Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS63 KLOT 241425
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
925 AM CDT SUN MAY 24 2015

.SHORT TERM...
310 AM CDT

SUNDAY AND SUNDAY NIGHT...

MAIN ISSUES FOR THE SHORT TERM FORECAST PERIOD WILL BE RAMPING UP
PCPN CHANCES AS WELL AS HIGH TEMPS FOR TODAY...ESPECIALLY ALONG THE
ILLINOIS LAKE MICHIGAN SHORE.  A LARGE AREA OF HIGH PRESSURE
CONTINUES TO SLOWLY SLIDE OFF THE MID ATLANTIC COAST WITH A RIDGE
AXIS EXTENDING BACK THROUGH THE UPPER MISSISSIPPI VALLEY.
MEANWHILE...LEE CYCLOGENESIS SLOWLY PERSISTS OVER ERN CO/NM. A
RETURN FLOW OF MOISTURE IS SETTING UP OVER THE CNTRL CONUS IN
GENERALLY SELY-SLY AROUND THE WRN PERIPHERY OF THE DEPARTING HIGH.
ALSO...A WEAK WARM FRONT/TROUGH APPEARS TO BE SEEING UP ACROSS THE
OHIO VALLEY WEST THROUGH SRN MO.  WINDS TO THE NORTH OF THE BOUNDARY
ARE PREVAILING SELY WITH PREVAILING SLY WINDS TO THE SOUTH. THE SELY
WINDS WILL CONTINUE TO KEEP THE IL SHORE OF LAKE MICHIGAN A BIT
COOLER THAN INLAND LOCATIONS.  HOWEVER...THE BOUNDARY IS EXPECTED TO
MOVE NORTH THROUGH THE DAY...PUTTING THE ENTIRE REGION UNDER SLY
FLOW EVENTUALLY.  THE MAIN IMPACT WILL BE ON TEMPERATURES.  WITH
LITTLE CHANGE TO THE OVERALL PATTERN...ANOTHER WARM DAY IS EXPECTED
FOR TODAY...THOUGH MORE EXTENSIVE CLOUD COVER COULD KEEP MAX TEMPS
LOWER BY A DEGREE OR 2.  DO NOT EXPECT A LAKE BREEZE TO
FORM...ESPECIALLY WITH STRENGTHENING WINDS OF 10-15 MPH...BUT RATHER
WITH SYNOPTICALLY SOUTHEAST FLOW PERSISTING INTO THE EARLY
AFTERNOON...THE ILLINOIS SHORE SHOULD BE COOLER THAN WELL
INLAND...BUT AS WINDS TURN SLY BY EARLY AFTERNOON OVER THE COOK
COUNTY SHORE...TEMPS SHOULD REBOUND INTO THE LOW 70S.  LAKE COUNTY
IL WILL REMAIN UNDER THE COOLER SELY FLOW A BIT LONGER...KEEPING THE
WAUKEGAN AREA COOLER THROUGH THE DAY...WITH HIGHS ONLY IN THE
LOWER 60S. LOCATIONS WELL INLAND SHOULD SEE MAX TEMPS TODAY RISING
INTO THE MIDDLE TO UPPER 70S...WITH THE PONTIAC METRO AREA HITTING
CLOSE TO 80F.

PCPN CHANCES FOR TODAY WILL BE A BIT TRICKY.  A WAVE OF SCT SHOWERS
IS MOVING NWD THROUGH WRN IL...ASSOCIATED WITH A WEAK SHORTWAVE
TRACKING UP THE WRN SIDE OF THE UPPER RIDGE WHICH IS ORIENTED FROM
THE SERN CONUS THROUGH THE UPPER MISSISSIPPI VALLEY.  THERE IS A
CHANCE FOR SOME OF THESE SHOWERS TO BRING SOME LIGHT RAIN TO THE
NWRN PORTIONS OF THE CWA...ALONG AND WEST OF THE I-39
CORRIDOR...INCLUDING THE ROCKFORD AREA.  OTHERWISE...THE GREATER
PCPN CHANCES WILL HAVE TO WAIT FOR A MUCH STRONGER SHORTWAVE
EXPECTED TO LIFT OUT OF THE SOUTH HIGH PLAINS LATER THIS MORNING.
THIS WAVE WILL TRACK NNELY TO THE UPPER MISSOURI VALLEY BY EARLY
THIS EVENING AND THEN AS THE UPPER RIDGE IS FORCES EWD...WILL THEN
TURN MORE NELY...REACHING THE MIDDLE MISSISSIPPI VALLEY LATE
TONIGHT.  THE MODEL GUIDANCE INDICATES A FEW STRONG LOW LEVEL JET OF
50-55KT DIRECTED INTO NRN IL LATE TONIGHT AS WELL.  THE STRONG LOW
LEVEL JET WILL HELP PUMP UP DEEP LAYER MOISTURE OVER THE REGION WITH
PWATS CLIMBING TO ARND 1.8 INCHES THIS EVENING.  THE TRICKER PARTS
TO THE WX/POP FORECAST HAS BEEN WHERE TO FOCUS THE CATEGORICAL POPS
AND HOW FAR EAST TO SPREAD THE HIGHER POPS AND HOW MUCH THUNDER TO
INDICATE WITHING THE WX.  HAVE LARGELY CONFINED THE CATEGORICAL POPS
TO THE VCNTY OF THE UPPER SHORTWAVE...OVER NWRN IL...INCLUDING THE
ROCKFORD AREA...BUT HAVE DROPPED OFF POPS TO THE SOUTHEAST...AWAY
FROM THE STRONGEST UPPER FORCING.  WHILE CURRENT THINKING IS THAT
MUCH OF THE CWA SHOULD SEE SOME MEASURABLE PCPN AT SOME POINT...IT
IS MOST LIKELY THAT THE ERN PORTIONS OF THE CWA...INCLUDING THE
CHICAGO METRO AREA AND NWRN INDIANA WILL LIKELY NOT SEE THE PCPN
UNTIL LATE TONIGHT OR EARLY TOMORROW MORNING.  THE OTHER CONCERN IS
THE THUNDER CHANCES.  FEEL THAT THE GREATER CHANCES WILL ALSO BE
CLOSER TO THE UPPER FORCING...OVER THE WRN PORTIONS OF THE CWA...BUT
THERE IS A CHANCE THAT THE ERN PORTIONS OF THE CWA COULD SEE SOME
ISOLD-SCT TS AS WELL LATE TONIGHT.  CURRENTLY...THE GREATEST
SENSIBLE WEATHER THREAT FROM THIS SYSTEM WILL BE LOCALLY HEAVY
RAINFALL DUE TO THE ANOMALOUSLY HIGH PWATS.  PER THE DVN PWAT
CLIMATOLOGY FOR MID TO LATE MAY...THE EXPECTED 1.75 INCH PWAT
FORECAST IS NEAR THE 99TH PERCENTILE.  SO...SOME OF THE STRONGER
SHRA/TSRA THAT DEVELOP WILL HAVE THE POTENTIAL TO PRODUCE LOCALLY
HEAVY RAINFALL.

KREIN

&&

.LONG TERM...
229 AM CDT

MONDAY THROUGH SATURDAY...

FOR MEMORIAL DAY...LARGEST CONCERN FOR THE DAY WILL BE ON PRECIP
TIMING/COVERAGE. GUIDANCE HAS BEEN RELATIVELY CONSISTENT THAT A
LOBE OF VORTICITY WILL BE LIFTING NORTH ACROSS THE MID-MISSOURI
VALLEY EARLY MON...WITH A SFC WAVE PROGGED TO BE OVER CENTRAL IOWA
BY DAYBREAK MON. THE CHANNEL OF NEARLY 2.00 INCHES OF PWAT AND
ANOMALOUSLY STRONG 850MB V-WIND OR MOISTURE TRANSPORT...WILL BE
STEADILY SHIFTING EAST/NORTHEAST ACROSS THE FORECAST AREA SHORTLY
AFT DAYBREAK. BY MID-MORNING THE MOIST PLUME WILL BE DEPARTING THE
WESTERN CWFA AND BY MIDDAY OR SHORTLY BEFORE...THE REMAINDER OF
THE FORECAST AREA COULD BE DRY. IN ADDITION TO THE PRECIP ENDING
BY MIDDAY...CLOUD COVER SHOULD QUICKLY ERODE WITH ONLY A FEW
CLOUDS LINGERING IN THE AFTERNOON HOURS. UNFORTUNATELY THE TRADE
OFF FOR A DRY HOLIDAY AFTERNOON WILL BE THE BREEZY CONDITIONS.
MIXING WILL BE MAXIMIZED GIVEN THE LACK OF CLOUD COVER...SO EXPECT
GUSTS TO NEAR 35 MPH AND POSSIBLY FLIRT WITH 40MPH FOR A FEW
HOURS. HAVE ALSO NUDGED TEMPS UP A DEGREE...WITH GENERALLY 80 TO
84 DEG EXPECTED.

THE WARM/MOIST AIR WILL CONTINUE TO ADVECT ACROSS THE REGION MON NGT
INTO TUE...WITH YET ANOTHER VERY MILD OVERNIGHT. HAVE TEMPS MAINLY
IN THE MID 60S BUT COULD SEE THIS NOT BEING WARM ENOUGH. THE
WILDCARD WILL BE CLOUD COVER...WHICH IS CLOUDS HOLD OFF
LONGER...TEMPS COULD STILL DIP INTO THE LOW/MID 60S. THE DEW POINTS
HOLDING IN THE 60S WOULD LIKELY SLOW THE RATE OF FALL OVERNIGHT.

TUESDAY THROUGH SATURDAY... 500MB TROUGH AXIS WILL REMAIN IN A
SLIGHTLY NEGATIVE ORIENTATION ACROSS THE CENTRAL CONUS...WITH A WEAK
SFC FEATURE LIFTING NORTH ACROSS THE MID-MISSOURI VALLEY TUE
MORNING. BROAD MID-LVL RIDGING WILL REMAIN OVER THE SOUTHEAST
CONUS...MEANWHILE HIGH-AMPLITUDE RIDGING CONTINUES ACROSS WESTERN
CANADA/ALASKA. THIS WILL MAINTAIN A RELATIVELY ACTIVE SOUTHWEST FLOW
PATTERN FOR THE CENTRAL CONUS/GREAT LAKES REGION THROUGH THUR/FRI.

LATER IN THE WEEK ENSEMBLES BEGIN TO NUDGE A 500MB VORT SOUTH FROM
CENTRAL CANADA WITH A SFC FEATURE PROGGED TO DEVELOP ALONG THE LEE-
SIDE OR THE NORTHERN PLAINS. CLOSER TO FRI/SAT...OPER SOLUTIONS
DEVELOP THIS SFC FEATURE WITH A FRONTAL BOUNDARY SLIDING SOUTH FROM
CANADA. CONFIDENCE REMAINS LOW ON HOW THINGS WILL EVOLVE LATER IN
THE WEEK...ALTHOUGH ENSEMBLES ARE DEMONSTRATING MINIMAL SPREAD THAT
THE UPSTREAM RIDGE WILL BEGIN TO FLATTEN WITH A SEMI-ZONAL
ORIENTATION DEVELOPING.

WILL CONTINUE TO CARRY PERIODIC CHANCES FOR SHOWERS/STORMS...AND
TEMPS GENERALLY SEASONAL TO SLIGHTLY ABOVE SEASONAL THROUGH THE BULK
OF THE EXTENDED.

BEACHLER

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 14Z...

* EAST TO SOUTHEAST WINDS INCREASING IN SPEED EARLY AFTERNOON THEN
  TRENDING SOUTH LATE AFTERNOON OR EARLY EVENING.

* LITTLE IN THE WAY OF SHRA THROUGH THE REST OF THE MORNING BUT
  COVERAGE INCREASES THROUGH THE AFTERNOON.

* CHANCE FOR EMBEDDED TSRA INCREASES MARGINALLY THIS EVENING AND
  MORESO TONIGHT.

MDB

//DISCUSSION...UPDATED 14Z...
INITIAL BAND OF SHRA HAS LIFTED NORTHEAST OF ALL TERMINALS EXCEPT
FOR RFD. RFD WILL LIKELY CONTINUE TO SEE A FEW HOURS OF STEADIER
SHRA WITH COVERAGE POSSIBLY WANING A BIT TOWARD MIDDAY. OTHERWISE
EXCEPT THAT RFD WILL SEE THE GREATEST COVERAGE OF SHRA THROUGH THE
DAY. EXPECT THAT THERE WILL BE AN INCREASE IN COVERAGE OF SHRA
ACROSS NORTHEAST IL AND A LESSER EXTENT ACROSS NORTHWEST IN.
FORCING WILL BE RATHER BROAD SUPPORTING SCATTERED COVERAGE VS.
SOMETHING BETTER ORGANIZED AND EXPECT THAT OCCURRENCE AT ANY TAF
SITE WOULD BE INTERMITTENT FOR THE MOST PART. CHANCES WILL
STEADILY INCREASE THROUGH THE AFTERNOON. TSRA POTENTIAL IS LIMITED
THROUGH THE AFTERNOON AND EVEN THIS EVENING. THE CHANCE DOES
MODESTLY INCREASE THIS EVENING THOUGH REMAINS LOW / NOT ZERO/ SO
HAVE REMOVED TSRA MENTION FOR MUCH OF THE EVENING HOURS EXCEPT FOR
RFD.

MDB

FROM 12Z...

A WEAK WARM FRONT LIFTING THROUGH THE REGION WILL BRING A CHANCE
FOR SOME SCT SHRA THIS MORNING. WHILE THE WARM FRONT REMAINS TO
THE SOUTH OF THE TERMINALS...WINDS SHOULD BECOME SELY AND THEN
VEER TO SLY TO SSWLY AS THE WARM FRONT PUSHES TO THE NORTH INTO
WISCONSIN. ALSO...BY EARLY EVENING AS THE WARM FRONT PUSHES TO THE
NORTH...LOW LEVEL MOISTURE WILL BE ON THE INCREASE AS A
STRENGTHENING LOW LEVEL JET TRANSPORTS COPIOUS AMOUNTS OF MOISTURE
INTO THE REGION. THE ONE FACTOR LOWERING CONFIDENCE IN TS COVERAGE
INVOF THE TERMINALS IS THAT THE MAIN UPPER LEVEL FORCING WILL
STILL BE TO THE WEST IN THE EVENING...SO...WILL WILL ONLY GO WITH
VCTS AND PROB30 TS MENTIONS AT THIS TIME.

CONFIDENCE IS HIGHER WITH THE WIND FORECAST. AS THE WARM FRONT
PUSHES TO THE NORTH OF THE TERMINALS AND WINDS BECOME SLY...WINDS
SPEEDS WILL ALSO INCREASE AS THE SFC PRESSURE GRADIENT STRENGTHENS
AND SOME MIXING OF THE STRONG LOW LEVEL JET BRINGS GUSTIER WINDS
AT THE SFC. WILL CARRY GUSTS TO 20KT THROUGH THE EVENING...BUT IT
IS POSSIBLE THAT GUSTS COULD BE CLOSER TO 25 KT OR SLIGHTLY HIGHER
TOMORROW NIGHT.

KREIN

//ORD AND MDW CONFIDENCE...UPDATED 14Z...

* HIGH CONFIDENCE IN AN EAST TO SOUTHEAST WIND DIRECTION THROUGH
  MUCH OF THE AFTERNOON. MEDIUM-HIGH CONFIDENCE IN TIMING OF
  SPEEDS TOPPING 10 KT. MEDIUM CONFIDENCE IN TIMING OF SHIFT TO
  SOUTHERLY WINDS.

* HIGH CONFIDENCE IN A LULL IN PRECIP THROUGH THE MORNING WITH
  MEDIUM-HIGH CONFIDENCE IN INCREASING SHRA CHANCES THROUGH THE
  AFTERNOON. LOW-MEDIUM CONFIDENCE IN HOW MUCH COVERAGE THERE WILL
  BE THIS AFTERNOON.

* MEDIUM-HIGH CONFIDENCE THAT TSRA POTENTIAL IS MINIMAL THROUGH
  MID AFTERNOON AND THAT IT INCREASES SLIGHTLY THIS EVENING AND
  MORESO TONIGHT.

MDB

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

MONDAY NIGHT...CHANCE OF SHRA/TSRA. MVFR POSSIBLE. GUSTY
SOUTHWEST WINDS.

TUESDAY...SHRA LIKELY/CHANCE TSRA. GUSTY SOUTHWEST WINDS.

WEDNESDAY...CHANCE OF SHRA/TSRA EARLY. WEST WINDS TURNING EAST.

THURSDAY...CHANCE SHRA/SLIGHT CHANCE TSRA. SOUTHEAST WINDS.

FRIDAY...CHANCE SHRA/SLIGHT CHANCE TSRA. SOUTHWEST WINDS.

SATURDAY...CHANCE SHRA. EAST WINDS.

KREIN

&&

.MARINE...
244 AM CDT

WARM/MOIST AIR WILL BE STEADILY LIFTING NORTH OVER THE
LAKE LATER TODAY AND CONTINUE THROUGH EARLY NEXT WEEK. THIS WILL
LIKELY ALLOW AREAS OF FOG TO DEVELOP...AND COULD BECOME DENSE AT
TIMES.

THE GRADIENT QUICKLY INCREASES LATE TONIGHT FROM THE
SOUTHWEST/SOUTH...WITH GUSTS NEARING 25-30KT FOR THE NEARSHORE
WATERS OF IL/IN THROUGH MON NIGHT. AS A RESULT HAVE HOISTED A SMALL
CRAFT ADVISORY FOR MON/MON NIGHT. WITH GUIDANCE TRENDING UP ON
GUSTS...IT IS POSSIBLE WE MAY SEE A GALE FORCE GUSTS OR TWO OCCUR
MON AFTERNOON IN THE IL/IN NEARSHORE WATERS. THEN ANOTHER WAVE WILL
LIFT NORTH TUE AND COULD BRING GUSTY WINDS YET AGAIN TO THE
NEARSHORE WATERS. EXPECT THE GUSTS NOT TO PUSH OUT FAR OVER THE OPEN
WATERS AS THE WATER REMAINS MUCH COLDER...WHICH WILL LIKELY ALLOW A
STABLE MARINE LAYER TO DEVELOP AND LIMIT HOW MUCH MIXING CAN OCCUR
FROM THE WINDS ALOFT TO THE SFC. IN ADDITION THIS WILL LIKELY LIMIT
HOW LARGE THE WATERS WILL BUILD.

BEACHLER

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
     LMZ745...4 AM MONDAY TO 4 AM TUESDAY.

&&

$$

VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)

FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.