textproduct: Raleigh

WHAT HAS CHANGED

* Forecast high temperatures Fri onward have been lowered.

KEY MESSAGES

As of 255 AM Thursday...

1) Becoming hot Fri-Sun, trending less so next Mon-Tue, then possibly dangerously so mid to late next week

2) Diurnally-maximized chances for convection will increase Fri into the weekend, followed by mainly dry conditions most of next week.

DISCUSSION

As of 255 AM Thursday...

KEY MESSAGE 1... Becoming hot Fri-Sun, trending less so next Mon- Tue, then possibly dangerously so mid to late next week

An MCV and related mid-level trough now over sern AL will weaken/ deamplify while progressing across GA and the srn Appalachians through tonight and across the Carolinas on Fri. Thereafter, a couple of sub-tropical, mid-level highs initially over nrn MX and the swrn N. Atlantic will merge and amplify a ridge across the mid- South and MS Valley Sun-Mon, during which time a convectively- amplified mid-level trough and possibly well-developed MCV will track in nwly flow from the lwr OH Valley to offshore the srn Middle Atlantic coast. As that trough moves east, a strong mid-level anticyclone related to the upstream ridging will drift ewd and park over the OH and TN Valleys next week.

At the surface, 1019 mb high pressure and associated continental air now stretching from just offshore the Middle Atlantic coast swwd and into NC will become absorbed/overwhelmed by a stronger high spanning the entirety of the lower mid-latitude and sub-tropical cntl N. Atlantic. Increasingly-hot, swly flow will be directed across the Carolinas and into both an Appalachian-lee/Piedmont trough and a wavy frontal zone forecast to extend from the mid MS Valley to the srn Middle Atlantic. Cntl NC will be situated to the south of that frontal zone until Sun, when it will likely settle swd and across NC. Following high pressure will build across and offshore the Middle Atlantic early next week, with associated ely/onshore flow directed into the Middle and South Atlantic coast, and which should regulate temperatures and curb the heat over cntl NC Mon-Tue. The intensifying heat across the interior Atlantic states, and especially over the OH and TN Valleys during that time, will then probably expand east of the Appalachians and into cntl NC mid to late next week, when dangerously hot conditions will become more likely.

KEY MESSAGE 2... Diurnally-maximized chances for convection will increase Fri into the weekend, followed by mainly dry conditions most of next week.

A shield of 700 mb-centered moisture will accompany the aforementioned mid-level trough as it progresses across NC on Fri. While mixed dewpoints mostly in the upr 50s-lwr 60s will limit instability to 500 J/kg or less, forcing for ascent and mid-level moistening accompanying the passing mid-level trough should prove sufficient for the development of scattered showers and perhaps a few storms.

Rain/convective chances will further increase especially by Sun, with the passage of the aforementioned backdoor cold front and probable MCV/mid-level trough in nwly flow aloft. The most intense storms Sun will be capable of producing damaging downbursts given what will be a hot and deeply mixed BL with steep low-level lapse rates and large dewpoint depressions around 30C. Ridging, at the surface Mon-Tue and aloft for the rest of next week, will then limit precipitation chances.

AVIATION /12Z THURSDAY THROUGH MONDAY/

As of 604 AM Thursday...

Through 12Z Fri: VFR conditions will continue across central NC through the next 24 hours, as weak high pressure drifts through the region. Any cigs will be high thin clouds. Surface winds will be light and variable early this morning then from the SW at 10 kt later this morning and for this afternoon.

Looking beyond 06z Fri, VFR conditions will dominate through at least the first half of Fri. The chance for showers and storms, mainly afternoon through evening, will increase late Fri and persist into the weekend. More numerous showers and storms are expected Sun/Sun night as a cold front moves in from the N.

CLIMATE

Record High Temperatures:

July 1: KGSO: 99/2012 KRDU: 103/2012 KFAY: 104/1959

RAH WATCHES/WARNINGS/ADVISORIES

None.