National Weather Service Weather Forecast Office

Area Forecast Discussion

931
FXUS64 KMRX 220740
AFDMRX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
340 AM EDT WED MAY 22 2013

.SHORT TERM (TODAY AND TONIGHT)...MORE CONVECTION EXPECTED TODAY
WITH PLENTY OF SHORT WAVE ENERGY ROTATING THROUGH THE MEAN UPPER
LEVEL TROUGH ACROSS MID AMERICA. WITH SOME HEATING AHEAD OF THE MAIN
FEATURE...CURRENTLY BUILDING NORTHEAST THROUGH WEST TENNESSEE AND
NORTHERN MISSISSIPPI...MODELS PROG RATHER DECENT INSTABILITY WITH
CAPES BUMPING UP TO AROUND 2000 J/KG OR HIGHER AND LIFTED INDICES AS
HIGH AS -8 BY EARLY AFTERNOON. BULK SHEAR NOT QUITE AS IMPRESSIVE
BUT STILL AROUND 30 TO 35 KTS MUCH OF THE FORECAST AREA WITH VALUES
APPROACHING 40 KTS ON THE PLATEAU DURING THE AFTERNOON.
THEREFORE...THERE IS A CHANCE FOR SEVERE CONVECTION MID DAY ON THE
PLATEAU AND POINTS EAST THROUGH THE AFTERNOON. HELICITY VALUES NOT
TERRIBLY IMPRESSIVE SO THREAT FOR TORNADOES WILL BE REDUCED. MODELS
SHOW WEAKENING FRONTAL BOUNDARY BUILDING INTO THE REGION TONIGHT
WITH ADDITIONAL SHORT WAVE ENERGY SWINGING ACROSS THE AREA SO WENT
WITH LIKELY PROBABILITIES FOR ADDITIONAL SHOWERS AND THUNDERSTORMS
MAINLY THROUGH LATE EVENING WITH PERCENTAGES DROPPING OFF AFTER
MIDNIGHT. TRIED TO STAY CLOSE A GUIDANCE BLEND FOR MAX TEMPS DURING
THE SHORT TERM WITH MAV MAXES A BIT TOO WARM MOST AREAS. STAYED
CLOSER TO THE MILDER MIN GUIDANCE TONIGHT.

.LONG TERM...(THURSDAY THROUGH TUESDAY)...UPPER TROUGH WILL MOVE
ACROSS THE OHIO AND TENNESSEE VALLEYS THURSDAY ALONG WITH A
SECONDARY COLD FRONT THAT WILL USHER IN UNSEASONABLY COOL AIR INTO
THE SOUTHERN APPALACHIANS. FORECAST SOUNDINGS SHOW AIR-MASS WILL
ONCE AGAIN BECOME MARGINALLY UNSTABLE WITH CAPES OF 1000-1500 J/KG
DURING THE AFTENOON. BEST INSTABILITY AND MOISTURE WILL BE ACROSS
THE NORTHERN HALF OF THE FORECAST AREA. HAVE INCLUDE LIKELY POPS
NORTH TO LOW-CHANCE SOUTH FOR THURSDAY AFTERNOON.

MODELS SHOW A GOOD DEAL OF COLD-AIR STRATU-CU AND SOME OROGRAPHIC
LIFT FOR THURSDAY NIGHT-ENDING FRIDAY MORNING. WILL MAINTAIN A GOOD
DEAL OF CLOUD-COVER AS WELL SCATTERED SHOWS. BEST CHANCES OVER THE
HIGHER TERRAIN WHERE NORTHWEST FLOW WILL PRODUCE OROGRAPHIC LIFT.

FOR FRIDAY THROUGH THE WEEKEND...UNSEASONABLY COOL AND DRY AIR-MASS
WILL BE RULE ACROSS THE SOUTHERN APPALACHIANS. WOULD NOT BE
SURPRISED TO SEE SOME FROST ACROSS THE NORTHEAST AND MOUNTAINS
FRIDAY NIGHT.

FOR EARLY NEXT WEEK..THE GFS AND ECMWF DIFFER GREATLY ON WHERE AND
EXTENT OF CONVECTION ALONG DEVELOPING WARM FRONTAL BOUNDARY ACROSS
THE OHIO AND TENNESSEE VALLEYS. THE ECMWF IS MUCH MORE AGGRESSIVE.
WILL TREND TOWARD THE GFS..BUT SOME ENSEMBLE MEMBERS DO AGREE WITH
SOME HIGHER POPS.

GENERALLY FOLLOWED THE GFS MOS THROUGH THE FORECAST PERIOD.

&&

.PRELIMINARY POINT TEMPS/POPS...
CHATTANOOGA AIRPORT, TN             84  62  83  57  73 /  70  60  20  20   0
KNOXVILLE MCGHEE TYSON AIRPORT, TN  84  63  80  56  71 /  70  60  50  30  10
OAK RIDGE, TN                       84  62  80  55  72 /  70  60  50  30  10
TRI CITIES AIRPORT, TN              85  61  78  54  67 /  70  60  60  50  10

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.

&&

$$