Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 021134
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
634 AM CDT THU OCT 2 2014

.UPDATE...
ISSUED AT 634 AM CDT THU OCT 2 2014

LATEST SURFACE REPORTS SHOW DENSE FOG BEGINNING TO SPREAD INTO THE
FAR WEST AND SOUTH OVER THE PAST COUPLE HOURS. THE DENSE FOG DOES
NOT APPEAR TO BE WIDESPREAD SO FAR...SO WILL CONTINUE TO HANDLE
WITH SPECIAL WEATHER STATEMENTS.

&&

.SYNOPSIS...
ISSUED AT 348 AM CDT THU OCT 2 2014

THUNDERSTORM COMPLEXES HAVE SET UP WELL SOUTH OF THE FORECAST AREA
OVERNIGHT AND EARLY THIS MORNING ACROSS OK...TROUGH SE KS INTO
CENTRAL PORTIONS OF MO AND IL. THIS IS WHERE A MID LEVEL SHORTWAVE
IN THE SW FLOW ALOFT WAS INTERACTING WITH GULF MOISTURE AND
INSTABILITY JUST NORTH OF THE EAST TO WEST ORIENTED...AND NEARLY
STALLED...WARM FRONT. OVER THE LOCAL AREA...SHOWERS STREAMING OFF
THE NORTHERN EDGE OF THESE COMPLEXES HAD REACHED AS FAR NORTH AS
MLI...BUT WILL LIKELY EXIT TO THE EAST BEFORE SUNRISE. EXTENSIVE FOG
LOOMS JUST TO THE WEST IN THE BROAD LOW LEVEL CONVERGENCE AND
PREFRONTAL MOISTURE AXIS OVER CENTRAL IA INTO MN. THE PRIMARY
SURFACE COLD FRONT AT 08Z REACHED FROM WESTERN MN THROUGH NW IA TO S
CENTRAL NEB AND WESTERN KS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 348 AM CDT THU OCT 2 2014

INITIAL CONCERN WILL BE TRENDS WITH EARLY MORNING FOG...AND THEN
FOCUS TURNS TO INCREASING THUNDERSTORM CHANCES AND SEVERE POTENTIAL
FOR LATER TODAY AND TONIGHT AS THE COLD FRONT PUSHES THROUGH THE
REGION. BASED ON THE LARGE SCALE FORCING AND CURRENT RADAR
TRENDS...THERE SHOULD BE A LULL IN THE CONVECTION THROUGH MUCH OF
THIS MORNING BEFORE THE MAIN UPSTREAM UPPER LEVEL TROUGH CURRENTLY
PRODUCING THUNDERSTORMS IN NEB APPROACHES TOWARD AFTERNOON. AN
EXTENSIVE AREA OF LOW CLOUDS AND FOG IN AN AREA OF BROAD LOW LEVEL
CONVERGENCE IN CENTRAL IA WILL LIKELY EXPAND EASTWARD INTO AT LEAST
THE WESTERN HALF OF THE FORECAST AREA AROUND SUNRISE...AND WILL NEED
TO MONITOR FOR A POSSIBLE DENSE FOG ADVISORY. THE BIG QUESTION
WILL BE WHETHER THESE LOW CLOUDS CAN BURN OFF...WHICH WILL BE TIED
TO HIGHER CLOUDS AND CONVECTIVE TRENDS. FOR NOW...WILL BANK ON
EXTENSIVE CLOUD COVER TO AGAIN TO HOLD TEMPERATURES DOWN OVER MUCH
OF THE AREA AS OCCURRED YESTERDAY. THUS HAVE HIGHS FROM THE UPPER
60S NORTHEAST TO MID 70S IN THE FAR SOUTH AND EAST...WHERE THERE
WILL BE A GREATER POTENTIAL FOR AT LEAST PARTIAL CLEARING IN THE
AFTERNOON.

MID LEVEL LIFT AND UPPER DIVERGENCE INCREASES DURING THE AFTERNOON
AS THE PLAINS TROUGH APPROACHES. HAVE TRENDED POPS ACCORDINGLY...UP
TO CATEGORICAL BY LATE AFTERNOON INTO EVENING. SPC HAS A DAY ONE
SLIGHT RISK OVER ALL BUT THE HIGHWAY 20 CORRIDOR INTO THE NORTHWEST
FORECAST AREA. IF ENOUGH BREAKS IN THE CLOUD COVER OCCURS OVER THE
SOUTHEAST...THERE MAY BE HIGH ENOUGH MUCAPE ALONG WITH
MARGINAL...MOSTLY UNIDIRECTIONAL DEEP SHEAR TO LEAD TO ISOLATED
SEVERE STORMS WITH LARGE HAIL AND DAMAGING WIND THE PRIMARY THREATS
WITH LATE AFTERNOON CONVECTION IN THE WARM SECTOR. BY EVENING...A
MORE LINEAR COMPLEX WILL BE LIKELY AHEAD OF THE ADVANCING COLD
FRONT. THIS WOULD PRESENT A RISK OF LOCALLY STRONG WINDS...BUT NOT
LIKELY SEVERE STORMS DUE TO THE THE DIURNALLY WANING INSTABILITY.
OVERALL...WIDESPREAD MODERATE TO LOCALLY HEAVY RAINFALL WILL BE THE
MAIN STORY...AND WITH THE RECENT STRETCH OF DRY WEATHER...HYDRO
ISSUES SHOULD NOT BE A CONCERN. CURRENT CONSENSUS HAS THE FRONT
CROSSING THE MS RIVER AROUND MIDNIGHT OR SO...THEN EXITING TO THE
EAST BY 3 AM. NW WINDS AND COLD ADVECTION WILL PULL IN A FRESH
CANADIAN AIRMASS...LEADING TO LOWS AROUND SUNRISE FROM THE MID 40S
NW TO MID 50S SOUTHEAST.

.LONG TERM...(FRIDAY THROUGH NEXT WEDNESDAY)
ISSUED AT 348 AM CDT THU OCT 2 2014

FRIDAY...COLD CORE L/W UPPER TROF STILL PROJECTED TO DIG ACRS THE GRT
LKS WITH A CLOSED UPPER LOW PIVOTING AROUND IN IT/S BASE THIS PERIOD.
BULK OF THE THU NIGHT PRECIP TO BE EAST OF THE CWA BY SUNRISE FRI...
WITH IN-WRAPPING DRY SLOT MAKING FOR VARIABLE CLOUDINESS FOR PORTIONS
OF THE DAY. LLVL CYCLONIC PRESSURE GRADIENT TIGHTNESS RULE COMBINED
WITH FCST TROP FOLD DOWN TO 450-500 MB SWEEPING ACRS THE REGION
WOULD DRIVE WEST TO NORTHWEST SFC WINDS OF SUSTAINED 20-30 MPH AND
GUSTS 40 TO 45 MPH WITH SOME BREAKS FOR MIXING INSOLATION. LATEST
00Z RUN MEDIUM RANGE MODELS NOW LESS BULLISH ON WRAP AROUND SHOWERS
FRI AFTERNOON...BUT WITH STEEP LOW TO MID LEVEL LAPSE RATES
DEVELOPING BY AFTERNOON WILL KEEP AT LEAST SOME SLIGHT CHC POPS ACRS
THE NORTHEASTERN QUARTER TO THIRD OF THE DVN CWA. STOUT INCOMING
LLVL COLD AIR ADVECTION TO KEEP HIGHS IN THE 50S EVEN WITH DEEP
MIXING AND OCCASIONAL SUNSHINE. UPPER LOW CENTER ACRS SOUTHERN WI AND
SATELLITE VORT MAX MAY ALLOW A BETTER CHC FOR WRAP AROUND STRATOCU
AND SHOWERS FRI NIGHT ACRS THE NORTHEASTERN HALF OF THE CWA. TOP
DOWN COOLING INDICATED ON FCST SOUNDINGS ARE NOT THAT FAR OFF SNOW
REACHING THE SFC ESPECIALLY AFTER 06Z SAT...GOOD CHC THAT SOME SNOW
OR RAIN/SNOW MIX WILL FALL JUST TO THE NORTH AND NORTHEAST IN SE MN
THROUGH WI. CLOUDS AND MIXING WINDS MAINTAINING AT 10-20 MPH FOR MOST
OF THE NIGHT SHOULD LIMIT FROST CHC INTO EARLY SAT MORNING...BUT
EXTENT OF COLD AIR ADVECTION  IN THE BOUNDARY LAYER ITSELF WILL STILL
MAKE FOR WIDESPREAD LOWS IN THE MID TO UPPER 30S. ANY CLEAR OUT WITH
SC WIND DECOUPLE TOWARD SUNRISE SAT WILL ALLOW FOR SOME LOWER 30S OR
EVEN A SHOT AT SOME UPPER 20S IN THE NORTHERN CWA.

SATURDAY AND SUNDAY...ONGOING WRAP AROUND CLOUD COVER...INSTABILITY
SHOWERS...NORTHWEST WINDS OF 15 TO 25 MPH...AND SFC TEMPS HAVING
TROUBLE WARMING OUT OF THE UPPER 40S TO LOWER 50S UNDER PASSING H85
MB COLD POOL WILL MAKE FOR A RAW SAT. CLEAR OUT DURING THE LATE
AFTERNOON AND SFC WIND DROP OFF WITH PASSING SFC RIDGE LOBE COULD SET
THE STAGE FOR MORE IDEAL FROST DEVELOPMENT SAT NIGHT...BUT AGAIN SOME
UNCERTAINTY HERE AS WELL WITH THE MODELS CONTINUING TO VARY ON
TIMING OF ONSET OF WEST TO SOUTHWEST SFC RETURN FLOW SAT NIGHT THAT
COULD LIMIT THE COLD POTENTIAL. EVEN WITH A QUICK TEMP DROP OFF
AFTER SUNSET SAT EVENING LOWS MAY BE MORE IN THE WAY OF MID TO
UPPER 30S IF THE SFC WINDS INCREASE AFTER MIDNIGHT. HIGH AMPLITUDE
NORTHWESTERLIES WILL STILL LOOK TO USHER AN EMBEDDED CLIPPER TYPE LOW
DOWN ACRS THE REGION BY SUNDAY...WHILE THE MAIN UPPER LOW OR VORTEX
TYPE FEATURE GYRATES BETWEEN THE GRT LKS AND JAMES BAY REGIONS.
TEMPS TO MODERATE SUNDAY INTO MONDAY WITH A CHANCE AT SOME SPOTTY
SHOWERS.

MONDAY THROUGH NEXT WEDNESDAY...AGREE WITH THE LATEST MEDIUM RANGE
SOLUTIONS THAT LATCH ON THE IDEA OF SUCH A LARGE COOL CORE ENTRENCHED
L/W TROF TO REMAIN ALONG AND JUST EAST OF THE REGION LONGER EARLY
NEXT WEEK...WHICH MAY KEEP TEMPS IN THE 50S AND 60S WITH OCCASIONAL
CHANCES AT SHOWERS OR LIGHT RAIN WITH PASSING VORT SPOKES AS UPPER
LOW SPIRALS JUST NORTH OF MN. THE PATTERN MAY FINALLY BREAK DOWN
TOWARD MID NEXT WEEK WITH THERMAL MODERATION BACK TO NORMAL BY WED.
WILL HAVE TO WATCH FOR ELEVATED RETURN FLOW/WAA TYPE PRECIP
DEVELOPING NEXT WED INTO THU IN THIS TRANSITION PERIOD.    ..12..

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING)
ISSUED AT 634 AM CDT THU OCT 2 2014

WIDESPREAD IFR AND VLIFR CONDITIONS WILL BE FOUND OVER EASTERN IA
EARLY THIS MORNING DUE TO LOW CLOUDS AND FOG AHEAD OF A SLOW
MOVING COLD FRONT. THESE CONDITIONS WILL BE SLOW TO IMPROVE...AND
THE TAF SITES WILL LIKELY REMAIN IN IFR UNTIL EARLY AFTERNOON.
THUNDERSTORMS ARE EXPECTED TO DEVELOP IN THE AFTERNOON AND BECOME
MOST WIDESPREAD FROM LATE AFTERNOON INTO EVENING. OUTSIDE OF THE
STORMS...CIGS ARE EXPECTED TO REMAIN AT LEAST IN MVFR RANGE. A
STRONG COLD FRONT WILL PUSH OUT THE PRECIPITATION LATE TONIGHT AND
PROVIDE A SHIFT IN WINDS TO THE NORTHWEST. THERE IS LOW CONFIDENCE
IN HOW FAST THIS FRONT WILL PUSH OUT THE CLOUDS AND FOG AND FOR
NOW...WILL CARRY MVFR CONDITIONS THROUGH THE NIGHT AT ALL SITES.

&&

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

$$

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





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