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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS61 KILN 210718
AFDILN

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE WILMINGTON OH
318 AM EDT TUE MAY 21 2013

.SYNOPSIS...
-- Changed Discussion --
A WARM AND HUMID AIR MASS WILL REMAIN IN PLACE THROUGH WEDNESDAY.
OCCASIONAL PERIODS OF SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE.
A COLD FRONT WILL MOVE THROUGH THE REGION ON THURSDAY...BEFORE
COOLER AIR SETTLES IN ON FRIDAY AND INTO THE WEEKEND.
-- End Changed Discussion --

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
SIGNIFICANT CHANGES WERE MADE TO THE FORECAST IN THE NEAR
TERM...AS A RAGGED MCS CURRENTLY MOVING ACROSS CENTRAL INDIANA IS
NOW EXPECTED TO IMPACT THE WESTERN PORTIONS OF THE ILN FORECAST
AREA. ALL MODELS...INCLUDING CONVECTIVE ALLOWING MODELS...FORECAST
A GRADUAL WEAKENING OF THIS FEATURE AS IT CONTINUES MOVING TO THE
EAST. MESOSCALE ANALYSIS SHOWS THAT THE NEAR-SURFACE THERMODYNAMIC
AIR MASS IS CURRENTLY SOMEWHAT FAVORABLE OVER INDIANA...WITH
MOIST-ADIABATIC PROFILES NEAR THE SURFACE...AND ELEVATED CAPE OF
AT LEAST A FEW HUNDRED J/KG ABOVE IT. THE ENVIRONMENT WILL BECOME
LESS FAVORABLE FOR THE SUSTAINING OF THIS CONVECTION...WITH MUCH
MORE INHIBITION (UP TO 100-150 J/KG) AND A NEAR-SURFACE INVERSION
OVER THE ILN CWA. HOWEVER...AS SOME ELEVATED INSTABILITY WILL
REMAIN IN PLACE...THE CONVECTION IS NOT EXPECTED TO DISSIPATE
ENTIRELY. THERE IS SOME SHEAR IN PLACE IN THE LOW LEVELS (30-40
KNOTS FROM 0-1KM...WHICH IS SOMEWHAT IMPRESSIVE). WINDS AHEAD OF
THE LINE ARE GENERALLY OUT OF THE SOUTH...AND WINDS AT 925MB ARE
OUT OF THE SOUTHWEST AND UP TO 40 KNOTS. THIS HAS LED TO SOME
ISOLATED POCKETS OF STRONGER WINDS ON THE LINE...AND EVEN A FEW
WEAK CIRCULATIONS. HOWEVER...IT IS UNLIKELY THAT THIS SHEAR WILL
BE REALIZED OVER THE ILN CWA...GIVEN THE MORE HOSTILE
THERMODYNAMIC ENVIRONMENT. THUS...THE SEVERE THREAT THIS MORNING
APPEARS LOW...THOUGH SOME GUSTY WINDS WILL CERTAINLY BE POSSIBLE.

ADDITIONAL DISCUSSION ON THE POTENTIAL FOR AFTERNOON STORMS WILL
BE ISSUED SHORTLY.
-- End Changed Discussion --

&&

.SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/...
-- Changed Discussion --
A FULL SHORT TERM FORECAST UPDATE WILL BE ISSUED SHORTLY.

PREVIOUS DISCUSSION FOLLOWS >
OVERALL PATTERN FOR THE SHORT TERM TIME PERIOD IS FOR A LOW OVER
THE NORTHERN PLAINS TO SLOWLY SHEAR EASTWARD TUESDAY THROUGH
TUESDAY NIGHT...BEFORE GETTING ABSORBED INTO A DEEPENING TROUGH
ACROSS THE GREAT LAKES. AS THIS SYSTEM BEGINS TO GET SHEARED INTO
SOUTHWESTERLY FLOW ACROSS OUR REGION...TIMING OF INDIVIDUAL PIECES
OF ENERGY AND ASSOCIATED CONVECTION BECOMES UNCERTAIN.

BASED ON THE NEAR TERM FORECAST DECAYING CONVECTION ACROSS OUR
ZONES TUESDAY MORNING...THERE WOULD BE A PORTION OF THE DAY
TUESDAY WHERE THE BOUNDARY LAYER WILL BE WORKED OVER. THEREFORE
THERE MAY BE SEVERAL HOURS DURING THE FIRST PART OF THE DAY
TUESDAY WHERE LITTLE TO NO CONVECTION IS OCCURRING IN OUR FORECAST
AREA. THIS SOLUTION IS BEING INDICATED BY THE MAJORITY OF COMPUTER
MODELS. BY LATE TUESDAY AFTERNOON INSTABILITY WOULD HAVE INCREASED
AND SUFFICIENT RECOVERY OF THE BOUNDARY LAYER IS EXPECTED TO HAVE
OCCURRED. FORCING ASSOCIATED WITH ANY SHORTWAVE ENERGY EJECTING
EAST FROM THE LOW OVER THE PLAINS WILL HELP TO TRIGGER CONVECTIVE
DEVELOP LATE TUESDAY AFTERNOON. ALTHOUGH EXACT TIMING AND
PLACEMENT OF THE CONVECTION IS HIGHLY UNCERTAIN AT THIS TIME...UP
TO 45 KT OF 0-6 KM SHEAR MAY BE PRESENT ACROSS THE NORTHWESTERN
HALF OF OUR FORECAST AREA. THEREFORE...IF CONVECTION DOES GET GOING
TUESDAY AFTERNOON AND EVENING ACROSS OUR NORTHWEST...THERE WILL
BE THE POTENTIAL FOR SOME OF THESE STORMS TO BECOME SEVERE. THE
MAIN THREAT FROM THESE STORMS WOULD BE DAMAGING WIND AND ISOLATED
LARGE HAIL. THIS THREAT IS BEING HIGHLIGHTED IN THE HWO.

CHANCES FOR SHOWER AND THUNDERSTORMS WILL CONTINUE INTO TUESDAY
NIGHT AND INTO THE DAY ON WEDNESDAY AS THE LOW PROGRESSES NEARER
TO OUR AREA. SHEAR AND INSTABILITY WILL DECREASE ON TUESDAY NIGHT
AND WEDNESDAY....WHICH SHOULD LESSEN THE OVERALL SEVERE THREAT.
HOWEVER...ON WEDNESDAY THERE MAY STILL BE SUFFICIENT INSTABILITY
TO COMBINE WITH ABOUT 35 KT OF 0-6 KM SHEAR TO PRODUCE ISOLATED
CHANCES FOR DAMAGING WINDS AND LARGE HAIL SHOULD STORMS GET
ORGANIZED.

BY WEDNESDAY EVENING THE BEST CHANCES FOR PRECIPITATION WILL SHIFT
EAST OF OUR AREA ALONG WITH THE BEST FORCING.

TEMPERATURES WILL BE ON A DOWNWARD TREND THROUGHOUT THE SHORT TERM
TIME PERIOD. ON TUESDAY EXPECT UPPER 80S ACROSS THE EAST TO LOWER
80S ACROSS THE WEST. BY WEDNESDAY...CLOUD COVER AND PRECIPITATION
WILL KEEP TEMPERATURES LOWER THAN TUESDAY. OVERNIGHT LOWS WILL
CONTINUE TO BE MILD BOTH TUESDAY AND WEDNESDAY NIGHT AS WE REMAIN
IN THIS WARM AND HUMID AIRMASS.
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
THE UPPER LEVEL TROUGH WILL PIVOT EAST ACROSS OUR AREA THROUGH THE
DAY ON THURSDAY. THIS COMBINED WITH SOME LINGERING
INSTABILITIES...WILL KEEP THE THREAT OF SHOWERS AND A FEW
THUNDERSTORMS GOING THROUGH THE AFTERNOON. AS THE TROUGH BEGINS TO
SHIFT EAST AND WE LOSE THE INSTABILITY...PCPN SHOULD TAPER OFF TO A
FEW SHOWERS THURSDAY NIGHT. COOLER AIR WILL BEGIN FILTERING INTO THE
AREA THROUGH THE DAY ON THURSDAY WITH HIGHS RANGING FROM THE UPPER
60S NORTHWEST TO LOW TO MID 70S SOUTHEAST.

SURFACE HIGH PRESSURE WILL BUILD DOWN FROM THE NORTH AND INTO OUR
AREA FRIDAY INTO SATURDAY...KEEPING A SEASONABLY COOL AIRMASS IN
PLACE THROUGH THE START OF THE WEEKEND. HIGHS ON FRIDAY WILL BE IN
THE MID TO UPPER 60S AND WITH THE SURFACE HIGH OVERHEAD...LOWS
SATURDAY MORNING WILL DIP INTO THE LOW TO MID 40S. THE SURFACE HIGH
WILL BEGIN TO SHIFT OFF TO THE EAST THROUGH THE REMAINDER OF THE
WEEKEND AS MID LEVEL RIDGING BEGINS TO ESTABLISH ITSELF ALOFT. THIS
WILL RESULT IN A GRADUAL RETURN TO WARMER TEMPERATURES THROUGH THE
REST OF THE HOLIDAY WEEKEND. MODELS ARE STILL TRYING TO SUGGEST THE
POSSIBILITY OF SOME ENERGY DROPPING DOWN FROM THE NORTHWEST LATE IN
THE WEEKEND. HOWEVER...TIMING AND PLACEMENT ARE HIGHLY VARIABLE SO
WILL MAINTAIN A DRY FORECAST AT THIS POINT.

&&

.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
LARGE SCALE UPPER LEVEL LOW CENTERED OVER THE NORTHERN PLAINS WILL
MAKE LITTLE EASTWARD PROGRESSION OVER THE NEXT 24 HOURS. REGION
WILL BE LOCATED IN A WARM...MOIST SOUTH/SOUTHWEST FLOW AT THE SFC
AND ALOFT.

FIRST ITEM OF CONCERN WILL BE THE QLCS TO OUR WEST ACROSS WESTERN
INDIANA AND EASTERN ILLINOIS. SOME MODELS WEAKEN THIS FEATURE TO
THE POINT THAT IT IS GONE BY THE TIME IT GETS NEAR OUR WESTERN TAF
SITES BETWEEN 09Z AND 12Z. OTHER MODELS TRY TO HOLD IT TOGETHER
INTO OUR WESTERN TAF SITES BEFORE COMPLETELY WEAKENING IT. AT THIS
TIME...HAVE NOT PLACED ANY CONVECTION IN THE TAFS AND WILL MONITOR
LINE/TRENDS AND UPDATE/AMEND ACCORDINGLY IF NECESSARY.

OTHERWISE...THE TIMING OF CONVECTION FOR TODAY IS FAIRLY MURKY AS
MODELS ARE NOT HANDLING MESOSCALE FEATURES AT THE SURFACE AND
ALOFT WELL. KEPT PREVIOUS FORECAST TREND TO ALLOW FOR SHOWERS AND
THUNDERSTORMS DURING THE PEAK HEATING OF THE DAY FOLLOWED BY A
LULL IN ACTIVITY THIS EVENING. FOR LATE TONIGHT INTO WEDNESDAY...A
MORE BONAFIDE DISTURBANCE AND DEVELOPING LOW LEVEL JET WILL LIKELY
BRING WIDESPREAD PRECIPITATION TO OUR AREA...BUT EXACT TIMING IS
STILL IN QUESTION AT THIS POINT. WINDS TODAY WILL BE LOCALLY GUSTY
FROM THE SOUTHWEST TO 25 KNOTS WITH GUSTINESS SUBSIDING TOWARD
SUNSET.

OUTLOOK...THUNDERSTORMS WILL BE POSSIBLE FROM TUESDAY NIGHT THROUGH
THURSDAY.

&&

.ILN WATCHES/WARNINGS/ADVISORIES...
OH...NONE.
KY...NONE.
IN...NONE.

&&

$$
SYNOPSIS...HATZOS
NEAR TERM...HATZOS
SHORT TERM...HATZOS
LONG TERM...JGL
AVIATION...HICKMAN