Area Forecast Discussion
Issued by NWS Sterling, VA

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967 FXUS61 KLWX 250059 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 859 PM EDT Wed May 24 2017 .SYNOPSIS... Low pressure will approach the area tonight before passing through Thursday. The cold front associated with the low will move through Thursday night and high pressure will return for later Friday into Friday night. The high will move offshore Saturday and a warm front will stall over the region for later Saturday through Sunday. A stronger cold front may pass through the area Monday. && .NEAR TERM /UNTIL 7 AM THURSDAY MORNING/...
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Large cutoff low is positioned over the Ohio Valley this evening with a front extending southward through the southeastern US. Warm moist air is streaming northward with a connection to the eastern Gulf and western Caribbean, overriding cooler air which has wedged southward to a position near the VA/NC border. Much of the convective activity this evening has remained in the warm sector, with precipitation becoming more of a stratiform rain as it spreads northward and into our region. This general trend is expected to continue for the overnight hours with widespread rain moving across the region. Some elevated instability will move overhead, so a few embedded non-severe thunderstorms are possible. Overall, looking at a moderate soaking rain, with total amounts ranging from 0.5-1.5". Where/if elevated convection develops, there may be localized heavier amounts. Some heavier amounts are also possible along the Blue Ridge and southeast-facing slopes as easterly flow increases overnight. While rates are not expected to be high enough to raise much of a true flash flood concern, there may be some localized minor flooding of small creeks/streams and in low lying and urban/poor drainage areas. Will continue mention in HWO. Temperatures tonight pretty much remain where they are this evening, in the 50s to around 60F.
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&& .SHORT TERM /7 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
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A dry slot will cause rain to dissipate for a period Thursday morning...but surface low pressure will build overhead by Thursday afternoon. The cutoff upper-level low will also move overhead during the day. A southerly flow ahead of the low will allow for moderate amounts of instability. Popup showers and thunderstorms are expected to develop later Thursday morning and afternoon. Thunderstorms may contain gusty winds and hail due to colder air aloft associated with the upper-level low. The low pressure will move away from the area Thursday night and the cold front associated with this system will pass through Thursday evening before moving off to the east and northeast Thursday night. Low pressure will continue to move up the New England Coast Friday. Breezy conditions are expected behind the low. A popup shower cannot be ruled out...but most of the time will be dry and seasonable. High pressure will briefly build overhead Friday night.
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/...
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Brief dry period expected Saturday morning. An upper level shortwave trough could increase PoPs Saturday afternoon into the evening before a boundary settles near/over our CWA Saturday night into Sunday. A cold front then slowly moves across Sunday night into Monday. Showers and thunderstorms possible during this period. Conditions begin to dry out on Tuesday before another weaker front approaches on Wednesday. High temperatures will be in the 70s and low 80s... some 60s at higher elevations.
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&& .AVIATION /01Z THURSDAY THROUGH MONDAY/...
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A soaking rain is expected to overspread the terminals this evening and overnight. Cigs/vsbys will continue to deteriorate and IFR conditions are expected this evening through late tonight. Steady rain will end toward Thursday morning. Cigs/vsbys will improve later Thursday...but popup showers and thunderstorms are expected later Thursday morning into Thursday night. VFR conditions are expected Friday and Friday night as high pressure builds in from the west. VFR conditions expected early on Saturday. Then sub- VFR conditions return Saturday afternoon and into Monday with rounds of showers and thunderstorms moving through our region with a boundaries stalled/moving through our region.
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&& .MARINE...
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An onshore flow will strengthen ahead of low pressure tonight. A Small Craft Advisory is in effect for the waters. Low pressure will move overhead Thursday and the gradient may weaken a bit. However...low pressure and its associated cold front will move away from the waters Thursday night. A Small Craft Advisory is in effect for portions of the waters Thursday into Thursday night and it will likely be needed Friday into Friday night. Dry conditions early on Saturday before periods of showers and thunderstorms move through Saturday night into Monday as front stalls and moves across our region. Winds will be below the SCA threshold Saturday into Monday.
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&& .TIDES/COASTAL FLOODING... An onshore flow will strengthen tonight and tidal anomalies will increase. The next high tide will be the higher of the two and the lunar phase is at a new moon...so minor flooding is likely during the high tide cycle later tonight into Thursday morning. A Coastal Flood Advisory is in effect for many locations along the western shore of the Chesapeake Bay and the Upper Tidal Potomac River. The flow will weaken and turn to the south Thursday before turning southwest Thursday night and eventually to the west and northwest Friday. Significant blowout should not occur until later Friday...so minor tidal flooding is possible during the high tide cycles Thursday through Thursday night. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Coastal Flood Advisory from 4 AM to 11 AM EDT Thursday for DCZ001. MD...Coastal Flood Advisory from midnight tonight to 8 AM EDT Thursday for MDZ014-018. Coastal Flood Advisory until 6 AM EDT Thursday for MDZ016-017. Coastal Flood Advisory from 4 AM to 10 AM EDT Thursday for MDZ011. VA...Coastal Flood Advisory until 6 AM EDT Thursday for VAZ057. Coastal Flood Advisory from 4 AM to 11 AM EDT Thursday for VAZ054. WV...None. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ532>534-537- 540>543. Small Craft Advisory until 9 AM EDT Thursday for ANZ530-531- 538-539. Small Craft Advisory until 6 AM EDT Thursday for ANZ535-536.
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&& $$ SYNOPSIS...BJL NEAR TERM...BJL/MM SHORT TERM...BJL LONG TERM...IMR AVIATION...BJL/MM/IMR MARINE...BJL/MM/IMR TIDES/COASTAL FLOODING...BJL

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