273
FXUS63 KDVN 202051
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
250 PM CST FRI NOV 20 2009
SYNOPSIS
12Z UA ANALYSIS SHOWS THE VERTICALLY STACKED UPPER LOW HAS MOVED
INTO CANADA WHILE A WEAK UPPER LEVEL RIDGE IS OVER THE WESTERN GREAT
LAKES. A WEAK TROF IN THE PLAINS WAS ASSOCIATED WITH SOME CI/CS PER
SATELLITE. SATELLITE TRENDS THROUGH MID DAY SHOW LOW LEVEL SC HAS
DEVELOPED ACROSS SOUTHERN IOWA/NORTHERN MISSOURI WHERE THE THICKEST
FOG WAS AT SUNRISE. 18Z SFC ANALYSIS HAS WEAK HIGH PRESSURE FROM THE
OHIO INTO THE MID MISSISSIPPI VALLEY AND ACROSS THE PLAINS. DEW
POINTS WERE GENERALLY IN THE LOW TO MID 40S WITH 30S AND 20S ACROSS
THE CENTRAL AND NORTHERN PLAINS.
SHORT TERM...TONIGHT AND SATURDAY
FOG DEVELOPMENT IS THE MAIN QUESTION OVER THE NEXT 36 HRS. SEVERAL
FACTORS POINT TO FOG LATE TONIGHT/SATURDAY MORNING. HOWEVER...THE
SAME FACTORS WERE THERE TWO DAYS AGO AND NO FOG OCCURRED. DENSE FOG
THAT DEVELOPED IN WESTERN IA DID NOT FULLY CLEAR UNTIL NEARLY 18Z
TODAY. SO...THIS EVENING WILL BE QUIET. AFTER MIDNIGHT...WILL GO
WITH AREAS OF FOG ACROSS THE ENTIRE AREA AND CONTINUE IT THROUGH
SATURDAY MORNING. WILL HOLD OFF ON ANY HEADLINES FOR LATE
TONIGHT/SATURDAY MORNING ATTM. HOWEVER...THE POTENTIAL IS THERE FOR
WIDESPREAD DENSE FOG TO DEVELOP AND THE NEED FOR HEADLINES.
TEMPERATURES TONIGHT/SATURDAY WILL BE DEPENDENT ON ANY FOG
DEVELOPMENT. IF FOG GET THICK ENOUGH...MAX TEMPS FOR SATURDAY MAY BE
A LITTLE TOO WARM. ..08..
LONG TERM...SATURDAY NIGHT THROUGH NEXT FRIDAY
..SEASONABLY MILD TEMPERATURES
CONTINUED DRY CONDITIONS INTO
MONDAY...THEN MODERATE TO HEAVY PRECIPITATION TUE/WED WITH NEXT STORM
SYSTEM...
FORECAST INITIALIZATION GOOD OVER NORTH AMERICA...AMERICAN MODELS
STILL BELOW AVERAGE INITIALIZING PACIFIC UPSTREAM ENERGY RESULTING IN
STILL TOO FAST AND NORTH PROGRESSION OF NEXT WEEK/S SYSTEM. PRIMARY
GUIDANCE USED A BLEND OF NAM-WRF...GFS.... UKMET THROUGH SUNDAY...
THEN UKMET...GEM-NH...HI RES ECMWF MONDAY INTO FRIDAY.
FRIDAY NIGHT THROUGH SUNDAY NIGHT...ONLY MINOR CHANGES TO TEMPS.
PARTLY CLOUDY TO MOSTLY CLEAR SKIES AND GENERALLY LIGHT SE WINDS. IF
SKIES CLEAR ENOUGH...AGAIN AVAILABLE LOW LEVEL MOISTURE SUPPORTS
PATCHY TO AREAS OF MORNING FOG SUNDAY AND MONDAY AM FOR LATER SHIFTS
TO CONSIDER. TEMPERATURES UP TO ~5 DEGREES ABOVE NORMAL. RISK OF
SPRINKLES OR VERY LIGHT RAIN OR DRIZZLE...MAINLY SUNDAY AM FAR WEST
SECTIONS AS LOW LEVELS MOISTEN WITH MODERATE BL CONVERGENT FLOW BUT
FORCING IS LIMITED. HENCE KEPT...LOW CHANCE POPS TO COVER THIS.
MONDAY THROUGH THURSDAY...INDICATIONS OF CONSIDERABLE LOW CLOUDS...
FOG AND DRIZZLE AND LIGHT RAIN TO DEVELOP LATE MONDAY INTO TUESDAY
AHEAD OF NEXT STORM SYSTEM. LATER SHIFTS SHOULD REASSESS THIS TREND
AS LOCAL TOOLS SUGGEST THIS COULD BE SIGNIFICANT EVENT WITH MOIST LOW
LEVELS AND CONVERGENT BL FLOW. RAISED POPS LATE TUESDAY INTO
WEDNESDAY WITH STILL SOME QUESTION WHEN MAIN ENERGY PASSES. LATER
SHIFTS SHOULD BE ABLE TO RAISE TO LIKELY POPS NEXT 12 TO 24 HOURS.
RAIN TOTALS STILL SUGGEST WIDESPREAD .25 TO .5+ INCH AMOUNTS.
LINGERING QUESTION OF HOW QUICKLY COLD AIR WRAPS IN WEDNESDAY INTO
THURSDAY WITH A MIX OF SNOW AND RAIN. CLOSE EXAMINATION SUPPORTS
AREA TO SEE SOME SNOW WITH POSSIBLY MINOR ACCUMULATIONS IF BACKSIDE
SHORT WAVE DIVES ACROSS AREA. KEPT SLIGHT CHANCE POPS ATTM WITH A
MIX VERBIAGE UNTIL TIMING OF CAA AND ENERGY CONFIRMED. SOME ENERGY
PHASING ISSUES DO REMAIN BUT TRACK ASSURED FOR AREA TO SEE SEASONABLY
MODERATE TO LOCALLY HEAVY PRECIPITATION.
FRIDAY...BELOW NORMAL TEMPERATURES AND DRY AS CANADIAN HIGH PRESSURE
MOVES IN. LOW LEVEL THERMAL FIELDS SUPPORT COLDEST AIR OF THIS FALL
SEASON...MINS MAY NEED TRIMMING BY UP TO 5 DEGREES. ..NICHOLS..
AVIATION
FOG/NO FOG ALONG WITH LIFR VSBYS/CIGS IS THE FCST QUESTION. LGT
WNDS...LIMITED MIXING AND CLRING SKIES ARE FAVORABLE FOR FG DVLPMNT.
MOST OF THESE FEATURES WERE PRESENT 2 DAYS AGO AND NO FG OCCURRED.
VFR CONDITIONS SHOULD BE SEEN THROUGH 03Z/21. AT SOME POINT BTWN
03Z-06Z PATCHY 3-5SM VSBYS WL DEVELOP. AFT 06Z/21 IF FG DEVELOPS
...VSBYS OF 3-5SM WL DEVELOP AND DROP QUICKLY. POTENTIAL THERE FOR
VLIFR VSBYS AND CIGS. HAVE OPTED TO GO WITH LIFR VSBYS/CIGS AT ALL
SITES IN THE 09Z-16Z TIME FRAME. ..08..
DVN WATCHES/WARNINGS/ADVISORIES
IA...NONE.
IL...NONE.
MO...NONE.
08/NICHOLS
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