Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 302350
AFDDVN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
650 PM CDT THU APR 30 2015

.SYNOPSIS...
ISSUED AT 256 PM CDT THU APR 30 2015

A MIDLEVEL VORT MAX MOVED THROUGH THE GREAT LAKES REGION TODAY AND
LEAD TO SOME CLOUDS ACROSS FAR EASTERN ZONES. NORTHERLY WINDS
TODAY AIDED IN BRINGING COOLER AND DRIER AIR INTO THE AREA. HIGH
PRESSURE WAS REINFORCING INTO THE AREA FROM THE NORTH. THESE
FEATURES LEAD TO CLEAR SKIES AND TEMPERATURES IN THE 60S TODAY.
THESE FACTORS WILL CONTINUE TO DOMINATE OUR WEATHER THROUGH MOST
OF THE SHORT TERM PERIOD.

&&

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 256 PM CDT THU APR 30 2015

MAIN FORECAST CONCERN FOR THE SHORT TERM IS THE POSSIBILITY OF
RAIN TOMORROW TOWARDS THE END OF THE PERIOD AS A SHORTWAVE IS
PROGGED TO MOVE INTO THE AREA LATE INTO THE PERIOD. AT THIS
TIME...I DO NOT THINK THE FORCING AND MIDLEVEL MOISTURE WILL BE
ENOUGH TO OVERCOME THE DRY AIR AT THE LOW LEVELS TO PRECIPITATE
BEFORE 00Z SATURDAY.

A DRY NORTH FLOW REMAINS IN PLACE ACROSS THE AREA THROUGH TONIGHT.
THIS WILL LEAD TO CLEAR SKIES. TEMPERATURES LAST NIGHT WERE LOWER
THAN MOST GUIDANCE. WITH LITTLE CHANGE IN THE AIRMASS FROM LAST
NIGHT TO TONIGHT...DECIDED TO GO ON THE LOW END OF GUIDANCE FOR
LOWS. DEWPOINTS THIS AFTERNOON ARE IN THE MID TO LOW
30S...SUGGESTING THAT WE COULD VERY WELL SEE LOWS INTO THE 30S
ACROSS THE AREA.

TOMORROW A WAVE APPROACHES THE AREA. LOW TO EVEN MID LEVELS ARE
DRY BEFORE THIS SYSTEM APPROACHES THE AREA. WITHOUT THE GULF OF
MEXICO RETURN FLOW I THINK THAT ANY PRECIP THAT DOES FALL WILL
HAVE TO MOISTEN THE LAYER. THE ECMWF SUGGESTS THAT WE SEE QPF
BEFORE 00Z AND THE REST OF THE MODELS KEEP QPF OUT...BUT ARE
CLOSE TO THE CWA. THE HIRES WRF ARW AND NMM MODELS SUGGEST THAT
PRECIP BREAKS UP AS IT APPROACHES THE AREA. IT IS WITH THESE
THINGS IN MIND THAT I DECIDED TO GO DRY. WE COULD SEE SOME VIRGA
ACROSS WESTERN ZONES AND I CANT RULE OUT A SPRINKLE. THESE DETAILS
SHOULD BECOME CLEARER TONIGHT AND INTO TOMORROW. OVERALL AT THIS
TIME SENSIBLE WEATHER SHOULD BE NICE TOMORROW.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)...CORRECTED
ISSUED AT 301 PM CDT THU APR 30 2015

A WARM AND ACTIVE PERIOD IS SETTING UP FOR THE DURATION OF THE
EXTENDED FORECAST. A WELL ADVERTISED SET UP OF A STALLED BOUNDARY IN
NORTHERN MISSOURI THROUGH INDIANA WILL BE THE WAVERING FOCUS FOR
SHOWERS AND THUNDERSTORMS THROUGHOUT THE EXTENDED.
MOISTURE...INITIALLY WILL BE A LIMITING FACTOR...FRIDAY NIGHT
THROUGH SUNDAY...AS THE SLOWLY INCREASING MOISTURE TRANSPORT REMAINS
TO THE WEST OF OUR CWA. HOWEVER...BY SUNDAY NIGHT...PWAT VALUES ARE
SOLIDLY OVER 1 INCH AND CONVERGENCE IS AIMED RIGHT AT EASTERN IOWA
AND NORTHWEST ILLINOIS. THUS...SLIGHT CHANCE POPS WEST AND SOUTHWEST
WILL INCREASE TO HIGH CHANCE AND LIKELY FOR SUNDAY NIGHT THROUGH
MONDAY NIGHT. SEVERE WEATHER SEEMS RELATIVELY UNLIKELY GIVEN WEAK
SHEAR VALUES...BUT SOME HAIL CANNOT BE RULED OUT. IN THIS INITIAL
PERIOD OF WAA STORMS...RAIN AMOUNTS OF 0.50 TO 1.50 SEEM ON TARGET.

FROM TUESDAY THROUGH WEDNESDAY...THE GFS AND ECMWF DIVERGE...IN THAT
THE ECMWF LIFTS THE BOUNDARY NORTH...WHILE THE GFS KEEPS A
CONVECTIVELY ACTIVE BOUNDARY IN PLACE...THE GFS ENSEMBLES SUPPORT A
SLOWER PROGRESSION AT LEAST THROUGH WEDNESDAY MORNING. IN ANY
CASE...PROBABILITIES FOR STORMS DECREASE FOR TUESDAY NIGHT THROUGH
WEDNESDAY....BUT INCREASE AGAIN WEDNESDAY NIGHT AND THURSDAY AS THE
MAIN SYNOPTIC WAVE LIFTS NORTHEAST. THIS WAVE WILL USHER IN A
STRONGER WIND FIELD ALOFT...AND COULD BRING A MORE NOTABLE SEVERE
WEATHER RISK. DETAILS ARE FAR FROM CONFIDENT ON ANY VARIABLE
SUPPORTING OR NEGATING THIS RISK...BUT THE LARGE SCALE PATTERN
SUGGESTS A THREAT.

RAINFALL THROUGH THURSDAY THIS WEEK APPEARS LIKELY TO TOTAL IN THE 1
TO 2 INCH RANGE FOR MOST OF THE CWA. THIS AMOUNT OF RAIN...THOUGH
FALLING AT RATES THAT COULD CAUSE LOCAL RUNOFF...IS UNLIKELY TO
RESULT IN MORE THAN IN BANK RISES ON LOCAL RIVERS.

ERVIN

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 626 PM CDT THU APR 30 2015

VFR CONDITIONS WITH FAIR SKIES THE NEXT 24 HOURS. SURFACE HIGH
OVERHEAD TONIGHT TO PRODUCE LIGHT AND VARIABLE WINDS...SHIFTING TO
THE SOUTH AT 5 TO 10 KTS BY MID DAY FRIDAY.

&&

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

&&

$$

SYNOPSIS...GIBBS
SHORT TERM...GIBBS
LONG TERM...ERVIN
AVIATION...NICHOLS


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