752 PM CDT
HAVE MADE SOME MINOR TWEAKS FOR TONIGHT. PRIMARY CHANGE WAS TO
TIGHTEN UP POP GRADIENT MORE ACROSS CWA...INCREASING POPS SLIGHTLY
FAR SOUTHERN CWA AND DROPPING THEM TO NEAR ZERO NORTH OF I-80.
EXTENSIVE HIGH CLOUDINESS CURRENTLY BLANKETS THE AREA...BUT AS THE
SHORTWAVE RESPONSIBLE FOR THIS MOISTURE ZIPS EASTWARD COULD BE A
PERIOD OF SLIGHT CLEARING FOR A TIME OVERNIGHT OVER NORTHERN CWA
BEFORE HIGH LEVEL MOISTURE MOVES BACK IN ASSOCIATED WITH THE
NEBRASKA SHORTWAVE. CLOUDINESS IS NOT OVERLY THICK...BUT GIVEN VERY
MARGINAL TEMPS IT MAY BE ENOUGH TO PREVENT MUCH FROST FROM FORMING
EXCEPT IN THE TYPICALLY COLD/SHELTERED VALLEYS. WHILE I THINK
FROST THREAT IS MINIMAL...NOT CONFIDENT ENOUGH IN IT NOT HAPPENING
TO PULL FROM THE GRIDS SO WILL LET IT RIDE ALONG WITH GOING
FORECAST TEMPS. IN FACT...THE CHANGES TO THE GRIDS WERE GENERALLY
SO MINOR THAT UPDATE TO ZFP APPEARED UNNECESSARY.
IZZI
//PREV DISCUSSION...
302 PM CDT
SHORT TERM...TONIGHT-THURSDAY...
PATCHY LIGHT RAIN MOVING INTO SOUTHERN COUNTIES OF THE FORECAST AREA
THIS AFTERNOON...IN ASSOCIATION WITH ELEVATED BAROCLINIC ZONE NORTH
OF SURFACE FRONT WELL SOUTH OF THE AREA AND A LEAD MID-LEVEL SHORT
WAVE TROUGH RIPPLING THROUGH THE REGION. WHILE RATHER DRY LOW/MID
LEVEL AIR MASS IS IN PLACE ACROSS THE FORECAST AREA...FAIRLY
VIGOROUS FORCING AIDED BY DIVERGENCE FROM COUPLED UPPER JET STREAKS
AND MID LEVEL FRONTOGENESIS IN 700-600 MB LAYER IS WRINGING OUT SOME
LIGHT RAIN ACROSS AREAS SOUTH OF THE ILLINOIS/KANKAKEE RIVER
VALLEYS. THE COUPLED JET STRUCTURE AND FRONTOGENETIC FORCING APPEAR
TO BREAK DOWN THIS EVENING...WHICH IS EXPECTED TO RESULT IN LIGHT
RAIN POTENTIAL SHIFTING A LITTLE FARTHER TO THE SOUTH TONIGHT
CLIPPING MAINLY JUST THE SOUTHERN PARTS OF THE LOWER TIER OF WFO LOT
COUNTIES OVERNIGHT. FOR NORTHERN PARTS OF THE FORECAST AREA...THE
MAIN FORECAST CONCERN TONIGHT IS WITH THE DEGREE OF RADIATIONAL
COOLING BETWEEN THE PATCHY THIN HIGH CLOUDS...DECREASING WINDS...
AND LOW DEW POINTS IN DRY AIR MASS. THIS WILL LIKELY ALLOW FOR TEMPS
FALLING INTO THE 30S IN MANY PARTS OF NORTHERN IL OUTSIDE OF THE
MORE URBANIZED PARTS OF THE CHICAGO METRO AND AREAS NORTH OF THE
THICKER CLOUD COVER SOUTH OF INTERSTATE 80. BASED ON THIS HAVE ADDED
PATCHY FROST MENTION FOR AREAS FROM ABOUT THE FOX VALLEY WESTWARD.
FORECAST CHALLENGES THROUGH MID-WEEK THEN SHIFT TO RAINFALL
POTENTIAL WITH DEVELOPING CLOSED UPPER LOW OVER THE OHIO VALLEY IN
RESPONSE TO STRONGER SHORT WAVE DIGGING INTO THE SOUTHERN PLAINS.
GUIDANCE IN GENERAL AGREEMENT IN CLOSING THIS FEATURE OFF BY
WEDNESDAY MORNING. AS HIS OCCURS...CYCLONIC FLOW WRAPS IN MOISTURE
FROM THE EAST WHICH ALONG WITH A SERIES OF VORT MAXES ROTATING
AROUND THE LARGER SCALE CIRCULATION WILL BRING THE THREAT OF PERIODS
OF RAIN/SHOWERS TO ESPECIALLY THE EASTERN/SOUTHEASTERN PARTS OF THE
CWA BEGINNING TUESDAY...AND GRADUALLY SPREADING WEST A BIT AS THE
UPPER LOW BECOMES MORE DEVELOPED AND BEGINS TO LIFT NORTH TOWARD THE
EASTERN LAKES WEDNESDAY AND THURSDAY. IN ADDITION TO THE VARIOUS
HARD TO TIME SMALLER VORT MAXIMA ROTATING ABOUT THE UPPER LOW...
NORTH-NORTHEAST FLOW DOWN THE LAKE WILL LIKELY AID IN LOW LEVEL
CONVERGENCE ALONG THE WEST/SOUTH SHORE OF THE LAKE. COOL AIR ALOFT
WILL RESULT IN STEEPENING LAKE INDUCED LAPSE RATES WHICH MAY GIVE
SOME CONVECTIVE ENHANCEMENT TO SHOWERS ACROSS THE EASTERN HALF OF
THE CWA TUESDAY NIGHT THROUGH WEDNESDAY NIGHT. WITH ALL OF THIS IN
MIND...HAVE CARRIED POPS TUESDAY-WEDNESDAY NIGHT RANGING FROM
GENERALLY LIKELY RANGE IN THE EAST TO LOW CHANCES FAR WEST.
UPPER LOW GRADUALLY LIFTS NORTHEAST INTO SOUTHWESTERN ONTARIO ON
THURSDAY...ALLOWING IN DECREASING POPS FROM THE WEST AS THE LOW
PULLS AWAY. LINGERING PRECIP BECOMES MORE LAKE-INDUCED AND AFFECTS
MAINLY NORTHWEST INDIANA LATER IN THE DAY.
GENERALLY RELIED ON BLEND OF MODEL TEMP GUIDANCE THROUGH THE NEAR
TERM...GENERALLY 35-40-ISH AT NIGHT DEPENDING ON CLOUDS AND 50-55 BY
DAY.
RATZER
LONG TERM...THURSDAY NIGHT-MONDAY
DEEP CLOSED H5 LOW AND VERTICALLY STACKED SURFACE LOW LIFT NORTHEAST
INTO EASTERN CANADA TO START THE PERIOD AND THEN WE GET INTO A MORE
ZONAL UPPER LEVEL PATTERN FOR THE REMAINDER OF THE EXTENDED PERIOD.
COLD H85 TEMPERATURES AT -3 OR -4C WITH NORTHWESTERLY WINDS WOULD
NORMALLY BE A GOOD LAKE EFFECT SET-UP FOR NORTHWEST INDIANA.
HOWEVER...RISING HEIGHTS ALOFT AND SURFACE HIGH PRESSURE BUILDING IN
FROM THE WEST SUPPORT THE RAPIDLY FALLING INVERSION HEIGHTS SEEN ON
BUFKIT SOUNDINGS OVER SOUTHERN LAKE MICHIGAN. THUS ONLY HAVE SLIGHT
POPS OVER EASTERN PORTER FOR LAKE EFFECT SHOWERS THURS NIGHT.
OUTSIDE LAKE EFFECT CLOUDS AND ANY SHOWERS AND OUTSIDE OF IMMEDIATE
DOWNTOWN CHICAGO...FRIDAY MORNING WILL BE QUITE CHILLY...IN THE LOW
TO MID 30S. DESPITE H85 TEMPERATURES RETURNING TO THE LOW POSITIVE
SINGLE DIGITS ON FRIDAY...COOL START WILL KEEP HIGH TEMPERATURES
BELOW AVERAGE IN THE MID 50S.
THE WEEKEND INTO EARLY NEXT WEEK LOOKS TO FEATURE TEMPERATURES
RETURNING CLOSER TO NORMAL FOR LATE OCTOBER WITH CONTINUED RISING H5
HEIGHTS AND SLOWLY INCREASING H85 TEMPS. A COLD FRONTAL PASSAGE AND
SHORT WAVE MAY TOUCH OFF ISOLATED SHOWERS SATURDAY NIGHT AND
ADDITIONAL SHORT WAVE ENERGY/VORTICITY MAXIMA PROGRESSING THE ZONAL
FLOW MAY BE ABLE TO TOUCH OFF ADDITIONAL RAIN SHOWERS FROM TIME TO
TIME ON SUNDAY AND MONDAY. OVERALL THOUGH...WITH A LACK OF RETURN
MOISTURE FLOW AND DRY AIR MASS OVERHEAD...PATTERN LOOKS PRIMARILY
DRY...SO KEPT POPS AT SLIGHT IN SAT NIGHT-MON NIGHT PERIOD.
RC
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 08Z...
* NO CONCERNS THROUGH THE REMAINDER OF THE NIGHT/TUESDAY MORNING.
* PRECIPITATION CHANCES TUESDAY NIGHT.
* FLIGHT CATEGORY DROPPING TO MVFR AND POSSIBLY IFR TUESDAY NIGHT.
* TIMING/MAGNITUDE OF WIND GUSTS TUESDAY NIGHT. BMD
//DISCUSSION...UPDATED 06Z...
EXTENDS NORTH OF A WARM FRONT INTO MISSOURI AND SOUTHERN/CENTRAL
ILLINOIS THIS EVENING...BUT THIS AREA WILL STAY TO THE SOUTH OF
THE TERMINALS OVERNIGHT WITH WEAK RIDGING IN PLACE OVER CENTRAL
ILLINOIS. HIGH CLOUDS FROM THIS SYSTEM WILL MOVE OVERHEAD
OVERNIGHT...BUT VFR CONDITIONS WILL PREVAIL. MEANWHILE...A WEAK
SURFACE TROUGH TO THE NORTH OF THE TERMINALS WILL DROP SOUTH
OVERNIGHT...CAUSING WINDS TO VEER FROM THE WEST TO THE NORTHWEST
IN THE MID-MORNING HOURS. LOW PRESSURE CURRENTLY OVER
OKLAHOMA/ARKANSAS WILL LIFT NORTHEAST AND DEEPEN THROUGH THE DAY
TUESDAY CAUSING A GRADUAL INCREASE IN THE WIND SPEEDS AS THE
GRADIENT TIGHTENS. MOISTURE WRAPPING AROUND THE LOW IS EXPECTED TO
APPROACH THE TERMINALS LATE TUESDAY NIGHT...CAUSING CIGS TO DROP
INTO MVFR...AND POSSIBLY IFR RANGE...AND PRECIPITATION. THERE ARE
SOME DISCREPANCIES IN TIMING PRECIP INTO THE AREA...BUT LEANED
TOWARDS SLOWER GUIDANCE FOR ONSET OF PRECIPITATION AS DRY AIR
CURRENTLY IN PLACE IS LIKELY BEING SATURATED TOO QUICKLY BY THE
MODELS. WIND SPEEDS WILL CONTINUE TO INCREASE OVERNIGHT TUESDAY AS
THE LOW DEEPENS AS IT SPINS OVER THE UPPER OHIO RIVER VALLEY.
GUSTS AROUND 20 KTS CAN BE EXPECTED BEGINNING IN THE EARLY MORNING
HOURS WEDNESDAY...BUT BEYOND THE CURRENT TAF PERIOD...GUSTS INTO
THE 30 TO 40 KT RANGE ARE POSSIBLE. BMD
//ORD AND MDW CONFIDENCE...UPDATED 08Z...
* HIGH CONFIDENCE IN VFR CONDITIONS THROUGH TONIGHT INTO TUESDAY
AFTERNOON.
* LOW TO MEDIUM CONFIDENCE IN PRECIP TIMING/COVERAGE.
* MEDIUM CONFIDENCE IN MVFR CONDS...LOW CONFIDENCE IN IFR TUESDAY
OVERNIGHT. BMD
//OUTLOOK FOR ORD/MDW FOR 12Z WEDNESDAY-12Z MONDAY...UPDATED 00Z...
* WEDNESDAY...CHANCE OF SHOWERS...STRONG WIND GUSTS
* THURSDAY THROUGH SATURDAY...VFR
* SUNDAY...CHANCE OF SHOWERS
SHEA
&&
.MARINE...
259 AM CDT
STORM FORCE WINDS NOW EXPECTED OVER MUCH OF LAKE MICHIGAN
WEDNESDAY AFTERNOON INTO THURSDAY. LOW PRESSURE OVER THE GULF OF
MEXICO WILL LIFT NORTH LATER TODAY AND TONIGHT AS IT DEEPENS. MODELS
CONTINUE TO TRACK THIS LOW FURTHER WEST WITH IT CENTERED ACROSS
NORTHWEST OHIO/SOUTHEAST LOWER MICHIGAN BY LATE WEDNESDAY NIGHT...
WHILE A RIDGE OF HIGH PRESSURE EXTENDS FROM ONTARIO SOUTH INTO THE
PLAINS. THE GRADIENT IS EXPECTED TO RAPIDLY TIGHTEN FROM LATE
TONIGHT THROUGH WEDNESDAY EVENING. WINDS SHOULD QUICKLY REACH GALE
FORCE AROUND OR SHORTLY AFTER DAYBREAK WEDNESDAY AND THEN REACH
STORM FORCE BY LATE WEDNESDAY AFTERNOON. STORM FORCE WINDS EXPECTED
TO CONTINUE THROUGH MIDDAY THURSDAY...UNTIL THE LOW BEGINS TO WEAKEN
AND LIFTS FURTHER NORTHEAST. CONTINUED HIGH END GALES ACROSS THE
NORTHERN THIRD OR SO OF LAKE MICHIGAN BUT STORM FORCE GUSTS ARE
STILL POSSIBLE THERE. CMS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...5 AM WEDNESDAY TO 4 PM
WEDNESDAY.
STORM WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-
LMZ741-LMZ742-LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...4 PM WEDNESDAY TO 3 PM
THURSDAY.
GALE WATCH...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565...10 AM
WEDNESDAY TO 10 PM THURSDAY.
&&
$$
