Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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955
FXUS63 KDVN 172332
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
632 PM CDT SUN MAY 17 2015

.UPDATE...
ISSUED AT 632 PM CDT SUN MAY 17 2015

KDVN RADAR SHOWED THE FEW SHOWERS AND THUNDERSTORMS THAT FORMED
OVER THE NW FORECAST AREA AT MID AFTERNOON HAVE SINCE DISSIPATED.
VISIBLE SATELLITE IMAGERY SHOWS A LARGE CLEARING UPSTREAM IN THE
SHARP...DEEP CYCLONIC FLOW OVER CENTRAL IA AND NORTHERN MO. WITH A
LACK OF A COHERENT LOW LEVEL BOUNDARY TO FOCUS CONVECTION...AND
THE DRY MID AND UPPER LEVELS WITH APPARENT SUBSIDENCE...FURTHER
CONVECTION LOOKS UNLIKELY THIS EVENING. HAVE UPDATED TO REMOVE THE
MENTION OF THUNDERSTORMS...KEEPING ONLY SLIGHT CHANCES FOR
ISOLATED SHOWERS GOING ACROSS THE NW OVER THE NEXT COUPLE HOURS.
WINDS SHOULD DIMINISH EARLY THIS EVENING AND THE LATE NIGHT/EARLY
MONDAY MORNING COLD FRONTAL PASSAGE STILL LOOKS DRY.

&&

.SYNOPSIS...
ISSUED AT 300 PM CDT SUN MAY 17 2015

PRESSURE PERTURBATION HAS EXITED EASTERN CWA WITH TEMPORARY BOUT
BOUT OF SUBSIDENCE AND LOW LEVEL DRYING ON VEERING SOUTHWEST
WINDS LEADING TO FAIRLY QUIET RADAR SCOPE WITH 18Z DVN RAOB
SHOWING COUPLE OF CAPPING INVERSIONS ABOVE 800 MB. HOWEVER...WITHIN
THE LAST 20-30 MINS SCATTERED STORMS HAVE FORMED IN NORTHWEST CWA
LIKELY AIDED BY ASCENT FROM CYCLONICALLY CURVED JET AND BACKING
LOW LEVEL WINDS AND INCREASING CONVERGENCE AHEAD OF WEAK SURFACE
TROUGH. PLENTY OF SHEAR WITH EFFECTIVE AND 0-6KM AT 40-45 KTS BUT
IN A RELATIVE MINIMUM OF INSTABILITY WITH SBCAPE AND MUCAPE BELOW
1000 J/KG ALTHOUGH TRENDS HAVE BEEN INCREASING AND WILL NEED TO BE
WATCHED FOR ISOLD STRONG TO POSSIBLY BRIEF SEVERE STORM WITH
THREATS BEING MAINLY HAIL WITH ENTRAINMENT OF DRY AIR ALOFT AND
GUSTY WINDS.

&&

.SHORT TERM...(THIS EVENING THROUGH MONDAY)
ISSUED AT 300 PM CDT SUN MAY 17 2015

ISOLATED TO SCATTERED STORMS EXPECTED TO PERSIST LATE THIS AFTERNOON
BEFORE DIMINISHING EARLY EVENING WITH LOSS OF HEATING. MOST FAVORED
AREA FOR OCCURRENCE WILL BE WEST OF THE MISSISSIPPI RIVER AND
ESPECIALLY ACROSS THE NORTHWEST CWA GIVEN PROXIMITY TO LIFT REGION
OF CURVED JET AND LOW LEVEL CONVERGENCE. AN ISOLD STORM MAY BECOME
STRONG WITH LOW RISK OF SEVERE. COLD FRONT TO MOVE THROUGH
OVERNIGHT AND EXIT EARLY MONDAY MORNING. CANT TOTALLY RULE OUT
SOME CHANCE OF PCPN IF ENOUGH CONVERGENCE... BUT TIMING AT DIURNAL
MIN AND LACK OF COHERENT TRIGGER ALOFT PRECLUDES ANY MENTION OF
PCPN WITH THE FRONTAL PASSAGE ATTIM. GUSTY SOUTHERLY WINDS 20 TO
35 MPH WILL DIMINISH WITH SUNSET. DECENT TEMP GRADIENT ON LOWS
TONIGHT WITH LOWER 50S NORTHWEST TO FEW MID 60S FAR EAST/SOUTHEAST.
SKIES WILL BE CLEARING AS WELL.

MONDAY...WINDY AND COOLER WITH MIXING AND COLD ADVECTION PRODUCING
WEST/NORTHWEST WINDS OF 20-30+ MPH. SKIES GENERALLY MOSTLY SUNNY
WITH PARTLY SUNNY POSSIBLE FAR NORTH. SOLAR INSOLATION WILL OFFSET
STRONG COLD ADVECTION SOME AND HAVE CONTINUED TO SIDE NEAR WARM
SIDE OF GUIDANCE BLEND WITH HIGH TEMP GRADIENT RANGING FROM AROUND
60/LOWER 60S NORTHWEST TO MID 70S FAR EAST/SOUTHEAST.

.LONG TERM...(MONDAY NIGHT THROUGH SUNDAY)
ISSUED AT 256 PM CDT SUN MAY 17 2015

MAIN FORECAST CONCERN FOR THE LONG TERM FORECAST ARE
THE CHANCES FOR PRECIPITATION ON WEDNESDAY AND AGAIN NEXT WEEKEND
WITH ANOTHER SYSTEM MOVING INTO THE AREA.  THESE TWO ROUNDS OF
PRECIPITATION WILL BE FLANKED BY PLEASANT SENSIBLE WEATHER.

AT THE BEGINNING OF THE PERIOD...HIGH PRESSURE WITH VERY DRY AIR
WILL BE ADVECTING INTO THE AREA.  DEWPOINTS IN THE 30S LOOK LIKELY
THROUGH WEDNESDAY.

ON WEDNESDAY A SYSTEM FROM THE WEST AND SOUTH APPROACHES.  THIS
HELPS TO INCREASE MOISTURE ACROSS THE AREA.  AT FIRST...I BELIEVE WE
WILL SEE VIRGA BEFORE THE RAIN SATURATES THE COLUMN.  I THINK THAT
WE WILL SEE RAIN EVENTUALLY SPREAD OVER THE AREA.  THERE IS NO CAPE
WITH THE LOW DEWPOINTS WITH THIS SYSTEM. WITH THE LACK OF AN UPDRAFT
AT -10C...I DO NOT SEE ANY THUNDER WITH THIS SYSTEM.  OVERALL TRENDS
OF THE MODELS SUGGESTS THAT HIGH CONFIDENCE SHOULD EXIST IN THE
SYNOPTIC FIELDS AS LITTLE CHANGE IN THE LAST FEW RUNS HAVE OCCURRED.

BETWEEN WEDNESDAY AND THE WEEKEND DRIER AIR STAYS IN PLACE AND
TEMPERATURES WARM TO NEAR AVERAGE ACROSS THE AREA. ON
SATURDAY...SW FLOW RETURNS TO THE AREA...INCREASING MOISTURE INTO
THE AREA. THIS...ALONG WITH A FEW RIPPLES IN THE FLOW COULD LEAD
TO RAIN AND EVEN ISOLATED THUNDERSTORMS NEXT WEEKEND. THE BEST
CHANCE FOR THUNDER AND RAIN APPEARS TO BE SUNDAY AGAIN AT THIS
TIME. MODELS ARE IN SOMEWHAT AGREEMENT WITH RESPECT TO THE
SYNOPTIC FEATURES. HOWEVER...THEY HAVE SHOWN GREAT RUN TO RUN
DIFFERENCES. THIS MEANS THAT I HAVE LOW CONFIDENCE IN THE OVERALL
SOLUTION NEXT WEEKEND.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z MONDAY EVENING)
ISSUED AT 632 PM CDT SUN MAY 17 2015

STRONG...GUSTY SOUTH WINDS WILL DIMINISH QUICKLY EARLY THIS
EVENING UNDER CLEARING SKIES. CONDITIONS WILL REMAIN VFR
OVERNIGHT WITH A MINOR WIND SHIFT FROM SW TO W WITH THE PASSAGE OF
A WEAK COLD FRONT. WINDS WILL INCREASE AGAIN MONDAY MORNING AND
REMAIN GUSTY FROM THE WEST TO NW AROUND 15 TO 25 KTS THROUGH THE
AFTERNOON. OTHERWISE...CONDITIONS WILL REMAIN VFR.

&&

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

$$

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



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