Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 200244
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
944 PM CDT TUE MAY 19 2015

.UPDATE...
ISSUED AT 939 PM CDT TUE MAY 19 2015

BASED ON 00Z RAOB DATA...THE DRY AIR IS SLIGHTLY DEEPER THAN WHAT
EARLIER MODELS INDICATED. GIVEN THAT THE DRY AIR IS SLIGHTLY
DEEPER...IT WOULD THEN TAKE LONGER TO SATURATE. ONE POSITIVE IS
THAT THE PROJECTED EASTERLY FLOW OFF THE LAKE IS NOT OVERLY STRONG
INDICATING THAT SATURATION WILL IN TIME WIN OUT.

THUS HAVE MADE ADJUSTMENTS TO THE GOING FORECAST TO SLIGHTLY DELAY
THE ARRIVAL OF THE PRECIPITATION OVERNIGHT.

&&

.SYNOPSIS...
ISSUED AT 312 PM CDT TUE MAY 19 2015

SYNOPSIS...AS OF 300 PM CDT...SUBSIDENCE ASSOCIATED WITH A LARGE
HIGH PRESSURE SYSTEM OVER THE UPPER MIDWEST AND NORTHERN PLAINS
BROUGHT MAINLY CLEAR SKIES TO EASTERN IOWA AND WESTERN ILLINOIS
INTO THE MID AFTERNOON TODAY. LIGHT NORTHWEST FLOW HAS CONTINUED
TO ADVECT DRY LOW-LEVEL AIR INTO THE FORECAST AREA. DEWPOINTS WERE
GENERALLY IN THE 30S.

THIS EVENING AND TONIGHT...TEMPS WILL FALL INTO THE 40S BUT MID AND
UPPER LEVEL CIRRUS CLOUDS...ALREADY VISIBLE OVER CENTRAL AND WESTERN
IOWA ON GOES IMAGERY...WILL STREAM IN FROM THE SOUTHWEST AND
CAUSE VALUES TO STABILIZE IN THE LOWER TO MIDDLE 40S.

&&

.SHORT TERM...(THIS EVENING THROUGH WEDNESDAY)
ISSUED AT 312 PM CDT TUE MAY 19 2015

WEDNESDAY...COLD CLOUD SHIELD ON IR SATELLITE IMAGERY...CURRENTLY
OVER THE CENTRAL PLAINS...HAS FORMED DOWNSTREAM OF A MID-LEVEL
LOW CENTERED NEAR THE FOUR CORNERS. THIS MID/UPPER LEVEL WAVE WILL
PROPAGATE ENE WITH TIME BRINGING A GOOD CHANCE FOR RAIN SHOWERS TO
THE SOUTHERN TWO-THIRDS OF THE DVN CWA ON WEDNESDAY.

TIME HEIGHTS SECTIONS DISPLAY DEEP NEGATIVE OMEGA WHICH IS MOST
FOCUSED BETWEEN 700-500MB AS PVA AND WAA SLIDE THROUGH.
ADDITIONALLY...NAM/ECMWF 1000-500MB COLUMN AVG RH PLOTS SHOW A
HIGHLY SATURATED ENVIRONMENT...VALUES GREATER THAN 95 PERCENT...AS
SE WINDS WITHIN THIS LAYER PULL 0.75-1.00 INCH PWAT VALUES
NORTHWARD INTO THE FORECAST AREA. COOL SFC TEMPS SUPPORT THE HIGH
SATURATION AT LOW-LEVELS. THE GFS IS SIGNIFICANTLY DRIER THAN THE
AFOREMENTIONED MODELS BUT WEIGHTED FORECAST MORE TOWARD THE WETTER
MODELS.

EXPECT A NORTH TO SOUTH GRADIENT IN RAINFALL ACCUMULATIONS
RANGING FROM A FEW HUNDREDTHS NEAR DUBUQUE TO AROUND 0.30-0.40
TENTHS OF AN INCH NEAR/SOUTH OF BURLINGTON WITH SOME LEEWAY FOR
THIS GRADIENT TO SHIFT NORTH OR SOUTH SLIGHTLY. THE BEST CHANCE
FOR SHOWERS WILL BE BETWEEN THE MID MORNING TO THE MID AFTN. MAX
TEMPS ONLY FORECAST IN THE LOWER TO MIDDLE 50S.

.LONG TERM...(WEDNESDAY NIGHT THROUGH TUESDAY)
ISSUED AT 312 PM CDT TUE MAY 19 2015

A RETURN TO MORE ACTIVE WEATHER BEGINNING THIS WEEKEND IS THE MAIN
FOCUS OF THE LONG TERM PERIOD.

AN UNSEASONABLY COOL AIRMASS WILL REMAIN IN PLACE WEDNESDAY NIGHT
INTO THURSDAY WITH A SURFACE RIDGE SLIDING SOUTH ACROSS THE FORECAST
AREA. UPPER RIDGING IS THEN FORECAST FOR FRIDAY WITH AFTERNOON
TEMPERATURES MODERATING BACK INTO THE LOW 70S.

ATTENTION THEN TURNS TO THE TRANSITION TO SOUTHWEST FLOW OVER THE
WEEKEND...LIKELY TO PERSIST INTO EARLY NEXT WEEK. WILL CONTINUE TO
CARRY POPS EVERY PERIOD FROM SATURDAY THROUGH TUESDAY. WHILE THERE
WILL UNDOUBTEDLY BE DRY PERIODS...CANNOT REASONABLY RESOLVE THEM
THIS FAR OUT. HOWEVER...A LOOK AT THE CURRENT AND PAST RUNS OF THE
GFS AND ECMWF...THE LAST 3 TO 4 RUNS HAVE BEEN DECENTLY
CONSISTENT IN FAVORING SUNDAY INTO MONDAY FOR THE HIGHEST COVERAGE
OF SHOWERS/THUNDERSTORMS AND MOST WIDESPREAD RAINFALL. THE MODEL
BLEND GUIDANCE OF LIKELY POPS FROM WEST TO EAST LOOKS REASONABLE.
IN TERMS OF SEVERE WEATHER POTENTIAL...THERE WILL LIKELY BE AT
LEAST ONE WINDOW OF LOW-LEVEL SEVERE WEATHER THREAT...BUT NOTHING
IN TERMS OF SIGNIFICANT INSTABILITY/SHEAR COMBINATION THAT WOULD
POINT TO A HIGHER END THREAT AT THIS TIME. THAT COULD CHANGE IN
THE COMING DAYS...BUT FOR NOW IT LOOKS LIKE MODERATE TO LOCALLY
HEAVY RAINFALL WILL BE THE MAIN HIGHLIGHT. REGARDING LONGER TERM
TEMPERATURES...LOOK FOR A GRADUAL WARMING TREND INTO EARLY NEXT
WEEK...WITH A RETURN TO THE 80S LIKELY.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING)
ISSUED AT 640 PM CDT TUE MAY 19 2015

VFR CONDITIONS WILL BE SEEN THROUGH 12Z/20 AS A STORM SYSTEM
SLOWLY MOVES NORTHEAST FROM THE SOUTHERN PLAINS. AFT 12Z/20 VFR
CONDITIONS ARE EXPECTED TO CONTINUE WITH -RA DEVELOPING. THE
POSSIBILITY DOES EXIST OF MVFR CONDITIONS DEVELOPING BUT THIS WAS
NOT INCLUDED IN THE 00Z TAFS DUE TO UNCERTAINTY REGARDING THE
DEPTH OF THE DRY AIR IN THE LOWER LEVELS.


&&

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

$$

UPDATE...08
SYNOPSIS...UTTECH
SHORT TERM...UTTECH
LONG TERM...RP KINNEY
AVIATION...08


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