Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 241528 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1028 AM EST Fri Nov 24 2017 .SYNOPSIS... High pressure will remain over the mid-Atlantic through tonight. A cold front will cross the region Saturday and move east of the Chesapeake Bay Saturday night. High pressure moves back into the area Sunday and remains through the middle part of the upcoming work week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 10am this morning, temperatures are rising through the upper 30s to lower 40s across the area after an unseasonably cold & frosty morning. With high pressure in strong control, satellite imagery depicts clear skies, which corroborates well with the dearth of dry air evident in water vapor imagery and the 12z upper air sounding highlighting a hefty low level inversion. Precipitable water value of 0.38 inches was also sampled this morning, which falls slightly below average for this time of year. High pressure will yield light and variable winds the rest of this morning, turning more southerly this afternoon and remaining light. This high will shift south and east through tonight, allowing for a light return flow, helping return high/low temperatures to more normal values for late November. No threat of precipitation expected across the CWA through tonight. Current gridded forecast is on track with no changes needed at this time.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... On Saturday, a cold front will cross the CWA and exit east of the Chesapeake late Saturday evening. With deep westerlies, expecting the shower activity to be limited, as both the GFS and ECMWF shows decaying rainfall as the front moves east. So am forecasting scattered showers primarily west of the Blue Ridge, with sprinkles along and east of Interstate 95. The impact from this front will be felt in the form of a gust wind, which will start early Saturday evening, giving wind gusts over the land 20-30 mph Saturday night through mid-day on Sunday. In favored upslope regions, rain showers will turn to snow showers early Saturday evening, with a 6-9 hour period of snowfall producing around an inch of accumulation before tapering to flurries after midnight Saturday night. && .LONG TERM /MONDAY THROUGH THURSDAY/... Long term is a period of transition from the trough-dominated weather over the weekend as a transient ridge move in from the western US. For Monday, the northeastern trough will be pulling east into the Canadian maritimes, with the ridge axis over the central US and a deep trough over California. At the surface, this will translate into weakening northwesterly flow as a sprawling area of surface high pressure moves over the eastern US. Skies will have few clouds and temperatures will start to rebound. By Tuesday, the eastern trough will be out of the picture, with the ridge in the central US having flattened out, but with an axis which will be over our area. The surface high will settle just to our southeast and allow a broad southwesterly flow to bring warmer air northward, with surface temps rising a bit above normal. By this time, the northern and southern stream portions of the system out west will be separating, with the much faster northern stream system moving into the Great Lakes. By Wednesday, the northern stream portion rapidly pushes east into the Canadian maritimes, while the much slower moving southern stream portion will still be crossing the central US. For us, this means that the high pressure off to our southeast will likely remain in control with continued southwesterly flow, resulting in a yet still milder day - temps likely reaching the 60s. Finally, by Thursday, the southern stream system pushes east towards us from the central plains, bringing a drop in temps, greater cloud cover and an increased risk of showers. This is contingent however on a predictable speed to this system`s movement, and as it will likely spend some time as a cut-off upper low over the southwest before making its way towards our region, the timing and track is more uncertain than normal. Either way, bottom line is that temps will be moderating through the week, with an uncertain chance of rain towards the end. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... VFR all terminals next 24 hours. Light and variable winds become southerly this afternoon. Generally VFR Saturday and Sunday, with somewhat stronger and more gusty south-southwest winds Saturday shifting to northwest behind a cold front by Sunday. Chance of showers is minimal and any showers should result in only brief and limited reductions in cigs and vsby. VFR overall Monday and Tuesday under high pressure. && .MARINE... Light winds for another day before another solid Small Craft Advisory event beginning Saturday evening and continuing through Sunday. There is even the potential for Gales north of North Beach including Annapolis and Baltimore with the initial pressure surge and 35kts as low as 925 mb and strong cold air advection over the warmer waters of the Chesapeake. Most likely sub SCA winds for the bulk of waters on Monday as high pressure pushes east across the area. By Tuesday, southerly channeling on the back side of the high may result in small craft advisory conditions. && .TIDES/COASTAL FLOODING... Anomalies have crept back up over much of our waters, but appear to have leveled off somewhat. With light winds expected again today, do not expect major fluctuations, so kept BTA steady and used a blend of Estofs and ETSS. Do not expect any coastal flooding, but sensitive sites may touch action stage. Will need to monitor the anomalies in case they do start rising again. With a southwest wind expected on Saturday, will also need to watch potential for an additional increase in anomalies as water starts piling up in the northern bay. By Sunday, northwest flow should help lower anomalies again. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...Lee NEAR TERM...Lee/BKF SHORT TERM...Lee/BKF LONG TERM...RCM AVIATION...Lee/RCM MARINE...Lee/RCM TIDES/COASTAL FLOODING...RCM

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