Forecast-Discussion
000
FXUS63 KLOT 060011
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
611 PM CST SUN FEB 5 2012
.DISCUSSION...
257 PM CST
PRIMARY FORECAST CONCERN TODAY REVOLVES AROUND CLOUDS/TEMPS THE NEXT
SEVERAL DAYS.
THE THEME OF THE FORECAST THIS NATIONAL WEATHERPERSON`S DAY COULD
BE: STRATUS...THE BANE OF OUR WINTER EXISTENCE! STRATUS THAT
ADVECTED IN FROM THE NORTHEAST HAS BEEN GRADUALLY MIXING OUT WITH
BACKING FLOW STARTING TO PUSH WHATS LEFT OF IT OVER THE LAKE
EASTWARD TOWARD MICHIGAN. MEANWHILE...STRATUS OVER THE CORNBELT HAS
HALTED ITS EASTWARD PROGRESSION THIS AFTERNOON...HOWEVER AS THE SUN
SETS EXPECT THE STRATUS TO BEGIN TO NOT ONLY RESUME ITS EASTWARD
MOTION BUT DEVELOP/EXPAND OVER NORTHERN ILLINOIS. LOW LEVEL MOISTURE
IS GREATER OVER NORTHERN ILLINOIS THAN TO THE WEST SO DESPITE MODELS
INSISTING CLEAR SKIES HAVE RATHER HIGH CONFIDENCE IN THE DEVELOPMENT
OF WIDESPREAD FOG...POSSIBLY DENSE...AND OR STRATUS
TONIGHT...ESPECIALLY WESTERN CWA. HARD TO SAY WITH CONFIDENCE
WHETHER THERE WILL BE DENSE FOG OR LOW STRATUS SO HAVE INCLUDED
POTENTIAL FOR FREEZING FOG IN THE GRIDS AWAY FROM DOWNTOWN CHICAGO
AND WILL HIT IT IN THE HWO.
MONDAY`S FORECAST HAS TREMENDOUS BUST POTENTIAL. PREPONDERANCE OF
THE EVIDENCE WOULD SUGGEST THAT FOG/STRATUS WILL STICK AROUND MOST
OF THE DAY ACROSS MUCH OF THE CWA. BEST CHANCES FOR SCATTERING OUT
SHOULD BE DOWNTOWN AND SE CWA. HAVE TAKEN A HATCHET TO FORECAST MAX
TEMPS TOMORROW AND NOW AM GOING BELOW ALL GUIDANCE WITH HIGHS IN THE
UPPER 30S TO LOWER 40S...WHICH IF STRATUS HANGS AROUND ALL DAY WOULD
STILL BE TOO WARM AS EVIDENCED BY THE MID AFTERNOON TEMPS IN THE 20S
OVER MUCH OF IOWA WHERE STRATUS HAS PERSISTED. CONVERSELY...IF
MODELS ARE RIGHT AND WE ACTUALLY ARE MOSTLY SUNNY TOMORROW THEN
HIGHS COULD EASILY PUSH 50F...SO THE RANGE IN PLAUSIBLE HIGHS
TOMORROW IS NEARLY 20F!
COLD FRONT MOVES THROUGH TOMORROW NIGHT AND USHERS IN A COLDER (WELL
MORE SEASONABLE) AIRMASS. CHANCES LOOK PRETTY GOOD FOR POST FRONTAL
STRATUS HANGING AROUND INTO AT LEAST WEDNESDAY. A CLIPPER SYSTEM IS
STILL PROGGED TO RIPPLE THROUGH THE REGION TUES NIGHT INTO EARLY
WEDNESDAY...WHILE MODELS REMAIN UNIMPRESSIVE LOOKING WITH QPF AM
STILL THINKING THIS SYSTEM COULD END UP PRODUCING A SWATH OF SOME
(LIGHTLY) ACCUMULATING SNOWFALL OVER AT LEAST PORTIONS OF OUR CWA.
HAVE BUMPED UP POPS SOMEWHAT TO THE CHANCE CATEGORY WHICH IS HIGHER
THAN GUIDANCE WOULD SUPPORT. IN ADDITION...STILL LOOKS LIKE THERE
WILL BE POTENTIAL FOR LIGHT LAKE EFFECT SNOW SHOWERS TUESDAY AND
POSSIBLY INTO TUESDAY NIGHT.
SOME MODERATION IN TEMPS IS EXPECTED THURSDAY BEFORE STRONGER COLD
FRONT ARRIVES THURS NIGHT POTENTIALLY BRINGING THE REGION ITS FIRST
DAY WITH BELOW AVERAGE TEMPS SINCE OUR ONE "COLD SPELL" THIS WINTER
BACK IN MID JANUARY. IN ALMOST COMICAL FASHION THE GFS AND ECMWF
HAVE BEEN CONSISTENTLY OPPOSITE OF EACH OTHER RUN AFTER RUN WITH
RESPECTS TO THE MAGNITUDE OF THE COOL DOWN. ONE RUN THE ECMWF IS
VERY COLD AND GFS MORE MODERATE AND THEN THE BOTH FLIP THE NEXT RUN.
THE LATEST ITERATION FROM THE 12Z RUNS THIS MORNING HAVE MODERATE
COOL DOWN IN GFS AND MORE FORCEFUL COLD SNAP IN THE ECMWF. MOST OF
THE MEDIUM RANGE GUIDANCE IS IN AGREEMENT IN SUGGESTING THAT
REGARDLESS HOW INTENSE THE COOL DOWN HEADING INTO THE WEEKEND THAT
IT LOOKS TO BE SHORT LIVED WITH A RETURN TO ABOVE IF NOT MUCH ABOVE
AVERAGE TEMPS HEADING INTO THE FOLLOWING WEEK. GRANTED CONFIDENCE IN
THAT IS FAIRLY LOW AS MEDIUM RANGE MODELS OFTEN STRUGGLE WITH HIGHER
AMPLITUDE FLOW.
IZZI
&&
.AVIATION...
//ORD AND MDW CONCERNS...UPDATED 00Z...
* SKC FOR A PERIOD OF TIME...HOWEVER WILL BE QUICKLY TURNING
TOWARDS IFR CONDS SHORTLY AFT MIDNIGHT.
* LARGE AREA OF STRATUS UPSTREAM SHOULD ARRIVE ARND 5Z...WITH CIGS
DROPPING TO ARND 500FT AGL ARND 8Z.
* VSBYS WILL LOWER TO ARND 1SM...POSSIBLY FURTHER REDUCTION
OVERNIGHT TO LESS THAN 1SM.
BEACHLER
//DISCUSSION...UPDATED 00Z...
SKIES HAVE FINALLY CLEARED OVER NORTHERN IL/NORTHWEST IN
AIRFIELDS...HOWEVER THIS APPEARS TO BE SHORT LIVED. LARGE AREA OF
STRATUS UPSTREAM ACROSS IOWA/WESTERN WISCONSIN/MINNESOTA STEADILY
SLIDES SOUTHEAST THIS EVENING. GUIDANCE HAS NOT HANDLED THE
DEVELOPMENT/PLACEMENT OF THIS AIRMASS VERY WELL...SO SIDING MORE
WITH CONSISTENCY IN THE FORECAST. BASED ON THE CURRENT
SPEED...THIS AIRMASS SHOULD ARRIVE ARND MIDNIGHT. CIGS WILL
STEADILY ARRIVE FROM THE WEST AND LOWER TO ARND 500FT AGL SHORTLY
AFT MIDNIGHT. A COUPLE HI-RES GUIDANCE MEMBERS HAVE BEGUN TO
SUGGEST FOG MAY REDUCE VSBYS TO 1SM SHORTLY AFT MIDNIGHT. HAVE
OPTED TO GO WITH 1SM BY 8Z AT ALL AIRFIELDS...MAY BE SLIGHTLY
EARLIER AT KRFD.
ONCE FOG AND STRATUS ARRIVE...EXPECT THIS AIRMASS WILL TAKE IT/S
TIME IN DEPARTING MON. FOR NOW THE THOUGHT IS THAT CIGS WILL
SLOWLY COME UP BY 17Z MON...THEN FURTHER IMRPOVEMENT BY 20Z. VSBYS
SHUD COME UP SLOWLY AS WELL. IF WINDS ARE STRONGER MON
MORNING...THEN EROSION AND IMPROVEMENT OF CIGS/VSBYS WILL BE MUCH
EARLIER.
BEACHLER
//ORD AND MDW CONFIDENCE...UPDATED 00Z...
* HIGH CONFIDENCE IN TIMING OF STRATUS AND LOWERING CIGS.
* MEDIUM CONFIDENCE IN VSBY FORECAST.
* HIGH CONFIDENCE IN WINDS THRU DAYBREAK MON.
* LOW CONFIDENCE IN WIND SPEEDS AFT 16Z MON.
* LOW CONFIDENCE IN TIMING OF CIGS/VSBYS IMPROVING MON
MIDDAY/AFTN.
BEACHLER
//OUTLOOK FOR ORD/MDW FOR 12Z TUESDAY-12Z SUNDAY...UPDATED 00Z...
TUESDAY...VFR. PATCHY MVFR CIGS WITH CHC OF SNOW SHOWERS.
WEDNESDAY...VFR. PATCHY MVFR CIGS IN LGT SNOW EARLY.
THURSDAY...VFR.
FRIDAY...VFR.
SATURDAY...VFR.
BEACHLER
&&
.MARINE...
305 PM CST
WITH A RIDGE OF HIGH PRESSURE SHIFTING ACROSS A PORTION OF THE
LAKE TODAY...WINDS HAVE REMAINED ON THE LIGHTER SIDE.
ALTHOUGH...LOW PRESSURE TO THE NORTH AS SHIFTED ACROSS THE REGION
AND HELPED THE PRESSURE GRADIENT ACROSS THE NORTHERN HALF OF THE
LAKE TO BECOME MORE ORGANIZED THIS AFTERNOON. THIS HAS RESULTED IN
WEST/SOUTHWEST WINDS TO INCREASE TO 15 TO 25 KT. EXPECT THIS TO
CONTINUE WITH EVEN AN INCREASE IN SPEED THROUGH TONIGHT...WITH THE
SOUTHERN HALF ALSO TO SEE THIS INCREASE. ALTHOUGH THIS WILL BE
SLOW...THE SOUTHERN HALF WILL GO FROM MORE LIGHT NORTH/NORTHWEST
WINDS TO EVENTUALLY WEST WINDS 15 TO 25 KT TONIGHT. WITH THIS AREA
OF LOW PRESSURE TO EXIT TO THE EAST ON MONDAY AND WINDS SLIGHTLY
DIMINISHING...A COLD FRONT ON THE BACKSIDE OF THIS LOW WILL WORK
ITS WAY DOWN THE LAKE INTO MONDAY NIGHT. WINDS WILL TURN TO THE
NORTH ON THE BACKSIDE OF THIS FRONT...WITH SPEEDS INCREASING ONCE
AGAIN TO 30 KT. EXPECT THESE SPEEDS AND HIGHER WAVES FOR MUCH OF
TUESDAY BEFORE A SLOW DIMINISHING TREND OCCURS.
RODRIGUEZ
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&
$$
NWS LOT Office Area Forecast Discussion
