National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS61 KLWX 130013 AAA
AFDLWX

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
813 PM EDT WED JUN 12 2013

.SYNOPSIS...
A COLD FRONT WILL REMAIN STALLED OUT NEAR THE MASON-DIXON LINE.
LOW PRESSURE WILL RIDE ALONG THE BOUNDARY...IMPACTING THE AREA
TONIGHT AND THURSDAY. THE COLD FRONT ASSOCIATED WITH THE LOW WILL
PASS THROUGH LATE THURSDAY AND HIGH PRESSURE WILL BUILD TOWARD THE
REGION FRIDAY AND THIS WEEKEND.

&&

.NEAR TERM /THROUGH THURSDAY/...
8PM UPDATE...LITTLE OCCURRING W/IN A COUPLE HUNDRED MILES OF THE
AREA...THOUGH STILL HUMID AND UNSTABLE ACROSS THE AREA. THE DENSE
DEBRIS UPPER CLOUD DECK STARTING TO EAT-AWAY AT THE INSTABILITY...
ESPEC ACROSS THE HIGHER TERRAIN. SCATTERED STORMS HAVE DOTTED THE
LANDSCAPE OF THE UPPER MIDWEST...MAINLY ACROSS NRN OHIO AND THE
MUCH LARGER AMNT OF ACTIVITY SURROUNDING CHICAGO/LAKE MI.

LOCAL GUIDANCE LIKE THE HRRR MODEL CONTINUING TO BRING SCATTERED
AND DISJOINTED BATCHES OF SHOWER/TSTM ACTIVITY LATER TONIGHT INTO
THE OVERNIGHT HRS...BUT THE MORE INTENSE NORTH-SOUTH ORIENTED MCS
IS BEING PROGGED MORE AND AN EAST-WEST BATCHES OF INDIVIDUAL CELLS
DRIFTING OFF TO SE. MONITORING THE UPPER MIDWEST CONVECTION...
THESE CELLS ARE ACTUALLY MOVING RELATIVELY SLOWLY...SO THEIR
FORWARD PROGRESS WON`T COVER TOO MUCH GROUND.

THE FOCAL POINT OF THE CONVECTION ACROSS THE REGION HAS BEEN AND
IS EXPECTED TO BE ALONG THE PSEUDO-STATIONARY BOUNDARY. THE
BOUNDARY IS ORIENTED OVER TOP THE SOUTHEAST RIDGE...WHICH IS LAID
OUT FROM THE UPPER MIDWEST DOWN THRU CNTRL WV AND TOWARD THE I-64
CORRIDOR.

FROM PREV DISC...GIVEN THE STEEPENING MID-LVL LAPSE RATES AND HIGH
DEEP- LAYER W-NWLY SHEAR...THERE IS STILL A POTENTIAL FOR DAMAGING
WINDS...LARGE HAIL AND HEAVY RAIN AS THIS THUNDERSTORMS DIVE SEWD
ACROSS THE CWA LATE TNGT. SEE HYDRO SECTION FOR DETAILS ABOUT THE
FLASH FLOOD WATCH.

NOT MUCH CHANGE IN OUR CONCERN FOR A SIGNIFICANT SEVERE WEATHER
EPISODE ON THU AFTN. AN UNSEASONABLY STRONG LOPRES SYSTEM WILL TRACK
EWD ACROSS PA TOMORROW WHILE A COLD FRONT APPROACHES FROM THE OH
VLY.

12Z MODELS SHOW SMALL DIFFERENCES WITH TIMING OF THE FRONT
DURING THE DAY BUT CURRENT THINKING IS FROPA WILL OCCUR LATE ENOUGH
IN THE DAY TO ALLOW FOR STRONG PRE-FRONTAL DESTABILIZATION EAST OF
THE BLUE RIDGE DURING THE MRNG ALTHOUGH THERE IS SOME UNCERTAINTY
WITH HOW DEBRIS CLOUDS FROM THE OVNGT MCS WILL IMPACT HEATING
INITIALLY. 09Z SREF SHOWS A DECENT CHANCE /GREATER THAN 40 PERCENT/
OF SBCAPE VALUES GREATER THAN 2000 J/KG BY THE AFTN FROM I-95 EAST.
COMBINED WITH STRONG WINDS ALOFT /BULK SHEAR VALUES 40 KT OR
GREATER/ AND DEEP LIFT...STORMS ARE EXPECTED TO QUICKLY ORGANIZE
DURING THE MIDDAY. DEEP-LAYER SHEAR PARALLEL TO THE FRONTAL BOUNDARY
FAVOR A LINEAR MODE OF CONVECTION WITH A LARGE BOWING SEGMENT
CERTAINLY POSSIBLE. SPC HAS PLACED AREAS EAST OF THE BLUE RIDGE IN A
MODERATE RISK FOR TOMORROW. THE GREATEST THREAT WILL BE WIDESPREAD
DAMAGING WINDS. LARGE HAIL AND A FEW TORNADOES WILL BE POSSIBLE.
BASED ON THE EXPECTED LOCATION OF THE WARM FRONT...THERE WOULD BE AN
ENHANCED RISK FOR A TORNADO NEAR THE MASON-DIXON LINE.

&&

.SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/...
LOPRES MVG OFF THE CST THU NGT...W/ ANY RESIDUAL SHRA EXITING DURING
THE EVNG HRS. LT EVNG THRU THE OVNGT SHUD BE DRY...W/ CLRG SKIES AS
NW WINDS PICK UP. THE SURGE OF DRIER AIR WL BE THE BIGGER IMPACT...
AS 30-35 KT AVBL IN H9-8 LYR...ALL W/ FVRBL MIXING POTL. HV INFUSED
SOME 30 MPH WIND GUSTS IN THE DATABASE BHD THE LOW...BUT GRDLY TAPER
THEM OFF OVNGT.

H5 TROF AXIS STEEPENS BY FRI MRNG...PROVIDING SOME STEEP LAPSE
RATES. THE MITIGATING FACTOR WL BE DOWNSLOPING WINDS/INCRSG
SUBSIDENCE FM BLDG SFC HIGH. HWVR...FEEL ITS PRUDENT TO HV SCHC/CHC
SHRA IN THE GRIDS...PRIMARILY FOR THE MID AFTN HRS. ONCE DIURNAL
MIXING RESUMES...BRZY CONDS WL RETURN. THE SYNOPTIC SCALE WNDS WL
DIMINISH BY MIDDAY...OUTSIDE OF ANY LCL GUSTS INVOF SHRA.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
HIGH PRESSURE BUILDS IN OVER THE WEEKEND FOR WHAT SHOULD BE A QUIET
WEEKEND. SATURDAY LOOKS SUNNY AND SEASONABLE. TEMPERATURES CREEP UP
ON SUNDAY AS A WARM FRONT MOVES THROUGH. THERE MAY BE MORE
CLOUDS...BUT THE CURRENT THINKING IS THAT ANY CONVECTION REMAINS TO
THE NORTHWEST OF THE CWA.

THE NEXT FRONT IS FORECAST TO AFFECT THE CWA MONDAY-TUESDAY OF NEXT
WEEK WITH A CHANCE OF SHOWERS AND THUNDERSTORMS.

&&

.AVIATION /00Z THURSDAY THROUGH MONDAY/...
VFR CONDITIONS EXPECTED THIS AFTERNOON AND EVENING.

TWO ROUNDS OF TSTMS POSSIBLE TONIGHT AND TOMORROW. FIRST ROUND
WOULD LIKELY BE OVERNIGHT...WITH POTENTIAL FOR HEAVY RAIN AND
GUSTY WINDS. VSBYS MAY BE REDUCED FOR RAIN AND FOG. 2ND ROUND OF
STORMS WOULD BE DURING THE DAY TOMORROW...LIKELY LATE MORNING TO
EARLY AFTERNOON FOR KMRB AND AFTER NOON FOR OTHER TAF SITES. THESE
STORMS MAY PRODUCE DAMAGING WINDS AND LARGE HAIL...ALONG WITH
PERIODS OF REDUCED VSBYS. FORECAST UPDATES LATER THIS EVENING AND
OVERNIGHT WILL REFINE TIMING AND IMPACTS OF THESE STORMS. WIND
GUSTS UP TO 20-25KT FROM THE S-SW EXPECTED DURING THE LATE
MORNING-AFTERNOON HOURS THU.

PRIMARILY VFR EXPECTED FRI THROUGH SUNDAY. THERE IS A CHANCE OF
SCATTERED SHOWERS/TSTMS FRI AND LATE SUNDAY...WITH POTENTIAL OF
BRIEF SUB-VFR CONDITIONS.

&&

.MARINE...
SHOWERS AND THUNDERSTORMS MAY IMPACT THE WATERS OVNGT. ANY
THUNDERSTORMS THAT DO DEVELOP WILL HAVE THE POTENTIAL TO PRODUCE
GUSTY WINDS.

SOUTHERLY WINDS INCREASE TO BETWEEN 20-30 KT AHEAD OF A COLD FRONT
ON THURSDAY. A SMALL CRAFT ADVISORY IS IN EFFECT ACCORDINGLY.
WIDESPREAD THUNDERSTORMS ARE EXPECTED AHEAD OF A COLD FRONT THURSDAY
AFTERNOON WITH THE POTENTIAL FOR DAMAGING WINDS. IT WILL LIKELY BE
EXTREMELY HAZARDOUS TO BE ON THE WATERS THU AFTN.

A NWLY SURGE WL COME BHD DEPARTING LOPRES THU NGT...W/ 30-35 KT
AVBL ASSUMING FULL MIXING. AM UNCOMFORTABLE MAKING THAT ASSUMPTION
LT IN THE EVNG FLLWG NMRS TSRA...BUT DO RECOGNIZE A SYNOPTIC SCALE
STRONG WND THREAT...SPCLY IN THE EVNG. WL THEREFORE RAISE A HIGH
END SCA FOR THU...KEEPING THE GLW PSBL WORDING IN THE SYN AND HWO.
THE SCA POTL LASTS INTO FRI...ALTHO THE WND GUSTS/SPDS WL GRDLY BE
DIMINISHING OVNGT AND THRU FRI. WL CONT SCA EVERYWHERE TIL 17Z
/1PM/ AS A STARTING POINT. ANTICIPATE FOR SOME WATERS...MD BAY
MAYBE?...THAT THE SCA MAY BE REQD LONGER.

&&

.HYDROLOGY...
FLASH FLOOD WATCH IN EFFECT FOR THE CWA TNGT AND THU. WET
ANTECEDENT CONDITIONS HAS RESULTED IN A 1-HR FFG AROUND AN INCH.
THERE IS A POTENTIAL FOR A COMPLEX OF SHOWERS AND STORMS OVER THE
OH VLY TO CROSS THE APPALACHIANS THIS EVE AND TRACK ACROSS THE
AREA LATE TNGT. IF THE COMPLEX HOLDS UP...IT WILL HAVE THE
POTENTIAL TO PRODUCE HVY DOWNPOURS WITH A QUICK INCH IN AN HOUR
POSSIBLE. THE BEST CHANCE FOR RAIN TNGT WILL BE OVER NRN MD AND
THE ERN WV PANHANDLE...WHERE A FRONTAL BOUNDARY RESIDES.

STEADY HEAVIER RAIN IS MORE LIKELY NORTH OF THE AFOREMENTIONED
BOUNDARY...WHICH LIKELY PUTS WIDESPREAD HEAVY PRECIPITATION NORTH OF
THE AREA ON THU. HOWEVER...EVEN CONVECTIVE ACTIVITY THAT DEVELOPS
SOUTH OF THE WARM FRONT WILL DEFINITELY BE CAPABLE OF PRODUCING 1-2
INCHES OF RAINFALL IN A SHORT PERIOD OF TIME.

&&

.TIDES/COASTAL FLOODING...
WINDS WILL BECOME SOUTHERLY AND GUSTY THURSDAY AFTERNOON AHEAD OF AN
APPROACHING STRONG COLD FRONT. ANOMALIES WOULD NEED TO REACH
APPROXIMATELY 3 FT FOR TIDAL FLOODING. WIND SPEED/DIRECTION WILL BE
FAVORABLE FOR INCREASED ANOMALIES FOR A FEW HOURS DURING THE
DAY...BUT IS NOT EXPECTED TO PRODUCE ANOMALIES THAT WOULD THREATEN
COASTAL FLOOD THRESHOLDS. HOWEVER...ANY LOCATIONS SUSCEPTIBLE TO
FLASH FLOODING FROM HEAVY RAINFALL AS WELL WILL STILL NEED TO
MONITOR THE SITUATION...AS THOSE THRESHOLDS ARE QUITE LOW. PLEASE
REFER TO THE HYDROLOGY SECTION.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...FLASH FLOOD WATCH FROM MIDNIGHT EDT TONIGHT THROUGH THURSDAY
     EVENING FOR DCZ001.
MD...FLASH FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR MDZ003-501-
     502.
     FLASH FLOOD WATCH FROM MIDNIGHT EDT TONIGHT THROUGH THURSDAY
     EVENING FOR MDZ004>007-009>011-013-014-016>018.
VA...FLASH FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR VAZ025>031-
     036-037-503-504.
     FLASH FLOOD WATCH FROM MIDNIGHT EDT TONIGHT THROUGH THURSDAY
     EVENING FOR VAZ038>040-042-050>057-501-502.
WV...FLASH FLOOD WATCH THROUGH THURSDAY AFTERNOON FOR WVZ050>053-
     055-501>506.
MARINE...SMALL CRAFT ADVISORY FROM 11 AM THURSDAY TO 1 PM EDT FRIDAY
     FOR ANZ530>543.

&&

$$
UPDATE...GMS