Severe Thunderstorm Warning 91, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
135 AM CDT THU JUN 18 1998

THE 05Z SURFACE ANALYSIS INDICATED A LOW PRESSURE NEAR HURON SOUTH
DAKOTA WITH A WARM FRONT STRETCHING THROUGH NORTHWEST IOWA INTO
SOUTHWEST IOWA.  WEAKENING LOW PRESSURE CENTER ALSO NOTED
OVER NORTH CENTRAL KANSAS.  POOLING OF DEW POINTS NOTED ACROSS THE
STATE WITH DEW POINT READINGS IN THE LOWER 70S.  THE 700MB 00Z
ANALYSIS SHOWED DRY AIR MOVING INTO EASTERN NEBRASKA WHILE AT 850MB
WARM MOIST AIR WAS PRESENT ACROSS REGION.  LOW LEVEL PROFILERS SHOW
50 TO 60 KNOT JET OVER EASTERN KANSAS INTO CENTRAL IOWA WITH UPPER
LEVEL JET NOSING INTO CENTRAL KANSAS.

CHALLENGE THIS FORECAST IS TIMING OF THUNDERSTORMS AND THE EFFECT
ON TEMPERATURES.

CURRENT SURFACE ANALYSIS APPEARS TO BE FOLLOWING LAST NIGHTS ETA RUN
BY DEVELOPING LOW PRESSURE NORTH INTO THE DAKOTAS WHILE LAST NIGHTS
NGM MOVED THE LOW ACROSS NEBRASKA.  NEW NGM AND ETA RUNS CONTINUE
THIS PATTERN.  BOTH MODELS PULL 500MB VORT ENERGY INTO WESTERN IOWA
TODAY WITH THE ETA A LITTLE MORE AGGRESSIVE.  MODELS STILL
INDICATING GOOD 700MB DRY PUNCH DURING THE AFTERNOON ACROSS EASTERN
IOWA.

NEW ETA RUN INDICATING LARGE DIVERGENT PATTERN AT 300MB TO SET UP
OVER DVN CWA AFTER 12Z WITH STRONG 850MB THETA-E RIDGE IN PLACE
DURING THIS SAME TIME.  MODEL PRECIPITABLE WATER REACHES 1.80 INCHES.
THIS EVENINGS DVN UPPER AIR RUN HAD ABOUT 1.40 INCHES.  ALSO NOTED
ON MODELS WAS GOOD 850-300 DIFLUENCE OVER TOP OF 850MB THETA-E
RIDGE.  THIS...ALONG WITH EXPECTED SLOW MOVEMENT...WILL HELP TO
PRODUCE WIDESPREAD HEAVY RAIN.  CURRENT CONVECTION OVER EASTERN
NEBRASKA SHOWING LITTLE MOVEMENT THUS WOULD EXPECT THIS TO
DISSIPATE THIS MORNING WITH NEW DEVELOPMENT THIS AFTERNOON CREATING
THE HEAVY RAIN AND POSSIBLE SEVERE WEATHER OVER EASTERN IOWA AND
NORTHWEST ILLINOIS.

THE 12Z THICKNESS PROGS WOULD CONTINUE SLOW EAST-NORTHEAST MOVEMENT
OF CONVECTION OVER NEBRASKA.  MAY WANT TO INCLUDE SCATTERED SHOWERS
THIS MORNING ASSOCIATED WITH WARM AIR ADVECTION. DRY SLOT MOVING INTO
SOUTHERN PART OF CWA MAY BRING WARMER THAN FWC TEMPS TO BRL AND MLI.

CID 83/60   DBQ 82/60   MLI 87/60   BRL 89/70

WEISSER