textproduct: Raleigh

WHAT HAS CHANGED

* No significant changes; updated aviation discussion

KEY MESSAGES

As of 305 PM Wednesday...

1) The heat and humidity will continue into late week, with a slight break over the weekend then returning early next week.

2) The chance for mostly diurnal convection persists into early next week, but with low confidence in the placement and timing details.

DISCUSSION

As of 305 PM Wednesday...

KEY MESSAGE 1... The heat and humidity will continue into late week, with a slight break over the weekend then returning early next week.

For the rest of the week, Thursday and Friday, Central NC will remain on the northern edge of a sub-tropical ridge, with a persistent surface trough driving continued extreme heat. While some scattered afternoon convection is possible, highs will reach the low 90s north to near 100 degrees in the south. Combining these temps with high humidity, expect heat indices of 100 to 108. A Heat Advisory has been issued for areas from Raleigh to the south and east for Thursday, and one may also be needed Friday for the Sandhills and Coastal Plain.

Over the weekend, temperatures will moderate slightly as high pressure slides off the Mid-Atlantic coast. This will generate a weak northeasterly surface flow behind the front and result in near- normal highs. However, lingering low-level moisture will maintain triple digit heat indices, while passing shortwaves continue to force typical isolated to scattered convection both afternoons.

Into the early and middle of next week oppressive heat returns as the upper-level ridge shifts east and the next incoming trough strengthens. Depending on how afternoon dew points mix out each day, heat index values will peak again up to 109 degrees for parts of the area. This secondary wave of high heat indices will likely require additional Heat Advisories for much of central NC early to mid week.

KEY MESSAGE 2... The chance for mostly diurnal convection persists into early next week, but with low confidence in the placement and timing details.

The overall central/E CONUS pattern will remain largely the same heading into the weekend, featuring a quasi-stationary NW-to-SE frontal zone (which could actually waver significantly in spots based on the whims of convective complexes and outflows) from the Midwest through Ohio Valley and NC. This front will be aligned with a swift and perturbed NW steering flow from the Upper Midwest through the Mid Atlantic, on the N and NE side of a building mid level ridge covering the interior Southeast, Gulf States, and lower Miss Valley. This will put central NC within the path of potentially multiple MCS remnants or MCVs tracking ESE or SE into our area over the next few days, all with poor predictability beyond 12-24 hrs. Through tonight, a mature convective complex now over S/E IN and W OH is expected to weaken as it continues pushing generally SE, but may still spawn a few showers and perhaps an isolated storm across our extreme W and S between late this afternoon into the early overnight hours. Deep layer bulk shear is expected to be 20-25 kts through tonight, but lingering 500-750 J/kg of CAPE will be increasingly overwhelmed by nocturnal CINH. Regardless of whether or not any convection survives this far SE, the veil of debris mid and high clouds will certainly pass overhead into Thu morning.

Confidence remains pretty good that the mid level pattern and surface frontal pattern will be maintained for at least a few days, again with deviations in frontal position, and we'll stay within a steamy air mass featuring a weak W to NW low level flow and above- normal high temps in the 90s. So any convection will be able to tap into this juicy air mass with late-day CAPE peaking near 1000-1500 J/kg. But the mid level lapse rates will stay modest, and with the light winds leading to a lack of distinct focus for convection, the coverage is likely to stay sub-climatology, isold to scattered at most, but with uncertain timing and placement. No widespread severe weather is expected in our area, however, for the next few days.

AVIATION /00Z THURSDAY THROUGH MONDAY/

As of 800 PM Wednesday...

VFR conditions will dominate at all TAF sites through the next 24 hours. Dry weather currently prevails with just some mid and high clouds across the region, and this should continue through the night. An upstream storm complex currently over KY should largely dissipate over the Appalachians before reaching central NC. However, it will spread more scattered-broken mid and high clouds SE into the area overnight after about 06z. Can't rule out an isolated shower or storm at any of the terminals on Thursday afternoon/evening, but with POPs only around 15-20% at most, and high-res models struggling to forecast convection in recent days, confidence is too low to include mention in the TAFs at this time.

Looking beyond 00z Fri: Isolated to scattered late-day showers and storms are possible each day Fri through Mon, although the predictability of this will remain rather low, reducing forecast confidence. A few hours of early-morning sub-VFR fog/stratus may occur each day starting early Fri morning, with the highest chances in areas that see rain.

RAH WATCHES/WARNINGS/ADVISORIES

None.