328 AM CDT
MAIN FORECAST CHALLENGE IN THE SHORT TERM WILL BE TIMING ARRIVAL OF
RAIN AND ISOLATED THUNDERSTORMS OVER THE NEXT 24 HOURS OR SO.
ADDITIONAL CHALLENGES ARISE BY EARLY NEXT WEEK. EARLY MORNING WATER
VAPOR IMAGERY SHOWS RIDGING OFF THE EASTERN SEABOARD EXTENDING
NORTHWESTWARD TOWARDS NORTHERN QUEBEC. AN UPPER LOW IS OBSERVED
SPINNING NORTHWARD ACROSS THE OHIO VALLEY TOWARDS THE LOWER GREAT
LAKES. A LONGWAVE TROUGH EXTENDS FROM NORTHERN MANITOBA SOUTHWARD
ACROSS WESTERN MN/IA/MO AND INTO ARKANSAS AND IS MOVING EAST. THIS
TROUGH WILL BE OUR MAIN WEATHER MAKER THROUGH THURSDAY. FURTHER
WEST...A BELT OF ZONAL FLOW IS FOUND OVER THE EASTERN PACIFIC AND
U.S. WEST COAST WITH A SERIES OF WEAKER UPPER LOWS SPINNING OFF THE
BRITISH COLUMBIA COAST. AT THE SURFACE...HIGH PRESSURE IS CENTERED
OFF THE COAST OF MAINE WITH LOW PRESSURE TAKING SHAPE ACROSS THE
NORTHERN PLAINS IN RESPONSE TO THE UPPER TROUGH AXIS. THIS LOW
PRESSURE WILL BECOME BETTER ORGANIZED AS IT APPROACHES AND PASSES
THE AREA OVER THE NEXT 36 HOURS OR SO.
TODAY AND THURSDAY...NARROW RIBBON OF CONVERGENCE EXTENDING FROM
EASTERN WISCONSIN SOUTHWARD ACROSS THE ROCKFORD AREA AND THEN
SOUTHWEST FROM THE QUAD CITIES TOWARDS QUINCY CONTINUES TO DRIVE
SCATTERED SHOWER DEVELOPMENT WITH A FEW THUNDERSTORMS ALSO
DEVELOPING IN MORE UNSTABLE AIR CLOSER TO THE MISSISSIPPI
RIVER. THIS ACTIVITY WILL PROBABLY CONTINUE TO FESTER OVER PRETTY
MUCH THE SAME AREAS THROUGH THE MORNING AS HEIGHT FALLS INCREASE AS
THE UPPER TROUGH APPROACHES FROM THE WEST. THE OTHER CONCERN IS FOG
POTENTIAL IN VICINITY OF THE WEAK TROUGH/CONVERGENCE WHERE WINDS
HAVE WEAKENED. DENSE FOG HAS DEVELOPED JUST TO THE WEST OF THE CWA
AS POCKETS OF CLEARING DEVELOP OUTSIDE OF THE SHOWER ACTIVITY. WITH
ADDITIONAL SHOWER ACTIVITY MOVING IN AND EXPECTED TO CONTINUE DENSE
FOG WILL HAVE A TOUGH TIME DEVELOPING ACROSS THE WESTERN CWA. WILL
MENTION FOG WITH CLEARING POCKETS POSSIBLY DEVELOPING DURING LULLS
IN SHOWER ACTIVITY. THE EASTWARD PROGRESSION OF THE UPPER TROUGH AND
THE ASSOCIATED SURFACE LOW WILL BE SLOW AND TIMING HOW QUICKLY THE
ACCOMPANYING RAIN MOVES ACROSS THE CWA CONTINUES TO BE TRICKY. THE
SHORT OF IT IS THAT THIS ISSUANCE WILL SLOW THE PROGRESSION FURTHER.
MODEL GUIDANCE SUPPORTS THIS AND ONE CONTRIBUTING FACTOR TO THE
SLOWER ARRIVAL IS LIKELY SUBSIDENCE ON THE WESTERN PERIPHERY OF THE
UPPER LOW OVER THE OHIO VALLEY. THE BULK OF THE AREA SHOULD REMAIN
DRY OUTSIDE OF THE FESTERING SHOWERS FAR WEST WITH MORE WIDESPREAD
RAIN LOOKING TO HOLD OFF UNTIL MID OR POSSIBLY LATE AFTERNOON ACROSS
WESTERN AREAS ALONG THE INTERSTATE 39 CORRIDOR. WILL BRING LOW
CHANCES INTO THE CHICAGO METRO AREA AND POINTS SOUTH TOWARD KANKAKEE
DURING THE EVENING BUT THIS MAY EVEN BE TOO FAST. RIGHT NOW...PRIME
PRECIP TIME SHOULD BE THIS EVENING AND TONIGHT ACROSS THE WESTERN
CWA AND THURSDAY MORNING INTO EARLY THURSDAY AFTERNOON ACROSS THE
EAST...INCLUDING THE CHICAGO AREA AS THE SURFACE LOW STRENGTHENS AND
MOVES ACROSS CENTRAL OR NORTHERN ILLINOIS. THE SYSTEM WILL THEN
SLOWLY SHIFT EAST GRADUALLY BRINGING AND END TO THE RAIN FROM WEST
TO EAST STARTING THURSDAY AFTERNOON WEST AS A COLD FRONT MOVES
BY.
FRIDAY THROUGH SUNDAY...COOLER AND DRIER AIR WILL MOVE IN THURSDAY
NIGHT AND FRIDAY MORNING ON BRISK WESTERLY WINDS WHILE H85 TEMPS
COOL TO BETWEEN 1 AND 3 C. THIS SHOULD HOLD HIGHS TO THE UPPER 50S
NORTH AND THE LOWER 60S SOUTH BUT THERE SHOULD BE A FAIR AMOUNT OF
SUNSHINE INTO EARLY AFTERNOON. A SECOND SURGE OF COOLER MID LEVEL
AIR DROPS SOUTHWARD DOWN THE WESTERN FLANK OF THE UPPER LOW. THIS
MAY BRING SCATTERED SHOWERS BACK TO THE AREA FRIDAY AFTERNOON AND
EARLY FRIDAY EVENING. THE UPPER LOW WILL THEN LIFT INTO EASTERN
CANADA SATURDAY MORNING AS DE-AMPLIFYING UPPER RIDGING APPROACHES
FROM THE WEST BRINGING WARM ADVECTION BACK TO THE REGION. THIS
SHOULD RESULT IN TEMPS A FEW DEGREES WARMER THAN FRIDAY. THE MID
LEVEL BAROCLINIC ZONE TIGHTENS UP SATURDAY NIGHT AS A FAST MOVING
SHORTWAVE MOVES SOUTHEASTWARD TOWARDS THE MID AND UPPER MISSISSIPPI
RIVER VALLEY. A SURFACE LOW WILL ALSO DEVELOP AND PASS OVER OR JUST
SOUTH OF THE AREA SUNDAY MORNING BRINGING A COLD FRONT WITH IT. IF
THE TIMING HOLDS THEN ANY PRECIP ASSOCIATED WITH THE SYSTEM WILL BE
CLEAR OF THE AREA SUNDAY AFTERNOON.
MONDAY THROUGH WEDNESDAY...MODEL AGREEMENT IS DECENT IN TERMS OF THE
GENERAL EVOLUTION OF THE UPPER FLOW PATTERN EARLY NEXT WEEK BUT
TIMING AGREEMENT IS LOW. A DEEP UPPER LOW IS EXPECTED TO DIG INTO
THE CENTRAL U.S. AND SPAWN STRONG CYCLOGENSIS SOMEWHERE ALONG THE
MISSISSIPPI RIVER VALLEY THEN DEEPEN AS IT PASSES THE AREA. BOTH THE
ECMWF AND GFS BRING IN WHAT COULD BE THE COLDEST AIR OF THE SEASON
TO DATE FOR THE MIDDLE PART OF THE WEEK.
MDB
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 20Z...
* LAKE BREEZY MAKING THE WINDS MORE EASTERLY FOR THE REST OF THE AFTERNOON.
* PRECIP ONSET/TIMING/TONIGHT
* MVFR AND LOWER CIGS LATE TONIGHT AND ON THURSDAY
KJB
//DISCUSSION...UPDATED 18Z...
LOW PRESSURE ACROSS IOWA IS EXPECTED TO SLOWLY MOVE EASTWARD ACROSS
NORTHERN ILLINOIS THROUGH THE PERIOD. SHOWERS AND THUNDERSTORMS WILL
REMAIN WEST OF THE TERMINALS THROUGH THE AFTERNOON...WITH ONLY A
SMALL CHANCE OF AN ISOLATED SHOWER REACHING KRFD.
TONIGHT THINGS GO DOWN HILL...ESPECIALLY AFTER MIDNIGHT. IT APPEARS
THE SHOWERS WILL BE SLOW TO PROGRESS EASTWARD DURING THE EVENING.
HOWEVER...AFTER 08 UTC A LEAD MID LEVEL DISTURBANCE...NOW ACROSS
SOUTHWESTERN MISSOURI...WILL LIFT NORTHWARD ACROSS ILLINOIS AND
ALLOW SHOWERS TO DEVELOP FARTHER NORTH AND EAST ACROSS THE AREA.
BUFFER MODEL SOUNDINGS INDICATE RAPIDLY MOISTENING PROFILES DURING
THE EARLY MORNING HOURS...WHICH LOOKS TO SUPPORT A PERIOD OF DECENT
RAINFALL ACROSS THE AREA THROUGH AT LEAST EARLY TOMORROW MORNING.
THEREFORE...I WOULD NOT BE SURPRISED TO SEE MVFR VIS IN SHRA DURING
THIS PERIOD.
I THINK THERE MAY BE A BREAK IN THE RAIN DURING THE LATE MORNING
HOURS AS THE INITIAL WAVE CLEARS THE AREA. HOWEVER...I EXPECT
ADDITIONAL SHOWERS TO DEVELOP ON THE BACK SIDE OF THE SURFACE LOW AS
A SECOND MID LEVEL DISTURBANCE MOVES ACROSS THE AREA IN THE AFTERNOON.
ASIDE FROM PRECIPITATION CHANCES...THE OTHER MAJOR CONCERN ARE CIGS.
CIGS WILL LIKELY DROP INTO THE LOWER MVFR RANGE BY THURSDAY MORNING.
I AM NOT EXPECTING MUCH IF ANY IMPROVEMENT IN THE CIGS DURING THE
DAY. SO LOW END MVFR WITH SOME PERIODS OF IFR CIGS ARE EXPECTED
DURING THE DAY ON THURSDAY.
KJB
//ORD AND MDW CONFIDENCE...UPDATED 20Z...
* HIGH CONFIDENCE IN VFR CONDITIONS THROUGH THE AFTERNOON
* MEDIUM TO HIGH CONFIDENCE ON WIND FORECAST
* MEDIUM CONFIDENCE ON PRECIP ONSET...HIGH ON INCREASING COVERAGE
KJB
//OUTLOOK FOR ORD/MDW FOR 00Z FRIDAY-12Z WEDNESDAY...UPDATED 12Z...
* THURSDAY NIGHT AND FRIDAY...SHOWERS. MVFR AND IFR POSSIBLE.
* SATURDAY...VFR
* SUNDAY THROUGH TUESDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE
VFR
SHEA
&&
.MARINE...
243 PM CDT
A LOW PRESSSURE COMPLEX EXTENDING FROM FAR SOUTHERN MANITOBA TO
THE LOWER MO RIVER VALLEY WILL STRENGTHEN AS IT MOVES EAST TO
WESTERN ONTARIO...WI AND IL OVERNIGHT. THE LOW WILL CONTINUE TO
DEEPEN AS IT MOVES E ACROSS LAKE MICHIGAN THU AND THU EVE.
A STRONG NW FLOW OF MUCH COOLER AIR FROM NORTHER CANADA WILL BE
USHERED SOUTHEASTWARD ACROSS THE UPPER GREAT LAKES IN THE WAKE OF
THE LOW. DUE TO THE STRENGHT OF THE LOW AND THE COLD AIR ADVECTION
NW GALES OF AROUND 35 KT ARE A GOOD BET FOR FRI INTO SAT.
TRS
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...GALE WATCH...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...9 AM FRIDAY TO NOON
SATURDAY.
&&
$$
