Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 262338
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
638 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 00Z...

* NORTH-NORTHEAST WINDS DIMINISHING BELOW 10 KT EARLY THIS
  EVENING...AND INCREASING NEAR 15 KT WITH A FEW HIGHER GUSTS
  MID/LATE MORNING MONDAY.

* POTENTIAL FOR BRIEF PERIOD OF HIGH-END MVFR CEILINGS MONDAY
  MORNING-EARLY AFTERNOON.

RATZER

//DISCUSSION...UPDATED 00Z...

TERMINALS WILL REMAIN SOUTHEAST OF SURFACE HIGH PRESSURE OVER
ONTARIO AND THE UPPER MIDWEST THROUGH THE TAF PERIOD. SIMILAR WIND
TREND EXPECTED MONDAY AS TODAY...THOUGH LIKELY A LITTLE LOWER
SPEED/GUSTS. LIGHT WINDS OVERNIGHT MAY SHIFT TO 340-350 DEG...BUT
EXPECTED TO BE PRIMARILY NORTH-NORTHEAST DURING DAYTIME HOURS.

PRIMARILY VFR CONDITIONS EXPECTED THROUGH THE PERIOD...THOUGH LOW
LEVEL MOISTURE WRAPPING SOUTH AROUND LOW PRESSURE SYSTEM OFF NEW
ENGLAND COAST WILL SWIPE AREA MONDAY AND MAY PRODUCE BRIEF PERIOD
OF HIGH-END MVFR CEILINGS MONDAY MORNING/EARLY AFTERNOON...THOUGH
FORECAST SOUNDINGS INDICATE FAIRLY SHALLOW MOIST LAYER WITH LOW
CONFIDENCE IN A PERSISTENT CEILING OVER TERMINALS. CLOUDS LIKELY
LIFT TO VFR ESPECIALLY INLAND IN THE AFTERNOON...AND SCATTER BY
MONDAY EVENING.

RATZER


//ORD AND MDW CONFIDENCE...UPDATED 00Z...

* LOW IN MVFR CIGS MONDAY...THOUGH HIGH ANY CIG WILL BE ABOVE
  1500 FT.

* HIGH ALL OTHER ELEMENTS.

RATZER

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

TUESDAY THROUGH THURSDAY. PRIMARILY VFR. NORTH-NORTHEAST WINDS.

FRIDAY...VFR. CHANCE OF SHOWERS FRIDAY NIGHT. SOUTHWEST WINDS
BECOMING EAST IN THE AFTERNOON.

SATURDAY...VFR. SOUTHWEST WINDS BECOMING SOUTHEAST IN THE
AFTERNOON.

RATZER

&&

.MARINE...
257 PM CDT

NORTHERLY WINDS WILL CONTINUE OVER THE OPEN WATER AS WELL AS
ONSHORE FLOW IN ILLINOIS AND INDIANA NEARSHORE AREAS THROUGH THE
WEEK. WINDS LOOK TO HOLD STEADY INTO THIS EVENING AND MAYBE EVEN
INTO OVERNIGHT. WITH THE FLOW HAVING BEEN NORTHERLY OVER THE LONG
FETCH OF THE LAKE...WILL CONTINUE THE SMALL CRAFT ADVISORY AT
LEAST FOR WAVES AND OCCASIONALLY FOR GUSTS THROUGH TONIGHT AND
INTO EARLY MONDAY MORNING. HIGH PRESSURE WILL GENERALLY PREVAIL
THROUGH MIDWEEK BEFORE SOUTHERLY FLOW KICKS IN EITHER LATE IN THE
WEEK OR MORE LIKELY NEXT WEEKEND.

MTF

&&

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

&&

$$

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