Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
736 FXUS61 KLWX 061407 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1007 AM EDT Sat Jul 6 2024 .SYNOPSIS... A cold front moves through the area through tonight. The front brings shower and thunderstorm chances east of the Blue Ridge today. Humidity decreases Sunday in the wake of the front with high pressure briefly building overhead. Heat, humidity, and daily thunderstorm chances return early next week. && .NEAR TERM /THROUGH TONIGHT/... Like the previous couple of mornings, the region is off to a quick start in terms of the heat and humidity. Mid-morning temperatures have already risen into the upper 80s to low 90s with dew points in the low 70s. This is currently contributing to heat indices well into the 90s. The 12Z KIAD sounding clearly shows the moisture-laden air mass with a precipitable water value of 1.82 inches and a mean mixing ratio of 14.9 g/kg. Given any dry air in the column is confined to the 700-600 mb layer, mixing will not be deep enough to draw this down to the surface. Thus, little change is expected with all heat products continuing as is. A weak front to the west will slowly slide east across the area today into tonight. The latest guidance and CAM output indicate conditions are going to remain mostly dry west of the Blue Ridge. In these areas, temperatures this afternoon reach the low 90s, but deeper mixing drops dew points to the 60s and eliminates any heat advisory concerns there. The same cannot be said for those east of the Blue Ridge where hot and very humid conditions persist. Particularly, those along and east of I-95 will see temperatures hit the upper 90s this afternoon and heat indices of 105-108. A Heat Advisory is in effect today for these areas. The development of the bay breeze in the mid to late afternoon will bring in mid to upper 70s dew points along the Western Shore during peak heating. The result in heat indices between 110-113 for several hours through early evening from Baltimore to St. Mary`s County. As a result, an Excessive Heat Warning has been issued for these areas of the Western Shore. Between I-95 and the Blue Ridge there is uncertainty regarding how much/where deep mixing occurs, and how low dew points drop this afternoon. Given that yesterday dew points dropped to around 70F along US-15, and better mixing is expected today, opted to not issue a Heat Advisory in the western Piedmont/foothills where heat indices max out between 100-102. The Heat Advisory was expanded to cover Orange, Culpeper, southern Fauquier, eastern Loudoun, the rest of Montgomery/Howard, and all of northeast MD. As the front reaches I-95, isolated to scattered thunderstorms are likely to develop ahead of it, but most of the convection pushes east of I-95 quickly. The highest storm coverage is expected over Southern MD and the Eastern Shore. A strong storm or two is possible, with damaging winds as the main threat. However, the overall severe threat is very low. Locally heavy rainfall could lead to an instance or two of flooding, though chances for this too are low. Lingering convection dissipates by late evening. As the front passes through Southern MD it begins to slow down, which could keep some shower/storm activity over the lower Chesapeake Bay through the night. Overnight lows drop to the 70s east of the Blue Ridge, and 60s to the west. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... The frontal boundary stalls just south of our area, over SE/south- central VAl Sunday. This brings dry conditions to most of the area, though cannot rule out a brief storm or two in Central VA or far southern MD. While still hot, highs in the low to mid 90s, the humidity levels are going to be noticeably lower Sunday. Mild conditions Sunday night as lows only drop to the low to mid 70s. A warm front lifts north through the area early Monday. Southerly flow returns and advects deep moisture over the area once again. Scattered afternoon to evening showers and thunderstorms return to the forecast Monday. High heat and humidity return as highs reach the low to mid 90s, and peak heat indices soar upwards of 100. && .LONG TERM /TUESDAY THROUGH FRIDAY/... A Bermuda high will remain in place offshore through next week, maintaining prevailing southerly flow locally. At mid-upper levels, broad troughing will reside across the center of the country, with southwesterly flow aloft locally. Multiple disturbances will pass off to our northwest over the course of the week, helping to increase chances for afternoon and evening showers and thunderstorms. The best chances for showers and thunderstorms may come Tuesday into Wednesday as a cold front drops southward toward the area. All in all, the pattern looks like a pretty typical mid- summer pattern through much of the week, with hot and humid conditions and daily chances for afternoon/evening thunderstorms. Each day looks to be humid, with dewpoints in the lower to middle 70s. Tuesday should be the hottest day of the long term period, with highs generally in the lower to middle 90s. Temperatures should cool slightly heading toward the end of the week as a weak cold front moves through (highs in the mid to upper 80s). Overnight temperatures will remain very warm, with lows generally in the lower to middle 70s for most. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... General VFR conditions are expected this weekend. A weak front slowly crosses the area today, then moves south on Sunday. Most terminals remain dry as afternoon showers/storms today focus east of DCA/BWI/MTN. Cannot rule out some VCTS for an hour or two this afternoon, but confidence and probabilities are too low to include in the TAFs at this time. Southwest to west winds today become north tonight, then light and variable Sunday as high pressure quickly passes over the area. A warm front lifts north of the area Monday, bringing southerly winds and a return of afternoon showers and thunderstorms. Prevailing VFR conditions are expected on both Tuesday and Wednesday, but temporary drops to sub-VFR may be possible either afternoon or evening. Winds will be out of the south on both Tuesday and Wednesday. && .MARINE... Winds turn southwest, then west through the day as a weak front slowly moves south across the local waters. Scattered showers and thunderstorms are possible this afternoon, mostly south of North Beach and over the Lower Tidal Potomac. Any strong storm could produce wind gusts in excess of 35 knots, in addition to lightning strikes. The front slowly pushes south of Southern MD late tonight, though it is forecast to stall just south of the area Sunday. While a thunderstorm or two is possible Sunday in the lower Chesapeake waters, mostly dry conditions are forecast. Winds turn north tonight, then are variable Sunday. A warm front lifts north across the waters early Monday, bringing the return of south winds at 10-15 knots. Scattered afternoon showers and thunderstorms return to the forecast Monday. Persistent southerly flow is expected over the waters on Tuesday and Wednesday. Winds may near SCA levels in channeled southerly flow Tuesday afternoon into Tuesday evening. && .TIDES/COASTAL FLOODING... Generally light southerly to southwesterly flow will result in elevated tide levels through the weekend. Vulnerable shoreline may come close to minor flooding during the early morning high tides. && .CLIMATE... While temperatures will be hot this afternoon, they will fall short of daily records as the local climate sites currently consist of records ranging from 102 to 105 degrees. However, a very warm night could lead to a couple record overnight low temperatures. Daily climate data runs from 1 AM EDT Saturday until 1 AM EDT Sunday. Some of the forecast numbers below have already occurred earlier this morning. Records (RERs) are only issued for DCA, IAD, BWI, and MRB, but other sites are shown for reference. ***Saturday night (July 6th)*** Current record (Year) Forecast low Washington-National (DCA) 83F (1999) 81F Washington-Dulles (IAD) 76F (2012) 76F Baltimore (BWI) 80F (1881) 81F Martinsburg (MRB) 75F (1900) 73F Charlottesville (CHO) 76F (2012) 74F Annapolis (NAK) 81F (2018) 82F Hagerstown (HGR) 78F (1999) 74F && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory until 8 PM EDT this evening for DCZ001. MD...Heat Advisory until 8 PM EDT this evening for MDZ005-006-008- 013-016-503>508. Excessive Heat Warning until 8 PM EDT this evening for MDZ011- 014-017-018. VA...Heat Advisory until 8 PM EDT this evening for VAZ050-051- 053>057-502-506-526-527. WV...None. MARINE...Heat Advisory until 8 PM EDT this evening for ANZ530. && $$ SYNOPSIS...KRR NEAR TERM...BRO/KRR SHORT TERM...KRR LONG TERM...KJP AVIATION...KJP/KRR MARINE...KJP/BRO/KRR TIDES/COASTAL FLOODING...LWX CLIMATE...BRO