Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 182044 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 344 PM EST Sat Feb 18 2017 .SYNOPSIS... A weakening area of low pressure will cross the area tonight. A backdoor cold front will enter the area Monday into Tuesday. Another disturbance early Wednesday. High pressure will be located off the southeast coast of the United States during the end of the week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... High pressure is located off the southeast US coast this afternoon. S/SW flow has been established, helping to push temperatures into the 60s and 70s. One exception is by the colder waters of the Chesapeake Bay, where a light onshore flow is holding temperatures in the 40s and 50s as of 2 PM. Closed low pressure in the upper atmosphere is located near Memphis and will open/weaken as it moves east tonight. The arc of precipitation associated with the low is expected to fall apart as it heads toward our area tonight, but models vary on what degree. Overall, atmospheric moisture is lacking and forcing resides more in the mid levels, so any precipitation that does fall will be very light rain showers (less than a tenth inch) or just sprinkles. The highest chance will be in the Potomac Highlands. Increased cloud cover is more certain for tonight. Low temperatures will only drop into the 40s...perhaps staying above 50 in a few locations. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... Low level trough axis extending between low pressure in Quebec and the weakening wave to the south will have cross the area early in the day. This will turn the wind direction to the W/NW and allow some cold air advection aloft. However, the downsloping flow with good mixing will allow temperatures similar or a few degrees cooler than today. Any morning clouds will thin though the day. Upper level pattern amplifies Sunday night into Monday, with a shortwave trough deepening the mean trough in New England. Meanwhile surface high pressure will be building into Quebec. A backdoor cold front will slip southwestward into the area. Winds will turn northerly on Monday, although cooler air aloft only slowly seeps southwestward. This will lead to a tricky temperature forecast, with temperatures near 70 likely persisting in central VA, while northeast MD may struggle into the 50s. Overall airmass remains dry though, with mostly sunny skies across the entire area. Flow turns a bit more onshore by Monday night as the low level ridge axis moves into New England. RH fields are still on the drier side though, with any sort of overrunning moisture signal for low clouds generally limited to the southern Potomac Highlands. The lows may depend on cloud cover, as dew points drop into the 20s and winds will be light. && .LONG TERM /TUESDAY THROUGH SATURDAY/... The tail end of a cold front, driven by low pressure departing up near Hudson Bay, will approach the area Tuesday, then cross the area Tuesday night. Most of the forcing will be removed well to the north of the area, so expect most showers along the front to be relatively scattered and in a weakening state as they pass through. The front will stall just to the south Wednesday before returning north as a warm front during the second half of the week. The next upper trough/low pressure should bring a cold front near the area during the first half of next weekend, though the track of the low and best forcing remain uncertain at this time. Overall, temperatures will be milder than normal by February standards for much of the week. && .AVIATION /21Z SATURDAY THROUGH THURSDAY/... VFR should prevail for the TAF period. SSW flow will turn W/NW late tonight as a trough axis passes. Chances for precipitation remain low, and if anything does occur, it would be more on the order of sprinkles. Cigs likely remain above FL050. This chance will end with daybreak. Some gusts of 15-20 kt possible as mixing increases on Sunday. A backdoor cold front will drop south toward the area Monday, with flow becoming northerly. Model RH still do not indicate of clouds, with only a limited signal for low clouds. Even if some stratus does form, it may be VFR. Mainly VFR expected Tue-Wed. Brief sub-VFR possible in - SHRA Tue night. SELY winds around 10 kts Tue become SWLY behind cold FROPA Tue night-Wed. && .MARINE... S/SW flow continues into tonight, generally 15 kt or less. A trough will cross the area tonight and turn winds to the NW by Sunday. Wind fields indicate marginal SCA conditions will be possible by Sunday afternoon, but temperatures will remain warm over cold water, so mixing is in question. The best opportunity would be on the upper Potomac and nearshore/inlets of the northern part of the Chesapeake Bay. The flow will turn north Monday and perhaps easterly by Monday night, as a backdoor cold front slips toward the waters. Gradient appears to remain weak enough that winds will stay less than SCA levels regardless of frontal position. With a front stalled near the waters, the gradient/winds should remain light enough to preclude any Small Craft Advisories during the middle part of the week. && .CLIMATE...
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Very warm temperatures grip the region and will persist through Sunday. Some readings are going to be close to records. Here is the list of records are our big airports. Saturday Sunday Sunday Site Record high Record high min Record high Washington/Reagan 77 in 2011 52 in 1981 74 in 1939 Baltimore/BWI 75 in 1976 47 in 1976 72 in 1997 Washington/Dulles 75 in 2011 46 in 1981 71 in 1997
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...DFH AVIATION...ADS/DFH MARINE...ADS/DFH CLIMATE...RCM

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