textproduct: Raleigh

WHAT HAS CHANGED

* Forecast confidence for rain continues to increase for Fri night- Sat, though considerable uncertainty in rainfall amounts and duration remain.

KEY MESSAGES

As of 300 AM Thursday...

1) Record heat will continue through Friday.

2) A strong cold front will sweep across central NC Friday evening, with a significant cooldown for the weekend. There is still some potential for patchy frost, but forecast uncertainty has increased.

DISCUSSION

As of 300 AM Thursday...

KEY MESSAGE 1... Record heat will continue through Friday.

An anomalously strong sub-tropical ridge centered in 00Z/15th upr air data over the TN Valley, with standardized 500 mb height anomalies ~2 sigma, will progress ewd and off the South Atlantic coast through 12Z Fri. On the nrn periphery of that ridge, series of MCVs from dissipated or weakening convection from the DelMarVa to nrn Middle TN will progress generally ewd and across the srn Middle Atlantic today. Deep layer flow will then strengthen and back to swly ahead of an intense, positively-tilted, full latitude, and increasingly-phased trough --one comprised of a srn stream cyclone now over CO and a vigorous nrn stream shortwave trough over MB-- forecast to stretch from wrn QC to the lwr MS Valley by 00Z Sat.

At the surface, an outflow boundary/wind shift across the Virginias and lwr OH Valley, related to the aforementioned dissipated or weakening convection there, will drift ssewd and probably across the nrn Piedmont and nrn Coastal Plain of NC by late this morning- midday. A synoptic front lags the outflow and was analyzed at 07Z from n-cntl DE through nrn VA and cntl WV. While this boundary will also move generally swd and in backdoor fashion across VA this morning, it will likely not move into the ne Piedmont and nrn Coastal Plain of NC until later this afternoon and evening, where it will briefly stall. The front will then retreat nwd later tonight and Fri, as mass response strengthens ahead of the intense trough aloft and a related surface cyclone forecast to deepen considerably while tracking across the Great Lakes and Northeast on Fri.

Temperatures today will be generally persistence ones equatorward of the approaching synoptic front, which will offer cooling throughout VA and only into the far ne Piedmont and nrn Coastal Plain of NC.

While heights throughout the column will fall ahead of the approaching trough aloft on Fri, related cooling will be limited over cntl NC until late in the day and more-so Fri night. As such, temperatures on Fri will again be near persistence ones, to perhaps a couple of degrees lower than previous days' warm sector ones. A gusty swly surface wind may take a little edge off the heat while also boosting the temperature at RDU to, or within a degree of, the latest 90 degree day and probably the third consecutive in this stretch, provided the backdoor front holds north of RDU as expected today.

KEY MESSAGE 2... A strong cold front will sweep across central NC Friday evening, with a significant cooldown for the weekend. There is still some potential for patchy frost, but forecast uncertainty has increased.

Aloft, a potent nrn stream s/w will drop into the upper MS Valley and track sewd across the Great Lakes Thu and Fri, deepening the trough over the ern US as it interacts with another s/w ejecting enewd from the cntl Rockies to the Great Lakes Thu/Thu night. The positively tilted trough will continue to amplify as it moves ewd across the eastern US and offshore over the weekend. Model spread has increased from Sat onward, with some more recent guidance showing a low developing within the trough over the Carolinas Sat/Sat night, possibly lingering over the region for awhile, slowing the troughs ewd progression, while others develop a low offshore. At the surface, an area of low pressure lifting newd across the mid-MS and OH Valley on Thu will deepen as it continues across the Great Lakes and Northeast US Thu night/Fri. The trailing cold front will move across central NC late Fri evening into Fri night, currently progged to be moving into the nw Piedmont around 00Z Sat. A ~1037 mb Canadian high centered over the s-cntl Plains on Sat will build into the region in the wake of the front as it tracks newd across the mid-MS and OH Valley regions on Sat. There is some uncertainty beyond Sat, with some models showing a coastal low developing as along the front as it moves offshore, while others show a more progressive front continue ewd over the Atlantic. The latter solution would allow the high to settle over the mid- Atlantic, while the former would take the high enewd across the nrn mid-Atlantic/Northeast US on Sun.

The varying solutions noted above will impact numerous weather parameters (temps, winds, precip, etc.), resulting in a low- confidence forecast Sat night onward.

The chance for rain continues to increase, as does the duration, coverage, and uncertainty. Forecast amounts are still somewhat light, with generally a quarter of an inch or less expected Fri night through Sat night. The low-level jet is expected to strengthen over the area Fri eve, with 25-35 kts at 925mb. The pressure gradient will also be quite strong as a ~1037 mb high builds ewd. Expect gusty winds with and behind the front Fri eve through Sat.

Temperatures should fall about 25-30 degrees from Friday aft to Sat morning. By Saturday, highs will be similar to the lows from Thu night (generally low to mid 60s). Keeping in mind the forecast uncertainty noted above, lows may drop another 10-15 degrees or so Sat night, as cold air advects into the area. For now expect lows to range from upper 30s NW to mid/upr 40s SE both Sat night and Sun night. However, if the more progressive solutions verify there could be some mid 30s lows over portions of the Piedmont both nights, possibly resulting in some patchy frost in the usual cooler, sheltered areas.

AVIATION /11Z THURSDAY THROUGH MONDAY/

As of 655 AM Thursday...

Light swly winds will persist ahead of an outflow boundary/wind shift that may shift surface winds to light nely/ely at Piedmont sites and RWI by late morning. That boundary will be followed by a backdoor cold front that will settle into the far ne Piedmont and nrn Coastal Plain of NC late this afternoon or this evening. IFR- MVFR restrictions are likely to develop behind that front, including at RWI, late tonight-Fri morning. While the front and post-frontal ceilings are likely to hold just to the north of Piedmont sites, by perhaps 10-30 miles, a slight swwd shift of the location of the boundary would result in an increasing likelihood for flight restrictions at Piedmont sites tonight as well.

Outlook: Gusty swly surface winds will develop ahead of a strong cold front on Fri, followed by a period of strong and gusty nwly surface winds with the passage of that front Fri night. There is a chance that the front will be accompanied by a shallow, broken line of convection (devoid of lightning) as it moves across cntl NC Fri night, followed by an area of post-frontal, stratiform rain that may linger into the day Sat.

CLIMATE

Record High Temperatures:

October 15: KGSO: 87/1985 KRDU: 88/1985 KFAY: 91/1931

October 16: KGSO: 85/1953 KRDU: 86/1925 KFAY: 90/1925

Record High Minimum Temperatures:

October 15: KGSO: 63/1985 KRDU: 66/1942 KFAY: 67/1928

October 16: KGSO: 66/1947

Latest 90 F days:

GSO: 10/12/1904 RDU: 10/10/1907 FAY: 10/26/1940

RAH WATCHES/WARNINGS/ADVISORIES

None.