Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 220343
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
943 PM CST FRI NOV 21 2014

.UPDATE...
ISSUED AT 940 PM CST FRI NOV 21 2014

THUS FAR LITTLE IN WAY OF ANY ICING BEING REPORTED. TEMPS HAVE
CONTINUED A GRADUAL ASCENT ALL EVENING LONG EVEN IN AREAS WHERE
THE WET BULB IS WELL BELOW THE FREEZING MARK. JUST HAVENT SEEN
SFC TEMPS DROPPING IN THE EVAPORATIONAL COOLING ATTENDANT TO THE
PCPN... BUT THIS MAY BE ATTRIBUTED TO THE FACT THAT UNTIL
RECENTLY THE RAIN HAS BEEN QUITE SPOTTY AND VERY LIGHT. EXPECT
CONTINUED UPTICK IN COVERAGE OF PCPN LATE THIS EVENING INTO THE
EARLY OVERNIGHT WITH PASSAGE OF SHORTWAVE AND ATTENDANT SURGE OF
WARM...MOIST ADVECTION. WONDER IF THE UPTICK IN COVERAGE AND EVEN
INTENSITY OF RAIN IN SOME AREAS MAY BE SUFFICIENT TO AGGRESSIVELY
WET BULB DOWN TO FREEZING TO ALLOW FOR SOME ICING WITH DEWPTS SO
DRY. MOST SUSCEPTIBLE OR FAVORED AREAS FOR LIGHT ICING (LESS THAN
0.1 INCH) WOULD APPEAR TO BE NORTH OF I-80 AND ESPECIALLY
NEAR/NORTH OF HWY 30. BOTTOM LINE... WILL CONTINUE THE ADVISORY
FOR MUCH OF CWA ALTHOUGH HAVE OPTED TO CANCEL THE ADVISORY FOR
PORTIONS OF EXTREME SOUTHEAST IA... WEST CENTRAL IL AND NORTHEAST
MO BASED ON ROAD TEMPS ABOVE FREEZING AND GIVEN GENERAL FOCUS OF
STEADIER RAIN LIKELY A BIT FURTHER NORTH. FORCING DEPARTS
OVERNIGHT FROM SOUTHWEST TO NORTHEAST AND SHOULD SEE DIMINISHING
TREND TO DRIZZLE WITH THREAT OF ICE ABATING ALL AREAS BY 12Z.

&&

.SYNOPSIS...
ISSUED AT 336 PM CST FRI NOV 21 2014

A LARGE MID AND UPPER LEVEL TROUGH OVER THE EASTERN THIRD OF THE
U.S. WILL PROPAGATE EASTWARD INTO THE NORTH ATLANTIC THROUGH
TONIGHT. CONSEQUENTLY...ZONAL MID-LEVEL FLOW WILL SET UP ACROSS THE
CENTRAL U.S. THROUGH SATURDAY AND SFC TEMPS WILL MODERATE INTO THE
30S AND 40S DURING THIS TIME. MOISTURE ADVECTION IN ADVANCE OF AN
APPROACHING TROUGH WILL RESULT IN LIGHT FREEZING RAIN TONIGHT AND A
WIDESPREAD RAINFALL SATURDAY NIGHT AND SUNDAY.

&&

.SHORT TERM...(THIS EVENING THROUGH TONIGHT)
336 PM CST FRI NOV 21 2014

TONIGHT...FREEZING RAIN ADVISORY IS IN EFFECT FOR THE ENTIRE CWA
THIS EVENING THROUGH TONIGHT. THE SOUTHERN THIRD OF COUNTIES WILL BE
THE FIRST TO WARM ABOVE FREEZING SO THE ADVISORY WILL END AT 3 AM
THERE BUT CONTINUE TO THE NORTH UNTIL 6 AM SAT.

ALTHOUGH SFC TEMPS HAVE RISEN INTO THE MID 30S ACROSS THE CENTRAL
AND SOUTH...THE AIR IS STILL EXTREMELY DRY WITH DEWPOINTS IN THE
SINGLE DIGITS TO MIDDLE TEENS. FOR THIS REASON BELIEVE TEMPS WILL
FALL OFF RATHER QUICKLY LATE THIS AFTN THROUGH RADIATIONAL COOLING.
ADDITIONALLY...EVAPORATIVE COOLING SHOULD KNOCK TEMPS TO FREEZING OR
SLIGHTLY BELOW AS THE RAIN MOVES IN.

LOW-LEVEL WAA REGIME WILL CAUSE 850 MB TEMPS TO INCREASE
DRAMATICALLY THROUGH TONIGHT. NAM SOUNDINGS INDICATE SIGNIFICANT
MOISTENING OF THE COLUMN THROUGH THIS EVENING. BY 03Z/SAT AT KCID
...NAM FORECAST SOUNDINGS SHOW HIGH SATURATION IN THE SFC-700 MB
LAYER AND REVEAL A STRONG LOW-LEVEL INVERSION THAT PEAKS AT +6 C AT
900 MB. WAA/PRESSURE ADVECTION IN SFC-750 MB LAYER WILL BE THE MAIN
DRIVER FOR ASCENT BUT THIS WILL BE COUPLED WITH A PERIOD OF DCVA AS
A VORT MAX...CURRENTLY SITUATED OVER NE KANSAS...MOVES THROUGH E
IOWA/W ILLINOIS BETWEEN 00Z-06Z/SAT. OMEGA TIME-HEIGHT SECTIONS
CLEARLY PICK UP ON THESE TWO FEATURES.

CONSENSUS OF THE SFC WET-BULB 0 C ISOTHERM IS FOR IT TO REACH THE
QUAD CITIES AREA BETWEEN 06Z-09Z AND DUBUQUE AROUND 11Z OR 12Z.
UNFORTUNATELY GROUND TEMPS ARE VERY COLD FOR THIS TIME OF YEAR...THE
11.20/12Z FROST DEPTH AT DVN WAS MEASURED AT 7 INCHES...SO SFC
GROUND TEMPS MAY LAG THE AMBIENT TEMP BY SEVERAL HOURS.

GENERALLY EXPECTING BETWEEN 0.05 TO 0.10 INCHES OF ICE ACCUMULATION
WITH SOME ISOLATED AREAS RECEIVING SLIGHTLY OVER 0.10 INCHES. THE
HIGHEST AMOUNTS WILL BE WELL NW OF A BURLINGTON-TO-PRINCETON LINE.
LOWER PRECIP AMOUNTS ARE FORECAST ACROSS THE FAR NW CWA AND SO TOO
ARE THE ICE AMOUNTS THERE.

.LONG TERM...(SATURDAY THROUGH FRIDAY)
ISSUED AT 336 PM CST FRI NOV 21 2014

FOCUS REMAINS ON THE DEVELOPING STORM SYSTEM THAT WILL BRING MUCH
WARMER TEMPERATURES...ALONG WITH AN EXTENDED PERIOD OF DRIZZLE...FOG
AND RAIN OVER THE WEEKEND. MODELS CONTINUE TO EVOLVE IN HOW THE
NORTHERN AND SOUTHERN STREAM SHORTWAVES AND SURFACE CYCLONES
MERGE...NOW DEPICTING A YET SLOWER PROCESS...WITH A SOMEWHAT WEAKER
CONSOLIDATED SURFACE LOW NOW FORMING SUNDAY NIGHT OR LATER OVER THE
GREAT LAKES. THIS STILL RESULTS IN AN EXTENDED PERIOD OF
WARM...MOIST ADVECTION WITH MODERATE TO SEASONABLY HEAVY RAINFALL
CENTERED ON THE SUNDAY INTO SUNDAY NIGHT TIMEFRAME. WINDY AND COOLER
WEATHER WITH SNOW SHOWERS THEN FOLLOWS EARLY NEXT WEEK AS THE LOW
LIFTS INTO EASTERN CANADA. BEYOND...AN ACTIVE NW RESULTING FROM A
DIGGING TROUGH OVER TH EASTERN U.S. WILL RETURNS BELOW NORMAL
TEMPERATURES WITH A POTENTIAL CLIPPER SYSTEM AROUND MIDWEEK.

SATURDAY...THE LEAD WAVE OF STRONG THETAE ADVECTION LIFTS NORTHEAST
OF THE AREA IN THE MORNING WITH FORECAST SOUNDINGS TRANSITIONING
TOWARD MORE A DRIZZLE EVENT DURING THE DAY AS DRY AIR WORKS IN ABOVE
850 MB. WILL CONTINUE THE TREND OF HIGHEST POPS FOR LOW QPF BUT YET
MEASURABLE LIGHT RAIN/DRIZZLE OVER THE EAST AND SOUTH. THE WARM
ADVECTION OVER THE COLD GROUND WILL BE FAVORABLE FOR FOG...
ESPECIALLY IN THE MORNING IN THE NW. TEMPERATURES SHOULD RISE WELL
INTO THE 40S AND POTENTIALLY LOWER 50S AS THE CURRENT AIRMASS OVER
EASTERN OK AND AR IS PULLED INTO THE AREA. BY SATURDAY
NIGHT...DEVELOPING LIFT OUT AHEAD OF THE SOUTHERN STREAM SYSTEM
MOVING INTO TX SPREADS ANOTHER ROUND OF THETAE ADVECTION. THIS WILL
INCREASE THE DRIZZLE BACK TO A DRIZZLE/LIGHT RAIN MIX FOR OVERNIGHT
WITH FOG REMAINING LIKELY AS WELL. TEMPERATURES WILL REMAIN STEADY
IN THE 40S.

SUNDAY THROUGH SUNDAY NIGHT WILL BE THE PERIODS OF STRONGEST UPPER
LEVEL LIFT AND LOW LEVEL CONVERGENCE IN A DEFORMATION ZONE OF THE
DEVELOPING SURFACE LOW OVER IL. WORKING A WARM CONVEYOR BELT OF PW
VALUES OVER 1 INCH...OR JUST OVER 200 PERCENT OF NORMAL...WIDESPREAD
MODERATE RAINFALL IS LIKELY AND HAVE QPF AMOUNTS OF 1 TO 1.25 INCHES
ALONG THE MS RIVER EASTWARD...WITH .5 TO 1 INCH TO THE WEST.
THIS WOULD LIKELY SET A NEW DAILY RECORD RAINFALL FOR MLI...WHERE
THE RECORD FOR THE 23RD IS .49 SET IN 1927. COLDER...DRYER AIR WILL
FOLLOW AS THE LOW LIFTS NORTHEAST INTO QUEBEC LATE SUNDAY NIGHT
INTO MONDAY...POSSIBLY LEADING TO A BRIEF CHANGEOVER TO LIGHT SNOW
BEFORE THE PRECIPITATION WINDS DOWN.

THE TIGHT CYCLONIC PRESSURE GRADIENT AND WILL KEEP WINDY CONDITIONS
WITH FLURRIES OR SNOW SHOWERS GOING MONDAY AND MONDAY NIGHT. THE
AXIS OF COLDEST AIR AT 850 MB ROTATES THROUGH MONDAY NIGHT INTO
TUESDAY...RETURNING LOWS TO THE TEENS...THEN LIMIT TUESDAY/S HIGHS
TO THE UPPER 20S TO LOWER 30S. MODEL CONSENSUS BRINGS A WEAK CLIPPER
SYSTEM THROUGH WED INTO WED NIGHT WITH POSSIBLE LIGHT SNOW
ACCUMULATIONS...BUT MODELS ARE IN POOR AGREEMENT WITH THE TRACK
OR INTENSITY OF THIS SYSTEM. A PASSING SURFACE RIDGE SUGGESTS
COLD AND DRY WEATHER FOR THANKSGIVING WITH ONLY SLIGHTLY WARMER
TEMPERATURES TO FOLLOW FRIDAY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 528 PM CST FRI NOV 21 2014

CONDITIONS TO CONTINUE DETERIORATING TO MVFR AND IFR TONIGHT AS
MOISTURE INCREASES. LIGHT FREEZING RAIN/DRIZZLE EXPECTED TO
DEVELOP AT ALL SITES THIS EVENING... WITH LIGHT GLAZING OF ICE
POSSIBLE ON EXPOSED SURFACES. WARMING TEMPS OVERNIGHT EXPECTED TO
RESULT IN PCPN CHANGING OVER TO LIGHT RAIN/DRIZZLE FROM SOUTH TO
NORTH... WITH ANY ICE ACCRUAL ABATING. ON SATURDAY... MAINLY
OCCASIONAL DRIZZLE WITH IFR TO MVFR CIGS. WINDS WILL BE
SOUTHERLY IN DIRECTION AT AROUND 10 KTS THROUGHOUT THE TAF CYCLE.


&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...FREEZING RAIN ADVISORY UNTIL 6 AM CST SATURDAY FOR BENTON-
     BUCHANAN-CEDAR-CLINTON-DELAWARE-DUBUQUE-IOWA-JACKSON-
     JOHNSON-JONES-KEOKUK-LINN-LOUISA-MUSCATINE-SCOTT-WASHINGTON.

     FREEZING RAIN ADVISORY UNTIL 3 AM CST SATURDAY FOR HENRY IA-
     JEFFERSON-VAN BUREN.

IL...FREEZING RAIN ADVISORY UNTIL 6 AM CST SATURDAY FOR BUREAU-
     CARROLL-HENRY IL-JO DAVIESS-MERCER-PUTNAM-ROCK ISLAND-
     STEPHENSON-WHITESIDE.

MO...NONE.
&&

$$

UPDATE...05
SYNOPSIS...UTTECH
SHORT TERM...UTTECH
LONG TERM...SHEETS
AVIATION...05






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