Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 281913 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 313 PM EDT TUE JUN 28 2016 .SYNOPSIS... A cold front approaches from the west today, as a pre-frontal trough remains over the local area. The front will slowly move across the region late this afternoon through tonight. Weak high pressure builds in from the north Wednesday and Thursday as the front stalls across the Carolinas. The next cold front approaches the region late in the work week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Latest surface analysis places the upstream cold front over the Ohio River with a pre-frontal trough over central Virginia. Aloft, GOES water vapor imagery and RAOB plots indicate shortwave energy over West Virginia/western Virginia. Water vapor imagery also depicts a deep plume of moisture streaming northeastward from the Gulf of Mexico. Precipitable waters have climbed to over 2 inches across the region, which is +2 standard deviations. Pre-frontal showers are expanding in coverage late this morning as the upper wave approaches from the west. This matches up well with inherited likely POPs, so no changes made to near term POP forecast other than to increase the Maryland Eastern Shore to categorical. Locally heavy rainfall still expected. Rainfall amounts in excess of 2 inches have been observed over the Maryland Eastern Shore. Temperatures also on track. Only other change made was to time POP`s late today through this evening. Confidence is increasing that a line of scattered showers and thunderstorms will develop ahead of the cold front over the Piedmont late today, even as dry air begins to work in from the west. Some clearing is expected with MLCAPE values progged to increase to 1,000 to 1,500 J/kg over the Piedmont this afternoon. Deep layer shear remains marginal as strongest height falls remain north of the region. Gusty winds are possible under the strongest storms. SPC maintains only a marginal risk for severe weather. Previous Discussion... Current analysis depicts low pressure over eastern Canada, with a surface cold front extending SW through western NY and into the Ohio Valley. A pre-frontal sfc trough is in place along/just E of The Appalachians. Ongoing widespread shower with embedded tstm activity over the Ches Bay and eastern Shore, with coverage more isolated to widely scattered across central and south central VA (with dry conditions over far se VA and ne NC). GFS/NAM reveal that although CAPE is very limited, elevated instability per negative showalter indices over much of the area has been sufficient when combined with decent lift to keep showers going along with a few tstms. Activity off to the W/SW of metro richmond likely to increase in coverage over the next few hrs and will carry likely POPS of 60-70% from the eastern shore back W/SW through cent ral and south central VA through the morning, tapered to only low chc POPS over the far SE through mid morning. However, expect highest coverage of precip to gradually shift E/SE through the late morning/early aftn hrs, with likely POPS overspreading se VA and ne NC by late morning through much of the aftn. Meanwhile, some breaks in the clouds are expected over central VA as POPS decrease somewhat by mid aftn onward. If enough clearing occurs this aftn, could see some marginally strong tstms develop, mainly W of ches Bay and SPC has this approximate area in a marginal risk for severe tstms. Still, greater effective shear of 30 Kt+ should stay N of the entire area closer to stronger h5 height falls since the upper low will be well to our north across Ontario. Given the continued moist airmass with precipitable waters around 2.00" and relatively weak steering flow aloft (at least through 18Z) locally heavy rain will be the main concern and will address in the HWO. Highs generally in the low-mid 80s today (possibly staying in upper 70s/around 80 depending on rain coverage through the aftn). Upper low tracks from NY state to New England later tonight, a slightly slower secenario compared to past model runs. Still expect the cold front to push through the local area, though the front may hang up near the coast. Height falls will result in cyclogenesis just off the Northeast coast Tuesday night. As the low wraps up, lingering mid level moisture across the northeast forecast area in concert with strengthening forcing for ascent is expected to produce scattered showers Tuesday evening. Best chances will be from the Northern Neck to the Eastern Shore. Drying late Tuesday night with a clearing sky inland. Partly- mostly cloudy near the coast. Lows range from the mid to upper 60`s. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY/... Broad, upper level trough pushes across the region Wednesday. The frontal boundary expected to stall in the vicinity of northeast North Carolina as high pressure builds in from the northwest. Departing 70+ knot upper jet and enough lingering mid level moisture (precipitable waters drop below 1.5 inches) should be enough for widely scattered diurnally driven showers and thunderstorms, mainly over far southern VA and ne NC. Highs generally in the mid 80`s under a partly cloudy sky. Best chances for measurable precipitation will be south of the Albemarle Sound Wednesday night, but will keep mention of slight chance showers. Lows generally in the low to mid 60`s N to upper 60s S. Surface high pressure centers along the Mid-Atlantic coast Thursday morning as the next upper level shortwave approaches from the west. Low pressure progged to develop over the Southeast states with an inverted trough extending northward over the central Appalachians. Upslope flow and the approaching wave will result in showers and thunderstorms over the higher terrain. GFS is wettest model and would support high chc POPS into the CWA while the NAm/GEM are drier. Expect much of the forecast area to remain dry, but will mention a 20-30% POP for showers coming off the higher terrain Thursday afternoon into areas W of the Bay. Otherwise, near seasonal temps again with highs forecast in the mid 80`s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Active northern stream upper trough will remain the dominant wx feature through the medium range period. Resultant W-NW flow will continue for the late week/Holiday weekend period. Meanwhile, at the surface, a rather stagnant pattern looks to set up with weak front/sfc trough dropping into the area and lingering over the local area. Warm, moist airmass (PW AOA 2" from Friday night through the weekend) in tandem with the boundary and numerous disturbances riding across the area in WNW flow aloft will bring a solid chance for mainly diurnally driven showers and tstms. Have continued solid chance pops each day during this period. Stronger front crosses the area by later Sunday into Monday. For temps, pattern favors temperatures hovering right around climo normal...with highs in the mid to upper 80s. Early morning lows generally in the 60s. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/...
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Numerous showers with some embedded thunder continue this aftn ahead of a cold frnt approaching fm the w. Expect areas of mvfr/ifr with the precip, with vfr elsewhere this aftn as several areas are drying out. Continued vcsh thru this eveng as some rain is still psbl until the frnt crosses the area Wed morng. Also prior to the fropa, some low cigs/vsbys are psbl late tngt after today`s rain, especially over kric and ksby. Vfr then for Wed aftn as the frnt drops thru the area. There will then be chances for rain each day for the remainder of the week, especially into the weekend.
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&& .MARINE... Early this morning, SSW winds were mainly 5 to 15 kt acrs the waters, and will remain at those speeds today into tngt, as a pre-frntl trof lingers ovr the area and then the cold front approaches fm the WNW. The front and accompanying wind shift to the N-NE drops through the waters Wed morning into Wed aftn with high pres pushing into the Great Lakes and OH Valley. This will maintain a NE to E flow later Wed and Thu. Weak front/sfc trough will meander over/just south of the area for the late week period, and will serve as the focus for late day convection over the region late in the week and through the weekend. && .CLIMATE... Chances to add to an already wet month mainly tonight and Tue. June has been another wet month at Richmond, the monthly total rainfall through the 24th stands at 6.92" and already makes this the 9th wettest June on record (2004 is wettest June with 9.93"). && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...LKB NEAR TERM...LKB/SAM SHORT TERM...LKB/SAM LONG TERM...MAM AVIATION...MAS MARINE...TMG CLIMATE...

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