Flash Flood Warning 68, NWS Baltimore/Washington

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
339 AM EDT FRI JUL 12 2013

.SYNOPSIS...
A COLD FRONT HAS BECOME STATIONARY ACROSS EASTERN VIRGINIA AND IS
PROVIDING THE FOCUS FOR HEAVY RAINFALL. THIS FRONT WILL REMAIN TO THE
SOUTHEAST OF THE AREA THROUGH SATURDAY. HIGH PRESSURE WILL BUILD
INTO THE REGION NEXT WEEK.
&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
LAST NGT/S HRRR RUNS...NAM/GFS HAD THE SOLN NAILED. SHRA/TSRA FILLED
IN...WITH COPIOUS RAFL ACRS CWFA...SPCLY IN A STRIPE FM CENTRL SHEN
VLY INTO THE WRN BURBS OF DC. THAT ACTIVITY ONGOING ATTM...W/ NMRS
FLOOD CONCERNS. SYNOPICALLY...SVRL FACTORS CONTRIBUTING TO THE
SHRA-- FIRST...HGTS HV BEEN DROPPING AS AN H5 LOW APPROACHES FM THE
GRTLKS. SECONDLY...CWFA W/IN RRQ OF AN UPR JET. ITS ONLY ABT 70
KT...BUT IT/S SUFFICIENT TO SUPPORT LIFT. THIRD...A STALLED CDFNT
WAVERING ALONG THE I-95 CORRIDOR. BELIEVE THAT THERE ARE A CPL WK
IMPULSES GLIDING ALONG THE STALLED SFC BNDRY.

THESE INGREDIENTS WL STILL BE IN PLACE TDA. IN FACT HGTS WL BE QUITE
LOW AS H5 LOW COMES VERY CLOSE TO CWFA. IN ADDITION...ELY H8 WNDS WL
INCREASE...NOT JUST LEADING TO AN OVERRUNNING SITUATION BUT ALSO
PUMPING IN ADDITIONAL ATLC MSTR. PWAT WL BE HOVERING BTWN 1.75-2.00
INCHES FOR MOST OF THE DAY.

THE BIGGEST ADJUSTMENT IN GDNC FM THE 18Z TO 00Z CYCLES IS WHETHER
THERE WL BE A PRE-DAWN BREAK IN THE ACTION. NOT ONLY THE 00Z GDNC
CYCLE...BUT ALSO THE LTST HRRR AND RADAR TRENDS SUGGEST THAT WON/T
BE HAPPENING. FURTHER...THERE/S A STRONGER SIGNAL THAT THERE WL BE A
WK LOW MVG UP THE BAY TWD MIDDAY. THEREFORE...CANT DISCERN A PART OF
THE DAY THAT WL BE DRIER THAN THE REST. WL HV DECENT LLVL CNVGNC AND
ULVL DIVGNC THRUT. IF THERE/S ONE WRINKLE...ITS THE FACT THAT SNDGS
LOOK SO SATD THAT INSTBY WL BE MINIMAL.

CONSIDERING MSTR AND FORCING...AM CONCERNED THAT FLOODING WL BE A
CONCERN. FOR SOME SPOTS /SHD TO FFX/...IT WL BE AN ONGOING ISSUE...
WHILE IT WL BE A NEW CONCERN. THEREFORE...A FLOOD WATCH WL BE
APPROPRIATE. CONSIDERING HVY RAFL RATES...WIBIS A FLASH FLOOD WATCH
FOR MOST OF CWFA TIL WRN MTNS.

HV LKLY/CAT POPS FOR ALL AREAS XPCT THE PTMC HIGHLANDS. MAXT WL BE
KEPT DOWN...SPCLY FOR THE WEST.
&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
DAYTIME ACTIVITY WL BE ONGOING INTO THE EVNG. HGTS WL START TO RISE
OVNGT. AM HOPEFUL THAT WL LEAD TO A LESSENING THREAT...AND WL TRAIL
POPS OFF OVNGT FM A PLATEAU OF LKLY. AS LONG AS THE SFC BNDRY
REMAINS...CANT COMFORTABLY REMOVE POPS FOR ANY PERIOD.

SAME BASIC CONCEPT EXTENDS INTO SAT. HGTS WL BE HIER AS H5 LOW
RETROGRADES IN RESPONSE TO BLDG RDG SFC-H5 FM WRN ATLC. HWVR...STILL
HV THE SAME FORCING MECHANISMS ON A HUMID AMS /PWATS DONT CHG TOO
MUCH/. WL HV POPS IN THE CHC CATEGORY.
&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
AS HAS BEEN WRITTEN IN THE PAST TWO NGTS XTND DSCNS THE MDL
PROJECTED UPR LVL AND SFC PATTERNS FOR THE LATTER PARTS OF THE FCST
HV BEEN QUITE ANOMALOUS FOR MID JUL. REGARDLESS THE CONTINUITY BTWN
THE MDLS HAS BEEN GETTING GRTR SHOWING A SMALL UPR LVL CUTOFF LOW
OVR WEST VIRGINIA SAT TRACKING FURTHER WWD...AS HIGH PRES BUILDS OVR
NEW ENGLAND AND THEN INTO THE MID ATLC FOR MUCH OF THE NEW WK.

W/ SO MUCH MOISTURE OVR THE AREA IT IS PSBL THAT DIURNAL TSTMS
COULD DVLP SUN AFTN. AFTR THAT THE UPR RDG IS PROGGED TO COVER
MUCH OF THE ERN U.S. THRU AT LEAST MIDWEEK. TEMPS XPCTD TO CLIMB A
LTL EACH DAY...W/ HIGHS XPCTD TO GET BACK INTO THE 90S TUE THRU PSBLY
FRI. TYPICAL MID JUL WARMTH AT NGT W/ LOWS IN THE M70S IN THE
CITIES...60S W OF THE I-95.

THIS MAY NOT BE A LONG LIVED HEAT WV AS BOTH GFS AND ECMWF ARE
IMPLYING A WEAK TROF REDIGGING OVR QUEBEC/NEW ENGLAND BY NEXT FRI.
THIS WOULD LKLY BRING A CD FNT INTO THE NERN U.S. FRI. IF THIS
DOES OCCUR THE MID ALTC WL AGN HV CHCS FOR TSTMS.
&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
NRMS-WIDESPREAD SHRA/TSRA THIS MRNG. VSBY IMPACTS WL BE LCLZD...BUT
POTENTIALY AOB IFR. DUE TO DIFFICULTIES PINPOINTING SPECIFICS IN A
TAF STYLE FCST...HV KEPT VSBYS IN MVFR. CIGS...ON THE OTHER
HAND...SHUD BE LWRG. ON TOP OF MVFR CIGS EVERYWHERE...AM TAKING
STRONG GDNC SIGNALS OF IFR FOR CHO.

FRI WL BE AN UNSETTLED DAY OVERALL. AN UPR LOW WL ROTATE TWD
AREA...SUGGESTING THAT ANY BINOVC WL ONLY QUICKLY FILL BACK IN.
FURTHER...NLY SFC FLOW AND ELY FLOW JUST OFF THE SFC WL INHIBIT MUCH
DRYING W/IN THE COLUMN. DO NOT XPCT CIGS TO RISE MUCH TAFTN. FURTHER
TSRA WL ONLY REINFORCE POTL RESTRICTIONS. CONDS CUD REALLY DROP FRI
NGT AS RAFL EXITS BUT MOIST LLVL CONDS PREVAIL.

AFTN TSTMS PSBL AT ALL AIRPORTS SUN AFTN...THEN HIGH PRES XPCTD TO
BUILD IN DURG THE FIRST PART OF THE NEW WK.
&&

.MARINE...
STALLED CDFNT WL BE NEARBY...SO WINDS VRBL AOB 10 KT. HVY RAIN IS
THE PRIMARY THREAT...BUT LCLY HIER WNDS PRESENT W/IN THESE
DOWNPOURS. WIBIS SMW/S AS APPROPRIATE.

MAY BE ABLE TO NUDGE THE FNT EWD FRI. IF SO...THERE CUD BE A SMALL
SURGE IN WNDS. STILL DO NOT HV HIGH CONFIDENCE IN THAT SCENARIO ATTM.
CONCERNS ARE THAT AN APPROACHING UPR LOW AND RIPPLES W/IN SFC FLOW
WL SUPPORT MORE SHRA/TSRA INSTEAD. AM KEEPING ALL WINDS BLO SCA
LVLS. BUT...ADDTL SMW/S MAY BE REQD.

IN THE XNTD PART OF THE FCST AFTN TSTMS WL BE PSBL ON THE WATERS
SUNDAY. OTHERWISE WINDS XPCTD TO RMN BLO SCA VALUES.
&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLASH FLOOD WATCH THROUGH THIS EVENING FOR DCZ001.
MD...FLASH FLOOD WATCH THROUGH THIS EVENING FOR MDZ003>007-009>011-
     013-014-016>018.
VA...FLASH FLOOD WATCH THROUGH THIS EVENING FOR VAZ025>031-036>040-
     042-050>057-501-502.
WV...FLASH FLOOD WATCH THROUGH THIS EVENING FOR WVZ051>053.
MARINE...NONE.

&&

SYNOPSIS...WOODY!
NEAR TERM...HTS
SHORT TERM...HTS
LONG TERM...WOODY!
AVIATION...HTS/WOODY!
MARINE...HTS/WOODY!

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