Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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884
FXUS63 KDVN 130520
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1120 PM CST FRI FEB 12 2016

...AVIATION UPDATE...

.SYNOPSIS...
ISSUED AT 350 PM CST FRI FEB 12 2016

LATEST SFC ANALYSIS WAS INDICATING TIGHT ARCTIC RIDGE GRADIENT
PUSHING ACRS THE CWA ATTM...WITH SOME ISALLOBARIC RISE SURGE
COMPONENT INDUCING SUSTAINED NORTHWEST WINDS OF 20 TO NEAR 30 MPH
AND GUSTS WELL OVER 30 MPH/NEAR 40 MPH AT TIMES THIS AFTERNOON.
THESE BRISK WINDS SHOULD DECREASE WITH LOSS OF MIXING INSOLATION
AFTER SUNSET. OTHERWISE...1044 MB HIGH CENTER WAS LURKING ACRS
EASTERN ND. ALOFT...THE CURRENT WATER VAPOR LOOP WAS INDICATING
CLOSED COLD CORE UPPER LOW OVER THE JAMES BAY REGION...A SHARP UPPER
RIDGE ACRS THE WESTERN ROCKIES...AND SUNDAY/S WX MAKER LOW OFF THE
PACIFIC NORTHWEST COAST.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 350 PM CST FRI FEB 12 2016

TONIGHT...WILL KEEP ONGOING WIND CHILL HEADLINES INTACT HI-LIGHTING
AREAS GENERALLY ALONG AND NORTH OF HWY 30 FROM 9 PM THIS EVENING...
TO 9 PM CST SAT MORNING. NOT MUCH CHANGE FROM ONGOING LOW TEMPS WITH
MAYBE A SLIGHT BUMP UP A DEGREE OR TWO AWAY FROM THE SNOW COVERED
AREAS OF THE FAR NORTHWESTERN CWA. SOME CONCERN THAT ALTHOUGH THE
WINDS WILL DECREASE OVERNIGHT TO 5-10 MPH BY SUNRISE SAT...THAT
EXTENT OF MIXING MAY STILL BE ENOUGH PREVENT TEMPS FROM DIPPING TO
THE COLDEST OF GUIDANCE VALUES AND THUS THE TREND UP SOME. THE
LATEST ECMWF MOS MAY HAVE PICKED UP ON THIS AND IS SEVERAL DEGREES
MILDER THAN EVEN THE ADJUSTED LOW TEMPS FOR TONIGHT FOR MOST OF THE
AREA. BUT WITH ONGOING STOUT COLD AIR ADVECTION OFF SNOW FIELDS TO
THE NORTHWEST OF THE CWA SUCH AS THE NORTHERN PLAINS/MN/NORTHWEST
IA...WOULD RATHER ERROR ON THE COLDER SIDE. OTHERWISE...MAINLY CLEAR
TONIGHT AS INCOMING CANADIAN RIDGE IMPLANTS ITSELF ALONG AND WEST OF
THE MS RVR VALLEY BE SAT MORNING.

SATURDAY...BOTH SFC AND UPPER RIDGING TO HAVE THEIR EFFECT ACRS THE
AREA WITH LIGHT WINDS AND SUNSHINE IN THE MORNING...BUT THAT
INSOLATION WILL GET DIRTIED/FILTERED BY OVERRUNNING CIRRUS FROM THE
WEST AS THE DAY PROGRESSES. STILL SOME LIGHT SOUTHEAST RETURN FLOW
LATE IN THE DAY BEHIND DEPARTING SFC RIDGE AXIS TO HELP TEMPS
RECOVER TO LATE AFTERNOON HIGHS IN THE UPPER SINGLE DIGITS IN THE
NORTHWEST...TO THE LOW TO MID TEENS ALONG AND SOUTH OF I80. JUST A
LOW CHC THAT THE EASTERN TIP OF LEAD WARM AIR ADVECTION WING SNOWS
WILL GET INTO THE FAR SOUTHWESTERN CWA BEFORE 6 PM CST.   ..12..

.LONG TERM...(SATURDAY NIGHT THROUGH NEXT FRIDAY)
ISSUED AT 350 PM CST FRI FEB 12 2016

MAIN FOCUS IS WITH ACCUMULATING SNOWFALL SAT NIGHT THROUGH SUNDAY
WITH CLIPPER SYSTEM.

WATER VAPOR SATELLITE IMAGERY SHOWS THE SHORTWAVE ENERGY DRIVING
THIS SYSTEM STILL OFF THE PACIFIC NORTHWEST COAST THIS AFTERNOON.
AS RESULT... WE CONTINUE WITH MODEL DIFFERENCES ESPECIALLY WITH
REGARDS TO LOCATION OF SFC WARM FRONT AND TRACK OF SFC LOW ALONG
WITH PRECIP AMOUNTS. HOWEVER... AS THE ENERGY COMES ASHORE NEXT
12-18 HOURS INTO MORE DENSE RAOB NETWORK EXPECT BETTER SAMPLING
TO YIELD MORE COHENSION ON THE DETAILS OF TIMING/LOCATION/AMOUNTS.

DESPITE THE UNCERTAINTY ON DETAILS... CONFIDENCE REMAINS HIGH ON
ACCUMULATING SNOW OVER THE ENTIRE CWA SECOND HALF OF THE WEEKEND.
OVERALL FAVORING THE ECMWF SOLUTION IN HANDLING OF SYSTEM PER ITS
BETTER RUN TO RUN STABILITY... WITH SOME INPUTS FROM GFS. LOW TO
MID LEVEL WARM ADVECTION AND INCREASING VERTICAL MOTIONS SHOULD
LEAD TO QUICK TOP DOWN SATURATION AND DEVELOPMENT OF SNOW FROM
SOUTHWEST TO NORTHEAST ACROSS THE CWA IN ROUGHLY THE MID-LATE EVENING
SATURDAY THROUGH DAYBREAK SUNDAY. CONCEPTUALLY FAVOR CONTINUED
WEST TO EAST PROGRESSION OF SNOW BAND ON SUNDAY WITH WARM ADVECTION
WING... AND EXPECT A LARGE PORTION OF THIS SNOW FROM THIS EVENT WILL
OCCUR IN THIS WAA FORCING. SOME MODELS INCLUDING GFS AND GEM
WETTER WITH LINGERING SNOWS INTO SUNDAY EVENING... BUT NOT SUPPORTED
BY JET STRUCTURE AND LACK OF FORCING OR DECREASE IN OMEGAS AND RELATIVE
HUMIDITY IN DENDRITIC GROWTH ZONE AS SHOWN BY AT LEAST ONE MODEL...
WHICH WOULD LEND TO MORE NEEDLES AND VERY LIGHT ACCUMS BY MID
SUNDAY AFTERNOON THROUGH EARLY EVENING. AS FOR SNOWFALL AMOUNTS...
TYPICALLY WITH THESE NORTHWEST SYSTEMS WE THINK OF THEM BEING
MOISTURE STARVED... BUT NOT SO THE CASE WITH THIS ONE AS 12Z
PRECIPITABLE WATER ANALYSIS SHOWS ANOMALOUSLY HIGH ATMOSPHERIC
MOISTURE CONTENT OF AROUND 0.5 TO 0.75 INCHES OR ROUGHLY 150% TO
250% OF NORMAL OVER PORTIONS OF THE PACIFIC NORTHWEST... AND SOME
OF THIS MOISTURE WILL BE ACCOMPANYING SYSTEM AS IT HEADS E/SE AND
SHIFTS ACROSS THE UPPER MIDWEST LATE IN THE WEEKEND. OVERALL WITH
FORCING AND MOISTURE INPUTS THINKING AROUND 0.1 TO 0.3 INCH LIQUID
QPF WITH THIS ENTIRE EVENT... WITH SLRS AT TIMES AROUND 15-20:1
FOR GENERAL RANGE ON ACCUMS FROM 2 TO 5 INCHES ACROSS THE CWA BY
TIME SNOW WINDS DOWN SUNDAY EVENING. HIGHEST AMOUNTS PROBABLY
NORTH WHERE HIGHER SLRS. WINDS WILL BE AROUND 10 TO 20 MPH AT
TIMES DURING AND JUST AFTER THE EVENT... AND COMBINED WITH THESE
AMOUNTS WILL LIKELY NEED AN ADVISORY.

LOOKING BEYOND... SIGNAL APPEARS TO BE INCREASING FOR ANOTHER
CLIPPER SYSTEM WITH SNOW LATER MONDAY NIGHT INTO TUESDAY.
UNCERTAINTY ON TRACK AND TIMING WITH NO DOUBT IMPACTS FROM
RECENTLY DEPARTED SYSTEM... THUS REASON FOR JUST LOWER CHANCE POPS
FOR NOW. THE POTENTIAL EXISTS FOR ONE FINAL CLIPPER SYSTEM MIDWEEK
BEFORE WELL ADVERTISED PATTERN CHANGE TO SEMI-ZONAL FLOW AND
INVASION OF MP AIRMASS LEADING TO WARMUP AND ABOVE NORMAL TEMPS
SECOND HALF OF THE WEEK INTO THE WEEKEND. FRESH SNOW COVER MAY
NEGATE THIS WARMING POTENTIAL INITIALLY... BUT EVENTUALLY SEE
POTENTIAL FOR HIGHS IN THE 40S AND POSSIBLY 50S LATE WEEK
DEPENDING ON SNOW MELT.    ..05..

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1120 PM CST FRI FEB 12 2016

AN ARCTIC HIGH OVER THE EASTERN DAKOTAS WILL PROVIDE MOSTLY CLEAR
SKIES AND DECREASING NORTHWEST WINDS AS IT MOVES SOUTHEAST INTO
IOWA OVERNIGHT THROUGH MUCH OF SATURDAY. THIS WILL KEEP CONDITIONS
VFR THROUGHOUT WITH LIGHT NORTH TO NORTHWEST WINDS DURING THE DAY
BECOMING SOUTHEAST AT ALL SITES SATURDAY EVENING. AN APPROACHING
WINTER STORM SYSTEM IS EXPECTED TO BRING DETERIORATING CONDITIONS
BEGINNING LATE SATURDAY NIGHT INTO EARLY SUNDAY MORNING. THE
EARLIEST ONSET MAY AFFECT THE BRL SITE...WHERE PROB30 WORDING FOR
LIGHT SNOW IS INCLUDED WAS USED IN THE SATURDAY EVENING PERIOD.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...WIND CHILL ADVISORY UNTIL 9 AM CST SATURDAY FOR BENTON-BUCHANAN-
     CLINTON-DELAWARE-DUBUQUE-JACKSON-JONES-LINN.

IL...WIND CHILL ADVISORY UNTIL 9 AM CST SATURDAY FOR CARROLL-JO
     DAVIESS-STEPHENSON-WHITESIDE.

MO...NONE.
&&

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...05
AVIATION...SHEETS



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