NWS Area Forecast Discussion
FORMAT: Decoded Original

FXUS63 KLOT 282120
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
320 PM CST MON JAN 28 2013

.DISCUSSION...
257 PM CST

VERY MILD AND MOIST CONDITIONS WILL CONTINUE TO ADVECT NORTH ACROSS
NORTHERN IL/NORTHWEST IN THIS EVENING...AS THE ATMOSPHERIC RIVER
PROGGED TO STRETCH FROM THE WESTERN GULF OF MEXICO NORTH TO THE OHIO
VALLEY/GREAT LAKES REGIONS ESTABLISHES ITSELF. TEMPS THIS AFTN HAVE
REMAINED IN THE MID/UPR 40S ACROSS THE CWFA WITH A FEW AREAS SOUTH
OF I-80 WARMING INTO THE LOW 50S. DEW PTS HAVE STEADILY RISEN
THROUGHOUT THE AFTN INTO THE LOW/MID 40S. VISIBLE IMAGERY SHOWS
CONSIDERABLE CLOUD COVER ACROSS THE REGION...HOWEVER A SMALL BREAK
IN THE CLOUDS EARLY THIS AFTN DID OCCUR ACROSS NORTHERN IL
STRETCHING NORTH INTO SOUTHEAST WISC AND CENTRAL LK MICHIGAN.

THE WARM FRONTAL BOUNDARY HAS ALREADY PUSHED NORTH TO CENTRAL IOWA
STRETCHING EAST THROUGH CENTRAL IL/IN. SOUTH OF THIS LINE ACROSS
CENTRAL MISSOURI TEMPS HAVE WARMED WELL INTO THE 70S WITH DEW PTS IN
THE UPR 50S...WHICH IS EXCEPTIONALLY RARE FOR LATE JAN. THIS RECORD
WARMTH WILL APPROACH THE CWFA OVERNIGHT...AND PROVIDE THE EXPECTED
RECORD HIGHS FOR TUE ACROSS THE REGION.

OVERNIGHT THE FOCUS REMAINS ON THE INCREASING LLVL MOISTURE AND
POTENT JET. 850MB WINDS WILL STEADILY INCREASE FROM THE
SOUTH/SOUTHWEST TO ARND 30-40KTS...THEN TUE WILL CONTINUE TO
INCREASE. DIRECTIONAL SHEAR WILL BE STEADILY INCREASING THROUGHOUT
THE NIGHT AS ELEVATED INSTABILITY BEGINS TO INDICATE CAPE VALUES
ARND 200-400J/KG BY 09Z TUE. HAVE MAINTAINED MENTION OF CONVECTION
OVERNIGHT. THE OTHER CHALLENGE REMAINS FOR THIS EVENING THROUGH THE
OVERNIGHT...RESIDING WITH POTENTIAL FOR DENSE FOG.

A FEW OBS THIS AFTN CONTINUE TO INDICATE REDUCED VSBYS ARND
1SM...WITH PNT HOVERING ARND 1/4SM. GIVEN THE ADDTL MOISTURE LIFTING
NORTH ADVECTING ACROSS SLOWLY THAWING AND MOIST SFC CONDS...IT
APPEARS AREAS OF DENSE FOG WILL REDEVELOP LATER THIS EVE. THE
CHALLENGE IS WILL BE FALL TO DENSE CRITERIA AND FOR HOW LONG WITH
THE EXPECTED PRECIP. SO HAVE OPTED TO HOLD OFF ON ISSUING A DENSE
FOG AT THIS TIME...GIVEN THE LOWER CONFIDENCE ON PLACEMENT/TIMING.

CONFIDENCE...MEDIUM.

TUESDAY...
TUE APPEARS TO BE THE DAY THAT WILL PRODUCE RECORD TEMPS WITH
GUIDANCE PUSHING HIGHS INTO THE 60S...AND IF SKIES WERE TO THIN
SLIGHTLY TUE AFTN A FEW AREAS ALONG AND SOUTH OF A PONTIAC TO
KANKAKEE LINE COULD WARM TO PSBLY THE MID/UPR 60S.

TEMPS WILL ONLY BE ONE PARAMETER TO BE CONCERNED WITH TUE...AS
ABUNDANT MOISTURE AND IMPRESSIVE LLVL SPEED/DIRECTIONAL SHEAR ARE
POISED TO PUSH OVERHEAD. AT THIS TIME SPC CONTINUES TO HAVE THE
SOUTH/SOUTHEAST PORTIONS OF THE CWFA PROGGED FOR A SLIGHT RISK OF
SEVERE WEATHER TUE. GIVEN SUCH A DYNAMIC AND CONTRASTING AIRMASS
BETWEEN THE WARM/MOIST AND COLD...THIS APPEARS TO BE SUCH AN
ANOMALOUS SETUP THAT IT WOULDN/T BE TOO MUCH OF A SURPRISE FOR
SEVERE WEATHER TO OCCUR. THE LARGEST CONCERN IS FOR DAMAGING
WINDS...ALTHOUGH WITH THE STRONG DIRECTIONAL LLVL SHEAR AND A MOIST
BOUNDARY IN THE VICINITY OF THE CWFA...A FEW THUNDERSTORM CORES
COULD SEE ROTATING UPDRAFTS. WHICH OPENS THE DOOR FOR AN ISOLATED
TORNADO TUE AFTN. WHILE THE FIRST HALF OF TUE LOOKS TO BE
QUIET...THINGS WILL RAPIDLY CHANGE FOR THE AFTN/EVE HOURS AS THE
SHORTWAVE APPROACHES FROM THE WEST.


THE OTHER CHALLENGE FOR TUE/TUE NGT WILL BE ON THE POTENTIAL
FOR HEAVY RAINFALL...WHICH COULD LEAD TO FLOODING. GUIDANCE
CONTINUES TO SHOW SOME CORRECTIONS WITH RESPECT TO THE AXIS OF
HIGHEST PRECIP TOTALS...HOWEVER IT APPEARS TO BE ZEROING IN ON A
CENTRAL IL/IN STRETCHING NORTH THROUGH NORTHEAST IL/NORTHERN IN.
THE COMBINATION OF THE ATMOSPHERIC RIVER...PWAT VALUES PROGGED TO
APPROACH 1.5" WHICH ENSEMBLES SUGGEST IS 5 TO 6 SIGMA ABOVE
CLIMO...HAVE OPTED TO PROCEED WITH A FLOOD WATCH. FURTHER
COMPLICATING THE FLOODING POTENTIAL WILL BE THE STILL MOIST TOP FEW
INCHES OF SOIL. WHILE IT APPEARS THE TOP FEW INCHES OF SOIL WILL
THAW...IT DOESN/T APPEAR THE ENTIRE COLUMN WILL THAW. WHICH WILL
FURTHER EXACERBATE THE RUNOFF OR PONDING CONCERNS. AT THIS TIME
GUIDANCE POINTS TOWARDS QPF TOTALS OF ARND 1.00" ALONG AND NORTHWEST
OF A LASALLE TO LAKE COUNTY IL LINE. EAST OF THIS LINE FORECAST
PRECIP TOTALS RAMP UP TOWARDS 2 INCHES. AT THIS TIME THE HIGHEST
RAINFALL TOTALS APPEAR TO BE ALONG AND EAST OF A FORD COUNTY IL TO
LAKE COUNTY IN.

FRONTAL PASSAGE HAS SLOWED SLIGHTLY WITH THE LATEST
GUIDANCE...ARRIVING ACROSS THE NORTHWEST CWFA ARND 00Z
WED...APPROACHING THE CENTRAL CWFA BY 6-9Z...AND SHOULD EVENTUALLY
PUSH THROUGH THE FAR SOUTHEAST CWFA BY 12Z WED.

CONFIDENCE...MEDIUM/HIGH.

WEDNESDAY THROUGH SUNDAY...
A RETURN TO WINTER IS POISED TO SLIDE BACK ACROSS THE REGION WED AND
CONTINUE THROUGH AT LEAST FRI...WITH A GRADUAL MODERATION SAT/SUN.

HIGH AMPLITUDE ANOMALOUS 500MB RIDGE WILL STEADILY PIVOT EAST...AS A
DEEP TROUGH SLOWLY SLIDES EAST ACROSS THE GREAT LAKES WED AND
LINGERS THROUGH THE FIRST HALF OF THE WEEKEND. FURTHER WEST A PAC-NW
RIDGE CONTINUES TO BE ADVERTISED TO WEAKEN THROUGHOUT THE NEXT FEW
DAYS...WHICH MAY AID IN FURTHER DE-AMPLIFICATION OF THE GREAT LAKES
TROUGH BY SAT/SUN.

MUCH COLDER AIR WILL CONTINUE TO ADVECT ACROSS THE GREAT LAKES
REGION...AS A POTENT THERMAL TROUGH OF -18 TO -20 DEG C CONTINUES TO
PUSH OVERHEAD THUR. GUIDANCE HAS INDICATED SOME WEAKENING IN THE
POTENCY OF THE COLD AIR. MUCH COLDER AIR WILL BE DISPLACED TO THE
NORTH ACROSS THE UPPER MIDWEST/NORTHERN GREAT LAKES...WHERE -24 TO
-26 DEG C AIR AT 850MB IS PROGGED. THIS IS RATHER IMPRESSIVE GIVEN
HOW ANOMALOUSLY WARM TUE WILL BE TO TRANSITION IN A 48HR PERIOD FROM
WARM/MOIST TO ARCTIC AIR THUR. IN THE LATER PERIODS CONFIDENCE
REMAINS HIGH THAT TEMPS WILL SLOWLY MODERATE BACK TO
SEASONAL...POSSIBLY LEANING ABOVE SEASONAL CONDS BY SUN.

EXTENDED PRECIPITATION FORECAST OUTLOOK...AFTER THE POTENT SHORTWAVE
PROGGED TO TRAVERSE THE REGION CYCLONIC FLOW APPEARS TO LINGER
THROUGH THUR NGT. THEN FOR FRI/SAT ANTI-CYCLONIC FLOW WILL BEGIN TO
PUSH THE PROLONGED WRAP-AROUND MOISTURE TO THE NE OF THE CWFA. THERE
APPEARS TO BE A WEAK VORT MAX THAT MAY ROTATE AROUND THE 500MB
VORT...AND SLIDE ACROSS THE UPPER MIDWEST TOWARDS THE CWFA WED/THUR.
GUIDANCE SUGGESTS THAT ENOUGH LIFT COULD BE AROUND IN THIS TIMEFRAME
TO PUSH PARCELS INTO THE DGZ...WARRANTING SOME LIGHT ACCUMS WED TO
EARLY THUR. THEN DRY AIR PUSHES IN FOR THE WEEKEND WITH THE
AFOREMENTIONED TEMPS RETURNING TO SEASONAL CONDS.

CONFIDENCE...MEDIUM/HIGH.

BEACHLER

&&

.CLIMATE...
330 AM CST

THE FOLLOWING RECORDS COULD BE IN JEOPARDY WITH THE UPCOMING WARM
SPELL TUESDAY...

JANUARY 29 ALL TIME JANUARY
HIGH WARM LOW RECORD HIGH
ROCKFORD 55 (1914) 35 (1989) 63 (1/8/2008, 1/31/1989)

CHICAGO 59 (1914) 38 (1924) 67 (1/25/1950)

IZZI

&&

.HYDROLOGY...
353 AM CST

USGS ANALYSIS OF STREAM FLOW ACROSS THE CWA INDICATES THAT
STREAM FLOW IS CERTAINLY BELOW AVERAGE OVER THE CWA...THOUGH LESS
SO OVER THE IROQUOIS...KANKAKEE...AND VERMILION RIVER BASINS
THAN SOME OF THE BASINS FARTHER NORTH. WIDESPREAD 1 TO 2 INCH
RAINFALL TOTALS APPEAR LIKELY NOW OVER MUCH OF THE REGION AS THE
UPPER TROUGH HAS SLOWED DOWN. LOCALIZED TOTALS OVER 3 INCHES COULD
OCCUR...PARTICULARLY WITH THE MORE INTENSE THUNDERSTORMS. THE
HEAVY RAINFALL AXIS MAY EXTEND FARTHER NORTHWEST AND ENCOMPASS THE
CHICAGO AREA FARTHER WEST INTO NORTH CENTRAL ILLINOIS...RAISING
CONCERNS FOR FLOODING ON ALL AREAS RIVERS.

THIS HEAVY RAIN WOULD BE FALLING ON FROZEN GROUND WITH VERY DEEP
FROST DEPTHS. A CHECK OF SOIL TEMPS HERE AT THE WFO THIS MORNING
SHOWS FREEZING TEMPS DOWN TO THE 40 INCH DEPTH WITH SOIL TEMPS IN
THE MID TO UPPER 20S DOWN TO 20 INCHES. THE RECORD WARMTH TUESDAY
WILL LIKELY ONLY AFFECT THE UPPER MOST SOIL DEPTH WITH MUCH LOWER
THAN AVERAGE INFILTRATION RATES DUE TO THE DEPTH OF FROST
LINE...SO GREATER RUNOFF WILL DRAMATICALLY INCREASE THE THREAT OF
FLOODING DESPITE THE LOWER THAN AVERAGE STREAM FLOW.

RIVER ICE SPOTTER REPORTS FROM 1/24 INDICATE THAT THERE IS A GREAT
DEAL OF ICE COVERAGE ON THE IROQUOIS AND KANKAKEE RIVERS...AND
THIS IS LIKELY THE CASE ON OTHER STREAMS/RIVERS AS WELL. THE
COMBINATION OF RECORD WARMTH AND RAPIDLY INCREASING STREAM FLOW
COULD RESULT IN A HEIGHTENED RISK OF ICE JAM FLASH FLOODING AS ICE
BECOMES DISLODGED AND SIGNIFICANT ICE FLOW BEGINS.

WHILE STREAM FLOW IS BELOW TO MUCH BELOW AVERAGE...THERE IS A
GREAT DEAL OF UNCERTAINTY AS TO HOW MUCH OF A MITIGATION THAT WILL
BE TO THE FLOOD THREAT. ORDINARILY RAINFALL OF THE MAGNITUDE THAT
IS BEING FORECAST IN JANUARY WOULD RESULT IN MAJOR AND POTENTIALLY
DEVASTATING FLOODING...AND WHILE ABNORMALLY LOW STREAM FLOW WILL
MITIGATE THE FLOOD THREAT SOMEWHAT THERE STILL IS POTENTIAL FOR
MAJOR FLOODING. IF FORECASTS REMAIN ON TRACK WITH CURRENT THINKING
THEN FLOOD WATCHES WILL LIKELY BE POSTED FOR MUCH OF THE REGION
FOR TUESDAY AFTERNOON AND NIGHT.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 2120Z...

* FEW-SCT CLOUDS AROUND 015 THROUGH 23Z OR SO THEN BECOMING BKN-
OVC TOWARD 00-01Z.

* WINDS BECOME S TONIGHT AND GUSTING TO 20-25 KT TUESDAY MORNING.

* SHRA THIS EVENING WITH SCT TSRA OVERNIGHT...THEN -DZ IN THE
MORNING AND +TSRA TUESDAY AFTERNOON.

* IFR TO LIFR CIGS/VSBY RETURN OVERNIGHT.

MDB/JEE

//DISCUSSION...UPDATED 2120Z...

UPDATED NEAR TERM CIG TRENDS TO ACCOUNT FOR DECREASE IN CLOUD
COVERAGE ACROSS FAR NORTHERN IL AND EXTREME NW IN. EXPECT THAT
THIS SCATTERING WILL REMAIN IN PLACE FOR A FEW HOURS BEFORE
FILLING BACK IN TOWARD 00-01Z.

MDB

FROM 18Z...

BUSY WEATHER CONTINUES. CIGS HAVE RISEN TO HIGH END IFR/MVFR THUS
FAR AS SLIGHTLY DRIER AIR MOVED INTO THE REGION AND THINKING CIGS
SHOULD REMAIN AROUND 015 FT THROUGH THIS EVENING. ALSO EXPECTING
WINDS TO BECOME VARIABLE ARND 4KT THIS AFTERNOON AS A WEAK SURFACE
RIDGE MOVES THROUGH NORTHERN IL. LOW PRESSURE CURRENTLY OVER THE
CENTRAL ROCKIES WILL EJECT OVER THE GREAT PLAINS TONIGHT AND
CREATE A ROLLER COASTER OF WEATHER AND TEMPERATURES TONIGHT THROUGH
WEDNESDAY MORNING.

THE LOWS WARM FRONT LIFTS NORTH THROUGH THE TERMINALS TONIGHT WITH
WINDS BECOMING SOUTH BEHIND IT. WHILE FORCING AND CAPE IS
MINIMAL...SHRA AND SCATTERED TSRA ARE LIKELY BTWN 06Z AND 14Z
ACROSS THE REGION. COVERED THE TS WITH A VCTS BECAUSE CONFIDENCE
IS LOW REGARDING HOW WIDESPREAD THE TS WILL BE AND WHEN IF AT ALL
IT WILL IMPACT ANY OF THE TERMINALS. THEREFORE WHILE VCTS IS
LISTED FOR 8 HOURS IN THE TAF...THE TERMINALS CAN EXPECT AT LEAST
ONE BRIEF PERIOD OF THUNDER. IF THUNDER IS VERY WIDESPREAD MORE
THAN ONE PERIOD OF THUNDER IS POSSIBLE OVERNIGHT. CIGS AND VSBY
WILL ALSO DROP TONIGHT AS MOISTURE INCREASES WITH THE WARM FRONT
PASSAGE. COULD SEE LOWER VSBY WITH HEAVIER SHRA/TSRA AND AT THE
FOG PRONE AREAS LIKE DPA AND RFD. IN FACT THERE IS A POSSIBILITY
OF DENSE FOG TONIGHT WHEN IT IS NOT RAINING...ONCE AGAIN
ESPECIALLY AT DPA AND RFD.

THE LOW PASSES TO THE NW TOMORROW MORNING WITH CONTINUING MOIST
CONDITIONS. SOUTH WINDS WILL BEGIN GUSTING TO 20-25 KT AS WELL.
ADDED -DZ IN THE MORNING TO ACCOUNT FOR LINGERING DAMPNESS AND
THINKING CIGS AND VSBY WILL REMAIN LOW. HOWEVER...LIKE TODAY IF
SUNSHINE POKES A FEW HOLES IN THE CIGS COULD SEE A PERIOD OF
IMPROVEMENT. THE LOWS COLD FRONT RACES THROUGH TOMORROW AFTERNOON
WITH +TSRA EXPECTED ALONG IT. TIMING IS PROBABLY NOT EXACT THIS
FAR OUT...BUT THINKING AN HOUR OR LESS OF TSRA IS LIKELY ALONG THE
LEADING EDGE OF THE FRONT. HEAVY RAIN IS ALSO POSSIBLE AFTER THE
TSRA.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 2120Z...

* MEDIUM-HIGH CONFIDENCE IN FEW-SCT CLOUDS CONTINUING FOR A FEW
HOURS...MEDIUM CONFIDENCE IN TIMING OF INCREASE BKN-OVC.

* HIGH CONFIDENCE IN VSBY TRENDS...MEDIUM-LOW CONFIDENCE IN HOW
LOW VSBYS WILL GET.

* HIGH CONFIDENCE IN SHRA TONIGHT...MEDIUM-HIGH CONFIDENCE IN
SCATTERED TSRA AND -DZ.

* HIGH CONFIDENCE IN +TSRA TOMORROW...MEDIUM CONFIDENCE IN TIMING.

MDB/JEE

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

TUESDAY NIGHT...TSRA/SHRA...IFR/MVFR CIGS AND VSBY.

WEDNESDAY...RASN BCMG SN...CIGS IMPROVING TO MVFR/VFR.

THURSDAY...MVFR/VFR CIGS.

FRIDAY AND SATURDAY...-SN FRIDAY NIGHT INTO SATURDAY WITH MVFR
CIGS PSBL. OTHERWISE VFR.

SUNDAY...VFR.

JEE

&&

.MARINE...
136 PM CST

LOW PRESSURE OVER EASTERN CO THIS AFTERNOON WILL MOVE TO LAKE
SUPERIOR BY TUE AFTERNOON. THIS WILL BRING A SURGE OF UNSEASONABLY
MILD AND HUMID AIR NORTHWARD ACROSS THE GREAT LAKES. STRONG SOUTH
TO SOUTHWEST WINDS WILL DEVELOP TUESDAY INTO TUESDAY EVENING BUT
WARM WIND MAY HAVE A DIFFICULT TIME MIXING DOWN TO THE COLD WATER.
EXPECT THERE WILL BE ENOUGH WIND ALONG THE SHORE TO NECESSITATE A
SMALL CRAFT ADVISORY FOR THE INDIANA SHORES. EXPECT WIDESPREAD
FOG AND POSSIBLY AREAS OF DENSE FOG ESPECIALLY OVER THE SOUTH PART
OF THE LAKE AS VERY WARM HUMID AIR SPREADS OVER THE COLD WATER
SURFACE. HAVE NOT ISSUED A DENSE FOG ADVISORY AT THIS TIME...BUT
AN ADVISORY MAY BE NEEDED LATER TONIGHT.

AS THE LOW MOVES NORTHEAST INTO ONTARIO TUESDAY EVENING A COLD
FRONT WILL MOVE SLOWLY ACROSS LAKE MICHIGAN. A SECOND WAVE OF LOW
PRESSURE MOVING ALONG THE FRONT WILL SLOW DOWN THE PROGRESS OF THE
COLD FRONT. THIS SECOND LOW PRESSURE WILL INTENSIFY AS IT MOVES
TO LAKE HURON BY MIDDAY WEDNESDAY. STRONG WEST WINDS WILL DEVELOP
WEDNESDAY...WITH GALES EXPECTED WEDNESDAY AFTERNOON AND WEDNESDAY
NIGHT OVER THE SOUTHERN HALF OF LAKE MICHIGAN. HAVE ISSUED A GALE
WATCH FOR THE SOUTH HALF OF THE LAKE.

STRONG WEST FLOW WILL CONTINUE THROUGH THURSDAY BEFORE DIMINISHING
THIS WEEKEND.

ALLSOPP

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...FLOOD WATCH...ILZ014-ILZ021-ILZ022-ILZ023-ILZ032-ILZ033-
ILZ039...6 AM TUESDAY TO 6 AM WEDNESDAY.

IN...FLOOD WATCH...INZ001-INZ002-INZ010-INZ011-INZ019...6 AM TUESDAY
TO 6 AM WEDNESDAY.

LM...GALE WATCH...LMZ080-LMZ567-LMZ669-LMZ671-LMZ673-LMZ675-LMZ777-
LMZ779-LMZ868-LMZ870-LMZ872-LMZ874-LMZ876-LMZ878...2 PM
WEDNESDAY TO 3 AM THURSDAY.

SMALL CRAFT ADVISORY...LMZ743-LMZ744-LMZ745...10 AM TUESDAY TO
10 PM TUESDAY.

&&

$$





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