🚀 go-pugleaf

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1138 AM CST TUE FEB 5 2013

DISCUSSION...
1100 AM CST

BECOMING MORE CONCERNED WITH SNOWFALL INTENSITY THIS AFTERNOON AND
WILL BE INCREASING SNOW AMOUNTS SLIGHTLY AND REFINING
TIMING. CLIPPER SYSTEM CONTINUES TO MOVE ACROSS THE UPPER GREAT
LAKES WITH A VORT MAX DRIVING A BAND OF INTENSE SNOWFALL ACROSS
SOUTHERN WISCONSIN WHICH IS MOVING SOUTHEAST. NEAR TERM GUIDANCE
WANTS TO TAKES THIS BAND MORE TO THE EAST BUT RADAR TRENDS
CONTINUE TO SUPPORT A SOUTHEAST MOVEMENT RIGHT INTO THE AREA
EARLY/MID AFTERNOON. 1/4-1/2SM VSBY HAS EXPANDED IN COVERAGE UNDER
THE SNOW BAND OVER THE LAST HOUR OR SO WITH SNOW AMOUNTS RANGING
FROM A HALF TO 1.5 INCHES UNDER THE BAND OVER A SHORT PERIOD OF
TIME. APPROXIMATE TIMING...THE LEADING EDGE OF THE BAND SHOULD WORK
INTO THE ROCKFORD AREA AROUND 18Z AND THE MORE INTENSE SHOWERS MAY
BE MORE SPOTTY THAT FAR NORTHWEST. TO THE EAST...SNOW SHOULD REACH
THE NORTHWEST CHICAGO METRO 1830-1900Z OR SO AND THE DOWNTOWN AREA
IN THE LATE IN THE 19Z HOUR. PEAK INTENSITY WILL LIKELY LAG THE
INITIAL SNOWFALL BY A SHORT TIME. NW INDIANA SHOULD SEE SNOW
ARRIVE IN THE 20Z HOUR. ASSUMING INTENSITY IS MAINTAINED...OVERALL
EXPECT ABOUT A 2 HOUR OR SO WINDOW OF SNOW WHERE ACCUMULATION
RATES COULD EASILY REACH 1 INCH PER HOUR AT TIMES. WILL GO AHEAD
AND REFINE POP TIMING IN THE FORECAST GRIDS AND INCREASE AMOUNTS
INTO THE 1-2 INCH RANGE...PARTICULARLY NORTH OF A ROCKFORD TO
VALPARAISO AGAIN...THE INTENSITY WILL BE THE BIGGEST ISSUE WITH
THIS BAND AND TIMING OF ARRIVAL JUST PRIOR TO RUSH HOUR IN THE
CHICAGO AREA COULD BECOME VERY PROBLEMATIC. SNOWFALL TOTALS WILL
LIKELY BE WELL BELOW ADVISORY CRITERIA BUT WILL ISSUE AN SPS TO
HIGHLIGHT THE THREAT.

MDB

//PREV DISCUSSION...
340 AM CST

TODAY...
IR IMAGERY EARLY THIS MORNING SHOWS A FEW BREAKS IN THE CLOUDS
ACROSS CENTRAL IL/IN...STRETCHING NORTH INTO NORTHCENTRAL IL. WITH
RIDGING OVERHEAD...WINDS HAVE IN MANY LOCATIONS GONE CALM...WHICH
HAS ALLOWED GOOD RADIATIONAL COOLING. HELPING THE COOLING THIS
MORNING WAS THE FRESH BLANKET OF SNOW FROM MONDAY...WITH TEMPS
ACROSS MUCH OF THE CWFA IN THE SINGLE DIGITS ABOVE ZERO...TO THE LOW
TEENS IN A FEW AREAS.

WEAK ANTI-CYCLONIC FLOW OVERHEAD WAS ORIENTED FROM CENTRAL MO
STRETCHING NORTHEAST THROUGH SOUTHERN ONTARIO...AHEAD OF YET ANOTHER
CLIPPER SYSTEM. THIS WEAK SFC RIDGE APPEARS TO BE SLIGHTLY STRONGER
THAN THE PREVIOUS ONES AND SHOULD AID IN KEEPING THE CLIPPER
SLIGHTLY FURTHER NORTH THAN THE PRIOR ONES. THUS THE BEST FORCING
WILL BE TO THE NORTH IN CENTRAL WISC STRETCHING EAST INTO LOWER MI.
WINDS WILL BECOME LIGHT FROM THE SOUTH ARND DAYBREAK...THEN INCREASE
SLIGHTLY AS THE BETTER PRESSURE GRADIENT APPROACHES FROM THE
NORTHWEST ALONG THE SOUTHERN PERIPHERY OF THE APPROACHING CLIPPER.

GUIDANCE HAS SHOWN SOME CORRECTIONS ON THE TIMING OF THE BETTER
MOISTURE BACK INTO NORTHERN IL/NORTHWEST IN ASSOCIATED WITH THE
CLIPPER...FOCUSED NOW ON A 13-15Z ARRIVAL OF THE BEST MOISTURE. THIS
CHANNEL OF MOISTURE SLOWLY PIVOTS EAST...WITH THE DEEPER MOISTURE
BEGINNING TO PEEL EAST OF THE CWFA ARND 21Z. AS THE MIXED LAYER
INCREASES LATER THIS MORNING...COUPLED WITH DEEPER
MOISTURE...PARCELS SHOULD BECOME AGITATED WITHIN THE DGZ THAT LGT
SNOW WILL OVERSPREAD NORTHCENTRAL/NORTHEAST IL AND EXPECT LIGHT
ACCUMS TO ACCOMPANY. TOTAL PRECIP WITH MOST CLIPPERS IS A CHALLENGE
GIVEN THE ORIGIN...AND THIS SYSTEM DOES NOT DEVIATE. GENERALLY THE
NORTHERN TWO-THIRDS OF THE CWFA SHOULD SEE A TOTAL QPF NO GREATER
THAN 0.05 INCHES...WITH TOTAL SNOW ACCUMS GENERALLY LESS THAN 1 INCH
ACROSS THE CWFA.

THE FOCUS OF ACCUMULATING SNOW WILL BE ALONG AND NORTH OF A DIXON TO
KANKAKEE LINE. ALONG A ROCKFORD TO EVANSTON LINE AND POINTS
NORTH...TOTAL SNOWFALL IS EXPECTED TO BE JUST UNDER 1 INCH.

GUIDANCE HAS CONTINUED TO FAVOR SLIGHTLY WARMER TEMPS TODAY...AS THE
850MB THERMAL TROUGH BEGINS TO SLIDE NORTHEAST. TEMPS WILL REMAIN
BELOW ZERO AT 850MB...HOWEVER WITH SOUTHERLY FLOW AT THE
SFC...WARMER AIR WILL BEGIN TO ADVECT NORTH ACROSS THE CWFA. 2M TEMP
PLUMES POINT TOWARDS TEMPS WARMING TO ARND 30 DEG THIS AFTN...WITH
POSSIBLY THE MID 30S ALONG AND SOUTH OF A LA SALLE TO KANKAKEE LINE.
HAVE OPTED TO NOT DEVIATE MUCH FROM PREVIOUS THINKING...EXCEPT DID
BUMP TEMPS UP A DEG. THE CHALLENGE WILL BE THE SNOWPACK.

TEMPERATURE CONFIDENCE...MEDIUM.
PRECIPITATION CONFIDENCE...MEDIUM.

TONIGHT THROUGH WEDNESDAY...
ANTI-CYCLONIC FLOW QUICKLY BUILDS INTO THE REGION TONIGHT WITH DRY
WEATHER EXPECTED. IN ADDITION IT APPEARS THE PATTERN BEGINS TO SHIFT
WITH NO NEW CLIPPERS TO TALK ABOUT...HOWEVER THE FOCUS WILL TURN
TOWARDS A SLOW WARMING TREND THUR. TEMPS SHOULD EASILY RADIATE
TONIGHT INTO THE LOW TEENS...WITH SLIGHTLY WARMER TEMPS ALONG THE
FAR SOUTHERN SECTIONS OF THE CWFA. WITH COOLER AIR STEADILY FLOWING
ACROSS LAKE MI...LAKE EFFECT PRECIP WILL CONTINUE FOR LOWER MI.

HIGH PRESSURE REMAINS OVERHEAD FOR WED MORNING SLOWLY SLIDING EAST
AND BECOMING CENTERED ACROSS THE MIDDLE ATLANTIC REGION WED NIGHT.
FLOW TURNS SOUTHERLY IN ADVANCE OF A DEVELOPING SOUTHERN PLAINS LOW.
THIS WILL ALLOW WARMER/MOIST AIR TO BEGIN ADVECTING NORTH INTO THE
CWFA. TEMPS ALOFT CONTINUE TO WARM THROUGHOUT THE DAY...WITH HIGHS
TOPPING OUT IN THE UPPER 20S TO LOW 30S. THE FAR SOUTHERN CWFA WHERE
LESS SNOWPACK EXISTS COULD SEE TEMPS WARM TO THE MID 30S. STEADY
TEMPS WED EVENING BEFORE POSSIBLY RISING AFTER MIDNIGHT...THE
WILDCARD FOR TEMPS WILL BE THE SNOWPACK...WHICH WILL MOST LIKELY
DIMINISH THE WARMING RATES. THUS HAVE OPTED TO KEEP TEMPS RATHER
SIMILAR IN THE MID 20S ACROSS THE BULK OF THE CWFA.

A CHANNEL OF MOISTURE WILL BEGIN TO DEVELOP FROM THE CENTRAL PLAINS
STRETCHING NORTHEAST THROUGH THE WESTERN GREAT LAKES. AT THIS TIME
HAVE OPTED TO BRING PRECIP INTO THE WESTERN CWFA LATE WED NIGHT.
TEMPS AGAIN ARE A CHALLENGE...AS IS PRECIP TYPE. AT THIS TIME FEEL
THAT A RAIN/SNOW MIX LOOKS FEASIBLE.

CONFIDENCE...MEDIUM.

THURSDAY THROUGH MONDAY...
AT THE ONSET OF THE EXTENDED PERIODS A ROBUST SHORTWAVE WILL SLIDE
ACROSS THE CWFA...AS A TRANSITION TOWARDS SEASONAL TO SLIGHTLY ABOVE
SEASONAL CONDITIONS FOR THE UPCOMING WEEKEND INTO EARLY NEXT WEEK.

FOR THURSDAY GUIDANCE HAS DEMONSTRATED CONSIDERABLE NOISE WITH
RESPECT TO THE PLACEMENT OF THE LOW...AS WELL AS THE TRACK THAT THIS
WAVE WILL TAKE. WITH THE DOWNSTREAM SFC RIDGE POSITIONED ACROSS THE
MIDDLE ATLANTIC REGION...WARM SOUTHERLY FLOW SHOULD ALLOW THE 850MB
THERMAL RIDGE OF 5 TO 7 DEG C TO PUSH OVERHEAD. DEW PTS HAVE RISEN
MARGINALLY OVER THE PREVIOUS FORECAST...AND APPROACH 30 DEG THUR
MIDDAY/AFTN. THIS PARAMETER DOES SHOW SOME HIGHER CONFIDENCE AS THE
ENSEMBLES ARE SUGGESTING MINIMAL SPREAD AT THIS TIME. 500MB TROUGH
DIGS INTO THE NORTHERN PLAINS PRE-DAYBREAK THUR...WITH MOISTURE
STEADILY ADVECTING ACROSS THE CWFA. THE BULK OF THE CWFA SHOULD SEE
PRECIP FALL AS LIQUID...WITH THE EXCEPTION BEING THE FAR NORTHERN
COUNTIES. FROM ROCKFORD TO WAUKEGAN TEMPS WILL HOVER IN THE LOW 30S
AND COULD SEE A RAIN/SNOW MIX. FURTHER NORTH IT APPEARS TEMPS WILL
REMAIN COLD ENOUGH TO SUPPORT ALL SNOW.

THIS WAVE THEN PUSHES EAST WITH JUST A BRIEF TOUCH OF COOLER AIR FOR
FRI...THEN MID-LVL RIDGING ARRIVES FOR SAT/SUN OVER THE GREAT LAKES
REGION AS A TROUGH DIGS INTO THE FOUR-CORNERS REGION. THIS WILL HELP
KICK WARMER AIR NORTH FROM THE WESTERN GULF FOR THE UPCOMING
WEEKEND. TEMPS FOR THE WEEKEND COULD BE FLIRTING WITH 40
DEG...POSSIBLY THE MID/UPR 40S FOR AREAS ALONG AND SOUTH OF A LA
SALLE TO KANKAKEE LINE BY SUN.

ENSEMBLES THEN SUGGEST THE RIDGING WILL BEGIN TO RELAX FOR EARLY
NEXT WEEK AS THE TROUGH OVER THE FOUR-CORNERS REGION SLOWLY PIVOTS
EAST TOWARDS THE SOUTHERN ROCKIES. THIS COUPLED WITH SOME LOWERING
OF THE HEIGHTS ACROSS THE GREAT LAKES...COULD ALLOW FOR TEMPS TO
RETURN TO MORE SEASONAL CONDITIONS EARLY NEXT WEEK.

CONFIDENCE...MEDIUM.

BEACHLER

&&

AVIATION...

//ORD AND MDW CONCERNS...UPDATED 18Z...

* BAND OF SNOW WILL MOVE ACROSS ORD AND MDW THIS AFTERNOON. IFR
  CONDITIONS AND UP TO 1-2 INCHES OF SNOW IN ABOUT A 2 HOUR PERIOD.

* MVFR CEILINGS AFTER THE SNOW ENDS.

* SOUTHWEST WINDS GRADUALLY SHIFTING MORE WESTERLY THROUGH LATE
  AFTERNOON AND BECOMING NORTHWEST THIS EVENING.

PAW

//DISCUSSION...UPDATED 18Z...

THE FIRST CONCERN FOR THIS AFTERNOON IS A SNOW BAND MOVING SOUTHEAST
OUT OF WISCONSIN. THIS BAND HAS A HISTORY OF VISIBILITIES BELOW 1
MILE AND SNOW ACCUMULATIONS UP TO 1.5 INCHES. IT SHOULD TAKE ABOUT
2 HOURS TO PASS THROUGH EACH TERMINAL.

MVFR CEILINGS WILL PREVAIL AFTER THE SNOW ENDS...WITH CLEARING
EXPECTED OVERNIGHT AS HIGH PRESSURE BUILDS INTO THE AREA FOR
WEDNESDAY.

PAW


//ORD AND MDW CONFIDENCE...UPDATED 18Z...

* MEDIUM TO HIGH CONFIDENCE IN TIMING AND DETAILS OF SNOW THIS
  AFTERNOON.

* MEDIUM CONFIDENCE IN CEILINGS AFTER THE SNOW ENDS.

* HIGH CONFIDENCE IN WIND TREND.

PAW

//OUTLOOK FOR ORD/MDW FOR 00Z THURSDAY-12Z TUESDAY...UPDATED 12Z...

THURSDAY...PSBL MVFR WITH LIGHT RAIN/SNOW.

FRIDAY...VFR.

SATURDAY...VFR. PSBL MVFR WITH RAIN/SNOW LATE IN THE DAY.

SUNDAY...MVFR. CHANCE OF RAIN.

MONDAY...MVFR. CHANCE OF RAIN OR SNOW.

KREIN

&&

MARINE...
315 AM CST

OVERALL...THE NEXT SEVERAL DAYS SHOULD BE RELATIVELY QUIET OVER
LAKE MICHIGAN.  A LOW PRESSURE SYSTEM WILL TRACK ACROSS FAR
NORTHERN LAKE MICHIGAN LATER TODAY. IN ADVANCE OF THIS
SYSTEM...WINDS WILL BECOME SOUTHWESTERLY AND INCREASE TO 15 TO 25
KT. AS THE LOW PASSES OFF TO THE EAST...WINDS SHOULD QUICKLY SHIFT
TO NWLY LATER TONIGHT...BUT AS HIGH PRESSURE BUILDS IN BEHIND THE
EXITING SYSTEM...EXPECT A SHORT PERIOD OF MODERATE NWLY WINDS
BEFORE SHIFTING MORE SOUTHERLY AGAIN AHEAD IN ADVANCE OF AN
ELONGATED TROUGH OF LAOW PRESSURE AND AN ASSOCIATED COLD FRONT.
SINCE THIS SYSTEM IS EXPECTED TO BE RATHER WEAK...DO NOT EXPECT
THE SWLY WINDS TO GET ANY STRONGER THAN 20-25 KT OVER THE OPEN
WATERS.

KREIN

&&

LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$