textproduct: Wakefield

WHAT HAS CHANGED

Marginal Severe risk has been expanded south to the north-side of the Richmond metro and through the Northern Neck and southeast MD.

KEY MESSAGES

1) Chances of showers and thunderstorms continue through Sunday. In addition, heat and humidity will persist through this weekend and into early next week.

DISCUSSION

As of 1015 AM EDT Saturday...

KEY MESSAGE 1...Chances of showers and thunderstorms continue through Sunday. In addition, heat and humidity will persist through this weekend and into early next week.

GOES water vapor channels depict SW flow aloft this morning between and upper trough over the Great Lakes and a subtropical ridge offshore. There is a shortwave trough over the upper Ohio Valley embedded within the flow in advance of the upper trough, and this feature is triggering convection this morning from northern WV to SW PA and the MD panhandle. At the surface, high pressure is centered well offshore, with a lee-side trough to the east of the Blue Ridge. Warm and humid with temperatures rising through the lower to mid 80s and dewpoints in the mid 70s.

The aforementioned shortwave trough is expected to push E across the northern Mid-Atlantic this afternoon and evening. Effective bulk shear is progged to reach ~30kt by this aftn, with MLCAPE potentially reaching 2000-3000J/kg. Additional showers/tstms are expected to develop in vicinity of the Blue Ridge and the lee trough this aftn when the convective temp is reached. The main question is how far southward extent of tstms. Given sufficient shear and instability, initial cellular convection has the potential to organize into line segments. The main threat will be damaging wind gusts with 800-1000J/kg of DCAPE and steep low- level lapse rates, but some large hail is possible in any initial cellular convection. SPC has expanded the marginal risk area southward to basically I-64 from the Louisa/Fluvanna line to the north-side of the RIC metro, then eastward to about Wallops Island. A slight risk has been added immediately N of the local area.

Otherwise, a normal summer time pattern will be in place with scattered cumulus clouds in the afternoon and temperatures reaching into the low 90s. Dew points will once again struggle to mix out through the day and remain in the low to middle 70s. The mix of heat and humidity will allow Heat Indices to be in the upper 90s and low 100s, but will remain shy of the 105F Heat Advisory Criteria. For Sunday, the weather pattern will remain quite similar with the chance of showers and thunderstorms along the Lee Trough, high terrain, and Sea Breeze in the afternoon. In addition to the showers and thunderstorms, the heat and humidity will persist with temps ranging in the low to middle 90s and Heat Indices between the upper 90s and low 100s but again remaining shy of the 105F Heat Advisory criteria.

By early next week, ensembles continue to hint on a more zonal pattern across the area with the strongest flow remaining north of the area. While at the surface high pressure continues to thrive off the coast continuing to usher in heat and moisture. During the early to mid-week stretch the chances of showers and storms persist with the best chance now possibly being late Tuesday into early Wednesday morning as a stronger cold front tries to move into the area. Outside of the daily chances of showers and storms, temperatures are expected to rise above normal with temperatures possibly reaching into the lower 90s. With dew points struggling to mix through the day as the high is offshore they will remain the low to middle 70s again allowing Heat Indices to be in the low 100s. Will note there is a possibility that some places could reach Heat Advisory criteria Monday through Wednesday but confidence at this time remains low.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

As of 150 PM EDT Saturday...

High pressure was centered offshore as of 18z. Meanwhile, there was a trough approaching from the NW. SCT CU have rapidly developed early this aftn in advance of the trough, with isolated showers/tstms SW of the terminals. Showers/tstms are expected to continue to develop this aftn and linger into this evening. Confidence is low with respect to direct impacts to any given terminal, but the highest chc is at RIC and SBY where PROB30 groups have been added for tstms and locally stronger wind gusts. Any showers/tstms are expected to dissipate later this evening, with some lingering mid clouds overnight, which should gradually dissipate later tonight into early Sunday morning. A weak boundary settles into the region Sunday, and this along with the sea-breeze could trigger a few showers/tstms (15-25% chc) Sunday aftn. The wind will be SW 8-12kt this aftn with occasional gusts to ~20kt outside of tstms, before diminishing to SSW 10kt or less tonight, and then generally W/WSW 8-12kt Sunday aftn.

Outlook: Primarily VFR Sunday night through Thursday. Mainly dry Monday, with a 20-40% chc of aftn/evening showers/tstms Tuesday/Wednesday, and ~20% Thursday.

MARINE

As of 325 AM EDT Saturday...

Key Message:

- Sub-SCA marine conditions are expected to prevail through the weekend and into early next week.

Bermuda high pressure remains centered offshore, keeping S-SW flow across the local waters. Winds are currently 10-15 kt with gusts to 20 kt with 2-3 ft seas (~4 ft well offshore), and ~1-2 ft waves. The wind is expected to gradually shift to S/SSE late this aftn and evening due to diurnal seabreeze influences. The pressure gradient relaxes slightly Sunday into early next week with a S/SW wind diminishing to ~10kt or less, which will allow for more of a true sea- breeze with the wind shifting to SE near the coast during the aftn/early evening hours. Seas through the forecast period will be 2-3 ft for the coastal waters and 1-2 ft in the Ches. Bay and lower James River. A weakening cold front or at least a prefrontal trough eventually looks to push south, getting closer to the local area by midweek Winds may periodically shift to the W-NW and increase, but any elevated winds would probably be short-lived.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...None. NC...None. VA...None. MARINE...None.