Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 011727
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
1227 PM CDT SAT AUG 1 2015

.SYNOPSIS...
ISSUED AT 343 AM CDT SAT AUG 1 2015

HIGH PRESSURE REMAINED IN PLACE ACROSS THE CENTRAL PLAINS AND
SOUTHERN MISSISSIPPI RIVER VALLEY THIS MORNING. CLOSER TO THE
LOCAL AREA...A WELL DEFINED MOISTURE GRADIENT WAS LOCATED ACROSS
OUR AREA WHERE DEWPOINTS IN THE SW WERE MID TO UPPER 60S. WHILE
ACROSS OUR NE ZONES...DEWPOINTS WERE IN THE MID 50S. AT H85 A
THETAE PUSH WAS LEADING TO THE DEVELOPMENT OF SHOWERS AND
THUNDERSTORMS ACROSS SE MN AND SW WI. THESE SHOWERS SHOULD DRIFT
TO THE S AND EAST THROUGHOUT THE MORNING WITH THE H85 PUSH.
THUNDERSTORMS WERE ALSO FORMING IN OUR SW ZONES. THIS WAS DUE TO A
WEAKLY CONVERGENT SFC FLOW AND SFC MOISTURE BOUNDARY.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 343 AM CDT SAT AUG 1 2015

MAIN FORECAST CONCERN FOR THE SHORT TERM ARE THE CHANCES OF RAIN
AND THUNDERSTORMS LATE THIS EVENING AND INTO THE OVERNIGHT HOURS.
A FAST MOVING VORT IN THE FLOW WILL LEAD TO THE DEVELOPMENT OF
SHOWERS AND THUNDERSTORMS ACROSS SD AND NE. THESE STORMS WILL THEN
TRACK EAST OR SE THROUGH THE LATE EVENING.

TODAY...SFC WINDS SHOULD TURN TO THE W SW AND USHER IN MORE MOIST
AIR INTO THE AREA. THE DEVELOPMENT OF AFTERNOON CU SHOULD BE THE
ONLY IMPEDIMENT TO THE SUN TODAY. LATER IN THE AFTERNOON THE
VORT MAX SHOULD APPROACH THE AREA FROM THE NW.

RATHER UNIMPRESSIVE WAVE ON WV SHOULD BE ROUNDING THE RIDGE THIS
AM AND THEN MARCHING TO THE SW. 00Z OBS SHOWED NO H5 HEIGHT FALLS
IN THE VICINITY OF THIS WAVE. REGARDLESS...MODELS HAVE HEIGHTS
DROPPING LATER TODAY AS THE WAVE APPROACHES THE AREA. THIS WAVE
SHOULD HELP TO TRIGGER CONVECTION TO THE NORTH AND WEST OF US.
GUIDANCE AND CONCEPTUAL MODELS SUGGEST THAT THIS CONVECTION SHOULD
GROW UPSCALE TO A MCS OR TWO AND MOVE TO THE EAST TONIGHT. WITHOUT
A WELL DEFINED FRONT IN THE AREA...THE MOVEMENT OF THE MCS WILL BE
DICTATED BY STEERING LEVEL WINDS AND H85 JET. MASS CONVERGENCE ON
THE H85 LEVEL SUGGESTS THAT CONVECTION WILL MOVE EAST ACROSS N IA
AND THEN AFTER 6Z START TO DIVE S AS WELL. THIS WOULD BRING THE
MCS INTO OUR AREA. THE H85 JET IS NOT THAT IMPRESSIVE BUT WOULD
LEAD TO DECENT SPEED AND DIRECTIONAL SHEAR IN THE LOW LEVELS. THIS
WOULD LEAD TO A POTENTIAL SEVERE WIND THREAT ACROSS THE AREA.
LAPSE RATES IN THE MODEL SOUNDINGS...ESPECIALLY THE NAM...ARE
IMPRESSIVE AND SUGGEST A HAIL THREAT AS WELL WITH THESE STORMS.

THAT BEING SAID...I STILL HAVE DOUBT IN THIS FORECAST. FOR ONE...DEEP
LAYER SHEAR IS UNIMPRESSIVE UNTIL THE WAVE GETS CLOSER TO THE AREA
NEAR 12Z. CONVECTION GROWING UPSCALE WOULD BE COLD POOL DOMINANT
AND MAY NOT BE ABLE TO MAINTAIN ITSELF IN SUCH WEAKLY SHEARED
ENVIRONMENT. EVEN MORE DISCONCERNING IS THE FACT THAT THE CAMS DO
NOT PRODUCE MUCH IN THE WAY OF CONVECTION OVERNIGHT. WHILE THE
CAMS MAY NOT ALWAYS NAIL THE AREA WHERE STORMS FORM....THEY
USUALLY DO A GOOD JOB OF NAILING WHETHER OR NOT THINGS WILL FIRE
ACROSS AN AREA. AS A RESULT....DECIDED TO STAY IN THE HIGH CHANCE
CATEGORY FOR POPS.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 343 AM CDT SAT AUG 1 2015

SUNDAY AND SUNDAY NIGHT...AT LEAST SCATTERED STORMS SHOULD BE FOUND
SUNDAY MORNING WITHIN ZONE OF WARM ADVECTION/ISENTROPIC ASCENT
ATTENDANT TO VEERING LOW LEVEL JET ABOVE SURFACE WARM FRONTAL ZONE
WITH ACTIVITY SLOWLY DECAYING AS JET WEAKENS. IN WAKE EXPECT
ATMOSPHERE TO RECHARGE DURING AFTERNOON WITH ENOUGH SOLAR INSOLATION
AND GUSTY SOUTHWEST WINDS BOOSTING TEMPS WELL INTO THE 80S TO
POSSIBLY AROUND 90 DEGREES IN SOME LOCATIONS DEPENDING ON AMOUNT OF
SUNSHINE. THESE TEMPS COUPLED WITH SURFACE DEW POINTS WELL INTO THE
60S TO LOWER 70S MAY YIELD STRONG INSTABILITY WITH SBCAPE OF
3000-4000 J/KG WHICH ALONG WITH PROGGED BULK SHEAR 0-6KM OF 30-40
KTS YIELDS FAVORABLE ENVIRONMENT FOR ORGANIZED SEVERE POTENTIAL.
ATTIM TARGETING POSSIBLY FAR EASTERN IA BUT ESPECIALLY NORTHERN IL
BEING ON FRINGE OF WARM EML. MAIN THREAT WOULD APPEAR TO BE DAMAGING
WINDS... WITH LARGE HAIL A SECONDARY THREAT. WOULD HAVE TO WATCH
FOR ANY LOCALIZED BACKING OF WINDS WHICH COUPLED WITH WARM FRONT
OR OUTFLOW BOUNDARY INTERACTION WOULD ENHANCE HELICITY AND YIELD SOME
TORNADO RISK. STORM CHANCES WOULD BE DIMINISHING BY MID SUNDAY EVENING
WITH PASSAGE OF COLD FRONT ATTENDANT TO SHORTWAVE MOVING THROUGH THE
GREAT LAKES.

MONDAY AND MONDAY NIGHT...HAVE REMOVED POPS MONDAY WITH GENERAL MODEL
CONSENSUS OF BUILDING IN BOUT OF SURFACE RIDGING IN WAKE OF COLD
FRONT PROVIDING SLIGHTLY COOLER AND LESS HUMID DAY. HOWEVER... MONDAY
NIGHT SURFACE RIDGE QUICKLY SHIFTS EAST AND RETURN FLOW DEVELOPS
WHICH WILL BRING ATTENDANT CHANCE OF SHOWERS AND STORMS BY LATE EVENING
AND OVERNIGHT...MAINLY SOUTHERN CWA.

TUESDAY THROUGH WEDNESDAY...HAVE SHIFTED RAIN CHANCES TO ROUGHLY THE
SOUTHERN 2/3RDS OF CWA IN SCENARIO CLOSER TO GFS OF BOUNDARY STALLED IN
OR NEAR SOUTHERN CWA AND UPPER LEVEL DISTURBANCES SHIFTING EASTWARD IN
FLATTENING FLOW. HOWEVER...DPROG/DT OF SEVERAL MODELS SHOW TREND
OF STRONGER INCOMING SURFACE HIGH WHICH RESULTS IN FRONT SETTLING
FURTHER SOUTH AND A MAINLY DRY SCENARIO... WHICH WILL NEED TO BE
RE-EVALUATED. WITH GRADUAL DRAW DOWN ON 850 MB TEMPS FROM MID TEENS TO
AROUND 12C TO 13C AND NORTH/NORTHEAST WIND SHOULD YIELD TEMPS NEAR TO
BELOW NORMAL... WITH HIGHS MID 70S TO LOWER 80S AND LOWS IN THE 50S TO
LOWER 60S.

THURSDAY THROUGH FRIDAY...HEAT DOME LOOKS TO BUILD BACK INTO THE PLAINS
WHILE COOLER TEMPS RESIDE AROUND GREAT LAKES WITH UPPER LOW. THE CWA MAY
RESIDE CLOSE ENOUGH TO BATTLE ZONE FOR ANOTHER ROUND OF RAIN CHANCES...WITH
TEMPS REMAINING NEAR TO BELOW NORMAL.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY AFTERNOON)
ISSUED AT 1226 PM CDT SAT AUG 1 2015

A BROAD AREA OF HIGH PRESSURE WILL PROVIDE VFR CONDITIONS THROUGH
MOST OF THE PERIOD. THERE REMAINS A POTENTIAL FOR A CLUSTER OF
THUNDERSTORMS TO MOVE INTO EASTERN IOWA AND NORTHEAST ILLINOIS
LATE TONIGHT...WHICH IS INCLUDED WITH PROB30 GROUPS AT CID AND
DBQ AROUND SUNRISE. SCATTERED THUNDERSTORMS MAY BE POSSIBLE
THROUGH SUNDAY MORNING...BUT CONFIDENCE IS TOO LOW TO INCLUDE IN
THE FORECASTS THAT FAR OUT. FURTHER SOUTH...THE LATE NIGHT/EARLY
SUNDAY MORNING THUNDERSTORM CHANCES HAVE BEEN REMOVED FROM MLI AND
BRL...WHERE THERE IS INCREASING UNCERTAINTY IN THE POTENTIAL FOR
THUNDERSTORMS.

&&

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

$$

SYNOPSIS...GIBBS
SHORT TERM...GIBBS
LONG TERM...05
AVIATION...SHEETS


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