Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
549 FXUS61 KLWX 171829 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 229 PM EDT Tue Sep 17 2024 .SYNOPSIS... Low pressure over the Carolinas will gradually weaken through Wednesday. Another low may develop off the coast during the second half of the week. A backdoor cold front may push into the area Saturday. Strong high pressure will build northeast of the area in its wake. && .NEAR TERM /THROUGH TONIGHT/... Low pressure over west-central North Carolina will continue to move toward the northwest today and tonight. Low clouds will continue to cover the forecast area, especially further south into central VA where the proximity to the low pressure system in NC is closer. Isolated to scattered showers will continue to inch further north throughout the day with the best chances for rain across central VA and parts of the lower Allegheny Front. It is a tricky forecast for rainfall totals through tonight and into early Wednesday. For areas north of I-66, a general swath of a few hundredths of an inch to half an inch are expected. Further south, totals will be higher where the rainfall will be heavier and more steady. Guidance has continued to hint at two relative maximums across the forecast area, 1) the eastern slopes of the Blue Ridge and 2) across portions of central VA into northern VA. The first area is more terrain induced whereas the second area of interest is where the low-level jet likely sets up late tonight and into early Wednesday. There may be a localized area of 1-2" across that area. Cannot rule out higher amounts across the eastern slopes of the Blue Ridge. For now, isolated instances of flooding remain possible later tonight and into Wednesday, especially across areas along/south of I-66 and along/east of the Blue Ridge. Highs will continue to climb into the mid to upper 70s across areas east of the Blue Ridge, with slightly cooler temps further south and west where more rain and cloud coverage will reside. Lows tonight in the middle 50s in the west and the lower to middle 60s in the eastern zones. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... The aforementioned low pressure will continue to move across western NC and further west on Wednesday. Rain will continue through most of the day for a large portion of the area, with the VA Piedmont likely receiving the most precipitation. Additional totals of 2-3" are certainly possible through the day on Wednesday as the low begins to break down and a coastal low forms off the Delmarva. Cannot rule out a rumble of thunder in the afternoon hours but overall convective activity should be fairly suppressed. Highs top out in the upper 60s to low 70s along and west of the Blue Ridge where the more cooler side of the low resides and a few degrees warmer further east towards the waters. Overnight lows Wednesday night drop down into the mid to upper 50s along the Allegheny Front and low 60s further east. As the coastal low begins to shift further northeast, expect shower chances to decrease from west to east during the day on Thursday. There may be some general clearing later in the day. Highs will top out in the upper 70s to near 80 for most areas. Northwesterly flow will allow temperatures to drop down into the upper 40s to low 50s along portions of the Allegheny Front Thursday night, with mid to upper 50s more common further east with low 60s near the waters. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Long term period continues to trend drier as model guidance keeps the trough axis offshore. A backdoor cold front is set to drop through the forecast area Friday afternoon and throughout the day on Saturday as an upper level trough deepens over Canada into New England. Cooler and drier air will move in with temperatures expected to stay below normal. High pressure will keep conditions primarily dry with a low pressure system off the coast of the Carolinas leading to slight chance of PoPs in the southeastern portions of the area through Monday. Precipitation chances increase elsewhere on Monday as a low pressure system approaches from the west. High temperatures will be in the upper 70s to low 80s on Friday with higher elevations staying in the mid to low 70s. Temperatures cool slightly each day with high temperatures on Monday expected to be in the low to mid 70s for most. High elevations will stay in the upper 50s to 60s. Overnight low temperatures will be in the 50s for most each night with metro areas staying in the low 60s. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Occasional light to moderate showers could bring IFR conditions to the terminals today with a better emphasis of IFR conditions due to lowered ceilings near CHO. Better chances for IFR conditions will be later tonight. Rain showers will likely continue off and on Wednesday with low pressure nearby. Winds northeast to east 5 to 15 kts through Wednesday. Gusts of 20 to 25 kts are possible, mainly each afternoon and evening, especially at terminals close to the waters and along the ridges. With the residual low pressure nearby, expect periods of MVFR to IFR conditions. Underneath a mid-level low pressure system on Thursday, scattered showers may develop across the area. Clouds should be abundant which may afford periods of sub-VFR conditions. Prevailing VFR conditions are expected Friday and Saturday with dry conditions at all terminals. Northeasterly winds on Friday shift to easterly on Saturday. && .MARINE... SCA conditions will persist through the day today. This is in association with a tightened pressure gradient from blocking high pressure to the north and low pressure moving inland across the coastal Carolinas. As a weakening area of low pressure tracks through the area, winds will be out of the east on Wednesday while likely remaining at SCA levels for at least portions of the waters. Winds will become more northeast Wednesday, then more northerly while diminishing on Thursday. Northeasterly winds are expected to stay below SCA criteria on Friday with winds gusting 10 to 15 knots. Winds shift more easterly on Saturday with Small Craft Advisories likely as winds gust 15 to 20 knots. && .TIDES/COASTAL FLOODING... With low pressure inland over the Carolinas and winds from a northeasterly direction, there have not been significant rises in anomalies, with the highest values greater than one foot along the Potomac. Advisories remain in effect, but most flooding will be marginal. Between the full moon and continued onshore flow, tide levels will likely remain elevated and near minor flood thresholds much of the week. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Coastal Flood Advisory until 10 PM EDT this evening for DCZ001. MD...Small Craft Advisory until 6 AM EDT Wednesday for MDZ008. Coastal Flood Advisory until 10 PM EDT this evening for MDZ014. Coastal Flood Advisory until 6 PM EDT this evening for MDZ016- 018. VA...Coastal Flood Advisory until 10 PM EDT this evening for VAZ054. Coastal Flood Advisory until 6 PM EDT this evening for VAZ057. WV...None. MARINE...Small Craft Advisory until 6 AM EDT Wednesday for ANZ530>534- 536>543. Small Craft Advisory until midnight EDT tonight for ANZ535. && $$ SYNOPSIS...ADS/ADM NEAR TERM...KLW/ADM SHORT TERM...KLW/ADM LONG TERM...AVS AVIATION...AVS/ADM MARINE...AVS/ADM TIDES/COASTAL FLOODING...LWX