FXUS63 KDVN 090549 AFDDVN AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE QUAD CITIES IA IL 1149 PM CST WED FEB 8 2012 .AVIATION... SFC-925 MB RIDGE AXIS WILL SLIDE ACROSS REGION OVRNGT. SKIES WILL REMAIN CLEAR WITH LIGHT WINDS 3-6 KTS BACKING TO SW THROUGH 12Z. PATCHY FOG POSSIBLE FOR A FEW HRS TOWARD DAYBREAK WITH VSBYS GENERALLY 3-6SM. ATTN THEN SHIFTS TO LARGE AREA OF STRATUS CURRENTLY MOVING EWD THROUGH NE AND SW IA ATTIM. EXPECT THE STRATUS TO CONTINUE MOVING EWD INTO MID AM THU AS SFC-925 MB RIDGE DEPARTS AND WINDS BECOME WESTERLY AT AROUND 15 KTS JUST ABOVE SFC. 00Z KOAX RAOB SHOWS MOISTURE VERY SHALLOW (ROUGHLY 100 FT THICK CENTERED AROUND AND JUST BELOW 890 MB). CHALLENGE BECOMES TIMING OF STRATUS INTO THE TERMINALS. SEVERAL FACTORS OR ELEMENTS MAKE THIS DIFFICULT WITH 1) STRENGTHENING FEB SOLAR INSOLATION... THAT MAY AID IN SLOWING EWD PROGRESSION... 2) INCREASED MIXING WITH W/SW WINDS INCREASING 10-15 KTS WITH SOME GUSTS... WITH POTENTIAL TAP DRY AIR ABOVE THE STRATUS TO ALSO PROMOTE EROSION. THE SLOWING ALSO DEPICTED IN MOST RECENT RUNS OF HRRR TOTAL CLOUD COVER PRODUCT... THUS WITH 06Z TAFS HAVE FOLLOWED SUIT AND PUSHED BACK ARRIVAL OF STRATUS WITH MVFR CIGS UNTIL AFTN TO EARLY EVE. && .PREV DISCUSSION... /ISSUED 305 PM CST WED FEB 8 2012/ SYNOPSIS... 12Z UA ANALYSIS HAS A RIDGE RUNNING FROM THE GULF COAST INTO EASTERN MONTANA. ARCTIC AIR WAS OVER NORTHERN CANADA WITH THE SOUTHERN EXTENT DOWN TO JAMES BAY. SATELLITE TRENDS THROUGH MID AFTERNOON HAD STRATUS TRAPPED UNDER AN INVERSION FROM THE PLAINS INTO CENTRAL ILLINOIS AND SOUTHEAST IOWA. THE 18Z SFC ANALYSIS HAD THE RIDGE FROM THE DAKOTAS INTO TEXAS. A WEAK TROF RAN FROM THE NORTHERN GREAT LAKES INTO WESTERN WISCONSIN. DEW POINTS WERE GENERALLY IN THE TEENS AND 20S ACROSS MUCH OF THE MIDWEST WITH 30S IN THE SOUTHERN PLAINS AND OHIO VALLEY. SHORT TERM...TONIGHT AND THURSDAY... THE SHALLOW LAYER OF STRATUS CLOUDS BELOW THE TRAPPING INVERSION IS NOT BEING HANDLED AT ALL BY THE MODELS. DIURNAL HEATING FROM THE SUN HAS STRENGTHENED THE INVERSION ABOVE THE CLOUDS CAUSING THE OVERALL CLEARING TREND TO SLOW. THE 950MB RH LEVEL ON THE RUC HAS DONE REASONABLY WELL IN DEPICTING WHERE THE CLOUDS CURRENTLY ARE. USING THE RUC 950MB RH TRENDS COMBINED WITH EXTRAPOLATION OF SATELLITE INDICATES THAT THE CLOUDS WILL REMAIN ACROSS ROUGHLY THE SOUTHERN 40 PERCENT OF THE CWFA FOR THE REMAINDER OF THE AFTERNOON. CLEARING IN THE SOUTH THIRD OF THE CWFA WILL BE SLOW DURING THE EVENING BUT CLEAR SKIES SHOULD BE SEEN ACROSS NEARLY ALL THE CWFA BY MIDNIGHT. AFTER MIDNIGHT ANOTHER UPPER LEVEL DISTURBANCE APPROACHES. THIS DISTURBANCE SHOULD JUST PASS THROUGH WITH NO NOTICEABLE AFFECTS. HOWEVER...IF THE LOW CLOUDS ARE STILL IN PLACE ACROSS THE SOUTH THIRD OF THE CWFA THEN ISOLATED FLURRIES WOULD BE POSSIBLE. FOR NOW IT APPEARS THAT THE LOW CLOUDS SHOULD EXIT THE CWFA AROUND OR SHORTLY AFTER MIDNIGHT. ASSUMING CLOUDS CLEAR TONIGHT...TEMPERATURES SHOULD BE QUITE CHILLY. THE CLEAR SKIES ON THURSDAY WILL GIVE WAY TO MORE CLOUDS THROUGH THE DAY. THE 950MB RH FIELD FROM THE WRF...ALTHOUGH NOT AS GOOD THE RUC...HAS A STRONG SIGNAL INDICATING THE LOW CLOUDS IN NEBRASKA/ KANSAS WILL ADVECT BACK INTO THE CWFA DURING THE MORNING HOURS. CLOUD COVER FOR THURSDAY HAS BEEN INCREASED BUT IT IS LIKELY TOO LOW. THERE IS SOME WEAK F VECTOR CONVERGENCE ACROSS THE AREA WHICH COULD PROMOTE THE DEVELOPMENT OF FLURRIES. HOWEVER...FORCING IS WEAK TO NON- EXISTENT SO THE CHANCES OF FLURRIES SHOULD BE VERY LOW. THE ARRIVAL OF CLOUDS ON THURSDAY SHOULD AID IN SUPPRESSING TEMPERATURES. 08.. LONG TERM...THURSDAY NIGHT THROUGH NEXT WEDNESDAY... THURSDAY NIGHT AND FRIDAY...DIGGING UPPER TROF ACRS CENTRAL CANADA AND INTO THE WESTERN GRT LKS STILL ON TRACK TO SHUNT AN ARCTIC FRONT THROUGH THE CWA BY FRI MORNING. VARYING AMOUNTS OF STRATUS AHEAD OF THIS PROCESS THU EVENING...AND PRE-FRONTAL SOUTHWEST SFC FLOW MAY HELP TEMPS FROM BOTTOMING OUT THU NIGHT BUT MAY STILL LEAN TOWARD THE COOLER SIDE OF GUIDANCE AS A BUFFER AGAINST SOME SFC WIND DECOUPLE IN A DRY SFC LAYER. STEEPENING CYCLONIC FLOW IN A POST- FRONTAL REGIME AND VORT SPOKE WILL LOOK TO WRING OUT LIGHT SNOW AND FLURRIES OUT OF ANY POST-FRONTAL STRATUS ON FRI. BREAKS IN CLOUD COVER AND PROJECTED STEEP LLVL LAPSE RATES MAY MAKE FOR MORE OF A DIURNAL SNOW SHOWER ACTIVITY AS OPPOSED TO STRATIFORM SNOW ESPECIALLY ACRS THE NORTHEAST TO EASTERN HALF OF THE DVN CWA. COLD AND BLUSTERY POST-FRONTAL CONDITIONS WITH HIGHS IN MAINLY IN THE 20S AND NORTHWEST WINDS OF 15 TO 25 MPH. CLEAR OUT FRI NIGHT AS STRONG 1040+ MB HIGH PRESSURE COMPLEX BUILDS DOWN ACRS THE PLAINS AND UPPER MS RVR VALLEY INTO SAT MORNING.WITH EXTENT OF INCOMING SFC RIDGE PRESSURE GRADIENT...EXPECT SOME MIXING NORTH WINDS TO MAINTAIN OVERNIGHT FRI INTO EARLY SAT MORNING TO PREVENT A BOTTOM OUT IN THE LOW SINGLE DIGITS OR EVEN BELOW ZERO. MAY STILL GO WITH LOW SINGLE DIGITS IN THE FAR NORTHWESTERN CWA...TO THE LOWER TEEN IN THE SOUTHEAST. SATURDAY AND SUNDAY...SREF AND LATEST SUITE OF 12Z RUN MEDIUM RANGE MODELS IN GOOD AGREEMENT OF SUGGESTING BOUT OF RIDGING TO MAKE FOR A FAIR BUT CHILLY WEEKEND. BRUNT OF HIGH PRESSURE CENTER PROJECTED TO SHUTTLE TO THE SOUTH OF THE AREA ACRS THE LOWER MS RVR VALLEY ON SAT WITH RIDGE LOBE EXTENDING THIS FAR NORTH. MAINLY SUNNY SKIES...LACK OF SNOW COVER AND CONTINUED MIXING NORTHWEST WINDS OF 10-20 MPH THROUGH AT LEAST MID AFTERNOON WILL HELP TEMPS GET INTO THE LOW TO MID 20S...OTHERWISE EXTENT OF COLD AIRMASS IN PLACE WOULD WARRANT HIGHS IN THE TEENS. SAT NIGHT MAY BE THE COLDEST NIGHT/SECOND NIGHT AFTER COLD FRONT RULE. CHANCE OF NEAR ZERO OR SUB-ZERO TEMPS IN NORTHERN PORTIONS OF THE CWA ESPECIALLY IN COLD AIR DRAINAGE LOCALS. LIGHT RETURN FLOW BEHIND PASSING RIDGE AXIS TO HELP TEMPS ON SUNDAY REACH THE MID TO UPPER 20S...BUT EXPECT INCREASING HIGH CLOUDS IN THE AFTERNOON AHEAD OF SOUTHERN STEAM WAVE DEVELOPING ACRS THE EASTERN GRT BSN. DEPENDING ON EXITING TIMING OF THE ROBUST HIGH PRESSURE COMPLEX...FIRST BOUT OF OVERRUNNING SNOWS MAY GET CLOSE TO OR EVEN INTO THE WESTERN CWA LATE SUNDAY NIGHT BUT FOR NOW WILL BANK ON THE STRENGTH AND SLOWNESS OF THE DENSE RIDGE. MONDAY THROUGH WEDNESDAY...BOTH THE 12Z RUN GFS AND ECMWF ARE TRENDING TOWARD ROLLING A LARGE CHUNK OF THE SOUTHERN STREAM WAVE OUT OVER THE REGION MON INTO TUE MORNING. SOME MOISTURE DRAW IN INCREASING WARM MOIST CONVEYOR UP OFF THE WESTERN GULF BEHIND RETREATING RIDGE COMPLEX WILL FUEL ANY ISENTROPIC LIFT OR ELEVATED FORCES AHEAD OF THIS WAVE. EARLY INDICATIONS BY LATEST 12Z RUN MODELS ESPECIALLY THE WETTER ECMWF NOW SUGGEST 2-4 INCHES OF SNOW POSSIBLE ON MONDAY AND INTO MONDAY NIGHT. WILL CONTINUE TO TREND UP THE POPS BUT SOME TIMING AND MOISTURE INFLUX STILL YET TO EB REFINED OVER THE NEXT 24-48 HRS. WITH THE CURRENT EXPECTED TIMING... SNOW SHOULD BE EAST OF THE CWA BY TUE MORNING AND WILL GO DRY WITH WAKE RIDING. SOUTHWESTERN TROF/SOUTHERN STEAM RELOADS BY MID NEXT WEEK WITH ANOTHER EVEN LARGER SYSTEM POSSIBLE WED THROUGH THU DEPENDING ON PHASING OF COURSE. ..12.. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...NONE. IL...NONE. MO...NONE. && $$