FXUS63 KLOT 050925
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
325 AM CST SUN FEB 5 2012
.DISCUSSION...
324 AM CST
NO SIGNIFICANT WEATHER CONCERNS FOR LATEST FORECAST PACKAGE NOR ANY
MAJOR ADJUSTMENTS TO GOING FORECAST. FOR TODAY...MAIN RIDGE AXIS
EXTENDS FROM CENTRAL PLAINS INTO NORTHERN GREAT LAKES REGION WITH A
SECONDARY RIDGE AXIS EXTENDING ACROSS NORTHERN ILLINOIS INTO
NORTHERN INDIANA. IR IMAGERY SHOWS BACK EDGE OF STRATUS SINKING
SOUTH AND ERODING UNDER ANTICYCLONIC FLOW LEAVING ALL OF CWA UNDER
CLEAR SKIES THIS MORNING...EXCEPT FOR SOME STRATUS BEGINNING TO MOVE
INTO NORTHERN ILLINOIS OFF OF LAKE MICHIGAN. WITH RECENT RAINFALL
ACROSS THE AREA...LIGHT WINDS UNDER RIDGE AXIS...DO EXPECT FOG TO
INCREASE IN COVERAGE THROUGH EARLY MORNING HOURS ACROSS SOUTHERN
PORTIONS OF THE CWA...THOUGH DRIER DEWPOINTS SINKING SOUTH WILL
TEMPER THINGS SOMEWHAT. TEMPERATURE FORECAST TODAY COULD BE SOMEWHAT
COMPLICATED DEPENDING ON HOW LONG FOG LINGERS OR IF AREAS OF STRATUS
TO THE NORTH/NORTHWEST PARK OVER THE FORECAST AREA...BUT ASSUMING WE
MIX OUT QUICKLY TODAY WITH H85 THERMAL TROUGH OVERHEAD...EXPECT
TEMPERATURES TO WARM INTO THE LOW TO MID 40S ACROSS THE AREA.
TONIGHT...MAIN RIDGE AXIS SLIDES SOUTH ACROSS THE AREA WITH LOW
LEVEL INVERSION DEVELOPING. SUSPECT THAT STRATUS/FOG SEEN THIS
MORNING UNDER THE RIDGE AXIS TO THE NORTH WILL BE ABLE TO DEVELOP
ONCE AGAIN TONIGHT...PARTICULARLY IF YOU BUY INTO THE NAM GUIDANCE
WHICH DOESNT HAVE TOO BAD A HANDLE WITH ONGOING STRATUS THIS
MORNING. GFS ON THE OTHER HAND SEEMS TO BE TOO DRY AND KEEPS
WINDS/MIXING A LITTLE TOO HIGH OVERNIGHT...WHICH IN THIS CASE SEEMS
TO BE A PRETTY SURE BET TO DECOUPLE.
MONDAY THROUGH TUESDAY...H85 THERMAL RIDGE MOVES OVERHEAD
MONDAY AND BARRING ANY ISSUES WITH LINGERING STRATUS...EXPECT
TEMPERATURES TO WARM NICELY INTO THE UPPER 40S TO NEAR 50S SOUTH OF
I-80 WITH MOSTLY SUNNY SKIES. THIS WARMUP WILL BE SHORT LIVED AS
COLD FRONT SINKS SOUTH ACROSS THE AREA MONDAY NIGHT. SYSTEM IS
MOISTURE STARVED...THUS WONT CARRY ANY POPS ALONG THE COLD FRONT
MONDAY NIGHT...BUT WITH COLD ADVECTION ON TUESDAY...DO SEE WEAK
INSTABILITY DEVELOP OFF OF LAKE MICHIGAN. OVERALL...DELTA TS ARE
MARGINAL AND INVERSION HEIGHTS ARE RELATIVELY LOW...BUT MAY SEE A
FEW SNOW SHOWERS DEVELOP OFF THE LAKE MOVING INTO NORTHERN ILLINOIS.
WEDNESDAY THOUGH NEXT WEEKEND...MODELS CONTINUE TO ADVERTISE WEST
COAST RIDGE AMPLIFYING WHILE LONGWAVE TROUGH DEVELOPS OVER EASTERN
CONUS WITH ARCTIC AIRMASS DIVING SOUTH...THOUGH HOW FAR SOUTH
REMAINS TO BE SEEN. GFS BRINGS AIR COLDER THAN -20C AT H85 INTO THE
REGION BY SATURDAY...WHILE LATEST ECMWF KEEPS THE BRUNT OF THE COLD
AIR WELL TO THE NORTH. STILL...WITH THE OVERALL PATTERN HAVING SOME
RUN-TO-RUN CONSISTENCY...EXPECT TO SEE TEMPERATURES THAT ARE LEAST
MORE SEASONABLE...IF NOT COLDER THAN NORMAL SHOULD GFS SOLUTION BE
CLOSER TO REALITY...AND MAY SEE THE COOLER TEMPERATURES STICK AROUND
FOR A WHILE IF BLOCKING PATTERN HOLDS UP. BMD
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 09Z...
* POTENTIAL FOR A PERIOD OF IFR/MVFR CIGS THIS MORNING.
* OUTSIDE POSSIBILITY FOR FOG/STRATUS TO MOVE NEAR THE TERMINALS
LATE TONIGHT/EARLY SUNDAY MORNING.
RATZER/RODRIGUEZ
//DISCUSSION...UPDATED 09Z...
AREA OF IFR/MVFR CEILINGS HAVE DEVELOPED ALONG THE WESTERN LAKE
MICHIGAN SHORE AND INTO FAR EAST/SOUTHEAST WISCONSIN EARLY THIS
MORNING. GOES 11-3.9 MICRON IR SATELLITE IMAGERY SHOWS THESE LOW
CLOUDS CONTINUING TO SPREAD SOUTH/SOUTHWEST TOWARD FAR NORTHEAST
IL AT THIS TIME. RECENT HIGH-RES NUMERICAL MODEL GUIDANCE SUGGESTS
THAT THIS TREND WILL CONTINUE THROUGH THE EARLY MORNING HOURS...
EXTRAPOLATION OF SATELLITE IMAGERY SUGGESTING IFR CIGS IN 900-1000
FT RANGE COULD AFFECT KORD BY OR SHORTLY AFTER 10Z OR SO...AND
KMDW BY 1030Z. HAVE THUS AMENDED TAFS TO INDICATE THIS...WITH A
TREND OF RAISING CLOUD BASES TO MVFR THROUGH MID MORNING AND
EVENTUALLY SCATTERING TO VFR BY EARLY AFTERNOON. FAIRLY LOW
CONFIDENCE WITH THE TREND DURING THE MID/LATE MORNING HOURS...AND
IMPROVEMENT COULD END UP BEING FASTER.
RATZER
PREVIOUS DISCUSSION FROM 06Z...
WITH MID/HIGH LEVEL CLOUD COVER CONTINUING TO SHIFT SOUTH OUT OF
THE REGION THIS MORNING...SKIES BECOMING CLEAR ACROSS MUCH OF THE
AREA. EXPECT CLEAR/VFR CONDITIONS FOR THE REMAINING OF THE
MORNING...BUT WITH THE OUTSIDE POSSIBILITY THAT CURRENT
STRATUS/FOG TO THE NORTH TO MOVE NEAR THE TERMINALS LATER THIS
MORNING. HAVE NOT INCLUDED ANY MENTION OF THIS STRATUS IN THE TAFS
AS CURRENT THINKING KEEPS THIS STRATUS TO THE NORTH AWAY FROM THE
TERMINALS. ALTHOUGH...IF THESE CLOUDS WERE TO CONTINUE
SOUTH...DISTANCE SPEED TOOL WOULD HAVE THESE CLOUDS REACHING THE
TERMINALS NEAR THE 15Z TIME FRAME. WITH HIGH PRESSURE SHIFTING
OVERHEAD...EXPECT VFR CONDITIONS FOR THE REMAINING OF THE TAF
PERIOD. WINDS TO REMAIN LIGHT OUT OF THE NORTH THIS MORNING AND A
PORTION OF SUNDAY BEFORE WINDS SHIFT MORE NORTHWEST AND EVENTUALLY
WEST BY SUNDAY EVENING.
RODRIGUEZ
//ORD AND MDW CONFIDENCE...UPDATED 09Z...
* MEDIUM-HIGH CONFIDENCE IN IFR/MVFR CEILING DEVELOPMENT FROM THE
NORTH OVER THE NEXT COUPLE OF HOURS.
* MEDIUM-LOW CONFIDENCE IN HOW QUICKLY CONDITIONS WILL IMPROVE
LATER THIS MORNING.
* MEDIUM CONFIDENCE IN LIGHT DETAILS OF LIGHT NORTH WINDS.
* LOW CONFIDENCE FOR FOG/STRATUS TO MOVE OVER HEAD LATE
TONIGHT/EARLY SUNDAY MORNING.
RATZER
//OUTLOOK FOR ORD/MDW FOR 12Z MONDAY-12Z SATURDAY...UPDATED 00Z...
MONDAY...VFR.
TUESDAY...CHANCE SNOW SHOWERS...OTHERWISE VFR.
WEDNESDAY...VFR.
THURSDAY...VFR.
FRIDAY...VFR.
RODRIGUEZ
&&
.MARINE...
255 AM CST
A WEAK TROUGH OF LOW PRESSURE WAS OVER THE CENTRAL GREAT LAKES
REGION EARLY THIS MORNING...WITH A WEAK TROUGH AXIS EXTENDING
WEST ACROSS CENTRAL LAKE MICHIGAN. THIS TROUGH WILL SCOOT OFF TO
THE EAST THIS MORNING...ALLOWING WEAK HIGH PRESSURE RIDGING TO
DEVELOP ACROSS CENTRAL AND SOUTHERN LAKE MICHIGAN. MUCH DEEPER LOW
PRESSURE MOVING SOUTHEAST ACROSS HUDSON BAY WILL TIGHTEN THE
PRESSURE GRADIENT ACROSS THE NORTHERN LAKES THIS AFTERNOON AND
THIS EVENING AS THE LOW TRACKS SOUTHEAST TOWARD WESTERN QUEBEC.
WEST-SOUTHWEST WINDS WILL INCREASE DURING THE LATE AFTERNOON HOURS
WITH A PERIOD OF 15-25 KT WINDS EXPECTED FROM LATE TODAY INTO
EARLY MONDAY. THE GRADIENT WILL THEN EASE A BIT DURING THE DAY
MONDAY IN THE VICINITY OF A PRESSURE TROUGH ASSOCIATED WITH A COLD
FRONT TRAILING THE CANADIAN LOW. HOWEVER...THE GRADIENT WILL
TIGHTEN UP AGAIN BEHIND THE FRONT LATE MONDAY INTO TUESDAY WITH A
PERIOD OF 20-25 KT NORTHERLY WINDS. STRONG CANADIAN HIGH PRESSURE
WILL BUILD SOUTHEAST FROM SASKATCHEWAN IN THE WAKE OF THE COLD
FRONT TUESDAY...WITH THE MAIN HIGH PRESSURE CENTER EVENTUALLY
DROPPING SOUTH ACROSS THE NORTHERN AND CENTRAL PLAINS THROUGH MID-
WEEK. WEAKER RIDGING WILL EXTEND EAST INTO THE WESTERN GREAT LAKES
REGION BY TUESDAY NIGHT HOWEVER...WHICH WILL ALLOW WINDS TO
DIMINISH FAIRLY QUICKLY LATE IN THE DAY TUESDAY AND TUESDAY NIGHT.
WHILE IT APPEARS THAT WINDS WILL REMAIN BELOW 30 KTS DURING THE
PERIOD AND NO GALE HEADLINES ARE EXPECTED AT THIS TIME...IT DOES
LOOK LIKE SMALL CRAFT ADVISORY CONDITIONS WILL LIKELY DEVELOP FOR
THE ILLINOIS/INDIANA SHORES ON SOUTHERN LAKE MICHIGAN BEHIND THE
COLD FRONT TUESDAY AND TUESDAY NIGHT.
RATZER
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
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