319 AM CDT
MAIN FEATURES OF THE FORECAST THIS MORNING ARE PRECIP POTENTIAL WITH
STORM SYSTEM MOVING THROUGH THE REGION TODAY THROUGH THURSDAY...A
PERIOD OF DRY WEATHER FROM THURSDAY NIGHT INTO SATURDAY...THEN
RELATIVELY MINIMAL RAIN THREAT WITH WINDY STORM WHICH MOVES THROUGH
THE UPPER MIDWEST SUNDAY.
A SURFACE LOW ASSOCIATED WITH A LEAD NORTHERN STREAM SHORT WAVE
TROUGH WAS EAST OF JAMES BAY EARLY THIS MORNING...WITH A SLOW MOVING
COLD FRONT TRAILING THROUGH SOUTHWEST WISCONSIN INTO EASTERN IOWA.
THIS FRONT WILL CONTINUE TO DRIFT TO THE EAST-SOUTHEAST INTO THE
FORECAST AREA THROUGH TONIGHT. NOT MUCH PRECIPITATION NOTED ALONG
THE FRONT AT THIS TIME...THOUGH MODELS CONTINUE TO DEPICT RAIN
BLOSSOMING WITH STRENGTHENING OF THE LOW LEVEL BAROCLINIC ZONE ON
THE COOL SIDE OF THE SURFACE BOUNDARY ACROSS IOWA AND WISCONSIN THIS
AFTERNOON. IN ADDITION...SPLIT FLOW APPEARS MORE PRONOUNCED IN
CURRENT MODEL RUNS THIS AFTERNOON WITH LESS PHASING OF NORTHERN AND
SOUTHERN STREAM SHORT WAVES THAN PREVIOUSLY DEPICTED. THERE ARE
SIGNS OF COUPLED UPPER JET STREAKS AIDING IN ENHANCING UPPER
DIVERGENCE ACROSS THE AREA WEST-NORTHWEST OF THE WFO CHICAGO CWA.
THIS SETS UP THE HEAVIEST PRECIP THROUGH THIS EVENING ACROSS
NORTHEAST IOWA AND SOUTHWEST WISCONSIN...AND WILL THUS RESULT
IN LOWER POPS FARTHER EAST ACROSS THE FA. MEANWHILE THE SOUTHERN
STREAM WAVE CONTINUES TO CLOSE OFF ACROSS THE SOUTHERN PLAINS
TODAY...WITH GUIDANCE IN CLOSER AGREEMENT NOW IN DEVELOPING SURFACE
LOW INTO FAR SOUTHWEST MISSOURI BY THIS EVENING BEFORE OCCLUDING
TONIGHT AS IT TRACKS ACROSS FAR SOUTHERN ILLINOIS AND THE LOWER OHIO
VALLEY. FORCING ALONG THE AFOREMENTIONED FRONTAL ZONE WEAKENS FROM
THE FORECAST AREA AND AREAS TO THE NORTHEAST TONIGHT AS THE NORTHERN
STREAM WAVE MOVES AWAY...WHILE MORE ORGANIZED DEEP ASCENT WITH THE
SOUTHERN STREAM CLOSED LOW SPREADS ACROSS TO LOWER MISSOURI AND OHIO
VALLEYS OVERNIGHT. BEST POTENTIAL FOR STEADIER PRECIP IS THEREFORE
LOOKING TO BE GREATEST OVER THE FAR WESTERN CWA TONIGHT...WITH THE
FAR EAST/SOUTHEAST PARTS OF THE CWA LOOKING LESS LIKELY TO SEE MORE
SIGNIFICANT RAINFALL. PRECIP SHOULD THEN TAPER FROM NORTHWEST TO
SOUTHEAST THROUGH THE DAY THURSDAY AS OLD LOW LEVEL FRONTAL ZONE
CONTINUES TO WEAKEN AND OCCLUDED SYSTEM TO OUR SOUTH TRACKS OFF
THROUGH THE OHIO VALLEY. ANY LINGERING LIGHT RAIN SHOULD MOVE OUT OF
THE FAR SOUTH/SOUTHEAST COUNTIES THURSDAY EVENING...WITH MODEL
FORECAST STORM TOTAL RAINFALL AMOUNTS RANGING FROM 0.25 TO 0.50
INCHES IN THE FAR WESTERN PARTS OF THE CWA TO LESS THAN 0.15 INCHES
IN THE FAR EAST.
TEMPS REMAIN A BIT TRICKY ACROSS THE FORECAST AREA TODAY...WITH
INCREASING THICKER CLOUD COVER AND FRONTAL PASSAGE ACROSS THE
NORTHWEST...AND MILDER PRE-FRONTAL AIR MASS ACROSS THE SOUTHEAST.
WITH TEMPS RELATIVELY MILD TO START WITH THIS MORNING HAVE GENERALLY
GONE WITH WARMER MET GUIDANCE NUMBERS...AND HAVE EVEN ADDED A COUPLE
OF DEGREES TO THIS IN THE SOUTHEAST PARTS OF THE CWA. HAVE FAVORED A
COOLER BLEND OF GUIDANCE THURSDAY IN COOL BLUSTERY NORTHEAST FLOW.
UPPER RIDGE THEN DEVELOPS EAST ACROSS THE MISSISSIPPI VALLEY AND
WESTERN LAKES THURSDAY NIGHT AND FRIDAY IN THE WAKE OF THE DEPARTING
UPPER LOW. FRIDAY MORNING MAY BE A CHILLY ONE ESPECIALLY ACROSS FAR
NORTH/NORTH CENTRAL IL GIVEN PROXIMITY TO SURFACE RIDGE AND THE
POTENTIAL FOR STRONG RADIATIONAL COOLING. LIGHT EAST FLOW AROUND THE
SURFACE HIGH WILL MAKE FOR DRY AND SLIGHTLY MILDER CONDITIONS
FRIDAY...THOUGH WARM ADVECTION AND STRONG RETURN FLOW DOESNT REALLY
SET UP UNTIL LATER FRIDAY NIGHT AND SATURDAY.
EYES THEN TURN TOWARD DEEP UPPER TROUGH OVER WESTERN CONUS HEADING
INTO THE WEEKEND. LONGER RANGE GUIDANCE CONTINUES TO BE CONSISTENT
IN DEPICTING A STRONG NEGATIVELY TILTED SHORT WAVE LIFTING FROM THE
PLAINS INTO THE UPPER MIDWEST BY EARLY SUNDAY. BOTH 00Z GFS AND 12Z
ECMWF INDICATE A 990 MB SURFACE LOW NEAR THE NORTH DAKOTA/MINNESOTA
BORDER BY SUNDAY MORNING. GFS/GEM/ECMWF ALL DEPICT BEST LOW LEVEL
MOISTURE ADVECTION REMAINS WEST OF THE MISSISSIPPI RIVER DURING THE
DAY SATURDAY...WITH THE LOW LEVEL MOISTURE EVENTUALLY SPREADING EAST
INTO THE FORECAST AREA BY SUNDAY AS THE OCCLUDED FRONT PUSHES ACROSS
THE AREA. MODELS ARE PRETTY STINGY WITH THE PRECIP DEVELOPMENT THIS
FAR SOUTH/EAST OF THE LOW...WITH MOST OF THE QPF DEVELOPING ALONG
THE FRONT AS IT SLOWS/STALLS ACROSS OUR FAR EASTERN COUNTIES IN
INDIANA AND EAST CENTRAL IL LATE SUNDAY. FORECAST SOUNDINGS AND
TIME/HEIGHT DEPICTIONS INDICATE MOISTURE IS RATHER SHALLOW HOWEVER
SUGGESTING ONLY LOWER CHANCE POPS. BY 12 MONDAY...GUIDANCE DIFFERS
ON HOW FAR EAST THE FRONT MAKES IT. THE 00Z GEM CLEARS THE
CWA...WHILE THE 00Z GFS/12Z ECMWF APPEAR TO HANG UP THE FRONT OVER
OUR FAR SOUTHEAST AS IT BECOMES MORE PARALLEL TO THE UPPER FLOW.
HAVE HELD ON TO SOME LOW CHANCE POPS SOUTH/SOUTHEAST HERE PER
GFS/ECMWF. DURING THE WEEKEND...TEMPS SHOULD AGAIN RISE INTO THE 60S
SATURDAY ESPECIALLY OVER THE SOUTHERN CWA...THOUGH IT APPEARS LOW
LEVEL THERMAL RIDGE ACTUALLY MOVES THROUGH SATURDAY NIGHT. LOW LEVEL
MIXING IS DEEPER BEHIND THE FRONT SUNDAY...SUGGESTING FAIRLY WINDY
CONDITIONS DURING THE DAY.
ANOTHER SHORT WAVE IS PROGGED TO APPROACH THE REGION IN SOUTHWEST
FLOW ALOFT MONDAY NIGHT OR TUESDAY...INCREASING PRECIP THREAT AGAIN
TOWARD THE VERY END OF THE EXTENDED FORECAST.
RATZER
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 08Z...
* LLWS AN ISSUE THROUGH THIS MORNING.
* SOUTHERLY WINDS PICKING UP BY MID DAY BEFORE FROPA LATE IN THE
AFTERNOON WITH WINDS SHIFTING TO THE NORTH...AND GUSTS
PERSISTING INTO THE OVERNIGHT HOURS.
* CHANCES FOR SHOWERS INCREASING BY THIS EVENING.
* CEILINGS ON THE DOWNWARD TREND THIS EVENING WITH MVFR CEILINGS
AND EVEN IFR CEILINGS A DEFINITE POSSIBILITY.
RODRIGUEZ
//DISCUSSION...UPDATED 06Z...
OUTSIDE OF POSSIBLE LLWS THIS MORNING...A RELATIVELY QUIET START
TO THE FORECAST PERIOD AS A TROUGH OF LOW PRESSURE AND ASSOCIATED
FRONTAL BOUNDARIES REMAIN TO THE WEST. EXPECT HIGH LEVEL CIRRUS TO
REMAIN ON THE INCREASE THIS MORNING WITH MID AND LOW LEVEL
CLOUD...CURRENTLY STRETCHING FROM SOUTHERN WISCONSIN SOUTHWEST
INTO IOWA...TO STAY TO THE WEST. THIS MID AND LOW LEVEL CLOUD
COVER WILL SLOWLY SHIFT EAST WITH TIME THIS MORNING BUT WITH RFD
THE ONLY TERMINAL TO OBSERVE THIS THROUGH MID DAY. SOME SHORT
RANGE GUIDANCE IS TRYING TO HINT AT THE POSSIBLITY OF SOME SHOWER
DEVELOPMENT IN AND AROUND RFD THROUGH 15Z THIS MORNING...BUT HAVE
STRAYED AGAINST THIS POSSIBILITY THINKING THAT MODELS MAY BE
OVERDOING THE MOISTURE. OBSERVED SOUNDINGS FROM THIS EVENING
CONTINUE TO SHOW A FAIRLY DRY AIR MASS IN PLACE...AND THINK THAT
THE BEST MOISTURE ADVECTION WILL REMAIN WELL TO THE WEST THROUGH
MID DAY. ITS NOT UNTIL FORCING SHIFTS EAST LATER THIS AFTERNOON AS
THIS SYSTEM SHIFTS EAST THAT THIS DEVELOPING AREA OF SHOWERS WILL
BEGIN TO REACH THE TERMINALS. EXPECT SHOWERS TO MOVE OVER RFD BY
THIS AFTERNOON WITH THE REMAINING TERMINALS TO OBSERVE THIS PRECIP
MORE TOWARDS THE 03Z TIME FRAME. AS THIS OCCURS...CEILINGS WILL
BEGIN TO FALL WITH MVFR A DEFINITE POSSIBLITY AND EVEN IFR
CEILINGS POSSIBLE MORE TOWARDS THE MIDNIGHT TIME FRAME.
SOUTHERLY WINDS AND GUSTS WILL BE PRESENT THROUGH THE AFTERNOON
BEFORE FROPA LATE THIS AFTERNOON. WITH WINDS SHIFTING
NORTH...GUSTS WILL ONCE AGAIN BE ON THE INCREASE AND LAST THROUGH
THE REMAINDER OF THE FORECAST PERIOD.
RODRIGUEZ
//ORD AND MDW CONFIDENCE...UPDATED 08Z...
* HIGH CONFIDENCE WITH LLWS.
* HIGH CONFIDENCE WITH WIND SPEED AND DIRECTION...WITH MEDIUM
CONFIDENCE OF TIMING FROPA LATER THIS AFTERNOON.
* HIGH CONFIDENCE OF SHOWERS...WITH MEDIUM CONFIDENCE OF
TIMING/TRENDS.
* MEDIUM CONFIDENCE OF TIMING/TRENDS FOR MVFR CEILINGS...WITH LOW
CONFIDENCE OF IFR CEILINGS.
RODRIGUEZ
//OUTLOOK FOR ORD/MDW FOR 12Z THURSDAY-12Z TUESDAY...UPDATED 00Z...
THU...MVFR CIGS AND -RA BECOMING VFR BY LATE MORNING.
FRI...VFR. WX NIL.
SAT...VFR. WX NIL.
SUN...VFR. SLGT CHC SHRA.
MON...VFR.
TRS
&&
.MARINE...
207 PM CDT
SOUTHERLY WINDS WILL REMAIN IN THE 20 TO 30 KT RANGE TONIGHT
INTO WEDNESDAY AHEAD OF AN APPROACHING COLD FRONT FROM THE UPPER
MISSISSIPPI VALLEY. THIS COLD FRONT WILL PUSH ACROSS FAR NORTHERN
LAKE MICHIGAN BY EARLY WEDNESDAY MORNING. THE COLD FRONT SHOULD
CLEAR THE ENTIRE LAKE BY WEDNESDAY EVENING. NORTH TO NORTHEASTERLY
WINDS WILL BE THE MAIN STORY BEHIND THIS FRONT AS THEY INCREASE
WEDNESDAY NIGHT. A SURFACE RIDGE OF HIGH PRESSURE EXTENDING FROM
THE PLAINS NORTHWARD ACROSS THE UPPER MIDWEST WILL BUILD IN ACROSS
THE NORTHERN PORTIONS OF THE LAKE WEDNESDAY NIGHT AND THURSDAY. AT
THE SAME TIME...A POTENT AREA OF LOW PRESSURE WILL MOVE ACROSS THE
MID MISSISSIPPI VALLEY EARLY THURSDAY. THE PRESSURE GRADIENT
ASSOCIATED WITH THESE TWO PRESSURE SYSTEMS APPEARS TO PRODUCE THE
STRONGEST WINDS...NEAR GALE FORCE...ACROSS THE SOUTHERN HALF OF THE
LAKE WEDNESDAY NIGHT INTO THURSDAY. THE SURFACE HIGH WILL FINALLY
BUILD ACROSS THE LAKE THURSDAY NIGHT INTO FRIDAY...PRODUCING A PERIOD
OF LIGHTER WINDS. HOWEVER...WINDS LOOK TO INCREASE OUT OF THE SOUTH
FRIDAY NIGHT INTO THE WEEKEND AS ANOTHER STRONG STORM SYSTEM
DEVELOPS ACROSS THE CENTRAL ROCKIES AND LIFTS NORTH NORTHEAST WARD
ACROSS THE UPPER MISSISSIPPI VALLEY BY THE END OF THE WEEKEND.
KJB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...ILLINOIS NEARSHORE WATERS UNTIL 10 AM
WEDNESDAY.
&&
$$
