Area Forecast Discussion
Issued by NWS Sterling, VA

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321 FXUS61 KLWX 240850 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 350 AM EST Sat Feb 24 2018 .SYNOPSIS...
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A stationary boundary situated across our area will gradually lift northward as a warm front through Sunday. A cold front will then pass through from the west by Sunday evening, with high pressure building in to the region through early next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Much of the area is covered in low clouds early this morning that are trapped below a hefty inversion based just a couple thousand feet off the ground, as sampled by the 00z KIAD sounding. Atop this inversion is a nice wedge of warm air aloft, with temperatures in the middle 50s at about 5kft. Back at the surface, temperatures early this morning range from the lower 40s west of the Blue Ridge to middle to upper 40s along and south of the D.C. metro area. Areas of dense fog have been persistent, relegated mainly along and north of the District, encompassing Baltimore and northeast MD. A Dense Fog Advisory remains in effect until 8am this morning for these areas. Outside of light drizzle in the fog plagued areas, the KLWX radar is mostly echo free. Do expect this to continue to be the case much of the morning across the area, at least east of the Blue Ridge mountains. We will start to see some showers encroach on our western and northern zones mid to late morning hours as a wave of low pressure moves northeastward over southern OH and WV. A stationary boundary snaking down the Appalachians and across North Carolina this morning will gain some momentum later today and gradually lift northward as a warm front through our area into tonight. As a result, highest rain chances will be this afternoon through the overnight period. Heaviest rain will be found across western MD, the Potomac Highlands, and the West Virginia Panhandle, where a half inch to an inch of rain could fall by Sunday morning. East of these areas, a tenth to a quarter of an inch can be expected, with lowest amounts across southern MD. With much of the area residing on the cool side of the frontal boundary today, temperatures stick in the upper 40s over northern MD to the middle 50s surrounding the metro areas. The locations favored to reside on the warm side of the boundaries are the southern portions of the Northern Piedmont, Central Foothills, and the Virginia Highlands, where highs will near 60 degrees and in to the middle 60s for the warm spots. Lows tonight won`t budge much, with middle 40s to our north to middle 50s to the south.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
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Come Sunday morning, a cold front will be moving eastward and nearing the western portions of our CWA. The aforementioned warm front will be lifting through and north of our area by Sunday morning, allowing much warmer temperatures to prevail. High temperatures will near 70 degrees for much of the area, with the cooler middle to upper 60s over the northern third of the CWA. Scattered shower activity Sunday morning will increase by midday as the front nears from the west. With the warmer temperatures and dewpoints creeping in to the lower 60s, along with frontogentical forcing, a slight chance of thunderstorms is possible as the front crosses the region by Sunday evening. Behind the front, clearing and drying conditions will win out Sunday night, with temperatures still above normal for late February, ranging from near 40 degrees to the north/west to around 50 degrees along our southern border. High pressure will build in from the west as we kick off the work week. The frontal boundary will linger along the Carolina coast on Monday, with the ECMWF indicating at least some rain chances for our southern zones. As such, will keep chance POPs for these areas on Monday, but the majority of our CWA will remain dry. Weak CAA behind the front on Monday will not prevent temperatures from reaching the upper 50s on Monday, with lows Monday night cooler in to the 30s area wide as CAA is a bit stronger and 850 temperatures reside at or just below 0C. This is in response to a low/mid level trough swinging through the region Monday evening.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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The middle of the week will be quiet as high pressure will be overhead. Tuesday will be the sunnier day; moisture will advance Wednesday due to return flow/warm advection as the center of the high will move into the western Atlantic. It remains to be seen if there will be any showers. GFS pointing that way more than ECMWF. Will back off PoPs for the period. Have greater confidence that the end of the week will end on the wet side, in spite of guidance timing/organizational differences. (ECMWF placing more emphasis on distinct southern stream shortwave/energy vs triple point from a well-defined northern stream system.) Either solution provides strong evidence of measurable precipitation, and neither scenario suggests there will be type issues until the back side (Friday night), when the qpf will be exiting.
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&& .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
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Widespread LIFR conditions at all area terminals this morning as low clouds and areas of dense fog envelop the region. Winds remain calm to light, favoring a southerly trajectory when registered by surface observations. LIFR VIS/CIGs will continue through mid morning, with some improvement to VIS, at least in terms of fog coverage, but low clouds and drizzle will persist. Rain chances increase this afternoon and evening as a wave of low pressure passes to the northwest of the terminals. Highest rain chances will be at MRB, but continued LIFR conditions expected through tonight. A cold front will move through the terminals Sunday afternoon, with plentiful rain chances and IFR/LIFR VIS/CIGs continuing ahead of it. Southwesterly breezes at around 10 knots, gusting to near 20 knots during the day on Sunday, will shift out of the northwest Sunday night and fall to less than 10 knots in the wake of the frontal passage. Conditions should improve to MVFR/VFR Sunday night, and back to VFR through Monday night as high pressure moves in from the west. Exception to this on Monday would be CHO, where some residual shower activity is possible as the aforementioned boundary lingers well to our south. This could result in periods of sub VFR conditions there. VFR conditions expected at this time due to high pressure.
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&& .MARINE...
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No advisories expected through tonight for our waters as winds will remain light as a stationary boundary to our south starts to lift northward as warm front. As a cold front approaches from the west on Sunday, winds will pick up and become gusty out of the south southwest Sunday morning, with SCA conditions looking likely through much of the day on Sunday until the front passes through our waters. The frontal passage may bring with it a gusty line of showers, with a slight chance of thunderstorms as well. High pressure will then build in to the region behind the front through Monday night, delivering lighter winds across our waters, and sub SCA conditions. Winds will remain below Small Craft Advisory thresholds due to high pressure. Southerly flow will increase late Wed in the wake of the high.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Dense Fog Advisory until 8 AM EST this morning for DCZ001. MD...Dense Fog Advisory until 8 AM EST this morning for MDZ003>006- 011-013-014-503>508. VA...Dense Fog Advisory until 8 AM EST this morning for VAZ053-054- 505-506. WV...Dense Fog Advisory until 8 AM EST this morning for WVZ052-053. MARINE...None.
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&& $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF LONG TERM...HTS AVIATION...BKF/HTS MARINE...BKF/HTS

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