Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210125 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 825 PM EST Mon Nov 20 2017 .SYNOPSIS... High pressure will build to our south through tonight. The high will move offshore Tuesday and a cold front will pass through Tuesday night into early Wednesday. High pressure will build back overhead later Wednesday through Thanksgiving Day. The high will build to our south for Friday and Saturday before a cold front moves through Saturday night. && .NEAR TERM /THROUGH TUESDAY/... High pressure is adrift toward the western Atlantic to our south this evening. Scattered high cirrus noted over the Ohio Valley is moving east into the area. That coupled with a developing low level jet will be less than ideal for radiational cooling after midnight, but temperatures are falling quickly this evening with low dew points and clear skies. Most places outside the cities will likely tank early, then rebound late. Lows will be below freezing where radiational cooling can get going early, but the cities should have trouble falling much below 40. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... High pressure continues sliding east off the coast on Tuesday as low pressure starts developing off the southeast coast late in the day. Strong southerly to southwesterly flow will bring warmer air north, so it will be breezy and somewhat milder, with highs likely to top 60 in warmer locales. High clouds will be thickening as the next series of shortwaves approaches, but otherwise dry weather expected. A lot of uncertainty remains regarding development and track of coastal low Tuesday night. American models still keep the system east of the region, with rain just scraping southern MD, while EC brings rain up to I-95 and Canadian guidance spreads rain across the entire CWA. Have tapered POPS gradually, with likely in southern MD, chance along I-95 and slight chance near I-81 in response. With the milder air brought north on Tuesday, this should be all rain across these regions. However, late at night the cold front currently entering the northwestern Plains will arrive, bringing colder air and showers along the Allegheny Front, which are likely to change to snow before the night is over. Lows will stay well above freezing east of I-81, but the Allegheny Front will drop below late. Cold front sweeps any rain east of the region early on Wednesday, with a gusty northwest wind and ongoing cold advection. Temps likely to not follow a normal diurnal trend, perhaps steady or slowly falling during the afternoon, but should not be as windy as Sunday. Otherwise, reasonable travelling weather is expected for the day before THanksgiving. Temps will be hovering near 50 much of the day along I-95, cooler west. High pressure builds east into the region Wednesday night, with diminishing wind and a return of more widespread sub-freezing readings. && .LONG TERM /THURSDAY THROUGH MONDAY/... High pressure will build into the region Thursday through Friday night. Dry conditions with plenty of sun expected each day and mainly clear skies each night. Despite the daytime sun, temperatures each period will be about 5 to 15 degrees below average with highs in the upper 40s to low 50 and lows in the upper 20s to near 30. Thursday will be the colder of the two days, with some moderation Friday as winds turn southwest. A storm system over eastern Canada will bring a cold front toward and across the mid-Atlantic Saturday and Saturday night. There is a chance for a few rain showers along the Mason-Dixon region Saturday with a chance of rain and snow showers in the Appalachians and along the Mason-Dixon regions Saturday night. Temperatures will be closer to normal Saturday. A gusty northwest wind will usher in cold air into the region Sunday. With that, a chance of snow showers are expected in the Appalachian Mountains. Below average temperatures expected to retake the region. High pressure will be in control on Monday. Dry conditions with below average temperatures across the region. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... Generally VFR through the TAF period. High pressure shifting east overnight will set up a low level jet over the terminals by early morning, so included a little low level wind shear in the TAFs - it may last a bit longer than currently indicated. Currently shown in BWI/IAD TAF (35-40 kts through 2000 feet) but not DCA as surface winds here will be a few knots higher thus shear a touch lower (but still non-zero, 25-30 kts through 2000 feet). After inversion breaks, should generally be a gusty S-SSW wind perhaps up to 30 knots at times during the day. A period of sub-VFR cigs and vis is possible Tuesday night depending on track of a coastal low pressure - American models are further east, while Canadian and European suites bring some rain into the terminals overnight. Solidly VFR Wednesday- Wednesday night with a gusty northwest wind of 20-30 knots during the day, diminishing a bit at night. VFR conditions Thursday through Friday night. Winds light and variable Thursday and Thursday night. Winds northwest becoming south around 10-15 knots Friday into Friday night. && .MARINE... Winds are in a bit of a lull right now but made no change to going headlines as winds will slowly ramp up beneath a developing low level jet tonight. SCA continues for Bay waters, and starts up again on the more sheltered waters by early Tuesday, with mixing expected to bring 20-30 knots gusts to the surface before midday Tuesday. This low level jet may be disrupted as a coastal low passes to the southeast Tuesday night, so relax SCA headlines as we head through the night. However, SCA likely to return Wednesday as another cold front blows through early in the day. Winds may start to relax again later Wednesday night. No marine hazards Thursday-Thursday night. Winds light and variable Thursday and Thursday night. Increasing winds from the southwest Friday into Saturday ahead of the next cold front may require more Small Craft Advisories. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from midnight tonight to midnight EST Tuesday night for ANZ531-539-542. Small Craft Advisory from 6 AM to 6 PM EST Tuesday for ANZ535- 536-538. Small Craft Advisory until midnight EST Tuesday night for ANZ532>534-537-540-541-543. Small Craft Advisory from 6 AM Tuesday to midnight EST Tuesday night for ANZ530. && $$ SYNOPSIS...RCM NEAR TERM...RCM/DHOF SHORT TERM...RCM LONG TERM...KLW AVIATION...RCM/KLW/DHOF MARINE...RCM/KLW/DHOF is the U.S. government's official web portal to all federal, state and local government web resources and services.