Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 210801 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 401 AM EDT SAT MAY 21 2016 .SYNOPSIS...
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Low pressure will track up the Mid-Atlantic coast today. Upper level low pressure will persist along the Mid-Atlantic coast tonight through Monday night. High pressure returns Tuesday and persists through mid-week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure is retreating off the New England coast this morning as low pressure moves toward the Smokey Mountains. An area of moderate to locally heavy rain is overspreading the area in association with convergence/moisture advection from a low level jet. The rain is having to overcome some dry air, so the better rates are delayed from the onset despite radar appearance. A few observations suggestion locations south of Charlottesville have already received an inch or more. Expect this shield of rain to progress northeastward during the morning hours. The heavier rain looks progressive enough to preclude much in the way of flooding. The main question of the day revolves around a mid-level dry slot. This is already working into SW VA, and indications are that the rain will shut off fairly quickly in the SW CWA. However, energy will be transferring to a coastal low by this afternoon, and may keep areas near and east of I-95 fairly wet in wrap-around (but lighter) moisture. Even where higher QPF isn`t depicted, wouldn`t rule out some light rain or drizzle at times. Meanwhile the upper level trough is expected to spark convection this afternoon in WV, and some of this activity may work toward Highland Co. The thick low clouds will mean little movement to temperatures...with highs struggling to reach 60F in many areas.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/...
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The best way to describe the short term period is "unsettled"...although gradually less so with time through Monday night. As energy rotates into the upper trough Saturday night, a closed low will eventually develop, reaching the Outer Banks by Monday, then perhaps drifting offshore by Monday night. With the subtlety in disturbances within this pattern, timing and placing the highest rain chances will be difficult. Have favored north/west Saturday night where greatest height falls and moisture will be. On Sunday, have brought a period of likely POPs across the area as trough axis/upper low moves overhead. Can`t rule out some thunder, although looks like a very minimal chance...best in the far west. Have calculated a "storm total" through Sunday, which ranges from less than one inch NE of Baltimore, with 1.5 to 2 inches from DC south/west. Of course, locally higher is possible. Expect shower chances to diminish Sunday night, only to renew Monday, with highest chances in the east closer to the upper low. There`s a little better chance of a thunderstorm or two on Monday as it looks like there will be a better chance of seeing some breaks of sun. The drying trend should begin in earnest Monday night. Sunday`s temperatures will largely depend on where it rains the longest, and models differ strongly regarding this. Splitting the difference maintains continuity of lower to mid 60s. Right now Monday is looking warmer...in fact guidance is has widespread 70s. Given unsettled pattern, played conservatively closer to 70. Overnight lows remain fairly constant in the 50s.
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&& .LONG TERM /TUESDAY THROUGH FRIDAY/...
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Upper level low pressure will be departing eastward on Tuesday...with convergence and warming temperatures aloft. Temps will rise and clouds will break, but still a slight risk of a shower is showing up in guidance. A ridge axis will approach from the west Wednesday, continuing the confluence and the warming. This ridge axis will weaken Thursday as southwesterly flow develops aloft, but heights will continue to build resulting in more warming. Instabiilty may result in convective showers or thunderstorms developing over the mountains and possibly moving east into the metro. Another weak ridge axis will cross the area Friday with heights remaining high, though a trough will be approaching from the west. More showers and storms may form over the mountains and advect into the metro.
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&& .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
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Shield of rain advancing NE across the area. Restrictions are taking some time as atmosphere needs to saturate. MVFR is eventually being reached, although IFR has been harder to come by so far. However, lower cigs are poised to our SW, and actually expect a decreasing trend through the day. Moderate rain will taper off by midday or so, but expect some light rain to continue at times through the afternoon, especially the metros. The forecast for tonight through Sunday night is rather uncertain with upper level low pressure moving through the region. It will be unsettled to say the least with MVFR looking likely for much of the time with occasional showers. Don`t have confidence to time in any IFR. Monday should see improved conditions but a lingering chance of showers, especially afternoon. VFR Tuesday and Wednesday with high pressure regaining control.
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&& .MARINE...
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Expect SE to E winds to increase this morning as low pressure develops off the coast. The strongest winds may actually occur through midday until clouds and rain can sufficiently limit mixing. However, no changes to the SCA at this time. Wind should diminish tonight, but will have to monitor for northerly channeling. N to NW flow will continue through Monday around 5-10 kt. Light and variable by Monday night.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 8 AM this morning to midnight EDT tonight for ANZ530>533-538>541. Small Craft Advisory until midnight EDT tonight for ANZ534-537- 542-543. Small Craft Advisory from 8 AM this morning to 7 PM EDT this evening for ANZ535-536.
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&& $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM

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