Area Forecast Discussion
Issued by NWS Wakefield, VA

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000 FXUS61 KAKQ 100203 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 903 PM EST Sat Dec 9 2017 .SYNOPSIS... Low pressure moves farther off the mid Atlantic coast this evening through tonight. Cold high pressure builds into the area Sunday through Tuesday. && .NEAR TERM /THROUGH SUNDAY/... * Have allowed all Winter Warnings to expire and these have been replaced with advisories. Other advisories have been extended through 7-10pm. Will be issuing an SPS for areas to the SE of the advisories where some light snow accumulations of less than one inch will be possible. Latest wx analysis indicates that the sfc low now accelerating NE off the mid-Atlc coast and intensifying down to ~995 mb. Winds over the local area are shifting from NNE to the NNW allowing colder air to move in and change the ptype back to predominantly snow. The next few hrs (through 7pm or so) should be the final portion of the storm for most of the CWA (lingering a few hrs more for the eastern shore). Likely to categorical POPs in effect through 00Z all zones, tapering to chc PoPs thereafter except for the northern Neck/eastern shore. Despite the presence of RRQ from ~175 KT upper Jet streak and 500 mb shortwave moving into the region, omega and full saturation through the DGZ/-12C to -18C layer has been minimal thus far and has limited snow intensity for much of the day. Does look like somewhat greater precip intensity will prevail through the next few hrs into early evening. Latest RAP/NAM 12 continue to approximate the changeover to all snow with ~1295m 1000-850mb thickness and 32F sfc wet bulbs. Additional snow accumulations will avg around 1", with 1-3" possible over the northern Neck and interior MD eastern shore as the band will tend to pivot and slow down a bit through the early evening in these areas. Also, models shows the cold air aloft/1000-850 mb thicknesses crashing below the critical 1295-1300 m over interior SE VA between 19-22Z and reaching the coast after about 22-23Z. Thus, increased snow amts for up to an inch of snow by evening in the SE. By later this evening, even as precip ends for most, skies will be slow to clear out as the upper level shortwave passes through the area. On the ern shore, some clouds will persist through at least 06-09Z. Due to some mixing, and more clouds, overnight temperatures will not be as cold as they could be (especially on the MD ern shore where the deepest snowpack will reside). Temperatures will fall below 32F between 03-06Z most areas, then into the 20-25F range west of I-95 and mainly 25-30 F elsewhere. Roads that had been wet will become slick and any snow that remains on the ground will become quite compacted. Will likely be issuing and SPS for black ice later tonight through Sunday morning for much of the region where snow has fallen. Sunday should be a cold day with high temps around 40 F north to the mid/upper 40s SE with mostly sunny skies. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... Genly a dry and quieter period with temperatures remaining near or a little below normal. Skies will avg partly cloudy north to mostly sunny/clear south for the most part. Lows Sun night in the 20s to lower 30s and highs Mon and Tue mainly in the mid/upper 40s N to the lower 50s SE. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The long term begins with the longwave trough entrenched over the eastern half of the US with multiple shortwave troughs expected to rotate through the longwave trough on Tuesday night/Wed and again Thurs night/Friday. Each of these shortwaves will have a strong clipper like surface low that will accompany the trough and swing a strong cold front through the region. At this point, the track of the shortwave does not appear to be far enough south or have enough moisture to cause any significant weather problems, other than to reinforce a cold air mass that will be in place through the work week. But there is some uncertainty with the models as the 12z GFS keeps the low track to the north of the area, but the 12z ECMWF now brings the second low on Thursday into Friday further to the south and has a little more moisture to work with. For now, have left a mention of some light snow showers of possibly a few flurries across northern portions of the CWA on Tuesday night in Wed morning and again for the second wave on Thursday into Thursday night. The warm advection with the second wave could be a little stronger and if enough moisture could be advected northward from the gulf coast, there could be a little more interest in this wave, but right now any pcpn would be expected to be light. The pattern finally breaks heading into the weekend with the long wave trough exiting and the flow become more zonal as a weak subtropical ridge begins to build over Southern Gulf of Mexico and Western Caribbean. For temperatures have leaned toward the colder Superblend/National blend of models on Tues night into Friday, which is a few degrees cooler than the MEX numbers. For the weekend, have remain on the cool side, but with the high sliding off the coast, could see temperatures recovering a little more than shown. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/...
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Widespread IFR conditions continue across the region as the area of precipition gradually shifts eastward. Expect most of the precip to move offshore by midnight with clearing from west to east. Clear sky should prevail over the CWA by Sunday sunrise. Quieter weather returns to the region through early next week.
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&& .MARINE... Developing sfc low pressure continues to push northeastward off the coast tonight as a secondary cold front slides through the Mid Atlc. As for headlines...have continued them for the most part with the exception of the James River where winds are now aob 15 kt. Expect at least 15-20 kt winds to continue through at least the first half of the day Sun over the Bay and Sound, with 15-25 kt sustained winds and gusts up to 30 kt over the ocean. Seas up to 8-9 ft over southern coastal wtrs, where the SCA is in effect until early Sun evening. Sub-SCA conditions then for Sun night and Mon with sfc high pressure over the SE states. Next chance for SCA conditions comes Tue as a cold front associated with a clipper system crosses the area. Low-end gales psbl post-frontal as well Tue night/Wed especially over northern coastal wtrs. && .AKQ WATCHES/WARNINGS/ADVISORIES...
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MD...Winter Weather Advisory until 10 PM EST this evening for MDZ021>025. NC...None. VA...None. MARINE...Small Craft Advisory until 4 PM EST Sunday for ANZ630>632-634. Small Craft Advisory until 1 PM EST Sunday for ANZ633-656-658. Small Craft Advisory until 7 PM EST Sunday for ANZ650-652-654.
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&& $$ SYNOPSIS...LKB NEAR TERM...LKB SHORT TERM...LKB/MAM LONG TERM...ESS AVIATION...LKB/JEF MARINE...MAS

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