Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 181829 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 229 PM EDT Tue Jul 18 2017 .SYNOPSIS...
-- Changed Discussion --
An upper level trough will affect the area through the rest of today. High pressure will then build in for Wednesday and Thursday, followed by the potential for additional disturbances Friday and into the weekend. Temperatures will be on the rise through the week with hot and humid conditions expected.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Upper level trough that moved overhead yesterday will remain in place through the remainder of today, providing additional chances for scattered afternoon showers/thunderstorms. Not much change in the air mass from yesterday, so nature of development likely to be similar to yesterday, developing off of subtle low level boundaries and terrain circulations. 12z IAD sounding and SPC mesoanalysis does depict mid levels a bit warmer with mid level lapse rates not quite as steep as yesterday, generally around 6.5 C/km. That being said, RNK sounding this morning did still report in excess of 7 C/km. This combined with surface temperatures near or slightly above 90F and dew points near 70F have allowed 2000 J/kg or so of MLCAPE to develop. Thus another pulse thunderstorm day with potential for isolated severe exists. SPC has placed part of the area in a Marginal Risk today. In addition, once again, there is very little shear/steering flow, so heavy rain and isolated flooding is again a possibility. Convective activity will wane during the mid to late evening hours as daytime instability lessens. Similar to last night, there is potential for patchy fog, especially in areas that see rainfall today. Lows tonight in the 60s/70s.
-- End Changed Discussion --
&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
-- Changed Discussion --
Upper trough will continue to slowly pull away on Wednesday as ridging builds in from the west. Thus, while a few isolated showers/storms are possible, most places should remain dry. Temperatures will be on the rise, with highs in the low to mid 90s. This combined with dew points near 70F will lead to heat indices around 100F or so east of the Blue Ridge and in the mid/upper 90s west. Quiet weather expected Wednesday night, but warm and muggy with lows in the 70s. Partly to mostly sunny skies expected for Thursday, with temperatures topping out again in the low-mid 90s, but will likely be even a couple degrees warmer than Wednesday. Some model guidance depicting a light westerly flow which may bring dew points down some, but not a given at this time. Heat indices again near or perhaps above 100F in some locations. Warm and muggy conditions continue Thursday night, with lows 70s to near 80F in the urban centers.
-- End Changed Discussion --
&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
A front should sag across the region Friday and Friday night bringing a chance for showers and thunderstorms. High temperatures will be in the middle 90s across much of the region. As the front stalls across the central portions of our region Saturday and Saturday night, the threat for additional showers and thunderstorms are expected. Highs will once again reach the middle 90s in many areas. The front will move north of the region as a warm front Sunday into Sunday night. Showers and thunderstorms will develop along and north of the front. Most of the activity should be focused across Maryland and northern Virginia. Highs will reach the middle to upper 90s with high heat indices during the afternoon. The heat lingers Monday and so do the chances of showers and thunderstorms as a cold front approaches from the west later in the day. The cold front could push through the area Monday night, bringing one final round of heavy showers and thunderstorms. High temperatures will be in the lower to middle 90s. On Tuesday, a broad ridge of high pressure will build in from the west. The heat and humidity will be elevated with highs in the middle 80s.
-- End Changed Discussion --
&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/...
-- Changed Discussion --
VFR overall through the next few days. Main weather concern this afternoon and evening will be scattered showers and thunderstorms. Overnight tonight, similar to last night, there will likely be some patchy fog around, although coverage/density is uncertain at this time. Winds mostly 10 knots or less. There is a possibility for a few isolated thunderstorms Wednesday as well, but risk lower. Mostly VFR, although with potential for showers and a few thunderstorms Friday through Sunday. Heavy downpours and gusty thunderstorms are possible in any storms. Winds generally less than 10 knots.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Mostly sub-SCA over the next few days, with main concern being gusty winds from any thunderstorm which develops near or over the waters during this afternoon and evening. There is a possibility for a few isolated thunderstorms Wednesday as well, but risk lower. No marine hazards expected Friday through Sunday. Winds west- northwest around 10 knots Friday and Friday night. Winds becoming southwest 5 to 10 knots Saturday into Sunday.
-- End Changed Discussion --
&& .TIDES/COASTAL FLOODING... South flow will maintain elevated water levels through Wednesday night. Water levels are expected to remain just below minor coastal flood thresholds during the afternoon/evening preferred high tide. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...MM NEAR TERM...MM SHORT TERM...MM LONG TERM...KLW AVIATION...MM/KLW MARINE...MM/KLW TIDES/COASTAL FLOODING...MM/BAJ

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.