325 AM CDT
A RATHER NOTICEABLE PATTERN CHANGE IS ON THE WAY BUT THE AREA WILL
SEE ANOTHER DAY OR TWO OF DRY AND MILD WEATHER BEFORE THE SHIFT
OCCURS. EARLY MORNING WATER VAPOR IMAGERY SHOWS A VERY BROAD UPPER
RIDGE IN PLACE OVER THE EASTERN CONUS AND THE WESTERN ATLANTIC WITH
A MORE PRONOUNCED RIDGE AXIS EXTENDING NORTHWESTWARD FROM THE
MID-ATLANTIC STATES INTO SOUTHERN MANITOBA. TO THE WEST...AN UPPER
TROUGH CARVED OUT OVER THE ROCKIES IS LIFTING NORTHWARD UP THE
WESTERN FLANK OF THE RIDGE. FURTHER WEST...ANOTHER TROUGH IS DIGGING
SOUTHEASTWARD TOWARD THE BRITISH COLUMBIA AND U.S. PACIFIC NORTHWEST
COAST. AT THE SURFACE... HIGH PRESSURE REMAINS PARKED OVER THE MID
ATLANTIC STATES WHILE LOW PRESSURE IS FOUND IN THE LEE OF THE
NORTHERN ROCKIES AND ACROSS THE NORTHERN PLAINS IN ASSOCIATION WITH
THE UPPER TROUGH.
TODAY AND TUESDAY...ANOTHER QUIET WEATHER DAY IS EXPECTED ACROSS THE
AREA TODAY. THE UPPER RIDGE WILL BE SHUNTED NORTHEASTWARD BY THE
UPPER TROUGH MOVING NORTHWARD INTO MANITOBA TODAY. H85 TEMPS WILL
COOL SLIGHTLY TODAY AND THERE MAY BE A BIT MORE IN THE WAY OF MID
AND HIGH CLOUD COVER AT TIMES WHICH WILL LEAD TO HIGHS CLOSE TO BUT
PROBABLY A FEW DEGREES COOLER THAN SUNDAY. A LAKE BREEZE WILL PUSH
INLAND DURING THE AFTERNOON AND WILL LIKELY DROP TEMPERATURES BY A
FEW DEGREES AS IT DOES SO. THE PATTERN CONTINUES TO SHIFT TUESDAY AS
THE UPPER TROUGH LIFTS INTO NORTHERN MANITOBA WITH A SHEARED VORT
MAX TRAILING IT TO THE SOUTH. SMALL POPS RETURN TO THE FORECAST
TUESDAY FOR WESTERN AREAS WITH SOME POTENTIAL FOR SHOWER DEVELOPMENT
THANKS TO THE TRAILING VORT...HEIGHT FALLS...AND THE PRESENCE OF THE
ENTRANCE REGION TO A DEVELOPING UPPER JET MAX PASSING OVERHEAD. IT
APPEARS A NARROW RIBBON OF DEEPER MOISTURE WILL ACCOMPANY THE WAVE
BUT WITH THE ANTECEDENT ATMOSPHERE BEING VERY DRY WILL KEEP POPS
MINIMAL FOR NOW. CHANCES WILL CONTINUE INTO THE EVENING AND SPREAD
EASTWARD. MILD TEMPS WILL CONTINUE DESPITE THE LOW RAIN CHANCES AND
SOME PERIODS OF INCREASED CLOUD COVER.
WEDNESDAY THROUGH FRIDAY...WHILE THE ONE TROUGH LIFTS ACROSS
MANITOBA THE MAIN LONGWAVE TROUGH AXIS WILL BECOME REINFORCED AND
BEGIN TO MOVE EASTWARD INTO WEDNESDAY. A MORE COHERENT SURFACE LOW
WILL DEVELOP ACROSS THE NORTHERN PLAINS THEN BUILD SOUTHWARD IN
CONJUNCTION WITH A DEVELOPING COLD FRONT. THE WHOLE SYSTEM WILL WORK
EASTWARD INTO WEDNESDAY NIGHT. RIGHT NOW IT LOOKS LIKE WEDNESDAY
WILL START OFF DRY WITH RAIN CHANCES INCREASING FROM WEST TO EAST
LATER IN THE DAY AHEAD OF THE APPROACHING COLD FRONT. THE BEST
CHANCES ARRIVE WEDNESDAY NIGHT AND CONTINUE INTO THURSDAY MORNING WITH A
SECONDARY SURFACE LOW DEVELOPING CLOSE TO THE AREA WHILE THE
ORIGINAL LOW MOVES INTO WESTERN ONTARIO. TIMING OF ALL OF THIS MAY
SLOW SOMEWHAT GIVEN THE AMPLITUDE OF THE PATTERN. WEDNESDAY WILL
REMAIN MILD THOUGH LIKELY SEVERAL DEGREES COOLER THAN TUESDAY...WITH
THURSDAY COOLER YET WITH ALL AREAS LIKELY TO BE HELD INTO THE 60S. A
BETTER SURGE OF COOLER AIR ARRIVES LATER THURSDAY NIGHT WITH H85
TEMPS COOLING TO 2-3 C WITH BRISK WESTERLY WINDS. WILL RETAIN SLIGHT
POPS FOR FRIDAY THOUGH THERE IS MODEL DISAGREEMENT AS TO HOW
PROGRESSIVE THE UPPER LOW WILL BE.
SATURDAY AND SUNDAY...A FAIR AMOUNT OF UNCERTAINTY SURROUNDS THIS
PERIOD. ECMWF AND GFS ARE AT ODDS WITH THE AMPLITUDE OF THE UPPER
FLOW PATTERN WITH THE LATEST ECMWF NOW BUILDING A SIGNIFICANT RIDGE
OVER THE AREA RESULTING IN ANOTHER BIG WARM UP FOR THE WEEKEND AND
INTO EARLY NEXT WEEK. THE GFS ALSO FAVORS A WARM UP AT THIS POINT BUT
IS MUCH WEAKER WITH THE FLOW FEATURES. EXPECT THAT TEMPS WILL NEED
TO BE RAISED FOR AT LEAST SATURDAY AS SOME LEVEL OF RIDGING ARRIVES
BUT WILL HOLD OFF ON BIG CHANGES UNTIL THINGS BECOME CLEAR.
MDB
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 18Z...
* WIND DIRECTION/LAKE BREEZE POTENTIAL. CMS
//DISCUSSION...UPDATED 18Z...
WINDS ARE THE PRIMARY CONCERN THROUGH THE PERIOD. ACAR SOUNDINGS
FROM THE PAST SEVERAL HRS INDICATE LOW LEVELS WINDS...950MB...
GENERALLY LESS THAN 10 KT...BUT INCREASING. FORECAST SOUNDINGS
SUGGEST LOW LEVEL WINDS INCREASING TO 12-16 KTS THIS AFTERNOON.
WHILE A LAKE BREEZE MAY FORM...AND PERHAPS ALREADY SHOWING UP ON
THE TERMINAL RADARS NORTH OF DOWNTOWN CHICAGO...THESE INCREASING
LOW LEVEL WINDS SHOULD BE STRONG ENOUGH TO PREVENT A LAKE BREEZE
FROM REACHING ORD/MDW. OVERALL GRADIENT SUPPORTS A PREVAILING
SOUTH/SOUTHEAST WIND INTO TUESDAY AFTERNOON WITH SPEEDS
DIMINISHING OVERNIGHT. WINDS BEGIN TO TURN MORE EASTERLY TUESDAY
AFTERNOON INTO TUESDAY EVENING...PERHAPS AIDED BY A LAKE BREEZE.
A WEAK WAVE WILL LIFT NORTHEAST ACROSS NORTHWEST IL AND SOUTHERN
WI TUESDAY MORNING INTO TUESDAY AFTERNOON. A FEW SHOWERS ARE
POSSIBLE WITH THIS FEATURE...POSSIBLY AFFECTING RFD. HAVE OPTED
TO LEAVE OUT ANY MENTION OF PRECIP WITH THIS FORECAST GIVEN
EXPECTED ISOLATED COVERAGE AND SHORT DURATION...BUT WILL NEED TO
BE MONITORED WITH LATER FORECASTS. CMS
//ORD AND MDW CONFIDENCE...UPDATED 18Z...
* MEDIUM CONFIDENCE REGARDING WINDS/SPEEDS. CMS
//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...
TUESDAY NIGHT THROUGH EARLY WEDNESDAY...VFR
LATE WEDNESDAY THROUGH THURSDAY...OCNL SHRA WITH CHC TSRA
FRIDAY AND SATURDAY...VFR
SUNDAY...CHC SHRA
SHEA
&&
.MARINE...
204 PM CDT
THE MAIN CONCERN DURING THE PERIOD WILL BE THE POTENTIAL FOR A
PERIOD OF LOW END GALES ON FRIDAY AND FRIDAY NIGHT. A POTENT AREA OF
LOW PRESSURE IS EXPECTED TO DROP SOUTHEAST ACROSS THE UPPER MISSISSIPPI
RIVER VALLEY AND ACROSS THE GREAT LAKES LATER THIS WEEK. THIS
SYSTEM LOOKS TO PRODUCE A PERIOD OF SIGNIFICANT WINDS ACROSS THE
LAKE AS MUCH COLDER AIR SPILLS ACROSS THE REGION.
KJB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
