034 FXUS61 KLWX 220157 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 957 PM EDT SUN MAR 21 2010 .SYNOPSIS... A POTENT UPPER LOW OVER THE SOUTHERN MISSISSIPPI VALLEY WILL SLOWLY TRACK TOWARD THE TENNESSEE VALLEY THROUGH MONDAY. THE LOW WILL CROSS THE REGION MONDAY NIGHT...AND OFF TO CAPE COD BY TUESDAY. HIGH PRESSURE WILL THEN BUILD IN FOR MID WEEK...AHEAD OF ANOTHER COMPLEX LOW PRESSURE SYSTEM. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... LATEST WV SAT LOOP SHOWS POTENT UPPER LOW PUSHING ACROSS THE SRN MS VLY THIS EVE. AT 01Z...SFC LOPRES IS LOCATED OVER CNTRL TN WITH ASSOCIATED COLD FRONT SITUATED FROM WRN KY TO SEWD INTO THE WEST COAST OF FL. IN ADVANCE OF THE UPPER LOW...AN ORGANIZED LINE OF HEAVY PRECIP AND EMBEDDED CONVECTIVE ELEMENTS CONTINUE TO PUSH NEWD JUST AHEAD OF THE COLD FRONT IN A REGION OF UPPER DIFFLUENCE. ANOTHER AREA OF PRECIP CONTINUE TO STREAM NORTHWARD OVER THE C APPALACHIANS/MID-ATLANTIC REGION IN ASSOCIATED WITH LLVL ISENTROPIC LIFT AND A MID-LVL JET MAX. REGIONAL RADAR SHOWS LIGHT SHOWERS MOVING THRU OUR REGION SO FAR THIS EVE BUT HAS HAD A HARD TIME REACHING THE GROUND THUS FAR WITH DRY AIR IN PLACE /AS CONFIRMED IN THE 00Z IAD RAOB/. THE COLUMN SHOULD QUICKLY SATURATE /AS EVIDENT IN THE 00Z RNK RAOB/ WITH LIGHT SHOWERS LATER THIS EVE ACROSS SWRN PORTIONS OF THE CWA. MAINLY LIGHT SHOWERS AND LOWER CIGS SHOULD GRADUALLY OVERSPREAD THE REST OF THE CWA FROM SW TO NE OVRNGT. WITH INCREASING CLD COVER...TEMPS WILL BE WARMER THAN THE PAST FEW NIGHTS WITH LOWS IN THE MU40S WEST OF THE BLUE RIDGE AND L50S TO THE EAST. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... THE STRONG UPPER LOW WILL MOVE ACROSS THE TN VLY AND TOWARDS THE CNTRL APPALACHIANS BY THE LATE AFTN. THE AFOREMENTIONED BAND OF HEAVY PRECIP AHEAD OF THE COLD FRONT WILL ENTER SWRN PORTIONS OF THE AREA DURING THE MRNG AND SWING THRU THE AREA DURING THE LATE MRNG AND AFTN. 18Z NAM/GFS SOUNDINGS SHOW 50-55 KT OF DEEP-LAYER SHEAR ALONG WITH 200-400 J/KG OF CAPE AHEAD OF THE COLD FRONT/DRY SLOT. INSTABILITY WILL BE MARGINAL ENOUGH TO MENTION CHANCE OF TSTMS. QPFS WILL RANGE FROM A HALF TO ONE INCH ACROSS THE AREA WITH ISOLATED HIGHER AMNTS IN CONVECTIVE BANDS. THE DYNAMICS OF THE SYSTEM WILL BE MOVING THIS ACTIVITY STEADILY ALONG...SO FLASH FLOODING OR HIGH QPF AMOUNTS NOT ANTICIPATED. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... GFS SHOWS SFC LOW OVR PA MON NGT MVG NE AWAY FROM AREA. ENOUGH LEFTOVER MOISTURE TO WARRANT CONT OF POPS INTO THE NGT AND INTO TUE. DRIER AIRMASS EXPECTED WED AND THU. FNT DROPS DOWN INTO THE AREA LATE WEEK WITH ANOTHER CHC FOR SHRA. TEMPS ARE FAIRLY CLOSE TO SEASONAL NORMS THROUGH THE PERIOD. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... MID-LVL CLDS WILL CONTINUE TO MOVE ACROSS THE AREA THIS EVE. MOISTURE WILL STREAM INTO THE REGION TNGT AS A POTENT UPPER-LOW OVER THE SRN MS VLY APPROACHES. PUSHED BACK ONSET OF LOWERING CLDS AND LIGHT RA A FEW HRS FROM PREVIOUS TAFS UNTIL LATE TNGT-ERY MRNG HRS WITH DRY AIR INITIALLY IN PLACE. IFR CIGS-VSBYS EXPECTED A FEW HRS AFTER START OF RA AROUND OR SHORTLY AFTR DAYBREAK. DID NOT HAVE ENOUGH CONFIDENCE TO MENTION A CB GROUP IN THE 00Z TAFS. HOWEVER MAY NEED TO INCLUDE IN NEXT SET OF TAFS IF MODELS CONTINUE TO SUPPORT CONVECTIVE ACTIVITY LATE MON MRNG AND AFTN. SELY WINDS WILL INCREASE DURING THE LATE AFTN MON WITH GUSTS 15-20 KT POSSIBLE. A FROPA AND WINDSHIFT TO THE SW EXPECTED DURING THE EVE MON. && .MARINE... SELY WINDS WILL INCREASE OVERNIGHT SUN INTO MON. SCA CONDITIONS WILL BECOME MORE LIKELY INTO THE DAYTIME HRS MON MORNING...AS A COMPLEX LOW PRESSURE SYSTEM APPROACHES FROM THE SW. THE LOW WILL MOVE OVER THE REGION LATE MON INTO TUE...W/ STEADY RAIN SHOWERS ON MON - MAINLY ENDING BY EARLY TUE. && .TIDES/COASTAL FLOODING... CURRENT WATER LEVELS OVER MANY OF THE TIDAL POTOMAC AND MD CHESAPEAKE BAY SITES BETWEEN 0.5-1.0 FT ABOVE NORMAL. AN APPROACHING LOW PRESSURE SYSTEM FROM THE SOUTHEAST WILL CREATE THE POSSIBILITY FOR AT LEAST MINOR COASTAL FLOODING AT TIMES OF HIGH TIDE ABOUT MON NGT AND TUE. WINDS LATE TONIGHT WILL BACK TOWARD SELY...W/ FAIRLY WEAK AND INTERMITTENT GUSTS - BUT THE EFFECT WILL BE A SLOW AND STEADY CHANNELING OF WATER UP THE BAY/TP. MODEL FORECASTS EXTEND THE HEIGHT DIFFERENCES ABOUT 1.5-2.5 FT ABOVE NORMAL IN SOME AREAS. REGARDLESS OF THE EXACT AMOUNT...THE STEADY SELY FLOW FOR AN EXTENDED PERIOD OF NEARLY A WHOLE DAY SHOULD CREATE A HEIGHTENED AWARENESS ACROSS COASTAL AREAS OF SRN/ERN MD FOR MINOR COASTAL FLOODING. HOWEVER...PHASE OF LUNAR CYCLE BETWEEN NEW AND FULL MOON IS NOT FAVORABLE FOR COASTAL FLOODING. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 9 AM TO 10 PM EDT MONDAY FOR ANZ530>543. && $$ UPDATE...KLEIN PREV DISC...GMS/RDH