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 Wed Mar 21 2018 .SYNOPSIS... Coastal low pressure will emerge off the Mid-Atlantic coast this morning and move northeastward in to the western Atlantic through early Thursday. High pressure will build in from the west through the end of the work week and first half of the weekend. Developing low pressure over the mid-Mississippi Valley Friday night will progress eastward, passing south of the area early Sunday as a strong area of high pressure develops to our north. This high pressure will ridge southward into the area briefly early next week. && .NEAR TERM /THROUGH TONIGHT/... Precipitation early this morning has mostly been observed north of I- 70 in Maryland and across the south southwestern portion of the CWA across Central VA. Areas to our south that have seen precipitation have observed a mix of snow/sleet/freezing rain, with Charlottesville finally changing over to all snow shortly before 2am this morning. With temperatures generally in the upper 20s to near freezing across much of the area, as precipitation fills in across the area that there will be a snow/sleet mix at the onset, especially in and around the metros and south and east of the I-95 corridor. This is due to a warm nose between 4-6kft, and eventually the column will dynamically cool as low pressure off the coast develops and low pressure over WV help increase precipitation area wide. This will allow snow to become the dominate p-type for much of the area by mid-morning. Low pressure will strengthen off the coast today, increasing snow across the area. Hi-res guidance shows the potential for snow banding to develop across northern and central MD late this morning and early afternoon, and this is where we have the highest accumulation amounts. As the low pulls away from the area late this afternoon and evening, expect snow to come to an end from west to east, with much of the area dry by midnight. Temperatures today will not budge much, holding in the lower 30s. Because of the additional mix of precipitation expected early this morning, and generally lower QPF values being depicted by the latest model guidance, we have skimmed back snow totals a bit for much of the area. Winter Storm Warning headlines continue for the entire area with this mornings package. Get the latest snow forecast on our winter weather page at && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Gusty northwest winds are expected overnight and into the day on Thursday. Lows tonight will hold in the 20s with winds remaining elevated. High pressure will start to build in from the west on Thursday and continue through Friday night, bringing moderating temperatures and dry conditions. && .LONG TERM /SATURDAY THROUGH TUESDAY/... High pressure over eastern Canada will be nosing into the area on Saturday. Latest guidance has low pressure system diving southeast from the Mid-Mississippi Valley, reaching the Carolina coastline by Sunday. The southwestern half of the CWA has the highest chance of getting precipitation, which given this setup and forecast temperatures, would most likely be snow. At this time range though, some uncertainty in the track and timing still exist. Will continue to highlight this threat in the HWO. The high will build southward and elongate for the beginning of the week. Monday and Tuesday will most likely end up dry, but with continued below normal temperatures. && .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/... Precipitation will fill in across the terminals this morning, with our eastern terminals see a snow/sleet mix at the onset, with all terminals transitioning to snow by mid-morning. Snow could be heavy at times, reducing visiblities to below 1SM. As a result, widespread IFR to LIFR conditions expected, and will continue into early Wednesday evening before precipitation moves off to the east. Gusty northwest winds prevail behind the system tonight and Thursday, with VFR conditions returning to the terminals and persisting through Friday. A storm system will pass south of the area late Saturday into early Sunday. Uncertainty is still high but latest guidance would suggest the highest chance of wintry precipitation is at CHO. && .MARINE... SCA conditions forecast for all waters thru tonight as coastal low pressure affects the area. SCA conditions will likely persist in to the day on Thursday before the pressure gradient relaxes late Thursday into Friday. High pressure builds to the north Saturday. Low pressure passes to the south Saturday night into Sunday, with NW winds becoming onshore. Winds are likely below SCA levels on Saturday but could come close Sunday depending on the low. && .TIDES/COASTAL FLOODING... Water levels are fairly steady, with over 1 foot anomaly in the mid Bay/lower Potomac to less than a half foot in the northern Bay. The only thing this lends certainty to is flooding remaining an issue at Straits Point for the next few cycles. Calvert (Solomons) and King George/Charles (Dahlgren), and perhaps DC SW Waterfront get close. How far up the Bay and Potomac the surge gets, given a stiff north wind, remains to be seen, and will have to be closely monitored. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Winter Storm Warning until 8 PM EDT this evening for DCZ001. MD...Winter Storm Warning until 8 PM EDT this evening for MDZ003>006-011-013-014-016-501>508. Winter Storm Warning until 8 PM EDT this evening for MDZ017- 018. Coastal Flood Advisory until 8 PM EDT this evening for MDZ017. VA...Winter Storm Warning until 8 PM EDT this evening for VAZ025>031-036>040-050>057-501>508. WV...Winter Storm Warning until 8 PM EDT this evening for WVZ050>053-055-501>506. MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ530>534- 537>543. Small Craft Advisory until 6 PM EDT this evening for ANZ535. Small Craft Advisory until midnight EDT tonight for ANZ536. && $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF LONG TERM...ADS AVIATION...ADS/BKF MARINE...ADS/BKF TIDES/COASTAL FLOODING...ADS is the U.S. government's official web portal to all federal, state and local government web resources and services.