FXUS61 KLWX 201925 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 325 PM EDT Fri Jun 20 2025 .SYNOPSIS... Less humid conditions are expected through Saturday as high pressure builds into the region. A prolonged period of very hot weather is expected Sunday into the middle part of next week as a large ridge of high pressure builds over the eastern United States. A risk of showers and thunderstorms returns during the middle to latter portions of next week as a frontal system approaches from the north. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Driest airmass in about a week has settled in across the area today with a precipitable water of 0.87 inches on the 12Z IAD sounding. Diurnal heating has resulted in a robust cumulus field, especially where there is some added lift from the terrain. A few CAMS have a brief shower or sprinkle developing out of this field, but believe that chance is less than the 15 percent that triggers a forecast mention. Moderate westerly winds (some gusts up to 20 mph) will subside with sunset as the gradient relaxes. Some thicker cirrus from the northwest will cross the area this evening, but there should be enough clearing to allow for temperatures to drop close to the dew points in outlying areas. That may result in some patchy river and ground fog. Most locations will drop to the 60s, with some 50s in the western valleys. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... Surface ridge slides offshore this weekend as strong ridging builds aloft. This leads to heat quickly ramping back up, with upper 80s/lower 90s Saturday and mid to upper 90s Sunday. Dew points begin to climb too, although the more oppressive values (upper 60s to perhaps low 70s) hold off until Sunday. While some areas could near Heat Advisory thresholds Sunday, a WSW wind (downsloping component) may promote dew points mixing down some during the afternoon. These nuances will be evaluated over the next couple forecast cycles before determining any areas that need an advisory. Overnight lows will likewise moderate, with 60s becoming less common as the weekend progresses. Secondarily, some guidance indicates a pop up shower or storm over the weekend, especially over the terrain. However, believe that subsidence should allow for dry conditions to prevail. NBM PoPs are generally less than 5 percent. Some waves of mid/high level clouds will cross along with diurnal cumulus, but overall there will be more sun than clouds. && .LONG TERM /MONDAY THROUGH FRIDAY/... A strong upper ridge will build over the Eastern US by early next week. The mid/upper-level anticyclone will become centered overhead by Monday and Tuesday with 500 hPa heights nearing 600 decameters. Heat and humidity will accompany this anomalously strong upper ridge, with temperatures reaching into the mid 90s to near 100, and dewpoints climbing into the lower 70s. This combination will result in heat index values climbing well above 100, and potentially even approaching 110 on Monday and Tuesday afternoons. Little relief will be felt each night with lows generally in the 70s. The prolonged heatwave will likely linger through the remainder of the week, although temperatures could drop a few degrees by the end of the week as the upper-level ridge starts to weaken slightly. No precipitation is expected early in the week as large scale subsidence beneath the upper-level anticyclone provides warming and drying aloft. Some afternoon showers and thunderstorms are possible by mid week as the upper-level ridge starts to slowly weaken. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... VFR conditions are expected today, continuing through the entire weekend, although some diurnal cumulus will likely develop each day. Westerly winds continue with the potential for gusts up to 20 knots through this afternoon, quickly subsiding with sunset. Winds turn southerly Saturday and southwesterly Sunday, generally remaining less than 10 kt. VFR conditions and light northwesterly winds are expected on both Monday and Tuesday. && .MARINE... Although a few westerly 18 knot gusts have been observed on the upper tidal Potomac this afternoon, overall winds are below advisory thresholds and will diminish quickly this evening. High pressure moving into the area pushes offshore early Saturday yielding a return to southerly winds this weekend. Some channeling effects will occur in the evening/overnight periods, with marginal advisory conditions possible on the wider waters Saturday night...perhaps Sunday night as well. Light northwesterly winds are expected over the waters on both Monday and Tuesday. && .TIDES/COASTAL FLOODING... A return to southerly flow will nudge tidal anomalies higher on Saturday. Although flooding is not forecast at this time, some guidance has Annapolis in particular very close to minor flood stage Saturday and Sunday evenings. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...DHOF/KJP AVIATION...ADS MARINE...ADS TIDES/COASTAL FLOODING...ADS