Area Forecast Discussion
Issued by NWS Wakefield, VA

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250 FXUS61 KAKQ 292004 AFDAKQ Area Forecast Discussion National Weather Service Wakefield VA 404 PM EDT Sat Apr 29 2017 .SYNOPSIS...
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Bermuda high pressure prevails off the Southeast Coast through the Monday. A backdoor cold front will drop south across the northern Delmarva peninsula tonight, then lifts back north as a warm front Sunday. A cold front pushes across the region Monday night with high pressure returning Tuesday.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Current wv imagery depicts a strong mid/upper ridge centered over the sub-tropical wrn Atlantic, with an active stream of convection on the nrn periphery of the ridge from the Central Plains through the Ohio Valley. At the surface, high pressure is co- located with the ridge aloft offshore, with a stationary front from the Midwest to the Northeast. Stratus from this morning along with a warm nose ~850mb has resulted in a rather strong cap this aftn, which has hampered cu development despite a very unstable airmass. Temperatures as of 19z average from the mid 80s to around 90, with unusually high dewpoints (that are in record territory for April) generally in the low 70s across the area. A shortwave trough is expected to track across PA/NJ late this aftn through the evening. This is expected to trigger iso/sct showers/tstms as depicted in the HRRR over NE MD and the nrn Delmarva mainly after 22z. Effective shear is progged to be 35-40kt in this region, which could result in some locally strong tstms in vicinity of an MLCAPE gradient over the Delmarva. MLCINH remains rather high in this area, so any development of tstms over the Lower MD Ern Shore will likely be conditional dependent on outflow from the N. The shortwave trough will drag the stationary boundary swd as a backdoor cold front late tonight. Mid-level instability persists overnight with the potential for showers/tstms in vicinity of the backdoor boundary. PoPs remain low ranging from 20-30%. Very mild for late April with lows in the upper 60s to low 70s.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/...
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The front lifts back to the N as a warm front Sunday as the upper ridge builds ahead of a trough digging across the Central Plains. 850mb temperatures actually peak tonight and then drop back to 14-16C by Sunday. Therefore, highs will be a few degrees lower mid/upper 80s, but still well above normal. One exception will be the Lower MD Ern Shore in vicinity of the boundary where highs should be 5-10F lower than today. There is a lack of a trigger for convection, so forecast PoPs area below 15%. Continued mild Sunday night with lows in the mid/upper 60s. A cold front approaches from the W Monday as the Central Plains trough lifts into the Great Lakes. The front is expected to slow as it pushes across the Appalachians with strong surface heating to the lee of the mountains. Therefore, Pops should be slow to increase through the aftn, and mainly over the Piedmont initially. The ridge will hold strong along the coast with the ern half of the area remaining dry through much of the day Monday. 500mb flow ahead of the trough reaches 70-80kt, which yields 0-6km bulk shear ~50kt. However, mid-level lapse rates are rather poor, which is limiting 0- 1km MLCAPE values of 500-600 J/kg once the strongest synoptic forcing arrives locally (mainly 00-06z). The SPC Day 3 marginal risk remains immediately W of the local area given some question as to how unstable the thermodynamic profile will become. PW values ~1.5in combined with strong forcing could result is some locally moderate to heavy rain. The cold front crosses the region Monday night and pushes offshore by 12z Tuesday. PoPs taper off from NW-SE from 06- 12z as drier air arrives from the NW. Highs Monday will generally be 80-85F with lows Monday night ranging from the upper 50s W to the low/mid 60s along the coast. Breezy Monday with a SW wind ~15 mph with gusts up to 25 mph. A trough aloft builds over the Ern Conus Tuesday as surface high pressure builds across the Southeast States. Temperatures will be lower, but still on the warm-side of normal with highs ranging from the mid 70s to near 80 under a mostly sunny sky. A wsw wind of 10-15 mph is expected with gusts up to 20-25 mph possible.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
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A secondary frontal boundary is expected to cross the area Tuesday night and should bring cooler air to the region. Isolated showers could occur north of the Delmarva, however westerly winds aloft should provide enough of a downsloping effect to keep the forecast dry into Wednesday. Lows Tuesday night in the 50s (lower 60s coastal SE VA/NE NC). Highs Wednesday in the mid-upper 70s (upper 60s to lower 70s beaches) under mostly sunny skies and sfc high pressure with light SW-W winds. Sfc high slides offshore Wednesday night with lows in the mid-upper 50s NW to lower 60s SE. A warm front is expected to lift north across the area on Thursday as low pressure develops along it Thursday night into Friday. Increased clouds and precipitation chances anticipated during this timeframe. SE winds become breezy at the coast on Thu and become more S Thu night into Fri. Overall, temperatures will be cooling with highs Thu/Fri in the upper 60s NW to low-mid 70s SE. Lows Thu night in the mid-upper 50s NW to lower 60s SE.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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A stationary front will stay north of the area through the forecast period. This should allow for VFR conditions through tonight. One exception to this may be at SBY this evening as a weak disturbance moves along the front which may help bring scattered showers and storms to the eastern shore, allowing conditions to briefly drop to sub VFR conditions. In addition, the guidance suggests some marine air will move into the eastern shore overnight into Sunday morning as the front briefly moves south of SBY, potentially allowing for MVFR conditions. Outlook...Mainly dry weather expected through the remainder of the weekend, although some convection is possible across Delaware tonight along a backdoor cold front. Next frontal boundary late Monday into Tuesday with possibility of showers and thunderstorms.
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&& .MARINE...
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Generally S-SW winds aob 15kt through Sunday night. Seas average 2-4ft tonight; 2-3ft Sun/Sun night. Waves average 1-2ft. Low-end SCA conditions should begin for the Bay around sunrise Monday morning when normal diurnal winds increase, however speeds will continue to increase into the aftn as the pressure gradient tightens substantially ahead of a strong cold front which is approaching the region. All waters should be within low-end SCA conditions by mid to late Monday morning (S-SW 15-20kt/seas 3-5ft/waves 3-4ft)... then solid SCA conditions by Monday aftn (15-25kt with gusts to around 30kt Bay, Sound, ocean/seas average 5-7ft/ waves 4ft). Strong SCA winds persist ahead of/along the cold frontal passage and then taper off rather quickly behind it as winds become more westerly 15-20kt (gusts around 25kt ocean). Seas may peak at 8ft in nrn coastal waters out near 20NM Monday night. SCA winds should end either by sunrise or by mid morning on Tuesday. Wind speeds become more SW again on Tue and remain breezy 10-15kt due to weaker cold air advection occurring. Seas will be slower to subside, therefore SCA flags should persist for the coastal waters through early Tue aftn srn waters and as late as midnight Tuesday night nrn waters. Fairly benign conditions anticipated for Wed/Wed night with high pressure over the area. Variable aob 10kt Wed/SE aob 15kt Wed night. A warm front is expected to lift north across the waters Thursday as low pressure develops along it Thursday night into Friday. SE winds persist on Thu and become more S Thu night into Fri. Wind speeds could increase to low-end SCA (15-20kt) and seas could build to 5ft due to a tightening pressure gradient. Will need to monitor the evolution of this potential system.
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&& .HYDROLOGY... Keeping flood advisory in Mecklenburg county going today, with VDOT continuing to report numerous roads closed in the Kerr Dam area, creating ongoing navigation concerns. && .CLIMATE... It still appears likely that Richmond and Norfolk will each end the month with the warmest April on record. Very warm temperatures expected today and an unseasonably warm April to date should combine to push the April 2017 average temperature above that which occurred in 1994. As noted below, both of the previous records on the books were established in 1994. This month`s temperatures look to end up around one degree above those values. Average temperatures / Record Average Temperature Through 4/28/17: APR 2017 Avg temp Record Location to date Avg temp Year -------- -------- ------ ---- Richmond 63.1 63.2 1994 Norfolk 65.3 64.7 1994 ********************************************* Record high temps for today 4/29: RIC...93 in 1974 ORF...92 IN 1974 SBY...89 IN 1974 ECG...90 IN 1974 Record high min temps for today 4/29: RIC...67 in 1956 ORF...66 in 1981 SBY...65 in 1974 ECG...67 in 1981 && .AKQ WATCHES/WARNINGS/ADVISORIES... MD...None. NC...None. VA...None. MARINE...None. && $$ SYNOPSIS...AJZ/MPR NEAR TERM...AJZ SHORT TERM...AJZ/MPR LONG TERM...BMD AVIATION...MPR/MRD MARINE...BMD HYDROLOGY...AKQ CLIMATE...AKQ

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