textproduct: Wakefield

WHAT HAS CHANGED

- There is a Slight Risk for severe weather for most of Virginia on Saturday. A 30% wind risk has been added for much of the northern half of the forecast area including the Richmond metro over to portions of the MD Eastern Shore.

KEY MESSAGES

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.

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 240 PM 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.

This afternoon, an anonymously strong upper-level dome of high pressure, with the current analysis placing the strength of the high at ~596 dm, remains in control of the weather pattern. At the surface, ~1021 mb high pressure is centered over the local area. Temperatures this afternoon have already climbed well into the mid- upper 90s, with a few locations already approaching 100 F. Temperatures will continue to climb over the few hours, with highs expected to range from the upper 90s to the lower 100s. The heat, combined with very humid conditions (dewpoints in the low to mid 70s, locally upper 70s to around 80) will allow for widespread heat indices around or in excess of 110 F into the early evening hours. Not much relief from the heat is expected tonight with low temperatures only dropping into the upper 70s and urban areas will likely see temperatures struggle to drop below 80 F. Heat indices likely remain elevated to 100+ F through ~10 PM (especially in the urban areas).

The upper pattern gradually starts to break down later tomorrow and especially Sunday into early next week. Similar to today, Saturday will see high temperatures in the upper 90s to the lower 100s with widespread heat indices of 110+ F. 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, we remain 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.

Extreme Heat Warnings remain in effect for most of the area this afternoon through Saturday evening. Heat Advisories remain in effect for the MD Beaches and northern Outer Banks. Sunday will likely need at least Heat Advisories for a majority of the forecast area, with the potential for Extreme Warnings in a few locations. We will revisit Sunday heat headline decisions in future forecast updates.

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.

With the strong ridge aloft, subsidence is favored. A stout cap is also in place over the area, which can be seen on the afternoon GOES visible satellite imagery with only limited afternoon cumulus just now beginning to form across the local area. Given this, combined with surface high pressure and a lack of forcing, expecting little to no shower or thunderstorm development this afternoon/evening, with dry conditions prevailing. However, it should be noted that if a storm can develop in this environment, surface-based CAPE values in excess of 4000 J/kg across a majority of the forecast area combined with steep low-level lapse rates would favor strong downbursts. As a result, SPC does have northern and western portions of the area highlighted in a Marginal Risk (level 1 out of 5) for severe weather this afternoon and evening.

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 out of 5) encompasses most of our VA and MD counties. Additionally, a belt of slightly higher flow/shear across the northern half 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. SPC has highlighted this area in a 30% wind risk for Saturday. 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 /18Z FRIDAY THROUGH WEDNESDAY/

As of 120 PM EDT Friday... VFR conditions will continue throughout the 18z/03 TAF period. FEW to SCT afternoon cumulus through ~23z-00z, with skies becoming mainly clear overnight into Saturday morning. Winds are light, ~5 knots, out of the S-SW, with variable winds along the coast. Winds will remain light into Saturday morning. Haze continues at PHF and RIC with occasional MVFR VSBY restrictions possible.

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 240 PM EDT Friday...

Key Messages:

- Sub-SCA marine conditions will prevail through the weekend, with mainly south-southwesterly winds.

- Elevated wind gusts from strong thunderstorms are possible during afternoon and evening hours Saturday and Sunday.

Surface high pressure is centered over the area extending into the SE CONUS from a strong upper air ridge over the East Coast. Winds are generally out of the SSW around 5-10 kt with waves around 1 ft and seas around 2 ft. Mostly south-southwesterly winds will continue through at least the weekend, likely into early next week. There will likely be some diurnal variances in wind speed and direction throughout the day from land/sea breezes over the next few days. Seas will remain around 2-3 ft with waves 1-2 ft through the weekend as well. Benign marine conditions will continue through at least the weekend, likely into mid week, as the high pressure remains dominant over the area and is slow to break down. The risk of isolated to scattered tstms increases over the next few days, which could produce some gusty winds Saturday and Sunday afternoon and evening. Any stronger wind gusts will be handled with SMWs if necessary.

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 until 8 PM EDT Saturday for MDZ025. NC...Extreme Heat Warning until 8 PM EDT Saturday for NCZ012>017- 030>032. Heat Advisory until 8 PM EDT Saturday for NCZ102. VA...Extreme Heat Warning until 8 PM EDT Saturday for VAZ048- 060>062-064>069-075>090-092-097>100-509>525-528>531. MARINE...None.