FXUS63 KDVN 102110
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
310 PM CST THU DEC 10 2009

.SYNOPSIS...
STILL A VERY COLD DAY ACROSS THE AREA THIS AFTERNOON WITH 
TEMPERATURES RANGING FROM JUST 3 UP AT KDBQ...TO 19 DOWN AT KEOKUK.  
OF NOTE...IN THE AREA WHERE THERE IS DEEP SNOWPACK OF AT LEAST 2-3 
INCHES DEEP...TEMPERATURES HAVE STAYED IN THE SINGLE DIGITS TO 
AROUND 10...AND AS THE SNOW GETS SHALLOWER THE TEMPERATURES WARM.  
WE HAVE OUR USUAL WARM SPOTS AROUND THE RIVER SOUTH OF KBRL...BUT 
OTHERWISE KMQB IS THE WARMEST TODAY...AND THEY HAD LESS THAN 2 
INCHES.  SURFACE WINDS OF 10 TO 20 MPH HAVE PRODUCED VERY COLD WIND 
CHILL VALUES...AND WE ARE STILL FLIRTING WITH WIND CHILL CRITERIA 
ALONG THE HIGHWAY 20 CORRIDOR.  UPPER AIR ANALYSIS SHOWS THAT WE 
HAVE A VERY DEEP...COLD AIRMASS WITH A 850MB TEMP OF -21 THIS 
MORNING ON OUR SOUNDING.  UPPER LEVEL JET IS ALSO SUPPRESSED TO 
SOUTH OF THE OHIO RIVER VALLEY THIS MORNING.    ..LE..

&&

.SHORT TERM...TONIGHT AND FRIDAY...
TONIGHT THE MAIN CONCERN IS TEMPERATURES...AND ASSOCIATED WIND CHILL 
VALUES.  WE WILL BE FLIRTING WITH WIND CHILL ADVISORY CRITERIA 
OVERNIGHT...DEPENDING ON WINDS AND HOW QUICKLY TEMPERATURES DROP OFF 
TONIGHT.  FOR NOW THE TEMPERATURE TRENDS AND WIND SPEEDS ARE SUCH 
THAT WE WILL BE JUST ABOVE...AND HAVE HELD OFF DOING A WIND CHILL 
ADVISORY FOR TONIGHT.  OVERNIGHT TEMPERATURES ARE ANOTHER 
BEAR...WITH NEGATIVE FEEDBACK FROM THE SNOW COVER FIGHTING WITH THE 
WEAK WARM AIR ADVECTION ALOFT.  WE ALSO HAVE SOME AC OR LOW END 
CIRRUS THAT THE MODELS ARE INDICATING WILL FLOW ACROSS THE AREA 
OVERNIGHT...WHICH MAY ALSO ACT TO KEEP TEMPERATURES UP.  THE GFS IS 
OVERDONE ON THIS...BRINGING IN FLURRIES AS WELL TO NORTHERN IOWA. 
HAVE GONE SLIGHTLY COLDER THAN THE ALREADY COLDER NAM GUIDANCE.  IT 
SEEMS TO HAVE ALREADY PICKED UP ON THE SNOWPACK OVER THE DES MOINES 
AREA...AND I SIMPLY EXPANDED THE COLD VALUES FROM OVER THERE TO OVER 
OUR SNOWPACK AREA.  WENT CLOSER TO GUIDANCE VALUES WHERE THERE IS 
LESS SNOW.

FRIDAY WE WILL HAVE CONTINUING WARM AIR ADVECTION...AND LIKELY SOME 
MORE SCATTERED MID CLOUDS LIKE TODAY...BUT THE COLD SNOWPACK IS NOT 
GOING TO LET US WARM UP VERY MUCH...AND ANTICIPATE TEMPERATURES 
BARELY RISING INTO THE TEENS NORTH...AND LOW 20S IN THE SOUTH.  
AGAIN...WENT WARMEST IN THE SOUTHEAST WHERE SNOWPACK IS LEAST...WITH 
A FEW MID 20S THERE.  WINDS TO REMAIN LIGHT ALL DAY...SO FEW WIND 
CHILL CONCERNS THEN.   ..LE..

.LONG TERM...FRIDAY NIGHT THROUGH NEXT THURSDAY...
THE BONE CHILLING COLD WILL CERTAINLY BE MAKING A FEW APPEARANCES 
THROUGH THE EXTENDED FORECAST...AS WE BEGIN THE PERIOD UNDER ARCTIC 
HIGH PRESSURE...AND AFTER A FEW DAYS OF MODERATION...WE SHOULD END 
UP STRONGLY INFLUENCED BY ANOTHER ARCTIC HIGH. THE DETAILS OF THIS 
MODIFICATION ARE VERY INCONSISTENT IN MODEL COMPARISONS...AND 
INTERNALLY THEY ARE INCONSISTENT FROM RUN TO RUN.  THUS...OUR 
FORECAST WILL MERELY TREND TOWARD A TEMPERED MODIFICATION FOR FRIDAY 
INTO MONDAY WITH WAA TAKING PLACE.  MODELS CONTINUE TO SHOW MOISTURE 
MOVING NORTH OVER THE AREA SATURDAY NIGHT...WITH SOME MODEST 
FORCING. THIS SHOULD RESULT IN A LIGHT SNOW THREAT...POSSIBLY A FEW 
INCHES. ON THE HEALS OF THIS EVENT...WAA CONTINUES...BUT HOW MUCH AT 
THE SURFACE WILL BE SEEN IS UNCERTAIN. IT APPEARS THAT THIS PATTERN 
IS MORE LIKELY TO RESULT IN CLOUDS AND FREEZING DRIZZLE FOR SUNDAY 
INTO MONDAY AS THERE IS PLENTY OF DRY AIR ALOFT TO PREVENT DEEP 
SATURATION. THUS...DESPITE THE LIGHT AND UNPREDICTABLE NATURE OF 
THIS EVENT...A WINTER WEATHER HEADLINE IS POSSIBLE.

BEYOND THIS EVENT...MODELS ARE COMING IN FASTER WITH THE ARRIVAL OF 
ARCTIC HIGH PRESSURE MONDAY...AND THIS PERIOD MAY NEED TO BE LOWERED 
FURTHER. TUESDAY AND WEDNESDAY APPEAR COLD UNDER SIMILAR 
TEMPERATURES TO WHAT ARE OUT THERE TODAY.  THAT SAID...THE HIGH 
PRESSURE STRENGTH IS STRONGER THAN THE CURRENT ONE...AND I WOULD NOT 
BE SURPRISED TO SEE COLDER TEMPERATURES THAN WE ARE NOW SEEING.  
LOOKING AT THURSDAY...MODELS ALL SHOW A WAVE TOPPING THE WESTERN 
RIDGE AND MOVING DOWN INTO THE TROF.  SOME WAA SNOW APPEARS 
POSSIBLE...ALONG WITH MODERATING TEMPERATURES.
...ERVIN...
&&

.AVIATION...
VFR CONDITIONS WITH SCATTERED AC AROUND 6KFT FLIRTING WITH THE 
NORTHERN TAF LOCATIONS OVERNIGHT.  SOUTHWEST WINDS TODAY GENERALLY 
10-15 KTS WITH SOME GUSTS TO 20 SHOULD DROP OFF EARLY THIS EVENING 
TO LESS THAN 10 KTS BY 03Z.  WINDS SHOULD STAY UNDER 10 KTS THROUGH 
FRIDAY.   ..LE..

&&

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

&&

$$

LE/ERVIN