textproduct: Raleigh

WHAT HAS CHANGED

As of 120 PM Saturday...

* Continued high confidence in areawide high rain chances Sun into Sun evening, although some timing refinements have been made including an earlier end to precip in the W (by midday Sun). Also expect a brief lull elsewhere for a few hours Sun before wraparound precip brings another round of precip to the N and E CWA Sun afternoon-evening. * No significant changes to the potential for a light snow coating in the far NE CWA and to the expected brisk and gusty winds Sun afternoon into Mon.

KEY MESSAGES

As of 210 PM Saturday...

1) After a relative lull this evening, rain spreads in overnight and continues through Sun morning in the W and through Sun night in the E. Brisk/gusty winds likely Sun/Sun night. Continued chance of a light dusting of wet snow in the far NE Sun evening.

2) After another cool day on Tuesday, above-normal temperatures will return on Wednesday and Thursday. Friday will turn slightly cooler behind a cold front that is likely to provide some light to moderate rain to the area.

DISCUSSION

As of 210 PM Saturday...

KEY MESSAGE 1... After a relative lull this evening, rain spreads in overnight and continues through Sun morning in the W and through Sun night in the E. Brisk/gusty winds likely Sun/Sun night. Continued chance of a light dusting of wet snow in the far NE Sun evening.

Overview: Confidence in the sfc and mid level pattern remains high. The deepening low and shortwave trough over the Great Lakes/Ohio Valley late today will dig into the Mid South tonight before taking on a negative tilt and intensifying further as it swings through VA/NC through Sun and moves off the Mid Atlantic coast Sun night. At the surface, the frontal zone will hold just to our S with weak high pressure nosing in from the NNE this evening, and one or two surface lows are expected to track along the front, moving from GA across srn SC through tonight before tracking NE along the coastal Carolinas early Sun and likely culminating in a bombing low off the N Outer Banks, VA Tidewater, and S Delmarva Sun night.

Lift/precip chances: Increasing and deepening forcing for ascent is likely starting late tonight and persisting into Sun, including strengthening mid level DPVA, high mid-level height falls of 250-300 m late tonight through Sun evening, and modest but focused upper divergence associated with two ideally juxtaposed jets, over the N Gulf states and off the Mid Atlantic coast. These mechanisms will deepen and intensify overall lift over central NC, and despite incoming PWs just 110-140% of normal, they still support widespread rain blossoming areawide starting after midnight tonight. Drier air aloft noted currently on WV imagery over E KS/OK is expected to swing into the W Carolinas Sun morning, yielding a downturn in pops over our W counties by midday, but the arrival of the strongest DPVA and resultant dynamic cooling attending peak upper divergence will support keeping high pops going through Sun afternoon and evening over the E CWA, with a second maximum pop from the Triangle to the N and E late Sun afternoon through Sun evening as the coastal surface low intensifies with wraparound moisture and mid level deformation spreading into the NE CWA. With generally good model consistency with amounts, confidence is high in total rainfall of one-half to two-thirds inch, with isolated higher totals possible.

Snow potential: With steepening lapse rates through the column corresponding to the deepening lift and resultant saturation in the mixed phase region aloft, the chance for a brief period of wet snow near the end of the precip event remains likely in the NE CWA, mainly very late Sun afternoon to late evening. Ensemble and high- res guidance suggests a low risk for impactful accumulating snow, likely due to the short duration, warm ground, and expected borderline surface wet bulb temps. HREF probabilities of a tenth of an inch of total accumulation (dusting) are fairly consistent with earlier LREF and other ensemble guidance, roughly 25%-50% NE of a line from Roxboro to Wilson, and this same area has a mostly sub-25% chance of a half inch or more of total snowfall. The most likely potential impacts in this area will be some briefly slick roads, particularly if a period of higher snow rates occurs. The latest WPC Prototype Snowband Probability Tracker does favor holding any substantial threat for banded snow to our N and NE as the coastal cyclone strengthens, suggesting that our overall impacts should be minor, but will continue to monitor model and observational trends.

Wind: As the low strengthens just off the coast of NE NC and SE VA and leads to a quickly tightening MSLP gradient, this along with increasing surface-based lapse rates fostering the potential mixing- down of stronger winds aloft is likely to result in brisk and gusty winds Sun/Sun night. The confidence in these stronger winds is high enough (and supported by new high-res guidance) such that the official forecast is a lean toward the higher NBM percentiles, and even this may not be strong enough if some ensemble members and deterministic models are correct in showing mean BL winds of 30-40 kts late Sun.-GIH

KEY MESSAGE 2... After another cool day on Tuesday, above-normal temperatures will return on Wednesday and Thursday. Friday will turn slightly cooler behind a cold front that is likely to provide some light to moderate rain to the area.

NW flow both at the surface and aloft between the departing cyclone over the Canadian Maritimes and high pressure over the northern Gulf will result in another cool day on Tuesday across central NC, albeit slightly modified, with highs in the mid-40s to 50. Lows will be in the lower-to-mid-30s. By Wednesday, the surface high will push east to become centered south of Bermuda, which will turn the low-level flow SW and aid a rebound in temperatures to back above normal. Forecast highs are upper-50s to lower-60s, with lower-60s to upper- 60s on Thursday. Lows will largely be in the 40s. Can't rule out some marginal fire weather concerns on Wednesday as SW winds gust up to 25-30 mph and RH values drop as low as ~30%.

A shortwave and associated surface low will track across the OH Valley and central Appalachians on Thursday, then the northern Mid- Atlantic and southern New England on Thursday night. The associated cold front will pass through central NC sometime late Thursday or early Friday. Some light rain is possible during the day Thursday, mainly in the north, with a band of heavier rain associated with the cold front likely to move through on Thursday night. While guidance has come into a bit better agreement compared to yesterday, there are still some timing differences, with the 12z ECMWF about 6-12 hours slower compared to the GFS. Regardless of which model, ensemble probabilities of rainfall exceeding an inch are virtually non-existent, with the GEFS mean more like a quarter to half inch and the ECMWF mean around a half to three quarters of an inch (highest NW, lowest SE). The system looks to be fast moving, and there will be a lack of instability. So heavy rain that puts a significant dent in the ongoing drought appears unlikely at this time. Temperatures will drop on Friday behind the front, but not by a lot, reaching values closer to normal.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

As of 1220 PM Saturday...

TAF period: Although all TAFs should begin as VFR this afternoon, all sites are expected to eventually drop to LIFR in low ceilings along with some visibility reductions. The general trend with the 18Z TAF package was to bring lower ceilings into the forecast more quickly, along with a slightly quicker arrival of rain at all sites overnight. While INT/GSO should lift to MVFR conditions after sunrise Sunday, RDU/RWI/FAY are expected to remain IFR/LIFR through the 18Z TAF period. As was mentioned in the 12Z discussion, still cannot rule out the potential for reduced ceilings to start immediately after precipitation comes to an end this afternoon, although that potential appears to be diminished. As low pressure deepens off the North Carolina coast tonight, the wind will back to the northwest with 15-20 kt gusts developing after sunrise.

Outlook: Rain will become more scattered at RWI Sunday afternoon/evening. Although flight conditions are expected to lift to VFR by 00Z Monday everywhere, the wind will continue to intensify Sunday afternoon and evening, with 20-30 kt gusts out of the northwest expected to continue through at least midnight, if not through the rest of the night. Expect another round of 20-30 kt wind gusts out of the northwest on Monday as well. Wind gusts should peak around 15 kt on Tuesday and 20 kt Wednesday/Thursday. A chance of rain will return to the forecast on Thursday.

RAH WATCHES/WARNINGS/ADVISORIES

None.