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000
FXUS63 KDVN 281231 AAB
AFDDVN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
631 AM CST SAT FEB 28 2015

.UPDATE...
ISSUED AT 630 AM CST SAT FEB 28 2015

A VERY COLD START TO SATURDAY MORNING IS BEING EXPERIENCED ACROSS
THE CWA TODAY. AFTER COPYING IN THE OBS...IT LOOKS AS THOUGH
BUCHANAN...DELAWARE AND PARTS OF LINN AND JONES COUNTY COULD HAVE
BEEN -20 OR EVEN COLDER FOR LOWS. CURRENT FORECAST IS ON TRACK
WITH 06Z GFS AND NAM SUPPORTING CURRENT FORECAST FOR TODAY AND
TONIGHT. HAVE MADE NO CHANGES TO THE FORECASTS EXCEPT FOR BLENDING
THE OBS INTO THE FORECAST. HAVE RECEIVED A REPORT OF VERY
LOCALIZED DENSE FOG AND SOME HOARFROST THIS. WILL NEED TO MONITOR
TO SEE IF THE SITUATION DETERIORATES.

&&

.SYNOPSIS...
ISSUED AT 240 AM CST SAT FEB 28 2015

HIGH PRESSURE WAS SITUATED DIRECTLY OVER THE CWA THIS
MORNING...RESULTING CLEAR SKIES. THIS ALONG WITH THE FRESH
SNOWFALL WAS LEADING TO TEMPERATURES BOTTOMING OUT. RECORD LOW
TEMPERATURES CONTINUE ACROSS THE AREA TONIGHT. MOLINE WAS -14 AT
MIDNIGHT...WHICH WAS A NEW RECORD. A SHORTWAVE TROUGH LOCATED OVER
SOUTHERN CANADA WAS MOVING TO THE SOUTH. THIS TROUGH WILL BE OUR
PRIMARY WEATHER PRODUCER IN THE SHORT TERM FORECAST PERIOD.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 240 AM CST SAT FEB 28 2015

MAIN FORECAST CONCERN FOR THE SHORT TERM IS THE CHANCE FOR
ACCUMULATING SNOW TODAY AND TONIGHT ACROSS THE AREA. CURRENT
INDICATIONS ARE THAT MOST OF THE SNOW SHOULD FALL SOUTH OF I80 AND
SHOULD BE LIGHT...WITH UP TO 1.5 INCHES FALLING ACROSS FAR
SOUTHERN PORTIONS OF THE CWA.

DECENT SHORTWAVE WILL MOVE OUT OF SOUTHERN CANADA TODAY. WITH IT
DECENT FORCING FOR ASCENT. EXTREMELY DRY AIR IS IN PLACE ACROSS
THE AREA...THIS DRY AIR HAS ALLOWED OUR TEMPS TO PLUMMET TONIGHT.
THIS DRY AIR WILL CONTINUE TO BE THE MAIN PLAYER IN OUR WEATHER
THROUGH TODAY. BY THE TIME MOISTURE ADVECTS INTO THE AREA THE
FORCING SHOULD BE MOVING OVER THE AREA...LEADING ME TO BELIEVE WE
WONT SEE MUCH SNOW. THE TRAJECTORY OF THE MOISTURE AND THE OVERALL
COLUMN SATURATION IS SUCH THAT MOST OF THE SNOW WILL BE SOUTH OF
I80. THE 4KM MODELS...THAT REPRESENT MESOSCALE FEATURES WELL...DO
NOT BRING US MUCH IN TERMS OF QPF AND MODEL REFLECTIVITY. THIS DRY
AIR WILL BE THE MAIN PROBLEM WITH THE FORECAST. IF WE CAN OVERCOME
THE DRY AIR...WE MAY SEE SOME MORE SNOW FURTHER NORTH. AS IT
STANDS NOW...MOST OF THE SNOW IS SOUTH OF INTERSTATE 80. WPC WWD
HAS THE 1 INCH CONTOUR JUST SOUTH OF THE QCA AND ALMOST 2 INCHES
ACROSS SOUTHERN PORTIONS OF THE CWA. THIS WILL BE A LONG DURATION
LIGHT SNOW EVENT FOR SOUTHERN PORTIONS OF THE CWA...CONTINUING
THROUGH SUNDAY.

AS FAR AS TEMPERATURES GO...USED THE RAWBLEND FOR TODAYS
HIGHS...THIS BROUGHT OUR HIGHS DOWN FROM THE DAY SHIFT.
OVERNIGHT...I USED THE SUPERBLEND FOR LOWS.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 240 AM CST SAT FEB 28 2015

A NOTABLE SHIFT SOUTH HAS BEEN OCCURRING IN GUIDANCE FORECAST OF THE
STORM SYSTEM SUNDAY IN THE PAST 24 HOURS...WITH NOW NEARLY ALL
GUIDANCE HOLDING SATURATION AND MODEST FORCING SOUTH OF INTERSTATE
80 SUNDAY MORNING...WITH FURTHER WEAKENING DYNAMICS AND COLD DRY
ADVECTION SUNDAY AFTERNOON. THUS...OUR POORLY CONFIDENT FORECAST
ISSUED YESTERDAY...IS NOW MORE CONFIDENTLY DRY.  I HAVE LOWERED SNOW
AMOUNTS BY ABOUT 50 PERCENT SUNDAY...WITH ONLY TRACE AMOUNTS AT MOST
OVER THE NORTH 1/2 OF THE CWA...AND ABOUT 0.5 TO 1.5 THROUGH THE
SOUTH. THIS PLACES THE LONG DURATION SNOW TOTALS ABOUT A HALF TO ONE
INCH NEAR IOWA CITY TO THE QUAD CITIES....TO AROUND 2 INCHES NEAR
BURLINGTON...TO NEAR 3 INCHES IN THE SOUTHEASTERN TIP OF MCDONOUGH
COUNTY. THESE AMOUNTS ARE VERY MARGINAL FOR ANY KIND OF ADVISORY IF
THEY OCCUR OVER A BROAD TIME PERIOD...AND THEY ARE NOT REPRESENTING
A HIGH CONFIDENCE EVEN AT THIS TIME...WITH SEVERAL MODELS HOLDING
ALL SATURATION ALONG AND SOUTH OF OUR SOUTH. EITHER WAY...IT WILL BE
COLD SUNDAY NIGHT...AS ANOTHER HIGH PRESSURE SLIDES INTO THE
REGION...OVER WHAT IS STILL FRESH FLUFFY SNOW COVER.
AFTER HIGHS IN THE 20S SUNDAY...WE WILL FALL TO THE SINGLE DIGITS
OVER THE NORTHERN 2/3RS OF THE CWA SUNDAY NIGHT...WITH LOWER TEENS
SOUTH.

MONDAY...WITH HIGH PRESSURE OVERHEAD...AND SUNSHINE THROUGH THE
EARLY AFTERNOON...WE SHOULD RECOVER THE MID TO UPPER 20S. NO DOUBT
THIS WILL FEEL VERY PLEASANT GIVEN THE LIGHT WINDS AND SUN.

OUR EYES THEN TURN TO A MOISTURE RICH SYSTEM ARRIVING MONDAY
NIGHT...AND LASTING THROUGH TUESDAY EVENING. THIS SYSTEM IS FORECAST
TO BRING PWAT VALUES NEAR 1 TO 1.25 INCHES TO THE CWA...WITH IS AN
INCREDIBLE ONE INCH HIGHER THAN OUR SOUNDING LAST EVENING WHERE WE
HAD A PWAT OF 0.04. THE CHALLENGES WITH THIS SYSTEM WILL TRANSITIONS
IN PRECIPITATION TYPE...FROM SNOW TO SLEET TO ICE...TO RAIN...THEN
BACK TO SNOW BEFORE ENDING. THIS TRANSITION MUST OCCUR IN ALL
PORTIONS OF THE AREA...THUS IT IS A COMPLICATED MESS OF A
FORECAST...AND I HAVE DONE ALL I CAN TO SIMPLIFY IT WHERE I CAN.
SO...BASED ON A BLEND OF ECMWF AND GFS TEMPERATURE TRENDS...OUR
FORECAST SHOWS SNOW SPREADING IN FROM THE WEST MONDAY EVENING AND
OVERNIGHT...WITH SLEET MIXING IN OVER SOUTHERN LOCATIONS TOWARD
MIDNIGHT. THROUGH THE EARLY MORNING HOURS...THE SLEET MIX SHOULD
SPREAD NORTHWARD...THROUGH HIGHWAY 30. THE SOUTH AFTER 3 AM WILL SEE
A MIX OF SLEET AND FREEZING RAIN POSSIBLE....AND THIS IS WHERE I SEE
OUR INITIAL HEADLINE NEEDED. THE CENTRAL AND NORTH WILL ALSO SEE A
WINDOW OF 6 TO 8 HOURS OF FREEZING MIX...FROM AROUND 5 AM TO NOON.
THE EXACT DETAILS OF THE FREEZING MIX WILL DETERMINE IMPACTS...AND
THOSE ARE NOT HIGH CONFIDENCE YET SINCE THIS IS A DAY 3 EVENT WE ARE
DISCUSSING. IN ANY CASE...THE ROBUST WARM MOIST ADVECTION SHOULD
PUSH WETBULB TEMPERATURES ABOVE 32 AREA WIDE BY 11 AM
TUESDAY...RESULTING IN A PERIOD OF NON HAZARDOUS WEATHER...I.E.
RAIN. BY EARLY AFTERNOON...COLD AIR WILL BEGIN SPREADING BACK INTO
THE NORTHWEST AS THE SYSTEM MOVES EAST...THIS SHOULD DRAW A DEEP
LAYER OF SUBFREEZING TEMPERATURES IN...THUS...IT SHOULD BE RAIN SNOW
MIX...GOING BACK TO ALL SNOW FROM WEST TO EAST TUESDAY AFTERNOON
THROUGH TUESDAY EVENING. SOME LIGHT SNOW AMOUNTS ARE POSSIBLE...BUT
COULD BE LIGHT ENOUGH NOT TO WARRANT ANY HEADLINE.

STRONG COLD ADVECTION TUESDAY NIGHT WILL DRAW MORE ARCTIC AIR BACK
TO THE MIDWEST...WITH LOWS OVER OUR REMAIN SNOW COVER FALLING TO THE
SINGLE DIGITS WEST TO LOWER TEENS. THIS COLD AIR WILL BE IN PLACE
WEDNESDAY THROUGH THURSDAY NIGHT...WITH HIGHS IN THE TEENS AND THE
LOWS -5 TO +5. PACIFIC AIR SHOULD SPREAD IN TO THE MIDWEST FRIDAY
WITH ZONAL FLOW ALOFT...RESULTING IN HIGHS IN THE MID 30S TO NEAR
40...SO THERE IS HOPE AT THE END OF THIS EARLY MARCH TUNNEL.

ERVIN

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 531 AM CST SAT FEB 28 2015

VFR CONDITIONS WILL GIVE WAY TO MVFR CEILINGS LATER IN THE DAY AND
TONIGHT WITH SN MOVING INTO THE AREA. AT THIS TIME...I HAVE LOW
CONFIDENCE THAT CID AND MLI WILL SEE MUCH MORE THAN A SHORT PERIOD
OF SN. AS SUCH...WENT WITH A PROB30 WHICH IS PRETTY MUCH WHAT THE
PUBLIC FORECAST HAS AS WELL. BRL WILL SEE SN THROUGHOUT THE
EVENING AND OVERNIGHT...WITH POSSIBLY THE HEAVIEST SN NEAR 12Z
SUNDAY. LOW CONFIDENCE ON DBQ SEEING MUCH MORE THAN FLURRIES AND
DONT HAVE ANY CONFIDENCE TO PUT IN A FM GROUP FOR IT.


&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...WIND CHILL ADVISORY UNTIL 9 AM CST THIS MORNING FOR BENTON-
     BUCHANAN-CEDAR-CLINTON-DELAWARE-DUBUQUE-IOWA-JACKSON-
     JOHNSON-JONES-LINN-MUSCATINE-SCOTT.

IL...WIND CHILL ADVISORY UNTIL 9 AM CST THIS MORNING FOR CARROLL-JO
     DAVIESS-ROCK ISLAND.

MO...NONE.
&&

$$

UPDATE...GIBBS
SYNOPSIS...GIBBS
SHORT TERM...GIBBS
LONG TERM...ERVIN
AVIATION...GIBBS