textproduct: Raleigh

WHAT HAS CHANGED

* Increased confidence in pockets of heavy downpours today, with a threat of localized flooding, especially in urban areas.

* Forecast high temps today have trended slightly lower.

KEY MESSAGES

As of 210 AM Tuesday...

1) Numerous showers and thunderstorms with areas of heavy rainfall remain possible today, with the greatest chance from our southwest sections NE to the Triad and Triangle regions and along the Virginia border. This will lead to a risk of isolated flooding.

2) Daily scattered showers and thunderstorms are expected to continue for the next 7 days, mainly each afternoon through evening.

DISCUSSION

As of 210 AM Tuesday...

KEY MESSAGE 1... Numerous showers and thunderstorms with areas of heavy rainfall remain possible today, with the greatest chance from our southwest sections NE to the Triad and Triangle regions and along the Virginia border. This will lead to a risk of isolated flooding.

Confidence is increasing in the potential for heavy downpours within showers and storms today. The current mid level pattern features a weak closed low over GA, while an offshore-centered anticyclone extends ESE toward the Southeast coast, and the westerlies remain displaced well to our N. This is leading to a steady SSE-to-NNW flow of moist and perturbed mid level flow across central NC, which will persist today through tonight as the low drifts N toward far SW NC. At the surface, a nearly stationary frontal zone stretches from the FL Panhandle across GA, the NC Foothills, and south-central and eastern VA. This front is likely to waver today as it succumbs to the whims of convective outflows and subtle mid level disturbances, but overall it should remain near or just NW of our N and W CWA borders today/tonight. That keeps us in the warm sector, with a plume of high PW (130%-140% of normal), especially over eastern and northern sections this afternoon and evening, with the high-PW area shifting N into VA overnight. While fairly high cloud cover for much of the day will curb insolation amidst mid level lapse rates mostly under 6 C/km, even modest heating of an already-muggy low level depth will still favor CAPE of 750-1500 J/kg, with minor waves aloft riding over our area supporting above-climo coverage of showers and storms today.

In addition to the high PW and bouts of weak dynamic forcing for ascent, other factors will exist which will favor a risk of localized flooding rains. These include a high warm-cloud (LCL-0C) depth of 4-4.5 km (favoring efficient warm rain processes), a somewhat slow cell motion (expected to be under 15 kts), possible training cells, and an added focus for ascent provided by outflows and confluent flow along the low-mid level shear axis, likely to be oriented SW-to-NE through the CWA, roughly from near CLT to near IXA. The recent rain surplus has also led to damp or nearly saturated soils (rainfall at GSO/FAY/RDU in the last two weeks is 200%-300% of normal). Will not issue a flood watch at this time, due to the expected limited coverage of the heavy downpours and the lingering uncertainty regarding exactly where the heavy rain might be focused. But if localized heavy rain does fall as expected, in particular over urban areas and highways, flood advisories or warnings may still be needed.

The severe weather risk is fairly low today due to the clouds and unimpressive CAPE and bulk shear, but a few of the strongest cells, particularly in our southwest, could generate pulse microbursts with straight-line winds over 40 kts this afternoon through early evening.

KEY MESSAGE 2... Daily scattered showers and thunderstorms are expected to continue for the next 7 days, mainly each afternoon through evening.

We're likely to stay within a weak flow pattern through early next week, with weak but persist low level flow sourced from the Atlantic and Gulf. The mid level low will continue to weaken as it lifts through far E TN/KY and gets caught up in the westerlies (specifically, broad troughing over the N Plains and N Great Lakes) through mid-late week, while the offshore ridge strengthens and drifts back W toward the Mid Atlantic coast, pushing the surface frontal zone well back to our NW and resulting in gradually rising heights over NC, especially in the E by the weekend. The flat Great Lakes trough will weaken, but a baggy mid level trough will hold from Ontario down through the Ohio Valley and lower Miss Valley into early next week. Pops are likely to stay on the high side, good chance to likely, through mid week, generally higher in the NW and SE (the latter from sea breeze action). But as that retrograding ridge builds into NC, we should trend to more typical chance pops for Fri through Mon. The risk of widespread severe weather appears low overall through the forecast, but some AI models do suggest a trend toward few stronger storms Sat into Mon and beyond. Regarding temps, highs will be a bit below normal and lows a bit above normal today and Wed, followed by above normal highs/lows by a category or two Thu into the weekend.

AVIATION /17Z TUESDAY THROUGH SUNDAY/

As of 105 PM Tuesday...

TAF period: Showers and thunderstorms will spread from east to west this afternoon. As of early afternoon, thunderstorm coverage has been minimal, but coverage should increase through the afternoon. No particular confidence in which terminals may have thunderstorms, but they will be possible at any site and will bring the potential for reduced cig/vis. Coverage of showers should begin to wane around sunset, with mostly dry conditions by midnight.

The bulk of the afternoon should have MVFR ceilings, although RDU/RWI have been VFR through the morning. IFR/LIFR ceilings will begin to expand into INT/GSO/RDU by 04-06Z. Meanwhile, to the east at FAY and RWI, flight restrictions will be conditional based on whether cloud cover is high enough to produce ceilings - it appears that visibilities should remain VFR at these sites, but if ceilings are able to form late tonight, they would likely be IFR. Flight conditions should rise back to MVFR at all terminals except FAY Wednesday morning, which will likely rise to VFR.

The wind will be out of the east around 5-10 kt this afternoon, dropping to 5 kt tonight and eventually veering to the south Wednesday morning.

Outlook: Diurnally driven showers and thunderstorms can be expected each day, although coverage will be less than today. Flight restrictions will be possible late each night into the next morning.

RAH WATCHES/WARNINGS/ADVISORIES

None.