Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
683 FXUS61 KLWX 170130 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 930 PM EDT Sun Jun 16 2024 .SYNOPSIS... High pressure over New England will drift offshore through the week. A warm front over the Tennessee River Valley will lift northeastward across the Mid-Atlantic through Monday, marking the beginning of a prolonged period of heat. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... A surface warm front is analyzed across the Tennessee Valley this evening, which will quickly lift to the north of the area by Monday morning. With ridging aloft centered south of the area, warm and moist advection has already commenced, with several areas of broken cloud cover noted across the region. Overall, the night will average partly cloudy, and it will be warmer and more humid than last night. Lows will be in the 60s for most of the area, and around 70 in the urban centers and along the water. Some guidance indicates showers may form along the Appalachians around sunrise in response to the warm front. Most areas will likely remain dry. && .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... For the start of the work week, a strong ridge aloft will become the main story for our region. The aforementioned warm front should be north of our region on Monday, resulting in noticeably warmer high temperatures as well as a more humid air mass as well. Given the increase in heat and humidity, and prior to the ridge aloft and associated subsidence increasing heading into midweek, there may be enough of a window for scattered showers and thunderstorms west of the Blue Ridge Mountains as a lee trough develops thanks to differential heating affects of the higher terrain. Flow will be modest in the mid and upper levels and light in the low levels, so heavy downpours and localized gusty winds would be the main threats with any stronger storms. Model guidance seems to have a consensus of around 1500-2500 J/kg of CAPE available in the aforementioned region. The one caveat is the presence of mid-level westerlies, which could squash most activity that tries to develop. Given the increase in heat and humidity and slow/chaotic storm motions in the vicinity of the terrain, some isolated heavy rain totals can`t be ruled out. Depending on mesoscale evolution, some cells could drift into the central Shenandoah Valley toward evening. Otherwise, most of the time/area will be dry. High temperatures tomorrow have decreased a bit in recent forecasts, with a noticeable trend of the worst of the heat being towards the end of the week. Latest forecast calls for highs in the low-mid 90s, with heat indices generally between 95-100 degrees. For folks west of the Blue Ridge however, we will have to see how thunderstorms may impact those highs. There is some increasing threat for a thunderstorm threat again on Tuesday in the same area, but amidst the building ridge aloft, the thinking is that coverage should certainly be less than what we see Monday. However, temperatures will trend hotter Tuesday as highs are expected to reach the mid 90s. Humidity may also be higher Tuesday, though guidance is still struggling with that aspect of the forecast. In the short term, given the uncertainty, and the very threshold nature of this event with regards to local heat advisory criteria, have decided to hold off for now. Thinking the best chance early in the week may be Tuesday afternoon for areas west of the Blue Ridge, where criteria is 100F heat index. Areas further east though, where criteria is 105F heat index, we may not quite reach that. It is important to note however that this level of heat is still dangerous and should not be taken lightly. This will be an extended period of very warm temperatures, likely peaking towards the end of this week into this weekend. We encourage all to follow all heat precautions in the coming week. Stay cool, stay hydrated, and take plenty of breaks if you must work outdoors. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... A broad upper level ridge will remain in place over our region with high pressure over much of the mid-Atlantic through the end of this week. An extended period of 90 degree plus temperatures is likely to continue through Saturday with potential for near record temperatures possible. The early season nature of this extended period of 90 degree plus weather combined with increasing heat indices that could peak between 100 and 105 will likely necessitate the need for some heat headlines by the end of this week into the weekend. Showers and thunderstorms are not expected at this time Wednesday into Thursday as the ridge should keep convection to the north over PA. Showers and thunderstorms will become increasingly possible late Friday and through the weekend. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... VFR conditions are likely at the terminals through the next several days. An isolated thunderstorm can`t be ruled out Monday or Tuesday afternoon near MRB and CHO, but confidence is too low to include in the TAF at this time. Not seeing a chance for that activity to make it east into the metro area at this time. Winds during this period will generally be out of the S/SE around 6 to 12 knots during with occasional gusts to around 18 knots during the afternoons. Bay/river breeze wind shifts will likely continue to affect DCA/BWI/MTN daily. VFR conditions are likely Wednesday through Saturday with winds generally out of the south. && .MARINE... Winds are generally going to be out of the south or southeast through the middle of the week. With a warm front passing tonight into Monday, gusty winds are forecast to be a little more widespread and of longer duration. Some timing adjustments and expansions have taken place with the Small Craft Advisories. Looking beyond Monday evening, the pattern will be very similar each day, with stronger winds picking up each afternoon/evening in southerly channeling. Thinking that SCAs will be needed most late afternoons and evenings during this timeframe over the Chesapeake Bay zones. && .TIDES/COASTAL FLOODING... A persistent southerly flow will lead to increased anomalies and some elevated tidal cycles. A few tidal sites will reach action stage with near minor tidal flooding possible, especially at Annapolis. && .CLIMATE... While hot temperatures are expected much of this coming week and especially this coming weekend, trends have been down early in the week overall. We could see a few records broken on Tuesday, but the hottest days appear to be Friday and Saturday, where several records come 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 currently 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) 94F Washington-Dulles (IAD) 94F (2018+) 94F Baltimore (BWI) 97F (1957+) 92F Martinsburg (MRB) 99F (1943) 93F Charlottesville (CHO) 96F (2014+) 93F Annapolis (NAK) 96F (1957) 87F Hagerstown (HGR) 95F (1957) 95F Friday Jun 21st Climate Site Record High Forecast High Washington-National (DCA) 99F (2012) 98F 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) 100F Washington-Dulles (IAD) 99F (1988) 100F Baltimore (BWI) 100F (1988) 98F Martinsburg (MRB) 102F (1933) 97F Charlottesville (CHO) 101F (1933) 99F Annapolis (NAK) 101F (1988) 94F Hagerstown (HGR) 100F (1988) 99F + indicates that value has been reached on multiple years, with the year displayed being the most recent. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ530-536-539- 542. Small Craft Advisory from 10 AM to 9 PM EDT Monday for ANZ530- 538-539-542. Small Craft Advisory until 2 AM EDT Tuesday for ANZ531>534-537- 540-541-543. && $$ SYNOPSIS...CJL NEAR TERM...ADS SHORT TERM...CJL LONG TERM...JMG AVIATION...ADS/CJL/JMG MARINE...ADS/CJL/JMG TIDES/COASTAL FLOODING...JMG CLIMATE...CJL