textproduct: Raleigh

WHAT HAS CHANGED

As of 204 AM Sunday...

* Slight increase in areal coverage of a brief period of snow, mainly from the Triangle north and east. The best chance for a light accumulation of snow is along the NC/VA border

KEY MESSAGES

As of 204 AM Sunday...

1) Two rounds of precipitation today into tonight, with the second wave favoring a brief period changeover to snow in the far NE. Gusty winds this evening in the 30 to 45 mph range as temperatures crash below freezing overnight tonight.

2) Gusty winds continue into Monday in the 25-35 mph range as the work week starts out below normal.

3) Temperatures look to rise above normal on Wednesday, until a frontal system late week looks to drop temperatures closer to normal.

DISCUSSION

As of 204 AM Sunday...

KEY MESSAGE 1... Two rounds of precipitation today into tonight, with the second wave favoring a brief period changeover to snow in the far NE. Gusty winds this evening in the 30 to 45 mph range as temperatures crash below freezing overnight tonight.

Overview: A vigorous upper-level trough is on track to bring a plethora of weather to our region through tonight with precipitation, gusty winds, a return to winter, as well as ending as a little snow in some spots. A strong shortwave presently over the MS to OH valley region will intensify as it digs into SE VA later this afternoon and evening, before deepening off the Mid-Atlantic coast late tonight and early Mon. At the surface, low pressure will form just off the NC coast near the Outer Banks early today and rapidly deepen to sub 970-mb off the coast of NJ Mon morning.

Precipitation: Everything appears on track with the overall expected waves of rainfall. The first batch of rain is just starting to blossom over the region from the west in association with deep lift and upper-level divergence combined with isentropic ascent and above- normal moisture values. This first wave will last until about early to mid-morning, earliest to end over the western Piedmont and slowest over the northern Coastal Plain. As a dry slot punches in late this morning, we should see a period of dry weather, especially across the west, where even a few peeks of sun could break out near the Triad and southern Piedmont. The second wave of precipitation is expected from early afternoon until late evening, roughly 1 pm to 10 pm, as the upper-low digs along the NC/VA border and DPVA rapidly increases. The combination of steepening lapse rates with the impressive CAA up to mid-levels will fuel deep lift for a deformation band developing mainly from the eastern Piedmont and Sandhills into the Coastal Plain. This wrap-around precip band will favor a brief period of snow (see snow section below), mainly in the 5 pm to 10 pm period. Total precipitation amounts have not changed much. The 00z HREF agrees well with prior estimates, ranging from a few tenths of an inch of rain over the southern Piedmont, a quarter to half inch along and north of I-40, and three quarters of an inch to near 1 inch of precipitation over the northern Coastal Plain.

Snow: As the surface low deepens offshore and strong CAA builds in from the WNW, temperatures will crash from the middle 40s late today into the low to mid 30s tonight and wind chills in the lower 20s. This will feel quite cold compared to the recent mild stretch. As this cold air builds in, there will be a narrow 3 to 5 hr window (5 pm to 10 pm) when the thermal profiles will be cold enough to changeover to snow, mainly for areas from the Triangle and to the north and east, roughly from Raleigh to Roxboro and Wilson to Roanoke Rapids. This is a slight increase in areal coverage compared to the prior forecast, where probabilities for a dusting of snow ranges from near 30 percent in NE sections of the Triangle, to 50-80 percent in the far NE Piedmont and northern Coastal Plain. Within the 3 to 5 hr window, there is a 1-3 hr window (6-9 pm) when lift will maximize in the DGZ and when wet-bulb temps drop to the low 30s, for mainly the NE Piedmont to northern Coastal Plain, from Roxboro to Henderson to Norlina to Roanoke Rapids to Enfield, or Granville, Vance, Warren, and Halifax Counties. In these areas, the probability of a half inch of snow is roughly 30 to 50 percent. Probabilities drop off significantly for an inch of snow to 20-30 percent via the HREF. In summary, current snow estimates point to a dusting around the Triangle, to near a half inch along the aforementioned counties and near the VA border. We cannot rule out a worse-case scenario of an inch of snow in isolated spots of these areas, but confidence to issue an advisory was too low at this stage. We will continue to monitor. Any accumulations, given warm ground temperatures, would be on grassy/elevated surfaces, so impacts should be limited.

Winds: The strong CAA combined with deep boundary-layer mixing and strong winds of 30-45 kt in the 925-850 mb layer will support a period of brisk/gusty winds starting in the late afternoon across the west and early to mid-evening in the east. Gusts from the WNW will peak between 30-45 mph, with some infrequent gusts to 50 mph not out of the question. Winds should gradually weaken overnight, but stay elevated in the 15-30 mph range into early Mon. Confidence to issue a Wind Advisory was not high enough but will continue to monitor trends through the day. As to fire concerns, wet ground from expected rain and colder temps should limit fire danger, but if rain amounts are less over the southwest, could see a low-end IFD criteria being met there.

KEY MESSAGE 2... Gusty winds continue into Monday in the 25-35 mph range as the work week starts out below normal.

Gusty winds will continue Monday with a tight pressure gradient in place with the strong low off the Mid-Atlantic coast and 1038-mb high pressure over the Mid MS valley. The low-level winds range from 25-30 kt, which should favor surface wind gusts in the 25 to 35 mph range over most of central NC. This will make for a cold feel to start the work week with some upper teens for wind chills Mon morning. The work week will see highs starting out 10-14 degrees below normal in the 40s, with low temperatures coldest Mon night into Tue in the lower to middle 20s.

KEY MESSAGE 3... Temperatures look to rise above normal on Wednesday, until a frontal system late week looks to drop temperatures closer to normal.

Temperatures are expected to jump back above normal on Wednesday as surface high pressure shifts off the southeast coast, allowing surface winds to shift to southerly over central NC. This should allow maximum temperatures to jump back into the upper 50s to low 60s on Wednesday afternoon, increasing further on Thursday into the 60s everywhere. This is up to 10 degrees above normal for this time of year. The next chance for rain will be Thursday into Friday as a cold front will move through the region. Models are coming into better agreement in regards to the cold frontal passage Thursday night into Friday. Ensemble guidance continues to show overall low rainfall totals, with the 50th percentile of the GEFS showing less than 0.5 inch of rain over the region and the European ensemble showing between 0.25-0.75 inch of rain. The front looks to bring temperatures back near or slightly above normal on Friday as high pressure starts to build back in over the region.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

As of 120 AM Sunday...

Widespread MVFR cigs continue to overspread central NC with a degradation to IFR to perhaps LIFR is expected over the next several hours. Confidence in prevailing IFR cigs is lowest at the Triad terminals, but these sites have a higher probability of brief vsby reduction to 1-3SM. A northwest wind shift this morning will bring gusty winds and should rapidly improve flight categories to MVFR/VFR in the Triad, but cigs will be more stubborn to lift at RDU/FAY/RWI until this afternoon. As cigs clear to MVFR/VFR and the initial wave of light/moderate rain and embedded showers lift northeast of the forecast area, wind gusts are expected to increase to 25-35kts into the evening and early overnight hours. Mostly light rain will return to the eastern TAF sites this afternoon with a brief changeover to snow possible at RWI towards 00z Mon. All sites are expected to return to VFR by 05z Mon.

Outlook: Windy conditions will prevail with NW wind gusts increasing to 25-35 knots Monday morning through the evening hours. VFR conditions are expected through Wed night with a cold front and pre- frontal rain bringing potential for sub-VFR conditions on Thurs.

RAH WATCHES/WARNINGS/ADVISORIES

None.