320 PM CDT
MAIN CONCERN FOR THE NEAR TERM...THE REMAINDER OF THE AFTERNOON AND
TONIGHT...WILL FOCUS ON PCPN POTENTIAL THIS AFTERNOON/EARLY EVENING
AND TEMPERATURES OVERNIGHT. LATEST SATELLITE IMAGERY SHOWS SCT-BKN
CU DEVELOPMENT ASSOCIATED WITH DIURNAL WARMING AND AN UPPER TROUGH
CROSSING THE MISSISSIPPI RIVER INTO NWRN IL. CU DEVELOPMENT IS NOT
QUITE AS VIGOROUS AS YESTERDAY...SO WILL ONLY CARRY SLIGHT CHANCE
POPS THROUGH THE REMAINDER OF THE DAYLIGHT HOURS. LATEST RADAR
IMAGERY SHOWS SOME SPOTTY ECHOES OVER NWRN/NCNTRL IL...THOUGH THERE
ARE NO REPORTS OF PCPN IN THE METARS. GIVE THE VERY DRY AIR AT THE
SFC...WITH DEWPOINTS IN THE 20S...EXPECT THAT MUCH OR ALL OF THE
ECHO IS VIRGA. HOWEVER...AS THE MAIN COLD POOL ASSOCIATED WITH THE
TROUGH MOVES ACROSS THE CWA OVER THE NEXT 4-5 HRS...THERE WILL BE A
GREATER POTENTIAL FOR SOME OF THE PCPN TO ACTUALLY REACH THE
GROUND. ALSO...WITH VERY STEEP LAPSE RATES AND WITH VERY LOW
FREEZING LEVELS...UNDER 5KFT...SOME MORE GRAUPEL WITH THE HEAVIEST
SHOWERS WILL BE A POSSIBILITY. FOR THE REMAINDER OF THE NIGHT...THE
DIURNAL CLOUD COVER WILL DISSIPATE AND SKIES WILL BECOME MOSTLY
CLEAR. WITH STRONG RADIATIONAL COOLING...LIGHT WINDS AND LOW
DEWPOINTS...EXPECT TEMPERATURES TO DROP INTO THE UPPER 20S TO AROUND
30F FOR MUCH OF THE CWA AWAY FROM LAKE MICHIGAN AND HEAVILY
URBANIZED AREAS. SO...WILL ISSUE A FREEZE WARNING FOR ALL COUNTIES
EXCEPT COOK COUNTY. HAVE INCLUDED THE OTHER LAKEFRONT COUNTIES IN
THE WARNING SINCE A MAJORITY OF THE COUNTY AWAY FROM THE LAKE SHOULD
DROP BELOW FREEZING.
FOR THE REMAINDER OF THE SHORT TERM FORECAST PERIOD...SATURDAY
THROUGH MONDAY...TEMPERATURES WILL BE ON THE INCREASE FOR BOTH MINS
AND MAXS. FOR THE WEEKEND...HIGH TEMPS WILL BE IN THE LOWER TO
MIDDLE 50S AND BY MONDAY...HIGHS SHOULD BE IN THE MIDDLE TO UPPER
50S. OVERNIGHT LOWS SHOULD...SIMILARLY...MODERATE AND DO NOT
ANTICIPATE MORE THAN JUST SOME PATCHY FROST FOR THE EARLY MORNING
HOURS. SATURDAY SHOULD BE MOSTLY SUNNY AND DRY AS UPPER LEVEL AND
SFC RIDGING BUILDS ACROSS THE AREA. THE NEXT CHANCE FOR SOME PCPN
WILL COME ON SUNDAY AS THE NEXT UPSTREAM SYSTEM DROPS OUT OF THE NRN
PLAINS AND ACROSS THE MIDWEST. THE MODELS ARE TRENDING A LITTLE
STRONGER WITH THIS SYSTEM WITH A VERTICALLY STACKED CLOSED LOW
DEVELOPING AS THE SYSTEM MOVES OVER ERN IOWA SUNDAY AFTERNOON. THE
PROGRESSION OF THE SYSTEM WILL THEN SLOW DOWN OVERNIGHT MONDAY AS
THE DEEPENING SFC LOW OFF THE NEW ENGLAND COAST EFFECTIVELY BLOCKS
PROGRESSION OF SYSTEMS TO THE WEST. SO...ANTICIPATE THAT PCPN MAY
LINGER OVER THE ERN PORTIONS OF THE CWA INTO MONDAY MORNING.
FOR THE LONGER TERM...FOR TUESDAY THROUGH FRIDAY...FORECAST
UNCERTAINTY INCREASES WITH TIME THROUGH THE PERIOD. THE GUIDANCE IS
RELATIVELY CONSISTENT IN KEEPING THE AREA DRY INTO TUESDAY NIGHT...
BUT CONFIDENCE IN THE FORECAST DECREASES BY WEDNESDAY AS THE MODELS
BEGIN TO DIFFER SIGNIFICANTLY...ESPECIALLY IN HOW THEY HANDLE THE
SOUTHERN STREAM ENERGY LIFTING OUT OF THE SOUTHERN ROCKIES AND INTO
THE SRN PLAINS. THE ECMWF WANTS TO CLOSE OFF A SRN STREAM SHORTWAVE
INTO A CLOSED LOW...WHILE MAINTAINING STREAM SEPARATION WITH A NRN
STREAM SHORTWAVE. THE GFS IS INDICATING A MORE PHASED
SOLUTION...BUT DOES SOMEWHAT EMPHASIZE THE NRN STREAM SHORTWAVE.
SO...WHILE EITHER SOLUTION WOULD POINT TO PCPN FOR THE AREA AT SOME
POINT FOR WEDNESDAY THROUGH FRIDAY...HAVE GONE WITH MORE GENERALIZED
CHANCE POPS RATHER THAN JUMP ON ONE SOLUTION OR THE OTHER AND WAIT A
FEW MORE CYCLES BEFORE COMMITTING TO HIGHER POPS.
KREIN
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 03Z...
* ISOLD SHRA POSSIBLE UNTIL ABOUT 05Z AS A COOL FRONT APPROACHES.
* LOW POTENTIAL FOR WIND GUSTS TO AROUND 20 KT IF ISOLATED SHRA CAN
IMPACT THE TERMINALS.
* WINDS SHIFTING FROM SOUTH/SOUTHWEST TO NORTHWEST TONIGHT AS
FRONT PASSES.
MDB
//DISCUSSION...UPDATED 03Z...
COOL FRONTAL BOUNDARY NOW JUST EAST OF THE MISSISSIPPI RIVER WITH
A BAND OF ISOLD-SCT SHOWERS CONTINUING TO MOVE EASTWARD ACROSS
NORTHEAST IL TOWARD NORTHWEST IN. SHRA SHOULD EXIT TO THE EAST OF
ORD/MDW BY AROUND 05Z AND GYY BY AROUND 07Z. RECENT OBS HAVE
INDICATED THAT SOME WIND GUSTS CONTINUE WITH THE SHOWERS...AND
EXPECT THAT A BRIEF PERIOD OF GUSTS TO AROUND 20 KT IS STILL
POSSIBLE AS SHOWERS MOVE OVER OR NEAR THE TERMINALS. ANY RAINFALL
WOULD BE LIGHT AND SHORT LIVED.
FROM 00Z...
AN UPPER LEVEL TROUGH AND AN ASSOCIATED SURFACE COOL FRONT ARE NOW
APPROACHING THE TERMINALS FROM THE WEST. BAND OF ISOLATED SHOWERS
CONTINUES TO MARCH EASTWARD FROM JVL-RFD-VYS-C75. MOST OF THE
RETURNS ON RADAR ARE NOT PRODUCING PRECIP AT THE GROUND BUT THERE
ARE EMBEDDED SHOWERS. THIS ACTIVITY WILL MOVE INTO THE CHICAGO
METRO TOWARD 01Z. SHOWERS THAT ARE MAKING IT TO THE GROUND HAVE
PRODUCED WIND GUSTS OF AROUND 25 KT OR BETTER IN SPOTS BUT THIS
THREAT SHOULD BE DIMINISHING NOW THAT THE SUN HAS GONE DOWN. WILL
CONTINUE VCSH MENTION IN THE TERMINALS FOR A FEW HOURS BEFORE
ACTIVITY SHIFTS TO THE EAST. VFR CIGS EXPECTED TO CONTINUE THOUGH
THERE MAY BE SOME LOWERING INTO THE 4000-6000 FT RANGE THOUGH
THESE CLOUDS MAY REMAIN SCATTERED IN COVERAGE. WINDS HAVE TURNED
SOUTHERLY AHEAD OF THE FRONT BUT WILL TURN SOUTHWEST THEN LIKELY
NORTHWEST TONIGHT AS THE FRONT PASSES. VFR CONDITIONS WILL
CONTINUE SATURDAY WITH WEST TO NORTHWEST WINDS IN THE 10-15 KT
RANGE BY EARLY AFTERNOON WITH SPEEDS DIMINISHING LATER IN THE
AFTERNOON AS A RIDGE OF HIGH PRESSURE ARRIVES THE A SHIFT TO A
MORE SOUTHERLY DIRECTION INTO EARLY EVENING.
MDB
//ORD AND MDW CONFIDENCE...UPDATED 03Z...
* HIGH CONFIDENCE THAT SHRA WILL REMAIN ISOLATED-SCATTERED AND ONLY
OCCUR BRIEFLY IF THEY PASS OVER THE TERMINALS.
* MEDIUM CONFIDENCE THAT WINDS WILL INCREASE WITH GUSTS TO AROUND
20 KT POSSIBLE AS SHOWERS PASS AND EXIT BY AROUND 05Z.
* HIGH CONFIDENCE THAT WINDS WILL SHIFT TO THE NORTHWEST TONIGHT
WITH MEDIUM CONFIDENCE ON TIMING OF THIS.
MDB
//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...
SUNDAY...CHANCE OF SHOWERS WITH MVFR CIGS POSSIBLE.
MONDAY...MVFR POSSIBLE EARLY...THEN VFR.
TUESDAY...VFR.
WEDNESDAY...CHANCE SHRA WITH MVFR POSSIBLE.
THURSDAY...MVFR POSSIBLE EARLY.
MDB
&&
.MARINE...
257 PM CDT
THE FIRST OF TWO UPPER LEVEL DISTURBANCES DURING THIS WEEKEND WILL
PASS ACROSS LAKE MICHIGAN TONIGHT. THIS WILL STEER A SURFACE COLD
FRONT OVER THE LAKE...VEERING THE WINDS TO WEST NORTHWEST
OVERNIGHT. ALONG AND AHEAD OF THE FRONT SCATTERED SHOWERS ARE
LIKELY...FAVORED MORE IN THE NORTHERN AND CENTRAL PART OF THE
LAKE. SOME THUNDERSTORMS ARE POSSIBLE...MAINLY THIS EVENING. THE
THERMODYNAMIC PROFILES DO CONTINUE TO FAVOR A SMALL CHANCE FOR
WATERSPOUTS THROUGH MIDNIGHT. IN THE WAKE OF THE FRONT WITHIN THE
NORTHWEST FLOW DURING LATE TONIGHT INTO SATURDAY...LAKE-ENHANCED
SHOWERS ARE EXPECTED ACROSS THE EASTERN PART OF THE LAKE. RIDGING
WILL BRIEFLY MOVE OVER THE LAKE LATE SATURDAY AFTERNOON INTO THE
EVENING BEFORE BRIEF BUT STRONG SOUTHERLY FLOW WILL OVERSPREAD THE
LAKE. WINDS TO 30 KTS ARE EXPECTED ACROSS THE CENTRAL AND SOUTHERN
PORTIONS OF THE LAKE. A SMALL CRAFT ADVISORY APPEARS POSSIBLE IN
THE NORTHEAST ILLINOIS AND NORTHWEST INDIANA NEARSHORE WATERS
DURING THE DAY AND EVENING SUNDAY.
MTF/SHEA
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FREEZE WARNING...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-ILZ010-
ILZ011-ILZ012-ILZ013-ILZ019-ILZ020-ILZ021-ILZ022-ILZ023-
ILZ032-ILZ033-ILZ039...2 AM SATURDAY TO 9 AM SATURDAY.
IN...FREEZE WARNING...INZ001-INZ002-INZ010-INZ011-INZ019...2 AM
SATURDAY TO 9 AM SATURDAY.
LM...NONE.
&&
$$
