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 20Z...
* WIND SHIFT TO THE N/NE LATE AFTERNOON/EARLY EVENING AS COLD
FRONT MOVES THROUGH THE AREA.
* CIGS TRENDING DOWN OVERNIGHT...TO IFR POSSIBLY LIFR.
* PRECIPITATION TIMING. BMD
//DISCUSSION...UPDATED 18Z...
A COLD FRONT IS SLOWLY PUSHING EAST ACROSS THE REGION WITH ISOLATED
TO SCATTERED SHOWERS OCCURRING ALONG THE FRONTAL BOUNDARY NEAR AND
WEST OF A LINE FROM MKE TO RFD. OUT AHEAD OF THE FRONT...SSW WINDS
HAVE BEEN DIMINISHING AS THE PRESSURE GRADIENT RELAXES. FORCING
ALONG THE FRONTAL BOUNDARY IS WEAK...AND WITH DRY LOW LEVEL AIR IN
PLACE...SHOWER ACTIVITY WILL CONTINUE TO BE SOMEWHAT ISOLATED WITH
OUTSIDE CHANCES OF IMPACTING THE TERMINALS THROUGH THIS EVENING.
MODELS IN DECENT AGREEMENT SHOWING FROPA FOR ORD/MDW AROUND 23-00Z
THIS EVENING. WINDS WILL SWITCH AROUND TO NORTH/NORTHEASTERLY...
BUT THERE MAY BE A SLIGHT DELAY IN GUSTS PICKING UP OUT OF THE
NORTH AS COLD AIR ALOFT FILTERS SOUTH. PRECIPITATION CHANCES WILL
INCREASE BEHIND THE FRONT AS BAND OF FRONTOGENESIS MOVES THROUGH
THE AREA. CIGS WILL LOWER AS THE COLUMN SATURATES...AND EXPECT
CONDITIONS TO DROP TO LOW END MVFR AND POTENTIALLY IFR OVERNIGHT.
UPSTREAM OBS ALREADY SHOWING IFR CIGS. MET GUIDANCE SEEMS TO HAVE
THE BEST LOCK ON THESE CIGS SUGGESTING IFR/LIFR CONDITIONS AFTER
MIDNIGHT ZULU THROUGH DAYBREAK THURSDAY...WHILE MAV/LAV GUIDANCE
ONLY TAKES DOWN HIGH END MVFR. CIGS SHOULD IMPROVE QUICKLY
THURSDAY AFTERNOON AS ANTICYCLONIC FLOW MOVES INTO THE AREA. BMD
//ORD AND MDW CONFIDENCE...UPDATED 20Z...
* HIGH CONFIDENCE IN WIND TIMING/DIRECTION...MEDIUM CONFIDENCE IN
WIND SPEED.
* MEDIUM-HIGH CONFIDENCE IN CIG TRENDS...WITH IFR CONDITIONS
EXPECTED...MEDIUM CONFIDENCE IN TIMING.
* LOW TO MEDIUM CONFIDENCE IN PRECIPITATION TIMING. BMD
//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...
THURSDAY NIGHT...VFR.
FRIDAY...VFR.
SATURDAY...VFR.
SUNDAY...VFR.
MONDAY...CHANCE OF SHRA LATE...OTHERWISE VFR.
TUESDAY...SHRA LIKELY...OTHERWISE VFR.
RODRIGUEZ
&&
.MARINE...
159 PM CDT
DEVELOPING SURFACE LOW OVER THE SOUTHERN PLAINS WILL DEEPEN AS IT
MOVES INTO SOUTHERN ILLINOIS TOMORROW MORNING. THE MORNING MODEL
RUNS HAVE TRENDED A BIT STRONGER WITH THE WINDS OVER THE SOUTHERN
PORTIONS OF THE LAKE AND BUFKIT SOUNDINGS NOW SUPPORT A PERIOD OF
GALE FORCE NORTHEASTERLY WINDS TONIGHT INTO THURSDAY MORNING. THERE
ARE DIFFERENCES IN THE TIMING OF THE STRONGEST WINDS...BUT THERE IS
ENOUGH CONFIDENCE NOW THAT THERE WILL BE A PERIOD OF GALES DURING
THIS TIME FRAME SO HAVE OPTED TO COVER THE RANGE OF TIME
POSSIBILITIES WITH A GALE WARNING. WINDS WILL DIE OFF TOMORROW
AFTERNOON AS SURFACE LOW THEN DIVES SOUTHEAST AND HIGH PRESSURE
BUILDS IN. THE NEXT BIG WIND MAKER WILL BE OVER THE WEEKEND AS AN
INTENSE SURFACE LOW TRACKS INTO THE UPPER MIDWEST. HAVE INTRODUCED
SOUTHERLY GALES INTO THE GRIDS SAT NIGHT INTO SUNDAY...WITH
POTENTIAL FOR 40KT+ WINDS A DISTINCT POSSIBILITY SUNDAY.
IZZI
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742...7 PM WEDNESDAY TO
3 AM FRIDAY.
SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...10 PM WEDNESDAY TO
3 AM FRIDAY.
&&
$$
