Area Forecast Discussion
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000
FXUS63 KLOT 251527
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1027 AM CDT SAT APR 25 2015

.UPDATE...
1014 AM CDT

ONLY MINOR CHANGES/UPDATES TO POPS THIS MORNING INTO THE
AFTERNOON...WITH SHOWERS TO PERSIST ACROSS MUCH OF NORTHERN
ILLINOIS AND NORTHWEST INDIANA THROUGH MID AFTERNOON. OUTSIDE OF
THE FAR NORTHERN TIER OF COUNTIES...SHOWERS ARE ONGOING OVER MUCH
OF THE CWA WITH MAYBE A RUMBLE OF THUNDER POSSIBLY BEING OBSERVED
OVER PORTIONS OF EAST CENTRAL ILLINOIS WELL SOUTH OF I80. THIS IS
OCCURRING AS UPPER LEVEL CENTER SLOWLY SHIFTS EAST INTO THE MID
MISSISSIPPI VALLEY AND SEVERAL VORT LOBES SWING ACROSS THE REGION.
SEVERAL OTHER ONGOING FORCING MECHANISMS OWING TO
FRONTOGENESIS/WAA ACROSS THE CWA WILL AID IN CONTINUED SHOWER
DEVELOPMENT THROUGH THE EARLY AFTERNOON...WITH SOME SLIGHT
NORTHWARD PUSH OF THIS PRECIP SHIELD INTO THE NORTHERN TIER OF
COUNTIES. AS THIS UPPER LEVEL SYSTEM SHIFTS EAST ACROSS THE
REGION TODAY...EXPECT PRECIP TO DIMINISH FROM NORTHWEST TO
SOUTHEAST INTO THE LATE AFTERNOON. BEST INSTABILITY REMAINS SOUTH
OF THE CWA AND WILL REMAIN THIS WAY FOR THE REMAINDER OF THE DAY.
HOWEVER...STEEPER MID LEVEL LAPSE RATES OVER THE SOUTHERN CWA
COULD ALLOW FOR CONTINUED RUMBLES OF THUNDER TODAY.

RODRIGUEZ

&&

.SHORT TERM...
306 AM CDT

THROUGH SATURDAY NIGHT...

MAIN FORECAST CONCERNS THIS MORNING WILL BE DEALING WITH PRECIP
CHANCES THROUGH THE DAY TODAY.

LOW PRESSURE IS MOVING ACROSS EASTERN KS/NE THIS MORNING IS PROGGED
TO DRIFT ESE ACROSS THE MID MISSISSIPPI VALLEY THIS EVENING. WARM
ADVECTION WING IS IN PLACE ACROSS MUCH OF ILLINOIS THIS MORNING AND
WILL RESULT IN SCATTERED SHOWERS THROUGH AROUND DAYBREAK BEFORE THE
FORCING SHIFTS OFF TO THE EAST. HOWEVER...MORE WIDESPREAD RAIN WILL
MOVE INTO THE REGION FROM THE SOUTHWEST MID MORNING INTO THE
AFTERNOON AS F-GEN BAND SETS UP ACROSS PORTIONS OF NORTHERN ILLINOIS
AND NORTHWEST INDIANA. THERE HAS BEEN A NOTABLE SHIFT SOUTH IN THE
GUIDANCE OVER THE PAST 24 HOURS WITH WHERE THIS BAND WILL SET UP
AND HAVE ADJUSTED POPS ACCORDINGLY. NAM IN PARTICULAR HAS A SHARP
CUTOFF BETWEEN THE I-88 AND I-90 CORRIDORS...AS COMPARED TO THE
GFS/ECMWF WHICH STILL BRING PRECIP UP PAST THE STATELINE. HAVE
HIGHEST POPS SOUTH OF I-90 BUT AM NOT AS BULLISH AS THE NAM AS FAR
AS THE NORTHERN CUTOFF ON PRECIP AND MAINTAIN HIGH CHANCE-LIKELY
POPS UP THROUGH THE STATE LINE. INSTABILITY IS PRETTY
MEAGER...MAINLY SOUTH OF A ROCKFORD TO RENSSELAER LINE THIS
MORNING...THEN MAINLY ALONG THE SOUTHERN TIER OF COUNTIES LATE
MORNING INTO EARLY AFTERNOON. GIVEN THE WEAK THERMODYNAMICS EXPECT
ANY LIGHTNING ACTIVITY TO REMAIN ISOLATED. F-GEN SHIFTS EAST OF
THE REGION AFTER AROUND 00Z THIS EVENING WITH MID LEVEL HEIGHT
RISES BUILDING IN BEHIND SHUTTING DOWN PRECIP.

IN ADDITION TO THE PRECIP...MODERATE NORTHEAST WINDS WILL BE IN
PLACE TODAY AS THE GRADIENT TIGHTENS NORTH OF THE LOW TRACK WITH
GUSTS OF 25 TO 30 MPH AT TIMES. COLD ADVECTION...CLOUD COVER...AND
RAIN WILL NOT ALLOW MUCH WARMING TODAY WITH TEMPERATURES ONLY
EXPECTED TO TOP OUT IN THE MID TO UPPER 40S. NORTHEAST WINDS REMAIN
BREEZY OVERNIGHT WITH TEMPS FALLING INTO THE MID TO UPPER 30S.

DEUBELBEISS

&&

.LONG TERM...
306 AM CDT

SUNDAY THROUGH FRIDAY...

OVERALL A RELATIVELY QUIET STRETCH OF WEATHER IS EXPECTED SUNDAY
THROUGH THE UPCOMING WEEK. HIGH PRESSURE BUILDS FROM THE CANADIAN
PRAIRIES INTO THE UPPER MIDWEST SUNDAY DRIVING H85 TEMPS DOWN TO
AROUND 0C TO -2C THOUGH THESE TEMPS WILL MODERATE TO +3 TO 4C BY
MIDWEEK BY LATE APRIL INSOLATION. THIS WARMING TREND WILL
TRANSLATE DOWN TO THE SURFACE AS WELL WITH TEMPS ONLY IN THE
MID/UPPER 50S AWAY FROM THE LAKE SUNDAY TO MID/UPPER 60S BY
WEDNESDAY. PERSISTENT N/NE FLOW WILL KEEP CONDITIONS COOLER NEAR
THE LAKE FRONT ALL OF NEXT WEEK AND ALLOW LAKE BREEZES TO PUSH
INLAND.

SURFACE PATTERN THROUGHOUT MUCH OF THE WEEK HAS WEAK RIDGING IN
PLACE ACROSS THE UPPER MIDWEST/GREAT LAKES WHICH WILL GREATLY LIMIT
PRECIP CHANCES. BOTH THE ECMWF AND GFS SHOW AN UPPER LEVEL
DISTURBANCE DIGGING INTO THE REGION WEDNESDAY THOUGH WITH PWATS OF
ONLY AROUND HALF AN INCH AND SOUNDINGS INDICATING NEGLIGIBLE
INSTABILITY...PREFER TO LEAN ON THE DRY GFS SOLUTION...THOUGH WILL
MAINTAIN SOME SLIGHT CHC POPS. THE TRACK OF THE UPPER WAVE DIVERGES
AFTER MIDWEEK RESULTING IN SOME DECENT DISAGREEMENT IN THE THERMAL
FIELDS OF THE MODELS THURSDAY AND FRIDAY RESULTING IN LOWER THAN
AVERAGE CONFIDENCE IN TEMPS THOSE DAYS.

DEUBELBEISS

&&

.AVIATION...

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

* FAIRLY STOUT EASTERLY WINDS TODAY.
* RAIN THROUGH MID AFTERNOON WITH A PERIOD OF LOWER MVFR CIGS AND
  VISIBILITY LIKELY LATER THIS MORNING INTO THE EARLY AFTERNOON.
  TEMPORARY IFR VISIBILITY POSSIBLE NAMELY AT MDW.

MTF/KJB

//DISCUSSION...UPDATED 12Z...

LOW PRESSURE OVER EASTERN KANSAS WILL SHIFT EASTWARD ACROSS THE
LOWER MISSOURI VALLEY TODAY...AND TO THE OHIO VALLEY BY THIS
EVENING. THIS SYSTEM WILL CONTINUE TO PRODUCE GUSTY EASTERLY WINDS
TODAY...THEN BECOMING MORE NORTH-NORTHEAST BY LATER THIS EVENING
INTO SUNDAY. CONFIDENCE IN THE WIND FORECAST CONTINUES TO BE
FAIRLY HIGH.

LIGHT RAIN SHOWERS ARE GRADUALLY INCHING THEIR WAY NORTHWARD
TOWARDS THE TERMINALS EARLY THIS MORNING. THESE SHOWERS HAVE BEEN
DISSIPATING A BIT AS THEY MOVE NORTHWARD OUT OF THE MORE FAVORABLE
MOISTURE. HOWEVER...PERIODS OF LIGHT RAIN STILL LOOK TO BE A
DECENT BET ACROSS THE AREA INTO MID AFTERNOON. WE EXPECTED THE
BETTER FOCUS FOR MORE MODERATE RAIN TO REMAIN MAINLY SOUTH OF THE
TERMINALS. WITH THE FARTHER SOUTH FOCUS OF THE BETTER RAIN...CIGS
NO LONGER APPEAR THAT THEY WILL FALL INTO THE IFR OR LIFR CATEGORY
DUE TO THE PRESENCE OF A CONTINUED EASTERLY LOWER LEVEL FLOW OF
SLIGHTLY DRIER AIR.

ANY LOWER CIGS THAT DEVELOP OVER THE AREA TODAY SHOULD IMPROVE
EITHER BY LATER THIS AFTERNOON...OR BY EARLY THIS EVENING AS DRIER
AIR WORKS BACK OVER THE REGION.

KJB

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

* MED-HIGH WITH WIND FORECAST.
* HIGH WITH RAIN OVER THE TERMINALS.
* MED-HIGH WITH CIG AND VISIBILITY FORECAST.

MTF/KJB

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

SUNDAY NIGHT...VFR. NORTH-NORTHEAST WINDS.

MONDAY...VFR. NORTHEAST WINDS.

TUESDAY...VFR. NORTHEAST WINDS BECOMING EAST.

WEDNESDAY...SLGT CHC -RA. BRIEF MVFR POSSIBLE. NORTH-NORTHWEST
WINDS BECOMING NORTHEAST.

THURSDAY...VFR. NORTH-NORTHEAST WINDS.

FRIDAY...VFR.

KJB

&&

.MARINE...
210 AM CDT

THE MAIN WEATHER CONCERNS OVER LAKE MICHIGAN WILL BE TODAY THROUGH
SUNDAY. AN AREA OF LOW PRESSURE WILL SHIFT EASTWARD FROM THE CENTRAL
PLAINS ACROSS THE CENTRAL MISSISSIPPI VALLEY TODAY...THEN OVER THE
THE OHIO VALLEY TONIGHT. OVERALL...THIS WILL RESULT IN SOME STRONGER
EAST-NORTHEASTERLY WINDS TODAY...FOLLOWED BY NORTHERLY WINDS LATER
TONIGHT INTO SUNDAY. WIND SPEEDS LOOK TO GENERALLY BE UP TO AROUND
25 KT THROUGH THE PERIOD. HOWEVER...THE ONSHORE COMPONENT TO THESE
WINDS COULD RESULT IN LARGER WAVES UP TO AROUND OR A BIT ABOVE 4
FEET ALONG THE ILLINOIS AND INDIANA NEAR SHORE WATERS THROUGH THE
WEEKEND.

THE WEATHER PATTERN FOR MUCH OF NEXT WEEK LOOKS TO FEATURE A RATHER
WEAK PRESSURE GRADIENT OVER THE REGION AS HIGH PRESSURE DOMINATES.
THIS SHOULD RESULT IN A VERY WEAK WIND REGIME FOR MUCH OF THE
PERIOD...AND HENCE WIND SPEEDS AND DIRECTIONS WILL LIKELY BE LARGELY
DRIVEN BY LAKE AND LAND BREEZE INFLUENCES.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 10 AM MONDAY.

&&

$$

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