textproduct: Wakefield

WHAT HAS CHANGED

- Upgraded Heat Advisory and Excessive Heat Watch in NE NC to an Extreme Heat Warning, which is now in effect through Saturday evening.

- Heat Advisory for OBX Currituck and MD Beaches extended through Saturday evening.

- Slight chance for thunderstorms introduced for the Piedmont late this afternoon and evening

- Slight risk for severe wx expanded to cover most of VA on Independence Day/Saturday

- Slight risk for severe wx northern portions of area Sunday

KEY MESSAGES

1) A prolonged and widespread heat wave will continue this afternoon through the holiday weekend, before breaking down early next week. This has the potential to be the most significant in both magnitude and duration since July 2012 for most of the forecast area.

2) The risk for thunderstorms gradually increases over the next few days. Any storm that develops could produce strong to severe wind gusts, frequent lightning, and heavy rain.

3) Temperatures gradually trend closer to normal by early next week, with the potentially for unsettled weather.

DISCUSSION

As of 305 AM EDT Friday...

KEY MESSAGE 1...A prolonged and widespread heat wave will continue through the holiday weekend, before breaking down early next week. This has the potential to be the most significant in both magnitude and duration since July 2012 for most of the forecast area.

Dangerously hot conditions peak today into Saturday. The synoptic pattern will be heavily influenced by an anonymously strong upper- level dome of high pressure, with current analysis placing the strength of this high at ~596 dm. The center of this feature will remain near the western border of our CWA today (as it was yesterday) before slowly shifting S tonight and breaking down Saturday into Sunday. A generally nebulous/weak flow pattern is present at the surface and will prevail through the remainder of the weekend. There will be the typical lee troughing that develops in the afternoon hours and this will focus a gradually increasing coverage of showers/storms over the next few days, coincident with the ridge breaking down and the associated height falls aloft.

Regarding the heat specifics, widespread highs in the upper 90s to lower 100s are expected today. Combined with humid conditions (dew points in the 70-75 F during peak heating), widespread heat indices around or in excess of 110 F are forecast from late this morning through most of the afternoon and evening. Some model guidance continues to hint at some locations flirting with the mid 100s. However, this would be likely be contingent on deep mixing processes with a resultant drop of the dew points into the the 60s. Based on what we saw yesterday, where dew points remained elevated or even increased some in the afternoon, this scenario seems unlikely. Similarly hot Saturday with most of the area likely to see 110 F heat indices, especially early. There is a higher risk for thunderstorms Saturday, particularly N of the NC/VA state line, and this could put an early end to dangerous heat indices. Regardless, am quite confident that at least the 10 AM-3 PM time period will be dangerously hot. A degree or two cooler by Sunday (but still very hot) as 850 mb temps begin to drop, cloud cover becomes a bit more prevalent, and additional chances for showers/storms return in the afternoon.

There have been a few adjustments to the headlines. First, confidence is moderately high in heat indices peaking around or just above 110 F for a good portion of NE NC today. Therefore, the previously issued Heat Advisory (for today) and Extreme Heat Watch (for Saturday) has been upgraded to an Extreme Heat Warning from 10 AM today through Saturday evening. Elsewhere, Extreme Heat Warnings remain unchanged and are also in effect through Saturday evening. Heat Advisories are in place today through Saturday for the MD beaches and OBX Currituck. Will revisit Sunday in future forecast updates, but at least a Heat Advisory appears likely for a majority of the forecast area.

KEY MESSAGE 2...The risk for thunderstorms gradually increases over the next few days. Any storm that develops could produce strong to severe wind gusts, frequent lightning, and heavy rain.

The convective potential is highly uncertain today. Strong instability is progged to develop given the very hot and humid airmass. However, the strong ridge aloft favors subsidence and forecast soundings show a rather stout cap just above the mixed layer. There are several CAMs that show isolated convective activity, but it is uncertain if this is mainly an artifact or if convective temperatures will actually be breached. Should an updraft survive through the cap, surface-based CAPE values in excess of 3000 J/kg and steep low-level lapse rates would favor strong downbursts. This potential is highly conditional and, again, it remains uncertain if any storms will actually form in our CWA in the first place. The best shot looks to be across the Piedmont and have drawn in a 20% PoP after 5 PM. There is Marginal Risk (level 1/5) from SPC across the N but any location that sees a storm would be at risk for the isolated severe potential.

There is higher confidence in at least scattered thunderstorm potential on Independence Day/Saturday as the ridge begins to break down. Would expect any storms to develop in the lee of the higher terrain or in the Piedmont, moving eastward in the deep-layer westerly flow into the evening. There is again a risk for severe- caliber wind gusts given the very favorable thermodynamic environment and a Slight Risk (level 2/5) encompasses most of our VA and MD counties. Additionally, a belt of slightly higher flow/shear across the northern third or so of our area could also allow for an area of enhanced severe potential where some potential for upscale growth into a cluster-type feature is possible. These storms could interfere with evening festivities so users are urged to closely monitor the weather and have a plan in place due to impacts from both the heat and storms.

Additional threats of strong-severe storms are on the table both Sunday and Monday, with higher confidence in more widespread coverage these days. Damaging wind gusts, heavy rainfall, and frequent lightning will be the primary storms threats.

KEY MESSAGE 3...Temperatures gradually trend closer to normal by early next week, with the potentially for unsettled weather.

The ridge becomes shunted to our south beyond Monday, with the upper- level flow turning quasi-zonal. This pattern is very typical for the middle of summer with daily chances for showers and storms expected in the midst of surface troughing and weak disturbances passing through aloft. Temperatures will also trend back toward seasonal norms for most of next week, generally in the lower 90s.

AVIATION /09Z FRIDAY THROUGH TUESDAY/

As of 550 AM EDT Friday... VFR conditions will continue through the 12z TAF period, with mostly clear skies prevailing outside of FEW-SCT aftn cumulus. Winds will generally be S-SW at 5-10 kt today and variable (especially early aftn) near the coast. The vast majority should stay dry, but a very isolated tstm cannot be ruled out late this afternoon and evening, mainly W/NW of RIC.

Outlook: Prevailing VFR conditions will continue through the weekend. There is potential for isolated to scattered showers/storms each afternoon and evening Saturday through early next week, which could lead to briefly degraded flight conditions at any terminal that sees any of this convection.

MARINE

As of 305 AM EDT Friday...

Key Messages:

- Sub-SCA marine conditions are expected to prevail through the weekend, with mainly southerly winds.

- Strong thunderstorm wind gusts are possible during the late afternoon and evening hours Saturday and Sunday.

High pressure extends from the Southeast to off the Mid-Atlatnic coast early this morning. The wind is generally SW 5-10kt and 10- 15kt offshore. Seas are generally 2-3ft with ~1ft waves in the Ches. Bay. High pressure remains over the local area over the next few days allowing for continued, mainly light, southerly winds. Some diurnal wind speed and direction variability is likely to prevail for the next several days (mainly S-SW in the morning, becoming S-SE in the late aftn/evening). Isolated to widely scattered tstms this weekend into early next week would be the only thing that would lead to brief higher winds and waves, with strong tstm wind gusts possible Saturday and Sunday, primarily during the late aftn and evening hours. Seas will be ~2ft later today through the weekend, with 1ft to occasionally 1-2ft waves in the Ches. Bay.

CLIMATE

Record Highs:

- Site: Fri 7/3 Sat 7/4 Sun 7/5

- RIC: 100/1954 100/2002 102/2012 - ORF: 99/1954 98/1997 98/2012 - SBY: 98/1954 100/1919 102/2012 - ECG: 98/1954 100/1997 100/2012

Record High Mins:

- Site: Fri 7/3 Sat 7/4 Sun 7/5

- RIC: 77/2014 77/1900 79/2012 - ORF: 78/2014 79/2012 80/1999 - SBY: 76/2014 78/2012 81/2012 - ECG: 78/2014 78/2012 77/2024

EQUIPMENT

KAKQ radar is down due to mechanical issues without an estimated time of return.

AKQ WATCHES/WARNINGS/ADVISORIES

MD...Extreme Heat Warning until 8 PM EDT Saturday for MDZ021>024. Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for MDZ025. NC...Heat Advisory from 10 AM this morning to 8 PM EDT Saturday for NCZ102. Extreme Heat Warning from 10 AM this morning to 8 PM EDT Saturday for NCZ012>017-030>032. VA...Extreme Heat Warning until 8 PM EDT Saturday for VAZ048- 060>062-064-067>069-075>078-080>086-088>090-509>523. Extreme Heat Warning from 10 AM this morning to 8 PM EDT Saturday for VAZ065-066-079-087-092-097>100-524-525- 528>531. MARINE...None.