Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 190918
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
318 AM CST FRI DEC 19 2014

.SYNOPSIS...
ISSUED AT 316 AM CST FRI DEC 19 2014

LATEST SFC ANALYSIS WAS INDICATING LARGE RIDGE AXIS HOLDING FIRM
FROM ACRS ONTARIO NORTH OF LK SUPERIOR...ALL THE WAY DOWN INTO THE
MID TO LOWER MS RVR VALLEY. LIGHT LLVL RETURN FLOW PATTERN TO THE
WEST OF IT ACRS THE CENTRAL AND NORTHERN PLAINS. EXTENSIVE STRATUS
DECK UNDER THE WEST HALF OF THE RIDGE AND INTO THE EASTERN PLAINS
IN RETURN FLOW INTERACTION ZONE...OPEN SKY SWATH FROM SOUTHWEST
OF DBQ SOUTHEASTWARD THRU THE QUAD CITES/EASTERN I80 CORRIDOR
WILL LOOK TO FILL BACK IN EARLY THIS MORNING. ALOFT...00Z UPPER
AIR ANALYSIS AND CURRENT WATER VAPOR LOOP INDICATED A VORT WING
MOVING ACRS EASTERN SD INTO SOUTHEASTERN MN...TAILING DOWN ACRS
CENTRAL INTO EASTERN IA ATTM. THIS FEATURE IS PRODUCING LIGHT SNOW
ACRS MN...AND MAY BE INDUCING THE PATCHY LIGHT FREEZING DRIZZLE
CURRENTLY OUT ACRS CENTRAL IA. NEG VORTICITY IS MOVING OUT OF EASTERN
NEB INTO WESTERN IA BEHIND THIS MAIN VORT. A FURTHER UPSTREAM VORT
NOTED ACRS WY...AND A MORE VIGOROUS VORT MAX NOTED ACRS SOUTHERN
ALBERTA.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 316 AM CST FRI DEC 19 2014

TODAY...BULK OF HIRES MODELS SUGGEST HIGH PRESSURE COMPLEX TO
HAVE IT/S EFFECT THIS MORNING MAINTAINING HIGHER CLOUD CIGS FOR
AWHILE...BEFORE AXIS STARTS TO SLIDE EASTWARD MIDDAY INTO THE
AFTERNOON ALLOWING THE LOWER DECK OUT WEST TO SEEP EASTWARD. AREA
OF LIGHT DRIZZLE/FREEZING DRIZZLE ACRS CENTRAL IA MOVING
NORTHEASTWARD AND MAY GET CLOSE TO THE NORTHWESTERN PORTION OF THE
CWA THIS MORNING...BUT WILL BANK ON DIURNAL EFFECTS AND THE RIDGE
STILL IN PLACE TO DEFLECT/EAT AWAY AT THIS PROCESS AND KEEP THE
DRIZZLE JUST TO THE WEST AND NORTHWEST OF THE CWA THIS MORNING...
ALTHOUGH IT WILL BE CLOSE AND WILL HAVE TO WATCH FOR UPDATES. THEN
EXPECT NVA OUT OF WESTERN IA FOR MUCH OF THE DAY WITH ONGOING CLOUDY
TO MOSTLY CLOUDY SKIES. SOME LIGHT SOUTHEAST SFC FLOW THIS AFTERNOON
TO HELP TEMPS MAKE IT A FEW DEGREES MILDER THAN YESTERDAY. THEN THE
UPSTREAM VORT NOTED ABOVE CURRENTLY ACRS WY WILL LOOK TO DIG ACRS
THE IA/MO BORDER BY LATE AFTERNOON AND EARLY EVENING. WITH RATHER
SHALLOW MOISTURE LAYER TRAPPED IN THE LOW LEVELS MAINLY UNDER H8
MB...THIS INCOMING WAVE MAY START TO PRODUCE SPOTTY DRIZZLE AGAIN
AS OPPOSED TO FLURRIES ACRS MO INTO CENTRAL IA...BUT AGAIN WILL BANK
ON ANY PRECIP REACHING THE SFC TO REMAIN WEST OF THE CWA LATE THIS
AFTERNOON AND INTO THE EVENING.

TONIGHT...EXPECT TEMPS TO HOLD STEADY IN THE MID TO UPPER 20S UNDER
STRATUS DECK AND CONTINUING LIGHT SOUTHEASTERLY SFC FLOW. AS THE
FIRST WEAK WAVE CONTINUES TO MOVE EAST ACRS THE SOUTH HALF OF IA
INTO IL DURING THE EVENING...THERE MAY BE A CHC FOR SOME SPOTTY LIGHT
DRIZZLE/FREEZING DRIZZLE TO BREAK OUT BUT WILL KEEP THE FCST DRY
THROUGH 06Z FOR NOW. A BETTER CHC AFTER MIDNIGHT AS THE STRONGER
WAVE ARRIVES OUT OF ALBERTA AND DIGS ACRS THE SOUTHWESTERN HALF OF
IA. MOISTURE DEPTH AND EXTENT OF LIFT STILL AT QUESTION...BUT WILL
INTRODUCE AT LEAST PATCHY LIGHT FREEZING DRIZZLE OUT OF THE
MOISTURE TRAPPED UNDER THE INVERSION ALOFT ACRS THE WESTERN CWA
AFTER MIDNIGHT. HOPEFULLY IT WILL BE SPOTTY AND LIGHT ENOUGH NOT TO
WARRANT SOME TYPE OF HEADLINE...BUT DAY SHIFT WILL HAVE TO REASSESS
AS WELL AS THE POSSIBILITY TO ADD SPOTTY CHC/S IN THE EVENING BEFORE
MIDNIGHT.    ..12..


.LONG TERM...(SATURDAY THROUGH NEXT THURSDAY)
ISSUED AT 316 AM CST FRI DEC 19 2014

THE LONG TERM WILL BEGIN WITH THE SAME CLOUDY AND DAMP REGIME WE
HAVE SEEN MANY TIMES OVER THIS PAST MONTH. TONIGHTS DRIZZLE...FOG
AND LOW CLOUDS LOOK TO REMAIN IN PLACE FOR SATURDAY THROUGH SUNDAY
NIGHT...WITH THE MAIN IMPACTS GREATLY DEPENDING ON HOURLY
TEMPERATURES. SHORT LIVED SUBSIDENCE SATURDAY BEHIND THE MID LEVEL
SHORT WAVE LATER TONIGHT WILL HOPEFULLY OFFER A LULL IN ANY
DRIZZLE...SO AFTER A MILD DAY IN THE MID TO UPPER 30S...WE WILL SET
UP FOR ANOTHER DRIZZLE/FZDZ EVENT BY SATURDAY NIGHT. THE DOMESTIC
MODELS ARE OFFERING COLD SURFACE CONDITIONS FOR SATURDAY
NIGHT...WHILE THE ECMWF IS MUCH MORE MILD. I BELIEVE THE ECMWF IS
MORE ON TARGET HERE AS THERE IS ALMOST NO REASON FOR COLD
SUBFREEZING AIR TO LINGER UNDER THIS STRATUS DECK. IN ANY
CASE...DESPITE LOWS IN THE LOWER 30S...ROADS AND SURFACES WILL NOT
BE ABLE TO RADIATE OUT SATURDAY NIGHT UNDER THE LOW CLOUDS WHICH
WILL ACTUALLY GIVE OFF LONG WAVE RADIATION TO THE SURFACES AS
WELL...LIKELY KEEPING ANY FZDZ MINIMALLY PROBLEMATIC. STILL...SINCE
WE ARE CLOSE ENOUGH TO 32 MUCH OF THE NIGHT IN THE NORTH...I WILL
MENTION IT IN THE GRIDS...BUT HOPEFULLY THIS IS NOT AN ADVISORY
EVENT. SHOULD THE ECMWF RISING TEMPERATURES BE CORRECT AS I
SUSPECT...WE SHOULD BE ABOVE FREEZING DURING THE TIME DRIZZLE OCCURS
SATURDAY NIGHT. THE DZ EVENT MAY LINGER THROUGH THE DAY SUNDAY...AND
AS MORE NOTABLE FORCING ARRIVES...IT MAY BECOME A INTERMITTENT LIGHT
RAIN IN THE NORTH...AND WILL ALLOW POPS TO BE MENTIONED AT THAT
TIME. IN THE END...IF THE DRIZZLE IS HEAVY ENOUGH...IT WILL NEED
MUCH HIGHER POPS FOR CONTINUALLY WETTING SURFACES ANYWAY.

SUNDAY NIGHT...WAA WILL BE RATHER STRONG AS THE COMPLICATED
NORTHWEST FLOW LOW PRESSURE SYSTEM ARRIVES. A SLOW MOVING SURFACE
LOW IS FORECAST NEAR IOWA...AS THE MAIN ENERGY DIVES WELL
SOUTH...CARVING OUT WHAT MAY BE INTENSE LOW PRESSURE OVER THE OHIO
VALLEY TOWARDS TUESDAY NIGHT. AS THIS OCCURS...BOUTS OF LIGHT RAIN
ARE LIKELY...EVENTUALLY CHANGING TO LIGHT SNOW BY LATER TUESDAY WHEN
THE SYSTEM BEGINS TO RAMP UP TO THE EAST. IN THE END...SUNDAY NIGHT
THROUGH MONDAY NIGHT MAY JUST BE A CONTINUATION OF THE RELATIVELY
MILD AND DAMP CONDITIONS WE HAVE BEEN QUITE FAMILIAR WITH THIS MONTH.

TUESDAY NIGHT INTO WEDNESDAY...WHILE LIGHT SNOW IS POSSIBLE DUE TO
ENERGY DIVING INTO THE RAPIDLY STRENGTHENING STORM TO THE EAST...OUT
BIGGEST SENSIBLE WEATHER WILL BE WIND...STRONG WINDS OF 20 TO 30 MPH
APPEAR LIKELY...WITH GUSTS OVER 35 POSSIBLE WEDNESDAY AFTERNOON AS
THE LOW TO THE EAST POTENTIALLY DEEPENS TO AROUND 970MB PER 00Z ECMWF

FOLLOWING THIS...AFTER A PERIOD OF COLD ADVECTION LASTING INTO
WEDNESDAY NIGHT...MODELS ARE GREATLY DIVERGENT. THE 00Z GFS OFFERS
NORTHWEST FLOW WITH NO SIGNIFICANT ARCTIC AIR...BUT LITTLE PCPN
THREATS. THE 00Z ECMWF HAS A PROGRESSIVE DEEP SYNOPTIC TROF MOVING
INTO THE LOWER ROCKIES BY DECEMBER 26...SPAWNING CYCLOGENESIS IN THE
WESTERN PLAINS. THAT SYSTEM WOULD IMPACT THE MIDWEST WITH MORE
CLOUDS/RAIN/POSSIBLE WINTER PCPN LATER ON THE 26/27. THERE IS NO
CERTAINTY OF THIS SYSTEM FROM MODEL TO MODEL...OR IN RUN TO RUN OF
ANY MODEL...SO MENTION OF A TRACK OF THAT POSSIBLE STORM SEEMS VERY
PREMATURE AT THIS TIME.    ERVIN

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1118 PM CST THU DEC 18 2014

NEARLY CALM WINDS AND VARIABLE CLOUD COVER WILL REMAIN IN PLACE
THROUGH THE REST OF THE NIGHT AS A RIDGE OF HIGH PRESSURE LINGERS
OVERHEAD. A DECK OF LOWER CLOUDS WITH MVFR CIGS WILL AFFECT
PRIMARILY THE DBQ SITE TONIGHT...BEFORE MORE WIDESPREAD LOWER
CLOUDS LOOMING JUST WEST OF THE RIDGE AXIS SPREAD INTO EASTERN IA
AND NW IL DURING THE DAY FRIDAY. CONFIDENCE IN THE EXACT TIMING OF
THIS TRANSITION TO MVFR CONDITIONS REMAINS LOW...BUT THERE IS A
GOOD LIKELIHOOD THAT ALL SITES HAVE CIGS AT OR BELOW 2500 FT BY 06Z
FRIDAY NIGHT.

&&

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

$$

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






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