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Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

000
FXUS63 KDVN 100929
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
329 AM CST WED FEB 10 2010

.SYNOPSIS...
THE WEATHER HAS QUIETED DOWN SIGNIFICANTLY ACROSS THE AREA FROM
YESTERDAY.  THE LOW PRESSURE SYSTEM HAS NOW MOVED EAST TO AFFECT THE
EAST COAST...AND WE ARE LEFT WITH SOME STRATUS...A FAIRLY TIGHT SURFACE
PRESSURE GRADIENT TO KEEP WINDS UP AND A RIDGE BUILDING INTO THE
AREA FROM THE WEST.  THE STRATUS HAS A LARGE HOLE IN IT OVER THE
FORECAST AREA...BUT EXPECT THAT PUDDLES OF IT WILL DRIFT ACROSS US
FOR THE REMAINDER OF THE OVERNIGHT HOURS.
..LE..

&&

.SHORT TERM...TODAY AND TONIGHT...
MAIN QUESTION IS CLOUDS AND TEMPERATURES TODAY AND TONIGHT.  THE
STRATUS IS THE LAST VESTIGES OF MOISTURE LINGERING BEHIND OUR STORM
SYSTEM...AND APPEARS TO BE TRAPPED UNDERNEATH THE INVERSION THAT
SHOULD BE FORMING BELOW 950MB AS ADDITIONAL COLD AIR MOVES INTO THE
REGION...AND ENHANCED BY RADIATIONAL COOLING.  THIS KIND OF STRATUS
IS TYPICALLY KIND OF HARD TO GET RID OF.  HOWEVER...THE MODELS
INDICATE THAT THE INVERSION GETS VERY SHALLOW DURING THE MORNING AS
THE SUBSIDENCE KEEPS WORKING ABOVE IT...THOUGH ALSO ENHANCING THE
TEMPERATURE DIFFERENCES.  THIS...ALONG WITH THE CONTINUED DRY
NORTHWEST FLOW SHOULD MANAGE TO FLUSH THE STRATUS OUT BY LATE
MORNING. IT MAY BE HARDER TO GET RID OF IN THE EAST HOWEVER...AS THE
MOISTURE AND INVERSION STAY SURPRISINGLY DEEP INTO THE LATE
AFTERNOON AND EARLY EVENING...DESPITE THE DRYING NORTHWEST FLOW AND
SUBSIDENCE.  THIS COLD AIR WILL KEEP TEMPERATURES CHILLY
TODAY...ONLY RISING INTO THE TEENS NORTH...AND LOW 20S SOUTH.
TONIGHT TEMPERATURES COLD GET VERY COLD IF NO CIRRUS COMES STREAMING
IN OVERHEAD.  THERE WILL BE A VERY STRONG UPPER LEVEL JET TO OUR
SOUTH...WHICH SHOULD KEEP ANY CONSISTENT CIRRUS FROM A SYSTEM IN THE
SOUTHERN STREAM FROM GETTING HERE...BUT HAVE CONCERNS FOR SOME
MOISTURE THAT APPEARS TO MOVE ALONG IN THE WEAKER FLOW OVER US...AND
WE COULD BE LOOKING AT SOME PATCHES OF CIRRUS OVERNIGHT TONIGHT.
THUS...HAVE NOT GONE AS COLD AS WE MIGHT IF THERE IS NO CIRRUS...BUT
WELL BELOW GUIDANCE.
..LE..

.LONG TERM...THURSDAY THROUGH TUESDAY...
MAIN CHALLENGE IS ON INCREASING SNOW CHANCES LATE WEEK INTO THE
WEEKEND AS ACTIVE N-NW FLOW CONTINUES.

HIGH LEVEL MOISTURE AND LIFT AHEAD OF AN APPROACHING CLIPPER-LIKE
SYSTEM WILL PRODUCE INCREASING HIGH CLOUDS THURSDAY. VERY COLD START
AND WEAK SURFACE WINDS UNDER THE DEPARTING SURFACE RIDGE WILL LIMIT
HIGHS TO THE LOWER TO MID 20S. 00Z SHORT TERM MODELS TRACK A WEAK
SURFACE LOW INTO THE MO VALLEY FRI NIGHT H8 WARM ADVECTION AND WEAK
MID LEVEL FORCING DEVELOPING ACROSS THE REGION. RESULTING QPF IS NOW
SHOWN REACHING INTO THE WESTERN HALF OF THE FORECAST AREA AND HAVE
INTRODUCED SLIGHT CHANCES FOR LIGHT SNOW WITH SOME UNCERTAINTY IN
TIMING AND WHETHER MOISTURE WILL BE SUFFICIENT FOR MEASURABLE
ACCUMULATIONS. THIS SURFACE LOW THEN PASSES SOUTH OF THE FORECAST
AREA FRI...PRIMARILY IN THE MORNING WITH SURFACE DEFORMATION ZONE
AND POSSIBLY MORE DIRECT HIT OF MID LEVEL QG FORCING SHOWN BY BETTER
MODEL CONSENSUS TRACKING DIRECTLY OVER THE FORECAST AREA. THIS
SUGGESTS A QUICK SHOT OF AT LEAST MODERATE DEEP LAYER LIFT...WHICH
ALONG WITH THE AVAILABLE MOISTURE...WOULD SUPPORT WIDESPREAD SNOW
ACCUMULATIONS AS HIGH 2 TO 4 INCHES...TYPICAL OF A CLIPPER SYSTEM.
WITH INCREASING CONFIDENCE...RAISED POPS TO 30 TO 50 PERCENT
RANGE...BUT WILL STAY CONSERVATIVE SINCE THIS SYSTEM IS STILL FAR
OUT AND HAVE KEPT SNOWFALL AMOUNTS IN 1 TO 2 INCH RANGE.

A POTENTIALLY MORE SIGNIFICANT SNOW EVENT STILL LOOKS TO FOLLOW
QUICKLY ON ITS HEELS OVER THE WEEKEND AS YET ANOTHER UPPER LOW DROPS
SOUTH OUT OF CENTRAL CANADA. THE GFS HAS HAD THE BEST RUN TO RUN
CONSISTENCY AND LOOKS HAUNTINGLY VERY SIMILAR TO THE SYSTEM THAT
JUST EXITED THE AREA THIS PAST EVENING. LOOKING BACK OVER LONG RANGE
WV SAT IMAGERY...THIS VORTEX OVER FAR NW MANITOBA APPEARS VERY
SIMILAR AT A SIMILAR POINT IN THE EVOLUTION OF THIS LAST SYSTEM. THE
00Z GFS TRACKS THIS DEVELOPING UPPER LOW SOUTH THROUGH THE NRN
PLAINS SAT...THEN S-SE ACROSS SW IA TO SRN IL LATE SUN. AT THE
SURFACE...LOW PRESSURE PASSES TO THE SW THEN S WITH AN INVERTED LOW
LEVEL TROUGH AND DEF ZONE SPREADING SNOW ACROSS FORECAST AREA LATE
SAT AFTERNOON THROUGH SUN. THE LATEST ECMWF IS A BIT WEAKER AND
FASTER WITH THE UPPER LEVEL LOW...WHILE THE WRF/NAM IS SLOWER...AND
THE GEM THE BIGGEST OUTLIER TRACKING THE ENTIRE SYSTEM WELL W OF THE
REGION. THE GFS ENSEMBLE NUMBERS OFFER POOR SUPPORT FOR THE
OPERATIONAL SOLUTION. GIVEN THIS LACK OF SUPPORT AND UNCERTAINTY IN
THE MODELS...ITS TOO EARLY TO RAISE POPS TO LIKELY FOR ANY GIVEN
PERIOD...BUT HAVE BUMPED SAT INTO 40 TO 50 PERCENT RANGE AND SAT
NIGHT TO 30 TO 40 PERCENT RANGE. IF THE AGGRESSIVE GFS SOLUTION
VERIFIES...COULD SEE ANOTHER WIDESPREAD...LIGHT TO MODERATE SNOWFALL
EVENT EXTENDING OVER 24 TO 36 HOURS OVER THE WEEKEND.

HIGH PRESSURE FOLLOWS FOR THE START OF NEXT WEEK FAVORING DRY
WEATHER MON AND TUE.

..SHEETS..

&&

.AVIATION...
THE MVFR LAYER OF STRATUS AFFECTING THE TERMINALS THIS MORNING
SHOULD LINGER FOR A SHORT TIME..BUT BY MID MORNING IT SHOULD BE
ERODING...AND GONE BY LATE MORNING AS LONG AS PROCESSES MENTIONED
ABOVE WORK OUT.  STRATUS SHOULD LINGER LONGEST AT KDBQ AND
KMLI...THOUGH DEFINITELY BY EVENING AS THE SURFACE RIDGING BUILDS IN
MORE STRONGLY.  OTHERWISE...VFR CONDITIONS WITH NORTHWEST WINDS
GRADUALLY DIMINISHING.
..LE..

&&

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

$$

LE/SHEETS