272
FXUS61 KLWX 042344 AAB
AFDLWX
AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
744 PM EDT SAT JUL 4 2009
SYNOPSIS
AN AREA OF LOW PRESSURE WILL PASS JUST SOUTH OF THE AREA SUNDAY
BRINGING GOOD CHANCES FOR SHOWERS. THE COLD FRONT ASSOCIATED WITH
THIS LOW WILL STALL OUT TO OUR SOUTH EARLY NEXT WEEK WITH A WEAK
COLD FRONT CROSSING THE AREA TUESDAY. HIGH PRESSURE WILL BUILD IN
TOWARDS THE MIDDLE OF THE WEEK.
NEAR TERM /UNTIL 6 AM SUNDAY MORNING/
THICK CI DECK SPREADING OVER THE RGN HAS SUPPRESSED BNDRY LYR
CNVCTN...AND CU FIELD HAS VIRTUALLY DISSIPATED. SUBSIDENCE
INVERSION NOTED ON MRNG RAOB ALSO LMTD VERTICAL DVLPMT OF ANY
CNVCTV CELLS...AND THUS PCPN DOES NOT APPEAR IMMINENT.
HAVE UPDATED FCST TO RMV POPS THRU EARLY PORTIONS OF FCST PD. WILL
SPREAD LOW POPS INTO WRN ZONES AFTER 7 PM...AND SPREAD SAME EWD
THRU LATE EVE AS PCPN SHIELD ENTERING WRN WV MOVES EWD. ATTM WILL
RETAIN ISOLD-SCT POPS LATE TNGT. PREV DISCUSSION FOLLOWS...
CURRENT ANALYSIS SHOWS A SURFACE TROUGH OVER THE REGION. AN UPPER-
LEVEL DISTURBANCE IS MOVING THROUGH THE OHIO VALLEY WHILE A WAVE
OF LOW PRESSURE AT THE SURFACE MOVES INTO THE MIDWEST.
THE COMBINATION OF THE PRESSURE TROUGH AND LIMITED INSTABILITY HAS
ALLOWED FOR A SCT-BKN CU DECK TO DEVELOP THIS AFTERNOON. ALTHOUGH AN
ISOLATED SHOWER CANNOT BE RULED OUT LATER THIS AFTERNOON AND EARLY
EVENING...MOST PLACES WILL END UP DRY DUE TO A STRONG MID-LEVEL CAP.
HIGH AND MID-LEVEL CLOUDS AHEAD OF THE UPPER-LEVEL DISTURBANCE
WILL INCREASE FROM WEST TO EAST INTO THIS EVENING. HOWEVER...MOST
PRECIPITATION WILL REMAIN OFF TO OUR SOUTH AND WEST CLOSER TO THE
SURFACE FEATURE. THE SURFACE LOW WILL TRACK INTO THE TENNESSEE
VALLEY OVERNIGHT. A BAND OF RAIN TO THE NORTH OF THIS LOW WILL
APPROACH THE REGION DURING THE OVERNIGHT HOURS. THE BEST CHANCE
FOR RAIN WILL BE ACROSS THE SOUTHWESTERN PORTION OF THE CWA
TOWARDS SUNDAY MORNING.
SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/
LOPRES...SFC AND H8...TO TRACK S OF CWFA SUN. GDNC HAS PULLED BACK
ON FWD SPD A PINCH...AND TRACK HAS MIGRATED A BIT FURTHER S THAN
PRVS RUNS...AS IT/S HAVING DIFFICULT RESOLVING EXACTLY WHERE THESE
FEATURES WL BE CENTERED. INIT PCPN WL BE FORCED BY H8 CNVGNC/LIFT
INVOF WMFNT/ISENT LIFT. THERE SHUD BE A FAIRLY SHARP NLY GRADIENT...
WHICH LKLY WL SLICE THRU CWFA. SUBTLE DIFFS EXIST AMONGST GDNC
RUNS...ALTHO THEY/RE QUITE SIMLR ON THE SYNOPTIC SCALE. WHILE GFS
MAY HV A SLGTLY BETTER INITIALIZATION...ITS QPF FIELD EXHIBITING
TYPICAL BIAS OF BEING TOO WIDESPREAD. SO...MET MOS LOOKS A LTL
BETTER ALBEIT FOR THE WRONG REASONS.
AT THIS STAGE...DO NOT WISH TO OUTRIGHT RMV POPS FOR ANY PART OF
CWFA ON SUN...ALTHO IT MAY END UP BEING A CLDY BUT DRY DAY ACRS NRN
MD/ERN WVA PNHNDL. INSTEAD...WL BLEND PERFERRED SOLN W/ PRVS FCST...
WHICH STILL PAINTS LKLY POPS ACRS CNTRL VA AND SRN MD...NEARER TO
THE TRACK OF SFC AND H8 LOWS. EVEN IF ENTIRE COLUMN NOT SATURATED...
CLDY SKIES WL LIMIT POTL INSTBY... WHICH WL BE ENHANCED BY WARM MID
LVLS. SO...WX GRIDS WL CARRY JUST SHRA. WL ALSO CARRY PRVS THOUGHT
OF MAXT STAYING WELL BLO AVG.
SYSTEM WL TRACK OFFSHR SUN NGT. HIEST POPS WL BE EZF-NHK SEWD...
INVOF SFC LOW. AS COOLER/DRIER AIR ADVECT IN FM THE N...BACK EDGE WL
WORK ACRS CWFA. IF PCPN CVRG MORE WIDESPREAD...FCST MAY END UP A BIT
TOO QUICK/OPTIMISTIC.
SFC-H8 HIPRES RDG WL WORK ACRS CWFA MON AS ZONE OF LOW MEAN LYR RH
CENTERS ACRS CWFA. THAT WL TRANSLATE TO A MOSUN/DRY DAY. MAXT WL BE
QUITE A BIT HIER THAN SUN IN SPITE OF CAA...OWING MAINLY TO INCRSD
INSOLATION. DEWPTS WL BE DOWN TO THE MID 50S.
LONG TERM /TUESDAY THROUGH SATURDAY/
STILL AN ACTV NLY STREAM ACRS CONUS/CNDN BRDR...W/ S/WV ENERGY
DROPPING SWD RELOADING TROF AXIS ACRS NEW ENGLND TUE...AND AGN
WED-WED NGT. HWVR...GDNC AT ODDS IN TERMS OF INTENSITY OF PVA...AND
SUBSEQUENTLY SRN EXTENT OF WK CDFNT DROPPING TWD MID ATLC. FORCING
WUD BE SUFFICIENT FOR DIUNRALLY DRIVEN POPS NEAR CLIMO MOST OF CWFA
TUE...W/ LOW END CHC POPS MNTND RIGHT ALONG MD/PA BRDR. BY WED...
CENTER OF H5 LOW SHUD BE FAR ENUF OFF THE NEW ENGLAND COAST SO
THAT WED WL BE A MOSUN-DRY DAY. TUE TEMPS WL BE RIGHT ARND CLIMO...
AND THEN DROP A CPL WED DUE TO CAA/NWLY FLOW.
MORE SUMMERLIKE WX WL RTN DURING THE 2ND HALF OF THE WK...AS BROAD
H5 RDG AXIS BLDS EWD. HGTS RISE THU-FRI AS FLOW BECOMES SLY ARND SFC
HIPRES. SUBSEQUENT RISES WL BE SEEN IN TEMPS AND DEWPTS...AND AS
SUCH NEAR CLIMO THUNDER CHCS CAN/T BE RULED OUT. AT THAT LVL...POPS
STILL WON/T APPEAR IN TXT FCSTS. MAXT WL APPROACH 90F BY FRI.
BY SAT...THE THREAT OF A PRE-FRNTL TROF WL BE ABLE TO FOCUS INCR
INSTBY LVLS...AND CHC TSRA WL APPEAR IN THE GRIDS/DATABASE. SFC
HIPRES OFF SE CONUS CST WL ADVECT PLENTY OF WARM/HUMID AIR INTO
RGN...AND MAXT POTLLY CUD TOP 90. WL STILL NEED TO SEE HOW FEATURES
WL INTERACT...NOT TO MNTN THAT GFS/ECMWF HNDLG APPCHG CDFNT AND ITS
S/WV ENERGY AT DIFFERING STRENGTHS.
AVIATION /00Z SUNDAY THROUGH THURSDAY/
SHIELD OF PCPN SPREADING SLOWLY EWD ACRS WV. ATTM...MAINLY MID-
AND UPR-LVL CLDS AT ALL TERMINALS. XPC THIS TREND TO CONT THRU
MUCH OF THIS EVE...WITH PSBLTY OF SHRA DVLPG LATE AT KCHO. SUBVFR
CIGS/VSBYS ARE POSSIBLE IN THE RAIN. ELSEWHERE...CONFIDENCE RMNS
LOW FOR DVLPMT OF PCPN TNGT.
PCPN XPCD TO SPREAD ACRS RGN SUN...WITH NRN GRADIENT STRADDLING
MID-ATLC RGN. THUS...CONFIDENCE HIGHEST IN CONTD PCPN AT KCHO WITH
DECRG CONFIDENCE WITH NWD EXTENT. WILL CARRY VCSH MOST TERMINALS
XCPT AT KCHO. SUB-VFR CIGS/VSBYS XPCD IN SHRA.
PREV EXTENDED DISCUSSION FOLLOWS...
IMPVG CIGS/VSBYS SUN NGT. THERE IS A SCHC AT DIURNALLY
DRIVEN SHRA/TSRA BY MIDWEEK...BUT CHC AT HITTING ANY ONE AIRFIELD
SLIM. OTRW...NO FLGT RESTRICTIONS ANTICIPATED THRU REST OF WK.
MARINE
HAVE UPDATED FCST TO RMV SMALL CRAFT ADZY GIVEN SUBSIDING WIND
GUSTS. WINDS XPCD TO RMN AOB 10 KT THRU TNGT. PREV DISCUSSION
FOLLOWS...
LOPRES WL TRACK S OF WATERS SUN-SUN NGT...SPREADING SHRA ACRS
WATERS. SHUD BE A FAIRLY SHARP CUTOFF ON N SIDE OF SYSTM...WHICH
MAY BISECT BAY. REGARDLESS...NO THUNDER OR HIGH WNDS XPCTD.
TRANQUIL CONDS MON-MON NGT...THEN A CPL S/WV ROUND H5 LOW OVR NEW
ENGLND TUE-WED. RSLT WUD BE FOR INCRSD WNDS...SPCLY IN WAKE OF S/WV
TUE. SCA PSBL.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.
UPDATE...KRAMAR
PREV DISCUSSION...LASORSA/HTS
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