Area Forecast Discussion
Issued by NWS Sterling, VA

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414 FXUS61 KLWX 310108 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 908 PM EDT MON MAY 30 2016 .SYNOPSIS... A weak cold front will enter the region from the west tonight and stall near or just south of the area on Tuesday. Another cold front will move in from the north Tuesday night and Wednesday, then also stall out. A third cold front will push in from the west Thursday night and Friday. && .NEAR TERM /THROUGH TUESDAY/...
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CWA is under the influence of two systems this evening. First, subtropical moisture feed around offshore ridge/remnants of Bonnie has been slowly edging east, allowing persistent showers to exit southern MD. Second, a weak cold front is crossing the Appalachians, with scattered convection (albeit weakening lightning trends) ahead of it. Despite analyzed instability ahead of it (500 J/kg MLCAPE on 00Z IAD sounding), most of the convection has had a very difficult time pushing east of I-81...although some shower activity is now reaching the Blue Ridge. There is another cluster of heavy showers in SE PA which may clip NE MD before dissipating. RAP/HRRR have had very poor handle on this convection, so have largely based forecast on radar trends and the idea that any lingering showers will gradually diminish with nocturnal cooling (which the models do show). Will need to keep an eye on radar though with the weak boundary and lingering instability. The other issue of the night will be fog development, as dewpoints will be slow to fall, if at all, over most of the area...and winds will be nearly calm. Guidance paints a muddled picture, and persistent clouds may hinder denser fog from developing. Will maintain patchy wording for now. Don`t see a need to adjust lows, which are forecast in the 60s in much of the area. On Tuesday, the front will be even more diffuse as it settles south across the region. Drier and sunnier conditions will be more likely the farther north and west you go. However, a few showers and thunderstorms may still develop over southern parts of the area. Highs in the lower to mid 80s expected.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/... Moisture from Bonnie will linger not far to the south for the next few days...but forcing will be weak. A backdoor front will try to come southward Tuesday night and Wednesday which will try to suppress the moisture further south and cool our area a bit. Temperatures will be warmest Tuesday ahead of this front with some sun...then drop a few degrees each Wednesday and Thursday. Lingering moisture and some sun-fueled instability...not to mention potential forcing of the stalling boundary itself...will still try to get some spotty showers and thunderstorms going each of the next few days...but coverage does not look high. More pop-up than anything organized. Things get a little more interesting late Thursday as the next front approaches but instability still looks relatively meager. Highs will stay in the 80s with lows mostly in the 60s. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... A weak cold front, associated with surface low well to our north over Canada, will move through the area during the day Friday bringing a chance for showers and thunderstorms to much of the area. Model divergence increases by next weekend, as long term guidance differs with position/strength of mid and upper level trough digging into the NE. Will maintain low-end pops for the possibility of unsettled conditions next weekend into early next week, with best shower and thunderstorm chances Sunday into Monday as cold front moves through. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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Convection to the west is dissipating, with perhaps a sprinkle reaching MRB. Shower developing along Blue Ridge west of IAD will be monitored. Meanwhile, MVFR clouds have pushing into the I-95 corridor. Guidance hints these should break apart within a few hours of midnight. Patchy fog is a concern tonight. MRB and CHO most likely to go down to IFR but its possible at the other terminals as well. Have handled vsbys conservatively due to muddled guidance (although notably MOS hits vsbys harder) and potential lingering cloud cover. Spotty shower/storms again Tuesday and Wednesday afternoons but coverage looks low...with slightly higher chances near CHO. Winds generally less than 10 kt through the period. Cold front moves through the area late Thursday into the day Friday, with a scattered showers and thunderstorms expected across much of the area. Confidence in the forecast going into the weekend remains low as upper level trough digs into the Northeast.
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&& .MARINE...
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Southerly channeling has resulted in a few 15-20 kt gusts over the central part of the MD Bay, but these have been isolated and brief, with 10-15 kt on average. Weak front will turn winds to the north by morning. Will need to watch possible surge behind backdoor front Tuesday night into Wednesday. Storms may impact waters (more-so with southern extent) over each of the next several days but odds are not great. Thunderstorm chances will be the main concern over the waters Friday (and perhaps into next weekend).
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...RCM LONG TERM...MSE AVIATION...ADS/MSE/RCM MARINE...ADS/MSE/RCM

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