Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210834 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 434 AM EDT Fri Oct 21 2016 .SYNOPSIS... A cold front will pass through the region today. An upper-level trough will pass through the area Saturday and high pressure will build into the region for Sunday. A reinforcing cold front will pass through the area Monday with high pressure returning for the middle portion of next week. && .NEAR TERM /THROUGH TONIGHT/... A cold front is moving through West Virginia early this morning while the mid-level trough axis associated with the boundary is passing through the Ohio Valley. A southerly flow ahead of the boundary has allowed for unusually warm conditions early this morning. The cold front is expected to pass through the area today. The boundary will pass through the Potomac Highlands by mid- morning before making its way through the Washington and Baltimore Metropolitan areas between 1 and 4 pm this afternoon. The cold front will pass through the Bay late this afternoon. Showers are likely along and just ahead of the boundary as it moves through the area. More showers are possible behind the cold front as a potent upper-level disturbance pass through the region. Confidence in max temp forecast is low since it will be highly dependent on the timing of the frontal passage. Max temps are forecast to range from the mid to upper 50s in the Allegheny the upper 60s and lower 70s for valley locations west of the Blue Ridge the upper 70s and lower 80s near Washington and Baltimore into southern Maryland. Temperatures are expected to drop quickly behind the cold front...into the 40s and 50s this afternoon west of the Blue Ridge Mountains and into the 50s and 60s east of the Blue Ridge Mountains by late this afternoon. The cold front will move off to the east this evening and the upper-level disturbance associated with the boundary will pass through during this time. Blustery northwest winds are also expected behind the front and this will cause temperatures to continue falling. A few showers are possible due to the passing o the upper-level disturbance...but precipitation amounts will be light. The upper-level disturbance will develop into a closed upper-level low overnight and the upper-level trough overhead will shift to a negative tilt. This will cause surface low pressure to rapidly intensify off to our north and east. A strengthening pressure gradient will cause gusty northwest winds overnight. Wind gusts around 50 mph are possible along the ridges of the Allegheny and Potomac Highlands as well as the Blue Ridge and Catoctin Mountains. A wind advisory may be needed for these areas. Elsewhere...frequent gusts around 30 mph are expected. The northwest flow will dry things out across most areas...but a few rain/snow showers are possible along the ridge tops along and west of the Allegheny Front. Snow may coat grassy surfaces above 3kft. A freeze is possible overnight across the ridge tops of the Allegheny and Potomac Highlands...mainly above 3kft. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Low pressure will continue to intensify as it tracks northward into Ontario Saturday. High pressure will remain over the MIdwest into the Gulf Coast States. A tight gradient between the departing low and the building high will continue to cause windy conditions. Cold advection will increase wind gusts around 35 to 45 mph are expected. A wind advisory may be needed for portions of the area. The best chance for wind gusts around 50 mph will be along the ridges. Max temps Saturday will be much chillier due to the northwest flow...ranging from the 40s in the mountains to the upper 50s and lower 60s near Washington and Baltimore into southern Maryland. High pressure will build to our south Saturday night through Sunday. Breezy conditions along with mainly clear skies are expected. Sunday may be a bit milder due to a downsloping westerly flow with highs in the 60s across most areas. A reinforcing cold front will approach Sunday night...but it should remain to our north. More dry and seasonable conditions are expected. && .LONG TERM /MONDAY THROUGH THURSDAY/... A reinforcing cold front will cross the area on Monday. GFS/ECMWF timing differ a bit. Splitting the difference suggests it may be a morning fropa. Although moisture and upper level energy remain to the northeast of the forecast area, nearer the lower heights in the base of the trough axis, cold advection will sweep the area during the day. As a result, the frontal passage should be dry, with perhaps a few more clouds. After that, expect mostly sunny and breezy conditions. It may be difficult to get frost Monday night due to a breeze (there`s still room for that to change), but temperatures should drop into the 30s in the mountains, lower-mid 40s elsewhere. After a day in the mid 50s-lower 60s Tuesday, radiational cooling should be better Tuesday night as the center of high pressure builds toward the Mid Atlantic. This may spell the end of the growing season for outlying/rural areas. The next storm system will be cutting across the Ohio Valley toward the Great Lakes toward midweek. While is should stay north/west of the area, its attendant cold front will approach by Thursday, potentially bringing showers back to the area. && .AVIATION /09Z FRIDAY THROUGH TUESDAY/... A southeast flow will continue to ahead of a cold front through this morning. Cigs may drop to MVFR/IFR levels during this time...but confidence is low. Do feel that if cigs do drop MVFR conditions are more likely vs. IFR since there is some wind underneath the inversion. A cold front will pass through the terminals...first across KMRB between 10 am and noon...then across the rest of the terminals between 1 pm and 4 pm. A wind shift to the northwest is expected behind the front with gusts around 20 to 25 knots likely. Showers are also expected with the frontal passage and a few showers may hang around into this evening as an upper-level disturbance passes through. MVFR conditions are possible in showers today. Gusty northwest winds will continue through Saturday evening. The highest gusts are expected Saturday when mixing will be strongest. Gusts around 35 knots are likely. Winds will diminish Saturday night...but breezy conditions will continue through Sunday as high pressure settles to the south. VFR conditions should prevail Monday-Tuesday. Could have some gusty northwest winds on Monday behind a cold front. && .MARINE... A southerly flow will continue through early this afternoon ahead of a cold front. Will continue with the Small Craft Advisory...but it will be marginal. The cold front will pass through the waters between 2 and 5 pm this afternoon. A wind shift to the northwest is expected behind the boundary and winds will become gusty. Winds will increase as the pressure gradient strengthens tonight through Saturday. A Gale Warning is in effect for the Bay and lower tidal Potomac River tonight...and for all the waters Saturday. The strongest winds are expected Saturday. Winds will diminish a bit Saturday night...but a Small Craft Advisory will likely be needed. More breezy conditions are expected Sunday into Sunday night. A cold front will cross the waters on Monday. Small Craft Advisories seem likely from this vantage point behind the cold front. Winds will be diminishing on Tuesday as the pressure gradient relaxes. && .TIDES/COASTAL FLOODING...
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A south to southeast flow has caused tidal anomalies to increase quickly this morning. Anomalies are expected to increase to around 1 to 1.5 feet above normal this morning as the south to southeast flow continues. A Coastal Flood Advisory is in effect for Anne Arundel and St Marys Counties for the high tide cycle this morning. Minor flooding is possible around high tide early this afternoon near Washington DC and Alexandria. Will have to monitor anomalies this morning. South to southeast winds will continue through early this afternoon before turning quickly to the northwest by the end of the day. Minor flooding is possible during the high tide cycle late this afternoon into this evening...but confidence is low because of the northwest flow that will be developing during this time. Anomalies will drop sharply tonight and blowout tides are possible for Saturday due to a strong northwest flow.
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&& .CLIMATE... Record high minimum temperatures were set at DCA...BWI...and IAD Thursday...October 20th. See the latest RER for more details. The passage of a cold front should prevent records from being reached once again today. Records for Oct 21st... DCA...High 85 in 1947...warm low 64 in 1984. BWI...High 90 in 1947...warm low 63 in 1947. IAD...High 86 in 1979...warm low 60 in 1979. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Coastal Flood Advisory until noon EDT today for MDZ014. Coastal Flood Advisory until 10 AM EDT this morning for MDZ017. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ530>534-537>543. Gale Warning from 6 PM this evening to 6 PM EDT Saturday for ANZ530>534-537>543. Small Craft Advisory from noon today to 6 AM EDT Saturday for ANZ535. Gale Warning from 6 AM to 6 PM EDT Saturday for ANZ535-536. Small Craft Advisory until 6 AM EDT Saturday for ANZ536.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...HTS AVIATION...BJL/HTS MARINE...BJL/HTS TIDES/COASTAL FLOODING...BJL CLIMATE...HTS is the U.S. government's official web portal to all federal, state and local government web resources and services.