Special Weather Statement, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
245 PM CDT TUE MAY 15 2012

.SYNOPSIS...
THE CWA IS BEGINNING TO EXPERIENCE A COLD FROPA FROM NORTHWEST TO
SOUTHEAST AS OF EARLY AFTERNOON...AND THUS FAR IT IS DRY. WHILE VERY
HIGH BASED CUMULUS HAVE FORMED...SURFACE DEWPOINTS HAVE MIXED DOWN
TO THE MID 30S TO LOWER 40S ALONG THE FRONT. IN
ADDITION...TEMPERATURES NEAR THE FRONT ARE IN THE UPPER 80S TO
90...RESULTING IN VERY LOW RH VALUES AROUND 20 TO 25 PERCENT.
OTHERWISE...TEMPERATURES AS OF 2 PM ARE IN THE LOWER TO MID 80S WITH
DEWPOINTS IN THE MID 40S TO LOWER 50S. AS THE FRONT
APPROACHES...FURTHER DROPS IN DEWPOINTS ARE EXPECTED.

&&

.SHORT TERM...TONIGHT AND WEDNESDAY...
THUNDERSTORM POTENTIAL TONIGHT WILL LIKELY BE MUCH LESS THAN ANY
MODEL SUGGESTS GIVEN THE MUCH LOWER FRONTAL SURFACE DEWPOINTS.
THUS...WILL KEEP MENTION OF AN ISOLATED STORM THROUGH 9 PM...BUT IN
REALITY IF NO STORMS FIRE BY 5 PM...THIS THREAT CAN BE REMOVED.
COVERAGE TO MENTION STORMS NEEDS TO BE 15 PERCENT OR HIGHER...THUS
THAT IS MY PERCENT CHANCE FORECAST. IN REALITY...THERE IS MORE LIKE
A 5 TO 10 PERCENT CHANCE OF STORMS IN ANY LOCATION. IT CERTAINLY IS
RARE TO SEE THE AFTERNOON DEWPOINT DEPRESSIONS OF 40 TO 50 DEGREES
THIS FAR EAST...AS THIS TYPE OF SPREAD IS MORE TYPICAL OF WESTERN
PLAINS...WEST OF A WARM SEASON DRYLINE.

LATE TONIGHT AND WEDNESDAY...NORTH TO NORTHEAST WINDS AND COLD
ADVECTION WILL COMMENCE...WITH LOWS FALLING THE MID 40S NORTHEAST TO
LOWER 50S SOUTH. WITH PLENTY OF SUN AGAIN...LOW DEWPOINTS...AND
DRYING GROUND..EXPECT ANOTHER DEEP MIXING DAY WEDNESDAY...WITH HIGHS
IN THE LOWER 70S EAST...TO MID 70S CENTRAL AND SOUTHWEST.    ERVIN

.LONG TERM...WEDNESDAY NIGHT THROUGH NEXT TUESDAY...
GENERALLY DRY UNTIL MONDAY...THEN CHANCES FOR THUNDERSTORMS.

OVERVIEW...INITIALIZATION GOOD ON KINEMATICS WITH BL TOO MOIST BIASES
CONTINUE.  VERIFICATION AT 18Z SUGGESTS A 50/50 MIX OF THE 80KM NAM-
WRF AND HI-RES ECMWF WITH ADJUSTMENTS TOWARD DRIER BL CONDITIONS AND
IMPACTS ON DIURNAL TEMPERATURES.  BEYOND DAY 3...A WEIGHTING OF A
60/40 TOWARD HI-RES ECMWF TO GFS DUE TO MOISTURE AND RUN TO RUN
CONTINUITY ISSUES.

WEDNESDAY NIGHT...SEASONABLY COOL AND MOSTLY CLEAR WITH LOWS MOSTLY
COOLER THAN GUIDANCE. LOCAL TOOLS SUGGEST AREAS THAT DECOUPLE MAY
NEED FURTHER LOWERING ON MINS BY UP TO 3 DEGREES FOR LATER SHIFTS.
LIGHT EAST WINDS AND SUBSIDENCE DO SUGGEST CALM TO NEARLY CALM
WINDS FOR SEVERAL HOURS.

THURSDAY INTO SATURDAY...UPPER RIDGING AND DECENT SOUTHERLY WINDS
FOR WARMER AIR ARRIVING TO RESULT IN FAIR SKIES WITH TEMPERATURES
ABOVE NORMAL. LARGE DIURNAL TEMPERATURES LIKELY MORE THAN GUIDANCE
WITH UPPER 70S TO 80+F THURSDAY AND LOWER TO MIDDLE 80S FRIDAY AND
SATURDAY AT A MINIMUM THAT MAY NEED RAISING A FEW DEGREES EACH DAY
MANY LOCATIONS FOR LATER SHIFTS. MINS IN THE 50S THURSDAY MORNING AND
MOSTLY IN THE LOWER TO MIDDLE 60S FRIDAY MORNING.  SUBSIDENCE AND NO
FORCING AND MOISTURE FOR PRECIPITATION IS INDICATED AS DRY SPELL
CONTINUES.

SATURDAY NIGHT THROUGH MONDAY...SLOWLY INCREASING CHANCE OF
THUNDERSTORMS BY MONDAY AS SLOW MOVING AND WEAKENING COOL FRONT
ARRIVES.  CHANCE POPS ARE SUGGESTED DUE TO POOR TIMING ISSUES FOR
LATER SHIFTS. SOME RISK OF SEVERE SUGGESTED WITH PM SBCAPES OF 1500-
2500+ J/KG SUGGESTED ATTM.  LOCAL PAST EVENTS SUGGEST AN EPISODE OR
TWO OF MCS SYSTEMS WITH MOSTLY LIGHT TO MODERATE AMOUNTS FOR THE
AREA.  HIGHS TO FALL INTO THE 70S BY MONDAY DUE TO CONSIDERABLE
CLOUDINESS FROM WEAK UPPER AND SFC LOW CONVERGENT FLOW. DEWPOINTS
SHOULD ALSO RISE AOA 60F FOR SOME HUMIDITY DURING THIS TIME PERIOD.

TUESDAY...KEPT SLIGHT CHANCE POPS ATTM BUT DRY AND NEAR SEASONABLE
TEMPERATURES SUGGESTED FOR LATTER PORTIONS OF MAY WITH MODERATING
HUMIDITY.    NICHOLS

&&

.AVIATION...
WIDESPREAD VFR WEATHER WILL CONTINUE THROUGH THE NEXT 24 HOURS...AS
A FRONT PASSES THROUGH EASTERN IOWA AND ILLINOIS LATE THIS AFTERNOON
AND EVENING...FOLLOWED BY HIGH PRESSURE. A VERY LOW CHANCE FOR AN
ISOLATED THUNDERSTORMS EXISTS AT ALL SITES BETWEEN 21Z TODAY AND
02Z/16. THIS THREAT IS TOO LOW TO PLACE INTO A TAF FORECAST AT THIS
TIME...BUT WILL BE WATCHED FOR FUTURE UPDATES. WINDS WILL BE 10 TO
20 KTS FROM THE WEST SOUTHWEST TODAY...AND TOWARDS 00Z...WILL BECOME
NORTH. AFTER 02Z...NORTH WINDS WILL DECREASE TO 5 TO 10 KTS AND
REMAIN NORTH TO NORTHEAST THROUGH 18Z/16.  ERVIN

&&

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

ERVIN/NICHOLS

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
452 AM CDT TUE MAY 15 2012

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-161000-
BUCHANAN-DELAWARE-DUBUQUE-BENTON-LINN-JONES-JACKSON-IOWA-JOHNSON-
CEDAR-CLINTON-MUSCATINE-SCOTT-KEOKUK-WASHINGTON-LOUISA-JEFFERSON-
HENRY IA-DES MOINES-VAN BUREN-LEE-JO DAVIESS-STEPHENSON-CARROLL-
WHITESIDE-ROCK ISLAND-HENRY IL-BUREAU-PUTNAM-MERCER-HENDERSON-
WARREN-HANCOCK-MCDONOUGH-SCOTLAND-CLARK-
452 AM CDT TUE MAY 15 2012

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF NORTH CENTRAL
ILLINOIS...NORTHWEST ILLINOIS...WEST CENTRAL ILLINOIS...EAST
CENTRAL IOWA...NORTHEAST IOWA...SOUTHEAST IOWA AND NORTHEAST
MISSOURI.

.DAY ONE...TODAY AND TONIGHT

THERE IS A CHANCE OF THUNDERSTORMS THIS AFTERNOON AND EVENING
MAINLY BETWEEN 4 PM AND 9 PM... AS A COLD FRONT MOVES THROUGH
THE OUTLOOK AREA. THE CHANCE OF THUNDERSTORMS HOWEVER WILL BE
LARGELY DEPENDENT ON THE AMOUNT OF LOW LEVEL MOISTURE... WHICH
REMAINS SOMEWHAT UNCERTAIN. IF SURFACE DEW POINTS CAN REACH
WELL INTO THE 40S OR LOWER 50S THEN ISOLATED TO SCATTERED
THUNDERSTORMS COULD BE EXPECTED TO DEVELOP AHEAD OF THE
FRONT... WITH A FEW POSSIBLY STRONG TO SEVERE CONTAINING HAIL
AND GUSTY WINDS.

.DAYS TWO THROUGH SEVEN...WEDNESDAY THROUGH MONDAY

THERE WILL BE A SLIGHT CHANCE FOR THUNDERSTORMS NORTH OF INTERSTATE
80 THURSDAY NIGHT INTO FRIDAY. A BETTER CHANCE FOR MORE WIDESPREAD
STORMS MAY OCCUR FROM LATE SUNDAY INTO MONDAY. IT IS TOO EARLY TO
DETERMINE IF ANY OF THESE EPISODES OF STORMS WILL HAVE THE POTENTIAL
TO PRODUCE SEVERE WEATHER.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION MAY BE NEEDED THIS AFTERNOON AND EVENING.

05/12

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
422 PM CDT TUE MAY 15 2012

IAZ040>042-051>054-063>065-076-ILZ001-152215-
LINN IA-KEOKUK IA-JOHNSON IA-JACKSON IA-IOWA IA-DUBUQUE IA-
DELAWARE IA-BENTON IA-BUCHANAN IA-CEDAR IA-JONES IA-JO DAVIESS IL-
422 PM CDT TUE MAY 15 2012

...STRONG WINDS ASSOCIATED WITH RAIN SHOWERS...

AT 4:17 CDT NATIONAL WEATHER SERVICE DOPPLER RADAR HAD A 40 MILE
WIDE LINE OF RAIN SHOWERS MOVING EAST AT 45 MPH. THE SHOWERS WERE
NORTHWEST OF A LINE FROM WARREN...ILLINOIS TO MILLERSBURG...IOWA.

STRONG GUSTY WINDS UP TO 45 MPH WILL BE POSSIBLE FROM THESE SHOWERS.
THE STRONG GUSTY WINDS ARE BEING CAUSED BY PRECIPITATION EVAPORATING
IN THE DRY AIR BELOW THE SHOWERS.

STRONG GUSTY WINDS WILL MAKE DRIVING DIFFICULT...ESPECIALLY FOR HIGH
PROFILE VEHICLES.

&&

LAT...LON 4260 9068 4251 9063 4251 9018 4247 8993
      4149 9230 4215 9231 4265 9119 4265 9100

08

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
518 PM CDT TUE MAY 15 2012

IAZ041-042-051>054-063>068-076-077-ILZ001-002-007-152300-
WASHINGTON IA-SCOTT IA-MUSCATINE IA-LINN IA-KEOKUK IA-JOHNSON IA-
JACKSON IA-IOWA IA-DUBUQUE IA-DELAWARE IA-BENTON IA-CEDAR IA-
CLINTON IA-JONES IA-JO DAVIESS IL-STEPHENSON IL-CARROLL IL-
518 PM CDT TUE MAY 15 2012

...STRONG GUSTY WINDS LIKELY WITH SHOWERS AND THUNDERSTORMS...

AT 5:15 PM CDT...NATIONAL WEATHER SERVICE RADAR SHOWED THE LEADING
EDGE OF A 40 MILE WIDE BAND OF SHOWERS AND A FEW THUNDERSTORMS FROM
LAKE SUMMERSET...ILLINOIS TO LONE TREE...IOWA. THESE SHOWERS AND
THUNDERSTORMS WERE MOVING EAST SOUTHEAST AT 45 MPH.

THE AIR UNDER THE PRECIPITATION IS VERY DRY AND MOST OF IT IS
EVAPORATING BEFORE REACHING THE GROUND. THUS WINDS GUSTING UP TO 35
MPH WILL BE POSSIBLE. SOME OF THE STRONGER STORMS MAY PRODUCE WINDS
GUSTING UP TO 50 MPH.

STRONG GUSTY WINDS WILL MAKE DRIVING DIFFICULT...ESPECIALLY FOR HIGH
PROFILE VEHICLES.

&&

LAT...LON 4151 9236 4152 9230 4193 9230 4252 9049
      4250 8940 4221 8939 4220 8968 4211 8968
      4116 9240

08

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
556 PM CDT TUE MAY 15 2012

IAZ052>054-063>068-076>078-087-088-ILZ001-002-007-009-015-024-152345-
WASHINGTON IA-SCOTT IA-MUSCATINE IA-LOUISA IA-LINN IA-KEOKUK IA-
JOHNSON IA-JEFFERSON IA-JACKSON IA-IOWA IA-HENRY IA-CEDAR IA-
CLINTON IA-JONES IA-JO DAVIESS IL-MERCER IL-ROCK ISLAND IL-
STEPHENSON IL-WHITESIDE IL-CARROLL IL-
556 PM CDT TUE MAY 15 2012

...STRONG WINDS ASSOCIATED WITH SHOWERS AND THUNDERSTORMS...

AT 5:50 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR HAD A 25
MILE WIDE BAND OF SHOWERS AND A FEW THUNDERSTORMS MOVING EAST
SOUTHEAST AT 45 MPH. THE LEADING EDGE OF THE SHOWERS AND
THUNDERSTORMS STRETCHED FROM GERMAN VALLEY...ILLINOIS TO
HEDRICK...IOWA.

THE DRY AIR BELOW THE PRECIPITATION IS HELPING TO PRODUCE WINDS
GUSTING UP TO 40 MPH. SOME OF THE STRONGER STORMS WILL BE CAPABLE OF
PRODUCING WINDS GUSTING UP TO 55 MPH.

SUDDEN STRONG GUSTY WINDS WILL MAKE DRIVING DIFFICULT...ESPECIALLY
FOR HIGH PROFILE VEHICLES.

&&

LAT...LON 4251 8993 4248 8940 4220 8939 4219 8968
      4194 8968 4193 8962 4179 8963 4091 9218
      4115 9219 4116 9222 4164 9230

08