Area Forecast Discussion
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000
FXUS63 KLOT 170908
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
408 AM CDT THU APR 17 2014

.DISCUSSION...
257 AM CDT

QUIESCENT WEATHER IS SET TO CONTINUE INTO THIS WEEKEND WITH AN
ENJOYABLE WEEKEND SHAPING UP IF YOU ARE A FAN OF 60S AND
POTENTIALLY 70S BY SUNDAY. THESE TEMPERATURES WERE THE PRIMARY
FORECAST CHALLENGE THIS MORNING.

SYNOPSIS...
THE MAIN ROSSBY WAVE ON THIS SIDE OF THE GLOBE IS RETRACTING
NORTHEAST FROM EASTERN CANADA WITH STILL LOW HEIGHTS AND A BROAD
BUT LOW AMPLIFIED TROUGH LEFT IN ITS WAKE ACROSS SOUTHERN CANADA
AND THE CENTRAL CONUS. WITHIN THAT FEATURE THERE ARE MULTIPLE
PERTURBATIONS WITH THE MOST WELL-DEFINED CIRCULATION ACROSS THE
UPPER GREAT LAKES AND RESPONSIBLE FOR OVER A FOOT OF SNOW FOR
PARTS OF THE TWIN CITIES INTO NORTHERN WI YESTERDAY INTO LAST
NIGHT. A NARROW PLUME OF MID-LEVEL PACIFIC MOISTURE ASSOCIATED
WITH THIS WAVE IS DRIFTING OVER THE AREA THIS MORNING. THAT IS
MOST OF THE CONTRIBUTION TO MEAGER 0.3 TO 0.4 REGIONAL PWATS
SAMPLED LAST EVE...AS THE LOW-LEVELS REMAIN QUITE DRY AND ACT AS A
HINDRANCE FOR MUCH OR ANY PRECIP ACROSS THE AREA TONIGHT. AT THE
SURFACE...THE SYSTEM LOW IS ENTERING WESTERN WI EARLY THIS MORNING
WITH A SURFACE COLD FRONT EXTENDING SOUTHWARD INTO IA AND MO. THE
BAROCLINICITY AND CONVERGENCE ALONG THIS FRONT WILL WEAKEN
CONSIDERABLY THIS AFTERNOON INTO EVENING AS IT MOVES INTO THE
AREA.

TODAY AND TONIGHT...
CLOUD COVER SHOULD UNDULATE SOME TODAY WITH THE PACIFIC MOISTURE
ALOFT AND SOME LOWER CLOUDS OOZING INTO NORTH CENTRAL IL BEHIND
THE SURFACE COLD FRONT. THERE LIKELY WILL BE A SHARP INCREASE IN
MID/HIGH CLOUDS THIS AFTERNOON FOR AREAS ALONG AND EAST OF
INTERSTATE 55 AS A SHEARING IMPULSE ACROSS WESTERN KS THIS MORNING
APPROACHES THE AREA. THE 850MB/925MB TEMPERATURE CLIMATOLOGY WOULD
SUPPORT UPPER 50S TO MID 60S ACROSS THE AREA...BUT THAT AS USUAL
WILL DEPEND ON DURATION OF SOME OF THE AFOREMENTIONED CLOUD COVER.
OFFSHORE FLOW IS EXPECTED ACROSS DOWNTOWN CHICAGO SO NO LAKE
COOLING TODAY...BUT AS WINDS TURN NORTHERLY THIS EVE AND A LAKE
COMPONENT LIKELY PUSHES INLAND...A FAIRLY QUICK DROP TO AROUND 40
DEGREES COULD OCCUR DURING THE MID TO LATE EVE. MOISTURE AND LIFT
SUPPORT FOR ANY RAIN WITH THE SHEARED WAVE TONIGHT CONTINUES TO
LOOK LESS AND LESS IMPRESSIVE...AND REALLY ONLY FOR AREAS ALONG
AND EAST OF INTERSTATE 55 IS THERE A LOW CHANCE. HAVE REFINED THE
TEMPORAL RESOLUTION SOME...BUT ALL IN ALL THIS IS A LOW CHANCE AND
QPF EVENT.

FRIDAY AND BEYOND...
BUILDING UPPER HEIGHTS OVER SURFACE RIDGING WILL BE SEEN ON FRIDAY.
THE LIGHT SURFACE FLOW SHOULD ALLOW FOR A SHARP LAKE BREEZE TO
DEVELOP WITH AROUND A 10 DEGREES CONTRAST FROM DOWNTOWN CHICAGO TO
OUTLYING AREAS. MOST OUTLYING AREAS MAY SEE SIMILAR TEMPERATURES TO
THAT OF TODAY.

THEN MODERATION WILL UNFOLD THIS WEEKEND AS GUIDANCE IS IN GOOD
AGREEMENT OF 500MB HEIGHTS ABOVE 570DM AND 850MB TEMPERATURES
CLIMBING TO 6C TO 10C THROUGH THE WEEKEND. THE MAIN JET STREAM
AXIS WILL BE IN SOUTHERN CANADA AND A CLOSED LOW OVER THE
SOUTHEAST U.S. WILL KEEP THE PATTERN LESS PROGRESSIVE AT OUR
LATITUDE THIS WEEKEND THAN ORIGINALLY FORECAST. WE CONTINUE THE
TREND OF THE PREVIOUS SHIFT TO COLLABORATE AN INCREASE IN
TEMPERATURES...NAMELY ON SUNDAY WITH SOUTHERLY FLOW UP TO THE LAKE
FRONT AND LESS CLOUD COVER. CLIMATOLOGY WOULD SUPPORT 70 DEGREE
TEMPERATURES UP TO THE NORTHERN FORECAST AREA AND DEPENDING ON
CLOUD COVER COULD REALIZE EVEN WARMER. THE NEXT SYSTEM IS FORECAST
TO MOVE OVER THE AREA AROUND MONDAY BUT AGAIN CONFIDENCE ON THIS
TIMING IS LOW. DEW POINTS LOOK TO BE UP INTO THE 50S AND POSSIBLY
LOWER/MID 60S WITH THIS PASSAGE...SO AS MENTIONED BEFORE A
POSSIBLE CHANCE FOR THUNDER. BUT THE SYNOPTIC LOOK AND MAGNITUDE
OF THIS SYSTEM WITHIN MODEL GUIDANCE PRESENTLY DOES NOT LOOK
IMPRESSIVE.

MTF

&&

.AVIATION...

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

* SSE WINDS VEERING TO WEST BY MIDDAY THURSDAY...THEN NORTH
  TO NORTHEAST LATE THURSDAY EVENING.
* POTENTIAL FOR LOW LEVEL WIND SHEAR EARLY THURSDAY MORNING.

BMD

//DISCUSSION...UPDATED 06Z...

LOW PRESSURE LIES OVER FAR NORTHEASTERN IOWA TONIGHT AND WILL FILL
AS IT LIFTS TO NORTHERN WISCONSIN BY MID MORNING THURSDAY. A COLD
FRONT STRETCHES SOUTH INTO CENTRAL MISSOURI. AHEAD OF THE
FRONT...STRONG LOW-MID LEVEL WINDS COULD RESULT IN LLWS...WITH THE
BEST CHANCES AT RFD WHICH WILL BE CLOSER IN PROXIMITY TO THE LOW
LEVEL JET. THE COLD FRONT WILL MOVE ACROSS NORTHERN ILLINOIS LATE
MORNING INTO EARLY AFTERNOON WITH PRECIP ALONG THE FRONT FAIRLY
UNLIKELY. WINDS TURN WSW BEHIND THE FRONT AND EVENTUALLY
NORTHWESTERLY IN THE EVENING. WINDS WILL CONTINUE TO VEER TO THE
NORTHEAST THURSDAY NIGHT.

BMD

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

* MEDIUM CONFIDENCE IN WIND DIRECTION/TIMING CHANGES IN DIRECTION.
* LOW CONFIDENCE IN LLWS.

BMD

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

FRIDAY...VFR. WX NIL.

SATURDAY...VFR. WX NIL.

SUNDAY...CHC RAIN. MVFR POSSIBLE.

MONDAY...CHC RAIN EARLY. OTRW...VFR/WX NIL.

TUESDAY...VFR. WX NIL.

WEDNESDAY...SLIGHT CHC RAIN. MVFR POSSIBLE.

KREIN

&&

.MARINE...
313 AM CDT

WEAKENING AREA OF LOW PRESSURE WILL LIFT FROM IOWA INTO WISCONSIN
TODAY WITH MODERATE SOUTHERLY FLOW AHEAD OF THE LOW. A SMALL CRAFT
ADVISORY REMAINS IN EFFECT...PRIMARILY FOR THE ILLINOIS NEARSHORE
WATERS...BUT EXPECT CONDITIONS TO IMPROVE BY MID MORNING AFTER WINDS
TURN WESTERLY AND DIMINISH BEHIND A COLD FRONT. HIGH PRESSURE WILL
BUILD ACROSS THE REGION AND SHOULD KEEP WINDS RELATIVELY LIGHT
FRIDAY THOUGH SATURDAY...THEN WINDS FRESHEN UP SOME SATURDAY NIGHT
INTO SUNDAY AHEAD OF ANOTHER WEAK LOW. OTHERWISE...IT APPEARS THE
NEXT CHANCE FOR MODERATE TO STRONG WINDS WILL BE FROM MIDWEEK ON
NEXT WEEK AS A POTENTIALLY MORE SIGNIFICANT LOW PRESSURE SYSTEM COULD
IMPACT THE REGION.

BMD

&&

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

&&

$$

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