textproduct: Raleigh

SYNOPSIS

A wedge front will remain quasi-stationary over western NC this evening, then be overtaken by a stronger cold front that will move east of the Appalachians and across central NC tonight. Yet another, reinforcing cold front will move across the region on Sunday, followed by high pressure that will settle across the Southeast through Tuesday.

NEAR TERM /THROUGH TONIGHT/

As of 123 PM Saturday...

Regional mosaic radar this afternoon displayed a line of convection stemming from western NC southwest through the Deep South/Gulf states. As expected, convection has been most vigorous across AL and GA where lapse rates are steeper and CAPE is higher. MLCAPE of ~100- 250 J/kg may develop across our area this afternoon/evening, but generally speaking the 12Z high-res guidance continues to keep much of the vigorous/concerning convection well to our south. However, the LLJ is expected to strengthen considerably just above the sfc between ~18 and 00Z (strongest across the northern Piedmont). As such, any showers (and isolated storms) that move across the area later today could mix some of these stronger winds aloft to the sfc causing a low-end localized damaging wind gust threat. Areas across the Piedmont to northern Coastal Plain would have the best chance for any diabatically enhanced gusts later this afternoon and evening. Showers and isolated storms should largely move east of the area by early tonight, behind which a sfc cold front will clear through central NC through Sunday morning. Additional QPF from this system should be highest in the Triad where a few tenths to a half inch is expected. Further south and east (especially south of Raleigh) may only see a few hundreds of an inch through 12Z Sunday.

Warm sswly sfc flow with gusts of up to 25 to 35 mph ahead of the convection will persist this afternoon before subsiding a bit overnight (although sites further east may mix periodically with some stronger wnwly gusts even overnight). Overnight lows will remain mild in the mid 40s NW to mid 50s SE.

SHORT TERM /SUNDAY AND SUNDAY NIGHT/

As of 110 PM Saturday...

* Windy with peak wind gusts of 35-40 mph possible

A vigorous mid/upper level trough will swing through the region on Sunday. The lead/effective cold front and associated weakening shower band will exit to the east around daybreak, giving way to west-east clearing through the morning. A secondary cold front is then slated to cross central NC during the afternoon.

Steepening low-level lapse rates will facilitate deep vertical mixing, tapping into a 30-35kt mean boundary layer flow(~40 at the top of mixed layer). This will result in frequent NWLY wind gusts of 30 to 35 mph area-wide Sunday afternoon. Higher-end, more localized gusts of 40 to 45 mph possible. These conditions will also support significant fire potential as well (See Fire Wx section below).

Temperatures will follow a non-diurnal curve, with daytime highs likely occurring in the late morning(west) to early afternoon(east), just prior to the arrival of the secondary cold frontal passage. Highs ranging from mid/upper 40s NW to lower 60s SE.

The pressure gradient will relax Sunday night as sfc high builds in from the west. Winds will diminish overnight with steady CAA. Overnight lows in the 25-30 F range, with some lowers 20s possible in outlying rural areas.

LONG TERM /MONDAY THROUGH SATURDAY/

As of 1250 PM Saturday...

* Near to above normal temperatures Mon-Wed, transitioning to below normal through the end of the week.

* Highest precipitation chances Wed and Thu, mainly liquid with a slight chance for a brief transition to snow as it moves out.

Outlook: Aloft, a broad longwave trough will generally sit over the region Mon/Mon night, with a couple perturbations in the flow as weak s/w disturbances move across. Meanwhile, a closed low over the Baja will move slowly ewd across nrn Mexico. Tue/Tue night, a potent nrn stream s/w will eject sewd across the upper MS Valley and Great Lakes, with a secondary s/w following behind it and amplifying the longwave trough south across the Plains. The srn stream low will open into a trough over the srn Plains and get picked up by the longwave trough. The longwave trough will shift ewd to over the eastern third of the CONUS, while the embedded shortwaves swing through it and across region Wed and Thu. Another nrn stream s/w will drop ssewd out of cntl Canada on Thu potentially closing off as it moves across the upper MS Valley and into the Great Lakes, while a secondary s/w following behind it further amplifies the longwave trough, shifting the axis wwd through Sat. At the surface, high pressure will ridge newd into the area as it settles over the Deep South Mon/Mon night. The high will weaken on Tue, with the ridge shifting south as a trough strengthens over the area ahead of an approaching frontal system. There are still some major differences amongst the medium-range guidance wrt how the system will evolve and if/were any subsequent areas of low pressure may develop along and/or ahead of the front as it moves into the region Wed/Wed night. Cold high pressure should build in behind the front and exit ahead of the next approaching system, however details remain uncertain. The result is continued forecast uncertainty from Wed onward.

Temperatures: Near normal temperatures on Mon will moderate to above normal for Tue and Wed ahead of the approaching front. In the wake of the front, temperatures will drop to below normal and likely remain there through the end of the week.

Weather: The best chance for precipitation will be Wed through Thu night with the passage of a potent s/w aloft and ahead of/with the front (and possible low) at the surface. Keep in mind the forecast uncertainty, as that also applies to P-types. P-type will depend on the temperature and the timing of the precipitation. While most of the precipitation should fall as rain, there is a slight chance for some snow to mix in early Thu morning and after sunset Thu as the cold air chases the precip out. Otherwise, the forecast is largely dry through the week.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

As of 725 PM Saturday...

Initially VFR conditions and occasionally gusty sswly surface winds may briefly become MVFR with the passage of a band of showers and mainly MVFR ceilings, both along a cold front that will move across cntl NC tonight. That rain band will likely increase in coverage and intensity as it moves across e-cntl and ern NC, including at RWI and FAY, late tonight-early Sunday, as a vigorous mid/upr-level trough catches up to it and enhances lift. Veering/shifting surface winds to wly/nwly will also result with the passage of the front.

The MVFR rain and cloud band should move fully east of cntl NC by 12Z Sun, after which time very strong and gusty wnwly surface winds will prevail with daytime heating through the day Sun. A band of 6-8 thousand ft ceilings and widely scattered, high-based showers may accompany a reinforcing cold front across especially the Piedmont of NC Sun afternoon. The weak/shallow character of the showers, and their high bases atop a very deep and dry boundary and sub-cloud layer, suggests most or all of the associated precipitation will sublimate/evaporate before reaching the surface. So while no visibility restrictions are expected, the localized cooling from sublimation/evaporation may locally and briefly enhance surface wind gusts, up to 35-40 kts.

Outlook: VFR, at least until a strong low pressure system may impact the Middle Atlantic region centered around the day Thu.

FIRE WEATHER

As of 130 PM Saturday...

* Significant Fire Risk across central and eastern portions of Central NC Sunday afternoon.

Significant Fire Risk is expected to develop across central and eastern portions of NC Sunday afternoon. Although a lead cold front will traverse the region late this evening and tonight, associated showers are expected to weaken and largely dissipate as the move east across central and eastern NC. This will leave the area will negligible rainfall and fail to recover dead fuel moisture levels.

In the wake of the lead front and in concert with a secondary cold front, steepening low-level lapse rates will promote efficient vertical mixing. Dewpoints will crash into the teens and 20s, causing RH values to bottom out between 20 to 25 percent Sunday afternoon. When combined with frequent NWLY wind gusts of 25 to 30 kts, conditions will become conducive to rapid fire spread and difficult containment.

CLIMATE

Record High Minimum Temperatures:

January 10: KFAY: 59/1937

RAH WATCHES/WARNINGS/ADVISORIES

None.