Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
774 FXUS61 KLWX 250751 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 351 AM EDT Tue Jun 25 2024 .SYNOPSIS... High pressure will remain over the area through tonight before pushing offshore. A strong cold front approaches from the Ohio River Valley before crossing the Mid-Atlantic region Wednesday evening through Thursday morning. This brings the next chance for showers and thunderstorms. High pressure briefly returns from the west Friday. Unsettled conditions are possible this weekend which comes with increasing heat and humidity. && .NEAR TERM /THROUGH TONIGHT/... In the wake of yesterday`s cold frontal passage, high pressure has settled over the Ohio Valley and Mid-Atlantic region. As noted by early morning observations, this has brought a seasonably cool and dry feel to the air, particularly in comparison to the previous week. Such temperatures range from the upper 50s to 60s, locally in the low 70s around the usual warm spots. This is coupled with dew points holding steady in the low/mid 50s. The GOES-16 nighttime microphysics channel shows little to no clouds over the area. This is expected to stay that way through daybreak, accompanied by nearly calm winds. As high pressure slowly weakens and drifts toward the south and east, winds are likely to shift to mainly west to southwesterly. This switch in the prevailing winds will allow for a warmer day than Monday. Forecast high temperatures rise into the low 90s which is around 3 to 6 degrees above late June climatology. Expect more sun than clouds today which should allow for a mostly sunny sky this afternoon. Conditions are dry through the evening and night which comes with much milder weather. A mainly south-southwesterly flow is expected which holds overnight lows in the upper 60s to mid 70s. Higher elevations likely stay in the low/mid 60s. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... A progressive array of shortwaves are forecast to track from southern Alberta toward the north-central tier of the U.S. today. These height falls will provide the next chance for any organized convective activity. Based on the latest Storm Prediction Center update, areas north of the Potomac Highlands and central Virginia are in a Slight risk for severe thunderstorms. The primary threats will be damaging wind gusts and isolated large hailstones. Some of the guidance does show some higher Supercell Composite indices along the Mason-Dixon Line given the backed flow. With that in mind, a brief tornado cannot be ruled out along this area of the Mid-Atlantic. The thermodynamic environment should become increasingly unstable as the boundary layer moistens through the day. This is in the presence of afternoon temperatures which should rise into the mid/upper 90s. The degree of low-level moistening is somewhat uncertain, but the consensus does raise dew points into the mid/upper 60s. This would support heat indices into the 100 to 104 degree range which does near Heat Advisory criteria. Will continue to monitor the need for any such heat-related products. Depending on how upstream activity survives the Appalachian chain, some early morning showers could push into areas west of I-81. However, the main show likely initiates along a lee-side trough during the afternoon hours. This occurs in the presence of rising buoyancy levels on the order of 2,000 to 2,500 J/kg. High-resolution guidance favors propagating this activity downstream toward the metro areas by the late afternoon to early evening. Model soundings indicate there is plenty of vertical shear to work with (35-40 knots), so expect storms to be reasonably well organized. Depending on how everything else plays out during peak heating, the cold front tracking through late Wednesday could bring additional thunder chances if any instability remains. Low temperatures on Wednesday night will mainly be in the 60s, locally in the low 70s along and east of I-95. Some residual shower chances persist into the first half of Thursday. During the morning hours, this frontal system should be located near the Delmarva Peninsula. Expect a drying trend through the day as post-frontal northwesterlies ensue. Forecast highs drop back down into the mid/upper 80s along with lower humidity levels. This eventually leads into a cooler night as most stay in the 60s, with mid/upper 50s over the mountains. && .LONG TERM /FRIDAY THROUGH MONDAY/... A quick-moving area of high pressure passes to our north on Friday. Mostly dry conditions are expected during the day, but some showers could develop in the evening/overnight around the Shenandoah Valley and Virginia Piedmont as the center of high pressure swiftly moves offshore by the evening and a shortwaves passes to the northwest. Temperatures look relatively cooler, topping out in the upper 80s. Lows hover in the 60s to low 70s. Confidence has increased for the potential of warm frontal precip on Saturday, focused in the afternoon and evening. With the warm front, temperatures get back into the 90s. The cold front associated with the approaching system looks to arrive Sunday, bringing another round of showers and thunderstorms. These could linger into early Monday as well, but surface high pressure looks to build in quickly behind the cold front on Monday. && .AVIATION /07Z TUESDAY THROUGH SATURDAY/... High pressure in charge of the forecast will maintain VFR conditions across the area through Wednesday morning. Initial northwesterly winds should gradually shift over to west to southwesterly today. The main action holds off until Wednesday afternoon through the evening and night. The potential for multiple rounds of showers and thunderstorms would favor restrictions at times. Additionally, some of these storms could become severe in nature which would bring stronger wind gusts and perhaps some hail. Winds shift to west-northwesterly late Wednesday into Thursday morning behind a well defined cold front. Sub-VFR conditions could linger into Thursday morning depending on how quickly the system exits. Expect an eventual return to VFR conditions on Thursday with northwesterly winds gusting up to 15 knots. Prevailing VFR conditions are expected Friday and Saturday. Mostly dry conditions are expected Friday as high pressure passes to the north, but some showers and thunderstorms could develop as early as Friday night with an approaching warm front. As the front moves through Saturday, shower and thunderstorm chances increase. Any that move over the terminals could bring brief restrictions. && .MARINE... Winds across the marine waters have diminished in strength as a ridge of high pressure has moved over the region. As the anticylone settles to the south and east, southerly channeling ensues by early this evening into the night. Small Craft Advisories will likely be issued for the Chesapeake Bay and lower tidal Potomac. Gusts up to 25 knots are possible for the more southern waters. Ahead of the slow moving cold front, southerly winds again pick up by Wednesday afternoon/evening which likely yields more Small Craft Advisories. Additionally, strong to severe thunderstorm activity may necessitate a number of Special Marine Warnings over the region. Initial activity likely nears the waters by the late afternoon on Wednesday. The convective threat persists through the evening and into parts of the night. This frontal system exits by Thursday morning with sub-advisory level winds expected for the day. Sub-SCA conditions are expected Friday as high pressure passes to our north. Winds increase out of the south on Saturday as a warm front approaches the waters, and could approach SCA criteria by the afternoon. && .TIDES/COASTAL FLOODING... Tidal anomalies decrease through this morning with NW flow. A return of southwest winds later this afternoon into Wednesday will bring another increase in water levels, although no flooding is forecast at this time. && .CLIMATE... Very hot temperatures are expected on Wednesday. Several records could be in jeopardy. Below is a list of record high temperatures for June 26th, the year the record was set, and the current forecast high temperatures for that day. A plus sign after the date signifies the record was set multiple times, with the most recent year indicated below. RERs are only issued for DCA, IAD, BWI, and MRB, but other sites are shown for reference. Wednesday Jun 26th Washington-National (DCA) 101F (1952) 98F Washington-Dulles (IAD) 95F (1998) 98F Baltimore (BWI) 99F (1954+) 99F Martinsburg (MRB) 102F (1943) 93F Charlottesville (CHO) 99F (1998) 97F Annapolis (NAK) 98F (1952) 94F Hagerstown (HGR) 98F (1954+) 93F && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BRO NEAR TERM...BRO SHORT TERM...BRO LONG TERM...CAS AVIATION...BRO/CAS MARINE...BRO/CAS TIDES/COASTAL FLOODING...LWX CLIMATE...LWX