Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220051 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 851 PM EDT MON APR 21 2014 .SYNOPSIS...
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HIGH PRESSURE HAS MOVED OFFSHORE. A COLD FRONT WILL PASS THROUGH THE AREA TUESDAY AFTERNOON AND EVENING. HIGH PRESSURE RETURNS FOR WEDNESDAY AND THURSDAY BEFORE MOVING OFF THE COAST FRIDAY. A COLD FRONT IS EXPECTED TO PASS THROUGH THE AREA SATURDAY.
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&& .NEAR TERM /THROUGH TUESDAY/...
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HI PRES WHICH GAVE THE AREA A BEAUTIFUL DAY HAS MOVED OFFSHORE. LOW PRES IS SITUATED OVER SWRN ONTARIO W/ AN ATTENDANT COLD FRONT EXTENDING FM MI TO TX. FCST MIN TEMPS GENERALLY RANGE FROM THE MID 40S TO LOWER 50S...ALTHOUGH SHELTERED/RURAL LOCATIONS NORTH AND WEST OF THE CITIES MAY DIP NEAR 40F. 12Z GUIDANCE TRENDED SLIGHTLY SLOWER WITH THE TIMING OF THE COLD FRONT COMPARED TO PRIOR RUNS BUT THE GENERAL THINKING STILL IS FROPA OCCURS DURING THE AFTN WEST OF I-95. THE COLD FRONT MAY NOT REACH THE CHSPK BAY UNTIL THE EVE. MODEST WAA PATTERN CONTINUES WITH SLY WINDS AHEAD OF THE FRONT. FCST MAX TEMPS ARE HIGHEST EAST OF THE BLUE RIDGE WHERE POST-FRONTAL CAA ARRIVES AFTER MAX HEATING AND THERE IS A BETTER CHANCE TO SEE BREAKS IN THE CLOUDS THAN IN THE MTS. HIGHS TUE RANGE FROM THE 60S IN THE MTS TO NEAR 80F IN THE CITIES AND IN CENTRAL VA. ADDED MORE DETAIL TO THE EXPECTED TIMING OF PRECIP WITH POPS INCREASED TO LIKELY FOR A 2-4 HR PERIOD DURING AND JUST PRIOR TO FROPA. KEPT SLIGHT CHANCES FOR THUNDER AS GUIDANCE CONSISTENT OF KEEPING THE BEST LIFT TO THE NORTH OF THE CWA WHILE THE BEST MOISTURE FLUX AND INSTABILITY STAYS TO OUR SOUTH.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/...
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THE COLD FRONT MOVES OFF THE EAST COAST TUE NGT WHILE HIPRES BUILDS IN FROM THE GREAT LAKES. A STRONG PRESSURE GRADIENT BETWEEN THESE TWO SYSTEMS WILL PRODUCE GUSTY NW WINDS BETWEEN 20-30 MPH TUE NGT AND WED. DESPITE THE CAA BEHIND THE FRONT...FCST MIN TEMPS TUE NGT WEIGHTED TOWARD WARMER BIAS CORRECTED MET GUIDANCE AS BOUNDARY LAYER STAYS WELL MIXED. SUB-ZERO H8 TEMPS FCST BY 12Z GUIDANCE. TEMPS WILL BE MODERATED BY SUNNY SKIES AND DOWNSLOPING FLOW ON WED. MAX TEMPS RANGE FROM THE 40S ALONG THE ALLEGHENY FRONT TO MID 60S IN CENTRAL VA AND ALONG THE I-95 CORRIDOR.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/... A DEEP RIDGE AXIS WILL TRAVERSE THE AREA THURSDAY NIGHT...WITH HEIGHTS FALLING AHEAD OF AN APPROACHING SHORTWAVE TROUGH FRIDAY. A WEAK COLD FRONT ACCOMPANYING THE APPROACHING UPPER-LEVEL TROUGH WILL MOVE THROUGH THE AREA ON FRIDAY BRINGING A CHANCE OF SHOWERS. THIS FRONT IS MORE OF A PRESSURE TROUGH/WIND SHIFT AXIS...WITH ANY APPRECIABLE AIRMASS CHANGE LAGGING UNTIL A SECONDARY COLD FRONT PASSES THROUGH THE REGION ON SATURDAY. MOISTURE LOOKS LIMITED WITH THE SECOND BOUNDARY...AND THAT PRECLUDES HIGHER RAIN CHANCES FOR MOST OR ALL OF THE AREA AT THE MOMENT. HIGH PRESSURE AND COOLER TEMPERATURES BRIEFLY MOVE ACROSS THE AREA SUNDAY...BEFORE ANOTHER DISTURBANCE APPROACHES THE AREA EARLY NEXT WEEK. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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VFR TNGT WITH LGT SLY WINDS. A COLD FRONT MOVES THRU THE TERMINALS BETWEEN 18Z TUE THRU 00Z WED. SHRA LIKELY WITH FROPA. FOR THE 18Z TAFS...CHANCES FOR TSRA TOO LOW TO INCLUDE IN 30-HR TAF SITES THIS FAR OUT. NW WINDS FOLLOWING THE FRONT WILL BECOME GUSTY TUE NGT AND WED AS HIPRES BUILDS IN FROM THE NW. GUSTS TO 30 KT POSSIBLE...ESPECIALLY AFTER A FEW HRS OF DAYTIME MIXING ON WED. NW WINDS DIMINISH WED NGT AND THU WITH HIPRES BUILDING OVERHEAD. MODERATE-HIGH CONFIDENCE IN SOUTHERLY WIND 5 TO 10 KNOTS WITH LOW CONFIDENCE SUB-VFR/SHOWERS FRIDAY...THEN MODERATE CONFIDENCE VFR WITH WESTERLY WINDS 5 TO 10 KNOTS FRIDAY NIGHT.
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&& .MARINE...
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SLY WINDS WILL DEVELOP TNGT AHEAD OF AN APPROACHING COLD FRONT. SLY FETCH WILL FAVOR CHANNELING IN THE OPEN WATERS OF THE BAY...WHICH WILL LIKELY ENHANCE WIND SPEEDS TO 15-20 KT SEVERAL HRS PRIOR TO FROPA ON TUE AFTN. SCA WAS ISSUED FOR THESE ZONES OF THE CHSPK BAY. SHOWERS AND POSSIBLY A FEW TSTMS TUE AFTN AND ERY EVE WITH FROPA. A GOOD PRESSURE SURGE BEHIND THE FRONT WILL BE ACCOMPANIED BY GUSTY NW WINDS TUE NGT. SCA ISSUED FOR ALL MARINE ZONES TUE NGT AND WILL LIKELY NEED TO BE EXTENDED INTO WED. THE CENTER OF HIPRES BUILDS CLOSE ENOUGH TO THE WATERS FOR WINDS ACROSS MOST OF THE MARINE ZONES TO SUBSIDE BELOW SCA LVLS WED EVE. SCA MAY NEED TO BE CONTINUED THOUGH IN SERN ZONES. SUB SMALL CRAFT ADVISORY CONDITIONS ARE EXPECTED IN A WEAK PRESSURE GRADIENT REGIME TO END THE WEEK. WINDS COULD HIT SMALL CRAFT ADVISORY LEVELS FOR A TIME BEHIND A FRONT THIS WEEKEND.
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&& .TIDES/COASTAL FLOODING...
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CBOFS GUIDANCE INDICATES ANOMALIES INCREASING TO ABOUT ONE FOOT BY TUE MRNG. THIS WOULD KEEP TIDAL LEVELS ABOUT ONE-QUARTER FOOT BELOW COASTAL FLOOD THRESHOLD AT ANNAPOLIS AND GREATER THAN ONE- HALF FOOT BELOW COASTAL FLOOD THRESHOLD AT BALTIMORE.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 PM TUESDAY TO 6 AM EDT WEDNESDAY FOR ANZ530-531-535>539-542. SMALL CRAFT ADVISORY FROM NOON TUESDAY TO 6 AM EDT WEDNESDAY FOR ANZ532>534-540-541-543. && $$ UPDATE...WOODY! PRVS...JRK/HAS/DFH

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