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000
FXUS63 KLOT 121138
AFDLOT
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
638 AM CDT TUE MAY 12 2009
.DISCUSSION...
403 AM CDT
THUNDERSTORM POTENTIAL OVERNIGHT TONIGHT AND THREAT OF STRONG TO
SEVERE STORMS WEDNESDAY AFTERNOON AND EARLY EVENING ARE MAIN
FORECAST CONCERNS.
LITTLE CHANGE IN FORECAST ELEMENTS FOR THE NEXT FEW DAYS NECESSARY
AS LATEST MODEL OUTPUT HAVE SIMILAR SOLUTIONS TO PREVIOUS RUNS
THOUGH LATEST RUNS HAVE TRENDED SOMEWHAT DEEPER/SHARPER WITH THE
UPPER TROUGH AS IT MOVES EAST ACROSS THE SOUTHERN CANADIAN PRAIRIE
AND THE NORTHERN PLAINS DURING WEDNESDAY. STILL...THE STRONG COLD
FRONT IS STILL PROGGED TO BE POSITIONED FROM SOUTH CENTRAL WI
ACROSS NORTHWEST AND FAR WEST CENTRAL IL AT 00Z THU.
THREAT OF THUNDERSTORMS TO INCREASE FOR OVERNIGHT AS STRONG SOUTH
TO SOUTHWEST FLOW IN PLACE ACROSS THE PLAINS EARLY THIS MORNING
ADVANCES EASTWARD ACROSS THE MS VALLEY DURING THE EVENING AS THE
WESTERN UPPER TROUGH PROGRESSES TO OVER THE NORTHERN AND CENTRAL
ROCKIES. THIS RESULTS IN STRONG MID AND EVENTUALLY LOWER LEVEL
THETA E ADVECTION AND ISENTROPIC LIFT ACROSS THE REGION. MODELS
IN GOOD AGREEMENT IN LIFTING A WARM FRONT NORTHEASTWARD THROUGH
THE LOCAL FORECAST DURING WEDNESDAY MORNING TEMPORARILY ENDING THE
THUNDERSTORM CHANCES BEFORE STRONG LOW LEVEL CONVERGENCE AHEAD OF
THE COLD FRONT APPROACHING FROM THE NORTHWEST AND STRONG LIFT IN
DIVERGENT MID-UPPER LEVEL FLOW SPREADS EAST ACROSS THE MID MS
VALLEY AHEAD OF THE UPPER TROUGH AXIS MOVING FROM THE PLAINS OVER
THE MO RIVER VALLEY LATER IN THE DAY.
BASED ON STABILITY AND ENERGY PARAMETERS AND WHERE LOW LEVEL AND
UPPER LEVEL FORCING INTERSECT AGREE WITH SPC ASSESSMENT OF AREA OF
GREATEST RISK OF STRONG TO SEVERE BEING ACROSS CENTRAL IL. SEE DAY
2 CONVECTIVE OUTLOOK /SWODY2/ FOR FURTHER DETAILS.
COLD FRONT TO HAVE PASSED THROUGH ALL BUT FAR EASTERN AND
SOUTHEASTERN PORTION OF THE FORECAST AREA BY 06Z THU WITH POP
VALUES DECREASING WEST TO EAST DURING THE NIGHT AS THE MID-UPPER
TROUGH PASSES BY DURING THE OVERNIGHT. LINGERING
ANOTHER SHORT WAVE TO BE MOVING ACROSS SOUTHERN CANADA AND THE
NORTHERN AND CENTRAL PLAINS FRIDAY DEVELOPING A STRONG WARM AIR
ADVECTION PATTERN WITH SHIFTING EAST FROM THE PLAINS ACROSS THE
MID MS VALLEY DURING FRIDAY MORNING BRINGING THE THREAT OF MORE
SHOWERS AND THUNDERSTORMS BACK TO THE AREA.
TRS
&&
.AVIATION...
1200 UTC TAFS...THE HIGH OVER SOUTHERN MICHIGAN WILL MOVE EAST TO
THE EASTERN PART OF LAKE ERIE BY 00 UTC. THE WIND WILL BECOME SOUTHEAST
AND THE SPEED WILL INCREASE TO 15 KNOTS. THE CLOUDS WILL INCREASE
WITH A CEILING OF 20000 F00T BROKEN CIRROSTRATUS THIS AFTERNOON.
THEN 8000 FOOT BROKEN ALTOCUMULUS CLOUDS WILL MOVE IN AFTER 04
UTC TONIGHT. ONCE THE INVERSION DISSIPATES LATER THIS MORNING...A
SOUTHEAST WIND WILL INCREASE TO 10 TO 15 KNOTS. THE INTENSE LOW...
THAT WILL MOVE FROM MANITOBA TO ONTARIO TONIGHT...WILL CREATE A
LARGE PRESSURE GRADIENT. THIS WILL KEEP THE WIND SPEED IN THE 10
TO 15 KNOT RANGE WITH GUSTS OVER NIGHT.
THE FORECAST MODELS SUCH AS THE GFS AND OUR LOCALLY RUN WRF MODELS
SHOW PRECIPITATION WEDNESDAY MORNING. THE MORNING THUNDERSTORMS
WILL BE ALONG A WARM FRONT THAT WILL MOVE NORTH THROUGH NORTHERN
ILLINOIS AND NORTHWEST INDIANA. WE WILL FORECAST TEMPO
THUNDERSTORMS FROM 11 UTC TO 12 UTC. THUNDERSTORMS WILL END AT OHARE
AIRPORT AROUND 15 UTC WEDNESDAY.
&&
.MARINE...
224 AM CDT
A LARGE HIGH WAS OVER SOUTHWEST MICHIGAN THIS EARLY MORNING. THIS
HIGH WILL MOVE EAST TO NEW YORK STATE BY WEDNESDAY MORNING. A LOW
WILL MOVE INTO SOUTHERN MANITOBA AND NORTHERN MINNESOTA WEDNESDAY
MORNING. THE PRESSURE GRADIENT BETWEEN THE HIGH AND THE LOW WILL
INCREASE OVER LAKE MICHIGAN. GALES COULD OCCUR WEDNESDAY. HOWEVER
THERE IS AN INVERSION OVER LAKE MICHIGAN AND THIS WILL BLOCK ANY
TRANSFER OF ENERGY FROM THE FASTER WIND ALOFT. WE WILL FORECAST
WIND SPEED JUST BELOW GALE. WE WILL NOT ISSUE ANY GALE WARNING AT
THIS TIME. THE LOW WILL MOVE TO NORTHERN ONTARIO BY THURSDAY
MORNING. A COLD FRONT TRAILING SOUTH FROM THE LOW WILL WILL MOVE
ACROSS LAKE MICHIGAN. THE WIND THEN...BE NORTHWEST AND THE SPEED
WILL DIMINISH
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...SMALL CRAFT ADVISORY...LMZ740-LMZ741-LMZ742-LMZ743-LMZ744-
LMZ745...7 AM WEDNESDAY TO 7 AM THURSDAY.
&&
$$
