textproduct: Raleigh

SYNOPSIS

A cold front will move across the region early tonight. Another area of cold high pressure will build briefly overhead Monday, then offshore ahead of coastal low pressure that will develop and rapidly strengthen while tracking along and offshore the South and Middle Atlantic coasts Monday night and Tuesday.

NEAR TERM /THROUGH TONIGHT/

As of 310 PM Sunday...

Water vapor imagery this afternoon depicted a strong short-wave ejecting east over the Great Lakes region. At the sfc, latest obs depict a sfc cold front moving east across central TN/KY. Ahead of this front, the MIMIC-TPW satellite depicted weak moisture advection into the Deep South/Southeast. With time, deeper moisture should stream into the southeast and into central NC, but any stronger upper forcing will remain well to our north. As such, expect just continued light rain to stream west to east across our area through the early overnight period. The actual cold front will pass through central NC late tonight through early Monday morning, with a brief period of 15 to 25 mph gusts possible between ~06 and 13Z for locations outside the northwest Piedmont where CAD will keep things stable. Additionally, a brief period of patchy dense fog will be possible, primarily across the southern/western Piedmont ahead of the front between ~03 and 8Z. Overnight lows in the upper 20s/lower 30s are expected.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

As of 310 PM Sunday...

Monday will serve as a transitory day, as central NC remains wedged between the departing system off the eastern seaboard, and a digging upper trough across central US. Expect cool nely sfc flow via a sfc high centered over New England with highs reaching the mid 40s to around 50 in the south.

By late Monday night, the potent upper trough will begin to lift across the TN Valley/eastern seaboard. Associated mid-level height falls and anomalous moisture will spill across the Deep South/southeast. At the sfc, a low is forecast to develop over the Gulf and ride north along the I-95 corridor through early to mid Tuesday afternoon.

These sfc and upper features, along with a deep pool of moisture will promote a good soaking of rain for us with amounts of 1 to 1.5 inches widely. Most of the guidance is in good agreement riding the sfc low through our Coastal Plain, keeping the warm sector along the coast/to our south. However, if this tracks slower and further west, there could be a brief window of high shear/low CAPE overlap in our far southeast counties. Hodographs are large and curved, which, in this scenario could promote storm organization. Think the chances are limited as of now (better chances down in Georgia), but we'll monitor trends as we get into high-res guidance range.

The sfc low and associated rain/moisture will quickly skirt offshore by late Tuesday afternoon, behind which nwly flow aloft and drying will persist through 12Z Wednesday. Overnight lows in the mid to upper 20s are expected behind the system Tuesday night with some gusty nwly winds of 20+ mph possible through Wednesday morning.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

As of 350 PM Sunday...

Chilly surface high pressure will build in from the west on Wednesday, weakening on Thursday. Looking aloft, WSW flow will largely prevail, with strong mid-level height rises and subsidence on Wednesday behind the departing shortwave over the Canadian Maritimes. This will bring cool dry weather on Wednesday and Thursday, with sunny skies on Wednesday giving way to increasing clouds on Thursday/Thursday night. Wednesday's forecast highs are mid-40s to 50 with lows Wednesday night in the mid-20s to 30. Thursday will be a bit milder with highs in the 50s, ahead of a dry cold front that moves through in the afternoon. Lows Thursday night will be in the mid-20s to lower-30s.

Meanwhile a second stronger Arctic high will move from the Northern Plains to the Upper MS and OH Valleys. This ~1030 mb high will reach the northern Mid-Atlantic and New England on Friday, building down the Eastern Seaboard. The next shortwave will also move from the Southern Plains into the Eastern US, spreading moisture into central NC that overruns the cold high pressure wedge. Both the 12z GFS and ECMWF depict a coastal low that moves NE from the northern Gulf Coast early Friday to along the coast of the Carolinas on Friday night. All of this results in fairly high confidence for precipitation over central NC on Friday and Saturday, and ensemble means depict half an inch to an inch of QPF. The exact timing and length of the event are unclear, particularly among the ensemble members which differ on the start time. Furthermore, the ECMWF depicts a slower moving and deeper shortwave that provides additional forcing for precipitation into Saturday, while the GFS and CMC dry us out by then. POPs increase to chance on Friday, highest (likely to categorical) on Friday night, decreasing to chance again on Saturday and Saturday night.

Given the cold high building down from the north, some frozen precipitation will be possible over the Piedmont at the start, but confidence is very low on details this far out. With southerly flow aloft quickly advecting in warmer air and a wedge of cold air remaining near the surface, this would suggest more of an ice threat vs snow. One limiting factor is the progressive nature of the pattern, allowing for the high to move east into the Atlantic. So if there is any frozen precipitation, an eventual changeover to plain rain everywhere is likely. The deterministic GFS is especially cold and less transient with the high, but it is an outlier even compared to its own ensembles. Even still, ECMWF and GFS deterministic and ensemble guidance have trended a bit colder overall, so it certainly warrants watching. Given the spread in guidance and that this is Days 6-7, confidence is low in precipitation type and is certainly subject to change. Continue to follow the forecast for the latest updates.

Temperature forecast confidence decreases substantially by Friday as the model spread increases. A lot will depend on the timing and placement of the cold high to the north, as well as the coastal low. But Friday looks to be a very chilly day, even if it is just cold rain, with highs in the 30s and 40s. Forecast highs this weekend range from upper-40s to upper-50s. Lows will generally be in the 30s.

AVIATION /00Z MONDAY THROUGH FRIDAY/

As of 640 PM Sunday...

24 hour TAF period: A line of rain is moving east across the area, oriented from northeast to southwest. While there have been some limited IFR ceiling observations at some sites, have not seen enough widespread IFR to support keeping this in TEMPO groups, although the chance for IFR ceilings is non-zero. The rain has remained light enough that there is no concern about visibility restrictions. As the line of showers moves through, ceilings will lift and the wind will veer from west to northwest. While the 18Z TAFs had prevailing gusts at all sites, the temperature profiles do not look favorably for an extended period of gusts, and switched the gusts at INT/GSO/RDU to a TEMPO group. Farther east, where profiles are more favorable for a longer period of gusts, kept a prevailing mention of gusts at FAY/RWI and even included a TEMPO group of higher gusts at FAY. The gust values have been coming up, and think that isolated gusts up to 30 kt may be possible at RDU/FAY/RWI. Skies should become mostly clear overnight, although did keep a mention of a few high clouds continuing through Monday.

Outlook: Another storm system will bring widespread rain and IFR or lower conditions late Mon night through Tue. VFR returns Wed and Thu under high pressure. Another late-week system may bring rain/showers late Fri-Sat.

RAH WATCHES/WARNINGS/ADVISORIES

None.