FXUS63 KDVN 262052
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
250 PM CST THU NOV 26 2009

.SYNOPSIS...
EXTENSIVE FIELD OF LOW CLOUDS CONTINUES TO SLOWLY ERODE FROM NW TO 
SE AS SURFACE AND UPPER RIDGING BUILDS IN FROM THE WEST. AT 
20Z...VISIBLE SATELLITE INDICATED THE BACK EDGE HAD ONLY PROGRESSED 
ONLY AS CLOSE AS CENTRAL IA AND SE MN. THE LACK OF SUN...ALONG 
WITH BRISK NW WINDS AND COLD ADVECTION UP THROUGH H8 HAS RESULTED IN 
STEADY TO FALLING TEMPERATURES TODAY. READINGS HAVE BEEN LIMITED TO 
THE 30S...AND CID HAS ACTUALLY DROPPED FROM 34 AT SUNRISE DOWN TO 31 
THIS PAST HOUR. LATEST SURFACE ANALYSIS INDICATED LOW PRESSURE OVER 
NORTHERN LAKE HURON AND A SURFACE RIDGE AXIS EXTENDING FROM EASTERN 
TX TO NW MN. WV AND VISIBLE SATELLITE IMAGERY INDICATED UPPER LEVEL 
MOISTURE AND MID AND HI LEVEL CLOUDS SPILLING OVER THE NRN ROCKIES 
UPPER RIDGE S-SE ACROSS THE DAKOTAS IN MN. THE EXTENT OF HIGH CLOUD 
COVER SPILLING INTO THE REGION TONIGHT...FOLLOWING THE CLEARING 
OF LOW CLOUDS...WILL BE CRITICAL TO HOW LOW TEMPERATURES WILL DROP.  

&&

.SHORT TERM...TONIGHT AND FRIDAY...
MINIMUM TEMPERATURES TONIGHT ARE THE PRIMARY CHALLENGE. 
PERSISTENCE...USING DISTANCE TIME FEATURE...SUGGESTS THE LOW CLOUDS 
CLEARING NW TO SE THROUGH THE FORECAST AREA BETWEEN 23Z TO 03Z. WITH 
ALREADY COOL TEMPERATURES AND AN AIRMASS WITH DEWPOINTS IN THE LOWER 
20S FILTERING IN FROM THE NW AND DIMINISHING WINDS UNDER THE 
INCOMING SURFACE RIDGE...WOULD HAVE THE POTENTIAL FOR ONE OF THE 
COLDEST NIGHTS OF THE SEASON SO FAR. HOWEVER...INCOMING HIGH 
CLOUDS...AND TRANSITION TO WEAK WARM ADVECTION OVER MOST OF THE AREA 
FROM 925 TO H8 SHOULD PREVENT THE AREA FROM SEEING MINS AS COLD AS 
THE TEENS OBSERVED UPSTREAM FROM NRN NEB TO EASTERN ND THIS MORNING. 
STAYED CLOSE TO GUIDANCE MINS FROM MID 20S NORTH TO UPPER 20S SOUTH. 

FRIDAY...LIGHT SE WINDS OUT OF THE AIRMASS UNDER THE DEPARTING 
RIDGE AND POTENTIAL THIN MID AND HIGH LEVEL CLOUDS WILL LIMIT THE 
DEPTH OF MIXING IN THE ELEVATED WARM ADVECTION REGIME. MIXING TO 
AROUND H9 SUPPORTS HIGHS CLOSE TO GUIDANCE IN THE MID 40S NE TO 
AROUND 50 SW. THIS WILL BE A RETURN TO ABOVE THE NORMAL 
TEMPERATURES THAT HAVE PREVAILED THIS MONTH SO FAR.     
..SHEETS..

.LONG TERM...FRIDAY NIGHT THROUGH NEXT THURSDAY...
A COLD FRONT...AHEAD OF A S/W MOVING THROUGH THE NRN PLAINS...WILL 
MOVE THROUGH THE CWFA SATURDAY AFTERNOON AND EVENING. THE FRONT 
SHOULD PASS THROUGH THE REGION DRY DUE TO WEAK FORCING AND LIMITED 
MOISTURE.  TEMPS SATURDAY SHOULD WARM WELL INTO THE 50S IN THE SLY 
FLOW AHEAD OF THE FRONT. THE FRONT SHOULD BE THROUGH THE CWFA BY 
MIDNIGHT WITH LOW CLOUDS INCREASING LATE SATURDAY NIGHT IN THE 
CAA BEHIND THE FRONT.  

FOR SUNDAY THROUGH THURSDAY THE MODELS ARE IN  AGREEMENT WITH 
OVERALL TRENDS ESPECIALLY THE FIRST PART OF THE WEEK. THE NRN PLAINS 
TROF IS STILL PROGGED TO MOVE EAST INTO MID/UPPER MS VALLEY BY 
MONDAY MORNING.  THE NRN END OF THE TROF IS PROGRESSIVE WHILE THE 
SRN PORTION ENDS UP CLOSING OFF OVER SRN AZ/NRN MEX.   MODELS ARE 
STILL SHOWING SOME LIGHT POST FRONTAL PCPN SUNDAY AND CONTINUING 
INTO SUNDAY NIGHT.  WILL CONTINUE THE 20 POPS OVER THE SRN CWA TO 
ACCOUNT FOR THIS POSSIBILITY.  TEMPS SUPPORT A RN/SN MIX IF THE PCPN 
OCCURS.  THE GFS/ECMWF BREAK OUT MORE SIGNIFICANT PCPN SUNDAY NIGHT 
TO OUR EAST AND SOUTH ALONG THE FRONT AS IT ENCOUNTERS BETTER 
MOISTURE.  AT THIS TIME THE ECMWF SUGGESTS THE BACK EDGE OF THE PCPN 
SHIELD WILL JUST BRUSH THE SERN EDGE OF THE CWFA WHILE THE GFS KEEPS 
THE PCPN FURTHER SE.  HAVE CONTINUED LOW POPS OVER THE SE TO COVER 
THE UNCERTAINTY. AGAIN LOW LEVEL TEMPS SUNDAY NIGHT SUPPORT A RN/SN 
MIX WITH ANY PCPN THAT OCCURS.

TUESDAY INTO THURSDAY THE LONG RANGE MODELS ARE AGREEING THAT A 
LARGE MID LEVEL TROF WILL SET UP OVER THE WRN HALF OF THE U.S. THE 
DIFFERENCE IS THE GFS DIGS THE TROF OVER THE MIDWEST WHILE THE 
ECMWF/GEM/UKMET DIG THE TROF OVER THE ROCKIES.  HAVE CHOSEN TO 
FOLLOW THE CONSENSUS AND USE THE ECMWF FOR MIDWEEK.  THIS RESULTS IN 
CONTINUED NEAR TO ABOVE NORMAL TEMPS AND DRY CONDITIONS TUESDAY AND 
WEDNESDAY.  WILL GO WITH LOW POPS WEDNESDAY NIGHT AND THURSDAY TO 
COVER THE ECMWF IDEA OF BUSHING THE CWFA WITH PCPN SHIELD ASSOCIATED 
WITH EJECTING SWRN U.S. CUTOFF.  ...DLF...

&&

.AVIATION...
DECK OF MVFR CLOUDS ASSOCIATED WITH THE DEPARTING STORM SYSTEM OVER 
THE GREAT LAKES...WILL GRADUALLY CLEAR FROM WEST TO EAST OVER THE 
AREA THIS EVENING. THE BACK EDGE OF THESE LOW CLOUDS...EXTENDING 
FROM SE MN INTO CENTRAL IA AT MID AFTERNOON...WILL LIKELY REACH CID 
AND DBQ BETWEEN 00Z AND 02Z. THE TRANSITION TO VFR WILL LIKELY OCCUR 
AT MLI AND BRL BETWEEN 01Z AND 03Z. VFR CONDITIONS WITH ONLY HIGH 
LEVEL CLOUDS WILL THEN PREVAIL OVERNIGHT INTO FRI AS A SURFACE RIDGE 
OVER THE CENTRAL PLAINS SLIDES EAST. NW WINDS FROM 12 TO 24 KTS WILL 
DIMINISH TO LESS THAN 10 KTS AFTER SUNSET...THEN BACK TO MORE 
WESTERLY AND BECOME LIGHT OVERNIGHT. LIGHT WINDS WILL INCREASE TO 5 
TO 10 KT FROM THE SOUTH BY FRIDAY AFTERNOON.  
..SHEETS..
&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.

&&

$$

SHEETS/DLF