Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221520 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1020 AM EST Sun Jan 22 2017 .SYNOPSIS... Low pressure will impact the area through Monday before moving away Tuesday. A cold front will pass through the area Wednesday into Wednesday night and an upper-level trough may build overhead for the end of the week. && .NEAR TERM /THROUGH TONIGHT/...
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Low clouds, areas of drizzle and fog will persist this morning. A weak surface low is located near the mouth of the Chesapeake Bay and N-NE winds will keep low level moisture in place. Drizzle/fog will slowly diminish across the northern Mid-Atlantic through mid-day. A dense fog advisory is in effect for these locations until 18z today. Weak mixing should help break up dense fog by this time. Previous discussion... Cutoff low pressure in the southern stream of the jet will track through the Gulf Coast States later today before tracking northeast into the Tennessee Valley and Carolinas tonight. A strengthening gradient between this system and high pressure over New England will allow for an easterly flow to develop and strengthen later today. This will cause moisture to move in from the Atlantic Ocean while at the same time warm and moist air from the Gulf of Mexico will overrun the surface cooler air in place. The overrunning will allow for more clouds along with periods of rain. The best chance for rain will be this afternoon through tonight when overrunning will be deepest. Rainfall amounts should be light through this evening...since the bulk of the forcing from the low will remain to our south. However...moderate rain is expected to develop overnight as the low-level jet strengthens in response to the approaching low. The strengthening gradient will also cause windy conditions...especially along the ridge tops and also across north-central Maryland into the Washington and Baltimore Metropolitan areas as well as southern Maryland. A Wind Advisory may be needed for portions of these areas with frequent gusts around 35 to 45 mph expected and gusts around 50 mph possible.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... The low will slowly pass through our area Monday before tracking to the north and east Monday night. A soaking rain is expected to start Monday morning...but a dry slot will slowly move into the area and this will decrease rainfall rates from south to north later Monday morning into Monday afternoon. Gusty east to northeast winds are expected Monday morning...but winds will gradually diminish throughout the day as the low moves overhead and the gradient subsides. The strongest winds are expected through midday Monday across north-central Maryland into the Washington and Baltimore Metropolitan areas and southern Maryland...and perhaps across the Blue Ridge Mountains. A Wind Advisory may be needed for portions of these areas. Depending on the track of the low...the dry slot may be strong enough for some breaks of sun to develop. The best chance for this will be across southern Maryland into central Virginia. Therefore...max temps will range from the 30s along the ridge tops above 3kft...to the lower and middle 40s across northern Maryland...to the middle 50s across central Virginia. Confidence in temperature forecast is low due to the uncertainty of how strong the dry slot will be. One other note is that with the upper-level low overhead...this may cause enough dynamical cooling for rain to mix with snow across the ridge tops of the Allegheny and Potomac Highlands. Accumulating snow is possible across these areas...especially above 3kft. As the low slowly moves away from the area Monday night...wrap around showers are likely across the area but rainfall rates will be much lighter compared to late Sunday night and Monday morning. Snow showers are possible along the ridge tops of the Allegheny and Potomac Highlands mainly above 3kft. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Center of sfc low expected to be moving northeastward near/off the Jersey coast by Tuesday morning...with a few lingering light scattered wraparound showers mainly from DC and to the N/NE. Upslope snow/rain showers could continue into mid-afternoon before moisture becomes too shallow for quality ice crystal formation. While rain will shift out of the area...breezy W/NW winds up to 20 kts and relatively warm conditions will remain Tuesday with drying on W/NW flow. Heights rise over the area Tuesday into Wednesday...ahead of next system. Unseasonably warm Wednesday with highs in the U50s/L60s. Cold front crosses the region Wednesday into Thursday...and, with limited moisture east of the mountains, expect most areas to remain dry. However, persistent upslope component through a saturated layer should lead to prolonged upslope snow showers...of varying intensity...Thursday afternoon through perhaps much of the weekend...with some snow perhaps spilling east of the Allegheny Front at times. Main impact east of the Allegheny Front will be a drop in temperatures back closer to seasonable averages Friday into the weekend. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/...
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Low clouds and area of dense fog will continue through mid- morning along with occasional drizzle. IFR conditions are expected during this time. Cigs/vsbys will likely improve a bit late this morning and afternoon...but IFR conditions will persist. Periods of light rain will develop this afternoon through this evening. A steadier rain is expected overnight into Monday. IFR conditions are expected during this time. Gusty east to northeast winds will develop overnight and persist into Monday morning before slowly diminishing later Monday. This is in response to low pressure moving overhead. Gusts around 30 to 40 knots are possible. A strong low-level jet is expected during this time with east to northeast winds around 50-60 knots expected around 2kft. This does pose a threat for low-level wind shear...but will leave out of the forecast for now since gusty winds are expected at this surface. This may cause more turbulence instead of low-level wind shear. Low pressure will move away from the area Monday night. Showers are still likely...but cigs/vsbys may improve a bit more as the flow gradually turns to the northwest. Becoming mostly VFR by midday Tuesday as low pressure system moves away...with only a few lingering light showers remaining. Though, breezy conditions will continue with gusts 20-25 kts...before subsiding Tuesday night. VFR Wednesday with dry weather...as high pressure briefly nudges into the area. Weak front moves through mostly dry Wednesday into Thursday with VFR prevailing.
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&& .MARINE...
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Dense fog expected over the waters through early afternoon. Low pressure will approach the waters through this evening. Winds will gradually strengthen this afternoon through this evening. A Small Craft Advisory is in effect for the Bay and lower Tidal Potomac River this afternoon. However...it will be marginal. There is higher confidence in solid SCA conditions this evening as winds continue to strengthen. The pressure gradient will rapidly strengthen late tonight into early Monday morning before gradually dissipating from south to north later Monday. A Gale Warning is in effect for the waters from late tonight through midday Monday. East to northeast winds will gust around 35 to 40 knots during this time. A Small Craft Advisory will likely be needed for portions of the waters later Monday through Monday night as the low slowly moves away from the area. Gusty NW winds exceeding SCA criteria remain Tuesday behind departing low pressure system. Winds slacken late Tuesday as influence from low wanes. Mostly dry cold front crosses the waters late Wednesday into Thursday...with gusty winds possibly to SCA criteria behind it Thursday afternoon.
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&& .TIDES/COASTAL FLOODING... Persistent easterly flow will increase the risk for minor tidal flooding during high tide cycles beginning Monday afternoon and lasting into early parts of Tuesday morning (especially at Annapolis, Solomons, and Straits). Developing westerly flow should allow for some decrease in anamolies later Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Dense Fog Advisory until 1 PM EST this afternoon for MDZ003>006-011-014-502-503-505>508. VA...None. WV...Dense Fog Advisory until 1 PM EST this afternoon for WVZ051>053-502-504. MARINE...Small Craft Advisory from 6 PM this evening to 1 AM EST Monday for ANZ535-536. Gale Warning from 1 AM to 1 PM EST Monday for ANZ530>543. Small Craft Advisory until 1 AM EST Monday for ANZ530>534- 537>543.
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&& $$ SYNOPSIS...MSE NEAR TERM...BJL/HSK SHORT TERM...BJL LONG TERM...MSE AVIATION...BJL/MSE MARINE...BJL/MSE TIDES/COASTAL FLOODING...LWX

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