446 FXUS61 KLWX 111408 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1008 AM EDT Thu Oct 11 2018 .SYNOPSIS... A cold front will approach from the west today before passing through tonight. Tropical Storm Michael is expected to pass southeast of the area tonight. High pressure will build toward the region Friday, but an upper-level disturbance will pass through Friday night into Saturday. High pressure will return for later Saturday into Sunday before low pressure and its associated cold front impacts the area early next week. && .NEAR TERM /THROUGH TONIGHT/... A cold front is situated across eastern Ohio this morning as Tropical Storm Michael resides over South Carolina, moving northeast at 21 mph. The bulk of shower activity this morning has moved north of the Mason Dixon Line into Pennsylvania. KLWX is still detecting some fast moving and widely scattered showers pressing off to the northeast at around 35 mph. The 12z IAD sounding sampled an anomalously moist atmosphere with a daily record PWAT of 2.17 inches, besting the old record of 1.92 inches. South southwesterly flow at the surface and aloft dominates, which will continue to pump in tropical moisture across the region. Cloudy skies will persist today for much of the region, with a few breaks possible over southern MD and central VA. With plenty of cloud cover in place, temperatures will range from middle 70s to near 80 degrees this afternoon. On going forecast remains on track with no significant changes needed at this time. Previous discussion follows: By late afternoon, lift associated with the mid to upper level jet along the approaching cold front will move overhead. Virtually all guidance is in agreement with this, and a low- level deformation zone extending north from Michael interacting with the cold front. Models differ, however, in just how productive this deformation zone is given the fact that northwest dry advection will be taking place as the front crosses. Believe that there will be at least scattered heavier showers and thunderstorms along the front, with the most likely area for widespread and persistent heavy rain across central Virginia to southern and central Maryland. Generally 1 to 3 inches of rainfall is expected across this area, with locally higher amounts of 6 inches possible over southern Maryland (where the periphery of the main precipitation shield of Michael is most likely to cross ). A Flash Flood Watch is in effect for this afternoon and tonight for these areas. Generally up to an inch with some locally higher amounts are expected for much of the rest of the CWA. More isolated instances of flooding are possible outside the watch area. Further expansions are possible depending on how near term trends evolve today. A northwest gradient behind the cold front will combine with the peripheral wind field of Michael resulting in gusty winds of not purely tropical origin tonight. Winds gusts of 30 to 45 mph are expected, with around 50 mph over the central and northern Virginia Blue Ridge Mountains and portions of Southern Maryland, where a Wind Advisory is in effect. Gusty winds combined with saturated soil will bring down some trees, possibly resulting in a few power outages. Any embedded convective elements aided by the interaction between the periphery of Michael and the cold front could enhance gusty winds late this afternoon and evening. The most favorable right- front quadrant dynamics ahead of Michael should remain largely to our south, but a brief spin up can't be completely ruled out over the southern-most reaches of Maryland. For these reasons, SPC has place much of the area under a Marginal Risk. The front and Michael will depart into the western Atlantic after midnight, with rain chances diminishing from west to east. We should be virtually dry by daybreak Friday. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Surface high pressure will begin building toward the region from the Ohio Valley Friday into Saturday. Much more seasonable temperatures akin to mid-October are expected, with highs in the upper 50s and 60s and lows in the 40s and 50s both days. Aloft, a rather sharp mid/upper shortwave will pivot across late Friday night. Isolated to scattered showers seem plausible with the approaching trough late Friday night into early Saturday morning, most likely across the Potomac Highlands. The highest elevations of 3000+ feet over the Allegheny Front could see a few wet snowflakes mix in late Friday night as 850 mb temps drop below freezing. With surface high pressure solidly overhead by Saturday evening, dry and mainly clear conditions are expected. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... High pressure will move offshore Sunday while low pressure and its associated cold front move through the Great Lakes. An upper-level ridge will be centered over the southeastern CONUS during this time while a an upper-level trough extends from the northern Plains into the Rockies. A southwest flow will allow for high and mid-level clouds to return for Sunday. An isolated shower/sprinkle cannot be ruled out either, but much of the day should be dry. Low pressure will pass by well to the north Sunday night through Monday and its associated cold front will approach Sunday night from the west before passing through Monday. Showers are possible ahead of the cold front during this time. The boundary will stall out overhead or just to the south for Monday night through Tuesday before another weak wave of low pressure rides along the boundary. More unsettled conditions are possible during this time. High pressure will likely return for the middle portion of next week as the boundary drops farther south. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... Seeing improving conditions at the terminals this morning as the bulk of shower activity has moved off to our north. MVFR/VFR CIGs will persist for many of the terminals through early afternoon. A cold front will approach from the west later this afternoon as Tropical Storm Michael nears but remains southeast of the terminals. This will induce widespread showers and isolated thunderstorms late this afternoon and this evening, with episodes of IFR conditions returning with any heavier showers/storms as the cold front crosses the area and Michael passes to our south and east. Gusty northwest winds will develop behind the cold front this evening, most likely beginning between 00z and 02z near KMRB and from 02z-05z for the rest of the terminals. Gusts around 30 to 35 knots are likely late this evening and overnight. Gusty northwest winds will continue Friday as well with 20 to 30 knots most likely. Winds will diminish Friday night as high pressure builds overhead. VFR conditions are expected from later this evening through Friday. An upper-level disturbance may trigger a few shower late Friday night into Saturday with possible MVFR conditions. High pressure will return for later Saturday through Saturday night. VFR conditions are expected Sunday into Sunday night. A cold front may trigger showers and brief MVFR conditions later Sunday night and Monday. Southwest winds ahead of the boundary Sunday night and Monday will shift to the north and northwest behind the boundary late Monday or Monday night. && .MARINE... Intermittent SCA gusts this morning across the lower Tidal Potomac and MD portion of the lower Bay given a stronger gradient. As a cold front approaches the waters this evening and Tropical Storm Michael nears to the south and east, strong gusty winds to gale force are anticipated for all waters this evening and persisting through Friday morning. Storm force winds are expected for a time late this evening into the overnight over the lower tidal Potomac and lower Maryland portion of the Chesapeake Bay. There will be the potential for waterspouts in an outer rain band over these lower marine zones, but the most favorable right-quadrant dynamics ahead of Michael should stay mainly to the south. In addition to strong winds tonight, waves will build to 5 to 8 feet over the open parts of the Bay, making navigating the waters difficult and dangerous. Winds will gradually subside Friday afternoon through Saturday, but Small Craft Advisories will likely be needed before winds go completely light by Saturday evening thanks to high pressure building overhead. A cold front will approach the waters from the west Sunday night into Monday before passing through late Monday or Monday night. Winds may reach SCA criteria during this time. && .TIDES/COASTAL FLOODING... A southerly flow will continue through this afternoon, and possibly into this evening. Elevated water levels will persist during this time with minor flooding expected for sensitive areas. A Coastal Flood Advisory is in effect for Washington DC, Annapolis, and Straits Point in St Marys County through this evening. A Coastal Flood Advisory may be needed for this evening for Alexandria, Baltimore and other locations, but confidence is too low at this time since the high tide will be occurring around the same time a strong offshore flow is developing. Strong northwest winds will develop late this evening and overnight behind a cold front and also as Michael moves offshore to our south and east. Tidal blowout conditions are possible Friday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 1 AM EDT Friday for DCZ001. MD...Flash Flood Watch from 2 PM EDT this afternoon through late tonight for MDZ011-013-014-016>018-508. Wind Advisory from 6 PM this evening to 6 AM EDT Friday for MDZ017-018. Coastal Flood Advisory until 11 PM EDT this evening for MDZ014. Coastal Flood Advisory until 8 PM EDT this evening for MDZ017. VA...Flash Flood Watch from 2 PM EDT this afternoon through late tonight for VAZ036-037-050-055>057-508. Wind Advisory from 6 PM this evening to 6 AM EDT Friday for VAZ507-508. WV...None. MARINE...Gale Warning from 6 PM this evening to 6 PM EDT Friday for ANZ530>532-535-536-538>542. Small Craft Advisory until 6 PM EDT this evening for ANZ534- 537-543. Storm Warning from 6 PM this evening to 6 AM EDT Friday for ANZ533-534-537-543. Gale Warning from 6 AM to 6 PM EDT Friday for ANZ533-534-537- 543. && $$ SYNOPSIS...BJL NEAR TERM...BKF/DHOF SHORT TERM...DHOF LONG TERM...BJL AVIATION...BJL/BKF/DHOF MARINE...BJL/BKF/DHOF TIDES/COASTAL FLOODING...BJL