Area Forecast Discussion
Issued by NWS Sterling, VA
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Issued by NWS Sterling, VA
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-- Discussion containing changed information from previous version are highlighted. --363 FXUS61 KLWX 201354 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 954 AM EDT Thu Jun 20 2024 .SYNOPSIS... High pressure will remain in place offshore through this weekend. A cold front will progress through on Monday, with high pressure building back in by Tuesday. && .NEAR TERM /THROUGH TONIGHT/...-- Changed Discussion --MORNING UPDATE: A thin upper-level cirrus deck is spread across much of the region as some mid-upper level moisture streams in from the west. This has had no affect on temperatures thus far, as the forecast in on track thus far with current values in the mid 70s to low 80s. Refer to the previous discussion for more forecast details, as nothing has been changed yet this morning. PREVIOUS DISCUSSION: Strong upper level ridging will remain centered overhead today. Large scale subsidence will keep conditions capped, resulting in dry conditions across the entire forecast area. A mix of sun and high clouds is expected throughout the day. While it will be yet another hot day, onshore flow around an area of high pressure offshore will keep it a bit cooler and less humid than one might expect given the very strong upper ridge overhead. High temperatures today should reach into the upper 80s and lower 90s for most, with low-mid 80s in the mountains. Dewpoints will be in the low-mid 60s. High pressure will remain in control tonight, leading to continued dry conditions. Overnight lows will be in the mid-upper 60s for most, with lower 70s in DC and Baltimore.-- End Changed Discussion --&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...-- Changed Discussion --Upper level ridging will start to break down a bit by Friday. As this occurs, the 850 hPa high will shift a bit further south, lessening the easterly component of the wind and resultant oceanic influence. Temperatures will be a few degrees warmer as a result, with highs in the mid 90s for most. As the upper ridge starts to weaken, a few afternoon thunderstorms may form over the higher terrain of the Potomac Highlands and Allegheny Front in response to daytime heating and resultant terrain circulations. These thunderstorms could potentially drift as far east as the Shenandoah Valley before dissipating in the evening hours. Dry conditions are expected further east. Friday night will feature warmer temperatures compared to preceding nights, with overnight lows generally in the low-mid 70s. Mid-level heights will continue to slowly decrease on Saturday. Meanwhile, flow at 850 hPa will turn westerly to southwesterly, allowing a more continental airmass to work into the region. This will result in even hotter temperatures, with highs in the mid-upper 90s. It will also turn more humid, with dewpoints increasing into the lower 70s. Peak heat indices of 100-105 appear likely across much of the forecast area, and Heat Advisories may potentially be needed as a result. Guidance hints that a weak southwest to northeast oriented surface trough may develop across the center of the forecast area. A few thunderstorms may form during the afternoon hours along this surface trough and slowly progress eastward through the evening hours. Mid- level flow (and as a result, shear) will be relatively weak, at around 15 knots, but instability will be plentiful (MLCAPE values over 2000 J/kg) within the hot and humid airmass. While the activity should be somewhat disorganized, storms may be capable of producing localized downbursts, given high levels of CAPE and DCAPE in place. Thunderstorm activity shoExpect this to be present today. uld gradually wind down through the evening hours, with dry conditions expected through much of the night. Saturday night will be warmer still, with overnight lows in the mid-upper 70s to the east of the Blue Ridge, with lower 80s even possible in DC and Baltimore.-- End Changed Discussion --&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Hot weather continues Sunday with highs likely in the mid 90s to near 100. Dew points are also forecast to be peaking during this time, so much of the area may need Heat Advisories. There will be a greater chance of showers and thunderstorms than the preceding days due to height falls ahead of a Great Lakes trough along with a lee surface trough. Even though NBM PoPs currently favor the evening hours, subtle timing differences could easily result in thunderstorms at any point during the afternoon. A localized severe weather risk could materialize with ample instability, although the local area will be on the southern periphery of stronger flow to the north. Cold front will push south into the area Monday. There are still some timing differences which would affect the temperature forecast as well as the coverage of showers and thunderstorms. Surface high pressure will build over the area by Tuesday. The post-frontal airmass won`t bring a huge relief in temperatures, with most areas still forecast to top 90 degrees. It will be less humid however. Model spread increases by mid-week with differences in how the next trough evolves. It does appear to heat back up as southwesterly flow resumes, along with some risk for a shower or thunderstorm. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... Prevailing VFR conditions and light southerly winds are expected at the terminals through Saturday. An afternoon thunderstorm can`t be ruled out at MRB Friday afternoon, and then at any of the terminals on Saturday. Thunderstorms are possible Sunday afternoon through Monday as a cold front approaches. && .MARINE... Persistent southerly flow is expected over the waters through Saturday. Winds may near low-end SCA levels in channeled southerly flow during the afternoon and evening hours on both Friday and Saturday. South to southwest winds may require Small Craft Advisories Sunday into Sunday night. Thunderstorms are possible Sunday afternoon into Sunday night as well. A cold front will push through Monday with a wind shift to the northwest. Additional thunderstorms are possible depending on the timing of the front. && .CLIMATE... Hot temperatures are expected much of this week and especially this coming weekend. The hottest days appear to be Friday through Sunday when several records could be in jeopardy. Below is a list of record high temperatures for Jun 21st, 22nd, and the 23rd and the year the record was set, and the current forecast high temperatures for those days. RERs are only issued for DCA, IAD, BWI, and MRB, but other sites are shown for reference. Friday Jun 21st Climate Site Record High Forecast High Washington-National (DCA) 99F (2012) 96F Washington-Dulles (IAD) 98F (1988) 96F Baltimore (BWI) 100F (2012+) 95F Martinsburg (MRB) 102F (1931) 93F Charlottesville (CHO) 99F (1933) 94F Annapolis (NAK) 100F (1988) 90F Hagerstown (HGR) 97F (1923) 95F Saturday Jun 22nd Climate Site Record High Forecast High Washington-National (DCA) 101F (1988) 99F Washington-Dulles (IAD) 99F (1988) 99F Baltimore (BWI) 100F (1988) 97F Martinsburg (MRB) 102F (1933) 95F Charlottesville (CHO) 101F (1933) 98F Annapolis (NAK) 101F (1988) 93F Hagerstown (HGR) 100F (1988) 97F Sunday Jun 23nd Climate Site Record High Forecast High Washington-National (DCA) 98F (1988) 100F Washington-Dulles (IAD) 96F (1988) 99F Baltimore (BWI) 97F (2010) 99F Martinsburg (MRB) 100F (1934) 96F Charlottesville (CHO) 100F (1894) 98F Annapolis (NAK) 98F (1988) 96F Hagerstown (HGR) 98F (1988) 96F && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...LFR NEAR TERM...CJL/CPB SHORT TERM...CPB LONG TERM...KJP AVIATION...KJP/CPB MARINE...KJP/CPB CLIMATE...