textproduct: Wakefield

WHAT HAS CHANGED

Trended temps up slightly for Saturday, with heat indices of 105+ likely for most of the region.

KEY MESSAGES

1) Smoke from Canadian wildfires will remain aloft into this evening, but potentially becomes surface-based overnight through Friday across much of the region, leading to poor air quality, reduced visibilities, along with slightly cooler temperatures.

2) Hot and very humid Saturday as the smoke gradually dissipates, with Heat headlines probable. Thunderstorm chances increase later in the day, and likely continue/redevelop Sunday. Expect locally heavy rain, and the potential for strong to severe storms.

DISCUSSION

As of 330 PM EDT Thursday...

KEY MESSAGE 1...Smoke from Canadian wildfires will remain aloft into this evening, but potentially becomes surface-based overnight through Friday across much of the region, leading to poor air quality, reduced visibilities, along with slightly cooler temperatures.

Waves of smoke aloft from wildfires over west-central Ontario will continue to get funneled SE into the area through tonight. For the most part, the smoke is less dense today compared to yesterday, and as a result, temperatures have risen into the mid 90s across much of the area. With dew pts in the low-mid 70s, heat indices are above 100F for most, with some localized spots of 105+ across east central VA and the eastern shore where dew pts are in the mid-upper 70s. Decided not to issue a short fused Heat Advisory given that it is mid July and not particularly widespread. Have maintained haze wording in the gridded database through the evening. The latest HRRR and RRFS depict some isolated/widely scattered showers/tstms pushing ESE from southern PA, and potentially brushing the MD eastern shore this evening. While this remains a low- probability scenario, a 20% PoP still seems reasonable and has been maintained.

Overnight, as the weakening sfc boundary drops south, the HRRR/RRFS sfc-based smoke plumes show reduced VSBYs moving into northern portions of the FA after ~06Z, and spreading into southern VA by 09-12Z. These models have been verifying well today across MI/northern OH/PA where VSBYs are currently 2Sm or less in smoke. Since this will be of higher impact than smoke aloft, have continued to include the mention of "smoke" in the public forecast for Friday. As we see a higher concentration of both vertically- integrated and sfc- based smoke, haze and some visibility restrictions in smoke appear likely , along with poor air quality. Expect to have additional Air Quality alerts in effect. High temperatures Friday should be cooler than today, perhaps by a lot depending on the smoke concentration. Lower dew pts filter in from the north as well so heat indices should only be in the 90s for most, with 100-105 possible in the far south. Additional isolated showers and storms firing along the piedmont trough and riding along the weakening ridge could conceivably make it into the south central VA and interior NE NC before weakening, but chances are again very low. Kept PoPs at 20%.

KEY MESSAGE 2...Thunderstorm chances increase this weekend, bringing the potential for locally heavy rain, along with very warm and humid conditions persisting into early next week.

The upper level ridge continues to gradually break down and become shunted to a position off the SE US coast over the weekend, as upper troughing re- establishes itself over the northern Mid- Atlantic and northeast CONUS. As low pressure tracks from the eastern Great Lakes into New England, it will send its attendant cold front south toward the local area this weekend. Ahead of the front, a series of shortwaves will track across the area from Saturday through Monday. As is typically the case this time of year, it now seems likely that the slowing/weakening front will become hung up and linger across our area into Monday.

While considerable uncertainty remains regarding the exact timing and coverage of storms, the upper flow turning WNW-NW over a hot, increasingly humid, and moisture-pooled boundary layer (PWs increasing AOA 2") will set up a climatologically favored pattern for locally heavy rainfall and downbursts. Moisture pooling along the slow-moving boundary beneath steep mid-level lapse rates will favor a hot, muggy, high-DCAPE setup capable of producing isolated to scattered damaging wind gusts and potentially some instances of flash flooding in urban or flood prone areas each day this weekend, with this activity potentially lingering into Monday. Deep-layer shear is respectable just ahead of the front in the 25-35 kt range for Saturday. This could support some convective line segments, again depending on the timing of the upper support. It is likely that due to weakening shear, the main threat later in the weekend would be heavy rainfall along the sagging/weakening frontal boundary, and Hampton Roads has been included with a Marginal Risk in the latest Day 4 ERO from WPC.

High temperatures Saturday will be well into the 90s, potentially the upper 90s in a few spots, along with high humidity. Heat indices Saturday are likely to reach 105F+ for most of the area given convection not being until late in the day. Therefore, heat headlines are likely, with even some potential for localized 110+ across interior SE zones. Not as hot Sunday (though still very warm and humid), with highs mostly in the lower 90s, with storms redeveloping earlier in the day. The SVR threat will tend to be lower but additional heavy rain is likely. Gradually trending cooler next week, with diminishing PoPs.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

As of 800 PM EDT Thursday...

While VFR conditions prevail at most terminals this evening, this will not last for long. Conditions will start to deteriorate as winds shift to the NE overnight and into tomorrow morning and bring in more surface-based smoke to the area. SBY will likely see the worst flight conditions, with RIC VIS also likely dropping down to at least 3SM tomorrow morning. A lot of the areas to our north in the thickest blanket of FU saw VIS drop below 1SM, so would not be surprised if there are some periods of much lower VIS than our current TAFs suggest, though timing is difficult so have not included mention of VIS that low for now. ORF and PHF will likely also see reduced VIS, but they are not forecast to see the reduction that RIC and SBY are at this time. ECG will likely see some HZ, but the thickest smoke is forecast to stay to the north. Winds will remain light from the southwest for the first part of tonight, then switch to the NE late tonight into tomorrow morning. The biggest question for tomorrow will when will conditions start to improve in terms of VIS, and confidence is too low to include that for now.

Outlook: Increasing rain chances are expected later Sat aftn (highest at RIC/SBY), gradually spreading SE Sat night. A few storms may be strong to severe w/ damaging winds and IFR- LIFR VSBYs will be possible in any storm. Showers/storms are expected to redevelop again Sunday, with additional flight restrictions.

MARINE

As of 145 PM EDT Thursday...

- Sub-Small Craft Advisory marine conditions persist through Saturday. Southerly flow becomes E-NE 10-15 kt behind a weak boundary Friday with smoke likely reducing visibility.

- Potential for marginal Small Craft Advisory conditions in elevated south and southwest flow expected Saturday night into Sunday ahead of another front.

A weak synoptic flow regime remains in place across the region today. Currently, winds are from the W and SW around 5 kt. Waves and seas are 1 and 2 ft, respectively. Winds become S or SSW 10-15 kt from late afternoon into the overnight hours. A weak frontal boundary drops southward very late tonight with winds becoming N and NE around 10 kt by sunrise. Onshore flow continues through the day, becoming E 10 kt by mid to late afternoon. Smoke from wild fires in Ontario is forecast to mix down to the surface behind the front on Friday. Visibility will be reduced and portions of area waters could approach the 1 NM criteria for a Marine Dense Smoke Advisory.

The latest guidance continues to show the potential for SCA conditions across the waters Saturday evening into Sunday morning. S and SW winds are expected, mainly 15-20 kt with gusts to 25 kt in the Ches Bay/lower James River and 20-25 kt with gusts 25-30 kt offshore (highest N and farther offshore). Waves in the bay will briefly build to 2-4 ft and seas increase to 4-6 ft N and 3-5 ft S during this period.

There is a low risk of rip currents across all beaches Friday. Increasing winds and seas will likely result in a moderate rip risk for the northern beaches on Saturday. Lingering swells may also require a moderate rip risk for the northern beaches on Sunday.

AKQ WATCHES/WARNINGS/ADVISORIES

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