textproduct: Raleigh

SYNOPSIS

A weak frontal zone will hold over the Carolinas through tonight. A strong Arctic cold front over the Ohio Valley will move southeast through the area Sunday. Frigid high pressure will build over the region Monday, then move to our south Monday night and Tuesday.

NEAR TERM /THROUGH TONIGHT/

As of 145 PM Saturday...

* Quiet and seasonable through this evening, then a chance of light rain late tonight across the southeast.

The latest surface analysis reveals an increasingly diffuse frontal zone across the Carolinas, with a dissipating theta-e gradient and a nearly uniform light surface flow over the CWA from the S and SW. Apart from a shield of orographically enhanced cirrus in our NW, insolation has been abundant today and should remain so for the rest of the afternoon, and this, along with milder Atlantic-source air working into the CWA, will support highs in the mid 50s to lower 60s.

The much-anticipated Arctic cold front is currently analyzed moving into the Ohio Valley and will approach NC tonight, as prominent mid level shortwave troughing swings through the Great Lakes and Ohio Valley toward the Appalachians with 100-200 m height falls. Above normal PWs will spread into central NC overnight, attending robust upper divergence in the right entrance region of the upper jet streak, although the weak surface ridging stretching across coastal SC/GA and Gulf coast will keep low level moisture return limited. While a prefrontal trough is likely to shift through the forecast area and to our SE prior to daybreak, the coldest air associated with the Arctic front should hold up just W of the higher terrain through tonight. That said, the uptick in MSLP gradient behind the prefrontal trough will likely produce some northwesterly gusts in the NW CWA in the predawn hours. Expect chance pops to spread into our far SW CWA and across the SE half of the CWA after 2 AM, but amounts will be quite small. Skies should trend to mostly cloudy, esp over the S and E, with lows 32-37 NW and 38-44 SE. -GIH

SHORT TERM /SUNDAY AND SUNDAY NIGHT/

As of 220 PM Saturday...

* A Cold Weather Advisory has been issued for all of central NC from Sun evening to mid morning Mon, for wind chills as low as 3F-10F. * Sustained winds of 15-25 mph and gusts up to 25-35 mph expected Sun morning through Sun evening. * Good chance of rain mainly over the S and E Sun morning through mid afternoon, perhaps ending with a brief rain/snow mix in the NE CWA.

The Arctic cold front is still expected to sweep SE through central NC through early afternoon Sun. Moisture depth ahead of the front is still in question, but should be sufficient from just off the ground up toward the mixed phase region for good chance to likely pops, mainly from the Triangle to the S and E, highest E in the Coastal Plain E of I-95 where better low level moisture will reside and where PWs are projected to reach 150% of normal. Overall amounts will continue to be low, given less moisture near the surface and above 700 mb, so totals should be around a tenth of an inch or less. Thermal profiles do support the potential for a brief wintry mix or changeover to light snow before ending, as the cold air rushes in and temps and dewpoints plummet. But this should be short-lived as the column dries out and we lose moisture both above -12C and in the lowest 150 mb. We can't rule out a quick dusting in the far NE CWA in places like Warrenton, Roanoke Rapids, and Tarboro, but this risk looks too low to include at this time, as the cold air may be largely chasing the moisture. Morning temps in the mid 30s to near 50 NW to SE should drop to the mid 20s to mid 30s by sunset, with quickly clearing skies as NW/downslope flow takes over. Winds should be strongest from midday through much of the afternoon, as strong CAA and incoming dense air combines with deepening mixing, yielding winds of 15-25 mph and gusts as high as 25-35 mph. Wind chills will plunge through the day, reaching the single digits in many areas by early evening, supporting the cold weather advisory starting at 6 PM and running through Mon mid morning. Wind speeds and gusts are a bit under thresholds for a wind advisory, but we'll continue to message that outdoor objects including holiday decorations could be tossed about. Models are consistent and in good agreement on winds decreasing sufficiently after sunset to allow a steep drop in air temps down to lows in the teens areawide, producing wind chills as low as 3 to 10 degrees above zero toward daybreak Mon. -GIH

LONG TERM /MONDAY THROUGH SATURDAY/

As of 1210 PM Saturday...

* Continued cold Tues morning, but warming trend expected Tues through Thurs night.

* Forecast confidence remains low for Thurs into Fri morning with our next precipitation chances.

A highly anomalous ~1040mb area of surface high pressure will be positioned over the southern/central Appalachians Mon morning will broaden as it spills across the Southeast and southern Mid-Atlantic into Tues morning. A weak pressure gradient and relatively favorable surface high location Mon night into Tues morning should support favorable conditions for excellent radiational cooling, especially with Mon afternoon dew points still in the single digits. However, a pocket of mid-upper level moisture shifting through the Ohio Valley Mon night will likely become orographically enhanced as it progresses east of the Appalachians and over the Mid-Atlantic after midnight. The thickness and areal extent will likely drive the temperatures into Tues morning. Latest forecast of mostly low 20s to upper teens remains in line with general consensus among the latest statistical guidance, but if the cloud cover is thinner than anticipated, then mostly mid/upper teens would be possible with urban areas around 20 degrees.

A compact shortwave shifting across the Great Lakes and Northeast Thurs into Fri will be embedded within predominantly zonal flow aloft and will drive our next precipitation chances. Amplitude and speed of this wave remains highly uncertain with this wave with an added complication of southern stream influence and/or phasing with the northern stream wave. Forcing for ascent is quite weak as the best H5 height falls, from an ensemble mean approach, will likely occur north of central NC over the northern Mid-Atlantic and Northeast with weakening 700 and 850mb WAA spreading into the Mid- Atlantic. This pattern will likely not support any significant/hazardous precipitation with forecast rainfall amounts of less than or equal to 0.10".

It is worth noting an alternative scenario which is primarily being driven by the ECMWF and its ensemble members. This forecast system suggests a more amplified shortwave and perhaps a brief phasing with the southern stream jet over the eastern CONUS. This would result in stronger horizontal WAA and development of weak MUCAPE ahead of the approaching cold front and support the potential for higher rainfall totals. This solution is considered an outlier among 00z guidance, but worth monitoring for the threat of stronger wind gusts and moderate to heavy rainfall in addition to lightning.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

As of 730 PM Saturday...

The next several hours will remain VFR. Overnight, LLWS looks likely at RDU/FAY/RWI as a 40-45kt southwesterly low level jet develops over the region ahead of a cold frontal passage. The cold front will bring the chance for strong winds, rain, and sub-VFR ceilings. Winds will veer from southwesterly to northwesterly overnight, with strong gusts starting around sunrise. Gusts are most likely between 20- 25kts, with the potential for infrequent gusts up to 30-35kts. Gusts should last through the day, not weakening until after the 24 hour TAF period. Additionally, light rain looks likely to impact RDU/FAY/RWI in the early morning hours with the passage of the cold front. MVFR ceilings also look briefly possible at RDU/FAY/RWI with the front, with the best chance at FAY.

Outlook: VFR conditions appear likely through Thursday.

RAH WATCHES/WARNINGS/ADVISORIES

Cold Weather Advisory from 6 PM Sunday to 9 AM EST Monday for NCZ007>011-021>028-038>043-073>078-083>086-088-089.