000
FXUS63 KDVN 070829
AFDDVN
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
329 AM CDT SUN SEP 7 2008
.SYNOPSIS...
LATEST SFC ANALYSIS WAS INDICATING CENTRAL PLAINS RIDE COMPLEX TO
THE SOUTHWEST OF CYCLONIC FLOW PATTERN OVER THE UPPER MS RVR VALLEY
AND INTO THE NORTHWEST GRT LKS. ANOTHER QUASI-STATIONARY FRONT WAS
LOCATED FROM THE DEEP SOUTHWEST PLAINS...NORTHEASTWARD ALONG AND
NORTH OF THE OH RVR VALLEY. ALOFT...MID AN HIGH LEVEL MOISTURE
FIELDS SEEN ON W/V IMAGERY WAS INDICATING BROAD SCALE CYCLONIC UPPER
FLOW PATTERN-L/W TROF NICELY. THIS IMAGERY WAS ALSO INDICATING A
RATHER COMPLEX VORT STRUCTURE/S RIGHT OVER THE CWA AND
EXTENDING/LOBING BACK WESTWARD ACRS THE CENTRAL PLAINS. A LARGER WAVE
WAS NOTED ROLLING SOUTHEASTWARD OUT OF THE LK WINNIPEG REGION AND
TOWARD NW MN.
&&
.SHORT TERM...TODAY AND TONIGHT...ONCE AGAIN...WITH A CLEARING SLOT
SEEN IN THE AC DECK BETWEEN FORCING FIELDS SWEEPING ACRS CENTRAL
INTO EASTERN IA...WILL HAVE TO WATCH FOR FOG FORMATION IN THE WEST
AND SOUTHWEST THROUGH SUNRISE AND WILL ADD AREAS OF FOG TO GRIDS THRU
9 AM...AND PROBABLY COVER ANY DENSE DEVELOPMENT WITH ANOTHER SPECIAL
STATEMENT AS IT SHOULD NOT BE WIDESPREAD ENOUGH FOR A HEADLINE. WILL
ALSO HAVE TO WALK OUT LINGERING LIGHT SHOWERS AND SPRINKLES OUT OF
WEST CENTRAL IL THROUGH 15Z...BUT SCTRD SPRINKLES MOVING ACRS FAR
NORTHEAST IA AND INTO WI SHOULD NOT MAKE IT INTO THE NORTHERN CWA
AND WILL REMOVE THE ONGOING MORNING POPS THERE.
THE REST OF THE DAY WILL BE CHARACTERIZED BY PARTLY TO MOSTLY SUNNY
SKIES...AS THE MAIN FORCING FIELDS AND DEEP ENOUGH SATURATION WILL
REMAIN TO THE NORTH OF THE CWA IN VIEW OF THE MAIN UPPER LOW
MENTIONED ABOVE THAT WILL CONTINUE TO PROPAGATE ACRS MN AND WI THRU
SUNDAY EVENING. TRAILING LLVL TROF AXIS INDUCED BY THESE PROCESSES
SHOULD SKIRT ACRS THE FAR NORTHERN CWA BY LATE AFTERNOON AND INTO
THE EVENING. WILL KEEP LOW CHC POPS IN THE VCNTY OF THIS FEATURE
/THE NORTHERN THIRD TO QUARTER OF THE FCST AREA/ LATER THIS
AFTERNOON AND INTO THE EVENING...BUT DON/T EXPECT MUCH MORE THAN A
FEW SPRINKLES POSSIBLY SKIRTING THE NORTHERN FRINGE. LOW TO MID
LEVEL THERMAL PARAMETERS REMAIN SOMEWHAT UNCHANGED...AND AS LONG AS
WE GET SOME INSOLATION...EXPECT WIDESPREAD HIGHS TODAY IN THE UPPER
60S TO LOWER 70S...WITH A FEW LOCATIONS WITH LONGER DURATION
SUNSHINE PUSHING THE MID 70S.
TONIGHT...LLVL CYCLOGENESIS TAKES OFF OVER THE SOUTHERN TO CENTRAL
PLAINS IN RESPONSE TO DIGGING WAVE DROPPING OUT OF THE NORTHERN
ROCKIES AND ACRS THE NORTHWEST HIGH PLAINS. ALTHOUGH BEST MASS
FIELDS OF LIFT DEVELOP AND REMAIN TO THE SOUTHWEST OF THE CWA THRU
12Z MON...SOME WINGS OF FORCING/ELEVATED BANDS DO SPREAD ACRS
SOUTHERN THIRD OF THE CWA AND POSSIBLY ACRS THE WEST AFTER MIDNIGHT
SUNDAY NIGHT. SOME LLVL SATURATION ISSUES TO OVERCOME FOR ANY
INITIAL PRECIP THAT GETS GENERATED TO REACH THE SFC...BUT COND P-DEF
PROGS AND FCST SOUNDINGS SUGGEST THE SOUTHERN THIRD TO GET RAIN
REACHING THE GROUND LATE TONIGHT...WHILE MAINLY ELEVATED HYDROMETEORS
/VIRGA TAKES OFF ACRS THE CENTRAL AND NORTHWESTERN CWA. ..12..
.LONG TERM...SUNDAY THROUGH NEXT SATURDAY...
...EARLY FALL MODERATE TO LOCALLY HEAVY PRECIPITATION EVENT MONDAY
MAIN FORECAST ISSUE...
AVERAGE INITIALIZATION TONIGHT...BLENDED HI-RES ECMWF AND UKMET
FORCING WITH SECONDARY FORCING INPUTS FROM 80 KM NAM-WRF. 00Z GFS
CONVECTIVE SCHEME RESULTING IN QPF AND FORCING TOO FAR INTO COOL AIR
AND DISCARDED DUE TO GRAVITY WAVE AND EVAPORATIVE COOLING ISSUES.
MONDAY...LAST FEW RUNS OF SOLUTIONS SHOWS PHASING OF UPPER WAVE WITH
GULF MOISTURE ALONG FRONT. THIS TO PRODUCE WAVE WITH EVIDENCE OF
WEAK OCCLUSION PROCESS OVER EASTERN IOWA. THIS WILL RESULT IN
MODERATE TO LOCALLY HEAVY RAIN AMOUNTS WITH HEAVIEST AMOUNTS NEAR
TRIPLE POINT OR ROUGHLY NORTH OF OTM TO NEAR MLI TO SQI AXIS. STRONG
EVAPORATIVE COOLING TO ALLOW MERCURY TO FALL INTO LOWER TO MID 50S
AFTER RAIN STARTS. ALONG AND AHEAD OF TRIPLE POINT AND 925-850 MB
FRONT TO SEE THIN AXIS OF SCATTERED NON-SEVERE CONVECTION WITH
STRATIFORM RAINS FURTHER INTO COOL AIR FROM COUPLING OF COLD AIR
ADVECTION AND EVAPORATIVE COOLING. FORCING SUGGESTS RIBBONS OF 120
TO 180 MILES OF RAIN FOR 3 TO 6 HOURS OF MODERATE TO BRIEF PERIODS OF
HEAVY RAIN MOST LOCATIONS FOR A COOL AND DAMP EARLY FALL DAY.
LOWERED MAX TEMPERATURES INTO UPPER 50S NW SECTIONS WITH TIMING
SUGGESTING ALONG AND WEST OF I-380 CORRIDOR MAX TEMPS MAY NEED
FURTHER LOWERING BY UP TO 5 DEGREES FOR LATER SHIFTS TO ASSESS. RAIN
AMOUNTS SUGGEST ALL AREA TO RECEIVE AT LEAST A HALF INCH OF RAIN WITH
AXIS OF .75 TO 1.25 AMOUNTS ~50 MILES EITHER SIDE OF A SIGOURNEY IOWA
TO QUAD CITIES TO NEAR STERLING LINE. MONDAY NIGHT...RAIN TO END BY
LATE EVENING WITH CLEARING NW TO SE BY DAYBREAK. COOLEST AIR OF THE
FALL SEASON SUGGESTS MINS NW TO FALL INTO UPPER TO MID 30S AND LATER
SHIFTS MAY NEED TO TRIM MINS A COUPLE MORE DEGREES IF CLEARING IS
FASTER THAN ANTICIPATED.
TUESDAY...COOL 850 MB TEMPERATURES OF +3 TO +6C SUPPORT WITH MINOR
BL MIXING AS SURFACE RIDGE WILL BE OVERHEAD FOR HIGHS IN THE MID 60S.
SOME FAIR WEATHER CUMULUS TO DEVELOP MID DAY FOR WELL BELOW NORMAL
TEMPERATURES AND CRISP FALL LIKE DAY. TUESDAY NIGHT...LOWS TRIMMED
EAST 1/2 TO 2/3 A COUPLE DEGREES AS RETURN FLOW TO NOT SET UP UNTIL
AFTER MIDNIGHT. IF SURFACE HIGH EVEN STRONGER AND SLOWER PROGRESSION
EAST MIN TEMPS MAY STILL BE TOO MILD MANY LOCATIONS WITH CLEAR
SKIES FOR GOOD RADIATIONAL COOLING.
WEDNESDAY AND THURSDAY...DELAYED POPS UNTIL LATE PM AND OVERNIGHT
WITH WARMING AHEAD FROM NEXT DISTURBANCE. NOT ENOUGH INSTABILITY AND
FORCING TO SUPPORT THUNDERSTORMS WITH SCATTERED SHOWERS AHEAD OF
FRONT. NEXT SYSTEM TO BE IMPACTED BY HURRICANE "IKE" AS HEADS INTO
NW GULF AND NEAR TX/LA. POOR CONFIDENCE IN PHASING ATTM SO KEPT
CHANCE POPS WITH CLARITY OF TIMING AND FORCING BETTER ASCERTAINED
NEXT 36-48 HRS. LIMITED INSTABILITY SUGGEST MARGINAL LOWER END
SEVERE RISK THURSDAY IF ENOUGH HEATING OCCURS IN PM INTO EARLY
EVENING HOURS.
FRIDAY AND SATURDAY...NO CHANGES MADE...BUT ISSUE OF HOW AND IF NEXT
FRONT INTERACTS WITH "IKE" FOR LATER SHIFTS TO ASSESS. AGAIN...THIS
WILL BE HARD TO DIAGNOSE FOR NEXT COUPLE OF DAYS. ..NICHOLS..
&&
.AVIATION...
WITH CLEARING OF AC AND THINNING OF CI...THE CID/DBQ AND POSSIBLY
THE BRL TERMINALS MAY BE IMPACTED BY MVFR TO IFR FOG THROUGH AT
LEAST 14Z. AFTER THAT...EXPECT A MAINLY VFR DAY WITH CU ABOVE 3K FT
AND SOME AC AT TIMES AS THE REGION WILL BE ALIGNED IN BETWEEN MAIN
FORCING REGIONS IN CYCLONIC MEAN FLOW PATTERN ACRS THE MIDWEST.
SCTRD HIGH BASED VFR SPRINKLES OR LIGHT SHOWERS MAY BE IN THE DBQ
VCNTY THIS AFTERNOON AND EARLY EVENING...BUT BETTER CHANCE FOR THIS
TO THE NORTH. OVERRUNNING RAINS OFF DEVELOPING LOW PRESSURE STORM
SYSTEM IN THE CENTRAL/SOUTHERN PLAINS MAY REACH THE BRL TERMINAL
AFTER 08Z TONIGHT...WITH CIGS AND POSSIBLY VSBYS DIPPING INTO THE
MVFR CATEGORY. EXPECT MAINLY A WEST-SOUTHWEST SFC WIND REGIME TODAY
WITH SPEEDS OF 6-11 KTS THROUGH 00Z TONIGHT...THEN A DECREASE.
..12..
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
12/NICHOLS
