444 FXUS61 KLWX 211904 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 304 PM EDT Thu May 21 2020 .SYNOPSIS... Low pressure over the Tennessee Valley will begin to lift north and east tonight and pass over the area late Friday night. Broad ridging will build over the eastern United States Saturday night through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... Cloudy to mostly cloudy conditions are observed over our area this afternoon as high pressure sits to our northeast and a surface low is to our south. Aloft a stalled upper level low is located over the Tennessee Valley. Easterly to northeasterly flow continues to advect moisture our way, and a few isolated rain showers have been observed moving into Central Virginia. This is expected to continue and increase through the rest of the day today, as rain showers become more scattered into numerous this evening over Central Virginia. High res guidance brings rain, which can be moderate at times, over Central Virginia into this evening. Upslope enhancement on the east side of the Blue Ridge in this region will increase rain rates over these areas. Rain amount totals are between 1 and 3 inches of rain, with isolated higher amounts, so a Flash Flood Watch is in effect (see Hydro section). As the upper level low moves northeast into tonight, the rain band will start to push north and east across our CWA into the morning hours. Low temperatures tonight will generally be in the 50s, maybe low 60s. && .SHORT TERM /FRIDAY MORNING THROUGH SATURDAY NIGHT/... Upper level low and surface low will be moving into the Mid-Atlantic through the day Friday. A band of rain will still be over our area during the first half of the day Friday as it progresses north and east along with the upper level low. As this rain band moves away and clouds break west of it, along with some instability and lift, could see a few thunderstorms developing Friday afternoon, mainly over Central Virginia and the Potomac Highlands. High temperatures will be between the mid 60s and upper 70s. Surface and upper level lows will move east and offshore on Friday night, but a chance of rain showers remain. Low temperatures will be in the 50s and 60s. Upper level low will be pushing offshore early Saturday as conditions continue to dry over our area, however upper level energy behind this system and some instability could produce afternoon thunderstorms on Saturday. High pressure will start building over our region Saturday night along with ridging aloft. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Mid to upper level ridging will take hold the second half of the holiday weekend as surface high pressure off the New England coast stretches a ridge down into the Mid-Atlantic region. As ridging begins to build, some linger upper level energy could be enough to spark some afternoon showers/storms across the Potomac/Allegheny Highlands. Otherwise, dry conditions and temperatures in the low to middle 70s expected. Continued dry conditions for your Memorial Day and into Tuesday as the upper ridge crests over the Mid-Atlantic and the ridge of high pressure remains strong over the Eastern Seaboard. Temperatures and humidity will tick upwards given southerly flow around the high to our east. With diurnal heating and increasing moisture, our mountain zones will reside on the western fringes of the surface ridge, with low end chance showers/storms possible both Monday and Tuesday afternoons. Better chance of rain comes Wednesday afternoon and evening as the high to our east nudges further eastward into the Atlantic and a weak shortwave tracks to our north. Temperatures will rise into the 80s with dewpoints in the 60s, so a bit better ingredients to support higher shower/storm chances during this time. && .AVIATION /THURSDAY THROUGH TUESDAY/... VFR to MVFR conditions expected for the rest of today, but expecting MVFR to remain over CHO along with rain showers. A rain band starts to spread north and east across our region tonight bringing restrictions over the terminals. IFR to LIFR due to VSBYs and CIGS are expected over the main terminals (IAD, DCA, BWI) after midnight, and possibly into Friday morning. Conditions will improve to VFR on Friday with a chance of showers remaining, maybe a TSRA near CHO in the afternoon, and a passing showers into Friday night. VFR on Saturday with afternoon TSRA possible. VFR conditions expected to persist at the terminals Sunday through Memorial Day as a ridge of high pressure at the surface and ridging aloft take hold. Winds will remain light and out of the ESE at less than 10 knots. && .MARINE... Small Craft Advisory is in effect through this evening over the lower Bay. Wind gusts may be marginal to Small Craft Advisory Criteria for tonight but not confident enough to issue it, as well as Friday morning. Winds will become light through Saturday night. High pressure building at the surface and aloft will maintain sub SCA conditions over the waters Sunday through Memorial Day as light east southeast winds prevail. && .HYDROLOGY... Surface low pressure will pass over southern portions of the forecast area this evening through Friday. Moisture associated with this system will be on the increase across southwestern portions of our forecast area this afternoon. Rain, moderate at times, will begin to spread across the region from southwest to northeast throughout later today across the southwest. Enhanced rainfall rates can be expected along the Blue Ridge in northeasterly flow. Numerous moderate rain showers will continue into Thursday night across the southwestern zones. The band of moderate rain showers will then begin to move a little more quickly as it pushes to the northeast on Friday. The result of this will be less of a flood threat as you move northeast. Most likely rainfall amounts are expected to be around 1-3", with the possibility of higher amounts in excess of 4" possible along the ridgelines, where upslope flow will enhance precipitation rates. This will cause creeks and streams to gradually rise, with the potential for flooding Thursday night into Friday. As a result of all of this, a Flash Flood Watch is in effect for several counties across the southwestern portion of our forecast area through late tonight. && .TIDES/COASTAL FLOODING... Anomalies remain elevated under an easterly flow with the threat for minor tidal flooding existing at D.C. Southwest Waterfront and Annapolis during the high tide cycle late tonight and early Friday morning. Elsewhere, Action stage will be achievable but minor flooding is not currently forecast. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...Flash Flood Watch through late tonight for VAZ025-036-037-503- 504-508. Flash Flood Watch from 8 PM EDT this evening through late tonight for VAZ026-038-039-507. WV...Flash Flood Watch from 8 PM EDT this evening through late tonight for WVZ505-506. MARINE...Small Craft Advisory until 9 PM EDT this evening for ANZ534- 537-543. && $$ SYNOPSIS...CJL NEAR TERM...IMR SHORT TERM...IMR LONG TERM...BKF AVIATION...IMR/BKF MARINE...IMR/BKF HYDROLOGY...CJL/IMR TIDES/COASTAL FLOODING...BKF