Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
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
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 221357 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 957 AM EDT Fri Jul 22 2016 .SYNOPSIS... High pressure has moved off the coast. A system will pass north of the region today, followed by a weak front moving in on Saturday. High pressure will then be in control of the area`s weather Sunday before another front enters the area Monday into Tuesday. && .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Large upper ridge remains centered across the Central Plains this morning, with the region sitting in north/northwest flow aloft on the northeastern periphery of the ridge. Storms have developed on the downwind side of this ridge, with the main forecast problem for today being the ongoing MCS in NW PA. The definite outcome of this system is the extensive cirrus shield overspreading the area. Although filtered sunshine is making it through, the clouds could knock a degree or two off today`s highs, especially NW. Still would expect low to mid 90s for most areas with heat indices up to 100. The second question is precip chances. The eastern side of the MCS is stratifying as expected as it moves into an unfavorable environment. Can`t rule out a dying shower making it to northern MD around noon, so have sped up the timing of POPs. Meanwhile storms have been redeveloping on its back side in response to strong theta-e advection. This will be the section to monitor. In addition, an upper level disturbance over southern Canada will race eastward and into the northeastern US at the same time a weak frontal boundary pushes southward into the eastern Great Lakes and Northeast to provide additional forcing. Ahead of these features, the low level moisture difference can be noted between the IAD and PIT. Modifying the IAD sounding for this moisture advection and warming BL, MLCAPEs could exceed 1500 J/kg this afternoon. Am unsure of extent of the suppressive effects of the upstream clouds and precipitation, but theta-e advection may be enough for additional showers and storms, especially northwestern parts of the area. Latest RAP/HRRR are hinting at this although run-to-run variability has been high due to the MCS. Have already made one forecast update to bump POPs in the NW, but may need another. Shear profiles are not impressive, with around 20 knots of 0-6KM shear, but any storm during the day has the potential to be pulse severe and any ongoing cold-pool driven convection later this evening has potential to become strong to locally severe. Any convective activity will wane after midnight. Lows tonight from the upper 60s to upper 70s.
-- End Changed Discussion --
&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Remnant frontal boundary will then push southward into the Mid- Atlantic on Saturday. By this time, will be primarily a moisture/dew point boundary. Current indications are that the front will move to about the DC metro by midday Saturday, separating mid 60s dew points to the north across PA/northern MD from low 70s DC southward. With MLCAPE values progged to reach 1500-2000+ J/KG and with 25-30 knots of 0-6KM shear, any convective activity that can fire Saturday afternoon along this boundary has the potential to become strong to locally severe. In addition, highs will range from about 90-97F, and when combined with increasing humidity, especially on southern side of boundary, heat indices are expected to reach from 100-105F. Thus a Heat Advisory may be needed for Saturday. Convection will once again wane Saturday night with lows in the 70s. Boundary will wash out for Sunday, but dew points not expected to recover past the mid 60s. Thus, should be looking at a mostly sunny and mainly dry day, although the region will still be entrenched in NW flow aloft, so will still need to monitor for any MCS activity upstream. Highs will reach 90-97F again, but with lower dewpoints, heat indices will be a little lower than Saturday, generally maxing out about 100F. Temperatures still warm Sunday night again with lows in the 70s. && .LONG TERM /MONDAY THROUGH THURSDAY/... Monday may end up being both the hottest and the stormiest day of the stretch. Low pressure tracking across southern Canada will drop a weak frontal boundary toward the area. Higher dewpoints will be drawn north in advance of the front, while 850 mb temps remain in the 20-22C range. This temperature/dewpoint combo may yield heat index values approaching 105. The inherent instability, lower heights, and focusing mechanism would be the necessary ingredients for thunderstorm development. It remains to be seen how it all comes together. The synoptic pattern doesn`t look much different for the middle of next week. The westerlies will remain in retreat up in Canada, permitting broad ridging to set up shop across the continental US. The core of this ridge will remain west of the Appalachians, though, meaning the local area won`t be seeing the worst of the heat. Daytime temperatures should still be in the 90s. However, drier air may attempt to filter in; that will be dictated by where the front stalls out. At this point, its not a forgone conclusion that the front will clear the area, so precip chances will linger in the extended...with reduced confidence. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
Primarily VFR through Sunday. Will have to monitor thunderstorms to the NW and what develops this afternoon, but confidence not high enough to put a mention in the TAFs now. MRB would be best candidate for storms, but can`t rule out DC/Baltimore. Isolated to scattered showers/thunderstorms again Saturday. Some patchy light fog also possible each morning, but again coverage not expected to be widespread. Southwest winds 5-10 knots today turn west-northwesterly Saturday before becoming light and variable Sunday. Scattered thunderstorm chances Monday, especially afternoon and evening. This looks to be the most likely day to see coverage, but specific impacts still questionable. Front will either be over or south of the terminals by Tuesday. Another round of storms possible, but confidence lower than Monday due to positional uncertainties.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Generally sub-SCA S/SW winds through this afternoon. The isolated 20 kt gusts from early this morning should be subsiding. Later this evening, will see an increase in speeds across the central Chesapeake and lower tidal Potomac again, and a Small Craft Advisory has been issued. This may need to be expanded by a few zones, and the higher winds could start by mid-afternoon. These winds will dissipate Saturday morning with sub-SCA winds expected Saturday into Sunday. Gradient winds should increase Monday ahead of front. It is unclear how significant that will be. Of greater...but not high...certainty will be the development of thunderstorms, which may contain local strong wind gusts. That front will either be over or south of the mid Bay and lower Potomac by Tuesday.
-- End Changed Discussion --
&& .CLIMATE... Record highs and warm lows for the upcoming weekend... Today... DCA...103 in 1926...83 in 2011 BWI...106 in 2011...81 in 2011 IAD...105 in 2011...76 in 2011 Saturday... DCA...102 in 2011...84 in 2011 BWI...102 in 2011...79 in 1978 IAD... 99 in 2011...76 in 2011 Sunday... DCA...101 in 2010...84 in 2011 BWI...101 in 2010...82 in 2010 IAD... 99 in 2010...78 in 2010 Monday... DCA...100 in 1930...79 in 1965 BWI...100 in 2010...77 in 1887 IAD... 98 in 2010...76 in 1965 && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EDT Saturday for ANZ534-537-543. && $$ SYNOPSIS...MM NEAR TERM...ADS/MM SHORT TERM...MM LONG TERM...HTS AVIATION...ADS/MM/HTS MARINE...ADS/MM/HTS CLIMATE...HTS

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