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000
FXUS63 KLOT 250909
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
409 AM CDT SAT MAY 25 2013

.DISCUSSION...
300 AM CDT

BELOW NORMAL TEMPERATURES AND PERIODIC CHANCES FOR SHOWERS OR
THUNDERSTORMS THROUGH THE WEEKEND WILL SET THE STAGE FOR A RAPID
WARMING TREND FOR NEXT WEEK.

FOR THE REMAINDER OF THE NIGHT AND INTO SATURDAY MORNING...A WEAK
SHORTWAVE OVERTOPPING A BUILDING RIDGE OVER THE CENTRAL CONUS WILL
BRING INCREASING CLOUDINESS AND A CHANCE FOR SOME LIGHT SHOWERS OR
SPRINKLES...PARTICULARLY FOR LOCATIONS WEST OF THE FOX VALLEY AND
THE I-55 CORRIDOR.  LATEST RADAR IMAGERY SHOWS SCATTERED SHOWERS
CROSSING THE MS RIVER INTO NWRN IL...BUT AS THEY MOVE INTO AN
ENVIRONMENT NOTED BY DRY LOW LEVEL CONDITIONS...THE SHOWERS SHOW A
DIMINISHING TREND.  HOWEVER...REPEATED SHOWER DEVELOPMENT WILL
EVENTUALLY MOISTEN UP THE LOWER LEVELS ENOUGH FOR SOME LIGHT PCPN TO
REACH THE GROUND.  TEMPERATURES HAVE ALREADY REACHED A MINIMA ACROSS
THE AREA AND SHOULD BEGIN TO SLOWLY RISE DURING THE REMAINDER OF THE
OVERNIGHT HOURS AS DENSER CLOUD COVER OVERSPREADS THE REGION AND
SHUTTING OFF ANY FURTHER RADIATIVE COOLING.

FOR THE REMAINDER OF SATURDAY AND INTO SATURDAY NIGHT...WILL
CONTINUE TO FOCUS ON PCPN CHANCES.  THE UPPER LEVEL PATTERN REMAINS
GENERALLY UNCHANGED OVER THE PAST 24-36 HRS WITH A HIGH
AMPLITUDE...SLOWLY PROGRESSIVE PATTERN CONTINUING.  THE MAIN CULPRIT
IS A DEEP UPPER LOW MAKING VERY LOW PROGRESS LIFTING NEWD THROUGH
NEW ENGLAND.  THIS IS HELPING BUILD THE UPPER RIDGE OVER THE CENTRAL
CONUS WHILE A SERIES OF SYSTEM MOVE INTO THE PACIFIC NORTHWEST.
WHILE THE UPPER LOW REMAINS OVER NEW ENGLAND...AND THE UPPER RIDGE
AXIS REMAINS TO THE WEST OF THE LOCAL AREA...PERSISTENT WEAK COLD
ADVECTION THROUGH DEEP LEVELS OF THE ATMOSPHERE WILL HELP KEEP
TEMPERATURES ON THE COOLER SIDE.  ALSO...AT THE SURFACE...HIGH
PRESSURE EXTENDS FROM HUDSON BAY...THROUGH THE EASTERN GREAT LAKES
TO THE TENNESSEE VALLEY.  THIS HAS KEPT NELY FLOW OFF OF LAKE
MICHIGAN...WITH THE RELATIVELY COLD LAKE WATERS HELPING TO KEEP
LAKEFRONT TEMPERATURES IN THE 50S.  THERE WILL BE LITTLE CHANGE
TODAY AS TEMPS WILL STILL REMAIN IN THE 50S ALONG THE LAKEFRONT.
THE INCREASING CLOUD COVER WILL ALSO HELP TO LIMIT DAYTIME
HEATING...WITH HIGHS REMAINING IN THE LOWER TO MIDDLE 60S.  A WARM
FRONT IS BEGINNING TO DEVELOP SEWD FROM A SFC LOW OVER THE WESTERN
PLAINS.  THIS WARM FRONT WILL INCREASINGLY BECOME THE FOCUS OF
FURTHER PCPN DEVELOPMENT THROUGH THE REMAINDER OF THE WEEKEND AND
INTO EARLY NEXT WEEK.  THE WARM FRONT WILL GRADUALLY BECOME MORE
FOCUSED...AND EXTEND EWD...THROUGH NEBRASKA...ALONG THE IA/MO
BORDER TO SRN IL/IN BY SUNDAY MORNING.  WHILE THE BOUNDARY REMAINS
TO THE SOUTH...INCREASING WARM ADVECTION AND ISENTROPIC LIFT THROUGH
THE LOWER LEVELS WILL HELP TO SPREAD PCPN FROM THE SOUTHWEST TO THE
NORTHEAST ACROSS THE CWA THROUGH THE WEEKEND...THOUGH PCPN SHOULD
GENERALLY BE   PCPN SHOULD BEGIN TO BECOME MORE WIDESPREAD ACROSS
THE CWA BY SUNDAY AND SUNDAY NIGHT AS THE WARM FRONT SLOWLY LIFTS
NWD. IT IS A LITTLE TOUGH TO SAY IF THE WEEKEND AND THE MEMORIAL DAY
HOLIDAY WILL BE A TOTAL WASHOUT...BUT PERIODS OF PCPN WILL LIKELY
IMPACT MUCH OF AREA.  AND WHILE THUNDERSTORMS WILL...SIMILARLY
LIKELY NOT BE WIDESPREAD...THERE WILL BE A PERSISTENT CHANCE FOR
ELEVATED CONVECTION IN THE PERSISTENT ISENTROPIC LIFT.

WHILE MEMORIAL DAY WILL LIKELY NOT BE DRY...AT LEAST TEMPERATURES
WILL BE ON THE INCREASE.  BY MONDAY...THE UPPER LOW WILL FINALLY
LIFT NEWD INTO NEW BRUNSWICK AND THE UPPER RIDGE WILL BEGIN TO
PROGRESS EWD.  THE MODELS ARE BEGINNING TO LOOSE FOCUS AND
CONTINUITY IN HANDLING THE EVOLUTION OF THE UPPER RIDGE AS THERE IS
LITTLE CONSENSUS ON THE TIMING AND STRENGTH OF ADDITIONAL SHORTWAVES
OVERTOPPING THE RIDGE...WHICH WILL IN TURN...LEAD TO SOME
UNCERTAINTY TO THE PCPN FORECAST.  THE ONE GENERAL CERTAINTY IS THAT
THERE WILL BE A SERIES OF SHORTWAVES TRACKING ACROSS THE
REGION...HELPING TO FOCUS THE PCPN INVOF THE WARM FRONT.

BY MONDAY NIGHT...THE WARM FRONT SHOULD LIFT WELL NORTH OF THE
AREA...INITIATING THE RAPID WARMING TREND AS PERSISTENT SWLY FLOW
DEVELOPS AT THE SFC WHILE THE UPPER RIDGE BUILDS ACROSS THE
MIDWEST.  HOWEVER...WITH A SFC RIDGE EXTENDING THROUGH THE SERN
CONUS...GULF MOISTURE WILL BE LIMITED THROUGH TUESDAY.  BUT BY
WEDNESDAY...THE RIDGE WILL RETREAT TO THE EAST...OPENING UP THE GULF
AND ALLOW MORE MOISTURE TO STREAM NWD.  SO...BY MID WEEK...EXPECT
THAT DEWPOINTS SHOULD REACH INTO THE MIDDLE TO UPPER 60S TO
ACCOMPANY THE HIGHER TEMPERATURES WHICH SHOULD REACH INTO THE MIDDLE
80S.  THE GFS/ECMWF ARE STILL BRINGING 850MB TEMPS AROUND 18C ACROSS
THE MIDWEST...WHICH WOULD IMPLY THAT TEMPS IN THE UPPER 80S ARE NOT
OUT OF THE QUESTION GIVEN ENOUGH SUNSHINE TO ALLOW FOR DEEP DEEP
MIXING.  AS USUAL...THE INCREASE IN GULF MOISTURE ACCOMPANYING THE
INCREASED HEAT WILL ALSO KEEP THE CHANCES FOR THUNDERSTORMS OVER THE
AREA.  SO...THE UNCERTAINTY IN THE CLOUD COVER WILL BE THE MAJOR
QUESTION MARK RIGHT NOW AS TO WHETHER THE REGION WILL SEE A REAL
TASTE OF SUMMER NEXT WEEK.

KREIN

&&

.AVIATION...

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

* EAST-SOUTHEAST WINDS GENERALLY 10 KTS OR LESS THIS MORNING AND
  EARLY AFTERNOON BECOMING MORE EAST WITH LAKE INFLUENCE MID
  AFTERNOON.

* LOW PROBABILITY OF SHOWERS FROM VFR MID LEVEL CLOUD DECK
  OVERNIGHT AND THROUGH THE DAY...HIGHER PROBABILITY SHRA WILL
  REMAIN WEST/SOUTH OF CHI AREA TERMINALS.

MDB

//DISCUSSION...UPDATED 09Z...

BANDS OF LIGHT RAIN CONTINUE TO MOVE INTO NORTH CENTRAL ILLINOIS
EARLY THIS MORNING BUT EASTWARD PROGRESS CONTINUES TO BE SLOWED BY
ABUNDANT LOW AND MID LEVEL DRY AIR. RFD WILL LIKELY SEE SOME LIGHT
RAIN OVER THE NEXT FEW HOURS. ACTIVITY EXTENDS NORTHWARD INTO
WEST CENTRAL WISCONSIN SO IT IS POSSIBLE THAT ORD/MDW/DPA SEE SOME
SPRINKLES OR EVEN A LITTLE LIGHT RAIN CLOSER TO 11/12Z BUT IT
LOOKS LIKE THE BULK IF NOT ALL OF THE ACTIVITY WILL REMAIN JUST TO
THEIR WEST. WILL LEAVE THESE SITES DRY FOR NOW WITH THE
PROBABILITY TOO LOW TO MENTION IN THE TAF AND THE EXPECTATION OF
THEM REMAINING DRY.

MDB

FROM 06Z...

HIGH PRESSURE IS CENTERED JUST EAST OF LAKE MICHIGAN WITH WEAK LOW
PRESSURE OUT ACROSS THE HIGH PLAINS. LIGHT AND VARIABLE LOW LEVEL
WINDS ARE IN PLACE AND WILL GRADUALLY BECOME MORE FOCUSED FROM THE
SOUTHEAST FROM WEST TO EAST THROUGH EARLY MORNING AS THE HIGH
DEPARTS. BANDS OF SHOWERS CONTINUE TO MOVE SOUTHEASTWARD ACROSS
NORTHEAST IOWA AND SOUTHWEST WISCONSIN WITH SOME EMBEDDED THUNDER
FURTHER WEST ACROSS NORTH CENTRAL IOWA. HAVE INCLUDED TEMPO FOR
SOME LIGHT RAIN AT RFD OVER FOR A FEW HOUR PERIOD BUT THE RAIN
SHOULD HAVE AN INCREASINGLY DIFFICULT TIME MAKING MUCH EASTWARD
PROGRESS WITH VERY DRY LOW AND MID LEVEL AIR ACROSS MUCH OF THE
AREA. WILL LEAVE THE REMAINING TERMINALS DRY FOR NOW. EXPECT THAT
CIGS AND VSBY WILL REMAIN VFR THOUGH CIGS MAY LOWER TO 5000-7000
FT AT TIMES OVERNIGHT...WITH MORE WIDESPREAD 6000-8000 FT CIGS
EXPECTED DURING THE DAY. THE SHOWER CHANCES WILL REMAIN HIGHEST
WEST AND SOUTH OF THE TERMINALS THROUGH THE DAY BUT RFD MAY HAVE A
HIGHER CHANCE THIS AFTERNOON AND EARLY THIS EVENING AS A WAVE
PASSES TO THE SOUTHWEST. CANNOT COMPLETELY RULE OUT SOME SPRINKLES
OR LIGHT RAIN AT THE OTHER TERMINALS TODAY HOWEVER. SOUTHEAST
WINDS WILL LIKELY TURN MORE EASTERLY AT ORD/MDW AND EVENTUALLY DPA
THANKS TO A LAKE BREEZE THAT IS EXPECTED TO DEVELOP THIS
AFTERNOON.

MDB

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

* HIGH CONFIDENCE IN WIND TRENDS...EXCEPT MEDIUM CONFIDENCE WITH
  DETAILS OF SHIFT TO EAST/LAKE BREEZE THIS AFTERNOON.

* MEDIUM CONFIDENCE THAT POTENTIAL FOR LIGHT VFR SHOWERS TO REACH
  ORD/MDW IS LOW...THOUGH HIGH CONFIDENCE IN CONDITIONS REMAINING
  VFR EVEN IF THEY DO.

MDB

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

SUNDAY...CHANCE OF SHRA AND A FEW TSRA ESPECIALLY LATER IN THE
DAY/NIGHT. MAINLY VFR.

MONDAY THROUGH THURSDAY...VFR. LOW PROBABILITY FOR PERIODIC
SHRA/TSRA ESPECIALLY MONDAY AND AGAIN THURSDAY. BREEZY SOUTH WINDS
WEDNESDAY AND THURSDAY.

RATZER

&&

.MARINE...
242 AM CDT

QUIET CONDITIONS PERSIST ACROSS LAKE MICHIGAN WITH AN AXIS OF HIGH
PRESSURE CENTERED JUST EAST OF THE LAKE. THE HIGH WILL BE SLOW TO
MOVE TO THE EAST WHICH WILL KEEP LIGHT AND SOMEWHAT VARIABLE WINDS
ACROSS THE LAKE TODAY...WITH AN ONSHORE COMPONENT DEVELOPING ALONG
THE SHORELINES. IT WILL LIKELY TAKE UNTIL MONDAY FOR A MORE
PERSISTENT SOUTHEAST FLOW TO SET UP AS LOW PRESSURE GRADUALLY
ORGANIZES ACROSS THE PLAINS AND THE HIGH SHIFTS TO THE EAST. WARMER
AIR WILL BE MOVING INTO THE REGION WHICH WILL LIMIT MIXING AND GUST
POTENTIAL BUT THE PRESSURE GRADIENT MAY BE STRONG ENOUGH AT TIMES TO
ALLOW FOR PERIODS OF 15-25 KT WINDS BY WEDNESDAY. WIND DIRECTION
WILL SHIFT FROM SOUTHEAST TO SOUTH THEN SOUTHWEST THROUGH THE WEEK.

MDB

&&

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

$$

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