Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 070305
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
905 PM CST FRI MAR 6 2015

.UPDATE...
823 PM CST

NO REAL CHANGES TO GOING FORECAST THIS EVENING WITH QUIET
CONDITIONS TO PERSIST...MAINLY ADJUSTING SKY AND TEMP TRENDS
OVERNIGHT. AS UPSTREAM SHORTWAVE ENERGY DROPS SOUTHEAST ACROSS THE
REGION TONIGHT...SURFACE TROUGH/FRONTAL BOUNDARIES WILL APPROACH
FROM THE NORTHWEST. THIS COINCIDING WITH ONGOING WAA WILL HELP
KEEP TEMPS NEARLY STEADY THROUGH LATE EVENING...UNTIL TEMPS SLOWLY
RISE THROUGH EARLY SATURDAY MORNING. UPSTREAM ENERGY WILL PROVIDE
AN INCREASE IN MID/HIGH LEVEL MOISTURE LATER TONIGHT INTO SATURDAY
BUT WITH CONDITIONS EXPECTED TO REMAIN DRY. DESPITE SOME GUIDANCE
INDICATING A BRIEF DURATION OF SOME DECENT FORCING CLOSER TO THE
12Z TIME FRAME ACROSS NORTHERN ILLINOIS...DRIER LOW LEVELS WILL
LIMIT ANY PRECIP DEVELOPMENT. IF ANYTHING WERE TO OCCUR...IT WOULD
BE ISOLATED FLURRIES EARLY SATURDAY MORNING.

RODRIGUEZ

&&

.SHORT TERM...
305 PM CST

THROUGH SUNDAY...

ONLY MINOR WEATHER CONCERN IN SHORT TERM IS WITH A
FRONTOGENETICALLY DRIVEN DISTURBANCE THAT WILL MOVE ACROSS THE
AREA ON SUNDAY. STRONG WESTERLY WARM ADVECTION WILL OCCUR ALOFT
TONIGHT. WHILE SOUTHWESTERLY WINDS WILL BE STEADY...THEY SHOULDNT
BE TOO STRONG TO PRECLUDE MODEST COOLING AT THE SURFACE MAINLY
AWAY FROM CHICAGO THROUGH PART OF THE OVERNIGHT...FOLLOWED BY A
RISING TREND TOWARD DAYBREAK. ONLY EXPECTING MID AND HIGH CLOUD
COVER TO DEVELOP TONIGHT AND HAVE DISCOUNTED THE STRATUS CLOUDS
GENERATED BY NAM/WRF GUIDANCE AS PER REGIONAL OBS.

A COLD FRONT TRAILING FROM LOW PRESSURE MOVING THROUGH THE
NORTHERN LAKES ON SATURDAY WILL CROSS THE AREA BY THE
AFTERNOON...BUT BETTER COOLING ALOFT WILL NOT ARRIVE UNTIL THE
EVENING. SOME HEATING ENERGY TOMORROW WILL GO TOWARD MELTING THE
SNOWPACK...THOUGH PROGGED 925 MB TEMPS SHOULD GENERALLY SUPPORT
LOWER 40S FOR HIGHS...WITH MID 40S POSSIBLE IN SOUTHERN CWA. MID
40S ARE FAVORED OVER THE CHICAGO HEAT ISLAND...WHILE SOME
LOCATIONS IN NORTH CENTRAL IL MAY NOT BREAK OUT OF THE UPPER 30S.
AN UPPER DISTURBANCE WILL MOVE ACROSS THE AREA ALONG WITH THE COLD
FRONT...BUT CLOUDS SHOULD BE MAIN INFLUENCE. HAVE MAINTAINED A DRY
FORECAST ON SATURDAY...THOUGH CANNOT COMPLETELY RULE OUT A SHOWER
OR SPRINKLE...WHICH HAS NOT BEEN MENTIONED IN THE GRIDS YET. WEAK
GRADIENT AND MOSTLY CLEAR/PARTLY CLEAR SKIES SATURDAY EVENING WILL
ENABLE TEMPS TO DROP OFF TO UPPER TEENS TO MID 20S...COOLEST WEST
OF FOX VALLEY. INCREASING CLOUDS WILL ARRIVE IN ADVANCE OF
AFOREMENTIONED FGEN DRIVEN DISTURBANCE DURING THE OVERNIGHT.

GUIDANCE INDICATES DECENT 850 MB AND 700 MB FGEN TRANSLATING
ACROSS THE AREA ON SUNDAY...BUT IN A WEAKENING PHASE. GGEM SEEMS
TOO BULLISH ON PRECIP COVERAGE/INTENSITY...WITH ECMWF SIMILAR IN
PATH OF THE FORCING WHILE GFS IS SLOWER AND FARTHER SOUTH. HAVE
GONE WITH SLIGHT TO LOW CHANCE POPS MAINLY NORTH OF INTERSTATE
80...BUT CONFIDENCE REMAINS FAIRLY LOW GIVEN POSITION/DIFFERENCES
AND NAM/SREF FAVORING A DRY FORECAST. SUSPECT THERE WILL BE PRECIP
AROUND GIVEN DECENT FGEN...THOUGH AM NOT TOO EXCITED WITH IT.
PTYPE WOULD LIKELY BE MAINLY LIGHT SNOW IN THE MORNING AND THEN
POSSIBLY A LIGHT RAIN/LIGHT SNOW MIX IN AFTERNOON IF PRECIP OCCURS
AS TEMPS WARM TO MID 30S TO AROUND 40.

RC

&&

.LONG TERM...
323 PM CST

SUNDAY NIGHT THROUGH FRIDAY...

SPRING LIKE TEMPERATURES FOR AT LEAST A PORTION OF THE AREA
CONTINUE TO BE FAVORED TUESDAY THROUGH FRIDAY...THOUGH OPERATIONAL
GUIDANCE OFFERS SOME UNCERTAINTY TODAY ON TIMING OF A POSSIBLE
BACK DOOR COLD FRONT IN THE MID TO LATE WEEK PERIOD. THERE WILL BE
LITTLE TO NO THREAT OF PRECIP UNTIL BEYOND DAY 7.

MAINLY CLEAR SKIES AND LIGHT TO CALM WINDS SUNDAY NIGHT WILL
ENABLE FAIRLY CHILLY CONDITIONS DESPITE WAA ALOFT. STRONG MARCH
SUN AND WAA WILL OVERCOME LIMITED MIXING TO RESULT IN HIGHS IN THE
LOWER TO MID 40S. DEPENDING ON HOW MUCH SNOW COVER REMAINS...TEMPS
ON TUESDAY COULD BE WARMER THAN LOWER-MID 50S IN CURRENT FORECAST
BASED ON 925 MB TEMPS OF +7 TO +8 CELSIUS. LOW-MID LEVEL TEMPS
WILL REMAIN MILD ON WEDNESDAY THROUGH FRIDAY AS A FAIRLY STRONG
MID LEVEL RIDGE DEVELOPS OVER THE CENTRAL CONUS. STAYED SOMEWHAT
CONSERVATIVE WITH HIGHS...WITH 12Z ECMWF STILL INDICATING
POTENTIAL TO MAKE A RUN FOR 60S ON WEDNESDAY. UNCERTAINTY CREPT IN
REGARDING A WEAK BACK DOOR COLD FRONT THAT COULD DROP SOUTH
SOMETIME IN THE WEDNESDAY-THURSDAY TIMEFRAME. EARLIER TIMING OF
FRONT...IF IT OCCURS...WOULD INTRODUCE SHARP COOLING LATER
WEDNESDAY...WHILE LATER TIMING WOULD KEEP THE COOLING CONFINED TO
THURSDAY...ESPECIALLY NEAR THE LAKE. THIS WILL BE THE MAIN FEATURE
OF NOTE TO WATCH UNTIL NEXT WEEKEND...WHEN A SLOW MOVING SYSTEM
MAY BE LIFTING NORTHWARD FROM THE GULF OF MEXICO.

RC

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 03Z...

* SOUTHWEST WINDS TURNING WEST SATURDAY AFTERNOON. GUSTS AROUND 20
  KT THROUGH THE DAY.

MDB

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

SOUTHWESTERLY WINDS WILL EASE UP THIS EVENING WITH GUSTS
DIMINISHING. LOW PRESSURE WILL PASS NORTH OF THE AREA SATURDAY
AFTERNOON WHICH WILL BRING A SHIFT TO WEST WINDS TO THE TERMINALS.
VFR IS EXPECTED TO CONTINUE BUT WILL PROBABLY SEE SOME LOWERING OF
CIGS TO AROUND 10 KFT LATE TONIGHT THROUGH DAYBREAK BEFORE THEY
SHIFT OFF TO THE EAST.

MDB

//ORD AND MDW CONFIDENCE...UPDATED 03Z...

* HIGH CONFIDENCE IN ALL FORECAST ELEMENTS.

MDB

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

SUNDAY...VFR. LOW CHANCE RAIN/SNOW. SOUTHWEST WINDS.

MONDAY THROUGH WEDNESDAY...VFR. SOUTHWEST WINDS.

THURSDAY...VFR. EASTERLY WINDS.

MDB

&&

.MARINE...
159 PM CST

LOW PRESSURE SHIFTING EASTWARD ACROSS JAMES BAY THIS AFTERNOON IS
SUPPORTING 30 KT SOUTHERLY WINDS OVER MUCH OF THE LAKE.
HOWEVER...WIND SPEEDS WILL GRADUALLY EASE THIS EVENING AS THE LOW
CONTINUES EASTWARD ACROSS NORTHERN QUEBEC. A SECOND AREA OF LOW
PRESSURE WILL TRACK EASTWARD OVER THE UPPER GREAT LAKES REGION ON
SATURDAY. THIS LOW SHOULD RESULT IN ANOTHER UPTAKE IN WIND
SPEEDS...ESPECIALLY FOLLOWING A COLD FRONTAL PASSAGE SATURDAY
AFTERNOON. THE NEXT BOUT OF STRONGER WINDS OVER THE LAKE LOOKS TO BE
MONDAY NIGHT INTO TUESDAY...WHEN ANOTHER LOW ACROSS SOUTHERN CANADA
SUPPORTS SOME STOUT SOUTHWESTERLY WINDS.

KJB

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...NEARSHORE WATERS
     UNTIL 4 AM SATURDAY.

&&

$$

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