textproduct: Raleigh

WHAT HAS CHANGED

As of 155 PM Tuesday...

* Confidence continues to increase for the potential development of a coastal low which will bring a period of snow and bitter cold to central NC sometime between Friday night and Sunday, though details on exact timing, amounts, and impacts remain uncertain.

KEY MESSAGES

As of 200 PM Tuesday...

1) Very cold Arctic air will stick around across central NC through the weekend, with much colder-than-normal temperatures, freezing daytime highs on Saturday, and dangerously cold wind chills near or below zero from Friday night into Sunday morning.

2) Confidence is increasing in the potential for a coastal low to bring a period of snow and bitter cold to central NC sometime between Friday night and Sunday, though details on timing, amounts, and impacts remain uncertain.

DISCUSSION

As of 200 PM Tuesday...

KEY MESSAGE 1: Very cold Arctic air will stick around across central NC through the weekend, with much colder-than-normal temperatures, freezing daytime highs on Saturday, and dangerously cold wind chills near or below zero from Friday night into Sunday morning.

A prolonged stretch of Arctic cold air will persist across central NC through the week and into the weekend, with temperatures running 1530F below normal. Highs will struggle to reach the upper 30s to low 40s most days, while lows fall into the teens and low 20s each night. Bitterly cold morning wind chills will be in the single digits to teens most days, with the coldest conditions likely Friday night into Sunday morning when wind chills could dip near or below zero. The coldest day in the forecast is expected to be Saturday with highs in the low to mid 20s CWA wide. This pattern is being driven by persistent longwave troughing over the eastern US allowing repeated Arctic high pressure systems building southeastward into the Mid-Atlantic through the forecast period.

KEY MESSAGE 2: Confidence is increasing in the potential for a coastal low to bring a period of snow and bitter cold to central NC sometime between Friday night and Sunday, though details on timing, amounts, and impacts remain uncertain.

Medium-range guidance and ensembles continue to signal the development of a very favorable synoptic pattern for a coastal low developing late this week into the weekend. A mid/upper level trough will dive southward across the Mississippi and Tennessee Valleys before cutting off just west of the Appalachian mountains. This would support a surface low developing along the Gulf shore, then sweeping across northern Florida, and deepen off the Carolina coast on Saturday bringing precipitation to Central NC.

Recent model trends favor a slightly farther west track of the upper low and surface cyclone, which has increased chances for snow inland across central NC. With the Arctic air mass already in place, and forecast soundings showing no warm nose aloft, precipitation would fall primarily as snow, with no sleet or freezing rain mixing in at this time. As the upper low moves across the region Saturday into Sunday northerly flow should help keep the cold air across central NC through the weekend during the precipitation.

While this Miller-A storm setup is one of the more favorable for snowfall across the area, significant accumulations are not guaranteed. Snowfall amounts will depend heavily on the location, timing, and interaction of the northern and southern stream flow. Another major factor in play is the location and proximity of the coastal low offshore.

At this time, confidence is highest for frigid temperatures over the weekend mixed with a chance of wintry precipitation as early as Friday night through Sunday morning. However, it is too early to pinpoint where the heavier snowfall will fall and where the narrow deformation band would be most likely.

AVIATION /00Z TUESDAY THROUGH SUNDAY/

As of 618 PM Tuesday...

Mostly clear skies and light winds forecast through the TAF period. Now that the afternoon gustiness has waned, there could be a brief period of marginal LLWS (25-30kts) at all sites through approx 03Z, but not enough to include in any TAFs. Mostly clear skies/light winds prevail into Wednesday.

Outlook: VFR conditions should continue through Friday, then we shift into increasing potential for an impactful winter storm this weekend with sub-VFR conditions especially at the eastern sites Saturday and Sunday.

CLIMATE

Record Low Temperatures:

January 27: KGSO: -7/1940, KRDU: 8/1940, KFAY: 11/1940 January 28: KGSO: -2/1940, KRDU: 1/2000, KFAY: 10/1935 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

Record Low Maximum Temperatures:

January 27: KGSO: 22/1940, KRDU: 25/1940, KFAY: 28/1940 January 28: KGSO: 23/1986, KRDU: 23/1897, KFAY: 32/1961 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

RAH WATCHES/WARNINGS/ADVISORIES

None.