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 SHORTAVE. 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 00Z...
* NO CONCERNS OVERNIGHT
SHEA
//DISCUSSION...UPDATED 00Z...
VFR CONDITIONS TO CONTINUE OVERNIGHT AND INTO THE MORNING HOURS.
ATMOSPHERE HAS DECOUPLED ALLOWING THE GUSTY WINDS TO ABATE. MAIN
BANDING OF PRECIP ACROSS CENTRAL ILLINOIS TO REMAIN IN THAT
CORRIDOR AND NOT MOVE ACROSS THE TERMINALS. OTHERWISE BESIDES THE
CIRRUS OVERHEAD AND NOW LIGHT WESTERLY WINDS...NO CONCERNS THROUGH
THE MORNING HOURS.
WINDS TO BECOME MORE NORTHERLY BY LATE MORNING AND FORECAST
GUIDANCE IS SUGGESTING THAT THE STRATUS SHIELD ACROSS NORTHERN MN
AND WI WILL SLOWLY PUSH SOUTH AND ACROSS ALL TERMINALS BY TUESDAY
EVENING. INTO THE EXTENDED TAFOR AND BEYOND WILL BE THE THREAT FOR
MVFR CIGS AND EVENTUALLY SHRA...BUT CONFIDENCE IS LOW ENOUGH
BEYOND 00Z/19 FOR TIMING OF SHRA...WILL KEEP THE PACKAGE DRY THIS
HOUR. WINDS WILL THEN BEGIN TO PICK UP OVERNIGHT TUESDAY AND INTO
WEDNESDAY MORNING.
SHEA
//ORD AND MDW CONFIDENCE...UPDATED 00Z...
* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS
SHEA
//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...
302 PM CDT
...ANOTHER ROUND OF STRONG WINDS HEADING FOR LAKE MICHIGAN WEDNESDAY
AFTERNOON INTO THURSDAY NIGHT...
MAIN FORECAST CONCERNS CENTER AROUND DIMINISHING WINDS THIS EVENING
FOLLOWED GALE AND EVEN POSSIBLE STORM FORCE WINDS STARTING WEDNESDAY
AFTERNOON AND RUNNING INTO THURSDAY NIGHT.
WEST WINDS CONTINUE TO SLOWLY DIMINISH ACROSS THE LAKE LATE THIS
AFTERNOON AS LOW PRESSURE OVER JAMES BAY WEAKENS. WINDS WILL CONTINUE
TO SUBSIDE THIS EVENING AND BECOME NORTHWESTERLY. WILL LET THE GALE
WARNING EXPIRE AND KEEP THE SMALL CRAFT HEADLINE GOING UNTIL EVENING
FOR THE IL SHORE AND TONIGHT FOR THE IN SHORE AS SCHEDULED. A
WEAKNESS IN THE PRESSURE GRADIENT WILL GLIDE ACROSS THE LAKE TUESDAY
MORNING ALLOWING FOR LIGHT NORTHERLY WINDS. A DEEPENING UPPER TROUGH
WILL MOVE INTO THE MISSISSIPPI RIVER VALLEY TUESDAY AFTERNOON
HELPING TO DEEPEN SURFACE LOW PRESSURE OVER THE GULF COAST. THIS LOW
WILL THEN ZIP NORTHWARD UP THE APPALACHIANS AND SHOULD BECOME BETTER
DEVELOPED OVER OHIO WEDNESDAY WITH PRESSURE POTENTIALLY FALLING TO
AROUND 29.0 INCHES BEFORE TURNING NORTHEASTWARD ACROSS SOUTHEASTERN
ONTARIO THURSDAY EVENING. THIS REPRESENTS QUITE A WESTWARD SHIFT IN
FORECAST TRACK BUT HAVE DECENT CONFIDENCE THAT THIS IS REASONABLE
GIVEN THAT THE UPPER TROUGH HAS BEEN OVER THE UPPER-AIR SOUNDING
NETWORK SINCE SUNDAY EVENING. AS A RESULT HAVE INCREASED WINDS OVER
THE LAKE RESULTING IN 40-45 KT GALES STARTING SOMETIME DURING THE DAY
WEDNESDAY CONTINUING INTO THURSDAY EVENING WITH THE DIRECTION SHIFTING
FROM NORTH-NORTHEAST TO NORTH THEN NORTHWEST DURING THAT TIME. MAY
STILL SEE SOME SHIFTS IN THE TRACK OF THE LOW AND RESULTING IN
ADJUSTMENTS TO THE FORECAST BUT MAY BE A BIT CONSERVATIVE ON THE
CURRENT WIND FORECAST IF THIS FURTHER WESTERLY TRACK VERIFIES. ALSO
HAVE SOME CONCERN THAT STORM FORCE GUSTS OF AROUND 50 KT MAY DEVELOP
AS WELL...ESPECIALLY WEDNESDAY NIGHT. HIGH PRESSURE WILL ARRIVE
BEHIND THE LOW FRIDAY BRINGING DROP OFF IN WIND SPEEDS.
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 4 AM TUESDAY.
GALE WATCH...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ740-LMZ741-LMZ742-
LMZ743-LMZ744-LMZ745-LMZ777-LMZ779-LMZ868-LMZ870-LMZ872-
LMZ874-LMZ876-LMZ878...7 AM WEDNESDAY TO 10 PM THURSDAY.
&&
$$
