textproduct: Raleigh

WHAT HAS CHANGED

* In addition to today's Heat Advisory, another Heat Advisory has been issued for our southern half for Sat. Additional heat alerts are likely for Sun and Mon.

* Shower/storm coverage should be higher today and into the weekend compared to the last couple of days, but still mostly scattered.

KEY MESSAGES

As of 250 PM Friday...

1) Dangerous heat and humidity will remain in place across portions of NC tomorrow through early next week.

2) There is a Marginal risk of severe thunderstorms through this evening areawide, and a Marginal to Slight risk of severe thunderstorms Saturday, with the higher risk over western and southern areas of central NC. Damaging winds are the primary threat.

DISCUSSION

As of 250 PM Friday...

KEY MESSAGE 1... Dangerous heat and humidity will remain in place across portions of NC tomorrow through early next week.

Early afternoon satellite data reveals convection crossing the mountains into the Mid Atlantic. Varying amounts of mid/high clouds have been present across central NC through much of the day but given mild morning low temps, there has been no problem seeing heat index values climb above 100 (before noon in many spots).

The Heat Advisory will remain in place until 8 pm tonight. The combination of loss of daytime heating plus the potential for rain cooled air from showers and storms should bring some degree of relief by this evening. Mid level heights and thicknesses remain relatively similar across the southern half of our forecast area on Saturday. As such, temps and dewpoints should yield similar heat index values along and south of a Stanly to Wayne Co line, and a Heat Advisory will be in effect from 11a-8p tomorrow as well.

With a stalled front lingering across the area and little in the way of backdoor cold air to cleanly push it through our area, dangerously hot heat index values can be expected across portions of the area Sunday and Monday and additional Heat Advisories may be needed through early next week.

KEY MESSAGE 2... There is a Marginal risk of severe thunderstorms through this evening areawide, and a Marginal to Slight risk of severe thunderstorms Saturday with the higher risk over western and southern areas of central NC. Damaging winds are the primary threat.

The latest surface analysis shows the primary synoptic frontal zone from the Midwest to the Mid Atlantic, with a trough trailing from DE S and SW through central NC. A series of old outflows along and S of this front generated from decaying/decayed MCSs are already spawning convection over NC, with storms having started over the E slopes of the S Appalachians and Foothills drifting SE into the W Piedmont, while another broken band of storms is tracking from central WV into E KY, also pushing SE. These boundaries will continue to track SE over VA/NC through this evening, with additional scattered convection over our area feeding on high PW (130-140% of normal) and 3000-4000 J/kg of SBCAPE, yielding a wet microburst threat with the deeper convection, although poor deep layer shear should limit storm organization. Coverage should be higher over the N than the S, given the mid level ridging and lower mid level lapse rates further S, but a stray shower or storm can't be ruled out anywhere given the strong heating, high moisture, and favorable instability. Activity should dwindle gradually during the early overnight hours.

Models continue to favor a substantial outflow passage SSW through much of central NC tonight into early Sat, while the synoptic front remains well to our N, aligned vertically with the stronger WNW mid level steering from the Midwest to the Mid Atlantic. This diffuse boundary is expected to set up over central NC Sat roughly from the Triad region through the central Coastal Plain, and N of this front will see higher low-level stability and a pool of sct-bkn morning stratus, which should help hold temps down a bit from today's readings. But along and south of this boundary, ample heating and very warm/moist air should support another round of moderate to high afternoon SBCAPE amidst continued-high PW, thus isold to sctd storms are again expected, with another primary threat from damaging straight-line winds, despite borderline lapse rates aloft and poor deep layer bulk shear.

As we'll stay within this steamy air mass into at least early next week with hot temps, high humidity, and above-normal PW, isolated to scattered afternoon/evening showers will remain possible. Most models show the mid level ridge gradually flattening, sinking southward and gradually retrograding to across the S Plains and Gulf Coast through the middle of next week, with another uptick in WNW mid level flow over our area. Thus, scattered diurnal-favored showers and storms will remain possible through mid week, although not every place will see activity every day.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

As of 145 AM Saturday...

TAF period: Generally VFR conditions are expected through 06z/Sunday. However,

A chance of thunderstorms is expected this afternoon into the evening. We included a PROB30 group between 19z today and 03z/tonight.

Looking beyond 06z Sun, scattered late-day showers and storms are possible each day through Monday. Otherwise, generally VFR conditions are expected. A few hours of patchy early-morning sub-VFR fog/stratus may occur each day, with the highest chances in areas that see rain.

CLIMATE

Record High Temperatures:

August 15: KFAY: 100/1935

August 17: KRDU: 99/1997 KFAY: 104/1954

August 18: KFAY: 98/1988

August 20: KFAY: 102/2007

Record High Minimum Temperatures:

August 15: KGSO: 77/1995 KRDU: 77/1995 KFAY: 78/2017

August 16: KGSO: 75/2016 KRDU: 76/2007 KFAY: 78/2005

August 17: KGSO: 75/2010 KRDU: 76/2024 KFAY: 78/2007

August 18: KGSO: 75/2017 KRDU: 77/1995 KFAY: 78/2021

August 19: KRDU: 77/1988 KFAY: 76/1940

August 20: KGSO: 77/1912 KRDU: 75/2007 KFAY: 78/2005

RAH WATCHES/WARNINGS/ADVISORIES

Heat Advisory from 11 AM to 8 PM EDT Saturday for NCZ042-073>078- 083>086-088-089.