Area Forecast Discussion
Issued by NWS Sterling, VA

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169 FXUS61 KLWX 271922 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 322 PM EDT Sat May 27 2017 .SYNOPSIS... Weak low pressure will shift east the area this evening. A trailing frontal boundary linger south of the area into Sunday morning. A weakening cold front will move east through the area Monday morning. Upper level low pressure will linger north of the Great Lakes Monday night through the remainder of the week with persistent weak high pressure over the Mid-Atlantic. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... As of 2pm, a weak upper level shortwave trough is over the northeastern CONUS with a 1011mb surface low stretching from OH to central VA. A weak ridge over the Midwest will continue to shunt this low east which will reach the coast late tonight. Areas south of this area of low pressure have had at least partly sunny skies today with temperatures in the low 80s. Persistent mid level clouds and patchy rain have kept temperatures in the upper 60s north of the low with 70s in between. GOES imagery depicts a transition from stable wave clouds to unstable cloud streets over central VA this afternoon. Greatest threat for thunderstorms is central VA and west through sunset. Bulk shear is decreasing as from a weak jet streak south of the shortwave shifting east. Expect SBCAPE values of 1500 j/kg or so in southern areas of the CWA through the rest of the afternoon. Isolated at best risk for severe thunderstorms 3-7pm down there with hail and damaging winds as main threats. Farther north, thunderstorm chances decrease as you move north into cooler/cloudier conditions. This activity will shift east with the pattern late this evening. Tonight, low pressure moves off with onshore flow filling in behind from high pressure centered over New England. This should allow low clouds to develop across the area with patchy fog west of I-95. Humid, but cool tonight with min temps near 60F. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/... Deep upper level low pressure approaches Lake Superior Sunday with a broad warm sector ahead. The cold/occluded front will push east across the Midwest Sunday. Low pressure looks to develop over IN Sunday afternoon and lift NE over the eastern Great Lakes Sunday night. This should keep most of the heavy rain potential north of the area. However, will stay the course with a heavy rain mention in the HWO for Sunday late afternoon/night as ingredients of PWATs of 1.5in and convergence from the wave approaching from the west. The front crosses the area Monday/Memorial Day morning with precip generally ending by midday. Increasing sunshine and 15C 850mb temps mixing down in westerly flow should allow max temps in the low to mid 80s. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Dry conditions expected Tuesday before a weak cold front moves through Tuesday night into early Wednesday. Some scattered showers and a few thunderstorm possible over our area but mainly dry conditions overall. Another cold front moves through Wednesday night into Thursday. This boundary could bring a chance of showers and thunderstorms Wednesday into Thursday, but ensemble spread leaning towards a drier solution. There is higher uncertainty into Friday and Saturday as models disagree, but again, the ensemble spread looks mostly dry. So overall during this period, we are looking into mostly dry conditions with periods of showers and maybe a thunderstorm. High temperatures will be in the 70s and 80s... some 60s at higher elevations. Low temperatures in the 50s and 60s, with some 40s. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Low pressure over the area shifts east through tonight. Thunderstorms generally over KCHO and south of the DC metros. Onshore flow in the wake of the low will allow low/IFR cigs by late tonight western DC metros. A cold front crosses the area Monday morning with thunderstorms mainly west of the DC metros Sunday night. Mostly dry/VFR conditions expected Tuesday into Thursday with sub-VFR conditions at times with boundaries moving through. Gusty winds expected on Wednesday afternoon/evening, up to 20 kt. && .MARINE... Sub-SCA southerly flow backs to onshore as low pressure shifts east over the area tonight. Flow shifts back to southerly but remains sub-SCA Sunday ahead of a weak cold front that crosses Monday morning. Mostly dry conditions expected Tuesday into Thursday with some showers and maybe a thunderstorm at times with boundaries moving through. Gusty winds expected on Wednesday afternoon/evening, up to 20 kt... a small craft advisory may be needed. && .TIDES/COASTAL FLOODING... Water levels hanging around a half-foot to one foot above astronomical normals this afternoon. Do not anticipate an appreciable change through evening. Fortunately, this is the lower of the two astronomical tides, so we believe that tides will come in under critical thresholds. The more sensitive sites likely to hit Action Stage, however. St George Island will come the closest. High tide at 4pm; latest indication suggest tide will peak an inch or two short. Onshore flow will begin to mark an increase late tonight into tomorrow. St George Island will be the most susceptible site (for minor flooding) early Sunday morning, although Solomons may come close. Widespread Action Stage at high tide elsewhere. Will issue the Advisory for St. Mary`s County, and hold off elsewhere. By early Monday morning, most sites should reach the minor threshold. That`s too far removed for an Advisory at this time. On the upper tidal Potomac, ETSS and HEC-RAS both suggest that high tide tonight will be just under minor threshold, with the subsequent tide cycles flirting with minor flood. Will not raise any headlines at this time. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Coastal Flood Advisory from 1 AM to 9 AM EDT Sunday for MDZ017. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BAJ NEAR TERM...BAJ SHORT TERM...BAJ LONG TERM...IMR AVIATION...BAJ/IMR MARINE...BAJ/IMR TIDES/COASTAL FLOODING...HTS

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