330 AM CDT
SHOWERS LAST EVENING AND OVERNIGHT HAVE REMAINED MAINLY JUST
NORTH OF THE LOCAL FORECAST AREA...THOUGH A FEW HAD CLIPPED FAR
NORTH CENTRAL AND NORTHEAST IL AS WELL AS FAR NORTHERN IN. EARLY
THIS MORNING SHOWERS WERE MORE NUMEROUS OVER EAST CENTRAL
WI...ALONG/NEAR THE MN-IA BORDER AND FROM WEST CENTRAL IA BACK
ACROSS SOUTHERN SD. THE SHOWERS...ESPECIALLY THOSE MOVING INTO THE
WESTERN GREAT LAKES...ARE WELL AHEAD OF THE ACTUAL SHORT WAVE
TROUGH WHICH AT 07Z EXTENDED FROM OVER LAKE WINNIPEG SOUTHWEST TO
FAR EASTERN MT.
WHILE THE SHORT WAVE TROUGH AXIS WAS STILL WELL UPSTREAM THE WARM
AIR ADVECTION HAD SPREAD FAR OUT AHEAD OF THE TROUGH. PROFILER
AND 88D NETWORKS INDICATING 850HPA WEST-SOUTHWEST FLOW OF 25-35KT
OVER NORTHERN IL INCREASING TO 40-50KT OVER MO...KS AND AND
NORTHERN OK. THIS WARM AIR ADVECTION IS RESULTING IN SIGNIFICANT
ISENTROPIC LIFT OVER THE BAROCLINIC ZONE THAT IS PROGGED TO EXTEND
FROM IA ACROSS NORTHERN IL AND FAR NORTHERN IN AT 12Z.
WITH CONTINUED SIGNIFICANT UPWARD VERTICAL MOTION THIS MORNING
DUE TO THE WARM AIR ADVECTION EXPECT MID LEVELS TO CONTINUE TO
SATURATE OVER THE AREA WHILE A TONGUE OF UPPER 40-LOWER 50
SURFACE DEW POINTS CURRENTLY NOSING NORTHEAST ACROSS THE MID MO
VALLEY QUICKLY SPREADS ACROSS THE MID MS VALLEY INTO NORTHERN IL
HELPING MOISTEN THE LOWER LEVELS. STILL...ONLY EXPECT SOME LIGHT
RAINFALL ACCUMULATIONS DURING THE MORNING BEFORE THE WARM AIR
ADVECTION FORCING AND RESULTING RAIN SHIFTS EAST OVER THE MIDWEST
AND UPPER OH VALLEY BY MIDDAY AS THE SHORT WAVE TROUGH DROPS
ACROSS THE UPPER MIDWEST. WITH THE TROUGH AXIS MOVING ACROSS THE
LOCAL AREA REACHING LAKE MI BY 00Z MON ANTICIPATE CLEARING TO
GRADUALLY SPREAD WNW-ESE ACROSS THE AREA LATER AFTERNOON AND THIS
EVENING IN SUBSIDENCE FOLLOWING IN THE WAKE OF THE SHORT WAVE.
MODELS HAVE CONTINUED THEIR TREND WITH TAKING THE NEXT
SYSTEM...CURRENTLY OVER WA...THAT POTENTIALLY BROUGHT RAIN TO
SOUTHERN PORTIONS OF THE FORECAST AREA LATE MONDAY AND MONDAY
NIGHT ON AN EVEN MORE SOUTHERLY TRACK FR OM THE OZARKS
NORTHEASTWARD JUST SOUTH OF THE OH RIVER MONDAY NIGHT AND TUESDAY.
WITH THE CONTINUED PUSHING SOUTH WITH THIS SYSTEM BY EACH MODEL
RUN HAVE FOLLOWED SUIT AND HAVE REDUCED POPS DURING LATE MONDAY
AND MONDAY NIGHT TO SLIGHT CHANCE AND LOW END CHANCE PERCENTAGES
ACROSS THE FAR SOUTH COUNTIES OF THE FORECAST AREA.
MODELS ALSO CONSISTENT IN THEIR RECENT TREND OF SHARPENING THE
UPPER TROUGH OVER THE REGION TUESDAY WITH A CLOSED UPPER LOW
FORMING BY TUESDAY AFTERNOON OR EVENING. WITH THE UPPER TROUGH
AXIS PROGGED ALONG/NEAR THE MS VALLEY AT 18Z TUE AND MOVING EAST
TO THE IN STATE LINE BY 00Z WED HAVE A SLIGHT CHANCE FOR SHOWERS
IN THE WESTERN COUNTIES...INCREASING TO CHANCE CATEGORY ACROSS
THE EAST DUE TO DEEP CYCLONIC FLOW...POTENTIAL FOR DIURNAL SHOWERS
AND DEVELOPMENT OF A LAKE EFFECT RAIN SHOWER SITUATION FOR THE IL
SHORES AND NORTHWEST IN BY THE END OF THE DAY.
A SMALL EASTERLY COMPONENT TO THE FLOW THROUGH THE LAKE EFFECT
CLOUD LEVEL WEDNESDAY EVENING PUT THE IL SHORE AREA...ESPECIALLY
CHICAGO AND THE SOUTH SIDE...AS WELL AND FAR NORTHWEST IN UNDER
THE GUN FOR LAKE EFFECT SHOWERS. DURING WEDNESDAY NIGHT THE CLOUD
BEARING LAYER WINDS BACK TO NEARLY UNIDIRECTIONAL OUT OF THE
NORTH SO EXPECT A MID LAKE BAND TO BE POINTED AT THE SOUTH END OF
THE LAKE WITH SHOWERS PUSHING INLAND SOUTH ACROSS THE KANKAKEE
RIVER.
BY THURSDAY MORNING THE THREAT OF LAKE EFFECT WILL HAVE SHIFTED
EAST OF THE FORECAST AREA AND DIMINISHED AS WINDS ARE TO BACK
FURTHER TO MORE NORTHWESTERLY AND MID LEVEL WARM IN RESPONSE TO
RISING HEIGHTS ALOFT AS THE UPPER LOW MOVES FURTHER AWAY OFF TO
THE NORTHEAST ACROSS NY AND THE UPPER ST. LAWRENCE VALLEY.
AFTER TEMPERATURES AROUND CLIMATOLOGICAL NORMALS TODAY THINGS TURN
COOLER FOR MID WEEK AS COOL AIR THAT HAS BEEN GRADUALLY SPREADING
SOUTH ACROSS MANITOBA AND ONTARIO MAKE FURTHER PROGRESS SOUTH
ACROSS THE UPPER MIDWEST AND UPPER GREAT LAKES TODAY AND TONIGHT
FOLLOWING THE PASSAGE OF THE SHORT WAVE THAT WILL BRING SHOWERS TO
THE AREA THIS MORNING. BY MIDDAY TUESDAY LOW AND MID LEVEL FLOW
VEERS TO OUT OF THE NORTH...ADVECTING THE COOL AIR EVEN DEEPER
ACROSS THE REGION. HIGHS TUESDAY THROUGH THURSDAY ARE ONLY
EXPECTED TO BE IN THE LOWER AND MID 50S WITH NIGHT TIME LOWS OUT
OF THE CHICAGO URBAN HEAT ISLAND DROPPING INTO THE MID AND UPPER
30S. THE END OF THE WEEK AND THE WEEKEND LOOK TO BE DRY WITH
MODERATING TEMPERATURES AS THE UPPER FLOW FLATTENS AND BECOMES
WEST-NORTHWEST. THIS WILL RESULT IN THE CANADIAN AIR MASS BEING
REPLACED BY A MILDER PACIFIC AIR MASS.
TRS
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* GUSTY WEST-NORTHWEST WINDS THIS AFTERNOON.
RATZER
//DISCUSSION...UPDATED 18Z...
REGION REMAINS UNDER INFLUENCE OF DEEP WINDY LOW PRESSURE SYSTEM
TO THE NORTHEAST OF THE GREAT LAKES. MID-LEVEL DISTURBANCE AND
ASSOCIATED WEAKER SURFACE LOW HAVE PASSED ACROSS THE FORECAST AREA
THIS MORNING...WITH COLD FRONT NOW MOVING OUT OF THE EASTERN
TERMINALS. RAIN ASSOCIATED WITH THIS FRONT AND MID-LEVEL
DISTURBANCE HAS EXITED THE AREA...AND OTHER THAN SOME LINGERING
PATCHY HIGH CLOUD FROM STRONG JET OVERHEAD THIS AFTERNOON...
SHOULD SEE A DECREASE IN THE MID CLOUD COVER AND CONTINUED VFR
CONDITIONS.
WITH THE WEAK SURFACE LOW AND COLD FRONTAL TROUGH HAVING MOVED
THROUGH THE TERMINALS...THE GRADIENT WILL AGAIN TIGHTEN THIS
AFTERNOON WHICH ALONG WITH STEEPENING LOW LEVEL LAPSE RATES WILL
PROVIDE A DEEP MIXED LAYER. FORECAST SOUNDINGS CONTINUE TO DEPICT
GUST POTENTIAL IN THE 25 KT RANGE THIS AFTERNOON UNTIL THE
BOUNDARY LAYER DECOUPLES THIS EVENING.
RATZER
//ORD AND MDW CONFIDENCE...UPDATED 18Z...
* HIGH CONFIDENCE ALL ELEMENTS.
RATZER
//OUTLOOK FOR ORD/MDW FOR 00Z TUESDAY-12Z SUNDAY...UPDATED 12Z...
MONDAY...VFR.
TUESDAY...CHC SHRA. MVFR CIGS POSSIBLE.
WEDNESDAY THROUGH FRIDAY...VFR.
IZZI
&&
.MARINE...
202 PM CDT
STRONG WEST-NORTHWEST WINDS...GALE FORCE ESPECIALLY ON THE CENTRAL
AND NORTHERN PARTS OF THE LAKE...WILL REMAIN THE MAIN FORECAST FOCUS
THROUGH MONDAY AFTERNOON.
DEEP LOW PRESSURE HAS BECOME NEARLY STATIONARY TO THE NORTH OF JAMES
BAY. THIS LOW WILL SLOWLY FILL AS IT CONTINUES TO WOBBLE OVER THE
JAMES BAY AREA THROUGH MONDAY...THEN WILL WEAKEN MORE QUICKLY AS IT
FINALLY MOVES OFF TO THE EAST ACROSS QUEBEC MONDAY NIGHT INTO
TUESDAY. WHILE THE LOW REMAINS STATIONARY TONIGHT AND MONDAY...
STRONG GRADIENT WINDS WILL CONTINUE TO INFLUENCE THE LAKES AND UPPER
MIDWEST. THE COMBINATION OF THIS TIGHT PRESSURE GRADIENT AND COLDER
AIR SPREADING ACROSS THE WESTERN LAKES WILL RESULT IN WINDS RISING
AGAIN TO GALE FORCE ON THE LAKE FROM LATER THIS AFTERNOON INTO
MONDAY. STRONGEST WINDS WILL BE ON THE NORTHERN END OF THE LAKE
WHERE SPEEDS MAY REACH 45 KTS AT TIMES TONIGHT AND EARLY MONDAY. ON
THE FAR SOUTH END...MARGINAL GALE FORCE WINDS OF 35 KTS WILL BE MORE
LIKELY AND WILL BE OF SHORTER DURATION MAINLY DURING TONIGHT. WINDS
WILL THEN DIMINISH ACROSS THE LAKE LATE MONDAY AND TUESDAY AS THE
OLD LOW FINALLY PULLS AWAY.
BASED ON THESE TRENDS HAVE EXTENDED GALE WARNING TO THE SOUTH END
OPEN WATER ZONES THROUGH 14Z/9 AM CDT MONDAY...AND WILL MAINTAIN THE
GALE WARNING FOR THE NORTH HALF OR SO OF THE LAKE THROUGH 20Z/3 PM
CDT MONDAY.
ANOTHER AREA OF LOW PRESSURE WILL DEVELOP AND LIFT NORTH ALONG THE
EAST COAST BY MID-WEEK...WHICH WILL AGAIN TIGHTEN THE PRESSURE
GRADIENT ACROSS THE GREAT LAKES AS HIGH PRESSURE ALSO BUILDS SOUTH
ACROSS THE PLAINS.
RATZER
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WARNING...LMZ080-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM MONDAY.
GALE WARNING...LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-LMZ567-
LMZ868 UNTIL 3 PM MONDAY.
SMALL CRAFT ADVISORY...NEARSHORE GARY TO MICHIGAN CITY IN UNTIL 4 AM TUESDAY.
SMALL CRAFT ADVISORY...NEARSHORE WINTHROP HARBOR TO GARY IN UNTIL 4 PM
MONDAY.
&&
$$
