Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
190 FXUS61 KLWX 180131 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 931 PM EDT Wed Jul 17 2024 .SYNOPSIS... A strong cold front will slowly cross the area through tonight. Showers and possibly a thunderstorm or two will accompany it overnight. Cool high pressure builds back into the area from the north Thursday as the front sinks south and east of region. The front will remain stalled to our south Friday before retreating back to the north this weekend into early next week. && .NEAR TERM /THROUGH THURSDAY/... A cold front, currently over southwest PA, will push through the region tonight. The strongest of the thunderstorms are across the Delmarva Peninsula. Scattered showers extend from northeastern West Virginia and across western and central Maryland ahead of the approaching cold front. Once convection wanes or dissipates later this evening, patchy fog could form in most places that received rainfall during this past afternoon and evening. Lows will drop into the 60s west of the Blue Ridge, and remain in the 70s to the east. The surface cold front will likely be south of the area by Thursday morning. However, some guidance is still slow enough with the frontal zone progression, combined with shortwaves aloft, that showers and a few thunderstorms could still develop through Thursday, mainly across the southern half of the area. It will be noticeably cooler with highs in the 80s for most, although some breaks of sun could allow some northern areas to reach 90. && .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... Previous discussion... Lower dew points will gradually advect in and will be most noticeable Thursday night when lows drop into the 60s for most of the area, with 50s in the mountains. High pressure will build north of the area and the front will reach its most southern extent Friday before stalling against the Bermuda high. Therefore, dry and seasonable conditions should prevail, although some increased cloud cover may persist in southern areas. Some guidance has moisture advancing back northward as quickly as Friday night, so we have some slight chance PoPs across the southern half of the area. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Key Messages: 1) No excessive heat! Temperatures will remain at or slightly below normal through much of the extended period. 2) Increased confidence for daily chances for showers and thunderstorms as a stalled front remains nearby. It`s a typical stagnant Summertime pattern as we head into the weekend and throughout much of next week. Synoptically, we`ll continue to monitor a deepening upper-level trough over the central Mississippi River Valley as it becomes blocked by the ridge over the Rockies and central Atlantic. As a result, a stationary boundary will remain draped across the Virginia and North Carolina border before slowly drifting north as a warm front Monday and Tuesday. Moisture will increase across the region leading to an uptick in daily chances for showers and thunderstorms. The highest coverage of thunderstorms appears to be Tuesday and Wednesday as the warm front lifts through and then eventually stalls near the region. This is highlighted by both the CSU and NSSL machine-learning probabilities which suggest a non-zero chance of severe weather during this time. As for temperatures, expect values closer to seasonable norms this weekend into early next week. Highs will push into the mid to upper 80s Saturday, with upper 80s and low 90s Sunday mainly east of the Allegheny Front. Temperatures come up a few more degrees Monday through Wednesday as the warm front crosses the region. This aligns with the 6-10 day and 8-14 day trends from the Climate Prediction Center with regards to temperature outlooks. With moisture increasing, we may get close to Heat Advisory criteria mid to late next week, although some uncertainty remains in regards to the intensity of heat during this time frame. Overnight lows through the period will fall into the mid to upper 60s and low 70s with light winds. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... Scattered showers will continue to push across the region late this evening and overnight, primarily leaning moreso on the MRB terminal. We can`t rule out a few additional showers that develop with frontal passage but confidence on intensity and location is low. There is also some potential of MVFR ceilings behind the storms in the metro areas, but confidence is low. Patchy fog could also develop if there are breaks in the clouds. The front will be south of the area Thursday, but showers and thunderstorms may still develop in its vicinity, which could affect CHO. VFR conditions appear probable Thursday night into Friday as high pressure builds to the north. Prevailing VFR conditions are expected throughout the weekend with intermittent sub-VFR conditions at times as a result of any showers and thunderstorms that form during the diurnal period. Winds will remain light out of the south throughout the weekend. VFR conditions continue into early next week, although the opportunity for sub-VFR remains during the afternoon and evening hours as a warm front lifts into the region. This will lead to increased chances for showers and thunderstorms at the terminals, although confidence remains low on which terminals will be affected. The highest coverage for thunderstorms appears to be by the middle and end of next week. && .MARINE... Winds will diminish behind the cold front tonight. Winds become northerly Thursday behind the front. A few thunderstorms are possible near southern Maryland through Thursday but seem unlikely to be strong. There`s still some potential for northerly channeling down the bay Thursday night, but it would be marginal for an advisory. Lighter winds are expected Friday and Friday night as high pressure builds to the north and the front stalls to the south. Sub-SCA level winds out of the south are expected this weekend into early next week. An SMW cannot be ruled out for any potential strong thunderstorms that look to pop up during the afternoon and evening hours. The greatest potential for a thunderstorm looks to come Monday through Wednesday as a warm front lifts into the region. && .CLIMATE... Here are daily high temperature records for July 17. Records (RERs) are only issued for DCA, IAD, BWI, and MRB, but other sites are shown for reference. A `+` sign indicates multiple years currently hold that record. ***WEDNESDAY, JULY 17TH, 2024*** LOCATION RECORD (YEAR) Washington-National (DCA) 102F (1980) Washington-Dulles (IAD) 100F (1997)+ Baltimore (BWI) 101F (1988) Martinsburg (MRB) 102F (1988)+ Charlottesville (CHO) 100F (1988)+ Annapolis (NAK) 100F (1900) Hagerstown (HGR) 100F (1953)+ && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Small Craft Advisory until 11 PM EDT this evening for MDZ008. VA...None. WV...None. MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ530>533-535-536-538>542. Small Craft Advisory until 5 AM EDT Thursday for ANZ534-537- 543. && $$ SYNOPSIS...EST NEAR TERM...KLW/DHOF SHORT TERM...KLW/DHOF LONG TERM...EST AVIATION...KLW/EST MARINE...KLW/EST CLIMATE...LFR