Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 222208
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
508 PM CDT TUE APR 22 2014

.DISCUSSION...
330 PM CDT

THE GENERAL TREND FOR THE NEXT SEVERAL DAYS SHOULD BE FOR A PERIOD
OF COOL AND DRY...FOLLOWED BY WARM AND WET...AND THEN COOL AND WET.

FOR THE REMAINDER OF THE AFTERNOON...SUNNY SKIES WITH SEASONABLE
TEMPERATURES WILL PREVAIL.  HOWEVER...A A VERY WEAK PRESSURE
GRADIENT OVER THE REGION AS A RIDGE OF HIGH PRESSURE BUILDS ACROSS
THE UPPER MIDWEST AND WESTERN GREAT LAKES...COMBINED WITH
DIFFERENTIAL HEATING BETWEEN THE WARMER LAND AND COLDER LAKE
MICHIGAN WATER...HAS GENERATED A LAKE BREEZE BOUNDARY...WHICH HAS
MOVED INLAND INTO NERN IL/NWRN IN.  TEMPERATURES ALONG THE LAKEFRONT
HAVE DROPPED INTO THE MIDDLE 40S...COMPARED WITH UPPER 50S TO LOWER
60S WELL INLAND.  FOR THE OVERNIGHT HOURS...THE CONCERN WILL BE
OVERNIGHT LOW TEMPERATURES AND A CHANCE FOR FROST.  SKIES SHOULD
REMAIN MOSTLY CLEAR WITH VERY LIGHT WINDS.  ALSO...THE AIRMASS WILL
CONTINUE TO DRY OUT WITH SFC DEWPOINTS DROPPING INTO THE UPPER 20S
TO LOWER 30S.  SINCE ABUNDANT SUNSHINE TODAY HAS WARMED THE
GROUND...DO NOT EXPECT THAT SFC TEMPS WILL RADIATE DOWN TO THE
DEWPOINT...BUT DO EXPECT TEMPS SHOULD DROP INTO THE LOWER 30S AWAY
FROM THE LAKEFRONT AND THE HEAVILY URBANIZED AREAS OF THE CHICAGO
METRO AREA.  ALSO...THE PONTIAC AREA SHOULD SEE TEMPS ONLY DROPPING
DOWN TO ARND 35F...SO WILL CONTINUE TO MENTION THE POSSIBILITY OF
AREAS OF FROST FOR LOCATIONS WHERE THE OVERNIGHT LOW TEMPERATURE
WILL DROP BELOW 35F.

WEDNESDAY SHOULD START OUT COOL AND DRY...BUT THE NEXT UPSTREAM
SYSTEM WILL BRING INCREASING CHANCES FOR RAIN DURG THE AFTERNOON
HOURS.  THE LATEST GUIDANCE TRENDS HAVE BEEN FOR A SLIGHTLY DELAYED
ONSET OF PCPN...LARGELY DUE TO THE VERY DRY LOW LEVELS WHICH WILL BE
SLOW TO SATURATE AND THE SLOW MOVEMENT OF THE HIGH PRESSURE PUSHING
OFF TO THE EAST.  INITIALLY...PCPN SHOULD START OUT AS OVERRUNNING
SHOWERS IN ADVANCE OF A DEVELOPING WARM FRONT LIFTING NEWD THROUGH
THE REGION.  THERE COULD BE A MINIMA IN PCPN WEDNESDAY NIGHT AS THE
WARM SECTOR AIR OVERSPREADS NRN IL/NWRN IN...BUT THERE WILL STILL BE
A LOW CHANCE FOR SOME SHOWERS...AND ANY PCPN WOULD LIKELY BE
ISOLD/SCT.  THE GREATER CHANCES FOR MORE WIDESPREAD AND HEAVIER PCPN
WILL COME BY THURSDAY.  THIS WILL BE THE WARM/WET PERIOD PREVIOUSLY
MENTIONED AS GENERALLY SOUTHERLY FLOW PREVAILS AHEAD OF AN
APPROACHING COLD FRONT WITH FLOW OFF OF A WIDE OPEN GULF OF MEXICO.
EXPECT THAT TEMPERATURES WILL REACH INTO THE LOWER TO MIDDLE 60S
WITH DEWPOINTS IN THE UPPER 40S TO LOWER 50S.  THE EXCEPTION TO THIS
MAY BE THE LAKE COUNTY ILLINOIS LAKEFRONT...INCLUDING THE WAUKEGAN
AREA...WHERE A WINDS SHOULD BE SLIGHTLY EAST OF SOUTH AND BRING SOME
LAKE COOLED AIR INLAND...KEEPING TEMPS IN THE LOWER 50S.  DOWNTOWN
CHICAGO COULD ALSO SEE SOME LAKE INFLUENCE...WITH TEMPERATURES
DROPPING OFF AFTER REACHING AN EARLY AFTERNOON HIGH AROUND 60F.  THE
MODELS HAVE TRENDED TOWARD A RELATIVELY CONSISTENT SOLUTION WITH
THIS SYSTEM WITH ONLY SOME SLIGHT TIMING ISSUES WITH THE SPEED OF
THE FRONT.  HAVE GONE WITH A FAIRLY BROAD BAND OF CATEGORICAL POPS
ALONG AND JUST AHEAD OF THE FRONT.  THE LATEST GUIDANCE ALSO
INDICATES INCREASING SFC BASED INSTABILITY AHEAD OF THE FRONT...SO
WILL CARRY AND CHANCE OF THUNDERSTORMS WITH THE PCPN.  SINCE THE
GREATEST INSTABILITY SHOULD BE SOUTH OF THE CWA...HAVE KEPT THE
PROBABILITY OF THUNDER LOWER THAN THE PROBABILITY OF PCPN...THOUGH
EXPECT THAT MUCH OF THE AREA SHOULD SEE AT LEAST SOME THUNDER AS THE
FRONT SWEEPS ACROSS THE REGION.  AS FOR THE SEVERE POTENTIAL...THE
DAY 3 SPC OUTLOOK COVERS THE CWA IN A "SEE TEXT" AREA.  A STRONG
SWLY LOW LEVEL JET OF 45-50 KT ABOVE 10-15KT SELY WINDS COMBINED
WITH MODEST CAPE COULD BRING A CHANCE FOR SOME STRONGER
STORMS...ESPECIALLY FOR THE SOUTHERN PORTIONS OF THE CWA.  THE TIME
OF GREATEST OPPORTUNITY FOR THUNDERSTORMS WILL BE FROM LATE MORNING
THROUGH EARLY EVENING THURSDAY.

FOLLOWING THE FRONTAL PASSAGE...FLOW ACROSS THE REGION WILL BECOME
MORE ZONAL AND THE REAL COLD ADVECTION WILL NOT SET UP UNTIL
SATURDAY.  WITH WLY FLOW SETTING UP AS THE MAIN SFC LOW MOVES
THROUGH WISCONSIN AND CENTRAL LAKE MICHIGAN EARLY FRIDAY...THERE
WILL STILL BE AN OPPORTUNITY FOR TEMPS IN THE UPPER 60S TO AROUND
70S.  A SECONDARY COLD FRONT SHOULD PUSH SOUTH ACROSS THE REGION
FRIDAY EVENING AND THE UPPER LOW CENTER PUSHED OVER THE ERN GREAT
LAKES.

THE EXTENDED FORECAST PERIOD...SATURDAY THROUGH TUESDAY...SHOULD BE
THE AFOREMENTIONED COOL/WET PERIOD.  BY SATURDAY...CANADIAN HIGH
PRESSURE WILL NOSE SOUTH ACROSS THE UPPER MIDWEST...SETTING UP AN
EXTENDED PERIOD OF SELY TO ELY FLOW OFF OF THE COLD WATERS OF LAKE
MICHIGAN.  ANOTHER DEVELOPING LOW PRESSURE SYSTEM IS EXPECTED TO
DEVELOP OVER THE PLAINS OVER THE WEEKEND WITH A MAIN LOW OVER THE
DAKOTAS AND A TRIPLE POINT LOW OVER THE CNTRL PLAINS.  A WARM FRONT
EXTENDING EAST OF THE TRIPLE POINT WILL BE KEPT SOUTH OF THE LOCAL
AREA BY THE CANADIAN HIGH PRESSURE...SO THERE WILL BE LITTLE
OPPORTUNITY FOR SIGNIFICANT WARMING THROUGH THE WEEKEND.  WHEN THE
SYSTEM FINALLY REACHES THE MIDWEST BY EARLY NEXT WEEK...THE MAIN LOW
WILL DISSIPATE AND THE TRIPLE POINT LOW WILL DEEPEN...BUT THERE IS
DECENT AGREEMENT AMONG THE LONGER RANGE GUIDANCE THAT THIS SFC LOW
SHOULD SLIDE SOUTH OF THE CWA...THROUGH SRN IL AND INTO THE OHIO
VALLEY.  SO...WARM SECTOR AIR WILL LIKELY NEVER REACH THIS FAR
NORTH...SO TEMPERATURES THROUGH THE WEEKEND AND INTO EARLY NEXT
WEEK WILL REMAIN WELL BELOW NORMAL...MIDDLE 40S TO MIDDLE 50S...WITH
PERIODIC CHANCES FOR RAIN.

KREIN

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 22Z...

* NONE

IZZI

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

HIGH PRESSURE IS TO OUR WEST WITH NORTHWEST FLOW OVER MUCH OF THE
REGION. A LAKE BREEZE IS NOW VISIBLE ON RADAR AND RIGHT NOW IT
DOES NOT APPEAR TO BE MOVING VERY MUCH. WINDS WILL TURN EAST AT
MDW ARND 1830Z AND EXPECTING THE LAKE BREEZE TO REACH ORD BY 20Z.

HIGH PRESSURE SPREADS OVER THE REGION THIS EVENING WITH WINDS
WEAKENING BUT REMAINING NE ACROSS THE REGION. THE NEXT LOW
PRESSURE SYSTEM MOVES OVER THE CENTRAL PLAINS TOMORROW AND VFR CIGS
WILL THICKEN FROM THE LATE MORNING THROUGH THE AFTN. WENT ON THE
SLOW SLIDE OF PRECIP AND THINK IT WILL MOVE INTO NORTH CENTRAL IL
AFTER 18Z AND THEN IMPACT THE EASTERN TERMINALS AFTER 00Z. WINDS
REMAIN E TO SE AT 5-9 KT TOMORROW.

JEE

//ORD AND MDW CONFIDENCE...UPDATED 22Z...

* MEDIUM-HIGH CONFIDENCE THAT PRECIP WILL REMAIN EAST OF THE
  TERMINALS THROUGH 00Z THURSDAY.

* HIGH CONFIDENCE IN ALL OTHER FORECAST ELEMENTS.

JEE/IZZI

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

WEDNESDAY NIGHT...CHANCE OF SHOWERS...OTHERWISE VFR.

THURSDAY...SHRA/TSRA LIKELY WITH PERIODS OF MVFR CIGS/VSBYS IN
THUNDERSTORMS.

FRIDAY...SLIGHT CHANCE OF SHOWERS...OTHERWISE VFR.

SATURDAY...CHANCE OF SHOWERS LATE...OTHERWISE VFR.

SUNDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

MONDAY...CHANCE OF SHOWERS...OTHERWISE VFR.

RODRIGUEZ

&&

.MARINE...
253 PM CDT

HIGH PRESSURE STRETCHES FROM THE UPPER MIDWEST INTO THE CENTRAL
PLAINS AND WILL BECOME CENTERED OVER LAKE MICHIGAN BY MIDDAY
WEDNESDAY. AS THIS OCCURS...WINDS WILL CONTINUE TO SLOWLY
DIMINISH...WITH LAKE BREEZES DEVELOPING THIS AFTERNOON AND AGAIN
WEDNESDAY AFTERNOON. LOW PRESSURE WILL MOVE ACROSS THE PLAINS
WEDNESDAY NIGHT WITH SOUTHEAST FLOW BEGINNING TO RAMP UP.
SOUTHEAST FLOW WILL INCREASE WITH SUSTAINED WINDS TO AROUND 25
KT...BUT STABLE CONDITIONS WILL HELP KEEP GUSTS TO AROUND 30 KT.
WINDS TURN SOUTHWEST THURSDAY NIGHT INTO EARLY FRIDAY AS THE LOW
LIFTS ACROSS LAKE MICHIGAN...THEN TURN NORTHWEST BY LATER IN THE
DAY FRIDAY AS A COLD FRONT SWEEPS ACROSS THE LAKE.

BMD

&&

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

$$

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