NWS Area Forecast Discussion
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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