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WHAT HAS CHANGED

As of 305 AM Thursday...

A Winter Storm Watch has been issued for all of central North Carolina from 4 PM Friday until Sunday afternoon.

KEY MESSAGES

As of 305 AM Thursday...

1) A Winter Storm Watch has been issued for all of central NC due to high confidence in at least light snow accumulations. The potential exists, but not guaranteed, for areas of significant snowfall to occur anywhere from the Carolinas into the Mid- Atlantic.

2) A prolonged Arctic air mass will result in well below normal temperatures across central NC from Thursday through at least the middle of next week.

DISCUSSION

As of 305 AM Thursday...

KEY MESSAGE 1... A Winter Storm Watch has been issued for all of central NC due to high confidence in at least light snow accumulations. The potential exists, but not guarantied, for areas of significant snowfall to occur anywhere from the Carolinas into the Mid-Atlantic.

A unseasonably strong mid/upper level low is expected to develop just south and west of central NC and bring widespread snowfall accumulations which will likely result in moderate to major impacts to the area. At the surface, cyclogenesis is likely just off the Southeast coast, where a weaker but still prevalent baroclinic zone is forecast over the Gulf Stream. The primary front is expected to be still draped across the Bahamas, setting up a probable instant occlusion low surface pattern. The low off the Carolina coast is expected to rapidly deepen Sat into Sat night, as stronger synoptic ascent overspreads the Gulf stream and the main synoptic front is pulled northward. On the backside of the low, an Arctic airmass will become locked in over the Mid-Atlantic as the low deepens off the coast, resulting in potentially record breaking low max temperatures during the event.

This pattern is favorable for at least light snow with high snow/liquid ratios within central NC, but also brings an incredibly difficult forecast challenge related to a deformation band on the north and west side of the deepening low. The likelihood of band formation, let alone its timing and placement, remains a point of considerable uncertainty and may not be ironed out until 24-36 hours before the event begins. However, the top analogs and latest suite of 00z model guidance highlights at least the potential for significant snowfall totals somewhere from the Carolinas into the Mid-Atlantic.

Very light snow may begin to fall as early as Fri afternoon across the northern Piedmont, but with marginally freezing surface temperatures at that time, little-to-no impacts are expected until after 4 PM Friday as temperatures drop. As the mid/upper level low begins to pivot down through the Tennessee Valley and close off Fri night, the low level mass response will result in a strengthening low/mid level WAA and low-level FGEN band to begin to develop over the Piedmont. Initially this area of snowfall will be slow moving and may result in 1-3" of snowfall before daybreak.

Widespread snowfall and increasing snow rates are expected to blossom over the area Sat as the mid/upper level low deepens and pivots across the Southeast. At this time, the deepest forcing for ascent will shift eastward across the state through Sat into Sat night as a significant deformation band on the backside of the low begins to develop towards the Carolina coast. How quickly this transition can take place and where the band eventually sets up will be key in pinpointing where the significant totals may occur. Reasonable high-end amounts of around +10" will be possible within this area. Continued forecast refinements should be expected as the details of this difficult but significant forecast become clearer.

KEY MESSAGE 2... A prolonged Arctic air mass will result in well below normal temperatures across central NC from Thursday through at least the middle of next week.

A prolonged period of Arctic air will be in place over central NC through at least the middle of next week. For today though, a Cold Weather Advisory remains in effect until 10 AM this morning for the far northern Coastal Plain, where apparent temperatures will range from 6 to 9 degrees.

A strong Arctic high presently over central Canada will slowly migrate south into the central and southern Plains of the US Fri and this weekend. It will slowly move east into the TN/OH valley and Mid- Atlantic region early next week. This pattern, along with the strong winter storm taking aim on the region, will favor a prolonged period of well below normal temperatures. The coldest period is shaping up to be Sat through Mon. Highs on Sat are currently projected to be in the 20s, but some guidance suggests we may hover in the teens, while on Sun we stay in the mid to upper 20s. As for lows during this time, single digits to lower teens are quite probable, with fresh snow cover also playing a role early next week. An Extreme Cold Watch may be needed for Sat night into Sun with wind chills ranging from minus five to near zero degrees. Temperatures may moderate some by Tue/Wed with highs nearing the 40s as ridging aloft slowly moves east from the Mid MS valley.

AVIATION /15Z THURSDAY THROUGH MONDAY/

As of 648 AM Thursday...

There is high confidence in VFR conditions through the 24-hour TAF period. Some brief gustiness may develop this morning at RDU, FAY, and RWI, mainly between 13 and 18z, due to some higher winds in the low-levels. These gusts may reach 18-20 kt from the NW. Any gusts will weaken by early this afternoon as the boundary layer winds decrease.

Outlook: A strong winter storm is forecast to impact the region starting as early as Friday evening and continue perhaps into early Sun. While exact details are not fully clear, there is increasing confidence for snow across the terminals, which could lead to LIFR/IFR visibilities, along with gusty NNE winds of 25-35 mph at times. VFR should return by Mon.

CLIMATE

Record Low Temperatures:

January 29: KGSO: -7/1940, KRDU: 7/2000, KFAY: 11/1986 January 30: KGSO: 4/1966, KRDU: 7/2014, KFAY: 8/2014 January 31: KGSO: 3/1966, KRDU: 3/1966, KFAY: 9/1934 February 1: KGSO: -4/1936, KRDU: 8/1981, KFAY: 1/1936 February 2: KGSO: 6/1971, KRDU: 5/1971, KFAY: 15/1971 February 3: KGSO: 7/1917, KRDU: 7/1980, KFAY: 10/1917

Record Low Maximum Temperatures:

January 29: KGSO: 23/1966, KRDU: 27/2014, KFAY: 28/2014 January 30: KGSO: 13/1966, KRDU: 19/1966, KFAY: 29/1966 January 31: KGSO: 22/1936, KRDU: 27/1948, KFAY: 22/1966 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 Watch from Friday afternoon through Sunday afternoon for NCZ007>011-021>028-038>043-073>078-083>086-088- 089.