057 FXUS64 KMEG 171650 AFDMEG AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE MEMPHIS TN 1050 AM CST SUN NOV 17 2013 .UPDATE... UPDATED FOR TORNADO WATCH. && .DISCUSSION... TORNADO WATCH THROUGH 7 PM LST NORTH OF A HARRISBURG ARKANSAS TO HUNTINGDON TENNESSEE LINE. CURRENT DRY LINE ACROSS NORTH CENTRAL ARKANSAS AND SOUTH CENTRAL MISSOURI WILL LIKELY BECOME MORE ATICVE OVER THE NEXT FEW HOURS AS IT PUSHES TOWARDS THE MS RIVER. A FEW OF THESE STORMS MAY BECOME SEVERE WITH DAMAGING WINDS AND A POSSIBLE BRIEF TORNADO. HAVE ADJUSTED THE HWO ACCORDINGLY. JAB && .PREV DISCUSSION... /ISSUED 944 AM CST SUN NOV 17 2013/ UPDATE... UPDATED TO REDUCE MORNING AND AFTERNOON RAIN CHANCES AND TO ADJUST SEVERE WEATHER WORDING. DISCUSSION... FIRST...CONVECTION WITH THE LOW LEVEL INSTABILITY AXIS MOVING FASTER EAST THAN PREVIOUSLY FORECASTED...SO HAVE ADJUSTED RAIN CHANCES ACCORDINGLY FOR THE REMAINDER OF THE MORNING. SECOND...AFTER ANALYSIS OF THE HRRR MODEL...CURRENT SIGNIFICANT MIXING IN THE OBSERVATIONS AHEAD OF THE FRONT IN NORTHWEST ARKANSAS...AND STRONG CAP DEVELOPING AHEAD OF THE FRONT OFF OF 12Z SGF SOUNDING...IT APPEARS THAT THE SEVERE THREAT WILL REMAIN ACROSS THE NORTHERN AND EASTERN COUNTIES FOR THIS AFTERNOON WHERE FRONTAL FORCING WILL BE STRONGEST. HELICITY VALUES NEAR 200 M^2/S^2 SUGGESTS WEAK TORNADOES WILL STILL BE POSSIBLE...THOUGH DAMAGING WIND GUSTS IS STILL THE PRIMARY SEVERE THREAT. HAVE ADJUSTED THE HWO ACCORDINGLY. THIRD...MADE SOME ADJUSTMENTS TO AFTERNOON CLOUD COVER AS MORE BREAKS IN THE LOW LEVEL MOISTURE IS ANTICIPATED...AIDING THE SOUTH TO SOUTHWEST WINDS TO REACH THE WIND ADVISORY CRITERIA EAST OF THE MS RIVER. JAB PREV DISCUSSION... /ISSUED 523 AM CST SUN NOV 17 2013/ DISCUSSION... /ISSUED 458 AM CST SUN NOV 17 2013/ EARLY MORNING GOES WATER IMAGERY SHOWED A DEEP UPPER LEVEL TROF OVER THE CENTRAL AND NORTHERN PLAINS. THIS FEATURE WAS LIFTING EAST AND BECOMING NEGATIVELY TILTED. A 160KT 200MB JET EXTENDED FROM NORTH TX ACROSS THE OZARK PLATEAU...WITH INCREASINGLY DIFFLUENT FLOW EVIDENT DOWNSTREAM OF THE JET CORE. CLOSER TO HOME... THUNDERSTORMS HAD FORMED ON THE SOUTHERN FLANK OF THE JET CORE OVER NORTHERN AR...INTO WEST TN. THIS CONVECTION WAS ROOTED IN AN ELEVATED LAYER...THUS FAR UNABLE TO TAP INTO THE GREATER HELICITY EMBEDDED IN A WEAK NOCTURNAL INVERSION BELOW 925MB. EXPECT THE SHOWERS AND THUNDERSTORMS TO SHIFT EASTWARD THROUGH THE DAY PERHAPS LEAVING AREAS WEST OF THE RIVER FREE OF RAIN LATER THIS MORNING. LATE MORNING AND EARLY AFTERNOON SEVERE CHANCES WILL LIKELY DEPEND ON STORMS BECOMING ROOTED IN THE BOUNDARY LAYER... TAPPING BETTER DIRECTIONAL SHEAR FOR MORE PERSISTENT AND ORGANIZED STORM STRUCTURES. NAM BUFR SOUNDINGS SUGGESTS THIS IS A DISTINCT POSSIBILITY...PARTICULARLY IN THE 18Z TO 21Z TIME FRAME. STORMS WILL HAVE BETTER CHANCES OF BECOMING SURFACED BASED WITH THE ARRIVAL OF A SURFACE COLD FRONT INTO EASTERN AR AROUND 21Z/3PM. STORMS MAY REFORM AS FAR WEST AS JONESBORO...FORMING A LINE THAT WILL PROGRESS SOUTHEAST INTO THE NORTHEAST MS TOWARD 03Z/9 PM. MAIN SEVERE WEATHER THREAT ACROSS THE MIDSOUTH WILL DAMAGING STRAIGHT LINE WINDS. 06Z NAM PROGGED 700MB WEST/SOUTHWEST WINDS OF 60 TO 75 KTS NORTH OF I40 THIS AFTERNOON...PERHAPS LEADING TO SOME BOWING LINE SEGMENTS. THERE WILL BE SUFFICIENT HELICITY AND CAPE FOR SECONDARY TORNADO THREAT DURING THE MID TO LATE AFTERNOON. THE NAM PROGGED 03Z/9PM SURFACE CAPE NEAR 1000 J/KG AND 3KM HELICITY NEAR 300 M2/S2 AT TUPELO. STORMS ALONG THE ADVANCING COLD FRONT WILL HAVE A SHOT AT BECOMING ROOTED IN THE BOUNDARY LAYER. OTHERWISE...HIGHER CINH AND LOWER ELEVATED CAPE SHOULD PREVAIL OVER NORTH MS AS THE NOCTURNAL INVERSION FORMS. TRANQUIL WEATHER WILL PREVAIL MONDAY THROUGH WEDNESDAY...COURTESY OF PACIFIC SURFACE HIGH PRESSURE AND ZONAL FLOW ALOFT. GFS AND ECMWF HAVE COME INTO BETTER AGREEMENT WITH RESPECT TO THE SPLIT UPPER LEVEL FLOW PATTERN LATE IN THE WEEK. BY THURSDAY...MIDLEVEL PACIFIC SUBTROPICAL MOISTURE WILL ACCOMPANY MODEST LOW LEVEL WARM ADVECTION TO SUPPORT A RETURN OF SCATTERED SHOWERS TO THE MIDSOUTH. BY LATE FRIDAY... COLLAPSING HEIGHTS OVER THE GREAT LAKES AND UPPER MIDWEST WILL DRIVE A SURFACE COLD FRONT THE MIDSOUTH LATE FRIDAY. COOLER AND MUCH DRIER MODIFIED ARCTIC AIR WILL SPREAD IN SATURDAY... WITH MIDLEVEL CLOUDS AND MOISTURE LIKEWISE PUSHING OFF TO THE SOUTH...INTO THE NORTHERN GULF OF MEXICO. NEXT WEEKEND/S WEATHER SHOULD BE MORE TYPICAL OF LATE NOVEMBER. PWB && .AVIATION... 12Z TAF SET IFR CIGS STILL HAVE YET TO MATERIALIZE EXCEPT AT KTUP. AREA OF SHRAS WITH EMBEDDED TSRAS CONTINUES TO DEVELOP AND PUSH EAST ACROSS THE CWA. CAN/T RULE OUT CIGS LOWERING TO IFR UNDERNEATH THE HEAVIER SHRAS/TSRAS...OTHERWISE EXPECT MVFR CONDITIONS TO PREVAIL THROUGH MUCH OF THE DAY AGAIN WITH THE POSSIBLE EXCEPTION OF KTUP. WOULD NOT BE SURPRISED TO SEE CONDITIONS RETURN TO VFR AT LOCATIONS SUCH AS KMEM AND KJBR THIS AFTERNOON. REDEVELOPMENT OF TSRAS IS EXPECTED ALONG THE FRONT THIS AFTERNOON INTO THIS EVENING. BEST CHANCES WILL OCCUR AT KMKL AND KTUP BETWEEN 23Z-05Z. SKIES WILL QUICKLY CLEAR BEHIND THE FRONT. STRONG S TO SW WINDS EXPECTED TODAY WITH SUSTAIN SPEEDS OF 10-17 KTS WITH GUSTS BETWEEN 15-28 KTS. WINDS WILL TURN AROUND TO THE NW AND EVENTUALLY N BEHIND THE FRONT. SPEEDS WILL DIMINISH TO BETWEEN 5-10 KTS AS WELL DURING THE OVERNIGHT HOURS. KRM && .PRELIMINARY POINT TEMPS/POPS... MEM 78 46 62 40 / 100 20 0 0 MKL 76 41 61 34 / 100 30 0 0 JBR 79 42 60 35 / 60 10 0 0 TUP 76 46 65 37 / 100 40 0 0 && .MEG WATCHES/WARNINGS/ADVISORIES... AR...WIND ADVISORY UNTIL 4 PM CST THIS AFTERNOON FOR CLAY-CRAIGHEAD- CRITTENDEN-CROSS-GREENE-LAWRENCE-LEE AR-MISSISSIPPI- PHILLIPS-POINSETT-RANDOLPH-ST. FRANCIS. MO...WIND ADVISORY UNTIL 4 PM CST THIS AFTERNOON FOR DUNKLIN-PEMISCOT. MS...WIND ADVISORY UNTIL 4 PM CST THIS AFTERNOON FOR ALCORN-BENTON MS- CALHOUN-COAHOMA-DESOTO-LAFAYETTE-MARSHALL-PANOLA-PONTOTOC- QUITMAN-TALLAHATCHIE-TATE-TIPPAH-TUNICA-UNION-YALOBUSHA. TN...WIND ADVISORY UNTIL 4 PM CST THIS AFTERNOON FOR CARROLL-CHESTER- CROCKETT-DECATUR-DYER-FAYETTE-GIBSON-HARDEMAN-HARDIN- HAYWOOD-HENDERSON-HENRY-LAKE-LAUDERDALE-MADISON-MCNAIRY- OBION-SHELBY-TIPTON-WEAKLEY. && $$