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. --274 FXUS61 KLWX 171805 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 205 PM EDT Mon Jun 17 2024 .SYNOPSIS...-- Changed Discussion --High pressure will remain anchored offshore through the week. A warm front will lift northeastward across the Mid-Atlantic through the evening, marking the beginning of a prolonged period of heat.-- End Changed Discussion --&& .NEAR TERM /THROUGH TONIGHT/...-- Changed Discussion --Latest mesoanalysis shows heat/instability building near a lee pressure trough along the I-81 corridor in the Shenandoah Valley. Latest CAMs continue to show scattered showers/thunderstorms in this area on the backside of the departing surface high. Given weak low and mid- level flow, convection will move slowly and/or lock to nearby terrain, resulting in a localized heavy rainfall threat. FFG is relatively high (2.5-4" in 1-3 hours), though slow storm motions and higher PWs could result in totals close to these values in a reasonable high-end scenario. Given the dry antecedent conditions and the somewhat conditional nature of the threat, no Flood Watch has been issued at this time. The increased heat and steepening low-level lapse rates could also aid in a few localized strong downbursts/gusty to perhaps damaging surface winds. Convection chances are highest near and west of the Blue Ridge Mountains and south of US-50 from around midday through early this evening. Some guidance also has convection in and around KCHO toward Nelson County, VA. Elsewhere, a dry and hot day is expected. Humidity will increase, but won`t be quite oppressive by early summer Mid- Atlantic standards. This should result in heat index values around or a degree or two higher than the air temperatures - generally in the lower to middle 90s. Low temperatures tonight will be in the 60s to lower 70s under a partly to mostly clear sky.-- End Changed Discussion --&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...-- Changed Discussion --Ridging will build aloft Tuesday into Wednesday. Subsidence could be weak enough to allow a few isolated showers or thunderstorms to develop near the Appalachians Tuesday afternoon, but most of the time/area will just be dry and hot. Latest HREF highlights the far western Alleghenies with an area of showers and thunderstorms drifting north along the periphery of the ridge. Temperatures will trend upward a bit Tuesday, then decrease slightly Wednesday as the center of the ridge reorients itself to the north and low-level flow pivots to off relatively cooler water. Have issues a Heat Advisory for parts of western Maryland into the eastern Panhandle of West Virginia given the overlap of heat and high humidity. There remains uncertainty on how much mixing there will be tomorrow afternoon, especially towards Petersburg into the Shenandoah Valley, so have left out that area from the advisory for now.-- End Changed Discussion --&& .LONG TERM /THURSDAY THROUGH SUNDAY/... Highly anomalous upper level ridging along the East Coast will slowly start to break down during the second half of the week, with flow aloft becoming more zonal in nature next weekend. As this occurs, the 850 hPa high to our northeast will also start to break down, allowing 850 hPa flow to shift from east-southeasterly on Thursday, to southwesterly next weekend. As 850 hPa flow gains a westerly component, an increasingly continental airmass will move over the region, leading to an increase in temperatures, despite the falling heights aloft. The strong upper ridge should suppress any convection on Thursday and Friday, leading to sunny skies both days. As temperatures rise at the surface and cool aloft, chances for popup afternoon and evening thunderstorms will return this coming weekend. Thunderstorm activity looks to remain relatively isolated on Saturday in the absence of appreciable large scale forcing for ascent. By Sunday, height falls associated with a trough tracking through the Great Lakes may lead to greater chances for thunderstorms. The main story through the long term period will be the heat. Temperatures are expected to reach into the lower 90s on Thursday. The hottest temperatures of this week`s heat wave are expected to occur on Friday, Saturday, and Sunday. High temperatures those days should make it into the mid-upper 90s, with around 100 possible in some spots. Overnight lows will also increase from the upper 60s to near 70 on Thursday night, to the mid-upper 70s by Saturday night. && .AVIATION /18Z MONDAY THROUGH SATURDAY/...-- Changed Discussion --VFR conditions are expected to prevail at the TAF sites through at least the first half of the week. A shower or thunderstorm could approach KCHO/KMRB this afternoon or early evening. If it does, brief restrictions would be possible (as would patchy fog later tonight into early Tuesday morning). Winds will generally be southerly to southeasterly at 6-12 kts with occasional daytime gusts to around 18 kts. Eastern terminals likely experience some river/bay breeze influence during the afternoon and early evening hours each day. VFR conditions and southerly winds are expected at the terminals on Thursday and Friday.-- End Changed Discussion --&& .MARINE... South to southeast winds will prevail through much of the upcoming week. Southerly channeling combined with bay/river breeze enhancements likely result in SCA level gusts each afternoon and evening. Otherwise, dry and hot weather is expected through the week. Low-end SCA level winds appear possible in channeled southerly flow during the afternoon/evening hours of Thursday and Friday. && .TIDES/COASTAL FLOODING...-- Changed Discussion --Persistent southerly flow continues, and tidal anomalies are hovering near one to one and a half feet above normal. This is enough to result in near minor flooding, particularly during the overnight high tide cycle near Annapolis the next couple of days.-- End Changed Discussion --&& .CLIMATE... Hot temperatures are expected much of this coming week and especially this coming weekend. We could see a few records broken on Tuesday, but 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 June 18th, 21st, and 22nd, 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. Tuesday Jun 18th Climate Site Record High Forecast High Washington-National (DCA) 97F (1944) 93F Washington-Dulles (IAD) 94F (2018+) 93F Baltimore (BWI) 97F (1957+) 92F Martinsburg (MRB) 99F (1943) 93F Charlottesville (CHO) 96F (2014+) 94F Annapolis (NAK) 96F (1957) 88F Hagerstown (HGR) 95F (1957) 94F Friday Jun 21st Climate Site Record High Forecast High Washington-National (DCA) 99F (2012) 97F Washington-Dulles (IAD) 98F (1988) 98F Baltimore (BWI) 100F (2012+) 96F Martinsburg (MRB) 102F (1931) 95F Charlottesville (CHO) 99F (1933) 97F Annapolis (NAK) 100F (1988) 91F Hagerstown (HGR) 97F (1923) 97F 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) 98F Martinsburg (MRB) 102F (1933) 96F Charlottesville (CHO) 101F (1933) 99F Annapolis (NAK) 101F (1988) 93F Hagerstown (HGR) 100F (1988) 97F + indicates that value has been reached on multiple years, with the year displayed being the most recent. && .LWX WATCHES/WARNINGS/ADVISORIES...-- Changed Discussion --DC...None. MD...Heat Advisory from noon to 8 PM EDT Tuesday for MDZ003-502. VA...None. WV...Heat Advisory from noon to 8 PM EDT Tuesday for WVZ051>053-504. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530-538- 539-542. Small Craft Advisory until 2 AM EDT Tuesday for ANZ531>534-537- 540-541-543.-- End Changed Discussion --&& $$ SYNOPSIS...DHOF/CPB NEAR TERM...CPB/DHOF SHORT TERM...CPB LONG TERM...ADM AVIATION...ADM/CPB MARINE...ADM/CPB TIDES/COASTAL FLOODING...LWX CLIMATE...LWX