Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 220917
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
317 AM CST SAT NOV 22 2014

.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 09Z...

* A SMALL CHANCE OF TEMPORARY LIGHT FZRA POSSIBLE PRIOR TO
  11Z...THOUGH BASED ON PAVEMENT TEMPERATURES THIS SEEMS MORE
  UNLIKELY.

* CIGS LOWERING TO IFR BY DAYBREAK AND THEN POTENTIALLY PERSISTING
  AT THAT LEVEL THROUGH THE REMAINDER OF THE TAF.

* IFR VISIBILITY IN DRIZZLE THIS MORNING WITH INTERMITTENT
  SHOWERS...ESPECIALLY THE MORNING AND EARLY AFTERNOON.

//DISCUSSION...UPDATED 06Z...

SCATTERED SHOWERS WILL MOVE NORTHEAST OVER THE REGION THROUGH 10Z-
12Z. COVERAGE OF THESE WILL LIKELY INCREASE SOME BUT OVERALL
REMAIN SCATTERED AND GIVEN THE FORCING...WILL ALSO REMAIN MAINLY
LIGHT IN INTENSITY. SOUTHERLY WINDS ARE CONTINUING TO STEER IN
GRADUALLY WARMING TEMPERATURES AS WE PASS THE MIDNIGHT HOUR. IT IS
LIKELY MOST OF THE AIRFIELDS AIR TEMPERATURES WILL REMAIN ABOVE
FREEZING AS SHOWER INTENSITY SHOULD NOT BE ENOUGH TO BRING
TEMPERATURES DOWN TO WET BULB VALUES. HOWEVER...PAVEMENT
TEMPERATURES ARE SLIGHTLY SLOWER TO RESPOND. THIS MAY LEAD TO
LIGHT FREEZING ON SURFACES BEFORE THEY WARM TO OVER 32. BY
DAYBREAK...THE SHOWER ACTIVITY SHOULD HAVE FURTHER DIMINISHED IN
COVERAGE WITH THE PASSAGE OF AN UPPER LEVEL DISTURBANCE...HOWEVER
MOISTENING LOW-LEVELS SHOULD PROVIDE AREAS OF DRIZZLE. IN
TANDEM...CIGS WILL BE FURTHER LOWERING INTO THE IFR CATEGORY AND
VISIBILITY MAY FOLLOW. IFR CIGS MAY PERSIST THROUGH ALL OF SATURDAY
AND EVEN IF THEY DO NOT THEY ARE LIKELY TO RETURN SATURDAY NIGHT.
RAIN SHOULD BE SPREADING NORTHWARD OVER THE AREA DURING OVERNIGHT
SATURDAY NIGHT.

//ORD AND MDW CONFIDENCE...UPDATED 09Z...

* HIGH IN SHOWERS...AT TIMES MODERATE IN INTENSITY...THROUGH 11Z
  WITH INTERMITTENT SHOWERS IN DRIZZLE AFTER. CONFIDENCE IS HIGH
  THAT FREEZING RAIN THREAT HAS DIMINISHED BASED ON WARMED
  PAVEMENT TEMPERATURES.

* HIGH IN IFR CIGS THIS MORNING AND THAT THEY WILL FALL TO AT
  LEAST 700 FT. LOW ON JUST HOW FAR THEY WILL DROP AND HOW LONG
  THEY WILL PERSIST...WITH THE POTENTIAL IT COULD BE THE ENTIRE
  TAF DURATION.

* MEDIUM IN DRIZZLE OCCURRING TODAY BUT LOW IN HOW FAR VISIBILITY
  WILL DROP WITH IFR POSSIBLE.

//OUTLOOK FOR ORD/MDW FOR 12Z SUNDAY-12Z FRIDAY...UPDATED 00Z...

SUNDAY...RAIN. HEAVY AT TIMES. IFR LIKELY. GUSTY S TO SE WINDS.

MONDAY...CHANCE -RASN EARLY AND -SN LATER. MVFR CIGS POSSIBLE.
GUSTY W TO SW WINDS.

TUESDAY...CHANCE OF FLURRIES. MVFR CIGS PSBL. BREEZY WEST WINDS.

WEDNESDAY...LIGHT SNOW POSSIBLE. MVFR CIGS/VIS POSSIBLE. WEST TO
SOUTHWEST WINDS 10 KT OR LESS.

THANKSGIVING DAY...VFR LIKELY.

MTF

&&

.MARINE...

242 PM...HIGH PRESSURE OVER THE SOUTHERN LAKES AND OHIO VALLEY
WILL MOVE SOUTHEAST TONIGHT REACHING THE CAROLINA COAST ON
SATURDAY AS LOW PRESSURE MOVES ACROSS NORTHERN ONTARIO AND JAMES
BAY TONIGHT. THE GRADIENT BETWEEN THESE TWO SYSTEMS WILL STEADILY
INCREASE OVER LAKE MICHIGAN TONIGHT WITH GALE FORCE WINDS
EXPECTED...POSSIBLY GUSTING AS HIGH AS 45KTS ACROSS THE NORTHERN
PORTION OF THE LAKE. THE GRADIENT WILL BEGIN TO WEAKEN LATER
SATURDAY AFTERNOON INTO SATURDAY EVENING...BUT ANOTHER LOW MOVING
ACROSS THE NORTHERN PLAINS SATURDAY NIGHT INTO SUNDAY WILL TIGHTEN
THE SOUTHERLY GRADIENT AGAIN. THIS LOW WILL BEGIN TO WEAKEN SUNDAY
EVENING AND THEN BE ABSORBED BY ANOTHER STRONGER LOW WHICH WILL
DEVELOP OVER THE SOUTHERN PLAINS SATURDAY NIGHT INTO SUNDAY...THEN
MOVE NORTH ACROSS LAKE MICHIGAN SUNDAY NIGHT INTO MONDAY MORNING.
THIS LOW HAS BEEN FORECAST TO DEEPEN TO AS LOW AS 975MB NEAR LAKE
SUPERIOR FOR SEVERAL DAYS. IF THIS OCCURS...WESTERLY HIGH END
GALES TO 45 KTS WOULD LIKELY DEVELOP MONDAY WITH THE POTENTIAL FOR
SOME STORM FORCE WINDS OR GUSTS. CMS

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FREEZING RAIN ADVISORY...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008-
     ILZ010-ILZ011-ILZ012 UNTIL 9 AM SATURDAY.

     FREEZING RAIN ADVISORY...ILZ019-ILZ020 UNTIL 6 AM SATURDAY.

IN...FREEZING RAIN ADVISORY...INZ002-INZ011 UNTIL 6 AM SATURDAY.

LM...GALE WARNING...LMZ080-LMZ261-LMZ362-LMZ364-LMZ366-LMZ563-LMZ565-
     LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-LMZ779-LMZ868-
     LMZ870-LMZ872-LMZ874-LMZ876-LMZ878 UNTIL 9 AM SATURDAY.

     SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 3 PM SATURDAY.

&&

$$

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