Severe Thunderstorm Warning 155, NWS Lincoln, IL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
221 PM CDT SAT JUL 5 2003

LATEST SURFACE ANALYSIS SHOWED A COMPLEX MIX OF CONVECTIVE
BOUNDARIES IN THE VICINITY OF CENTRAL ILLINOIS...WITH A NEARLY
STALLED FRONTAL BOUNDARY UPSTREAM OVER THE UPPER MIDWEST AND CENTRAL
PLAINS. MAIN CONCERNS REMAIN SHOWER/THUNDERSTORM CHANCES AND
POTENTIALLY DANGEROUS HEAT/HUMIDITY THROUGH THE SHORT TERM.

12Z MODEL AGREEMENT WAS RESPECTABLE WITH REGARD TO THE FEATURES
EXPECTED TO IMPACT CENTRAL ILLINOIS...THOUGH THE EXPECTED PROBLEMS
WITH THE IMPORTANT MESOSCALE FEATURES PERSIST. THE BIGGEST NEARBY
(NON MESOSCALE) DIFFERENCE IS WITH THE STRENGTH OF THE SYSTEM MOVING
ALONG THE U.S./CANADA BORDER MONDAY AND TUESDAY...BUT THE RESULTING
FRONTAL SPEED ACROSS ILLINOIS IS PRETTY MUCH THE SAME. GUIDANCE
TEMPERATURES CLOSE AND REASONABLE...SO WILL NOT STRAY TOO FAR.

TONIGHT...THERE IS DOUBLE BARREL THREAT FOR SHOWERS/STORMS ACROSS
FORECAST AREA ONCE AGAIN TONIGHT...BUT I WONDER IF MUCH WILL
MATERIALIZE ACROSS THE FORECAST AREA THIS TIME. NUMEROUS OUTFLOW
BOUNDARIES EXIST ACROSS ILLINOIS...WITH THE MOST IMPRESSIVE ONE OVER
EAST CENTRAL ILLINOIS AT THE MOMENT. INSTABILITY IS STILL HIGH...
WITH CAPE VALUES FROM 2000-4000 J/KG AND LI VALUES FROM -6 TO -8.
THERE IS ALSO LITTLE CAPPING/CIN TO BE FOUND. OUR FIRST THREAT WILL
BE THIS EVENING WHEN DIURNAL INSTABILITY IS MAXIMIZED ALONG THE
OUTFLOW BOUNDARIES...BUT THE COVERAGE SHOULD BE MINIMAL GIVEN THE
LACK OF FORCING ASIDE FROM THE NEARLY STATIONARY OUTFLOW BOUNDARIES.
THE SECOND THREAT WILL BE OVERNIGHT WHEN A MCS (FROM THE VICINITY OF
NEBRASKA AND SOUTH DAKOTA) TRACKS TOWARD NORTHERN ILLINOIS ON THE
NOSE OF THE LOW LEVEL JET (AND IN ADVANCE OF A DECENT LOOKING UPPER
SHORT WAVE IN THE WESTERLIES). THE THICKNESS PATTERN AND CORFIDI
VECTORS SUGGEST THE MCS WILL MOST LIKELY IMPACT THE FAR NORTHERN
SECTIONS OF THE FORECAST AREA AND POINTS NORTH. WILL CARRY ISOLATED
CHANCE OF EVENING SHOWERS/STORMS OVER THE CWA...WITH LIKELY
NORTH/LOWER CHANCE SOUTH OVERNIGHT.

SUNDAY...MUCH LIKE TODAY ABUNDANT HEAT...HUMIDITY AND INSTABILITY.
CONVECTIVE BOUNDARIES WILL LIKELY BE AROUND ONCE AGAIN FROM
NOCTURNAL CONVECTION...SO SEE LITTLE REASON TO DROP GOING CHANCE OF
SHOWER/STORMS IN FORECAST. HEAT INDICES WILL APPROACH ADVISORY
CRITERIA ONCE AGAIN WITH AFTERNOON HIGHS AND DEW POINTS CHANGING
LITTLE FROM THE PAST FEW DAYS. WILL LEAVE ADVISORY DECISION TO
MIDNIGHT SHIFT ONCE AGAIN AS DEBRIS/OUTFLOW FROM OVERNIGHT STORMS
COULD KEEP INDICES DOWN.

SUNDAY NIGHT AND MONDAY...FAIRLY POTENT UPPER WAVE WILL TRACK ALONG
THE U.S./CANADA BORDER DURING THE PERIOD...WITH THE ASSOCIATED
SURFACE LOW EXPECTED TO PULL ANY LINGERING SURFACE BOUNDARIES NORTH
OF ILLINOIS. THIS SHOULD FOCUS SHOWER/THUNDERSTORM ACTIVITY (BOTH
NOCTURNAL MCS SUNDAY NIGHT AND DIURNAL MONDAY) NORTH OF THE FORECAST
AREA.

TUESDAY...COLD FRONT ASSOCIATED WITH SYSTEM MENTIONED IN PARAGRAPH
ABOVE IS EXPECTED TO DROP INTO ILLINOIS DURING THE DAY. THIS FRONT
WILL WORK ON THE UNSTABLE AIRMASS THAT WILL STILL BE IN PLACE ACROSS
CENTRAL ILLINOIS TO BRING A CHANCE OF SHOWERS AND THUNDERSTORMS.

WEDNESDAY THROUGH SATURDAY...MODELS/ENSEMBLES STILL IN GENERAL
AGREEMENT WITH RESPECT TO A PATTERN CHANGE FOR THE SECOND HALF OF
THE WEEK...THOUGH AGREEMENT ON THE SPECIFICS AND MODEL CONSISTENCY
IS NOT TOO GOOD. BUILDING RIDGE ACROSS CENTRAL U.S. ON WEDNESDAY
SHOULD EVENTUALLY PUSH COLD FRONT SOUTH OF ILLINOIS...BUT WILL
CONTINUE MENTION OF SHOWERS/STORMS WEDNESDAY UNTIL FROPA. UPPER
RIDGING/SURFACE HIGH STILL EXPECTED TO BE DOMINANT WEATHER FEATURE
ACROSS REGION FOR THURSDAY THROUGH SATURDAY...SO WILL CONTINUE WITH
DRY FORECAST. HOWEVER...THE CURRENTLY PROGGED RIDGING IS A BIT
FLATTER THAN IN PREVIOUS DAYS AND MAY ALLOW A DISTURBANCE TO ROLL
THROUGH BEFORE THE END OF THE PERIOD. BUT...FOR NOW...WILL HOLD OFF
ON ADDING ANY PRECIPITATION.

.ILX...NONE.

BAK

ILZ027>031-036>038-040>057-061>063-066>068-071>073-061100-

HAZARDOUS WEATHER OUTLOOK...UPDATED
NATIONAL WEATHER SERVICE LINCOLN IL
725 PM CDT SAT JUL 5 2003

THIS HAZARDOUS WEATHER OUTLOOK IS FOR PORTIONS OF CENTRAL AND
SOUTHEAST ILLINOIS.

.DAY ONE...TODAY AND TONIGHT

THERE WILL BE A RISK OF SEVERE THUNDERSTORMS THIS EVENING AND
OVERNIGHT ACROSS CENTRAL AND SOUTHEAST ILLINOIS. THE MAIN THREATS
FROM THESE STORMS WILL BE DAMAGING WINDS...LARGE HAIL...VERY HEAVY
RAINFALL...AND AN ISOLATED TORNADO.  THERE IS A GREAT POTENTIAL FOR
SOME LOCATIONS ACROSS CENTRAL AND SOUTHEAST ILLINOIS TO RECEIVE
EXTENSIVE RAINFALL.

.DAYS TWO THROUGH SEVEN...SUNDAY THROUGH FRIDAY

THUNDERSTORMS WILL CONTINUE TO BE A THREAT THROUGH WEDNESDAY. THE
STRONGEST STORMS WILL BE IN THE LATE AFTERNOON AND EVENING HOURS.
THE PRIMARY SEVERE WEATHER THREAT WILL CONTINUE TO BE DAMAGING WINDS
AND HEAVY RAINFALL. ALSO ON SUNDAY...DANGEROUS HEAT IS POSSIBLE
ACROSS PARTS OF CENTRAL AND SOUTHEAST ILLINOIS WITH HEAT INDICES OF
100 TO 105 DEGREES.

.SPOTTER INFORMATION STATEMENT...

SPOTTER ACTIVATION WILL BE NEEDED THIS EVENING AND OVERNIGHT.

&&
THIS PRODUCT...ALONG WITH OTHER WEATHER...HYDROLOGIC
AND CLIMATE INFORMATION...IS AVAILABLE ON THE WEB AT:

HTTP://WWW.CRH.NOAA.GOV/ILX. THIS ADDRESS IS ALL
IN LOWER CASE.

EH