478
FXUS63 KDVN 071943
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
243 PM CDT SUN SEP 7 2008
SYNOPSIS
BROAD UPPER TROF WITH SEVERAL EMBEDDED S/W/S REMAINS OVER MUCH OF
THE NORTHERN HALF OF THE U.S. TODAY. A COUPLE OF THE S/WS WERE
LOCATED UPSTREAM FROM THE MID MS VALLEY THIS MORNING. THE FIRST
WAS MOVING THROUGH MN EARLY THIS AFTERNOON AND WAS PRODUCING SOME
ISOLATED TO SCT TSRA OVER NORTH CENTRAL IA. THE SECOND AND MORE
POTENT WAVE WAS OVER WRN MONTANA. AT THE SURFACE TEMPS HAVE WARMED
NICELY INTO THE UPPER 60S AND LOW 70S THIS AFTERNOON AHEAD OF A
WEAK COLD FRONT OVER NW IA.
SHORT TERM...TONIGHT AND MONDAY
MODELS ARE IN DECENT AGREEMENT WITH MODERATE PCPN EVENT OVER THE
CWFA TOMORROW. ABOUT THE ONLY QUESTION IS WHERE THE AXIS OF
HEAVIER QPF WILL SET UP. FOR TONIGHT WILL CONTINUE TO CARRY SOME
LOW POPS FOR ISOLATED TSRA/RW-- OVER THE FAR NORTH BEFORE
MIDNIGHT. CURRENT TSRA OVER NCNTRL IA APPEARS TO BE TRACKING A
LITTLE N OF E WHICH SHOULD KEEP IT JUST NORTH OF THE
CWFA...BARRING ANY MORE DEVELOPMENT TO THE SOUTH. OTHER SCT SHRA
OVER WEST CENTRAL AND SW IA APPEAR TO BE JUST VIRGA BASED ON THE
LACK OF ANY PCPN BEING REPORTED SO FAR. WILL CONTINUE TO MONITOR
FOR THE NEED TO EXPAND PCPN AREA FURTHER SOUTH. S/W DROPPING
THROUGH WRN MT THIS AFTERNOON IS PROGGED TO SPIN UP A SURFACE LOW
ALONG THE FRONT CURRENTLY FROM NW IA INTO SWRN NE. THE LOW IS
FORECAST TO LIFT ENE THROUGH NRN MO AND CENTRAL IL MONDAY. THE
MODELS HAVE ALL BACKED OFF SOME ON THE TIMING AND ARE NOW
FAVORING A LATE NIGHT ONSET OF THE PCPN SPREADING FROM THE FAR SW
JUST BEFORE 12Z TO THE NERN CWFA BY LATE MORNING. BASED ON PW/S
AROUND A HALF INCH AND MODERATE FORCING THANKS TO A 40 TO 50KT H8
JET AHEAD OF THE H8 LOW...EXPECT TO SEE MAX RAINFALL AMOUNTS IN
THE 1.0 TO 1.5 INCH RANGE BY LATE MONDAY. HAVE GONE WITH AN AXIS
OF MAX QPF SLIGHTLY SOUTH OF THE NAM/GFS PLACEMENT DUE TO THE
LOCATION OF THE STRONGER LOW LEVEL FORCING AND WITH THE STEEPER
MID LEVEL LAPSE RATES OVER SOUTHERN IA AND NRN MO...ESPECIALLY
MONDAY MORNING. MOST OF THE THUNDER SHOULD BE ALONG AND SOUTH OF
THE HWY 34 WHERE THE LOW LEVEL FORCING WILL BE STRONGEST. FURTHER
NORTH IN THE MORE STABLE AIR...EXPECT MAINLY STRATIFORM RAIN WITH
EMBEDDED THUNDER. SEVERE THREAT LOOKS MARGINAL SINCE AIRMASS
SHOULD SATURATE QUICKLY DURING THE MORNING. IF THERE ARE ANY
SEVERE STORMS THE MAIN THREAT WOULD BE LARGE HAIL. THE RAIN
SHOULD KEEP TEMPS DOWN MONDAY. AREAS IN THE WEST WHERE THE RAIN
WILL BEGIN AROUND SUNRISE MAY NOT RISE OUT OF THE 50S WHILE LOW TO
MID 60S ARE EXPECTED OVER THE REST OF THE CWA.
..DLF
LONG TERM...MONDAY NIGHT THROUGH NEXT SUNDAY
A REASONABLY ACTIVE PATTERN WILL CONTINUE WITH TEMPERATURES
REMAINING BELOW NORMAL. A BLEND OF THE ECMWF/UKMET IS PREFERRED.
RAIN WILL END FROM WEST TO EAST MONDAY NIGHT AS THE SFC WAVE PULLS
OUT OF THE AREA. MIN TEMPERATURES TO BE DEPENDENT UPON HOW FAST THE
CLOUDS MOVE EAST OF THE AREA BUT EXPECT THE FAR NORTHWEST/WEST TO BE
THE COLDEST BY TUESDAY MORNING.
TUESDAY THROUGH WEDNESDAY WILL BE QUIET AND COOL AS HIGH PRESSURE
MOVES ACROSS THE REGION. THERMAL TROF MOVING THROUGH ON TUESDAY WILL
KEEP TEMPERATURES IN THE 60S. FAVORED COLD AREAS IN THE NORTHEAST
CWFA AND WAPSI VALLEY MAY SEE MINS NEAR 40 TUESDAY NIGHT. RETURN
FLOW IS SLOW TO DEVELOP ON WEDNESDAY SO THE DAYLIGHT HOURS SHOULD
REMAIN DRY.
WED NIGHT THROUGH THURSDAY NIGHT THE NEXT SFC WAVE WILL MOVE THROUGH
THE REGION. BEST PRECIP CHANCES APPEAR TO BE ON THURSDAY AS THE SFC
WAVE AND COLD FRONT MOVE THROUGH THE AREA.
FRIDAY ON GETS MORE COMPLICATED. THE WILD CARD WILL BE WHERE IKE
GOES. DPROG/DT OF THE GLOBAL MODELS INDICATE THE ECMWF HAS BEEN TO
SLOW DOWN THE PROGRESS OF THE FRONT THAT MOVES THROUGH
THURSDAY/THURSDAY EVENING WHILE AT THE SAME TIME MOVING IKE FURTHER
WEST. IF THE ECMWF TRENDS ARE CORRECT...IKE WOULD MAKE LANDFALL ON
THE SOUTHEAST TEXAS COAST WHICH WOULD CAUSE THE THURSDAY COLD FRONT
TO STALL JUST TO THE SOUTH AND EAST OF THE CWFA. ASSUMING THIS
HAPPENS...PRECIP MAY LINGER INTO FRIDAY BEFORE ENDING.
SATURDAY/SUNDAY ARE EXTREMELY DEPENDENT ON WHERE IKE GOES. FOR NOW
WILL GO WITH THE IDEA THAT ANOTHER SFC WAVE MOVES THROUGH THE AREA
ON SATURDAY BRINGING ANOTHER ROUND OF RAIN AND GO WITH SILENT 20
POPS FOR SUNDAY TO ACCOUNT FOR THE UNCERTAINTY OF IKE. ...08...
AVIATION
VFR CONDITIONS WITH LIGHT SW-W WINDS ARE EXPECTED THIS EVENING.
CIGS AROUND 5-6KFT SHOULD SPREAD OVER THE AREA BY 06Z. SCATTERED
SHRA WITH ISOLATED TSRA MAY MOVE CLOSE TO KCID AND KDBQ BTWN 21Z
AND 03Z. SFC WINDS WILL GRADUALLY TURN TO THE NE OVERNIGHT AHEAD
OF A SURFACE LOW MOVING NE OUT OF KS. CONDITIONS DETERIORATING
AFTER 09Z WITH WIDESPREAD MVFR CIGS/VSBYS IN LIGHT TO MODERATE
RAIN BY 15Z MONDAY. AREAS OF IFR CONDITIONS WILL BE POSSIBLE SOUTH
BY LATE MORNING. BETWEEN 14Z AND 18Z SCT TSRA WILL IMPACT KBRL
WITH ISOLATED TSRA POSSIBLE AT KMLI/KCID/KDBQ.
DVN WATCHES/WARNINGS/ADVISORIES
IA...NONE.
IL...NONE.
MO...NONE.
DLF/08
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