Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 042322
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
622 PM CDT FRI SEP 4 2015

.SYNOPSIS...
ISSUED AT 330 PM CDT FRI SEP 4 2015

THE DOMINANT WEATHER FEATURE REMAINS AN UPPER LEVEL RIDGE AXIS
REACHING FROM TX TO WI. A WEAK LOW WAS OVER LOWER MI AND MUCH LARGER
TROUGH WAS UPSTREAM OVER THE PACIFIC NW. AT THE SURFACE...A WEAK
PRESSURE GRADIENT WAS OVER THE LOCAL AREA...BETWEEN HIGH PRESSURE
OVER ONTARIO AND LOW PRESSURE IN NORTHERN PLAINS. A WEAK LOW LEVEL
BOUNDARY LINGERED FROM JUST NORTH OF PRINCETON STRETCHING W-NW
ACROSS NW IL INTO FAR SW WI. AREA RADARS HAVE BEEN SHOWING
PERSISTENT BUT ISOLATED ISOLATED SHOWERS IN THIS BROAD LOW LEVEL
CONVERGENCE AXIS OVER W CENTRAL AND FAR NW IL SO FAR TODAY. A VERY
AUGUST-LIKE HEAT AND HUMIDITY CONTINUES TO BUILD UNDER THIS RIDGE
AXIS...WITH MOST OF THE FORECAST AREA ONCE AGAIN IN THE UPPER 80S
AND LOWER 90S WITH DEWPOINTS IN THE UPPER 60S TO LOWER
70S...RESULTING IN HEAT INDEX READINGS IN THE MID 90S TO AROUND 100.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 330 PM CDT FRI SEP 4 2015

PERSISTENCE IS THE RULE IN THE NEAR TERM AS THE NEARLY STATIONARY
UPPER LEVEL RIDGE AXIS ALLOWS LITTLE CHANGE IN SENSIBLE WEATHER IN
THE FORECAST AREA. MUCH ABOVE NORMAL TEMPERATURES AND UNCOMFORTABLE
HUMIDITY WILL BE THE MAIN STORY...ALONG WITH CHANCES FOR VERY
ISOLATED SHOWERS AND THUNDERSTORMS.

LATE THIS AFTERNOON AND EVENING...THE WEAK BOUNDARY LINGERING ACROSS
THE EAST MAY AGAIN LIGHT UP WITH ISOLATED THUNDERSTORMS AS
CONVECTIVE TEMPERATURES IN THE LOWER 90S ARE MET. WITH WEAK WIND
PROFILES AND LACK OF SHEAR...ANY CONVECTION WILL BE SHORT
LIVED...WITH THE PRIMARY THREAT BEING A FEW LIGHTNING STRIKES AND
BRIEF HEAVY DOWNPOURS. OUTFLOW BOUNDARIES AND STEEP MID LEVEL LAPSE
RATES MAY ALLOW THESE TO PERSIST UNTIL WELL AFTER DARK AND WILL
MENTION ISOLATED COVERAGE UNTIL ABOUT 10 PM. AT THE SAME TIME...HEAT
INDEX READINGS WILL REACH THE UPPER 90S TO NEAR 100 THROUGH 7 PM.

OVERNIGHT...A SHORTWAVE CURRENTLY TRIGGERING CONVECTION IN NW IA
WILL TOP THE RIDGE WELL TO OUR NORTH...WHILE A WEAK MEANDERING UPPER
LEVEL VORTEX CONTINUES TO SPIN OVER LAKE MI OVER WESTERN LOWER MI.
SHOWERS AND THUNDERSTORMS WILL BE MOST LIKELY NEAR THESE
FEATURES...AND COULD SPILL INTO THE FAR NORTHEAST AND EAST TOWARD
SUNRISE WHERE THE UPPER CAP IS WEAKEST AND ABOVE THE WEAK LOW LEVEL
CONVERGENCE AXIS. THE GFS AGAIN LOOKS OVERDONE WITH ITS WIDESPREAD
QPF COVERING MUCH OF THE FORECAST AREA OVERNIGHT INTO SATURDAY
MORNING...LIKELY DUE TO MOISTURE ISSUES. HOWEVER...ELEVATED
CONVECTION...AS EVIDENT BY THE PATCHY ACCAS THE PAST SEVERAL
DAYS...WILL LIKELY AGAIN BE PRESENT. GIVEN THE NEGATIVE MID LEVEL
THETAE LAPSE RATES AND 6 TO 6.5 DEG C/KM MID LEVEL THERMAL LAPSE
RATES...THIS ELEVATED CONVECTION CANNOT BE RULED OUT AND WILL CARRY
SLIGHT CHANCE POPS OVER THE EASTERN HALF OF THE FORECAST AREA AROUND
SUNRISE INTO MID MORNING. PERSISTENCE SUPPORTS MINS IN THE UPPER 60S
TO LOWER 70S.

SATURDAY...THE COMBINATION OF MINOR WARMING ALOFT AND THE WASHING
OUT OF THE LOW LEVEL BOUNDARY DUE TO A STRONGER LOW LEVEL SOUTHERLY
FLOW SUGGESTS A LOWER POTENTIAL FOR ISOLATED SHOWERS AND
THUNDERSTORMS AND WILL MAINTAIN A DRY FORECAST FROM MID MORNING AND
BEYOND. WITH THE SAME AIRMASS AND DEEP MIXING AGAIN TO NEAR 850
MB...TEMPERATURES SHOULD AGAIN REACH THE UPPER 80S TO LOWER 90S.
DEWPOINTS IN THE UPPER 60S TO LOWER 70S WILL AGAIN PUSH THE HEAT
INTO THE MID AND UPPER 90S.

.LONG TERM...(SATURDAY NIGHT THROUGH NEXT FRIDAY)
ISSUED AT 330 PM CDT FRI SEP 4 2015

SATURDAY NIGHT AND SUNDAY...MAIN CRUTCH OF BROAD UPPER RIDGE WILL
LOOK TO ADJUST ACRS THE MS RVR VALLEY INTO THE WESTERN GRT LKS SAT
NIGHT. THUS WOULD THINK THE CWA WOULD BE MAINLY DRY...BUT WITH AN
ONGOING ELEVATED UNSTABLE LAYER AND POSSIBLE CONVERGENT WAA
WINGS/EVEN IF SUBTLE/...THERE COULD STILL BE HIGH BASED BUBBLING
ISOLATED TO WDLY SCTRD SHOWERS OR STORMS IN SPOTS BUT WILL KEEP THE
FCST DRY FOR NOW WITH LOWS IN THE MID 60S TO AROUND 70. AS NORTHERN
PLAINS FRONTAL SYSTEM ORGANIZES TO LEE OF NORTHERN ROCKIES/NW HIGH
PLAINS UPPER TROF SUNDAY...THE CWA COULD BE IN MORE OPTIMUM FLOW AND
MIXING WARM SECTOR ENOUGH TO PRODUCE WIDESPREAD 90 TO 95 DEGREE
TEMPS IF THE INSOLATION WILL BE THERE AND NOT FILTERED. IF SFC DPTS
CAN REMAIN IN THE LOWER 70S OR NEAR 70 AND NOT MIXED DOWN... THOSE
KIND OF AMBIENT TEMPS MAY PRODUCE HEAT INDEX READING AROUND 100 IN
SPOTS. AS FOR FRONTAL TIMING AND ASSOCIATED CONVECTION SUNDAY
NIGHT...THE 12Z GFS MAKES PRECIP ACRS THE NORTHWESTERN THIRD OF THE
CWA BEFORE 06Z MONDAY...WHILE THE NEW ECMWF REMAINS LARGELY DRY THRU
MIDNIGHT. THE LATEST MODEL TRENDS SUGGEST THAT AS THE PRECIP SPREADS
EAST TO AND EAST OF THE MS RVR LATE SUNDAY NIGHT INTO MONDAY
MORNING...THE FORCING WEAKENS SOME AND PRECIP MAY WEAKEN IT BUMPS UP
AGAINST LINGERING RIDGING FROM THE GRT LKS TO THE EAST CENTRAL
PLAINS.

MONDAY AND TUESDAY...12Z RUN MEDIUM RANGE MODELS CONTINUE TO
ADVERTISE LARGE DIGGING UPPER TROF ACRS THE ROCKIES AND PLAINS...
WHILE THE LLVL BOUNDARY SAGS THRU THE CWA AND ALIGNS GENERALLY FROM
WEST-TO-EAST SOMEWHERE ACRS FROM THE CENTRAL PLAINS TO THE
SOUTHWESTERN GRT LKS MORE PARALLEL TO NORTHERN FRINGE OF FLATTENING
SOUTHCENTRAL TO SOUTHEASTERN CONUS RIDGE. WHILE CLUSTERS OF SHOWERS
AND THUNDERSTORMS MAY FESTER ON MONDAY IN THE VCNTY OF THIS
FEATURE...STILL SOME UNCERTAINTY ON HOW FAR NORTH OR SOUTH THE
FRONTS AXIS WILL LAY OUT AS WELL AS SOME SIGNS OF A LACK OF DECENT
CONVERGENCE ON IT DURING THE DAY. A MORE ORGANIZED PRECIP THREAT MAY
COME LATER MONDAY NIGHT INTO TUE AS LLVL CYCLOGENESIS BLOSSOMS ACRS
THE SOUTHWESTERN PLAINS UNDER DIGGING UPPER TROF AXIS...WITH THE
RESULTANT LOW PRESSURE EJECTING OUT ALONG THE FRONTAL SYSTEM. THIS
MAY EVEN MAKE FOR A MCS-TYPE EVENT EITHER OVER PORTIONS OF THE CWA
OR CLOSE TO IT LATE MON NIGHT INTO TUESDAY MORNING WITH HEAVY RAIN A
THREAT DUE TO AND IDEAL PRE-WAVE THTA-E FEED UP OFF THE WESTERN
GULF. SOME MODEL DISCREPANCIES MAKING FOR LIMITED CONFIDENCE NOW FOR
LATER TUE INTO WED MORNING...WITH SOLUTIONS VARYING FROM A TEMPORARY
REPRIEVE FROM THE STORMS AS BOUNDARY SAGS SOUTH POST-WAVE...TO THE
FRONT TRYING TO RETREAT BACK NORTH MAKING FOR WARM FRONTAL TYPE
PRECIP REGIME BY TUE NIGHT. POPS THROUGH THIS PERIOD WILL HAVE TO
RIDE WITH THE MODEL DISCREPANCIES. TEMPS COULD BE ALL OVER THE PLACE
BECAUSE OF CONVECTIVE DEBRIS AND FRONTAL PLACEMENT AND WILL HAVE TO
GO WITH GENERAL BLEND.

WEDNESDAY THROUGH NEXT FRIDAY...BOTH THE LATEST RUN GFS AND ECMWF
NOW SUGGEST THAT WED MAY BE A IN-BETWEEN DAY WITH LITTLE ORGANIZED
PRECIP...BEFORE ANOTHER UPPER TROF AHEAD OF A STRONG COOL PUSH OUT
OF CANADA DIGS ACRS THE REGION SOMETIME LATE WED NIGHT THRU THU FOR
THE NEXT PRECIP WINDOW. THE 12Z ECMWF IS MESSY AND SLOWER WITH
LINGERING PRECIP UNDER THE PASSING TROF THRU FRIDAY...WHILE THE GFS
SHUNTS COLD FRONT THROUGH BY MIDDAY THU WITH A DRY AND CANADIAN-
COOLED POST-FRONTAL REGIME INTO THE START OF THE NEXT WEEKEND. THIS
PERIOD FOR NOW WILL BE TRENDED TOWARD THE GFS AND AWAIT FURTHER
MODEL RUNS AND TRENDS TO FINER TUNE.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 619 PM CDT FRI SEP 4 2015

A MAINLY DRY AND VRY FORECAST CYCLE IS EXPECTED OVER EASTERN IOWA
AND NORTHWEST ILLINOIS THROUGH SATURDAY EVENING. A FEW ISOLATED
SHOWERS ARE POSSIBLE JUST EAST OF DBQ EARLY THIS EVENING...AND
AGAIN TOWARDS MORNING...BUT COVERAGE IS VERY ISOLATED AND NOT
INCLUDED IN TAFS. OTHERWISE...MUCH LIKE LAST NIGHT...SOME PATCHY
MORNING FOG IS LIKELY...BUT COULD AVOID TAF SITES EXPECT FOR
DBQ...WHERE I HAVE INCLUDED IFR TO LIFR VISIBILITIES DUE TO FOG
OVERNIGHT AND EARLY SATURDAY MORNING.
ERVIN

&&

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

$$

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



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