🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1233 PM CDT WED MAY 8 2013

.DISCUSSION...
1145 AM CDT

ONLY VERY MINOR CHANGES MADE TO THE GOING FORECAST FOR THIS
AFTERNOON.

THE 1017MB SURFACE RIDGE REMAINS PARKED OVER THE AREA AND WHILE
THERE IS DEEP MIXING UNFOLDING...THERE IS LITTLE WIND ALOFT TO BE
MIXED DOWN. THE ONLY REAL DRIVING FORCE FOR WIND IS ON THE
MESOSCALE LEVEL OFF THE LAKE. MESONET OBSERVATIONS INDICATE THE
LAKE BREEZE IS MAKING PROGRESS INLAND AND SHOULD REINFORCE ITSELF
THROUGH MID-AFTERNOON. THE CONVERGENCE ALONG THIS WILL LIKELY
DEVELOP CU. FURTHER TO THE SOUTH ACROSS NORTHWEST
INDIANA...SUBTLE CONVERGENCE IN THE 900-1000MB LAYER ALONG WITH
SLIGHTLY HIGHER POOLED MOISTURE /TDS IN THE LOW 50S/ HAS ALLOWED
FOR 500-800 J/KG WHICH IS BEGINNING TO BE REALIZED WITH CU.
YESTERDAY SAW WIDELY ISOLATED SHOWERS AND BELIEVE THAT THAT COULD
HAPPEN AGAIN AS THE CONVERGENCE UNDULATES THROUGH THE AFTERNOON.
THE INSTABILITY IS ENOUGH TO CONTINUE TO WARRANT THE MENTION OF A
SMALL THUNDER CHANCE. TEMPERATURES ARE ON TRACK WITH AROUND 80
DEGREES IN PLACES AWAY FROM THE LAKE...WHERE MID 50S WILL HOLD ON
THE IMMEDIATE LAKE FRONT.

LOOKING AHEAD TO THURSDAY FOR SOME INITIAL THOUGHTS...12Z MODEL
GUIDANCE HAS MAINLY SHOWN A DEEPENING TREND IN THE SURFACE LOW
EXPECTED TO LIFT THROUGH THE AREA DURING THURSDAY EVENING. WITH
THIS HAS COME SLIGHTLY STRONGER WIND FIELDS AND A FURTHER NORTH
PUSH IN THE SURFACE INSTABILITY...AS WELL AS IN THE ELEVATED
BAROCLINIC ZONE WHICH LOOKS TO BE A HEALTHY FOCUS FOR SUSTAINED
RAINFALL IN THE EVENING. WILL MORE THAN LIKELY BE ADJUSTING QPF
UPWARDS...ESPECIALLY IN THE NORTHERN FORECAST AREA...AS WELL AS
INCREASING POPS. TEMPERATURES LOOK TO REMAIN VERY TRICKY DUE TO
THE CLOUD COVER...PRECIP...AND WARM FRONT IN ADVANCE OF THE LOW.

MTF/RC

//PREV DISCUSSION...
354 AM CDT

PRIMARY CONCERN THIS FORECAST CYCLE IS WITH PRECIP/THUNDERSTORM
POTENTIAL WEDNESDAY NIGHT INTO FRIDAY...WITH LOW PRESSURE SYSTEM
WHICH WILL TRACK ACROSS THE FORECAST AREA. OTHER FEATURES OF THE
NEXT SEVERAL DAYS INCLUDE WARMTH TODAY...CHILLY WX BEHIND A SHARP
COLD FRONT WHICH MOVES THROUGH THE REGION SATURDAY...THEN A RAPID
WARM-UP EARLY NEXT WEEK.

IN THE NEAR TERM...ANOTHER WARM AND DRY SPRING DAY IS IN STORE TODAY
FOR THE FORECAST AREA AS UPPER LEVEL PATTERN REMAINS QUITE BLOCKY
ACROSS THE CONUS. MID-LEVEL SHORT WAVE RIDGE WILL BUILD OVERHEAD
WITH WEAK SURFACE HIGH PRESSURE LINGERING OVER THE GREAT LAKES. THIS
WILL SUPPORT CONSIDERABLE SUNSHINE...LIGHT EAST-NORTHEAST SURFACE
WINDS AND LAKE BREEZES AND CONTINUED MODERATION IN LOW LEVEL
TEMPERATURES WITH HIGHS IN THE UPPER 70S/AROUND 80 IN MANY AREAS...
EXCEPT 60S ALONG THE LAKE MICHIGAN SHORE. HAVE MAINTAINED A SLIGHT
CHANCE POP FOR AN ISOLATED AFTERNOON SHRA/TSRA ACROSS THE FAR
SOUTHEAST PORTION OF THE CWA...ALONG THE NORTHERN PERIPHERY OF THE
LOW LEVEL MOISTURE GRADIENT WHICH EXTENDS BACK ACROSS IL/IN FROM THE
CLOSED LOW TO OUR EAST. WRF-NAM FORECAST SOUNDINGS YIELD ABOUT 100
J/KG OF MLCAPE THIS AFTERNOON TOWARD THE DANVILLE AND RENSSELAER
AREAS...WHERE CONVECTION ALLOWING MODELS INCLUDING THE WRF-NMM AND
HRRR SUGGEST LOW-COVERAGE ISOLATED DEVELOPMENT AGAIN POSSIBLE
SIMILAR TO YESTERDAY AFTERNOON.

ATTENTION THEN TURNS TO THE WEST LATER TODAY...AS MID-LEVEL SHORT
WAVE ENERGY CURRENTLY OVER THE PLAINS SLOWLY APPROACHES THE AREA.
LOW LEVEL RETURN FLOW DEVELOPS ACROSS AREAS MAINLY WEST OF THE
MISSISSIPPI THIS AFTERNOON IN RESPONSE TO THIS FEATURE...WHILE
WARMER MID-LEVEL TEMPS AND DRIER LOW LEVELS PROVIDE CAPPING FARTHER
EAST INTO IL. SOUTH-SOUTHWEST 925-850 MB LOW LEVEL JET EVENTUALLY
DEVELOPS INTO WESTERN IL OVERNIGHT...THOUGH THE THE MAIN JET AXIS
AND FOCUS FOR THETA-E ADVECTION/MOIST CONVERGENCE AND MOISTURE
TRANSPORT REMAINS LARGELY INTO SOUTHEAST IA AND FAR WESTERN IL
THROUGH 12Z THURSDAY. THUS HAVE KEPT POPS WEST GENERALLY WEST OF
CHICAGO-KANKAKEE AREAS AND MAINLY ACROSS NORTH CENTRAL IL THROUGH
THURSDAY MORNING. FORCING AND MOISTURE TRANSPORT THEN DEVELOP EAST
ACROSS NORTHERN IL/IN THURSDAY MORNING...AS POSITIVE TILT SHORT WAVE
CONTINUES TO SLOWLY PROPAGATE EASTWARD WITH DEVELOPMENT OF SURFACE
LOW PRESSURE WAVE WHICH ALSO MOVES ACROSS SOUTHERN PARTS OF THE CWA
DURING THE AFTERNOON AND EVENING HOURS. SPC HAS MAINTAINED THE
SLIGHT RISK FOR THE SOUTHEAST HALF OF THE CWA IN THEIR DAY 2 OUTLOOK
ALONG/SOUTH OF DEVELOPING STATIONARY/WARM FRONT ASSOCIATED WITH THE
SURFACE LOW. WRF-NAM FORECAST SOUNDINGS ACROSS THAT PORTION OF THE
FORECAST AREA INDICATE THE POTENTIAL FOR 500-1500 J/KG MLCAPE DURING
THE MIDDAY AND AFTERNOON HOURS...WHICH COMBINED WITH EFFECTIVE SHEAR
VALUES 25-40 KT MAY SUPPORT SOME ORGANIZED CONVECTIVE STORM
STRUCTURES AND THE POTENTIAL FOR ISOLATED DAMAGING WIND/LARGE HAIL
PRODUCING STORMS. THE UPPER TROUGH AND ITS ASSOCIATED SURFACE LOW
CONTINUE TO MOVE EAST ACROSS THE AREA THURSDAY EVENING...WITH THE
STRONGER FORCING AND BAROCLINIC ZONE EVENTUALLY SHIFTING TO THE
EAST/SOUTH OF THE CWA BY EARLY FRIDAY MORNING. GUIDANCE SHOWS SOME
SPREAD IN PLACEMENT OF HEAVIER QPF WITH THIS SYSTEM...THOUGH WOULD
EXPECT THE HIGHEST AMOUNTS ALONG/SOUTH OF THE MAIN BAROCLINIC ZONE
WHICH WOULD SUPPORT THE POTENTIAL FOR GREATER AMOUNTS ACROSS THE
CENTRAL AND SOUTHERN PARTS OF THE CWA. BLENDING GUIDANCE QPF OUTPUT
SUGGESTS RAINFALL AMOUNTS RANGING FROM 0.35 INCH FAR NORTHWEST TO
1.0-1.2 ACROSS THE SOUTH. SCATTERED SHOWERS MAY LINGER INTO FRIDAY
ESPECIALLY ACROSS SOUTHERN COUNTIES OF THE CWA...AS A WEAKER
SECONDARY SHORT WAVE DIGS IN BEHIND THE FIRST...AND CLOSER TO
RETREATING LOW LEVEL BAROCLINIC ZONE ASSOCIATED WITH THE SAGGING
COLD FRONT.

TEMPERATURE FORECAST FOR THURSDAY IS A LITTLE COMPLICATED BY THE
TRACK OF THE LOW...WHICH WILL LIKELY RESULT IN EAST-NORTHEAST WINDS
ACROSS NORTHERN COUNTIES...AND SOUTHERLY WINDS SOUTH OF THE LOW
TRACK. COVERAGE OF CLOUDS/RAIN ALSO MAKES FOR A LOWER CONFIDENCE
TEMP FORECAST...THOUGH MODEL THERMAL FIELDS INDICATE HIGHS RANGING
FROM NEAR 70 ALONG THE IL/WI BORDER TO THE LOW/MID 70S FAR SOUTH. OF
COURSE WINDS OFF THE LAKE WILL KEEP THINGS COOLER ALONG LAKE
MICHIGAN. FRIDAY WILL BE COOLER STILL...WITH 50S NEAR THE LAKE AND
LOW/MID 60S WELL WEST/SOUTH. COLDER WEATHER IS YET TO COME OVER THE
WEEKEND HOWEVER...AS STRONG SHORT WAVE DIGS ACROSS THE UPPER MIDWEST
AND NORTHERN LAKES AND AMPLIFIES UPPER TROUGH ACROSS THE REGION
SATURDAY. A STRONG COLD FRONT WILL PUSH SOUTHEAST ACROSS THE AREA
DURING THE DAY WITH A FEW SHOWERS...AND UNSEASONABLY COOL AIR
SPREADING ACROSS THE REGION LATE SATURDAY THROUGH SUNDAY. HIGHS ON
SUNDAY...MOTHERS DAY...MAY NOT RISE ABOVE 60 IN SOME SPOTS ALTHOUGH
STRONG MAY SUN MAY HELP. AS QUICK AS WE COOL DOWN SATURDAY
HOWEVER...LONGER RANGE MODEL GUIDANCE CONTINUES TO INDICATE THAT THE
UPPER TROUGH WILL BE PROGRESSIVE ALLOWING A LARGE UPPER RIDGE TO
DEVELOP INTO THE REGION BY TUESDAY. 850 MB TEMPS APPROACH +20 C IN
BOTH GFS AND ECMWF OUTPUT BY TUESDAY AFTERNOON...SUGGESTING 80+
DEGREES IS NOT OUT OF THE QUESTION.

RATZER

&&

.AVIATION...

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

* LIGHT EASTERLY WINDS...BECOMING LIGHT AND VARIABLE THIS EVENING.

* INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS DURING THE DAY ON
  THURSDAY.

PAW

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

A BROAD HIGH PRESSURE RIDGE IS OVER THE AREA THIS AFTERNOON WITH
LIGHT WINDS AND VFR-LEVEL CLOUDS. THE RIDGE WILL MOVE TO THE EAST
OVERNIGHT. THEN A FRONTAL SYSTEM WILL BE MOVING INTO THE AREA ON
THURSDAY. CLOUDS INCREASING AHEAD OF THIS FRONTAL
SYSTEM...BECOMING VFR-LEVEL CEILINGS BY DAWN ON THURSDAY. CHANCES
FOR SHRA AND TSRA INCREASING THROUGH THE DAY AND INTO EVENING
THURSDAY. CONFIDENCE IS LOW IN THE EXACT TIMING OF PRECIPITATION
AND CEILING/VISIBILITY DETAILS AT THIS POINT.

PAW

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

* HIGH CONFIDENCE IN WIND TREND THIS AFTERNOON AND EVENING.

* MEDIUM CONFIDENCE IN SHRA/TSRA OCCURRING ON THURSDAY...LOW
  CONFIDENCE IN TIMING AND DETAILS.

PAW

//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...

THURSDAY NIGHT...SHRA/TSRA LIKELY...MVFR WITH IFR POSSIBLE.

FRIDAY...MVFR CIGS POSSIBLE...MAINLY EARLY. GUSTY NORTH-NORTHEASTERLY
WINDS.

SATURDAY THROUGH MONDAY...GENERALLY VFR.

TUESDAY...STRONG SOUTHERLY WINDS...OTHERWISE VFR.

KJB

&&

.MARINE...
142 AM CDT

A BROAD AREA OF HIGH PRESSURE WILL CONTINUE TO DOMINATE ACROSS THE
GREAT LAKES TODAY. THIS WILL RESULT IN ANOTHER DAY OF LIGHT AND
VARIABLE WINDS ACROSS THE LAKE. A COLD FRONT IS STILL EXPECTED TO
BEGIN DROPPING SOUTHWARD DOWN THE LAKE ON THURSDAY AND INTO THURSDAY
EVENING. IN THE WAKE OF THIS FRONT...WINDS WILL BECOME NORTH AND
INCREASE UP TO 25 TO 30 KT FOR A PERIOD INTO FRIDAY MORNING.
IN ADDITION TO WINDS...A WEATHER DISTURBANCE IS EXPECTED TO RESULT
IN A SURFACE WAVE OF LOW PRESSURE...WHICH SHOULD MOVE ALONG THE
FRONTAL BOUNDARY ALONG...OR JUST SOUTH OF THE LAKE INTO FRIDAY
MORNING. THIS LOOKS TO RESULT IN DECENT CHANCES FOR SHOWERS AND
THUNDERSTORMS...ESPECIALLY ACROSS THE SOUTHERN PORTION OF THE LAKE
DURING THIS PERIOD.

THE WINDS SHOULD TO ABATE FOR A PERIOD LATE FRIDAY AND INTO SATURDAY
AS ANOTHER SURFACE RIDGE OF HIGH PRESSURE BUILDS OVER THE LAKE.
HOWEVER...ANOTHER COLD FRONT STILL LOOKS TO TAKE AIM ON THE LAKE
LATER SATURDAY AND SATURDAY EVENING. THIS WILL ONCE AGAIN LEAD TO A
PERIOD OF STRONGER NORTHWESTERLY WINDS INTO SUNDAY MORNING.

ANOTHER PERIOD OF LIGHT AND VARIABLE WINDS LOOKS TO SET UP AGAIN FOR
LATE SUNDAY AND INTO MONDAY OF NEXT WEEK AS ANOTHER AREA OF SURFACE
HIGH PRESSURE BUILDS ACROSS THE WESTERN LAKES. HOWEVER...ONCE THIS
HIGH SHIFTS EAST MONDAY NIGHT...IT APPEARS THAT A STRONG PRESSURE
GRADIENT WILL SET UP ACROSS THE WESTERN LAKES...AS A POTENT STORM
SYSTEM MOVES EASTWARD ACROSS CANADA. THIS LOOKS TO RESULT IN SOME
STRONG SOUTHERLY WINDS OVER THE LAKE FOR TUESDAY OF NEXT WEEK.

KJB

&&

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

$$


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