760 FXUS61 KLWX 161225 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 825 AM EDT Thu May 16 2024 .SYNOPSIS... Drier conditions are expected today through Friday as low pressure slowly pushes off the Mid-Atlantic coast and weak high pressure builds in. Increased shower and thunderstorm chances return this weekend as another low pressure system pushes across the region. High pressure briefly returns Monday and Tuesday ahead of a slow moving cold front set to cross by the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... MID-MORNING UPDATE... Fog this morning has started to burn off, more gradually west of the Blue Ridge. This trend is expected to continue over the next few hours. PREVIOUS DISCUSSION FOLLOWS... A brief reprieve in the active weather pattern over the last few days as weak mid-level ridging builds into the region and low pressure pushes further off the Mid-Atlantic coast. With mid-level ridging/weak high pressure set to take over this afternoon and evening additional clearing will ensue. A mix of sun and clouds can be expected for most locations due in part to downsloping north to northwest flow around departing low pressure offshore. 00z model soundings do indicate some high based strato- cumulus across the area this afternoon and evening with perhaps a spotty shower or isolated thunderstorm tied to the mountains during the peak heating period. Added sunshine today and subtle downslope flow should boost temperatures into the mid to upper 70s across much of the region. Mountain locations and those adjacent to the bay will see highs in the upper 60s and low 70s. Dry conditions will continue tonight with weak mid level ridging sitting to the south of the region. Skies will remain partly cloudy with areas of patchy fog especially in river and mountain valley locations. Lows tonight will fall back into the mid to upper 50s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... By Friday, clouds will be on the increase once again as low pressure approaches from the Ohio River Valley. The day will likely start off dry with weak mid-level ridging/high pressure sitting across the southeast U.S. The brief reprieve in active weather won't last long as a warm front lifts in from the south and west Friday afternoon/evening. South to southwesterly flow will ensue as a result allowing ample moisture advection to push north ahead of the approaching upper level low pressure system from the Ohio River Valley Saturday. Skies will likely remain partly to mostly cloudy before becoming overcast Friday evening and night. The warm front combined with modest surface heating and increasing dewpoints (upper 50s and low 60s) should allow for enough of a spark for widely scattered thunderstorms Friday afternoon/evening especially west of the Blue Ridge. The severe weather threat appears to be low given limited shear and CAPE. Isolated instances of flooding could be possible due to the slow movement of thunderstorm activity (i.e pulse/multicellular modes). High temperatures Friday will be in the mid to upper 70s. Moisture increases by Friday night with increased rain chances and lows dipping down into the mid to upper 50s. It's a soggy start to the weekend as an upper level trough/slow moving low pressure system push across the central Appalachians and toward the VA/NC coast. Expect fairly widespread shower and thunderstorm activity Saturday with decreasing coverage as the low pushes east toward the coast late Saturday night into Sunday. Severe weather does not appear to be a concern at this point given limited CAPE and shear with ample cloud cover overhead. Localized flooding could be the bigger concern given repetitive rounds of rain and rich moisture (high PWATS around the the percentile) funneling in. For those with plans outdoors Saturday appears to be the wettest compared to Sunday even though models continue to stall the low offshore. High temperatures will struggle to get out of the mid to upper 60s (low 60s across the PA/MD line and mountains) Saturday afternoon. Lows Saturday night will fall back into the mid to upper 50s. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... A split flow regime persists across the country to finish out the weekend. For Sunday, a slow moving upper trough will pass by to the south across the Carolinas. Given the close proximity of the frontal system to the local area, some rain chances will loom for at least the first half of the day. This is particularly the case for those south of I-66/U.S. 50. With the Mid-Atlantic region in a modified cold-air damming wedge, temperatures remain seasonably cool thanks to northeasterly onshore winds. The latest forecast package calls for mainly 60s on Sunday which is nearly 10 degrees below average for mid-May. Any rain chances wane by later in the day as the frontal system slowly exits the Carolina coast. Expect a dry start to the work week as northern stream ridging sets up over the northeastern U.S. through Tuesday. Depending on model solution, some shower activity could return to areas west of I-95 by late Tuesday. Temperatures are able to rebound owing to the building heights aloft coupled with a greater amount of sunshine. Return flow does not really kick in until mid-week which should hold down humidity levels. By Wednesday, daily highs return to the 80 degree mark, accompanied by prevailing southerly winds. This ushers dew points into the low/mid 60s which will make conditions feel a bit more humid. Additionally, global ensembles show a large uptick in instability profiles. Ultimately this will bring a better chance for diurnal convection, particularly in advance of a cold front tracking through late Wednesday. Despite the frontal passage, temperatures are not expected to drop much, but a decrease in humidity levels is more likely for later in the week. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... Skies continue to clear this morning allowing for areas of dense fog to sprout up between western and southern terminals (i.e KCHO, KMRB, KHGR, KSHD, KCJR, and KFDK). GOES Nighttime Microphysics RGB continues to show the bulk of fog across the Potomac Highlands, Shenandoah Valley, and Virginia Piedmont with visibility values bouncing between a 1/4 to 2 miles. Within the corridor itself mid and high level clouds remain prevalent leading to less fog formation. Even here, patchy and locally dense fog is likely through daybreak (at least 14z/10am) due in part to ample moisture trapped within the low levels. Vsbys will improve beyond 14z/10am with ceilings likely to scatter out in many locations later this morning and into the afternoon as downsloping north to northwest flow pushes drier air into the region. Expect strato-cumulus to dot the skies at all terminals this afternoon and evening with cigs running between 050-090 feet. A spotty shower or t-storm cannot be ruled out during the peak heating period at terminals west of KMRB. Winds will turn to the north and northwest today at 5-15 kts with gusts up to 25 kts at times. This is due in part to the gradient between low pressure offshore and weak high pressure building in at the surface. Low ceilings and/or fog may redevelop tonight into Friday morning especially at valley terminals (i.e KMRB, KSHD, KHGR, and KCHO). Confidence is slightly lower on fog formation given weak mid level ridging aloft and drier air filtering south on north to northwest flow. Flight conditions will slowly deteriorate Friday afternoon into Friday evening especially at terminals west of the corridor. This is due to increased shower and thunderstorm coverage as a warm front lifts into the area. Low cigs and vsbys will continue into Friday night and Saturday as widespread shower and thunderstorm activity associated with an upper level low pressure system pivots across the terminals. Given northeasterly onshore flow within the cold-air damming wedge, low ceilings are a possibility on Sunday. Thus, sub-VFR conditions are possible along with some shower activity. Given little change in wind direction, these lower ceilings could persist into Monday morning. Otherwise, conditions trend drier through the rest of Monday with mostly sunny skies and VFR conditions expected. && .MARINE... SCA conditions are expected for all waters today with a tightened gradient across the region. North to northeasterly gusts up to 25 kts are possible through late afternoon with winds gradually diminishing this evening and into the overnight hours. Lighter winds are expected Friday into Friday night with weak high pressure sitting south of the waters. SCA conditions return Saturday under increased onshore east to northeast flow. Low pressure will pass south of the waters Saturday night into Sunday leading to a continuation of SCA conditions. This will be especially true over middle and lower portions of the bay and lower tidal Potomac where a bit more channeling could occur. Numerous showers and perhaps a few thunderstorms will accompany this system through Saturday into early Sunday. Winds Saturday night into Sunday will gradually shift to north-northeasterly as the low slides across the region. Prolonged northeasterly onshore flow will bring near 20 knot gusts to portions of the waters. Therefore, Small Craft Advisories may be needed on Sunday, perhaps lingering into Sunday night. Given high pressure along coastal New England and low pressure off the Carolinas, additional northeasterly winds could approach advisory levels even into Monday. && .TIDES/COASTAL FLOODING... Waters levels will gradually decrease today with north to northeast flow behind departing low pressure. Tidal anomalies will begin to rise again Friday and into the weekend given a fairly prolonged period of east to southeasterly onshore flow. A number of sites will return to Action stage, with the more sensitive locations pushing into Minor. Elevated water levels likely persist into Monday given little change in the overall wind direction. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ530>543. && $$ SYNOPSIS...EST NEAR TERM...CAS/EST SHORT TERM...EST LONG TERM...BRO AVIATION...BRO/KRR MARINE...BRO/EST TIDES/COASTAL FLOODING...BRO