Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 261953
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
253 PM CDT SUN APR 26 2015

.SHORT TERM...
252 PM CDT

THROUGH TUESDAY...

A QUIET WEEK OF WEATHER IS STILL SET TO UNFOLD WITH A
QUASI-BLOCKED PATTERN DURING THE FIRST HALF OF THE WEEK KEEPING
SYSTEMS FROM IMPACTING THE AREA...AND THEN ONLY GRADUAL
MOISTENING OF THE ATMOSPHERE DURING THE LATTER PART. FOR
TONIGHT...THE SURFACE HIGH CENTER WILL BE POISED FROM ONTARIO
THROUGH THE TWIN CITIES...WITH STILL A LIGHT GRADIENT ACROSS THE
FORECAST AREA. THIS SHOULD RESULT IN SOME WIND ACROSS THE CHICAGO
METRO AND INTO NORTHWEST INDIANA. AS FOR NORTH CENTRAL
ILLINOIS...WIND SPEEDS WILL LIKELY FALL OFF TO NEAR OR CALM BY
LATE EVENING AS AN INVERSION SETS UP. AFTERNOON DEW POINTS AND
TEMPERATURE TRENDS UPSTREAM LAST NIGHT WOULD SUPPORT LOWER TO MID
30S AND HAVE GENERALLY GONE WITH THAT...WHICH LINES UP WELL WITH
BIAS-CORRECTED GUIDANCE. THE COLLABORATIVE DECISION WITH
NEIGHBORING WFOS WAS TO HOLD OFF ON A FROST ADVISORY HEADLINE FOR
NORTHWEST...NORTH CENTRAL...AND CENTRAL ILLINOIS...BUT SOME FROST
IS STILL EXPECTED AND IN THE FORECAST FOR OUTLYING AREAS WEST OF
I-57.

THE SYNOPTIC GRADIENT WILL EASE FURTHER MONDAY AND ESPECIALLY MONDAY
NIGHT INTO TUESDAY. ONSHORE FLOW WILL BE SEEN MONDAY AND THEN MORE
OF A TRUE LAKE BREEZE PUSH IS LIKELY ON TUESDAY. THE CLIMATOLOGICAL
TEMPERATURE DIFFERENCE BETWEEN LAKESIDE AND THE FAR WEST/SOUTHWEST
METRO FOR AN ALL-DAY ONSHORE FLOW IN LATE APRIL IS AROUND 10
DEGREES...WITH SLIGHTLY LESS ON A LAKE BREEZE DAY. THOSE TRENDS
WERE CAPTURED WELL BY THE PREVIOUS FORECAST...SO HAVE MADE LITTLE
CHANGES. TEMPERATURES SHOULD BE FAIRLY SIMILAR MONDAY AS TO
TODAY...WITH AN OVERALL MODERATION ON TUESDAY INTO WEDNESDAY.

MTF

&&

.LONG TERM...
252 PM CDT

TUESDAY NIGHT THROUGH SUNDAY...

UPPER RIDGING WILL MOVE OVER THE AREA TUESDAY AND BASICALLY BE
HELD IN PLACE WITH A DEEP CLOSED LOW DOWNSTREAM OFF THE NEW
ENGLAND COAST. THIS WILL DOMINO EFFECT TO WEAKENING A COLD FRONT
APPROACHING THE AREA WEDNESDAY. HAVE CONTINUED THE FORECAST DRY IN
THAT TIME PERIOD. TEMPERATURES LOOK TO RE-MODERATE ON FRIDAY INTO
THE WEEKEND WITH GLOBAL MODELS INDICATING HEIGHTS AND 850/925MB
TEMPERATURES ABOVE EARLY MAY NORMALS. RIGHT NOW CONFIDENCE IS
INCREASING ON HIGHS IN THE 70S AT LEAST FOR ONE OR TWO DAYS IN
THAT FRIDAY-SUNDAY PERIOD. DEPENDING ON HOW STRONG SOUTHERLY FLOW
MATERIALIZES...THEN THE WARMTH MAY REACH ALL THE DAY TO THE LAKE
SHORE / DOWNTOWN CHICAGO. THE ATMOSPHERE LOOKS TO MOISTEN INTO THE
WEEKEND BUT SLOWLY IN A QUASI-ZONAL FLOW.

MTF

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 20Z...

* NORTHEAST WINDS AT/ABOVE 10 KT.

* POTENTIAL FOR MVFR CEILINGS MONDAY MORNING.

RODRIGUEZ

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

QUIET/DRY CONDITIONS EXPECTED FOR THE FORECAST PERIOD AS HIGH
PRESSURE IN PLACE WILL REMAIN SITUATED ACROSS THE REGION.
GENERALLY CLEAR SKIES TODAY INTO TONIGHT COULD TRANSITION OVER TO
A PERIOD OF MVFR CEILINGS MONDAY MORNING. IF THIS WERE TO
OCCUR...THESE WOULD LIKELY CONTINUE INTO THE AFTERNOON AND BE
AROUND 2500 FT. NORTHEAST WINDS TODAY WILL CONTINUE AND DIMINISH
OVERNIGHT...BUT INCREASE ONCE AGAIN EARLY MONDAY MORNING.

RODRIGUEZ

//ORD AND MDW CONFIDENCE...UPDATED 20Z...

* HIGH CONFIDENCE WITH WIND SPEED/DIRECTION.

* LOW CONFIDENCE WITH MVFR CEILINGS MONDAY MORNING.

RODRIGUEZ

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

MONDAY NIGHT THROUGH THURSDAY...PRIMARILY VFR. NORTH-NORTHEAST
WINDS.

FRIDAY...VFR. CHANCE OF SHOWERS FRIDAY NIGHT SOUTHWEST WINDS.

SATURDAY...VFR. SOUTHWEST WINDS.

KJB

&&

.MARINE...
126 AM CDT

THE COMBINATION OF A SURFACE RIDGE OF HIGH PRESSURE OVER ONTARIO AND
THE UPPER MIDWEST AND LOWER PRESSURE OVER THE EASTERN LAKES
REGION...WILL CONTINUE TO RESULT IN A MODERATE NORTHERLY WIND UP
AROUND 25 KT TODAY THROUGH MONDAY. THIS WILL PARTICULARLY BE THE
CASE OVER THE SOUTHERN HALF OF THE LAKE. THE SURFACE GRADIENT WILL
WEAKEN CONSIDERABLE LATER MONDAY AND TUESDAY AS THE SURFACE RIDGE OF
HIGH PRESSURE SETS UP OVER THE LAKES REGION. THIS SHOULD RESULT IN A
WEAK WIND REGIME THROUGH AT LEAST MIDWEEK OVER THE LAKE.
THEREFORE...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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