Severe Thunderstorm Warning 87, NWS Louisville, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LOUISVILLE KY
321 PM EDT MON MAY 17 2010

.SHORT TERM (TONIGHT AND TUESDAY)...

...SEVERE THUNDERSTORMS POSSIBLE THIS AFTERNOON...

AN AREA OF LOW PRESSURE CENTERED OVER THE EASTERN KENTUCKY/OHIO
BORDER HAS MOVED LITTLE TODAY AND WILL REMAIN QUASI-STATIONARY
TONIGHT AS IT PHASES WITH AN UPPER LEVEL TROUGH TRANSLATING ACROSS
THE OHIO VALLEY. THIS SYSTEM WILL THEN BEGIN TO SLOWLY MOVE
NORTHEAST DURING THE DAY TOMORROW.

A SEVERE THUNDERSTORM WATCH HAS JUST BEEN ISSUED THROUGH 01Z FOR
MOST OF SOUTH CENTRAL KENTUCKY AND PORTIONS OF THE BLUEGRASS REGION.
SHOWERS AND THUNDERSTORMS HAVE BEGUN TO INCREASE OVER THE PAST HOUR
OVER THE WESTERN PORTIONS OF THE FORECAST AREA. STEEPENING LAPSE
RATES ALOFT AS THE UPPER LOW MOVES EASTWARD WILL LEAD TO INCREASED
INSTABILITY THIS AFTERNOON. STRONG TO SEVERE STORMS ARE POSSIBLE
THROUGH THE EARLY EVENING HOURS. THE MAIN THREATS WITH ANY SEVERE
STORMS WILL BE DAMAGING WINDS AND LARGE HAIL. THESE SHOULD WEAKEN
AFTER SUNSET. COVERAGE OF SHOWERS WILL DECREASE THROUGH THE NIGHT
WITH THE BEST CHANCE FOR SHOWERS BY TOMORROW MORNING ACROSS FAR
NORTHERN PORTIONS OF THE CWA.

LOW STRATUS WILL BUILD BACK DOWN OVERNIGHT WITH CONDITIONS TOMORROW
LIKELY SIMILAR TO THIS MORNING. A FEW AREAS COULD SEE SOME PATCHY
FOG BY SUNRISE TOMORROW MORNING. AM NOT SURE OF THE COVERAGE OF
DENSE FOG AT THIS TIME SO WILL LET LATER SHIFTS EVALUATE THIS.
TOMORROW WILL BE ANOTHER CLOUDY AND COOL DAY FOR MOST OF THE AREA.
THERE WILL BE A CHANCE FOR SHOWERS AND DRIZZLE THROUGH THE DAY
TOMORROW...MAINLY ACROSS THE NORTHERN HALF OF THE FORECAST AREA.
TEMPS WILL BE MUCH COOLER THAN NORMAL WITH HIGHS REACHING ONLY INTO
THE LOWER TO MID 60S.

.LONG TERM (TUESDAY NIGHT - MONDAY)...

A RATHER AMPLIFIED BLOCKY MID-LEVEL FLOW PATTERN WILL BE THE RULE
DURING THE EXTENDED PERIOD OF FCST. AS ONE UPPER LOW FINALLY DEPARTS
THE OH VALLEY ON WED...AN UPPER RIDGE WILL BUILD IN...ONLY TO BE
REPLACED BY ANOTHER UPPER LOW FCST TO PROGRESS ACROSS THE CENTRAL
U.S. THU-FRI AND ACROSS THE GREAT LAKES SAT. THERE ARE SOME TIMING
DIFFERENCES IN THE MEDIUM RANGE GUIDANCE...BUT THE OVERALL SYNOPTIC
PATTERN IS SIMILAR.

IN THE DAY TO DAY WEATHER...DESPITE THE UPPER LOW PULLING AWAY ON
WED...TROFINESS ALOFT IS PROGGED TO STILL LINGER ACROSS OUR AREA
WHICH SHOULD KEEP LOW CLOUDS OVER MUCH OF OUR REGION...ESPECIALLY
ERN AREAS. WITH A NW SFC WIND AND LOW CLOUDS...TEMPS AGAIN WILL BE
COOL...ONLY 60-65 FOR MAXS OVER NRN AND ERN AREAS...WITH MID TO UPR
60S WRN AREAS. THIS WOULD BE ABOUT 10 DEGREES BELOW NORMAL. THERE
SHOULD ALSO BE LINGERING SCT LIGHT RAIN SHOWERS OR DRIZZLE TUE NIGHT
AND WED MORNING ACROSS NRN AND ERN AREAS.

PARTIAL CLEARING AND DRY WEATHER WILL OCCUR WED NIGHT INTO THU...BUT
THIS WILL BE SHORT-LIVED AS NEXT SYS APPROACHES OUR AREA.
OPERATIONAL GFS IS FASTEST IN BRINGING IN MOISTURE THU AFTERNOON
ALTHOUGH ITS EVOLUTION APPEARS A BIT SUSPECT. 12Z ECMWF IS A BIT
SLOWER AS IS CANADIAN GEM. INITIAL AXIS OF MOISTURE MAY ALSO TEND TO
DISSIPATE AS IT ENCOUNTERS STG UPPER RIDGE OVER OUR AREA. AS A
RESULT...WILL KEEP A CHANCE OF SHOWERS/TSTMS CONFINED TO THE WRN
PARTS OF OUR FCST AREA THU AFTERNOON. LOW-LEVEL WARMING SHOULD BOOST
MAX TEMPS THU INTO LOWER-MID 70S.

FOR THU NIGHT AND ESPECIALLY FRI...BETTER FORCING AND LOW-LEVEL
MOISTURE ADVECTION WILL COMBINE WITH A DESTABILIZING AIR MASS TO
PRODUCE A MUCH BETTER CHANCE OF SHOWERS/TSTMS. WILL UP POPS INTO
LIKELY CATEGORY FOR FRI AS ALL OPERATIONAL MODELS AND GFS ENSEMBLES
ARE SUPPORTIVE. LOCALLY HEAVY RAINFALL IS LIKELY.

SCT PRECIP SHOULD LINGER FRI NIGHT AND PERHAPS INTO SAT MORNING
BEFORE DRY WEATHER RETURNS AS NEXT UPPER RIDGE BEGINS BUILDING TO
OUR WEST. THIS WILL BE THE START OF A MAJOR WARM-UP WITH HIGHS
GENERALLY IN THE LOWER 80S SAT AND MID-UPPER 80S SUN AND MON...AND
BEYOND.

&&

.AVIATION (18Z TAF ISSUANCE)...

THE CHALLENGE FOR THE FIRST HALF OF THE TAF PERIOD WILL BE THE
DEVELOPMENT OF PRECIPITATION AND THUNDERSTORMS AS WELL AS WHETHER
CIGS WILL LIFT AT SDF AND LEX. AN UPPER LEVEL LOW WILL SWING ACROSS
THE REGION THIS AFTERNOON AND EVENING SPARKING SHOWERS AND
THUNDERSTORMS. THESE SHOULD MAINLY AFFECT BWG. HOWEVER WILL CARRY A
CB GROUP AT SDF AND LEX AS STORMS MAY BE ABLE TO FIRE THAT FAR NORTH
ESPECIALLY IF SOME OF THE LOW CLOUDS CAN BREAK UP. CIGS AT SDF AND
LEX WILL LIFT A BIT THIS AFTERNOON WITH HEATING AND MAY BECOME
VFR FOR A FEW HOURS.

AFTER RAINS END THIS EVENING A LOW STRATUS DECK WILL BUILD DOWN
OVERNIGHT. EXPECT CIGS TO AGAIN DROP TO IFR OR LIFR AFTER AROUND
06Z. WITH THIS VIS WILL DROP AS WELL. WILL KEEP THE VSBYS IN THE
MVFR RANGE FOR THIS TAF PACKAGE. HOWEVER...CONDITIONS MAY
DETERIORATE TOWARD SUNRISE AS THEY DID THIS MORNING.

&&

.LMK WATCHES/WARNINGS/ADVISORIES...
KY...NONE.
IN...NONE.
&&

SHORT TERM........EES
LONG TERM.........TWF
AVIATION..........EES

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