CHANCE COMES
  THIS EVENING WITH GUSTY WINDS AND VERY HEAVY RAINFALL POSSIBLE.

MDB

//DISCUSSION...UPDATED 14Z...

LAST OF MORNING CONVECTION IS NOW WORKING ACROSS THE CHI METRO AND
SHOULD CLEAR TOWARD 16Z AND A BIT LATER AT GYY. HEAVIEST RAINFALL
AND LOWEST VSBY /SUB 1SM AT TIMES/ LOOKS TO SKIRT TO THE SOUTH OF
ORD. TS HAS BEEN SPOTTY IN THIS NEXT BAND. WINDS LOOKS TO SHIFT TO
THE WEST AND MAYBE GUSTS INTO THE TEENS AS THE HEAVIER PRECIP
PASSES WITH WINDS MORE OF A CHALLENGE BEHIND THE LINE. WINDS HAVE
TURNED LIGHT NORTHEAST ACROSS NORTHWEST IL BUT THE COMPLEX IS LESS
ORGANIZED THAN IT WAS SO THE WIND FIELDS MAY BE LESS AFFECTED.
WILL HIGHLIGHT THE WEST SHIFT THEN BRING BACK SOUTHWEST OR
VARIABLE. HAVE BETTER CONFIDENCE IN SPEEDS BEING RATHER LIGHT IF
NOT CALM FOR A TIME. LARGER SCALE SOUTHWEST WINDS LOOK TO RE-
ESTABLISH THEMSELVES LATE THIS MORNING. NO CHANGES TO AFTERNOON OR
EVENING FORECAST AT THIS POINT.

MDB

UPDATED 12Z...

THE FIRST BATCH OF SHOWERS WITH EMBEDDED THUNDERSTORMS IS PASSING
THROUGH...WITH THE BULK OF THE THUNDER ACTIVITY CONFINED FROM
ABOUT MDW SOUTH. EXPECT THIS AREA TO CONTINUE EAST. THE NEXT BATCH
OF SHOWERS AND THUNDERSTORMS LOOKS TO ARRIVE IN A FEW HOURS. THERE
HAS BEEN A WEAKENING TREND WITH THESE STORMS. CURRENT FEELING IS
THUNDER ACTIVITY WITH THIS WAVE WILL REMAIN SOUTH AND WEST OF THE
TERMINALS...SO CARRYING SHRA ONLY FOR NOW...BUT THE CHANCE IS NOT
ZERO. MVFR CONDITIONS HAVE OCCURRED BEHIND THE FIRST WAVE OF
SHOWERS AND STORMS AND EXPECT THIS TO CONTINUE THROUGH THE SECOND
ROUND OF SHOWERS WHICH SHOULD CLEAR THE TERMINALS BY EARLY
AFTERNOON.

THE BEST CHANCE FOR STORMS IS STILL LATER IN THE DAY AND INTO
SATURDAY NIGHT. THIS IS WHEN OVERALL CONVERGENCE/FOCUS AHEAD OF
THE APPROACHING COLD FRONT INCREASES...AS WELL AS AN OVERALL
BETTER ENVIRONMENT FOR THUNDERSTORM DEVELOPMENT/ORGANIZATION. IF
THE FRONT STALLS A BIT LATER TONIGHT...TSRA CHANCES MAY LINGER
LONGER THAN CURRENT TAFS INDICATE.

KMD

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH CONFIDENCE IN BAND OF SHRA/EMBEDDED TSRA MOVING THROUGH
  NEXT 1-2 HRS.

* HIGH CONFIDENCE IN CIG/VSBY IMPROVING LATE MORNING. MEDIUM-HIGH
  CONFIDENCE IN SUB 1SM VSBY BRIEFLY OCCURRING AT MDW.

* MEDIUM CONFIDENCE IN SHIFT TO WEST WINDS WITH STORMS...LOW
  CONFIDENCE IN DIRECTION AFTER THAT THROUGH LATE MORNING BUT
  MEDIUM CONFIDENCE IN SPEEDS BEING UNDER 10 KT IF NOT UNDER 7 KT.

* MEDIUM CONFIDENCE THAT SHRA/TSRA CHANCES ARE LOW THIS AFTERNOON
  AND MEDIUM-HIGH CONFIDENCE IN BEST CHANCES THIS EVENING. LOW-
  MEDIUM CONFIDENCE IN TIMING.

MDB

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

SUNDAY-MONDAY...LOW CHANCES OF TSRA.
TUESDAY...SLIGHT CHANCE OF SHRA.
WEDNESDAY-THURSDAY...VFR LIKELY.

KMD

&&

.MARINE...
244 AM CDT

STILL SEEING GUSTS TO NEAR 20 KT ON THE NORTHERN HALF OF THE
LAKE...BUT DO EXPECT THE PRESSURE GRADIENT TO RELAX TONIGHT INTO
SATURDAY AS HIGH PRESSURE ALONG THE ATLANTIC COAST CONTINUES EAST.
A TROUGH OF LOW PRESS SURE AND FRONTAL BOUNDARY WILL CROSS THE LAKE
ON SATURDAY NIGHT. CONFIDENCE IS LOWER WITH REGARDS TO OVERALL
WIND DIRECTION AND SPEEDS SATURDAY EVENING INTO SATURDAY NIGHT AS
PERIODS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED ALONG THIS
FRONTAL BOUNDARY. A SERIES OF WEAK LOW PRESSURE SYSTEMS AND
ASSOCIATED COLD FRONTS WILL THEN PASS THROUGH THE LAKE THROUGH
MONDAY WHILE HIGH PRESSURE BUILDS INTO THE NORTHERN CENTRAL
PLAINS. WINDS SHIFT TO WEST- NORTHWEST BEHIND THE STRONGER COLD
FRONTAL PUSH MONDAY NIGHT AND REACH 20 KT OR POSSIBLY HIGHER
TUESDAY.

KMD

&&

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

$$

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