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 14Z...
* PRECIP ONSET/TIMING/DURATION
* MVFR AND LOWER CIGS INTO THE PLANNING PERIOD
SHEA/KJB
//DISCUSSION...UPDATED 12Z...
VFR CONDITIONS ACROSS THE BOARD WILL BE COMING TO AN END BY
TOMORROW. COLD FRONT THAT HAS BEEN SLOWLY MEANDERING THE MIDWEST
WILL MOVE OVER THE NEXT 24 HOURS...AND CHANCES FOR PRECIP WILL BE
ON THE RISE. WEAK SHOWERS ACROSS RFD THIS MORNING WERE LARGELY DUE
IN PART WEAK CONVERGENCE ALONG WITH SOME ELEVATED INSTABILITY THIS
MORNING. WITH AN APPROACHING UPPER LEVEL TROUGH...AND HEIGHT
FALLS...FEEL THESE SHOWERS COULD EASILY POP UP THROUGH THE
MORNING...THOUGH THE BETTER TIMING WONT BE UNTIL LATER TODAY.
FORECAST GUIDANCE CONTINUES TO SLOW DOWN THE ONSET OF PRECIPITATION
AND DID PULL BACK THE TIMING ACROSS THE BOARD. SYNOPTIC FLOW WILL
SUPPORT SOUTHEAST WINDS THROUGH THE DAY AND INTO THE AFTERNOON
WINDS MAY PICK UP INTO THE LOWER DOUBLE DIGITS. GUIDANCE HAD
ORIGINALLY INDICATED THAT THERE WOULD BE A LAKE BREEZE THAT MAY
PUSH THROUGH...FEEL THAT THERE WONT BE MUCH OF A PULL BEYOND
120...AND WILL KEEP THE MENTION AT JUST THAT. AS THE SHOWERS BEGIN
INTO THE OVERNIGHT HOURS...THERE ARE CONSISTENT SIGNALS THAT CIGS
WILL FALL THROUGH IFR...WITH THE POTENTIAL FOR LIFR. DUE TO THE
LOW CONFIDENCE ON WHEN THE ONSET FOR PRECIP WILL BE FOR
ORD...FIND IT A LITTLE TOO DIFFICULT TO ZERO IN ON AN EXACT TIME.
ONCE TRENDS START TO PLAY OUT...WILL NEED TO UPDATE ACCORDINGLY.
SHEA
//ORD AND MDW CONFIDENCE...UPDATED 14Z...
* HIGH CONFIDENCE IN VFR CONDITIONS THROUGH THE AFTERNOON
* MEDIUM TO HIGH CONFIDENCE ON WIND FORECAST
* LOW CONFIDENCE ON PRECIP ONSET...HIGH ON INCREASING COVERAGE
SHEA/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...
256 AM CDT
BROAD AREA OF HIGH PRESSURE CONTINUES TO DRIFT EAST ACROSS NEW
ENGLAND STRETCHING NORTH THROUGH EASTERN QUEBEC...MEANWHILE AN
AREA OF LOW PRESSURE CONTINUES TO DEVELOP ACROSS SOUTHERN
MANITOBA. THIS LOW PRESSURE IS EXPECTED TO LIFT NORTHEAST.
ASSOCIATED WITH THIS LOW PRESSURE SYSTEM WILL BE YET ANOTHER WEAK
LOW PRESSURE SYSTEM...THAT IS EXPECTED TO RAPIDLY DEEPEN AS IT
APPROACHES THE GREAT LAKES REGION THURSDAY INTO FRIDAY. GUIDANCE
CONTINUES TO SUGGEST THAT THE PRESSURE GRADIENT WILL TIGHTEN
SUBSTANTIALLY...AND CREATE GALE FORCE WINDS. AT THIS POINT HAVE
HELD OFF ON ANY HEADLINES...HOWEVER CONFIDENCE CONTINUES TO GROW
THAT GALE CRITERIA WILL PROBABLY BEGIN TO OCCUR SOMETIME EARLY
FRIDAY MORNING. IT APPEARS A FEW GUSTS MAY APPROACH 40KT WITH THIS
SYSTEM.
THEN AFTER THIS POTENT LOW PRESSURE SYSTEM LIFTS NORTHEAST AWAY
FROM THE GREAT LAKES REGION...MODEL GUIDANCE IS BEGINNING TO HINT
AT YET ANOTHER POTENT LOW PRESSURE WILL APPROACH THE GREAT LAKES
REGION TUE. THIS SECOND SYSTEM TAKES ON A CLASSIC FALL LIKE
SETUP.
BEACHLER
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
