Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 291910 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 310 PM EDT Fri Jul 29 2016 .SYNOPSIS...
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An area of low pressure will pull away from the coast this afternoon and evening. A frontal boundary across the Carolinas will return north Saturday. An area of low pressure will track along the front on Sunday. The front will move southward again on Monday, with high pressure building in early next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Radar across the area is quiet as of 2pm. Subsidence in the wake of departing low pressure as well as slightly lower dewpoints are contributing to the lack of activity. SBCAPE near 1000 j/kg per mesoanalysis, so still believe a few showers or a thunderstorm possible. Terrain circulations likely are the primary instigator. Whatever develops should diminish upon sunset. However, 850 mb return flow will arrive tonight as the front makes its return approach. We will also have the leading edge of vorticity advection arriving toward dawn from the Ohio Valley. Therefore, shower or thunderstorm activity will become possible once again. Have overnight chance PoPs west of I-95, highest in the mountains.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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A trough axis will cross the area Saturday-Saturday night. Anticipate moisture transport ahead of the trough, with the southwest flow dragging the weak quasi-stationary boundary back north again. So, we once again will be dealing with a marginally unstable, sheared environment with weak surface and PVA forcing. Therefore, expect conditional instability, the extent of which will be predicated by how much daytime heating we will receive. In the end, there is sufficient evidence to increase PoPs to categorical, with locally moderate to heavy rain possible. SPC outlook for Saturday carries a MRGL risk area to account for the potential of wet microbursts. In addition, believe there once again will be a local flood threat. Believe the will be a break Saturday night, due in part to loss of daytime heating. However, shortwave passage will also play a role, so the timing may need to be adjusted. But, the lower heights aloft likely to induce low pressure once again for Sunday. Again, have focused highest PoPs with the diurnal cycle. That may need to be adjusted. High temperatures will be limited by lack of insolation and anticipated rain Saturday, and slight cool thermal advection Sunday. Minimal change anticipated for lows through the period.
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&& .LONG TERM /MONDAY THROUGH FRIDAY/...
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The front that has been meandering over our area for the past week or two looks like it will finally push offshore by Monday night as a 1020+ mb surface high moves in from the north. Before then, a few showers and thunderstorms will again be possible Monday. But after that conditions look much more seasonably mild and less humid through the middle part of next week. The high will move offshore by the end of the week likely leading to increasing heat and humidity once again.
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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VFR conditions through the late afternoon and evening hours. Thunderstorms, if any, will be limited. There may be a slightly better chance overnight as the recently departed cold front returns as a warm front. However, odds still too slim to mention at this time. Probability for flight restrictions will improve Saturday as shortwaves will act upon an increasingly warm, moist, and unstable atmosphere. Still a bit too far out for specific timing. Have focused on midday and afternoon hours in the TAFs, limited restrictions to MVFR at worst. However, local downpours possible, which could briefly create IFR or below. In addition, there also will be a gusty wind threat. Those storms likely to exit at some point in the evening on Saturday. However, additional storms possible on Sunday...again with possible flight restrictions. Generally VFR expected Monday and Tuesday with northwesterly flow around 10 knots.
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&& .MARINE...
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Winds have diminished to 10 knots or less. Anticipate similar speeds for the next several days. Showers and thunderstorms return Saturday, some of which may contain heavy rains and gusty winds. Additional thunderstorms possible Sunday. Any hazards will come from these winds. A cold front will finally push offshore early next week. A brief period of Small Craft Advisory winds cannot be ruled out immediately behind the front in northwest flow.
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&& .TIDES/COASTAL FLOODING...
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Water levels running about a half-foot above astronomical normals at this time. There may be a slight decrease tonight, but that will increase once again on Saturday as storms will return-- drawing moisture north. Sensitive locations may threaten minor thresholds both Saturday and Sunday. The overnight tide cycle will be the higher astronomically; that`s where the better risk is.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...DFH AVIATION...HTS/DFH MARINE...HTS/DFH TIDES/COASTAL FLOODING...HTS

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