Area Forecast Discussion
Issued by NWS Sterling, VA

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056 FXUS61 KLWX 291915 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 315 PM EDT Thu Sep 29 2016 .SYNOPSIS... Upper level low pressure will rotate over Kentucky through Friday before lifting north towards Michigan over the weekend. Persistent onshore flow and periods of heavy rain will occur across the Mid-Atlantic through Friday. The low is forecast to track to the northeast early next week. High pressure will build into the area during the first part of the new week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... A PNS was issued around 11 am with 30+ hour rainfall totals which have been fairly impressive...but in most cases (not all) the rain has fallen over a long enough time and into dry ground/low stream levels that flood problems have been minimal. The IAD and DOV VWP`s continue to Low level easterly flow of 30 knots. Yesterday I thought this would prove to be a big problem for the eastern slopes of the mountains. So far this has not materialized. A possible reason may be the convection off the Delmarva which to some degree is blocking the heavier rainfall from reaching the western side of the Bay. Despite this there is still a potential that a band of heavy rainfall could set up over one particular area. Hence the flash flood watch will remain in effect overnight. SPC continues to have the extreme southern portion of CWA in a marginal risk. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/... Beginning Friday the upper level low will gradually retrograde and move north as it begins to weaken. Rain rates are expected to gradually become less intense as activity becomes more scattered through the day. Gradual drying trend continues into Saturday...as the upper low continues to weaken and drift northward. While not a washout by any means...scattered shower activity will remain possible. Temperatures should climb back into the low/mid 70s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Influence of upper-level low finally begins to diminish late in the weekend into early next week as it passes by to our north and moves out to sea...while high pressure builds into the area in its wake. Most of Sunday appears dry...aside from some possible lingering early morning showers. Remaining dry with temperatures near climatology as high pressure remains over the area through early next week. This is a week away...but the word "Matthew" may be on everyone`s minds next Tue or Wed. This is currently well south of Puerto Rico but is forecast to make a northward turn and be positioned between Cuba and Turks and Caicos in the first part of next week. GFS and Euro have very different solutions on location and timing but one solution has this along the Mid Atlantic coast during the middle of next week. But the middle of next week is along way away. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... Upper level low will continue to impact the area through Friday...bringing periods of IFR/LIFR to all the terminals. Low ceilings are possible through Friday night with persists onshore flow. Gradual improvement Saturday...with a return to VFR by Sunday. && .MARINE... Solid SCA for all waters for the remainder of the afternoon and tonight. SCA has been extended through Friday afternoon. Gradient should begin to relax by later Friday evening...with SCA winds becoming less likely Saturday into the Weekend. && .TIDES/COASTAL FLOODING... Anomalies running around 1.5 feet to as much as 2 feet on the lower Potomac. Due to these higher anomalies which are forecast to persist, have upgraded St. Marys County to a Coastal Flood Warning. Have extended all other Coastal Flood Advisories for another high tide cycle. These products will likely need to be extended into Saturday as anomalies will change little with persistent easterly flow. Annapolis and DC SW Waterfront will be very close to moderate flood levels in multiple upcoming high tides as well, particularly if anomalies continue to increase. Did not have the confidence to upgrade to warnings at this time. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Flash Flood Watch through Friday morning for DCZ001. Coastal Flood Advisory until midnight EDT Friday night for DCZ001. MD...Flash Flood Watch through Friday morning for MDZ003>006-011- 013-014-016>018-501>508. Coastal Flood Advisory until 8 PM EDT Friday for MDZ016. Coastal Flood Warning until 6 PM EDT Friday for MDZ017. Coastal Flood Advisory until 10 PM EDT Friday for MDZ011-014- 018. VA...Flash Flood Watch through Friday morning for VAZ025>031- 036>040-050>057-501-502-505>508. Coastal Flood Advisory until 8 PM EDT Friday for VAZ057. Coastal Flood Advisory until midnight EDT Friday night for VAZ054. WV...Flash Flood Watch through Friday morning for WVZ050>053-055- 501>504. MARINE...Small Craft Advisory until 7 PM EDT Friday for ANZ530>543. && $$ PRODUCTS...WOODY! TIDES/COASTAL FLOODING...ADS

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