textproduct: Raleigh

WHAT HAS CHANGED

As of 350 AM Saturday....

Minor adjustments to the snowfall totals, but the forecast remains on track for portions of central North Carolina to see a major winter storm and perhaps even brief blizzard conditions.

KEY MESSAGES

As of 350 AM Saturday....

1) A Winter Storm Warning is in effect for all of central North Carolina until Sunday morning. Widespread snow accumulations of 4-8 inches, with areas of 10+ inches possible, and blowing/drifting snow resulting in moderate to major impacts to travel today into Sunday morning.

2) A prolonged Arctic air mass in place will result in well below normal temperatures across central NC from today through much of next week.

3) Precip chances return by the middle of the week. Timing of precip, and precip type, remain in question

DISCUSSION

As of 350 AM Saturday....

KEY MESSAGE 1... A Winter Storm Warning is in effect for all of central North Carolina until Sunday morning. Widespread snow accumulations of 4-8 inches, with areas of 10+ inches possible, and blowing/drifting snow resulting in moderate to major impacts to travel today into Sunday morning.

A major winter storm is beginning to take shape early this morning with conditions expected to deteriorate through the morning hours in the western Piedmont and elsewhere this afternoon into the overnight hours. Regional radar mosaic imagery and SPC mesoanalysis highlight two areas of ongoing snowfall, which will be described separately below.

The first is occurring over southwest VA into the NC Piedmont and foothills driven by weak H850 WAA and strengthening FGEN as the mid/upper level trough approaches, which is currently pivoting across the Mid-Mississippi and Ohio Valleys. This area is expected to remain mostly light but fill in through daybreak as the H850 band slowly collapses southward and the mid/upper trough begins to close off and transition to neutrally-tilted by 18z. This should result in widespread 0.1" to around 0.3" of liquid equivalent across the western Piedmont, which at roughly 15:1 snow-liquid ratios (SLR), will equate to an area of 1.5 to roughly 4 inches through the morning hours. Areas in the eastern Piedmont and western Sandhills may not receive much snowfall before 18z, but this is likely to change through the afternoon and result in widespread 3-7 inches with locally higher amounts of up to 10 inches. Some areas of the eastern Piedmont may see a QPF minimum relative to surrounding areas. The general consensus within 50th percentile ensemble guidance suggests 0.25 of liquid equivalent is still favored in this area and translates to around 4 inches.

The second is a well developed area on regional radar across the eastern Sandhills and southern/central Coastal Plain and is being driven by a strengthening H925 FGEN band. This area is surprisingly not being resolved well within the hi-res guidance, but rather the global and regional models; such as the GFS, Canadian reg/nh, and NAM 12km. These models suggest liquid equivalent of 0.3 to 0.6 will be possible within this area by 18z and would produce 3 to as much as 6 inches (with SLR of closer to 11:1 at this time) before the afternoon hours. If observational trends hold and the global models do handle its evolution well, then as the mid/upper trough negatively tilts and brings significant synoptic forcing overtop this band, it is reasonably possible that 0.75 to 1 inch of liquid equivalent falls and results in a swath of 10-15 inches of snow. This swath would likely fall within a larger area of 4-8 inches in the Coastal Plain into the eastern Sandhills.

Blowing and drifting snow will be possible throughout the day as wind gusts increase to around 25 mph, but will be increasingly likely after 00z, especially in the Coastal Plain and eastern Sandhills, and to a lesser extent the eastern Piedmont. At this time, the surface low off the coast is expected to rapidly deepen to sub-990 by 06z and sub-980 by 12z Sun and produce the strongest wind gusts of 30 to 40 mph and infrequent gusts up to 45 mph. These winds combined with falling/blowing snow may result in brief blizzard conditions in the Coastal Plain into the eastern Sandhills, which would drop visibilities to 1/4 mile or less at times.

When all is said and done as precipitation moves out of the area Sun morning, storm total amounts should range from 3-7 inches in the Piedmont and 4-9 inches in the Coastal Plain and eastern Sandhills. This will result in moderate to major travel impacts, even in the absence of the higher end amounts. Major to potentially extreme impacts to travel and infrastructure should be expected where the significant snow amounts of 10-12+ inches occur. Travel will become dangerous or even impossible in these locations Sat evening into Sun morning.

KEY MESSAGE 2... A prolonged Arctic air mass in place will result in well below normal temperatures across central NC from today through much of next week.

Cold weather headlines remain in place for today through mid-morning Sunday. A Cold Weather Advisory remains in place through 1 AM Sunday, followed by an Extreme Cold Warning from 1 AM Sunday to 10 AM Sunday morning. Wind chills most of today will hover in the single digits with highs only in the low to mid 20s with falling temps through the day and winds gusting to 20 to 30 mph. Tonight, colder air builds in and the pressure gradient strengthens. Wind gusts out of the north will increase with speeds of 30 to 35 mph, although some infrequent gusts to 40 mph over the Coastal Plain along/east of I-95 are also possible. With lows projected to be in the lower teens most areas, wind chills will range from near zero in the south to 5 below in the north. HREF probabilities for wind chills at or below -5 degF are over 50-percent along/north of US-64. The Extreme Cold Warning will be allowed to expire mid-morning Sunday as temperatures rise but still remain cold for highs Sun in the upper 20s to low 30s.

The Arctic air mass will remain entrenched over the region into much of next week. With anticipated snow cover in place, lows Sun night could range from the single digits to lower teens, where another Cold Advisory may again be needed. Highs will remain below normal much of next week, although we do see a somewhat moderating trend for highs Tue and Wed with highs in the upper 30s to mid 40s before falling back Thu in the mid 30s to low 40s with our potential next weather system.

KEY MESSAGE 3... Precip chances return by the middle of the week. Timing of precip and precip type remain in question

There is an increasing signal among the global ensembles that a weak system will move through the Mid Atlantic by the middle of next week. Unfortunately there remains some significant differences among the Canadian/GFS/EC ensemble clusters with respect to when precip will move through the area and exactly what form that precip will take. The EC based clusters tend to bring the system through earlier than other solutions with a rain/snow mix on Wednesday, with some suggestions that the cold air may chase the moisture out of the area Wednesday night. The GFS and its family of ensembles are a bit slower with the arrival of the precip suggesting the potential for rain/snow at the onset on Wednesday, changing to rain, then changing back to snow on the back end as cold air returns on Thursday. Thus confidence in this period is high for precip but low for exact timing of onset/ending and finer details of p-type. Will maintain a middle of the road rain/snow mix forecast for Wednesday into Thursday and tighten up the timing a bit once a clearer scenario emerges.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

As of 700 AM Saturday...

Snow and flight restrictions, still spatially separate over the nw Piedmont (INT/GSO) and in the Coastal Plain (RWI and just east of FAY), will continue to blossom and fill in throughout cntl NC today, then gradually end from west to east and return to VFR overnight. The most-prolonged and heaviest, banded snow will probably result at FAY and RWI this evening, when blizzard conditions in snow and blowing snow will be possible for a few hours this evening. Those winds, nely ones, will also strengthen and become increasingly gusty this morning and more-markedly especially at FAY and RWI this evening, while backing to nly, as coastal low pressure explosively deepens off the NC coast.

Outlook: Skies will clear and favor VFR conditions Sun and be accompanied by lingering, nwly gustiness through sunset Sun. The next chance of flight restrictions will be at the end of the forecast period or just beyond, as the next frontal system impacts the region.

CLIMATE

Record Low Temperatures:

January 31: KGSO: 3/1966, KRDU: 3/1966, KFAY: 9/1934 February 1: KGSO:-4/1936, KRDU: 8/1981, KFAY: 1/1936

Record Low Maximum Temperatures:

February 1: KGSO: 27/1971, KRDU: 28/1900, KFAY: 32/1981 February 2: KGSO: 30/1951, KRDU: 31/1994, KFAY: 31/1948 February 3: KGSO: 23/1996, KRDU: 24/1996, KFAY: 30/1961

RAH WATCHES/WARNINGS/ADVISORIES

Winter Storm Warning until 7 AM EST Sunday for NCZ007>010- 021>026-038>041-073>076-083-084. Cold Weather Advisory until 1 AM EST Sunday for NCZ007>011- 021>028-038>043-073>078-083>086-088-089. Extreme Cold Warning from 1 AM to 10 AM EST Sunday for NCZ007>011-021>028-038>043-073>078-083>086-088-089. Winter Storm Warning until 1 PM EST Sunday for NCZ011-027-028- 042-043-077-078-085-086-088-089.