Key MESSAGE 1, While a warming trend is still expected through this weekend, elevated smoke from Canadian wildfires continues to complicate the temperature forecast. Available smoke guidance suggests this smoke layer mainly over Virginia, will sink south into North Carolina on Friday. In fact, some guidance suggests the layer of smoke may lower closer to the surface and lead to some reductions to visibility, especially across northern portions of Eastern NC, along HWY 64. Yesterday we saw a sharp gradient in temperatures for areas underneath the smoke compared to areas with full sunshine. It appears that gradient will be over ENC today, with temperatures most impacted across Virginia. If the smoke does, indeed, fill back in from the north on today, then temperatures would likely be impacted. Last few synoptic runtimes of the HRRR keep the densest smoke just N of the FA, though there will be some evidence of the across the northern areas mentioned above.
The uncertainties with temperatures also complicated the decision to issue heat headlines or not. The potential impact from smoke plus afternoon mixing out of lower dewpoints could be enough of a limiting factor to keep the risk of 105+ heat indices lower today. If the smoke ends up having less of an impact as the HRRR suggests, then heat indices would likely be higher. Moistening southerly flow should lead to higher dewpoints today. Even with somewhat muted afternoon heating, the temp/dewpoint combo appears more supportive of heat headlines compared to yesterday. Have gone slightly below NBM with a HiRes blend for temperatures inland as RTMA shows that NBM was a tad too warm THU, though performed well with Tds. Nbm/consmos blend for OBX. Current forecast calls for MaxAppT values in the 105-109deg range for most of the area, with areas near the Crystal Coast possibly exceeding 110deg briefly before the afternoon seabreeze pushes through. Because of this, have issued a Heat Advisory for all zones except for NOBX where MaxAppT are forecast to reach triple digits, but remain below criteria for any headlines.
KEY MESSAGE 2, There are several factors expected to support an increasingly active pattern from the weekend into next week, but also with some important considerations.
Upper level troughing is forecast to develop across the Eastern U.S. With ridging shifting away from the area. The lack of subsidence, alone, can help support a more active pattern. Additionally, persistent southerly flow east of the trough, potentially with a subtropical connection, should act to enhance low-mid level moisture across the area. Meanwhile, heating of a moistening boundary layer should lead to sufficient instability and reduced inhibition in support of periods of convection. Today, showers and tstorms re-enter the forecast increasing moisture convergence ahead of a front approaching from the N this afternoon may get enough of a initiating force from the seabreeze to warrant SChc-Chc PoPs this afternoon into this evening.
At the surface, the front approaching the area this afternoon will lift back Nward into VA tonight, acting to "warm-setor" the entire FA for the weekend. Lee- side troughing and, eventually, a frontal boundary that will reach the FA by MON should provide areas of enhanced low- level forcing this weekend. Spc has portions of the FA outlined in a Marginal Risk (lvl 1/5) of severe thunderstorms SAT. This threat for day 2 mostly encompasses the potential for stronger storms that develop W and N of the FA in the afternoon reaching NWernmost zones after sunset SAT. Spc day 3 outlook for SUN features a Slight Risk (lvl 2/5) for a portion of the FA, and a Marginal Risk (lvl 1/5) for the remainder of the area. Moisture pooling and low level convergence will be maximized SUN afternoon into SUN night as the cold front approaches. Pwats peak on the order of 2 and 3/4in with increasing afternoon and evening instability through the weekend. Additionally, while guidance remains mixed, there is a modest signal for low pressure development across the northeastern Gulf. Whether this obtains tropical characteristics or not, it could act to enhance rainfall along the Southeast U.S. Coast if it ends up getting pulled north ahead of the above-mentioned upper trough. Not all guidance show this though, as some ensemble members take the low west across the northern Gulf Coast. The National Hurricane Center has maintained a 20% probability of development over the next 7 days, and it is something we will be monitoring through the weekend and into next week.
Tropics aside, deterministic and machine learning guidance continue to show a good signal for some strong to marginally severe thunderstorm potential during this period of active weather. Right now the signal is the strongest on Sunday. Given increased forcing from the approaching front and the potential tap of subtropical moisture, heavy rain and some hydro impacts may eventually be realized.
12z Friday through Tuesday Predominant VFR flight cats are expected to prevail through the period, though some patchy fog lingers this morning. There remains an elevated layer of smoke from Canadian wildfires that is meandering around the region. Guidance suggests this should remain elevated and not impact visibilities today. Winds will be light and variable through the morning with a low end chance decoupled sites seeing subVFR patchy fog. Oaj has dipped down to IFR VIS but should see improved VIS after sunrise, so have carried a tempo MVFR group for one hr at the 12Z TAF time. Fri afternoon sees a return of showers and tstorms development potential along the seabreeze. Not high enough PoPs to warrant any subVFR mention explicitly in the TAFs, but have included VCSH wording in the afternoon into the evening for all terminals. With the 12z update, have added a couple hr prob30 group for OAJ with PoPs in the upper 20%s for a few hours.
Outlook (Friday night through Tuesday): Guidance suggests smoke from Canadian wildfires may try to work down to the surface Friday night with reductions to VIS possible. It's unclear whether or not smoke impacts will last into the weekend. Otherwise, the risk of TSRA is expected to slowly increase Saturday night, becoming more likely from Sunday into early next week. Sub-VFR conditions can be expected along with the TSRA impacts.
Latest surface and buoy obs indicate SW winds 5-10kt inside, 10-15kt outside with seas 1-3ft with SW wind waves ~2ft on top of 1-2ft weak ESE longer period swell. A cold front approaches from the N through the day today, lifting back into VA sometime this evening. This will lead to a slight wind shift over Nern waters where the winds becoming southeast or east for several hours. Eventually, Serly flow will return for all waters tonight behind the departing boundary.
Outlook (Friday night through Tuesday): Southwesterly winds are seas are expected to build to 20-30kt over the weekend as the gradient sharpens in advance of another front approaching the region. Over the outer coastal waters, frequent gale-force gusts appear possible for several hours Saturday night into Sunday morning. It may not quite reach the threshold for a Gale Warning there, but the increased winds are notable. Seas will quickly respond to the winds, building to 4-7ft by Saturday night. Marine headlines appear probable for coastal waters and PamSound for this timeframe. Elevated winds and seas are expected to last into early next week for the nearshore coastal waters. For the outer waters, elevated winds and seas may last for much of the week.
Nc, heat advisory from 11 am this morning to 8 pm EDT this evening for ncz029-044>047-079>081-090>092-094-193>196-198-199- 204-205. Marine, none.
