Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 231847
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
147 PM CDT SAT AUG 23 2014

.UPDATE...
ISSUED AT 139 PM CDT SAT AUG 23 2014

DEBRIS CLOUDS AND EASTERLY FLOW IN WAKE OF LINEAR MCS IS HOLDING
TEMPS DOWN INTO THE 70S WITH SOME LOWER 80S FAR SOUTH.
SHOULD SEE CONTINUED DECREASE/THINNING OF CLOUDS REST OF THIS
AFTERNOON BUT LIKELY STAY MOSTLY CLOUDY EAST...TIMING NOT FAVORABLE
WITH PEAK HEATING EXCEPT SOUTHWEST CWA WHERE UPPER 80S TO L90S
STILL SEEM PLAUSIBLE. ELSEWHERE IN CWA THOUGH I HAVE LOWERED HIGHS
INTO THE LOWER TO MIDDLE 80S... BUT WOULD NOT BE SURPRISED TO SEE
FAR E/NE SECTIONS ONLY TOP OUT IN THE UPPER 70S. ALSO HAVE LOWERED
POPS NEXT FEW HOURS WITH GENERAL SUBSIDENCE IN WAKE OF MCS
SUPPRESSING ANY DEVELOPMENT... BUT THEN MAY SEE AT LEAST ISOLD TO
WIDELY SCATTERED PCPN DEVELOP LATE AFTERNOON ALONG RESIDUAL
BOUNDARIES WITH HEATING. UPDATED GRIDS/ZFP/PFM HAVE BEEN SENT.

&&

.SYNOPSIS...
ISSUED AT 327 AM CDT SAT AUG 23 2014

HIGHLY AMPLIFIED UPPER RIDGE DOMINATES THE MISSISSIPPI VALLEY WHILE
AN UPPER LOW DIGS INTO THE PACIFIC NORTHWEST.  AT THE SURFACE...LOW
OVER NEBRASKA WITH A DIFFUSE STATIONARY FRONT BISECTING IA FROM THE
SOUTHWEST CORNER TO NEAR THE QUAD CITIES. ENVIRONMENT REMAINS
LARGELY THE SAME AS RECENT MORNINGS WITH WEAK LOW LEVEL
CONVERGENCE...WEAK FLOW ALOFT...AND WEAK SHEAR...BUT ABUNDANT
MOISTURE AND INSTABILITY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 327 AM CDT SAT AUG 23 2014

SCATTERED CONVECTION IS EXPECTED TO CONTINUE TO FESTER THIS
MORNING.  HIGH PRECIPITABLE WATERS AROUND 2 INCHES WILL YIELD HIGH
RAINFALL RATES...WHICH WILL BE AGGRAVATED BY SLOW STORM MOVEMENT DUE
TO THE WEAK FLOW ALOFT.  WET AND UNSTABLE ENVIRONMENT ALSO SUGGESTS
DOWNBURST NEAR-SEVERE WINDS ARE A POSSIBILITY...AND ESPECIALLY EARLY
IN THE STORM EVOLUTION WHEN UPDRAFTS ARE RAPIDLY STRENGTHENING.

MEANWHILE...AREA OF STORMS OVER SW IA IS EXPECTED TO EXPAND SOUTHWARD AS
IT LIFTS NE DUE TO INCREASING LOW LEVEL JET FEEDING INTO IT FROM THE
SW.  IF THIS IN FACT EVOLVES AS PROGGED...THEN AS CONVECTION MOVES
INTO EASTERN IA LATER THIS MORNING...IT WOULD BE IN A WEAKENING
PHASE AS IT MOVES AWAY FROM OUT THE LLJ BUT SHOULD STILL HOLD
TOGETHER INTO EASTERN IA AND NW IL.

TEMPERATURES TODAY WILL ONCE AGAIN NEAR 90. WITH DEW POINTS IN THE
70S...THIS WILL MEAN HEAT INDEX READINGS NEAR OR JUST ABOVE
100...ESPECIALLY IN THE SOUTHERN THIRD OF THE CWFA. ONE FLY IN THE
OINTMENT COULD BE PRECIP AND CONVECTIVE CLOUD DEBRIS.  THE LONGER
THE CLOUDS LINGER...THE GREATER THE POTENTIAL FOR HEAT INDICES NOT
TO REACH 100.  EITHER WAY IT WILL BE WARM AND MUGGY.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 327 AM CDT SAT AUG 23 2014

THIS STRETCH OF THE WARMEST WEATHER OF THE SEASON IS LIKELY TO
PERSIST WELL INTO NEXT WEEK WITH CONTINUED NEARLY DAILY CHANCES FOR
THUNDERSTORMS. WHILE DETAILS AND TIMING REMAIN UNCERTAIN...A PATTERN
SHIFT IS LIKELY TO TAKE PLACE BY LATE IN THE WEEK...PROVIDING A
RETURN TO BELOW NORMAL TEMPERATURES AND DRIER CONDITIONS.

SUNDAY...A STRENGTHENING SOUTH TO SOUTHWEST LOW LEVEL FLOW RESULTING
FROM THE PLAINS LOW LIFTING N-NE INTO CANADA WILL WASH OUT THE LOW
LEVEL CONVERGENCE AND PROVIDE DEEPER MIXING. 00Z MODELS HAVE
CONVERGED TO BETTER AGREEMENT SHOWING A GENERAL RANGE OF 21 TO 23
DEGREES CELSIUS AT 850 MB OVER THE AREA...WHICH WOULD GENERALLY
SUGGEST HIGHS IN THE LOWER TO MID 90S. HOWEVER...WITH CONTINUED HIGH
PW OVER ESPECIALLY THE EAST AND POSSIBILITY OF OCCASIONAL CLOUD
COVER...HAVE TRENDED HIGHS A BIT LOWER AND CLOSER TO
GUIDANCE...WHICH HAS TRENDED TOO WARM OVER THE PAST SEVERAL DAYS.
THE COMBINATION OF HIGHS FROM THE UPPER 80S NORTH AND NORTHEAST TO
THE LOWER 90S CENTRAL AND SOUTH AND DEW POINTS HOLDING IN THE LOWER
70S WOULD PUSH HEAT INDEX VALUES INTO A 100 TO NEAR 105 RANGE MAINLY
SOUTH OF I-80 IN THE AFTERNOON AND A HEAT ADVISORY MAY BE NEEDED.
FORECAST SOUNDINGS SUGGEST A STRONG ENOUGH CAP TO PREVENT DAYTIME
THUNDERSTORMS AND KEPT POPS BELOW SLIGHT CHANCES.

SUNDAY NIGHT THROUGH NEXT WEEK...MODELS CONTINUE TO VARY
CONSIDERABLY WITH THE TIMING OF A WEAK COLD FRONT MONDAY...WHICH
LARGELY WASHES OUT TO KEEP VERY WARM AND HUMID CONDITIONS IN PLACE
THROUGH AT LEAST TUESDAY. THE GFS REMAINS A MORE PROGRESSIVE OUTLIER
BY MID TO LATE WEEK WITH A FASTER BREAKDOWN OF THE UPPER LEVEL RIDGE
AND THE ENSUING ONSET OF AN UPPER TROUGH AND SURFACE HIGH BY THU AND
FRI. AT THE SAME TIME...THE ECMWF AND CANADIAN HAVE A LESS PHASED
CONFIGURATION OF THE UPPER LEVEL FLOW BY THU AND FRIDAY...SHOWING A
SURFACE LOW MOVING OUT OF THE CENTRAL PLAINS SPREADING PRECIPITATION
INTO THE REGION. THUS...A LOW CONFIDENCE EXTENDED PERIOD CONTINUES.
NEAR ADVISORY HEAT AND HUMIDITY IS MAINTAINED FOR MONDAY AND
TUESDAY...WITH HIGHS TRENDING BACK TO ONLY THE 70S FOR THURSDAY AND
FRIDAY. THUNDERSTORM CHANCES ARE GREATEST TUESDAY NIGHT AND
WEDNESDAY WITH LOW CONFIDENCE...SLIGHT CHANCE TO CHANCE POPS NEARLY
EVERY PERIOD FROM SUNDAY NIGHT THROUGH FRIDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1253 PM CDT SAT AUG 23 2014

IN WAKE OF EXITING LINEAR MCS THIS AFTERNOON WILL SEE AREAS OF STRATUS
DEVELOP WITH IFR AND MVFR CIGS... AND MAY SEE A FEW SHOWERS AND
STORMS REDEVELOP ALONG RESIDUAL BOUNDARIES. TONIGHT THE SIGNAL FOR
ANY DEVELOPMENT OF SHOWERS AND STORMS IS GREATEST TO THE EAST OF THE
TERMINALS AND ALSO WELL TO OUR NORTHWEST. SURFACE FRONT GENERALLY
SOUTH OF THE TERMINALS WILL BEGIN TO GRADUALLY LIFT NORTH OVERNIGHT.
ABUNDANT MOISTURE AIDED BY RECENT RAINFALL SHOULD ALLOW FOR FOG AND
LOW CLOUDS TO DEVELOP NEAR AND NORTH OF THE BOUNDARY... WITH CONDITIONS
DETERIORATING TO MVFR AND IFR WITH AREAS OF VLIFR. IMPROVING CONDITIONS
EXPECTED FROM MID SUNDAY AM THROUGH EARLY SUNDAY AFTERNOON AS
BOUNDARY LIFTS THROUGH AND WINDS TURN SOUTHERLY AROUND 10 KTS WITH
SOME HIGHER GUSTS.


&&

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

$$

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





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