Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 291416 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1016 AM EDT Thu Sep 29 2016 .SYNOPSIS...
-- Changed Discussion --
An upper level low over Kentucky through Friday will lift northward across the Great Lakes 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 late in the weekend and into early next week. High pressure will build into the area during the first part of the new week.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Where bands of rain have set up there have been some totals of over 4" since Wednedsay morning. Other places have received significantly less. Low level easterly flow is ongoing according to both the IAD and DOV VWP`s. A possible reason that more heavier rain has not transported into the Mid Atlantic may be the convection that has formed off the Delmarva. This is more often seen on southerly flow when a line of storms develops over the Panhandle of FL which shuts off heavy rainfall further north. With that in mind we remain concerned about the next 24 hours. In the short term our eyes are on a band over eastern NC which is tracking slowly to the north. If this reaches I-95/Beltway at rush hour this would prove problematic. And persistent low level easterly flow means we have to keep our guard up for bands of heavy rainfall which could be aided by an upslope component. SPC currently has SW portion of CWA in a marginal risk. While ML CAPE remains relatively poor (At best 1000 J/KG), effective bulk shear values AOA 40 kts suggest transient supercell structures are possible across the marginal risk area...with isolated hail/wind threats. Furthermore, nearby frontal boundary and strongly backed low-level flow suggest an isolated tornado is also possible across the far southwest.
-- End Changed Discussion --
&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... By Friday...ridging across the central CONUS begins to weaken. This will allow the upper-level low to gradually retrograde and lift back to the north as it begins to become vertically stacked and fills/weakens. Rain rates are expected to gradually become less intense as activity becomes more scattered through the day. For now...did not adjust the expiration time of the Flash Flood Watch...though that will need to be revisited later today. Current thinking is that flooding issues would be more localized Friday. Gradual drying trend continues into Saturday...as vertically-stacked upper-level low continues to weaken and drift northward. While not a washout by any means...scattered shower activity will remain possible. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Influence of upper-level low finally begins to diminish by 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. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... Upper-level low will continue to impact the area today through Friday...bringing periods of IFR/LIFR to all the terminals. Heaviest rain expected today into Friday. Isolated thunderstorms are also possible today. Low ceilings are possible through Friday night with persists onshore flow. Gradual improvement Saturday...with a return to VFR by Sunday. && .MARINE...
-- Changed Discussion --
Solid SCA fo0r all wates today...as BUFKIT soundings and high- resolution guidance show winds remaining just below Gale. SCA currently expires at 12z Friday...though that may need to be extended into Friday afternoon. Gradient should begin to relax by later Friday evening...with SCA winds becoming less likely Saturday into the Weekend.
-- End Changed Discussion --
&& .TIDES/COASTAL FLOODING...
-- Changed Discussion --
Anomalies running around 1.5 feet. Since an easterly component to the wind will be in place through at least early Friday, water will only be reinforced. Pondered going with a Watch for the lower reaches (St Mary`s Co primarily... due to the susceptibility of St George Island) but ultimately opted not to since flow should be pushing water away from that part of the Potomac. However confidence is sufficient to extend Advisories through the Friday morning tide cycle. That`s not saying that moderate flooding is out of the question at some point between now and the weekend; rather certainty is too low to issue a Watch at this time. Water levels will continue to be an issue through at least Saturday.
-- End Changed Discussion --
&& .LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...Flash Flood Watch through Friday morning for DCZ001. Coastal Flood Advisory until noon EDT Friday for DCZ001. MD...Flash Flood Watch through Friday morning for MDZ003>006-011- 013-014-016>018-501>508. Coastal Flood Advisory until 10 AM EDT Friday for MDZ011-016. Coastal Flood Advisory until 8 AM EDT Friday for MDZ014-017- 018. VA...Flash Flood Watch through Friday morning for VAZ025>031- 036>040-050>057-501-502-505>508. Coastal Flood Advisory until 10 AM EDT Friday for VAZ057. Coastal Flood Advisory until noon EDT Friday for VAZ054. WV...Flash Flood Watch through Friday morning for WVZ050>053-055- 501>504. MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ530>534- 539>541-543. Gale Warning until 10 AM EDT this morning for ANZ530>534- 539>541-543. Small Craft Advisory until 8 AM EDT Friday for ANZ535>538-542.
-- End Changed Discussion --
&& $$ UPDATE...WOODY! PREVIOUS...MSE/HTS

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.