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Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
669 FXUS61 KLWX 121339 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 939 AM EDT Mon Aug 12 2024 .SYNOPSIS... Surface high pressure builds over the region from the Midwest through mid to late week. Precipitation chances return for the end of the week as a low pressure system approaches the area. This slow moving system maintains an unsettled pattern into portions of the weekend. && .NEAR TERM /THROUGH TONIGHT/... A northwesterly flow continues to advect in cooler and drier conditions into the region this morning. Clear to mostly clear skies are expected to continue through the early afternoon periods with near average temperatures in the mid 80s. .Previous Discussion A surface frontal zone remains stalled across the Carolinas. On the cool/drier side of this boundary, 07Z/3 AM temperatures have fallen into the 60s, locally into the mid/upper 50s around the cooler spots. Across the higher terrain, some locations have even plunged to around 50 degrees. Within the elongated belt of cyclonic flow aloft, some mid-level clouds continue to stream eastward across the area. However, GOES-16 nighttime satellite imagery does show plenty of breaks in this cloud deck. While not readily evident on satellite and surface observations, a few areas of patchy fog are possible across the Potomac Highlands through just after sunrise. Through the day, the stalled boundary remains over the Carolinas while a broad surface high edges eastward from Mississippi River Valley. The presence of high pressure makes for a quiet start to the work week. Owing to a light but steady northwesterly wind, humidity levels remain on the lower side for mid-August standards. Today`s high temperatures will be in the low/mid 80s, with 70s across the mountains. Despite passing high clouds at times, expect plenty of sunshine along with continued northwesterly winds. With high pressure settling over the area into the night, winds should go calm allowing for a seasonably cool night ahead. The forecast calls for low temperatures in the low/mid 60s, accompanied by mainly mid/upper 50s along and west of the Blue Ridge Mountains. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... A positively-tilted upper trough across New England will exit into the waters early Tuesday morning. At the same time, the synoptic-scale pattern yields another round of northwesterly flow aloft as heights builds across the Great Plains. This regime will favor continued near to below average temperatures, reduced humidity levels, and a dry forecast. Within this northwesterly flow regime, a series of perturbations will track from the central U.S. toward the Eastern Seaboard. Any such wave aloft could spark and isolated shower here or there. However, the dry air mass in place should generally offset any real threat of shower activity through mid-week. Tuesday`s forecast highs stay fairly close to the previous day. A slight warm up is possible by Wednesday given more sunshine. Given forecast soundings depict mixing up to around 800-775 mb, could easily see highs being a smidge higher than currently shown. As of now, the forecast calls for widespread mid 80s across lower elevations in the area. Mountains locations are likely in the 70s. Overnight lows stay fairly close to climatology each night. && .LONG TERM /THURSDAY THROUGH SUNDAY/... On Thursday, the upper trough over the Northeast will be on its way out with brief upper ridging building over our area Thursday into Friday before another trough digs south along the East Coast over the weekend. The arrival of this second trough is currently progged to coincide with the exit of surface high pressure to the east and a low pressure system moving into the Great Lakes/SE Canada. Mostly dry conditions are expected Thursday and Friday with either surface high pressure or upper ridging in place. However, guidance is inconsistent on the strength and placement of the ridge and the following trough, resulting in some uncertainty. Latest NBM brings PoPs in by Friday, but 00z guidance continues to trend later with the arrival of PoPs. For now, limiting PoPs on Friday to chance PoPs or less, but better chance for rain appears to be Saturday. Temperatures during the extended are expected to be near or below normal in the 80s, with lows in the 60s to low 70s. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... VFR conditions are likely through mid-week given the influence of high pressure over the region. With a frontal zone well to the south over the Carolinas, surface winds largely stay out of the northwest. An eventual shift to northerlies is expected by Wednesday. Afternoon winds may gust up to around 10 knots each day before subsiding after dark. VFR conditions are expected Thursday and Friday. Light N/NW flow on Thursday shifts southerly Thursday night into Friday as surface high pressure slides east. && .MARINE... Quiet conditions are expected over the marine waters through mid-week. While a stray shower here or there is possible at some point, high pressure should maintain a mainly dry pattern. Winds stay out of the north to northwest, accompanied by gusts staying around 10 knots or less. No hazardous marine conditions are expected Thursday and Friday. Light N/NW winds over the waters on Thursday shift southerly Thursday night into Friday as surface high pressure slides east. Winds could pick up on Friday with southerly channeling, but the arrival of the next system has been trending later, so winds aren`t currently expected to approach SCA criteria until Saturday. && .TIDES/COASTAL FLOODING... With current tidal anomalies generally averaging between 0.25 to 0.50 feet, water levels remain below Action Stage at the local sites. This should stay that way given persist northwesterly winds. A gradual ramp up is possible at more sensitive locations by later in the week. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BRO NEAR TERM...BRO/JMG SHORT TERM...BRO LONG TERM...CAS AVIATION...BRO/CAS MARINE...BRO/CAS TIDES/COASTAL FLOODING...