358 AM CDT
MAIN FORECAST CONCERNS ARE WITH PRECIP CHANCES TODAY AS WELL AS
INTO THE END OF THE WEEKEND...WITH A POSSIBLE BRIEF WARM UP EARLY
NEXT WEEK.
LATEST SATELLITE IMAGERY SHOWING A LARGE AREA OF HIGH LEVEL CIRRUS
MOVING ACROSS PORTIONS OF NORTHERN ILLINOIS AND NORTHWEST INDIANA
EARLY THIS MORNING...WITH SOME MID/LOW LEVEL CLOUD COVER MOVING
EAST ACROSS THE LAKE. ALTHOUGH...THIS HIGH LEVEL CIRRUS IS RATHER
THIN AND STILL RESULTING IN MOSTLY CLEAR CONDITIONS. WITH THESE
CLEAR SKIES AND CALM CONDITIONS...TEMPERATURES HAVE BEEN ABLE TO
FALL INTO TO THE LOW AND MID 30S THIS MORNING WITH WARMER TEMPS
NEAR THE LAKE. WITH THESE FALLING TEMPS...HAD INCLUDED THE
REMAINDER OF THE CWA IN THE FROST ADVISORY THIS MORNING WITH THE
EXCEPTION OF COOK COUNTY. THERE ALSO REMAINS SOME ISOLATED AREAS
OF FOG THIS MORNING...WITH VISIBILITIES HOLDING AROUND 2-4SM AND
EVEN SOME BRIEF PERIODS OF VIS AROUND 1-3SM. THIS IS MOST LIKELY
DUE IN PART TO SOME AREAS WHICH RECEIVED SOME SHOWERS/MOISTURE
YESTERDAY EVENING. DONT EXPECT TOO MUCH EXPANSION OF THIS
FOG...MAINLY REMAINING ISOLATED. ALTHOUGH...WITHIN THESE
AREAS...LOWER VISIBILITY COULD BE OBSERVED.
LATEST SATELLITE IMAGERY SHOWING THE NEXT WAVE TO BRING OUR AREA
SOME SHOWERS UP ACROSS THE NORTHERN PLAINS...WITH ASSOCIATED CLOUD
COVER AND LIGHT SHOWERS ALSO PRESENT. THIS MID LEVEL WAVE AND
SURFACE TROUGH AXIS WILL DIG SOUTH THROUGH THE MIDWEST TODAY AND
REACH THE CWA LATER THIS AFTERNOON. NOT ONLY WILL FORCING BE ON
THE INCREASE...BUT MUCH COLDER AIR ALOFT WILL SHIFT SOUTHWARD.
THIS WILL RESULT IN STEEP LOW AND MID LEVEL LAPSE RATES. THESE TWO
FEATURES COINCIDING WITH ONE ANOTHER WILL ENABLE SHOWERS TO
DEVELOP WITH THE WESTERN PORTION OF THE CWA OBSERVING THE BETTER
CHANCES THIS AFTERNOON. THEN THIS TROUGH AXIS WILL SHIFT EAST WITH
FORCING EXPANDING EAST ACROSS THE REMAINDER OF THE CWA WITH THE
OVERALL BEST CHANCES FOR THE CWA TO OBSERVE SHOWERS COMING IN THE
LATE AFTERNOON AND EARLY EVENING. THERMAL PROFILES OVER THE LAKE
DURING THIS TIME FRAME WILL NOT ONLY BE FAVORABLE FOR SHOWERS BUT
EVEN THE POSSIBILITY FOR THUNDER AS VERY LOW AND MID LEVEL LAPSE
RATES WILL BE IN PLACE AS THE COLDEST AIR ALOFT MOVES OVERHEAD.
THEN WITH THIS UPPER LEVEL TROUGH SHIFTING EAST...THIS
PRECIP/CLOUD COVER WILL ALSO SLOWLY SHIFT EAST. AS CLEAR SKIES
SLOWLY WORK BACK IN FROM THE WEST...TEMPS COULD FALL ONCE AGAIN
WITH SIMILAR CONDITIONS/TEMPS POSSIBLE TONIGHT. A BRIEF PERIOD OF
RIDGING ON SATURDAY WILL RESULT IN FAIR CONDITIONS BUT THIS WILL
BE ONGOING AS THE NEXT SYSTEM APPROACHES FROM THE WEST. ANOTHER
TROUGH WILL DIG SOUTHEAST OUT OF THE NORTHERN PLAINS SATURDAY
NIGHT INTO SUNDAY WITH SURFACE REFLECTION PUSHING THROUGH DURING
THE DAY SUNDAY. SHOWERS WILL DEVELOP OUT AHEAD OF THIS
SYSTEM...WITH MODELS IN FAIR AGREEMENT OF THE EVOLUTION OF THIS
SYSTEM. WITH THE BEST CHANCES ACROSS THE NORTHERN CWA...HAVE
RAISED POPS ON SUNDAY. THEN CLEARING ON MONDAY WITH A WARMING
TREND EXPECTED THAT DAY INTO TUESDAY WITH MAX TEMPS POSSIBLY
REACHING THE LOWER 60S.
RODRIGUEZ
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 08Z...
* POTENTIAL FOR IFR VSBYS IN PATCHY FOG EARLY AM.
* CHANCE OF CONVECTIVE SHOWERS VERY LATE AFTN/EVENING.
RATZER
//DISCUSSION...UPDATED 08Z...
FOG REMAINS QUITE PATCHY ACROSS THE AREA AT 08Z. VSBYS WHICH HAD
DROPPED AS LOW AS 3/4SM AT PWK EARLIER HAVE IMPROVED TO 7SM
BENEATH HIGH CLOUDS. STILL APPEARS THAT CIRRUS DECK WILL MOVE OFF
TO THE EAST OF THE AREA TOWARD SUNRISE ALLOWING STRONGER RADIATIVE
COOLING AND DECREASING TEMPERATURE-DEW POINT SPREADS...THOUGH AM
EVEN LESS CONFIDENT THAN EARLIER ABOUT FOG DEVELOPMENT AND IMPACTS
ON ORD/MDW/GYY TERMINALS. THEREFORE HAVE GONE A LITTLE MORE
OPTIMISTIC WITH 08Z AMENDMENTS.
RATZER
PREVIOUS DISCUSSION FROM 06Z...
MAIN CONCERN FOR TERMINALS THIS MORNING IS WITH THE POTENTIAL FOR
PATCHY DENSE FOG TO DEVELOP...MAINLY AT ORD/MDW/GYY WHERE THURSDAYS
AFTERNOON AND EVENING WET THE GROUND AND VERY WEAK SURFACE PRESSURE
GRADIENT IS NOW RESULTING IN CALM WINDS. BROKEN CIRRUS DECK
CURRENTLY OVERHEAD IN ASSOCIATION WITH UPPER JET STREAK IS
EXPECTED TO SHIFT EAST THE TERMINALS AROUND 10Z...WHICH WILL ALLOW
FOR STRONGER RADIATIONAL COOLING THROUGH SUNRISE AND DEVELOPMENT
OF PATCHY DENSE FOG. EVEN WITH HIGH CLOUDS OVERHEAD...VSBYS
ALREADY VARYING FROM 3/4SM TO 1 1/2SM AT NEARBY KPWK. CURRENT
THINKING IS THAT FOG WILL REMAIN SHALLOW/PATCHY UNTIL HIGH CLOUDS
CLEAR HOWEVER. SHOWERS DID NOT DIRECTLY IMPACT RFD AND DPA...WHICH
SUGGESTS PATCHY IS LESS OF A CONCERN AT THOSE LOCATIONS.
NEXT MID LEVEL DISTURBANCE AND ASSOCIATED SURFACE TROUGH CURRENTLY
OVER THE EASTERN DAKOTAS WILL MOVE INTO THE FORECAST AREA BY
TONIGHT. APPROACH OF TROUGH WILL ALLOW WINDS TO BACK TO THE
SOUTHWEST ONCE NOCTURNAL INVERSION MIXES OUT BY MID-MORNING.
MODEL FORECAST SOUNDINGS INDICATE INSTABILITY DEVELOPING AGAIN
DURING THE LATE AFTERNOON AND EVENING HOURS DUE TO COLD AIR ALOFT
WITH APPROACHING DISTURBANCE. HAVE INDICATED PROB30 FOR SHRA AT
THIS TIME AS LOW LEVEL AIR IS RELATIVELY DRY...THOUGH STEEP LOW
LEVEL LAPSE RATES ARE PROGGED TO EXTEND TO NEARLY 9000 FT.
RATZER
//ORD AND MDW CONFIDENCE...UPDATED 08Z...
* LOW CONFIDENCE IN PATCHY FOG AND IFR VSBYS THIS AM.
* MEDIUM CONFIDENCE IN TIMING/COVERAGE OF SHOWERS LATE TODAY AND
THIS EVENING.
RATZER
//OUTLOOK FOR ORD/MDW FOR 12Z SATURDAY-12Z THURSDAY...UPDATED 00Z...
SAT...VFR. WX NIL.
SUN...PREVAILING VFR...CHC SHRA WITH LCL MVFR
MON...VFR. WX NIL.
TUE...VFR. WX NIL.
WED...VFR...SLGT CHC -SHRA.
TRS
&&
.MARINE...
155 AM CDT
SEVERAL UPPER LEVEL DISTURBANCES/CLIPPER SYSTEMS SHOULD AFFECT THE
WEATHER OVER LAKE MICHIGAN FOR THE NEXT FEW DAYS. EACH DISTURBANCE
LOOKS TO PROVIDE AN INCREASE IN THE WINDS AND GOOD CHANCES FOR LAKE
EFFECT/LAKE ENHANCED SHOWERS AND EVEN SOME THUNDERSTORMS.
THE FIRST CLIPPER SYSTEM WILL RACE SOUTHEASTWARD ACROSS THE LAKE
LATER TODAY AND TONIGHT. THE ASSOCIATED SURFACE TROUGH OF LOW
PRESSURE SHOULD INDUCE AN INCREASE IN THE SOUTH TO SOUTHWESTERLY
WINDS LATER THIS AFTERNOON AND DURING THE EVENING. THIS SHOULD
PROVIDE A WINDOW OF 15 TO 25 KT WINDS INTO THIS EVENING BEFORE THE
WINDS ABATE. THE OTHER CONCERN WITH THIS SYSTEM WILL BE THE THREAT OF
SOME THUNDERSTORMS AND WATERSPOUTS TONIGHT. VERY COLD TEMPERATURES
ALOFT ASSOCIATED WITH THE UPPER LEVEL DISTURBANCE SHOULD PROVIDE A
FAVORABLE THERMODYNAMIC SETUP FOR THUNDERSTORMS AND WATERSPOUTS. THE
WATERSPOUT THREAT WILL LIKELY BE THE HIGHEST DURING THE LATER
EVENING AND OVERNIGHT HOURS AS THE SURFACE TROUGH PROVIDES A GOOD
SURFACE CONVERGENCE ZONE. THIS THREAT WILL DIMINISH ON SATURDAY
MORNING.
THERE WILL BE A BRIEF QUIET PERIOD DURING THE DAY ON SATURDAY AS A
SURFACE RIDGE OF HIGH PRESSURE BUILDS IN ACROSS THE LAKE.
HOWEVER...ANOTHER CLIPPER SYSTEM LOOKS TO AFFECT LAKE MICHIGAN ON
SUNDAY AND SUNDAY NIGHT. THIS SYSTEM APPEARS TO BE THE STRONGEST OF
THE TWO...AND THEREFORE THE SOUTHERLY WINDS THAT IT INDUCES ON
SUNDAY COULD APPROACH LOW END GALE FORCE. WILL STAY CONSERVATIVE AND
CAP THE WINDS AT 32 KT AT THIS TIME. AT THE LEAST...THIS LOOKS TO
PRODUCE A GOOD CHANCE OF SMALL CRAFT CONDITIONS FOR THE NEAR SHORE
WATERS ON SUNDAY.
NEXT WEEK IT APPEARS THAT THE WEATHER PATTERN WILL REMAIN ACTIVE
ACROSS THE CENTRAL CONUS. HOWEVER...AT THIS TIME THE STRENGTH OF THE
STORM SYSTEMS REMAIN IN QUESTION.
KJB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FROST ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-
ILZ032-ILZ033-ILZ039 UNTIL 7 AM FRIDAY.
IN...FROST ADVISORY...INZ001-INZ002-INZ010-INZ011-INZ019 UNTIL 7 AM
FRIDAY.
LM...NONE.
&&
$$
