Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
473 FXUS61 KLWX 170806 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 406 AM 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/... This section will be updated shortly due to technical issues. It`s really not until Tuesday morning into Tuesday afternoon when more widespread rain chances move into the region, however. Most of us will see a continuation of cloudy skies with perhaps a little drizzle/spotty shower activity making it as far north as central Virginia. Areas of drizzle are likely north of I-66/US-50 by late tonight into Tuesday morning as steadier light to moderate showers push into central VA and the central Shenandaoh Valley. PWATS will likely increase into the 1.0-1.5" range this evening before hopping up into 1.25-1.75" late tonight into Tuesday. No flooding is expected given antecedent drought concerns. Rain amounts through Tuesday will range between a tenth to a half an inch areawide. Heaviest totals of a half to one inch are possible across the central Virginia Blue Ridge Mountains due in part to an easterly upslope enhancement. Outside of the rain will be the wind. Gusts up to 30 mph are possible along the higher ridges of the WV/VA Highlands and central Virginia Blue Ridge. Elsewhere, gusts of 15 to 25 mph are possible, especially in areas along the waters. Lows tonight will be in the low to mid 60s with a few low 50s in the western mountains. Slightly cooler conditions are expected Tuesday with highs in the mid to upper 60s and low 70s west of the Blue Ridge, and mid 70s further east. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... On and off rain chances look to continue through midweek as low pressure slowly moves north through the Carolinas into the central Appalachians region. Model guidance continues to shift the system further south and west of the region Tuesday into Wednesday with uncertainty remaining in regards to the placement of the low along the coast Thursday into late week. This is due largely in part to a lack of a steering mechanism aloft, blocking high pressure to the north, and lack of a front at the surface. Most of the modeling has the low basically spinning over the Carolinas into the central Appalachians before meandering back toward the coast Thursday. The bulk of any substantial rainfall looks to fall Tuesday into Wednesday. Flooding does not appear to be a concern given the antecedent drought concerns. With the track of the system further south, rainfall amounts have come down substantially over the last 24-36 hours. Most locations will see a 0.25" to 0.75" of rain with 1" to 2" rain totals across the central VA Piedmont and central Shenandoah Valley. Some upslope enhancement is possible on the eastern facing slopes of the central Virginia Blue Ridge where localized 2" rain totals are possible. Some instability and bulk shear around 25 knots associated with the system as it pivots into and through the Carolinas could lead to a few spotty thunderstorms Tuesday night through Wednesday afternoon, though confidence is very low. With added cloud cover and increased rain chances, expect temperatures to struggle. Lows Tuesday night will fall into the upper 50s and low to mid 60s, with highs Wednesday in the upper 60s and low to mid 70s. && .LONG TERM /FRIDAY THROUGH MONDAY/... There`s been a notable shift in 00Z guidance compared to 24 hours ago with respect to the upper level pattern for Friday into the weekend. At least at the moment, the theme is consistent amongst ensembles per cluster analysis. The ridge/trough orientation is now situated such that the trough axis remains offshore, and if it does cut off, does not result in a closed low retrograding over the southeastern states. The backdoor cold front is still forecast to push into the area Saturday as a strong trough moves across eastern Canada, but this appears to bring about a drying/cooling trend as strong high pressure builds to the northeast. Winds maintain more of a northeasterly trajectory such that maritime moisture does not rotate back inland. With all that said...low pressure will likely be positioned somewhere offshore, so if there were to be more clouds and/or rain chances, it would likely be across eastern parts of the forecast area. Temperatures will be near or above normal Friday, becoming below normal by Sunday. Model spread increases Monday. High pressure may hold strong, although warm frontal processes may be nearing the Appalachians. Temperatures will likely remain a little below normal. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... MVFR to IFR CIGs will likely return this morning as low pressure pushes further into the Carolinas. Drizzle and rain shower activity will move into terminals south of the corridor late tonight before spreading north Tuesday morning into Tuesday afternoon. IFR ceilings are likely during this time with the bulk of the rain falling late Tuesday morning into Tuesday night. The best chance of IFR CIGs is 12Z-18Z Tuesday, then again Tuesday night (though some guidance has IFR CIGs developing as early as 04Z-06Z from SE to NW). Rain showers will likely continue on and off through Wednesday as low pressure meanders nearby. Winds will remain E/NE 5-15 kts through Wednesday. Gusts of 15-25 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 sub-VFR conditions. Chances for notable weather seem to be decreasing Friday and Saturday, with VFR conditions now looking most likely. However, will have to keep an eye on offshore low pressure. Northeasterly winds may gust to around 20-25 kt Saturday. && .MARINE... SCA conditions will continue 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. At this time, the risk of gale force winds appears low, though some gusts around 30 knots have been observed over the mid bay. 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. North to northeast winds continue Friday into Saturday. As long as low pressure remains sufficiently offshore, sub-advisory conditions would occur Friday. A backdoor cold front may introduce stronger winds at some point between Friday night and Saturday night. Advisories may be needed depending on the timing of the front. && .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. Have not extended advisories since anomalies may drop slightly tonight into Wednesday. However, 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 6 PM EDT this evening for ANZ535. && $$ SYNOPSIS...ADS NEAR TERM...KLW SHORT TERM...KLW LONG TERM...ADS AVIATION...ADS/KLW MARINE...ADS/KLW TIDES/COASTAL FLOODING...LWX