Severe Thunderstorm Warning 103, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
200 AM CDT SUN AUG 11 2002

DYNAMIC AND CHALLENGING FORECAST AS ATMOSPHERE UNDERGOING SIG PATTERN
CHANGE. THIS PRESENTS DIFFICULTIES AS MODELS CHANGING SOLUTIONS
WITH EACH RUN...AND UNFORTUNATELY EXPECT THIS TO REMAIN TRUE NEXT 24 HRS.

CLOSED UPPER LOW NORTH OF LAKE SUPERIOR. STRONG SHORTWAVE DIVING THROUGH
ALBERTA CANADA WITH 100+ KT JET FOLLOWING SIMILAR PATH. SYSTEM
WILL AID IN CARVING LONGWAVE TROUGH THROUGH CENTRAL US BY MIDWEEK WITH
MUCH COOLER AIRMASS. AT SURFACE...SOME HINTS OF WEAK BOUNDARY IN
PRESSURE AND WIND FIELDS FROM CENTRAL NE THROUGH NORTHERN IL INTO EASTERN WI.
NEW CONVECTION DEVELOPING OVER NORTHERN NE ON NOSE OF 20-30 KT LLJ ON
COOL SIDE OF WEAK SURFACE BOUNDARY. CLOSER TO HOME...LIGHT FOG BECOMING MORE
WIDESPREAD WITH AMPLE BOUNDARY LAYER MOISTURE AND TEMP/DEWPT SPREADS
CLOSING TO UNDER 5 DEGS.

MANY CONCERNS THIS FORECAST CYCLE...WITH TEMPS AND PCPN CHCS NEAR TERM ISSUES
FOLLOWED BY POTENTIAL FOR HEAVY RAIN AND SEVERE WX LATE MON-TUE WITH
STRONG SYSTEM...AND EXTENT OF COOL DOWN BY MIDWEEK.

AS MENTIONED EARLIER...FORECAST QUITE CHALLENGING WITH PATTERN CHANGE AND
MODELS OFFERING DIFFERENT SOLUTIONS NEARLY EVERY RUN.
HEAVY RAIN APPEARS A CERTAINTY...RATHER IT/S MERELY A QUESTION OF TIMING.

NEAR TERM...CHALLENGE IS POTENTIAL FOR CONVECTION THIS AFTERNOON.
LLVL FLOW BACKS WITH MODELS INDICATING DEVELOPING SFC-H8 WARM FRONT IN CLOSE
PROXIMITY. UPPER FORCING IS LACKING...BUT STRONG SURFACE HEATING EXPECTED
WITH MAXES REACHING U80S TO L90S WHICH WILL BE AT OR VERY NEAR CONVECTIVE
TEMPS...SO CAN/T RULE OUT ISOLD CONVECTION.

TONIGHT...STRENGTHENING LLJ AND MOISTURE TRANSPORT WITH BOUNDARY NEARBY SUPPORT
POTENTIAL FOR SOME CONVECTION. DIFFICULTY EXISTS IN TRYING TO PINPOINT
LOCATION. AVN WITH LOCATION OF THETA-E AXIS AND LLJ SUGGESTS
CONVECTION WANTING TO DEVELOP SOUTH AND LIFTING NORTH WHILE ETA HINTING AT
POTENTIAL MAINLY ALONG AND NORTH OF I-80. WILL CONTINUE CHC POPS.

MONDAY...VERY TRICKY WITH TEMPS...PCPN COVERAGE AND SEVERE POTENTIAL.
ANTICIPATE SCATTERED MORNING CONVECTION DIMINISHING WITH LOSS OF NOCTURNAL LLJ.
STRONG COLD FRONT (SLOWER ON 00Z RUNS WITH UPPER SYSTEM DIGGING OUT WEST)
MARCHING THROUGH IA AND EXPECT DECENT LINE OF CONVECTION TO FORM ALONG FRONT
DURING AFTERNOON AND PROPAGATE INTO CWA BY EVENING. WORDING WILL BE
TRICKY AND WILL HAVE TO GO WITH MORNING AND AGAIN IN THE AFTERNOON VERBIAGE TO
ACCOUNT FOR THIS THINKING. GOING WITH BECOMING PARTLY SUNNY IN ANTICIPATION
OF DEBRIS THINNING...AND WITH SLOWER FRONTAL MOVEMENT LEANING TOWARD
BLEND OF WARMER MAV/MET GUIDANCE. SEVERE POTENTIAL SOMEWHAT TRICKY WITH DEGREE
OF SOLAR INSOLATION PLAYING ROLE...BUT FEEL WITH SUCH STRONG DYNAMICS
THE LIKES OF WHICH WE/VE NOT SEEN IN SOME TIME...SHOULD BE SUFFICIENT ALONE TO
GENERATE SOME SEVERE WX.

HEAVY RAIN CONCERNS REALLY MON NIGHT-TUE. AVN AND LATEST UKMET SUGGEST SECOND
PIECE OF ENERGY HOLDING BACK BEFORE EJECTING OUT ON TUE.
THIS WOULD FAVOR REGENERATION OF CONVECTION ALONG FRONTAL ZONE OVER REGION
MONDAY NIGHT AND GIVEN HEFTY DYNAMICS AND COPIOUS MOISTURE HEAVY RAIN WOULD
APPEAR FAIRLY CERTAIN AND WILL CONTINUE WITH WORDING IN ZONES.
FRONT EAST ON TUE BUT HINTS OF WAVE MOVING ALONG FRONT WITH AFFORMENTIONED
ENERGY EJECTING OUT FROM ROCKIES...SO RAIN COULD POSSIBLY LINGER WELL
INTO TUE AND POSSIBLY EVEN TUE EVE DEPENDING ON TIMING. WILL RAISE POPS TUE.
MAINLY RAIN WITH SEVERE STRATIFICATION IN COLDER AIRMASS.
TEMP FORECAST QUITE CHALLENGING TUE WITH COLD ADVECTION AND CLOUDS/PCPN WILL
BE STRUGGLE TO HIT 70 DEGS.

OVERALL...LOOKS FAIRLY CERTAIN LIKE HEAVY RAIN EVENT OVER CWA WITH WIDESPREAD
RAINFALL OF 1+ INCHES BY TUE EVENING WITH AREAS OF 2 TO 4 INCHES
REASONABLE AND WILL CONTINUE WITH ESF HIGHLIGHTING HEAVY RAIN AND POSSIBLE
LOW END FLOODING.

.DVN...
IA...NONE.
IL...NONE.
MO...NONE.

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