Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 311736
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1236 PM CDT THU JUL 31 2014

.UPDATE...
ISSUED AT 1226 PM CDT THU JUL 31 2014

DIURNAL CONVECTION THIS AFTERNOON WILL PROBABLY OCCUR BUT IS
QUESTIONABLE. THE 12Z SOUNDING SHOWS A CAPPING INVERSION ABOVE
700MB. RAP TRENDS KEEP THIS CAP IN PLACE UNTIL NEARLY SUNSET SO
ANY CONVECTION THAT DOES GET GOING WOULD BE SHALLOW IN NATURE.

ANOTHER VARIABLE IN THE DIURNAL CONVECTION IS THE THIN HAZE OF
ELEVATED SMOKE ACROSS THE AREA WHICH IS HELPING TO FILTER THE
HEATING FROM THE SUN. THIS FILTERING IS VERY SUBTLE ON VISIBLE
SATELLITE BUT IT IS THERE.

BASED ON SATELLITE TRENDS...DIURNAL CLOUDS WILL CONTINUE TO
DEVELOP BUT ANY CONVECTION APPEARS TO BE ROUGHLY 2 HOURS AWAY FROM
OCCURRING. LIKE YESTERDAY IT WILL BE QUITE ISOLATED IN NATURE.

&&

.SYNOPSIS...
ISSUED AT 321 AM CDT THU JUL 31 2014

VERY WEAK/DIFFUSE SFC FLOW PATTERN ACROSS THE AREA EARLY THIS AM WITH
WEAK RIDGING SOUTH AND SUBTLE TROUGH/WIND SHIFT EVIDENT IN MSLP
FIELD AND OBS FROM EASTERN WI INTO NORTHEAST IA. MAINLY CLOUD-FREE
BUT HAZY SKY WITH SOME SHALLOW GROUND FOG IN RIVER VLYS AND OTHER
LOW LYING AREAS. STAGNANT/BLOCKY PATTERN ALOFT CONTINUES WITH DEEP
LAYER CYCLONE REMAINING ANCHORED OVER JAMES BAY AND ASSOCIATED
LONG-WAVE TROUGH ENCOMPASSING EASTERN HALF OF CONUS...WHILE RIDGING
PERSISTS OUT WEST. RESULTANT NW FLOW ALOFT OVER THE NATIONS
MIDSECTION INJECTED WITH SEVERAL IMPULSES... MOST NOTABLY A PAIR
LOCATED UPSTREAM WITH LEAD VORT DIVING S/E THROUGH ND AND ANOTHER
VORT JUST BEHIND IT OVER SASKATCHEWAN... WHICH MAY HAVE SOME ROLE IN
CONVECTIVE POTENTIAL LATER TDY/TNGT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 321 AM CDT THU JUL 31 2014

SMOKE FROM FIRES IN CANADA TO MAINTAIN MILKY HAZE IN OUR SKY TDY WITH
DIURNAL CUMULUS OF SCT-BKN COVERAGE ONCE AGAIN LATE AM THROUGH PM.
TEMPS TO WARM 1-3 DEGS MANY LOCATIONS FROM YSTDY WITH WARMING OF
AIRMASS (1-2C AT 850 MB)... WITH LOWER 80S COMMONPLACE. CONTINUE WITH
STRAY SHOWER POSSIBLE THIS AFTN MAINLY EASTERN CWA ATTENDANT TO SUBTLE
TROUGH/WIND SHIFT BUT WOULDN/T AT ALL BE SURPRISED TO SEE A CLEAN
RADAR EITHER WITH CAPPING INVERSION IN 600-700 MB LAYER EVIDENT IN
MODEL SOUNDINGS AND SAMPLED ON 00Z DVN RAOB... AS WEAK RIDGING ALOFT
FURTHER AMPLIFIES AHEAD OF APPROACHING LEAD VORT MAX FROM ND. POSITIVE
VORTICITY ADVECTION ALBEIT WEAK BEGINS TO OVERSPREAD WESTERN CWA
LATE TDY IN ADVANCE OF THE VORT MAX... AND THIS COULD BE SUFFICIENT TO
ERODE MID LEVEL CAP AND ALLOW FOR AT LEAST ISOLD CONVECTION TO DEVELOP
OR PROPAGATE INTO WESTERN CWA LATE AFTN INTO EARLY EVE. THE SECONDARY
VORT OVER SASKATCHEWAN WILL FOLLOW FOR TONIGHT AND MAY ALLOW FOR
PERCOLATION OF ISOLD CONVECTION WELL AFTER DARK... THUS WILL MAINTAIN
SLIGHT CHC POPS THIS EVE INTO THE OVRNGT BEFORE TAPERING OFF AND SHIFTING
EAST. LOWS TONIGHT SHOULD BE MAINLY IN THE UPPER 50S TO AROUND 60F
WITH MID 50S POSSIBLE IN LOW LYING AND COOL DRAINAGE AREAS BENEATH
CLEAR TO PARTLY CLOUDY SKIES. PATCHY FOG ALSO ANTICIPATED ESPECIALLY
IN THE RIVER VALLEYS.

.LONG TERM...(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 321 AM CDT THU JUL 31 2014

FORECAST FOCUS ON RAIN CHANCES AS WE FLIP THE CALENDAR TO AUGUST.

FRIDAY THROUGH SATURDAY...NORTHWEST FLOW ALOFT WITH SEVERAL
DISTURBANCES DROPPING SOUTHEAST IN THE FLOW. THE TROUGH ACTUALLY
BECOMES REINFORCED WITH A NICE COLD POCKET ALOFT ROTATING DOWN INTO
THE CWA. FORECAST SOUNDINGS INDICATE 500 MB TEMPERATURES OF ABOUT
-15C AND SURFACE DEWPOINTS IN THE LOWER 60S. MODELS CONTINUE TO
PAINT SOME QPF OVER THE CWA ESPECIALLY IN OUR NORTHERN COUNTIES.
WITH AN UNCAPPED ATMOSPHERE AND STEEP LAPSE RATES SCATTERED SHOWERS
AND THUNDERSTORMS SHOULD DEVELOP ESPECIALLY DURING THE AFTERNOON/
EARLY EVENING. FREEZING LEVELS ARE 10-11K FT WHICH MAY SUPPORT NEAR
SEVERE HAIL IN SMALL BUT VIGOROUS UPDRAFTS WITH CAPES PUSHING INTO
THE 1000-2000 J/KG RANGE. MAXIMUM TEMPERATURES WILL BE IN THE LOWER
80S WITH LOWS IN THE LOWER 60S.

SUNDAY THROUGH TUESDAY...THE LARGE SCALE PATTERN WILL UNDERGO A
CHANGE TO A MORE ZONAL FLOW DURING THIS PERIOD. THE MIDWEST WILL BE
ON THE EDGE OF THE HEAT DOME CENTERED IN THE SOUTHERN ROCKIES/
SOUTHERN PLAINS SO RIDGE RIDERS MAY TRIGGER PERIODIC EPISODES OF
THUNDERSTORMS. TOO EARLY TO GET SPECIFIC BUT DEPENDING ON WHERE A
MEANDERING WEST-EAST BOUNDARY SETS UP THERE COULD BE SOME HEAVY
RAINFALL...AS THE UPPER LEVEL WINDS ARE PROGGED TO BE RATHER LIGHT
AND STORMS WOULD BE SLOW MOVING. WITH THIS TYPE OF PATTERN THE
AFTERNOON TEMPERATURES SHOULD WARM INTO THE 80S WHICH IS TYPICAL OF
EARLY AUGUST.

WEDNESDAY...ECMWF/GFS STILL LOOKING INTERESTING AS A POTENT SHORT
WAVE BREAKS OFF FROM A DEEP CLOSED LOW IN THE GULF OF ALASKA REGION.
DEPENDING ON THE TIMING/LOCATION OF THE STORM SYSTEM THERE COULD BE
SIGNIFICANT RAINFALL AND/OR SEVERE WEATHER IN OR NEAR THE DVN CWA.
BEHIND THE SYSTEM MAXIMUM TEMPERATURES SHOULD DROP INTO THE 70S LATE
NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY AFTERNOON)
ISSUED AT 1226 PM CDT THU JUL 31 2014

VFR CONDITIONS ARE EXPECTED THROUGH 06Z/01 AS HIGH PRESSURE SLOWLY
MOVES EAST FROM THE PLAINS. DIURNAL CONVECTION IS POSSIBLE THROUGH
SUNSET BUT WILL BE VERY ISOLATED...AND...THE PROBABILITY OF A SHRA
OR TSRA AFFECTING A TAF SITE IS AT BEST 5 PERCENT. AFT 06Z/01 VFR
CONDITIONS ARE EXPECTED TO CONTINUE. HOWEVER...PATCHY MVFR
CONDITIONS MAY DEVELOP PRIOR TO SUNRISE DUE TO LIGHT WINDS.

&&

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

$$

UPDATE...08
SYNOPSIS...MCCLURE
SHORT TERM...MCCLURE
LONG TERM...HAASE
AVIATION...08





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