Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 242343 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 743 PM EDT Sun Jul 24 2016 .SYNOPSIS... A warm front will lift north of the area tonight. A cold front will approach from the northwest late Monday. This front may stall across the region during the middle of next week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... MCS that earlier was over western PA and OH has progressed southeastward and is now moving through northeastern WV and southern PA, and about to move into western Maryland. While the actual line of thunderstorms that was severe earlier in the Pittsburgh area has weakened, seeing additional showers/thunderstorms develop ahead of the line, especially over the higher terrain. West- northwest flow aloft and corfidi vectors support continual movement of the activity into the region. The area lies along a CAPE gradient with MLCAPE values over eastern WV and northern VA between 1000-2000 J/KG and about 500 J/KG northeastward towards Philadelphia. Bulk shear values are low, about 25 knots or less, but given amount of instability in WV/VA, some pulse severe storms are possible, and will have to continue to monitor cold-pool driven convective line entering MD. Previous discussion... Additional thunderstorms may develop late this evening or even after midnight, as theta-e advection will serve to provide moisture. The best chance will be north of Martinsburg- Baltimore, but can`t rule out activity down to the US-50 corridor. Otherwise warm and muggy conditions are expected as dew points rise on return flow. Can`t rule out some fog if skies clear enough behind the disturbance. && .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... The primary issue for Monday will be the heat, and have issued a Heat Advisory for areas east of the Blue Ridge in addition to the Winchester-Hagerstown corridor. WSW flow will advect warm and moist air into the area, and any lingering mid clouds should clear by midday. Widespread mid to upper 90s are expected with possibly a few 100s. Model consensus for dew points is the low 70s, but there is some spread. If everything came together just right, heat indices could near 110 east of I-95, but it`s likely the temperatures and dew points will balance themselves via mixing to fall short of that mark. Thunderstorms will provide little relief for most of the day east of the mountains, as any forcing remains well to the NW, so most of the storms will be terrain-based. Some of these may gradually propagate to the SE by evening as a cold front approaches from the NW. The better shear will be north of the region, but with moderately high CAPE expected, there could be some stronger storms, especially to the NW. Still have POPs in the chance range as the front gets strung out parallel to the upper flow. However, have lingered storm chances well into the night as the boundary sinks southward. The front will remain stalled across the area on Tuesday. The highest chances of storms will be south of the front, which at this time looks to be south of I-66. Due to weak flow, the storms could be heavy rain producers. Temperatures will back off slightly, but the heat index will still approach 100 across much of the area. Perturbations interacting with the front will keep a threat of storms across southern areas into Tuesday night. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Quasi-stationary front remains near the area Wednesday into next weekend, with temperatures remaining above normal, and at least isolated shower/storm chances possible nearly each day. Some guidance is hinting that ridging will retreat to the south just enough Wednesday and Thursday for H85 temps (and thus sfc temps) to fall a few degrees from the early week highs in the M/U90s. Though...temps in L/M90s are still above normal. The gradual "cooling" trend continues Friday into next weekend, with afternoon highs generally in the U80s/L90s as broad troughing develops and heights lower further. Shortwave moving through the flow could concentrate thunderstorm coverage late in the week...though spatiotemporal placement is uncertain at this forecast range. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Primarily VFR conditions should prevail through the night. However, scattered showers and thunderstorms have developed and will push eastward across the region. Have introduced mention of VCTS at all TAF sites except CHO which should remain south of the convective activity. May also see some brief reductions in visibility with any heavier showers/storms. Some patchy fog also possible, especially if rain occurs. VFR through most of Monday with storm chances increasing (but still scattered) during the late afternoon through evening. Some storms may persist into the night as the front drifts south. This front will stall on Tuesday, with the highest chance of storms near CHO. Frontal boundary remains near the area through the end of the week, with at least afternoon thunderstorms possible. && .MARINE... Light and variable flow will become southerly by this evening and become SW on Monday. At this time, winds expected to be less than 15 kt, although flow may increase some Monday evening. A bigger hazard will be thunderstorms, although the best chance may await until Monday evening, and renew on Tuesday, especially for southern waters. A frontal boundary remains near the waters through the end of the week, with gusty winds possible in any thunderstorms. && .CLIMATE... Here are the record highs and warm lows for the next three days. Monday`s numbers appear to be the most vulnerable. Sunday... DCA...101 in 2010...84 in 2011 BWI...101 in 2010...82 in 2010 IAD... 99 in 2010...78 in 2010 Monday... DCA...100 in 1930...79 in 1965 BWI...100 in 2010...77 in 1887 IAD... 98 in 2010...76 in 1965 Tuesday... DCA...103 in 1930...79 in 1987 BWI...101 in 1940...80 in 1940 IAD....98 in 2012...76 in 2005 && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory from noon to 8 PM EDT Monday for DCZ001. MD...Heat Advisory from noon to 8 PM EDT Monday for MDZ003>006-011- 013-014-016>018-503>508. VA...Heat Advisory from noon to 8 PM EDT Monday for VAZ028-030-031- 036>040-050>057-501-502-505-506. WV...Heat Advisory from noon to 8 PM EDT Monday for WVZ052-053. MARINE...None. && $$ SYNOPSIS...ADS NEAR TERM...ADS/MM SHORT TERM...ADS LONG TERM...MSE AVIATION...ADS/MM/MSE MARINE...ADS/MSE CLIMATE...WFO LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.