Area Forecast Discussion
Issued by NWS Sterling, VA

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899 FXUS61 KLWX 220057 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 857 PM EDT Fri Apr 21 2017 .SYNOPSIS... A cold front push southeast across the region tonight. The front will stall to the south Saturday and low pressure will develop along the boundary...impacting our area for the weekend through early next week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... The cold front appears to be near the Blue Ridge at this hour. The last of the severe weather consolidating over the Northern Neck and Virginia portion of the Chesapeake Bay. The remainder of the evening and the first part of the overnight should be dry. Frontal passage will be marked mainly by a wind shift. However, upon widening the focus, additional showers and thunderstorms can be found across eastern Kentucky and western Virginia. These showers/storms will be riding along the frontal boundary. Although instability will be gone, the precipitation likely will arrive late in the overnight/pre-dawn. Am maintaining chance PoPs (for showers) to account for this activity...especially southwest of the Potomac River. Temperatures will be mild this evening, but will be dropping into the 50s overnight. Will be touching up low temperature forecast shortly. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... The front stalls in the Carolinas Saturday as a slow moving wave of low pressure moves eastward along it. High pressure nosing in from the north may produce a dry period Saturday especially in Maryland, but chance of rain extends through the day, with greater risk as one heads further south and west. By Saturday night, rain looks likely as the low approaches and some decent FGEN develops over our region. This FGEN and the low itself may shift southward on Sunday as a shortwave passes to our north, displacing it, but the low is then expected to start pushing back north Sunday night, ending any gap in the rain by the end of the night. Given continuing uncertainty among guidance as far as timing and amounts of rainfall, have not added any flood mention to HWO yet, but certainly if some areas get the rain modeled, we could have one. The question is whether several inches of rain can indeed fall over any one area over the next few days. With cool Canadian high pressure wedging southward on the east side of the mountains and the air mass becoming saturated with the nearby front and approaching low, the weekend will be quite cloudy and cool, with temperatures below normal. Sunday looks like the coolest day, with highs likely to get stuck in the 50s. Temperatures Saturday will be rainfall-dependent, but may also be stuck in the 50s. Lows at night will probably nudge into the 40s. && .LONG TERM /MONDAY THROUGH FRIDAY/... Low pressure along the southeast coast will remain cutoff from the jet stream and slowly drift northeastward early next week, keeping the area in a cool and dreary pattern. The wind and subsequently the temperatures do an about-face around midweek with significantly warmer temperatures (possibly near 90) by next weekend. One interruption in the warming trend will be a front boundary that may clip the region Thursday. Other than that, temperatures will start the week at levels more typical for early March, and end the week at levels more typical for late June. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... All thunderstorms have pushed south/east of the terminals. We are in a VFR period at this time, and it should last into Saturday morning. Rain will spread back into the area as we head through the day with lowering cigs and vis returning. Tempered the restriction forecast for Saturday. Focused on the higher confidence MVFR. IFR still possible, with increasing likelihood as we progress through the weekend. In fact, its looking like a significant period of IFR will be possible Saturday night into Sunday night with northeast winds. Sub-VFR likely early next week with low clouds/northeasterly onshore flow around 10 knots. && .MARINE... Thunderstorm risk continues across the lower Tidal Potomac and mid Chesapeake Bay, but this threat will be waning as the storms continue to travel east ahead of a cold front. The front should cross the waters late evening for the upper waters, and just after midnight for the mid Bay/lower Potomac. Rain will spread back across the waters Saturday. Believe this will provide a stabilizing layer, and thus am forecasting winds under the Small Craft Advisory threshold for Saturday and Saturday evening. Better risk of SCA Sunday as low pressure to the southwest starts to intensify, increasing the gradient. Northeasterly flow between high pressure to the north and low pressure to the south may result in Small Craft Advisory level gusts across the waters early next week. && .TIDES/COASTAL FLOODING... A persistent onshore flow will develop behind a cold front Saturday through early next week. Elevated water levels are expected during this time...and minor flooding cannot be ruled out near times of high tide...especially Sunday into Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...HTS SHORT TERM...RCM LONG TERM...DFH AVIATION...HTS/RCM/DFH MARINE...HTS/RCM/DFH TIDES/COASTAL FLOODING...BJL

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