Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 240112 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 912 PM EDT Fri Jun 23 2017 .SYNOPSIS... Tropical air will envelop the area today. A cold front will cross the area late tonight into Saturday. High pressure will return Sunday and persist through early next week. && .NEAR TERM /THROUGH SATURDAY/... Besides a few showers across the region late this afternoon and early this evening...the LWX CWA has been quiet especially compared to our neighbors to the west and north. This will change tonight as remnants of TD Cindy and a cold front will move into the Mid- Atlantic region. Showers will spread across the region tonight with embedded heavy showers and gusty winds. The atmosphere is moist with an observed PWAT from KLWX of 1.9 at 00z. Sfc dewpts in the 70s will give to moderate instability across the region tonight. Shear is also moderate with near 50kts of 0-6km bulk shear. Thunderstorms are possible as the cold front crosses the region overnight. Hi-res guidance depicts some line segments that may produce stronger winds and severe thunderstorm warnings can not be ruled out overnight. Seems like the best chance will be across the northern half of the outlook area. Rainfall amounts of 0.75- 1 in are expected across the northern half and will taper off to around 0.25 in across the Central Foothills/southern MD overnight with higher amounts in heavier bands/thunderstorms. Elsewhere...a strong LLJ will be on top of the region tonight and widespread showers will likely bring down gusty winds. Gusts 35-45 mph can not be ruled out across the region into early Saturday morning. The cold front should cross the region by 8AM Saturday morning and drying will occur behind it. Prev discussion... Latest GFS/NAM prog timing to be so quick that all precip will be east of the forecast area by the start of the period. Am a little bit caution of that solution, and have lingered some precip into the Saturday morning hours. Then we`ll need to assess how quickly front leaves area; there are some suggestions in may get caught up across southern Maryland or the Virginia tidewater. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... High pressure will be building across the area this weekend, with no other weather hazards. Perhaps there will be a reinforcing boundary Sunday, but moisture looks scant for even clouds. Accepted a MOS blend for temps. Sunday will be the cooler day, with lower dewpoints also advecting in Saturday. && .LONG TERM /MONDAY THROUGH FRIDAY/... Surface high pressure sets to the west on Monday as a slow moving upper level trough slides east into Tuesday with surface westerly flow. Below normal temperatures, with showers and thunderstorms possible during this period. Conditions should become drier as surface high settles overhead Tuesday night. The high will move offshore on Wednesday and continue moving west into Thursday as flow becomes more southerly. Temperatures will be on the rise as dry conditions continue into Friday, when guidance suggest a boundary will bring showers and thunderstorms over our area. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... A cold front, infused with tropical moisture, will cross the terminals tonight, most likely after midnight but before dawn. At this point, kept restrictions at MVFR. There is a decent potential of local/brief IFR, probably due more to reduced vsbys in heavy rain. There may also be localized wind gusts. Where these gusts aren`t realized, there is a 50-70 kt wind max several thousand feet off the deck, so low-level wind shear will be a concern. The front will be east of the terminals by Saturday morning. VFR conditions will prevail for the weekend. Mostly dry/VFR conditions expected Monday into Wednesday as surface high pressure settles in. Some scattered showers and thunderstorms possible Monday afternoon into Tuesday as upper air disturbance moves through, which could cause periods of sub- VFR conditions. && .MARINE... Update...A Gale Warning is in effect for all waters late tonight into Saturday morning. Showers and thunderstorms will be capable of producing gusty winds on the waters during this time. Southwest winds 10-15 kt with some gusts to 20 kt. Those winds will be increasing ahead of a cold front tonight. Small Craft Advisories remain in effect. There will be a 50+ kt low level jet several thousand feet off the waters overnight. Do not believe this will mix down in the gradient flow, but local punches may near heavier showers. Marine Warnings may be required tonight. Northwest flow Saturday will contain better mixing. The gradient will decease Saturday night. Have not extended the Advisory further at this time. Mostly dry conditions expected Monday into Wednesday as surface high pressure settles in. Some scattered showers and thunderstorms possible Monday afternoon into Tuesday as upper air disturbance moves through. Winds gusts will be below the small craft advisory criteria. && .HYDROLOGY... As mentioned above, precip waters will be exceeding 2 inches, so heavy rain expected in storms tonight. However, only 0.1 to 0.3 inches fell this morning, so soils were not saturated. Further, storms look to be progressive. So, while heavy rain expected, believe that the soil will be able to handle it overall, based on flash flood guidance. Thus, will not post any Watches at this time. Local minor flooding is possible, especially in the Potomac Highlands. && .TIDES/COASTAL FLOODING... A coastal flood advisory is in effect for Anne Arundel, Baltimore and Harford counties late tonight into Saturday morning. Anomalies around one foot are expected during this time. Beyond that, northwest winds should lead to levels returning close to normal. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Coastal Flood Advisory from 2 AM to 2 PM EDT Saturday for MDZ011-014-508. VA...None. WV...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ530>543. Small Craft Advisory from 8 AM to 6 PM EDT Saturday for ANZ530>543. Gale Warning from midnight tonight to 8 AM EDT Saturday for ANZ530>543. && $$ SYNOPSIS...RCM are expected during this time. Beyond that, northwest winds sho NEAR TERM...HSK/HTS SHORT TERM...ADS/HTS LONG TERM...IMR AVIATION...HSK/IMR/HTS MARINE...HSK/IMR/HTS HYDROLOGY...HSK TIDES/COASTAL FLOODING...HSK is the U.S. government's official web portal to all federal, state and local government web resources and services.