textproduct: Raleigh

WHAT HAS CHANGED

* Nothing appreciable

KEY MESSAGES

As of 315 PM Monday...

1) Hot, with scattered to locally numerous convection with strong to locally damaging wind gusts ahead of a backdoor front that will settle into cntl NC Tue evening through early Wed

2) Above-normal rain chances continue through Tue, primarily over the N and E. Lesser coverage is expected Wed through Fri, with more widely scattered storms, then rain chances increase again heading into next weekend. Above-normal heat will return briefly from the Triangle south and east late in the week, but it won't be nearly as intense or widespread as the recent heat wave.

DISCUSSION

As of 315 PM Monday...

KEY MESSAGE 1...Hot, with scattered to locally numerous convection with strong to locally damaging wind gusts ahead of a backdoor front that will settle into cntl NC Tue evening through early Wed

In the mid/upr-levels, convectively-perturbed swly flow will persist across the Southeast, between a very slow-moving cyclone over the mid MS Valley and a sub-tropical ridge across the swrn N. Atlantic. While associated heights will remain generally neutral, and with some tendency for the flow to be anticyclonic around the ridge, small MCVs from upstream convection will probably focus mesoscale lift amid moist and conditionally unstable profiles characterized by PWs around 2-2.25" and 125% of normal. One such MCV, from deep convection over AL/GA last evening, has tracked with its associated mid-level cloud shield newd and into the srn Piedmont of NC this afternoon. It should continue to progress newd and across the nrn NC Piedmont and s-cntl to sern VA through this evening. Another MCV appears to have developed, according to KRAX and KCAE mid-level velocity data, within a convective cluster that has more recently developed out of cntl SC. This feature will follow a similar trajectory as the first, though slightly farther east (across the Sandhills and ern Piedmont) and trailing by a couple of hours.

At the surface, the pattern will remain a generally persistence one in and around cntl NC, with an Appalachian-lee trough extending across the NC Piedmont. A weak lee and increasingly frontal low over the Middle Peninsula of VA this afternoon will sag swd with an associated backdoor, outflow-reinforced front and into at least n- cntl NC Tue evening-night.

In this similar/persistence pattern, though more-moist at the surface and through the mid/upr-levels, multi-cell convection will continue to focus ahead of the aforementioned MCVs and along outflow, with newd propagation across most all of cntl NC through the evening. While most areas will generally be impacted, its inherent multi-cell nature will favor heavy, convective rain for some and barely measurable, decaying stratiform rain for others.

Although DCAPE has decreased given the increasing deep moisture (PWs around 2" vs 1.5" of Sun), moderate to strong instability (highest and in excess of 3000-3500 J/kg centered in the srn Coastal Plain and ern Sandhills) will support water-loaded/wet microbursts, though probably fewer in number than Sun given the diminished DCAPE. The environment will be very similar yet again on Tue, with probably similar coverage and risk of downburst winds.

While temperatures Tue will also probably be a couple or so degrees less hot on average than those of today, slightly richer moisture/higher surface dewpoints will probably yield yet another day of heat index values of 100 to 105 F for all but the nw Piedmont. Another Heat Advisory may be needed for a portion of the Sandhills and Coastal Plain, where heat index values may reach or marginally exceed 105 F.

KEY MESSAGE 2... Above-normal rain chances continue through Tue, primarily over the N and E. Lesser coverage is expected Wed through Fri, with more widely scattered storms, then rain chances increase again heading into next weekend. Above-normal heat will return briefly from the Triangle south and east late in the week, but it won't be nearly as intense or widespread as the recent heat wave.

PWs will remain around 150% of normal over northern and NE NC Tue, ahead of a baggy mid level shortwave trough extending from New England through PA and the Ohio Valley to AR. The corresponding surface cold front will approach but remain to our N and NW, keeping us firmly in the warm sector with a surface trough holding through the Piedmont. Steering flow and deep layer bulk shear will remain weak Tue, keeping the overall severe threat in check despite expected moderate SBCAPE and DCAPE near 800 J/kg (although convective debris cloudiness may curb our instability somewhat). But the risk of localized heavy rain rates will persist over the northern and NE CWA, given a likely slow storm motion and the potential for training and congealing cells within a high-PW environment, thus pockets of minor urban flooding can't be ruled out. WPC continues a marginal risk of excessive rainfall over our NE half Tue.

Previous model runs had favored the mid-level trough and associated surface cold front dropping SE into, if not fully through, NC, Wed and Wed night. But more recent model solutions have trended toward a less-phased trough, with its northern portion pushing E off New England and the northern Mid Atlantic Wed, while the slower southern portion drifts E over the central and lower Miss Valley into W KY and W TN. This results in a flat shortwave ridge over the Carolinas mid-week, and a surface front that holds near or N of the NC/VA border (although the Piedmont troughing appears anchored in place). With weak steering flow, possible warm mid levels and a downturn in PW, we should see reduced shower/storm coverage Wed/Thu, with just widely-scattered, late-day garden-variety convection. The southern portion of the mid level shortwave trough is expected to deamplify and finally progress eastward, passing by to our N by late Thu into early Fri. While this may accelerate our mid level flow (esp across our N) Fri, the flat W-E ridging to our S should still limit moisture transport into central NC, with few other mechanisms to force ascent, and expect another day of spotty shower/storm coverage.

By the weekend, the strengthening blocking ridge over the central Rockies and Four Corners region will allow longwave troughing to gradually dig over the eastern CONUS, with strengthening NW flow allowing perturbations to dive SE into our area. This should result in an upward trend in moisture, clouds, and shower/storm chances by Sat/Sun.

Regarding temps, readings are expected to stay generally above normal through mid to late week, peaking on Friday when highs should reach the mid to upper 90s. This heat won't be nearly as intense or long-lived as our most recent heat wave. But we do have patches of Extreme levels of experimental Heat Risk popping up by Fri over portions of the area, along with heat indices peaking at or just over 105F, so small areas of heat headlines may be needed.

AVIATION /18Z MONDAY THROUGH SATURDAY/

As of 200 PM Monday...

In a very similar and persistent pattern as Sunday, scattered to locally numerous showers/storms with strong wind gusts and cell motions to the northeast will develop and overspread cntl NC through this evening. The probability of occurrence at any given point/site is generally between PROB30 and TEMPO range, with a hedge toward the latter reflected again with the 18Z TAFs. Light sswly surface winds and VFR conditions are otherwise expected except for a small risk of stratus and mist/fog especially where rain occurs beforehand. Diurnal cumulus on Tue may initially develop with bases in MVFR range, with the greatest coverage and chance of ceilings at FAY and RWI, owing to the presence of richer low-level moisture than recent days.

Outlook: Scattered to locally numerous convection will probably result again each afternoon through mid-week, as a series of mid- level disturbances overspread a persistent, Appalachian-lee/Piedmont surface trough and eventually a backdoor front likely to settle into and become quasi-stationary over NC Tuesday night through Thursday morning. Morning stratus/mist may also result in areas that receive convective rain the previous afternoon-evening.

RAH WATCHES/WARNINGS/ADVISORIES

Heat Advisory from noon today to 8 PM EDT this evening for NCZ024- 025-040>043-075>078-085-086-088-089.