Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 221946
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
146 PM CST SAT NOV 22 2014

.UPDATE...

917 AM...MORNING UPDATE...TEMPERATURES HAVE WARMED INTO THE UPPER
30S AND LOWER 40S WITH THE THREAT OF FREEZING RAIN OVER AND LET
ADVISORY EXPIRE AT 9 AM.

FOCUS NOW SHIFTS TO THE POTENTIAL FOR DENSE FOG ACROSS THE FAR
NORTHERN AND NORTHWEST PORTIONS OF THE CWA TODAY AND TONIGHT.
VISIBILITIES CURRENTLY BETWEEN 1/2SM AND 2SM. NOT EXPECTING MUCH
IMPROVEMENT IN THESE AREAS TODAY SO ADDED FOG TO THE FORECAST...
GENERALLY NORTH OF I-80 BUT CONFIDENCE REGARDING HOW SOON DENSE
FOG MAY BECOME PREVAILING AND THEN HOW LONG IT WILL LAST IS STILL
LOW. BUT A DENSE FOG ADVISORY FOR PORTIONS OF THE NORTHERN CWA MAY
BE NEEDED LATER TODAY OR THIS EVENING. CMS

&&

.SHORT TERM...
315 AM CST

THROUGH TONIGHT...

THE PRIMARY CONCERNS WITH THE FORECAST CENTER ON FREEZING RAIN
THREAT EARLY THIS MORNING...THEN RAIN POTENTIAL AND AMOUNTS THROUGH
THE REST OF THE WEEKEND.

AN AREA OF SHOWERS IS MOVING QUICKLY NORTHEAST OVER THE IMMEDIATE
REGION AS OF 315 AM. THIS IS WITHIN STRENGTHENING FORCING FROM A
SHORT WAVE TROUGH...AND THIS GREATER LIFT IS COINCIDENT ON THE NOSE
OF A 45 KT LOW-LEVEL JET PER VAD WIND PROFILERS. OVERALL MUCH OF
THIS FORCING AND MODEST SHOWER ACTIVITY WILL CONTINUE TO SHIFT EAST
THROUGH SUNRISE. STEADILY RISING TEMPERATURES HAD LEVELED OFF SOME
VERY EARLY THIS MORNING WITH THE HEAVIER PRECIP INTENSITY...ALTHOUGH
A SLOW INCREASE SHOULD RESTART PRIOR TO DAYBREAK AND PERSIST THROUGH
TODAY AS WARM ADVECTION WINS OUT. TEMPERATURES OF 31 TO 33 AS OF
315 AM MAINLY REMAINED IN THE NORTHERN FORECAST AREA...INCLUDING
ROCKFORD AND THE NORTH CHICAGO METRO...AND PARTS OF NORTHWEST
INDIANA INCLUDING VALPARAISO. PAVEMENT TEMPERATURES FROM A HANDFUL
OF SOURCES VARIED SOME...BUT FOR THE MOST PART WERE ABOVE FREEZING
IN CHICAGO AND SOUTHWARD FROM THERE. SO WILL CONTINUE ADVISORY AS
IS FOR NOW AND MAKE A REASSESSMENT JUST PRIOR TO 6 AM TO SEE IF
ANY PARTS NEED TO CONTINUE TO 9 AM.

WHILE MUCH OF THE MODEST PRECIP SHOULD SHIFT EASTWARD EARLY THIS
MORNING...BROAD ASCENT IN THE MID-LEVELS WILL REMAIN WITH AN UPPER
SPEED MAXIMUM MOVING OVERHEAD. THIS PROBABLY WILL BE ENOUGH FOR
SCATTERED/INTERMITTENT SHOWERS ESPECIALLY THROUGH EARLY AFTERNOON.
IN THE LOWER-LEVELS...HIGH DEW POINT AIR WILL CONTINUE TO BE
ADVECTED NORTHWARD ESTABLISHING THE LOW CLOUDS. ISENTROPIC OMEGA
WITHIN THESE LOWEST LEVELS LOOKS TO SUPPORT AREAS OF DRIZZLE...AND
ALREADY SEEING INDICATIONS OF THIS NEAR THE DVN RDA. SO CONTINUE
AREAS OF DRIZZLE WORDING. TEMPERATURES WILL BE THE WARMEST THEY HAVE
BEEN SINCE LATE ON THE NIGHT OF NOVEMBER 10TH...WITH 40S EXPECTED
AREAWIDE AND EVEN 50 TAGGED SOUTH OF INTERSTATE 80 IN SOME
LOCATIONS. TONIGHT TEMPERATURES SHOULD BASICALLY HOLD STEADY AND
MAYBE EVEN RISE SOME. IF TEMPERATURES ARE ABLE TO DROP A FEW
DEGREES...THE THREAT FOR FOG BECOMES HIGHER...ALTHOUGH FORECAST
SOUNDINGS GENERALLY DO NOT LOOK TO SUPPORT ANYTHING DENSE GIVEN
THE ALREADY PRESENT LOW CLOUD DECK.

RAIN SHOULD BEGIN TO DEVELOP WITHIN GREATER MOISTURE ADVECTION AND
CONVERGENCE ACROSS CENTRAL ILLINOIS LATER TONIGHT AND SPREAD
NORTHWARD INTO THE FORECAST AREA. GREATER INTENSITY LOOKS TO BE
SEEN BEYOND TONIGHT INTO SUNDAY.

MTF

&&

.LONG TERM...
315 AM CST

SUNDAY ONWARD...

SUNDAY THE REGION WILL REMAIN IN A BROAD WARM AIR ADVECTION REGIME
AHEAD OF A PAIR OF TROUGHS APPROACHING FROM THE WEST. BROAD DEEP
SOUTHERLY FLOW WILL CONTINUE TO USHER WARMER AND INCREASINGLY MORE
MOIST AIR INTO THE REGION. BROAD ISENTROPIC ASCENT WILL CONTINUE TO
SUPPORT AT LEAST SOME OCNL SHOWERS OR DRIZZLE EARLY BEFORE BUILDING
INTO A STEADIER/HEAVIER RAIN LATER IN THE DAY AS THE STRONG SOUTHERN
STREAM SHORTWAVE BEGINS LIFTING NORTHEAST INTO THE REGION. IF EARLY
PORTION OF THE DAY ISNT TOO WET/SHOWERY THEN HIGHS COULD REACH WELL
INTO THE 50S...ESPECIALLY SOUTHERN CWA AS GUIDANCE IS FOCUSING THE
BETTER FORCING NORTH EARLY.

THE NORTHERN AND SOUTHERN STREAK SHORTWAVES ARE STILL PROGGED TO
BEGIN PHASING OVER THE WESTERN GREAT LAKES REGION SUNDAY NIGHT INTO
MONDAY. GUIDANCE CONTINUES TO SUGGEST THAT AN IMPRESSIVELY MOIST AIR
MASS WILL BE TRANSPORTED NORTH INTO THE REGION SUNDAY INTO SUNDAY.
GIVEN THE MAGNITUDE OF FORCING AND AMPLE MOISTURE WITH PWATS NEARING
2 STANDARD DEVIATIONS ABOVE AVERAGE SOME HEALTHY RAINFALL TOTALS
LOOK LIKELY...WITH AMOUNTS SUNDAY INTO SUNDAY NIGHT PROBABLY ENDING
UP CLOSE TO AN INCH. LONG DURATION OF THE PRECIP SHOULD RESULT IN
LITTLE MORE THAN MAYBE SOME MINOR PONDING OF WATER IN LOW SPOTS. RFC
CONTINGENCY FORECASTS DO SUGGEST SOME RESPECTABLE RISES ON AREA
RIVERS...THOUGH IF CURRENT QPF VERIFIES RIVERS WILL REMAIN BELOW
FLOOD STAGE.

AS NORTHERN AND SOUTHERN STREAM SYSTEMS PHASE GUIDANCE IS IN
AGREEMENT THAT THE SURFACE LOW WILL RAPIDLY...AND POTENTIALLY
EXPLOSIVELY IF THE GFS VERIFIES. THERE IS A FAIRLY LARGE SPREAD IN
MODEL GUIDANCE WRT JUST HOW DEEP THE LOW GETS MONDAY AFTERNOON WITH
THE GFS AND SEVERAL OF ITS ENSEMBLE MEMBERS IN THE BETWEEN 961 AND
966MB...WHILE THE ECMWF IS A STILL IMPRESSIVE BUT LESS EXTREME 979.
LACK OF STRONG HIGH PRESSURE IN THE WAKE OF THIS SYSTEM WILL
MITIGATE THE MAGNITUDE OF THE WINDS SOME...BUT LATEST GUIDANCE HAS
TRENDED STRONGER WITH WINDS AGAIN MONDAY. STILL POSSIBLE THERE WILL
BE SOME WAFFLING IN GUIDANCE FOR THE MONDAY TIME RANGE AS MODELS
OFTEN STRUGGLE WITH PHASING SYSTEMS...BUT HAVE FOLLOWED THE TREND
FROM THE DAY SHIFT OF STRONGER WINDS MONDAY WITH GUSTS OF 35-40 MPH
POSSIBLE. IF THE MORE EXTREME GFS MODEL CAMP VERIFIES THEN GUSTS
COULD NEAR ADVISORY CRITERIA MONDAY...A TREND WORTH WATCHING THE
NEXT COUPLE DAYS.

WARM CONVEYOR BELT PRECIP SHOULD GET SHUNTED NORTH OF THE AREA LATER
SUNDAY NIGHT...HOWEVER MODELS SUGGEST THAT DEFORMATION PRECIP COULD
POTENTIALLY WRAP AS FAR SOUTH AS OUR CWA MONDAY...ESPECIALLY
NORTHERN CWA. COLDER AIR WILL COME FLOODING IN ON THE STRONG
WESTERLY WINDS MEANING ANY DEFO PRECIP THAT DOES FALL WOULD
TRANSITION TO SNOW/SNOW SHOWERS MONDAY MORNING. FAR TOO SOON TO HAVE
MUCH CONFIDENCE IN ANY POTENTIAL ACCUMS...BUT BETTER THREAT OF SNOW
ACCUMS LOOKS TO REMAIN NORTH OF THE AREA WITH ACCUMS...IF
ANY...PROBABLY ON THE LIGHT SIDE IN OUR AREA.

STRATUS DECK LIKELY GETS LOCKED IN MONDAY NIGHT TEMPERING THE LOW
TEMPS A BIT BUT MAGNITUDE OF THE COLD AIR ADVECTION SHOULD STILL
ALLOW 20S ACROSS THE AREA. CLOUD COVER MAY STICK AROUND INTO A GOOD
CHUNK OF THE DAY TUESDAY AS THE HEART OF THE COLD AIR MASS TRAVERSES
THE AREA WHICH LOOKS TO RESULT IN VERY LITTLE TEMP RECOVERY FROM
OVERNIGHT LOWS TUESDAY MORNING.

BRIEF AND SOMEWHAT MUTED SHOT OF WARM AIR ADVECTION TUESDAY NIGHT
INTO WEDNESDAY SHOULD OCCUR AHEAD OF A CLIPPER SYSTEM...POTENTIALLY
BRINGING SOME LIGHT SNOW TO THE AREA WEDNESDAY. MEDIUM RANGE
GUIDANCE VARIES WITH RESPECT TO THE TRACK OF THIS SYSTEM SO
MAINTAINING POPS IN THE LOWER END OF THE CHANCE SPECTRUM FOR NOW.
APPEARS LIKELY THAT ANOTHER BLAST OF UNSEASONABLY COLD AIR WILL
FOLLOW THIS CLIPPER IN TIME FOR THANKSGIVING AND THE START OF THE
LONG HOLIDAY WEEKEND WITH HIGHS ONCE AGAIN HEADING BACK DOWN INTO
THE 20S.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* PATCHY IFR CIGS...TO LOW END MVFR CIGS THIS AFTN. LIKELY
  TRENDING BACK TOWARDS IFR OVERNIGHT THRU SUN MORNING.

* VSBY WILL HOVER BETWEEN 3-6SM THIS AFTN...POSSIBLY FALLING TO
  JUST UNDER 3SM OVERNIGHT THRU SUN MORNING.

* LOW-LEVEL WIND SHEAR DEVELOPING TONIGHT. ARND 2KFT AGL FROM THE
  SOUTHWEST NEARING 45KT.

* RAIN SHOWERS DEVELOPING EARLY SUN MORNING...INCREASING IN
  COVERAGE CLOSER TO MIDDAY.

BEACHLER

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

VERY MOIST AIR MASS CONTINUES TO FEED NORTHEAST ACROSS NORTHERN
IL/NORTHWEST IN AIRFIELDS THIS AFTERNOON. LITTLE IMPROVEMENT TO
THE CIGS IS EXPECTED...AS A RESULT HAVE HELD CIGS DOWN ARND LOW
END MVFR THIS AFTN AND WILL LIKELY TREND BACK TOWARDS IFR CONDS
OVERNIGHT. GENERALLY EXPECT CIGS ARND 500-900FT AGL THRU THE
OVERNIGHT HOURS. WIND DIR WILL NOT CHANGE MUCH THIS
AFTN/EVE/OVERNIGHT...MAINLY FROM THE SOUTH WITH SPEEDS ALSO NOT
CHANGING MUCH ARND 10-12KT. GIVEN HOW MOIST THE ATMOSPHERE
IS...PERIODIC ROUNDS OF DRIZZLE CAN BE EXPECTED THRU THIS
AFTN/EARLY EVE WILL A LULL LATE THIS EVE. WIND SHEAR IS ALSO
POISED TO DEVELOP THIS EVENING...WITH WINDS ARND 2KFT AGL FROM THE
SOUTHWEST INCREASING TO 40-45KT.

GUIDANCE HAS CONTINUED TO SUGGEST DEVELOPING RAIN SHOWERS AFT
MIDNIGHT/EARLY SUN...SO HAVE HELD ONTO THE MENTION OF LGT RAIN
EARLY SUN. THEN IT APPEARS THE BETER COVERAGE FOR PERHAPS MORE
STEADY RAIN WILL OCCUR LATE SUN MORNING...AND COULD PERSIST THRU
SUN AFTN.

BEACHLER

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE IN CIGS HOLDING AT LOW END MVFR...AND MEDIUM
  CONFIDENCE ON TIMING CIGS TRENDING BACK TOWARDS IFR.

* HIGH CONFIDENCE IN WIND DIR/SPEED.

* MEDIUM CONFIDENCE IN LOW-LEVEL WIND SHEAR.

* HIGH CONFIDENCE IN DRIZZLE THRU THIS AFTN...THEN MEDIUM
  CONFIDENCE IN TIMING OF ENDING THE MENTION OF DRIZZLE.

* HIGH CONFIDENCE IN LIGHT RAIN DEVELOPING EARLY SUN WITH BETTER
  COVERAGE LATE SUN MORNING/AFTN. MEDIUM CONFIDENCE IN PRECISE
  TIMING OF RAIN IMPACTING TAF SITES.

BEACHLER

//OUTLOOK FOR ORD/MDW FOR 00Z MONDAY-12Z SATURDAY...UPDATED 12Z...

SUNDAY NIGHT...RAIN AND IFR PROBABLE. SOUTHERLY WINDS.
MONDAY...CHANCE OF RAIN AND SNOW. STRONG WEST TO SOUTHWEST WINDS.
TUESDAY...MVFR CIGS POSSIBLE. WESTERLY WINDS.
WEDNESDAY...CHANCE OF SNOW AND MVFR. SOUTHWEST WINDS.
THURSDAY...FLURRIES AND MVFR POSSIBLE. NORTHWEST WINDS.
FRIDAY...VFR PROBABLE. SOUTHWEST WINDS.

MTF

&&

.MARINE...
325 AM CST

AN ACTIVE PATTERN OVER THE LAKE IS EXPECTED TO CONTINUE THROUGH THE
UPCOMING WEEK. THE SOUTHWEST GALES SEEN OVER THE LAKE EARLY THIS
MORNING WILL DIMINISH BY MID-LATE MORNING AS THE PRESSURE GRADIENT
SOMEWHAT DIMINISHES. SMALL CRAFT ADVISORY CRITERIA WINDS WILL
CONTINUE THOUGH ACROSS THE IL AND IN NEARSHORES A GOOD PART OF
THE DAY. IT DOES LOOK LIKE WIND SPEEDS WILL DIMINISH TO MORE 15-25
KT FOR THE EVENING AND THEN RE-INCREASE OVERNIGHT WHERE ANOTHER
ADVISORY MAY BE NEEDED.

MODERATELY STRONG SOUTHERLY FLOW WILL CONTINUE SUNDAY IN ADVANCE OF
THE COMPLEX LOW PRESSURE SYSTEM ORGANIZING TO OUR WEST. BY SUNDAY
NIGHT...LOW PRESSURE TRACKING EAST FROM THE NORTHERN PLAINS WILL
BEGIN TO MERGE WITH LOW PRESSURE TRACKING NORTHEAST FROM THE
SOUTHERN PLAINS. MODELS SUGGEST THIS PHASING OF THE TWO LOWS WILL
TAKE PLACE VERY NEAR LAKE MICHIGAN SUNDAY NIGHT WITH A BRIEF PERIOD
OF LIGHTER WINDS NEAR THE CENTER OF THE DEVELOPING STORM SYSTEM. THE
LOW IS FORECAST TO CONTINUE TO RAPIDLY INTENSIFY AS IT MOVES NORTH
MONDAY ALLOWING FOR WESTERLY GALES TO DEVELOP ON THE LAKE IN ITS
WAKE MONDAY. WHILE MODEL AGREE IN THE GENERAL IDEA OF A STRONG LOW
NORTH OF LAKE SUPERIOR BY MIDDAY MONDAY...THEY VARY CONSIDERABLY ON
HOW STRONG THE LOW WILL BE RANGING FROM 28.5 INCHES TO AROUND 29.0
INCHES. IF THE STRONGER SOLUTIONS WERE TO VERIFY THEN A PERIOD OF
STORM FORCE WEST WINDS COULD OCCUR MONDAY...DESPITE THE LACK OF ANY
STRONG HIGH PRESSURE MOVING IN BEHIND THE STORM. IF THE WEAKER
SOLUTIONS PAN OUT THEN LOWER END GALES WOULD STILL LIKELY OCCUR
MONDAY. IT IS LIKELY THAT A GALE WATCH WILL BE ISSUED FOR THE
MONDAY/MONDAY NIGHT TIME FRAME LATER TODAY. WINDS WILL EASE TUESDAY
AND BACK TO SOUTHERLY TUESDAY NIGHT INTO WEDNESDAY AHEAD OF A
CLIPPER BEFORE ANOTHER SHOT OF STRONG AND POSSIBLY GALE FORCE NORTH
OR NORTHWEST WINDS DEVELOP THURSDAY-ISH TIME FRAME.

MTF/IZZI

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM SATURDAY.

&&

$$

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