027 FXUS61 KLWX 110027 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 827 PM EDT Sun May 10 2020 .SYNOPSIS... High pressure slowly moves off shore as a clipper system moves through this evening and into Monday. High pressure settles over our region Tuesday through Wednesday. Front will move to the north of our region on Thursday and stalls through the end of the week. && .NEAR TERM /THROUGH MONDAY NIGHT/... Low pressure will track through the Ohio Valley into Pennsylvania tonight and the cold front associated with this system will move into the Potomac Highlands late this evening before making it into the Baltimore and Washington Metropolitan areas after midnight. A few showers may accompany the frontal passage, but with limited moisture precipitation amounts will be light. There is also the threat for locally gusty winds with shower activity later this evening near the Allegheny Highlands. This is because there is low-level dry air and steeper low- level lapse rates in place. However, the lapse rates should diminish some over the next couple hours so the threat for damaging wind gusts is low at this time. Will continue to monitor throughout the rest of the evening. Increased clouds and a steady south to southwest wind ahead of the front should keep temps milder than last night (40s for most areas, near 50 in Washington/Baltimore, and lower to middle 50s over southern Maryland). The cold front will move off to the east early Monday morning and an upper-level trough will build overhead as an upper-level low passes by to the north. Any leftover showers across eastern areas early Monday morning should dissipate behind the cold front. However, there will be some instability that develops late Monday morning into Monday afternoon, and this may trigger a shower or two. Precipitation amounts will be light and much of the time will be dry. For locations along/west of the Allegheny Front, there will be more showers due to an upslope flow and there will be enough cold air for some snow showers (especially above 3kft). Snow accumulations around an inch or so is possible for elevations above 3kft. Max temps Monday will range from the 30s above 3kft along the Allegheny Front, to the 50s for the valleys west of the Blue Ridge, to the lower 60s around Washington DC into central VA and southern MD. Temps will be around 10-15 degrees below climo. Breezy conditions are expected as well due to cold advection increasing the mixing layer and a stronger gradient ahead of approaching high pressure. West to northwest winds will frequently gust around 20 to 30 mph. Winds should weakened by nightfall and skies will slowly become mostly clear. The combination of light winds and clear skies may lead to some good radiational cooling especially over central Virginia where rain is least likely. Some Frost/Freeze concerns will be possible for portions of northern and central Virginia, WV and western Maryland mainly west of the Blue Ridge. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... High pressure will build over our region on Tuesday. Skies should be mostly clear with winds mainly out of the west. Gusty winds of 20 to 25 mph will be possible due to the pressure gradient and some stronger winds aloft being mixed to the surface. Daytime temps should hover in the 50s and lower 60s with cooler temps out near the Allegany front. Tuesday evening will be another chilly night but temps should remain mostly above the freezing in the mid 30s. Areas along the Allegany front will likely experience another night of below freezing temps. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Surface high pressure will be overhead Wednesday but will be moving to the east. This will allow some moderation to the airmass, though WNW flow will continue aloft. High temperatures will end up in the 60s for most, still a little below normal. There will be a large scale pattern shift late in the week that guidance has a good handle on. As a closed low slowly dives toward the west coast, upper level ridging will be maintained over the eastern CONUS, with a large Bermuda-type surface high off the east coast. A series of low pressure systems will take shape in the Plains and ride around the ridge toward the Great Lakes. The first such system will push a warm front northward through the area on Thursday. A few showers may occur with this feature, especially over the Appalachians closer to the best forcing. With additional clouds and later timing, temperatures on Thursday will likely remain near or slightly below normal. The finer scale uncertainties remain for the end of the week. The warm front will likely be north of the area Friday, which should lead to above normal temperatures -- in the 80s for many. After that, the strength of Canadian high pressure will determine if the front returns back south as a backdoor cold front, or if the southern ridge wins out and we remain in the warm sector. The former would result in slightly cooler temperatures and higher rain chances, while the latter would result in above normal temperatures. There still could be a some showers, and a higher chance of thunderstorms (due to being in the warm sector), as the next wave of low pressure rides along the front later Saturday or Sunday. This low may push the front back southward late in the weekend. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... VFR conditions are expected most of the time through Monday. A few showers are possible overnight into early Monday, and again late Monday morning into Monday afternoon. However, precipitation amounts will be light (if any). South to southwest winds will turn to the west and northwest behind a cold front Monday morning. Frequent gusts around 20 to 25 knots are expected Monday behind the cold front. Winds will diminish around sunset Monday evening, Clear skies and light winds expected Monday night into Tuesday with some gusty winds returning for all terminals Tuesday. VFR conditions will persist. VFR expected Wednesday. A few showers possible Thursday with a warm front, though chance of impacts is low at this time. There could be another chance of showers and a few thunderstorms Friday depending on the proximity of the front as it wavers to our north. && .MARINE... A south to southwest flow will continue tonight ahead of an approaching cold front. An SCA is in effect for the middle Bay and lower Tidal Potomac River tonight. The SCA may need to be extended farther north into the northern Chesapeake Bay, but confidence is too low to do so at this time due to a weaker gradient. The cold front will pass through early Monday morning and gusty west to northwest winds are expected behind the boundary. An SCA is in effect for all of the waters Monday. The SCA may need to be extended into Monday night for portions of the waters. Another round of gusty winds are possible Tuesday with more SCA conditions. Light winds are expected Wednesday with high pressure. Southerly flow will begin increasing Thursday as the high moves offshore and a warm front lifts north. Winds could be near Small Craft Advisory levels, especially Thursday night into Friday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...Freeze Watch from late Monday night through Tuesday morning for VAZ025-026-503-504-507-508. WV...Freeze Watch from late Monday night through Tuesday morning for WVZ505-506. MARINE...Small Craft Advisory until 6 PM EDT Monday for ANZ532>534-537- 540-541-543. Small Craft Advisory from 9 AM to 6 PM EDT Monday for ANZ530- 531-535-536-538-539-542. && $$ SYNOPSIS...BJL NEAR TERM...BJL/JMG SHORT TERM...JMG LONG TERM...BJL/ADS AVIATION...BJL/ADS/JMG MARINE...BJL/ADS/JMG