Severe Thunderstorm Warning 126, NWS Quad Cities, IA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
239 AM CDT WED JUL 26 2000

SYNOPTIC PICTURE THIS MORNING SHOWS SLIGHTLY DE-AMPLIFIED FLOW AT
500H ACROSS U.S...WITH TROUGH OVER OHIO VALLEY...RIDGE OVER
ROCKIES...AND VIGOROUS SHORT WAVE OVER MINNESOTA.  AT THE SURFACE
THE TROUGH ASSOCIATED WITH THIS SHORT WAVE EXTENDS INTO EXTREME
NORTHWEST IOWA FROM A 1007 LOW IN NORTH CENTRAL MINNESOTA. MCS THAT
INITIATED IN NORTHWEST MINNESOTA THIS AFTERNOON NOW IN NORTH CENTRAL
IOWA...BEARING DOWN ON THE SOUTHWEST PORTION OF THE DVN CWA. ISOLATED
THUNDERSTORMS ARE ALSO BRAKING OUT IN THE DBQ AREA.

THE ETA/NGM/AVN MODELS INITIALIZED WELL AT 500H AND THE SURFACE.
ALL THREE MODELS CAPTURED THE ONGOING PRECIP TONIGHT FAIRLY WELL...
WITH ETA AND AVN BEST.

THE PRIMARY FORECAST CONCERN THIS PACKAGE IS THE THREAT OF SEVERE
WEATHER OVER THE NEXT 24 HOURS.  SPC HAS ENTIRE CWA IN SLIGHT RISK
DAY 1.  OUTFLOWS FROM ONGOING CONVECTION WILL SET OUT BOUNDARIES
THAT WILL PROVIDE FOCUS AS FRONT APPROACHES AREA LATE THIS AFTERNOON.
CAPES WILL NOT BE VERY HIGH...BUT VEERING WINDS...GOOD VVS...GOOD
THETA-E...AND PVA WILL EXIST FROM 18Z TO 09Z...WITH 21Z TO 09Z PERIOD
BEING FAVORED.  CURRENT MCS THUNDERSTORMS WILL MOVE ACROSS SOUTHERN
HALF OF CWA THIS MORNING...WITH SCATTERED THUNDERSTORMS
SPREADING NORTH ALSO...DECAYING INTO SHOWERS AS THE MORNING
PROGRESSES.  SECOND HALF OF THE DAY WILL SEE RECOVERY...WITH
SCATTERED CONVECTION POSSIBLE LATE DUE TO STRONG VVS...ESPECIALLY
NORTH. BETWEEN 00Z AND 06Z VVS WILL BEGIN SHIFTING SOUTH.  STRONG
OR SEVERE THUNDERSTORMS WILL BE POSSIBLE FROM LATE AFTERNOON INTO
THE LATE NIGHT HOURS...TRANSITIONING INTO HEAVY PRECIP.  FLASH
FLOOD GUIDANCE VALUES ARE HIGH...SO HYDRO PROBABLY NOT A SIGNIFICANT
CONCERN.

FRONT WILL PASS THROUGH DVN AROUND 16Z-17Z THURSDAY...SLIDING SOUTH
OF THE CWA INTO NORTH CENTRAL MISSOURI THURSDAY EVENING.  TROUGHING
AT 500H CONTINUES THROUGH 72 HOURS.

WILL NOT MAKE SIGNIFICANT CHANGES TO CURRENT PACKAGE...EXCEPT MAYBE
TRIMMING BACK THURSDAY PRECIP PER QPF GUIDANCE FROM ALL MODELS...
WHICH INDICATED PRECIP WILL BE MOVING EAST AND SOUTH OF THE AREA.
WILL KEEP CLOSE TO CURRENT EXTENDED/FRI THROUGH SUN/ WHICH HAS CHANCE
PRECIP EACH DAY...ALTHOUGH SATURDAY LOOKS LIKE BEST CHANCE DUE TO
STRONG SECONDARY SHORT WAVE.

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

ARKELL

N

IAZ040>042-051>054-063>068-076>078-087>089-098-099-ILZ001-002-007-
009-015>018-024>026-034-035-MOZ009-010-262025-

SIGNIFICANT WEATHER OUTLOOK
NATIONAL WEATHER SERVICE QUAD CITIES IA IL
425 AM CDT WED JUL 26 2000

...SEVERE THUNDERSTORMS POSSIBLE FOR NEXT 24 HOURS...

A DECAYING MESOSCALE CONVECTIVE SYSTEM WILL TRANSIT THE FORECAST
AREA THIS MORNING...FROM NORTHWEST TO SOUTHEAST...WITH THUNDERSTORMS
DIMINISHING TO SHOWERS.  THIS CONVECTION WILL SET UP BOUNDARIES THAT
MAY BECOME THE FOCUS FOR THUNDERSTORMS LATER THIS AFTERNOON.  VEERING
WINDS WITH HEIGHT...MODERATE CAPES..AND STRONG VERTICAL VELOCITIES
WILL PROVIDE ADDITIONAL IMPETUS FOR THUNDERSTORM DEVELOPMENT THIS
AFTERNOON INTO TONIGHT...TRANSITIONING INTO HEAVY RAIN LATE TONIGHT.
THE PRIMARY THREAT WILL BE FOR HIGH WINDS AND LARGE HAIL.  HOWEVER...
ISOLATED TORNADOES WILL ALSO BE POSSIBLE. FLASH FLOOD GUIDANCE
VALUES ARE HIGH...SO FLASH FLOODING WILL PROBABLY NOT BE A
SIGNIFICANT CONCERN.

SPOTTER ACTIVATION MAY BE REQUIRED THIS AFTERNOON AND/OR TONIGHT.

REA

N