Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 290751 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 351 AM EDT Thu Oct 29 2020 .SYNOPSIS... A front will remain stalled over our region through Friday. The remnants of Zeta along with a secondary low will move along the front today through Friday. High pressure briefly builds into our region on Saturday before a powerful cold front moves through Sunday into early Monday. High pressure builds over our region through the later parts of next week. && .NEAR TERM /THROUGH TONIGHT/... A frontal boundary remains stalled over our region this morning with a light southerly flow advecting in moist air into our region. Tropical Storm Zeta is currently located in northern Alabama this morning and is moving NE at 31 mph. The current track from the Hurricane Center has the center of Zeta moving just south of the DC metro. This will place us on the favorable wet side of the storm which will set up our region to receive a decent amount of rain today into Friday. The outer bands of rain are starting to move into our region with rain expected to overspread all of our region over the next couple of hours. Rain will start out as light this morning but an extended period of moderate to heavy rain is expected later this morning and into this afternoon. PW`s ahead of the Zeta are running in the 1.6 to 1.7 range and are expected to continue to rise through this afternoon. The high PW`s combined with the tropical air mass from Zeta will lead to a swath of 1 to 3 inches of rain throughout our region over the next 36 hours with locally higher amounts near 4 inches possible. The possibility of 2 to 3 inches of rain in a 24 hour period will lead to the threat for isolated to scattered flooding. The main areas of concern will be our urban areas along with areas along the Blue Ridge Mountains. I think overall the flood threat should be isolated due to dry antecedent conditions with FFG running from 2.5 to 3 inches in an hour. The biggest concern will be clogged storm drains along with small to moderate sized streams that could receive 2 to 3 inches in multiple locations and translate the water further down stream. A flood Watch is in effect through 10pm this evening. The heaviest rain should start to shift eastward out of our region later this evening with mainly light rain and showers continuing through the overnight periods. A secondary low will form along the frontal boundary and shift eastward through our region bringing additional precipitation to our region during the early morning periods of Friday. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... The remnants of Tropical Storm Zeta will have shifted off the east coast by Friday morning. The front that has hovered in our area will remain stalled over our region through Friday afternoon. A surface low pressure system will form and move along the frontal boundary bringing another round of rain to our region during the early parts of Friday morning. The low should track to our south over portions of central Virginia sparing our area of the heaviest rain. As the low approaches the coast, it will interact with an upper level trough along with an upper level jet and strengthen considerably along the MD/VA eastern seaboard. The main cyclogenesis should occur during the morning periods of Friday as the low transitions off of the eastern seaboard. A burst of moderate rain will be possible on the west side of the low which could impact areas along and east of the I-95 corridor. This additional rain on top of the moderate to heavy rain we are expecting today could lead to isolated to scattered instances of flooding especially in our urban areas and along the Blue Ridge Mountains. The main threat from the strengthening low will be the increasing winds that will be focused over our marine waters. The front and surface low should full move off the coast Friday afternoon with a few lingering showers possible into the evening periods. The pressure gradient should weakened as the front pulls further away from the coast which will allow winds to weakened but 18 to 20 knots winds will continue to be possible for areas east of the I-95 corridor through early Saturday. Showers will end by late Friday evening and dry conditions are expected through Saturday. High pressure will briefly build to our north over southern PA bringing cooler and drier conditions to our region on Saturday. Saturday morning temps will hover in the low to mid 30s along and west of the I-95 corridor with upper 30s to low 40s along the Bay. A Freeze Watch has been issued for our remaining counties along the MD/PA border along with Jefferson County WV and western Loudoun. The high pressure will shift off to our northeast by Saturday evening leading to a weak return flow forming ahead of a weak cold front. Daytime highs on Saturday will be mild in the upper 40s to low 50s. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... A powerful cold front will be approaching from the west on Sunday, but will not arrive until Sunday night. Thus, we will see a mild southwest flow which should allow temps to moderate significantly compared to Saturday`s chilly temps, with a rise of 10 or more degrees possible. This, however, would only bring temps back to near normal. The front will cross the region late Sunday into Sunday evening, with some showers along or just behind the front possible. Will have to watch for potential low-topped convection, as well as for a burst of gusty winds behind such a powerful front. Gradient winds will be strong behind the front, particularly on Monday as low pressure strengthens to our northeast, providing a windy and chilly start to the work week. Humidity will also be low, and if it wasn`t for the rains we will get today, there could be a fire weather concern. Winds could approach advisory criteria on Monday, which might cause minor damage, mainly to trees. Temps Monday will be well below Sunday, and in fact stand a good chance of being the coldest so far this season, with temps potentially staying in the 30s and 40s all day long. This would lead to another widespread freeze potential, with likely the coldest night of the season thus far Monday night. Temps in most suburbs could reach the 20s, especially if the wind slackens late at night. High pressure passing to our south should allow for a lighter, more westerly wind on Tuesday, shifting southwesterly on Wednesday, which will provide a dry mid-week with milder temperatures. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... Rain will overspread all of our terminals this morning with moderate to heavy rain expected later this morning and into this afternoon. Ceilings have dropped down into the MVFR to IFR range for all of our terminals except for MRB. I expect ceilings to drop into the IFR range for all terminals through this evening with a period of LIFR ceilings as the moderate rain moves through our region. Visibility will also drop down into the IFR category with periods of LIFR and VLIFR during heavy rain. The heaviest rain should move out of all our terminals later this evening with light rain and showers continuing into Friday morning. A second round of heavy rain will be possible Friday morning as another low moves through our region. Strong gust winds will be possible for terminals along and east of the I-95 corridor with winds becoming northerly Friday afternoon. Rain should completely stop by Friday afternoon with ceilings increasing into the MVFR range and eventually VFR by Friday evening. Clouds will start to break Friday evening with mostly clear to partly cloudy skies by Saturday morning. VFR conditions expected on Saturday. Main aviation concern Sunday and Monday will be the strong cold front and gusty winds along and after the front crosses the region, along with a few showers. Sub-VFR conditions may briefly occur with showers late Sunday, but VFR should prevail overall. Winds could gust to 50 mph, however. Some low-topped convective showers could also bring gusty winds with the front Sunday. && .MARINE... A stalled boundary will remain in place over the waters through Friday. The remnants of Zeta along with a secondary low will bring strong and gusty winds to our marine waters today through early Saturday. A Gale Warning is in effect through early Friday morning with a Small Craft Advisory continuing through Friday. There is a potential for another round of Gale level winds late Friday morning and into Friday afternoon but confidence remains low at this time. Small Craft Advisories will likely need to be extended into early Saturday morning but winds are expected to taper off on Saturday afternoon and SubSCA conditions are expected for the majority of Saturday. Strong gusty winds are the main concern Sunday and Monday as a powerful cold front blasts across the region. Gales look very possible, possibly in two waves - one late Sunday with the front, and one on Monday as low pressure strengthens to our northeast. && .TIDES/COASTAL FLOODING... Elevated water levels are expected today as the remnants of Zeta pass through. Minor flooding cannot be ruled out during this time, but latest forecast track suggests that anomalies will not build sufficiently to produce any flooding. Will continue to monitor the track of Zeta and water level anomalies, however, as a track farther north across our waters will increase the chances for minor flooding. Refer to the National Hurricane Center for the latest on Zeta. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Flood Watch through this evening for DCZ001. MD...Flood Watch through this evening for MDZ004>006-011-013-014- 016>018-503>508. Freeze Watch from late Friday night through Saturday morning for MDZ004>006-505-507-508. VA...Flood Watch through this afternoon for VAZ025>027-029>031- 036>040-503-504-507-508. Flood Watch through this evening for VAZ050>057-501-502-505- 506. Freeze Watch from late Friday night through Saturday morning for VAZ505. WV...Flood Watch through this afternoon for WVZ505-506. Freeze Watch from late Friday night through Saturday morning for WVZ053. MARINE...Small Craft Advisory from 7 AM this morning to 1 PM EDT this afternoon for ANZ532>534-537-540>543. Small Craft Advisory from 10 PM this evening to 6 PM EDT Friday for ANZ532>534-537-540>543. Gale Warning from 1 PM this afternoon to 10 PM EDT this evening for ANZ532>534-537-540>543. Flood Watch through this evening for ANZ535. Small Craft Advisory from 7 AM this morning to 6 PM EDT Friday for ANZ530-531-535-536-538-539. && $$ SYNOPSIS...JMG NEAR TERM...JMG SHORT TERM...JMG LONG TERM...RCM AVIATION...RCM/JMG MARINE...RCM/BRO/JMG TIDES/COASTAL FLOODING...

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