Severe Thunderstorm Warning 135, NWS Jackson, KY

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JACKSON KY
305 PM EDT FRI JUL 28 2000

BIGGEST CONCERN THIS GO AROUND IS THE POTENTIAL FOR HEAVY CONVECTIVE
RAINS...ESPECIALLY ON SATURDAY.

IN THE NEARER TERM CONVECTION HAS DEVELOPED ACROSS THE AREA THIS
AFTERNOON WITH SUPPORT FROM NOSE OF UPPER JET AND OUTFLOW FROM MCS
WHICH DIED OVER CENTRAL KY. REMAINING DAYTIME CONVECTION MAY NEED TO
BE DEALT WITH IN THE START OF THE FIRST PERIOD.

BEYOND THE CURRENT SITUATION...THE THERE ARE DIFFERENCES AMONG THE
MODELS...ESPECIALLY ON SATURDAY. ALL MODELS ARE TRENDING FURTHER
NORTH WITH THE HEAVY RAINFALL POTENTIAL...WITH THE NGM FURTHER NORTH
THAN THE ETA OR AVN. EVEN THOUGH THE TREND IS FURTHER NORTH...PREFER
TO STICK WITH THE ETA SINCE THE AVN IS IN MUCH BETTER AGREEMENT WITH
IT.

FOR THE SPECIFICS...ANY REMAINING CONVECTION SHOULD DIE OFF FOR THE
MOST PART THIS EVENING. TOWARD MORNING THERE IS A RETURN OF UPWARD
VERTICAL MOTION DUE TO DIVERGENCE ON THE RIGHT SIDE OF AN
ANTICYCLONICALLY CURVED UPPER JET. THE GREATEST VERTICAL MOTION IS
CENTERED JUST TO OUR NORTH NEAR THE OHIO RIVER AT 12Z. SO THERE IS
AN INCREASED CHANCE OF THUNDERSTORMS AGAIN LATE TONIGHT...
ESPECIALLY NORTH.

ON THURSDAY...THE UPPER SUPPORT JUST DESCRIBED CONTINUES. MEANWHILE
PRECIPITABLE WATER CLIMBS TO 1.5 TO 2 INCHES. IN ADDITION BOTH THE
ETA AND AVN SHOW A MID LEVEL SPEED MAX MOVING OVER THE NORTHWESTERN
PART OF THE AREA DURING THE AFTERNOON...WITH 700 MB WINDS OF 40 TO
45 KNOTS. THIS WOULD SUPPORT SEVERE POTENTIAL ALONG WITH THE HEAVY
RAIN POTENTIAL. HOWEVER...ONE QUESTION MARK INVOLVED FOR THE SEVERE
THREAT IS THE DEGREE OF INSTABILITY. CLOUDS AND ONGOING PRECIP COULD
LIMIT HEATING.

SUPPORT IS STILL PRESENT INTO SATURDAY NIGHT...WITH INCREASED UPWARD
MOTION THEN AGAIN BY DAWN. ON SUNDAY WE ARE STILL IN THE WARM SECTOR
OF THE STORM SYSTEM ALL DAY...WITH THE SURFACE FRONT STILL OFF TO
OUR NORTHWEST NEAR THE KY/IN BORDER. EVEN WITHOUT AS STRONG OF
SUPPORT LATER IN THE DAY...THINK THAT CONVECTION WILL AGAIN DEVELOP
WITH HEATING.

WITH ALL THIS SAID...WILL GO ABOVE NGM MOS POPS MOST PERIODS. WILL
GO HIGHEST ON SATURDAY IN THE NORTH WITH A 70 PERCENT POP AND MENTION
OF POSSIBLE HEAVY RAINFALL. WILL HOLD OFF ON ANY FLASH FLOOD WATCH
AT THIS TIME. HEAVIEST RAIN IS NOT LIKELY UNTIL THE SECOND
PERIOD...FLASH FLOOD GUIDANCE VALUES ARE RUNNING FAIRLY HIGH...AND
THE AREA MOST LIKELY TO SEE HEAVY RAIN ON SATURDAY HAS MISSED MOST
OF THE STORMS TODAY. MIDNIGHT SHIFT MAY NEED TO CONSIDER A FLASH
FLOOD WATCH IF 00Z MODELS SHOW GOOD SUPPORT FOR HEAVY RAIN.

FOR TEMPS...THINK THAT NGM MOS IS TOO WARM FOR HIGHS EACH DAY.
CLOUDS AND PRECIP SHOULD KEEP IT COOLER. LOWS SEEM REASONABLE.

EXTENDED FORECAST...
AGREEMENT AMONG MODELS THAT THE CLOSED UPPER LOW CURRENTLY OVER OVER
THE GREAT LAKES WILL WEAKEN AND DROP SOUTHWEST EARLY IN THE NEW
WEEK. THIS PLACES US UNDER A MOIST SOUTHWEST FLOW STRETCHING ALL THE
WAY TO THE LOWER MS VALLEY OR NORTHERN GULF OF MEXICO. NO
SIGNIFICANT CHANGE IN SURFACE AIR MASS IS EXPECTED...SO THE CHANCE
OF SHOWERS/THUNDERSTORMS WILL PERSIST EACH DAY...WITH SEASONABLY
WARM TEMPERATURES.

.JKL...NONE.

HAL