Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 312338
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
638 PM CDT FRI JUL 31 2015

.SYNOPSIS...
ISSUED AT 330 PM CDT FRI JUL 31 2015

A WEAK COLD FRONT LINKED TO AN UPPER LEVEL TROUGH MOVING THROUGH
ONTARIO REACHED ROUGHLY FROM CENTRAL LOWER MI...SW ACROSS SOUTHERN
LAKE MI...NORTHERN IL AND JUST SOUTH OF THE I-80 CORRIDOR ACROSS
EASTERN IL AND IA AT MID AFTERNOON. DUE TO GULF MOISTURE SUPPRESSED
WELL TO THE SOUTH AND WEST...AND THE SOMEWHAT DRY AIR IN THE MID AND
UPPER LEVEL NW FLOW...THE FRONT WAS ACTING MAINLY AS A SURFACE DRY
LINE WITH LITTLE CLOUD COVER OVER THE FORECAST AREA. REGIONAL RADARS
SHOWED THUNDERSTORMS BREAKING OUT ALONG THE WESTERN END OF THE E-W
BOUNDARY ACROSS NEB...WHERE THE WEAK BOUNDARY WAS MEETING UP WITH
RETURNING GULF MOISTURE. STRONGER MIXING BEHIND THE FRONT WAS
RESULTING IN GUSTY NW WINDS AND DEWPOINTS IN THE 50S ACROSS THE
NORTH...WHILE DEWPOINTS WERE IN THE UPPER 60S TO AROUND 70 ACROSS
THE SOUTH. TEMPERATURES WERE MAINLY IN THE LOWER TO MID 80S...WITH A
FEW UPPER 80S IMMEDIATELY ALONG THE BOUNDARY.

&&

.SHORT TERM...(THIS EVENING THROUGH SATURDAY)
ISSUED AT 330 PM CDT FRI JUL 31 2015

MAIN CHALLENGE IS THE LOW POTENTIAL FOR THUNDERSTORMS THROUGHOUT.
TONIGHT...BROAD CONVERGENCE ALONG THE BOUNDARY...EXPECTED TO BE
ROUGHLY ALONG OR SOUTH OF THE IA/MO BORDER INTO W CENTRAL IL...MAY
RESULT IN AT LEAST ISOLATED THUNDERSTORMS OVERNIGHT AS NEGATIVE MID
LEVEL THETAE LAPSE RATES OVERSPREAD THE AREA LATE TONIGHT. THIS
CONVECTION IS ALSO INDICATED BY SOME OF THE HIGH RES CONVECTIVE
ALLOWING MODELS...BUT GENERALLY STAYING SOUTH OR SW OF THE FORECAST
AREA. WILL THUS CONTINUE WITH ONLY SLIGHT CHANCES FOR SHOWERS AND
THUNDERSTORMS DUE TO THE LOW CONFIDENCE. A SEPARATE AREA OF AT
SLIGHT CHANCE POPS IS CARRIED IN THE FAR NORTH...WHERE WEAK
CONVERGENCE ALONG A SURFACE TROUGH MAY BE SUFFICIENT ENOUGH UNDER
THE INCREASINGLY UNSTABLE MID LEVELS TO  TRIGGER ELEVATED CONVECTION
LATE TONIGHT INTO EARLY SATURDAY MORNING. OTHERWISE...SKIES SHOULD
REMAIN MOSTLY CLEAR TONIGHT WITH MINS AS LOW AS NEAR 60 IN THE
DRIEST AIR ACROSS THE NORTHEAST...TO THE LOWER TO MID 60S ELSEWHERE.

SATURDAY...A WEAK SURFACE RIDGE AND DRY NW FLOW ALOFT SHOULD PROVIDE
ANOTHER DRY DAY...SIMILAR TO TODAY BUT SLIGHTLY WARMER WITH LIGHTER
WINDS TURNING MORE SOUTHERLY BY EVENING. WITH A SIMILAR AIRMASS...
AND ACCOUNTING FOR WARMING ALOFT...WILL HAVE HIGHS FROM THE LOWER TO
MID 80S NORTHEAST TO THE UPPER 80S TO NEAR 90 SW. HIGHER HUMIDITY
LEVELS WILL BEGIN CREEPING INTO THE SOUTHWEST AND WEST...WHERE
DEVELOPING LIGHT SOUTH WINDS WILL RETURN DEWPOINTS TO  UPPER 60S TO
NEAR 70. WEAKER MIXING OVER CENTRAL AND NORTHEAST SHOULD KEEP VALUES
IN A SLIGHTLY MORE COMFORTABLE LOWER TO MID 60S RANGE THROUGH MOST
OF THE DAY.

.LONG TERM...(SATURDAY NIGHT THROUGH NEXT FRIDAY)
ISSUED AT 330 PM CDT FRI JUL 31 2015

SATURDAY NIGHT AND SUNDAY...BULK OF 12Z MODEL RUNS SUGGEST WAVE
EMBEDDED IN NORTHWESTERLIES AND ASSOCIATED LLVL FRONT WILL ACT UPON
MORE OPTIMUM RETURN FLOW FOR STORM CLUSTER GENERATION TO THE
NORTHWEST ACRS NORTHEASTERN NEB/EASTERN DAKOTAS AND MN SAT EVENING.
MCS FORCING TOOLS AND OTHER CONVECTIVE SUPPORT PARAMETERS MAXIMIZE
MORE ACRS MN AND INTO WI WHERE RESULTANT MCS WILL MORE LIKELY
PROPAGATE ACRS LATE SAT NIGHT INTO SUNDAY MORNING. BUT OTHER TAILING
FORCING AHEAD OF THE INCOMING FRONT AND PRE-FRONTAL WARM AIR
ADVECTIVE SUPPORT SHOULD GENERATE SCTRD SHOWERS/STORMS ACRS THE
LOCAL AREA POSSIBLY INTO THE NORTHWESTERN THIRD OF THE CWA BEFORE
MIDNIGHT WITH AREAS FURTHER TO THE EAST STILL CAPPED AND DRY. BUT
THIS SHOULD ERODE FROM W-E AFTER MIDNIGHT FOR INCREASED STORM
DEVELOPMENT INTO EARLY SUNDAY MORNING. BUT LATEST PROGS SUGGEST THE
BETTER LATE NIGHT LLJ CONVERGENCE OCCURS TO THE NORTHEAST ACRS
WI...WITH VEERING LLVL FLOW LOCALLY. SHEAR PROFILES DURING THIS MAX
COVERAGE TIME AFTER MIDNIGHT MARGINAL AND ONLY SEE THE CHC FOR
ISOLATED SVR STORMS AT THIS TIME. LOCALLY HEAVY RAIN WHERE STORMS
CLUSTERS MANAGE TO OCCUR MAY BE THE PRIMARY THREAT.

SUNDAY VERY UNCERTAIN WITH THE SAME OLD SCENARIO OF HOW LONG
CONVECTIVE DEBRIS AND OUTFLOW LINGERS DURING THE DAY TO LIMIT
HEATING AND INSTABILITY BUILD UP. THE MAIN INCOMING FRONT NOT
PROGGED TO PUSH EAST ACRS THE MS RVR UNTIL GENERALLY AROUND MID
SUNDAY EVENING OR SO. DEEPER SHEAR PROFILES MORE ROBUST BY SUNDAY
EVENING...AND IF CONVECTIVE DEBRIS CAN CLEAR ENOUGH TO ALLOW FULL ON
PRE-FRONTAL HEATING MUCH OF THE CWA MAY WARM INTO THE MID TO UPPER
80S...WITH SOME SITES HITTING 90. THIS COMBINED WITH POOLING SFC
DPTS AT LEAST INTO THE LOWER 70S MAY MAKE FOR SBCAPES OF 3500-4500+
J/KG BAY LATE AFTERNOON. THUS THERE COULD BE MORE POTENTIAL FOR
STRONGER STORMS BY SUNDAY EVENING AS OPPOSED TO SAT NIGHT. CURRENT
ASSESSMENT MAKES FOR THE SCENARIO WHERE A LINE OF STORMS DEVELOP ON
THE FRONT OR WHERE FRONT INTERACTS WITH LINGERING OUTFLOW/WARM
FRONTAL BOUNDARIES RIGHT OVERHEAD OF THE CENTRAL TO EASTERN CWA
SUNDAY EVENING...WITH THEM THEN TAKING OFF ACRS THE NORTH HALF OF IL
SUNDAY NIGHT. ALL MODES OF SEVERE WEATHER MAY BE POSSIBLE IF THIS
SCENARIO UNFOLDS... WITH DAMAGING WIND PRIMARY.

MONDAY THROUGH WEDNESDAY...MOST OF MONDAY MAY BE A POST-FRONTAL DRY
AND LESS HUMID DAY UNDER PERSISTENT NORTHWESTERLY FLOW ALOFT. BUT
RETURN FLOW WILL LOOK TO ORGANIZE NOCTURNALLY UP THE PLAINS AND MO
RVR VALLEY MON NIGHT. THERE WILL BE A CHC FOR THE RESULTANT
CONVECTION TO BLEED INTO PORTIONS OF THE DVN CWA AS THE MON NIGHT
INTO EARLY TUE MORNING PERIOD PROGRESSES. LONGER RANGE INDICATIONS
AND MEDIUM RANGE MODEL ENSEMBLES INDICATE WARM DOME GATHERING
STRENGTH AND BULGING NORTH UP THE ROCKIES AND WESTERN PLAINS INTO
THE MID WEEK PERIOD. THIS COULD PLACE THE DVN CWA ON THIS FEATURE/S
NORTHEASTERN FLANK AND DUMPING ZONE FOR RIDGE-RIDING MCS/S OR UNDER
A PORTION OF THE POTENTIAL RING OF FIRE PATTERN. THE 12Z GFS SHOWS
NO MERCER AND KEEPS THE STORM CLUSTERS COMING ESPECIALLY DURING THE
EVENING AND OVERNIGHT PERIODS...WHILE THE 12Z ECMWF IS MORE BULLISH
WITH GRT LKS L/W TROFFINESS-NORTHEASTERLY PUSH THAT THE STORM
TRACK GETS SHUNTED WEST AND SOUTH OF THE LOCAL FCST AREA BY LATER
WED. BUT WITH LOW CONFIDENCE...DAILY CHC POPS WILL HAVE TO RIDE AT
THIS POINT.

NEXT THURSDAY AND FRIDAY...THE 12Z ECMWF WOULD BRING MAINLY DRY AND
BELOW NORMAL TEMPS TO THE REGION UNTIL FRI NIGHT WHEN THE PATTERN
STARTS TO BREAK DOWN FROM THE WEST AND FLATTENED FLOW USHERS AN MCS
ACRS IA. THE 12Z GFS KEEPS THE STORM TRACK GOING UNTIL LATER FRI
WHEN IT UNDERGOES PATTERN AMPLIFICATION WITH SEASONABLY DEEP GRT LKS
TROFFINESS AND SHARP RIDGE ACRS THE ROCKIES...ALLOWING DRY WX AND
WELL BELOW NORMAL TEMPS TO SPILL DOWN ACRS THE UPPER MS RVR VALLEY
FOR THE START OF THE WEEKEND. AGAIN WITH SUCH MODEL DISCREPANCIES
WILL HAVE TO KEEP AT LEAST LOW CHC POPS INTO THE END OF THE EXTENDED.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SATURDAY EVENING)
ISSUED AT 633 PM CDT FRI JUL 31 2015

VFR CONDITIONS ARE EXPECTED THROUGH 00Z/02 AS HIGH PRESSURE MOVES
INTO THE GREAT LAKES. A CLUSTER OF TSRA IN SOUTHWEST IOWA WILL
CONTINUE TO MOVE EAST SOUTHEAST ACROSS NORTHERN MISSOURI AND INTO
SOUTHERN ILLINOIS THROUGH 09Z/01. AFT 00Z/02 A NEW ROUND OF TSRA
IS EXPECTED TO AFFECT EASTERN IOWA AND NORTHERN ILLINOIS.

&&

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

$$

SYNOPSIS...SHEETS
SHORT TERM...SHEETS
LONG TERM...12
AVIATION...08


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