Area Forecast Discussion
Issued by NWS Sterling, VA

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640 FXUS61 KLWX 180130 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 930 PM EDT Sun Jul 17 2016 .SYNOPSIS... Weak high pressure will remain over the area through Monday morning. A cold front will approach from the northwest late Monday and cross the region on Tuesday. High pressure will build in Wednesday and remain in place through Saturday. A cold front may cross the region Sunday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... While the theme of the night is high pressure centered offshore, there are a couple weak boundaries across the area: a weak front which has slipped into the NW, and another boundary pushing northward from central VA. However, these are generally dew point/subtle wind shift boundaries, as the 00Z IAD raob indicates a stable and dry environment. For the rest of the night, some cirrus will continue to spill in from the west, but otherwise mostly clear skies are expected. Patchy fog is possible, especially south of the southern boundary where dew points are highest. Temperatures appear to be on track at this time to lows in the 60s and lower 70s. && .SHORT TERM /6 AM MONDAY MORNING THROUGH WEDNESDAY/... Things look more active on Monday but much uncertainty remains. Front pushing southeast from Canada looks to move through early Tuesday...a bad time if you want convection. What most likely would happen is that storms well ahead of the front develop in association with a weak leading shortwave and surface trough. Higher resolution models (NSSL/ARW/NMM WRFs, NCAR Ensemble, NAM, HRRRX) indicate the trough activating with at least scattered storms near the I-81 corridor around 16-18Z, pushing to the southern MD Bay by evening (GFS/ECMWF remain relatively dry). Thought this warranted a little bump in POPs as well as a faster arrival time. There is 25-35 knots of 0-6km shear and decent CAPE, so a few strong/severe storms not out of the question...but there are also hints of a westerly flow which may try to suppress convection. There`s lesser agreement on whether upstream storms propagate into NW zones later in the evening. Bottom line...not a lot of confidence in potential thunderstorms on Monday aft/eve but potential definitely exists especially in our NW zones. With the SW to W flow ahead of the front, temps should spike into the mid 90s in our warmer locales. Heat indices will be in the upper 90s to possibly just above 100 for most locations east of the Blue Ridge. On Tuesday...any showers/storms depend on just how fast the front moves through...as well as a push of drier air aloft. Right now have them mostly in our southern zones...which makes sense given expected frontal position. Temps will be on their way down. Tuesday night into Wednesday...Canadian high pressure will provide a cooler and drier air mass with sunshine. Lows in the 50s and 60s with highs in the 70s and 80s. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As high pressure remains in the area Thursday expect dry and comfortable weather, with near seasonable temperatures (M/U 80s), and relatively low humidity (dewpoints U50s/L60s). We turn hot (highs in the M90s) but stay dry Friday. Though, humidity gradually increases as southwest flow develops, which will make it begin to feel slightly more uncomfortable. Cold front then approaches the area next weekend. Still some uncertainty with how far the front pushes through the area. Current forecast has chance pops returning Saturday and Sunday afternoon with front nearby and hot/humid atmosphere. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... VFR and dry conditions through this evening. Some patchy fog possible again late tonight, but coverage appears to be less than Sunday morning. CHO area may be most favored with highest dew points, but there may also be some gradient wind. Therefore have left mention out of TAFs for now. Next chance of showers/thunderstorms will arrive Monday afternoon through evening with next frontal system. Reductions below VFR possible along with potential for strong wind gusts. The best chance may be at MRB, but scattered storms will be possible across much of the area. TAF mention will be included as period draws closer and details refined. A stray storm may pop up Tuesday but odds are low. VFR conditions prevail Wednesday through Friday under high pressure. && .MARINE... Winds are now turning SW/S this evening as a weak boundary pushes north. Seeing some 10-15 kt obs. Will have to monitor these, as channeling could develop on the Bay as the night progresses, but confidence low on which, if any, areas reach SCA criteria. Southerly flow increases Monday with marginal SCA conditions expected late Monday into Monday night out ahead of next frontal system. Isolated to scattered showers/thunderstorms also possible Monday into Tuesday. NW flow behind front Tuesday- Tuesday night may also bring SCA conditions with northerly channeling. High pressure builds in Wednesday then remains through Thursday. Winds should gradually increase Friday as southerly flow redevelops over the area. && .TIDES/COASTAL FLOODING... Anomalies are still near astronomical normals this evening but could increase a bit as southerly flow develops ahead of the next front. Sensitive sites (Annapolis) may briefly reach minor thresholds on Monday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from noon to 9 PM EDT Monday for ANZ530>543. && $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS/RCM LONG TERM...MSE AVIATION...ADS/MSE/RCM MARINE...ADS/MSE/RCM TIDES/COASTAL FLOODING...RCM/ADS

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