Severe Thunderstorm Warning 75, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
300 PM CDT THU JUN 17 2010

.SYNOPSIS...
UNSEASONABLY STRONG 994 MB CYCLONE 2-3 STANDARD DEVIATIONS FROM
NORMAL CENTERED IN ND WITH IMPRESSIVE COLD FRONT EXTENDING ALONG THE
MN/DAKOTAS BORDER TO EXTREME NW KS. VERY UNSTABLE AIRMASS AHEAD OF
THE FRONT WITH CURRENT TEMPS 90+ WITH DEWPOINTS 70+. BEHIND THE FRONT
DEWPOINTS DROP OFF DRAMATICALLY INTO THE 20S WITH GRADIENT WEST
WINDS GUSTING TO 50 KNOTS. CLUSTERS OF STORMS WERE LOCATED IN ND AND
NORTHERN MN WITH OTHER STORMS JUST STARTING TO ERUPT ALONG THE COLD
FRONT IN EXTREME WESTERN MN. HAD A FEW STORMS EARLIER TODAY IN THE
WESTERN DVN CWA BUT HAVE SINCE DISSIPATED AS THEY OUTRAN THE BETTER
MOIST AXIS AND FORCING FURTHER TO THE WEST. CURRENT TEMPS IN THE DVN
CWA WERE IN THE 80S WITH DEWS IN THE 60S TO LOWER 70S.  ..HAASE..

&&

.SHORT TERM...TONIGHT AND FRIDAY...
FULLY EXPECT A MATURE LINEAR MCS TO FORM REMAINDER OF THIS AFTERNOON
FROM WESTERN MN TO WESTERN IA...AND THEN PROGRESS EAST. OPERATIONAL
MODELS FAIRLY SIMILAR IN BRINGING THIS SQUALL LINE INTO OUR WESTERN
CWA THIS EVENING WITH POTENTIAL FOR DAMAGING WINDS OF 60-70 MPH AND
ISOLATED LARGE HAIL. MODERATE RISK REMAINS FOR SEVERAL COUNTIES IN
THE CWA AND WILL MENTION SEVERE WORDING IN THE GRIDS/ZFP ONLY IN THE
MODERATE RISK AREA. MCS SHOULD DIMINISH OVERNIGHT AS IT CONTINUES TO
MOVE EAST OR SOUTHEAST. HAVE NOT ISSUED A FLASH FLOOD WATCH FOR THIS
EVENT YET BUT LOCALLY VERY HEAVY RAIN MAY CAUSE FLASH FLOODING IN
SOME SPOTS. WILL CONTINUE TO MONITOR THE PROGRESS OF THIS SITUATION
AND A FLASH FLOOD WATCH CAN ALWAYS BE ISSUED THIS EVENING.
THERMODYNAMICALLY SPEAKING THE GREATEST INSTABILITY IS TO OUR WEST
AND THIS IS WHERE THE MOST INTENSE ACTIVITY SHOULD REMAIN. TIME WILL
TELL. WILL FORECAST MIN TEMPS IN THE LOWER TO MID 70S SO THE MUGGIES
ARE BACK WITH A VENGEANCE.

FRIDAY...POTENTIALLY A MORE WIDESPREAD AND MORE INTENSE SEVERE
WEATHER EVENT UNFOLDING FOR FRIDAY LATE AFTERNOON INTO FRIDAY NIGHT.
AS IMPULSE PASSES BY TO THE NORTH TO SUPPLY SOME DYNAMICS AND MID
LEVEL WINDS INCREASE TO OVER 50 KNOTS MODERATE TO STRONG DEEP LAYER
SHEAR EXPECTED. COLD FRONT WILL BE APPROACHING FROM THE WEST WITH
THE AIRMASS AHEAD OF THE FRONT HAVING MLCAPES OF 2000-3000 J/KG.
SURFACE DEWS SHOULD BE AT LEAST IN THE LOWER TO MID 70S WITH TEMPS
AROUND 90. THIS RAISES THE POTENTIAL FOR A WIDESPREAD WIND DAMAGE OR
DERECHO EVENT WITH AT LEAST 70-80 MPH WINDS. THESE SPEEDS ALONG WITH
SATURATED SOILS COULD EASILY BLOW OVER MANY MORE TREES THAN USUAL IN
THIS TYPE OF EXTREME EVENTS. EXPECTING A HIGH END EVENT WITH
CURRENTLY SPC HAVING THE ENTIRE CWA IN SLIGHT RISK WITH UPGRADE TO
MODERATE RISK POSSIBLE. WILL MENTION SEVERE WORDING FOR FRIDAY
AFTERNOON IN OUR WESTERN CWA AS COLD FRONT APPROACHES FROM THE WEST.
STAY TUNED TO LATER FORECASTS AND HAZARDOUS WEATHER OUTLOOKS
CONCERNING THIS SCENARIO.

PRECIPITABLE WATERS WILL BE APPROACHING 2.00 INCHES SO CERTAINLY THE
THREAT OF TORRENTIAL RAINS WITH RATES OF 2 INCHES PER HOUR RAISING
THE RISK FOR FLASH FLOODING ON ALREADY SATURATED SOILS. ANY
WIDESPREAD HEAVY RAINS WOULD ALSO GREATLY AGGRAVATE OR CAUSE NEW
RIVER FLOODING.  ..HAASE..

.LONG TERM...FRIDAY NIGHT THROUGH NEXT THURSDAY...
...SIGNIFICANT SEVERE WEATHER EVENT FRIDAY NIGHT...THEN A HIGHER END
HEAVY RAIN EVENT SUNDAY INTO MONDAY...POTENTIALLY DANGEROUS FLASH
FLOODING POTENTIAL MAIN CONCERN INTO MIDDLE OF NEXT WEEK...

OVERVIEW...AS DISCUSSED YESTERDAY...GUIDANCE TRENDING TOWARD MAJOR
CONVECTION INTO FRIDAY NIGHT TO SET UP OUTFLOW BOUNDARY WITH A 18-30
HOUR DRY PERIOD AHEAD OF NEXT MCS EVENT.  THEN SUBSEQUENT CONVECTIVE
EVENTS WILL FOLLOW 18 TO 30 HOURS LATER INTO WEDNESDAY OR EVEN
THURSDAY WITH AREA REMAINING NEAR BATTLE-ZONE WITH HIGH RISK OF VERY
HEAVY RAINFALL AND INCREASING HIGH END BOW ECHO TO LOW-MID STRENGTH
DERECHO POTENTIAL INTO MIDDLE OF NEXT WEEK. BIGGEST CONCERN ARE HEAVY
RAINS THAT COULD RESULT IN A MAJOR FLASH FLOODING AND FLOODING RISK.
ALSO A HIGHER END SEVERE RISK FROM STRAIGHT LINE WINDS OF 60 TO OVER
80+ MPH INCREASINGLY POSSIBLE BY EARLY NEXT WEEK.  GUIDANCE USED A
70/30 BLEND OF HI-RES ECMWF/GEM-NH MIX WITH THE GFS. CONFIRMATION OF
MAGNITUDE OF MCS EVENT/S/ SUNDAY...MONDAY SHOULD BE ASCERTAINED NEXT
24 HOURS.

FRIDAY NIGHT...UPPED POPS TO LIKELY WEST TO HIGH CHANCE EAST WITH A
MODERATE SEVERE WEATHER EVENT WITH NW 1/2 FORECAST AREA MOST
SUSCEPTIBLE FOR SEVERE WEATHER.  LOCAL TOOLS SUGGEST STRONG COOL POOL
TO DEVELOP WITH WIDESPREAD 40 TO 60+ MPH WINDS WITH ISOLATED 60 TO
70+ MPH INTO LATE EVENING HOURS.  ISOLATED HAIL UP TO 1.25 INCHES AND
EVEN A BRIEF TORNADO CAN/T BE RULED OUT OVER NW 1/4 TO 1/3 AREA UNTIL
CIRCA 9 TO 10 PM.  MOST LOCATIONS SHOULD RECEIVE MAINLY MODERATE
RAINFALL AMOUNTS WITH LOCALIZED 1 TO 1.5+ INCH AMOUNTS.  HIGH PW/S UP
TO NEAR 2 INCHES TO PRODUCE RAINFALL RATES OF 1 TO 2 INCHES THAT
COULD RESULT IN LOW END FLASH FLOODING IN URBAN AND LOW LYING
LOCATIONS. KEPT LOWS IN THE UPPER 60S NW TO LOWER 70S SW AS FRONT
PASSES BEHIND MCS BOWING COMPLEX.

SATURDAY...POTENTIAL ENERGY RELEASED TO ALLOW FOR STRONGER SFC HIGH
TO MOVE IN BEHIND LATENT HEAT ENHANCED SFC WAVE AND UPPER AIR VORT
MAX TO ALLOW FOR DRY PERIOD AND SLIGHTLY COOLER AND LESS HUMID.
LOWERED HIGHS 2 TO 4 DEGREES WITH SOME LOCATIONS POSSIBLY STILL A
COUPLE OF DEGREES TOO WARM FOR LATER SHIFTS TO REASSESS.  SATURDAY
NIGHT...CLOUDS TO INCREASE LATE WITH SOME SHRA/TSRA TO POSSIBLY
ARRIVE TOWARD DAYBREAK.  LOCAL FORCING TOOLS SUGGEST PRECIPITATION
ARRIVAL MAY BE A FEW HOURS STILL TOO QUICK.  LOWS IN NE SECTIONS ALSO
MAY NEED LOWERING BY 2 TO 3 DEGREES.

SUNDAY/MONDAY...RISK OF A HIGH END FLASH FLOODING EVENT.  HIGH END
MCS/S/ WITH LOTS OF HEAVY RAIN AND RISK OF SEVERE WEATHER IN FORM OF
STRAIGHT LINE WINDS UP TO 70 MPH OVER SOUTH 1/3 TO 1/2.  LOCAL TOOLS
SUGGEST HEAVIEST RAIN TO FALL ROUGHLY 40 MILES EITHER SIDE OF A
WILLIAMSBURG TO MONMOUTH LINE WHERE 1 TO LOCALLY 4 PLUS INCH AMOUNTS
SUGGESTED. VERY MOIST SOILS WOULD RESULT IN MODERATE TO HIGHER END
FLASH FLOODING RISK WITH HIGHER END RIVER FLOODING.  SINCE STILL
SEVERAL DAYS OUT...WILL EMPHASIZE THIS ONLY IN THIS DISCUSSION AND
REVIEW MAGNITUDE OF THIS RISK FRIDAY.  LOCAL MEDIA PARTNERS AND
INTERESTED INDIVIDUALS SHOULD CLOSELY MONITOR THIS SITUATION. TEMPS
HAVE LOWERED HIGHS SIGNIFICANTLY AND EVIDENCE STILL TOO HIGH OVER
NORTH 1/3 TO 1/2 BY AT LEAST 2 TO 5 DEGREES FOR LATER SHIFTS TO
RECONSIDER. LOWS MADE ONLY MINOR CHANGES TO.

TUESDAY AND WEDNESDAY...MINOR CHANGES...EVIDENCE NEXT MCS EVENT WITH
HIGHER TEMPS AND INSTABILITY TO BE A STRONG BOW ECHO TO DERECHO
WITH SIGNIFICANT AREAS OF 80+ MPH POSSIBLE.  AS DISCUSSED
YESTERDAY...THIS ALSO SHOULD BE BETTER DETERMINED FRIDAY.  HIGHS WILL
BE A CHALLENGE AS CONVECTIVE OUTFLOW MAY RESULT IN HIGHS 5+ DEGREES
WARMER OR COLDER DEPENDING ON LOCATION.

THURSDAY...HAVE SLIGHT CHANCE POPS WITH EVIDENCE OF MODEL CONVECTIVE
INSTABILITY ISSUES.  NWP INITIALIZATION TOOLS SUGGEST MAJOR CHANGES
POSSIBLE IF NOT PROBABLE TO SUBSEQUENT RUNS FOR DAY 7 INTO NEXT
WEEKEND. KEPT TEMPS ABOVE NORMAL AND HUMID FOR NOW.   ..NICHOLS..

&&

.AVIATION...
VFR CONDS REMAINDER OF THIS AFTERNOON BUT SQUALL LINE SHOULD BE
MOVING INTO EASTERN IA THIS EVENING FROM THE WEST. MVFR TO OCNL IFR
IN THUNDERSTORMS. STORMS SHOULD WEAKEN AND DIMINISH OVERNIGHT.
ANOTHER ROUND OF WIDESPREAD STORM SHOULD ARRIVE LATE FRIDAY
AFTERNOON OR EVENING. VFR CONDS OUTSIDE OF THUNDERSTORMS. SOUTH
WINDS 10 TO 15 KNOTS THROUGH FRIDAY.  ..HAASE..

&&

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

&&

HAASE/NICHOLS