Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 211855 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 255 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 /THROUGH TONIGHT/... Latest surface analysis indicated a cold front is currently stretched from near State College PA southwest across far western MD and central WV into eastern KY. A stalled warm front extends southward from near State College towards Baltimore and Annapolis, then east across the Eastern Shore. Aloft, a strong shortwave is located well to the north over the Great Lakes with another over the western Plains. Weak ridging is present over the southeastern US. While its a pretty potent front and there is sufficient moisture and instability across our region, the relative lack of mid and upper level forcing seems to be limiting convection at the moment. This may change over the next few hours now that the cold front is entering the CWA since we will at least have some surface forcing entering the picture, though the upper levels still seem relatively weak forcing-wise. Have maintained chance to likely pops into this evening with the front expected to reach DC metro this evening, and clear the region by midnight. Given the instability and good shear present, there is potential for organized storms, but think that the lack of upper level forcing means the marginal risk from SPC should cover the risk. Will need to watch storm interaction with the stubborn warm front located over Maryland, as that could be a focal point for severe, but otherwise best instability is over Virginia. With the front sliding down, precip chance should end from NW to SE overnight, with temps sliding into the 40s NW and 50s elsewhere, and humidity dropping. && .SHORT TERM /SATURDAY 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 /18Z FRIDAY THROUGH WEDNESDAY/... Slowly improving conditions at BWI/MTN this afternoon as the stubborn warm front slowly pushes east and low clouds/fog break. Main concern through this evening is going to be scattered showers and thunderstorms which may briefly reduce cigs and vis while also bringing the potential for some strong wind gusts and hail. This threat should end towards 0Z as the cold front slides south and winds shift northerly. Should have a VFR period overnight into early Saturday, but then rain may spread back into the area as we head through the day with lowering cigs and vis returning. Looking like a significant period of IFR is 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... Main concern this afternoon/evening is potential for a gusty thunderstorm to cross the waters, necessitating a special marine warning. Storm risk should end later this evening behind cold front as winds shift northerly. SCA potential remains Saturday as high pressure nudges south, but odds look pretty low still so have not issued yet especially given relative stability. 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...RCM SHORT TERM...RCM LONG TERM...DFH AVIATION...RCM/DFH MARINE...RCM/DFH TIDES/COASTAL FLOODING...BJL

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