Severe Thunderstorm Warning 65, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
144 PM CDT THU MAY 21 1998

THE 18Z SURFACE ANALYSIS INDICATES STATIONARY FRONT OVER SOUTHWEST
NEBRASKA INTO NORTHEAST KANSAS AND ACROSS CENTRAL MISSOURI.  LOW
PRESSURE ALSO NOTED OVER NORTHWEST KANSAS WHICH IS DEVELOPING A
DRY LINE OVER WESTERN KANSAS.  THIS MAY ALSO BE HELPING TO DRAW
HIGH 70 PLUS DEW POINTS INTO CENTRAL KANSAS.  THE 12Z UPPER AIR
ANALYSIS INDICATED A STRONG SHEAR ZONE AT 850 MB ALONG THE NEBRASKA-
KANSAS BORDER AND THE IOWA-MISSOURI BORDER. THIS ZONE CONTINUED AT
17Z PER THE LIKELY FOCUSING MECHANISM FOR CURRENT CONVECTION. CURRENT
CONVECTION OVER NORTHWEST MISSOURI AND SOUTHWEST IOWA SHOULD CONTINUE
TO DEVELOP TO THE SOUTH. RAIN COOLED AIR PRESENT OVER IOWA WITH
NEGATIVE SURFACE MOIST FLUX CONVERGENCE PER ADAP.

THE FORECAST PROBLEM TODAY IS WHETHER ANY CONVECTION OVER AREA
TONIGHT AND TOMORROW AND WHETHER OR NOT SEVERE.  ALSO CLOUD COVER
ON TEMPERATURES.

THE FIRST COMPLEX THIS MORNING BRUSHED THE SOUTHERN EDGE OF THE CWA
WITH THE SECOND NOW APPEARING TO DEVELOP EVEN FARTHER TO THE SOUTH.
NEW DEVELOPMENT FROM TOP-MKC POSSIBLY INITIATING ON WEST SIDE OF
OUTFLOW FROM THE FIRST COMPLEX.  THE THIRD COMPLEX OVER CENTRAL
NEBRASKA LOOKS TO BE DEVELOPING ON SOUTHWEST FLANK SO PROGRESSION
VERY SLOW.  THIS DEVELOPMENT MAY ALSO BE AIDED BY SOME INCOMING
DIVERGENCE AROUND 200-300MB.  CENTRAL KANSAS AND SOUTH CENTRAL
NEBRASKA MAY BE THE PLACE TO WATCH THIS EVENING.

BOTH NGM AND ETA SHOW LOW LEVEL SHEAR AXIS WELL TO THE NORTH OF
THIS MORNINGS UPPER AIR RUNS THUS NOT SURE HOW WELL EITHER MODEL
WILL PERFORM WITH CURRENT SITUATION.  BOTH DO HOWEVER AGREE ON
BRINGING IN STRONG CLOSED LOW INTO CENTRAL PLAINS LATE FRIDAY INTO
SATURDAY.  THIS INCREASES LOW LEVEL SOUTHERLY FLOW ACROSS THE AREA
WITH WARM AIR ADVECTION INCREASING GREATLY.  BOTH MODELS DO
INDICATE DIVERGENT FLOW AROUND THIS TIME ALSO SO LATE FRIDAY INTO
SATURDAY MAY BE INTERESTING...ESPECIALLY SATURDAY.

STRONG LOW LEVEL JET SHOULD DEVELOP TONIGHT AIDING IN THE
DEVELOPMENT OF MORE THUNDERSTORMS.  SHEAR AXIS AND NUMEROUS OTHER
BOUNDARIES WILL ACT AS LIFT WITH SOUTHERLY WINDS TRANSPORTING
ADDITIONAL MOISTURE TO THE AREA.  ETA INDICATING HIGHEST THETA
AIR OVER NORTHERN MISSOURI WITH BEST ADVECTION SLIGHTLY NORTH OF
THIS.  THIS SHOULD SPREAD AT LEAST RAIN OVER SOUTHERN THIRD OF CWA
WITH A SLIGHT CHANCE OVER THE DUBUQUE AND GALESBURG AREA.  FWC
NUMBERS NOT OUT OF LINE WITH JUST HIGH AND MID CLOUDS EXPECTED AND
THEN STRONG SOUTHERLY WIND AT 850 ADVECTING IN WARNER AIR.  WOULD
MAYBE THINK ABOUT BUMPING UP LOWS A CATEGORY OR TWO OVER ILLINOIS
ZONES AND ALSO ADD SOME POPS...ESPECIALLY SOUTHERN GROUP.

CID 56/60   DBQ 53/30   MLI 55/50   BRL 59/70

WEISSER