🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1229 PM CDT TUE MAY 7 2013

.DISCUSSION...
357 AM CDT

FOCUS IN NEAR TERM REMAINS ON TEMPERATURES AND LOW CHANCE POTENTIAL
FOR ISOLATED SHRA/TSRA ACROSS SOUTHEAST CWA THIS AFTERNOON.
ATTENTION THEN SHIFTS TO RAIN/THUNDERSTORM CHANCES WITH AN AREA OF
LOW PRESSURE SYSTEM THAT WILL AFFECT THE AREA THURSDAY INTO FRIDAY
AND COLDER TEMPS WITH A STRONGER COLD FRONT EXPECTED TO PASS THROUGH
SATURDAY. LITTLE CHANGE IN THERMAL FIELD ALOFT THROUGH WEDNESDAY...
THOUGH MODERATION OF A FEW DEGREES IN SURFACE TEMP EXPECTED EACH
DAY.

IN THE NEAR TERM...SENSIBLE WEATHER WILL REMAIN MUCH THE SAME TODAY
INTO WEDNESDAY ACROSS THE FORECAST AREA. CUT-OFF UPPER LOW WHICH
AFFECTED THE MIDWEST OVER THE WEEKEND AND NOW OVER THE SOUTHERN
APPALACHIANS THIS MORNING WILL DRIFT SLOWLY NORTHEAST ACROSS THE
MID-ATLANTIC REGION THROUGH WEDNESDAY. OUR FORECAST AREA REMAINS IN
GENERALLY SUBSIDENT AIR BENEATH WEAK UPPER RIDGING BETWEEN THE EAST
COAST LOW AND ANOTHER WEAK CIRCULATION OVER THE DAKOTAS. EAST AND
NORTHEAST FLOW IN THE LOW-MID LEVELS MAINTAINING RELATIVELY DRY AIR
ACROSS THE REGION WITH MAINLY ONLY PATCHY MID/HIGH CLOUD LAYERS AT
TIMES. LOW LEVEL MOISTURE WHICH HAS WRAPPED CYCLONICALLY INTO
CENTRAL IN/IL AROUND THE LOW TO OUR SOUTHEAST HAS LED TO A
DISCONTINUITY ACROSS OUR FAR SOUTHEAST COUNTIES OF THE CWA HOWEVER...
WHICH HIGH-RES GUIDANCE CONTINUES TO SUGGEST MAY BECOME A FOCUS FOR
ISOLATED SHRA/TSRA THIS AFTERNOON. INDEED WITH SFC DEW POINT TEMPS
IN THE MID-50S ALONG AND JUST SOUTH OF THIS CONFLUENCE ZONE IS
EXPECTED TO SUPPORT MODEST INSTABILITY DURING PEAK HEATING...WITH
FORECAST MLCAPES ON THE ORDER OF 100-300 J/KG ALONG AN AXIS ROUGHLY
FROM SOUTH BEND TO RENSSELAER OR SO. WINDS/CONVERGENCE ARE EXPECTED
TO BE RELATIVELY WEAK...WITH LITTLE LARGE SCALE FORCING NOTED...
THOUGH CONVECTION-ALLOWING MODELS HAVE SUGGESTED THE POTENTIAL FOR
ISOLATED SHRA/TSRA THERE FOR THE PAST COUPLE OF DAYS AND FEEL THIS
REMAINS WORTHY OF SOME SLGT CHANCE POPS. SIMILAR SET-UP NOTED ON
WEDNESDAY TOO...THOUGH GUIDANCE MAY BE OVER FORECASTING SFC DEW
POINT TEMPS A BIT AND RESULTING CAPE VALUES.

UPPER TROUGH MOVING THROUGH FASTER WESTERLY FLOW ACROSS CANADA
TONIGHT AND WEDNESDAY HELPS GIVE THE EASTERN UPPER LOW A NUDGE
WHICH EASES THE BLOCKING CURRENTLY IN THE UPPER PATTERN ACROSS THE
REGION. THIS ALLOWS WEAK SHORT WAVE TROUGH TO APPROACH FROM THE
WEST LATE IN THE DAY WEDNESDAY...WITH MODEST WARM/MOIST ADVECTION
DEVELOPING FROM MISSOURI INTO EASTERN IA BY 00Z ON 15-20 KT 850 MB
JET. MODEL SOUNDINGS INDICATE A LITTLE WEAK CAPE ACROSS NORTHERN
IL BY AFTERNOON...THOUGH THIS IS AGAIN LIKELY OVERDONE DUE TO HIGH
MODEL SURFACE DEW POINTS. ALSO...A SHALLOW WARM LAYER IS NOTED
AROUND 600 MB PROVIDING SOME WEAK CAPPING TO THE THERMODYNAMIC
PROFILE AND SUGGESTING LITTLE THREAT FOR SHRA/TSRA UNTIL AFTER
SUNSET. GUIDANCE SHOWS SOME DIFFERENCES IN DETAIL WITH STRENGTH OF
THE APPROACHING SHORT WAVE AND RESULTING LOW LEVEL RESPONSE
WEDNESDAY NIGHT...RANGING FROM STRONGER/FASTER AND FARTHER NORTH
GFS TO THE WEAKER/SLOWER AND FARTHER SOUTH ECMWF SOLUTION.
SREF/GEM APPEAR TO BE A FAIRLY GOOD COMPROMISE IN THE MIDDLE OF
THE MODEL SPECTRUM WITH RESPECT TO AMPLITUDE WITH THIS SYSTEM AND
HAVE BASICALLY USED THIS BLEND FOR MAIN GUIDANCE WITH THIS LOW.
THE RESULTING SCENARIO WOULD EXPAND THE POTENTIAL FOR SHRA/TSRA
ACROSS MAINLY WESTERN/NORTH CENTRAL IL WEDNESDAY NIGHT AS LOW
LEVEL JET AND WAA/MOIST ADVECTION AXIS DEVELOPS INTO THE
AREA...AND ACROSS THE ENTIRE CWA THURSDAY AS THE UPPER TROUGH AND
SURFACE WAVE MOVE ACROSS THE AREA. SURFACE WAVE PASSES OFF TO THE
EAST THURSDAY EVENING WITH COLD FRONT SAGGING SOUTHEAST ACROSS THE
CWA THROUGH THE NIGHT AS THE UPPER TROUGH AXIS PASSES OVERHEAD.
THE FRONT LAYS OUT IN LINE WITH UPPER FLOW INTO FRIDAY WITH PRECIP
THREAT DECREASING FROM THE NORTH AS MODEST LOW LEVEL COLD/DRY
ADVECTION INCREASES.

MEDIUM RANGE MODEL SOLUTIONS REMAIN VERY CONSISTENT IN BUCKLING THE
UPPER FLOW ACROSS NORTH AMERICA HEADING INTO THE WEEKEND AS STRONG
SHORT WAVE DIGS SOUTHEAST OUT OF WEST CENTRAL CANADA FRIDAY NIGHT
AND AMPLIFIES DEEP UPPER TROUGH OVER ONTARIO AND THE GREAT LAKES
INTO SATURDAY. A SHARP COLD FRONT IS PROGGED TO PLOW SOUTHEAST
ACROSS IL/IN DURING THE DAY SATURDAY WHILE THE MAIN UPPER/SURFACE
LOWS PASS NORTH OF LAKE SUPERIOR. WHILE SOME SHOWERS ARE POSSIBLE
WITH THE FRONT...THE REAL STORY WILL BE A PUSH OF MUCH COLDER AIR
WHICH REACHES -4 C OR SO AT 850 MB SATURDAY NIGHT. HIGH PRESSURE
BUILDING SOUTHEAST ACROSS THE PLAINS WILL LIKELY HELP PRODUCE A GOOD
DEAL OF SUNSHINE ACROSS THE AREA SUNDAY...THOUGH HIGH TEMPS WILL
LIKELY HAVE TROUBLE GETTING MUCH ABOVE 60 IN MOST AREAS. THE GOOD
NEWS IS THAT THIS UPPER TROUGH LOOKS TO BE FAIRLY PROGRESSIVE...
WITH INDICATIONS OF A QUICK AND SIGNIFICANT WARM-UP NEXT WEEK.

RATZER

&&

.AVIATION...

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

* LIGHT NORTHEAST WINDS THIS AFTERNOON AND EVENING.

PAW

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

A BROAD AREA OF HIGH PRESSURE DOMINATES NORTHERN ILLINOIS AND
NORTHWEST INDIANA AGAIN THIS AFTERNOON...AND WILL MOVE LITTLE
OVERNIGHT INTO WEDNESDAY. THIS WILL RESULT IN VERY QUIET WEATHER
WITH ONLY A FEW HIGH LEVEL CLOUDS ACROSS THE AREA. LIGHT NORTHEAST
WINDS WILL BECOME VARIABLE OVERNIGHT AND NORTHEAST AGAIN ON
WEDNESDAY.

PAW

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

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

PAW

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

WEDNESDAY NIGHT...VFR.
THURSDAY...CHC TSRA WITH MVFR PSBL IN TSRA. OTHERWISE VFR.
FRIDAY...CHC SHRA. PSBL MVFR EARLY.
SATURDAY...CHC SHRA.
SUNDAY AND MONDAY...VFR.

KJB

&&

.MARINE...
149 AM CDT

A BROAD AREA OF HIGH PRESSURE WILL CONTINUE TO DOMINATE ACROSS THE
GREAT LAKES THROUGH WEDNESDAY. THIS WILL RESULT IN LIGHT WINDS
AND QUIET WEATHER ACROSS LAKE MICHIGAN FOR THE NEXT COUPLE OF DAYS.
HOWEVER...LATER IN THE WEEK...A COLD FRONT IS EXPECTED TO DROP
SOUTHWARD ACROSS THE LAKE...AND THIS LOOKS TO RESULT IN SOME
STRONGER NORTH WINDS UP TO 20 TO 25 KT FOR A PERIOD ON THURSDAY AND
THURSDAY NIGHT. IN ADDITION TO THIS...IT ALSO APPEARS THAT AN UPPER
LEVEL DISTURBANCE WILL DRIVE A SURFACE TROUGH OF LOW PRESSURE ACROSS
THE SOUTHERN LAKES AND OHIO VALLEY REGIONS THURSDAY NIGHT INTO
FRIDAY. THIS COULD RESULT IN SOME SHOWERS AND THUNDERSTORMS ACROSS
SOUTHERN LAKE MICHIGAN DURING THIS PERIOD.

FOLLOWING THIS SYSTEM...A RIDGE OF HIGH PRESSURE IS EXPECTED TO
TEMPORALLY MOVE ACROSS THE LAKE...BEFORE A SECOND COLD FRONT MOVES
ACROSS THE LAKE ON SATURDAY OF THIS COMING WEEKEND. THIS WOULD
LIKELY ALSO LEAD TO ANOTHER PERIOD OF SOME ENHANCED NORTHERLY
WINDS.

KJB

&&

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

$$


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