textproduct: Raleigh

WHAT HAS CHANGED

As of 100 PM Friday...

While precipitation chances have increased, Saturday night's low temperature forecast has also increased slightly, decreasing the chance for accumulating snow late Saturday night into Sunday.

KEY MESSAGES

As of 100 PM Friday...

1) Increased fire danger until 7 PM EST this evening. Humidity improves Sat as a weak upper-level system brings a low-end rain chance Sat morning.

2) After Saturday's cold front, precipitation will likely begin after midnight Saturday night into Sunday as an upper trough approaches the southeastern United States. The trough will help to spin up a surface low along the Atlantic coastline Sunday. With this forecast update, the chance for precipitation has increased with higher confidence that the surface low which develops will be close enough to the coast (as opposed to farther out to sea) to contribute to a wider precipitation shield that covers a majority of North Carolina. The highest precipitation rates are likely to occur on Sunday morning.

3) Cold early next week with temperatures in the teens -- 10 to 15 degrees below normal -- for consecutive mornings.

DISCUSSION

As of 100 PM Friday...

KEY MESSAGE 1... Increased fire danger until 7 PM EST this evening. Humidity improves Sat as a weak upper-level system brings a low-end rain chance Sat morning.

The increased fire danger across the Piedmont, roughly from The Triangle and points west into the Triad and western Piedmont, will remain in effect until 7 PM EST this evening. By tonight, we should see humidity values improve into the 30s and eventual 40s over the Piedmont with gusts diminishing tonight.

Humidity values will improve further on Sat as the high along the SE coast this afternoon shifts out into the Atlantic, resulting in a southerly return flow persisting through Sat. Humidity values are forecast to only bottom out in the upper 30s to mid 40s during the day Sat. And despite some gustiness developing, this should keep any fire danger at a minimum. Increasing WAA will overspread the west and northwest Piedmont Sat morning and provide enough isentropic lift to favor some light rain, mainly across the Triad region. Rainfall amounts look very minimal, as the HREF/REFS 90th percentile shows only a few hundredths of an inch. Any rain would taper off by midday with a partly to mostly cloudy sky.

KEY MESSAGE 2... After Saturday's cold front, precipitation will likely begin after midnight Saturday night into Sunday as an upper trough approaches the southeastern United States. The trough will help to spin up a surface low along the Atlantic coastline Sunday. With this forecast update, the chance for precipitation has increased with higher confidence that the surface low which develops will be close enough to the coast (as opposed to farther out to sea) to contribute to a wider precipitation shield that covers a majority of North Carolina. The highest precipitation rates are likely to occur on Sunday morning.

Model guidance indicates that the mid and upper levels of the atmosphere will be cold enough with enough saturated to generate snow aloft. What has had the greatest potential as a limiting factor for snowfall for several days has been the surface temperatures. Highs on Saturday should be in the 50s across most of the area, with colder air moving into the area overnight Saturday night and continuing into Sunday. The climatologically favored source for cold air in central North Carolina snowstorms is to the north over New York or the Great Lakes, but in this scenario, high pressure is all the way in southwestern Texas. While the wind will take on a northerly component Saturday evening through Sunday evening, the forecast for low temperatures Saturday night has continued to creep upward slightly, with all locations forecast in the 30s. Even if temperatures are slow to rise on Sunday, the new high temperature forecast on Sunday has also increased by 3 to 5 degrees, ranging from the mid 30s to the mid 40s. Even if snow is falling, unless the rates are very high, it will be hard for snow to accumulate on surfaces that have only been below freezing for a brief period of time. The maximum amount of snow in the forecast is around an inch, likely to the north of the Triangle.

The current thinking is that precipitation will initially fall as rain Saturday night, with some snow possibly mixing in late overnight to the west of US-1. Precipitation coverage will increase overnight, with most of the area receiving precipitation Sunday morning. The best chance for snow will be west of US-1, although the chance for any precipitation will decrease the farther west you go. By Sunday afternoon, rain is likely east of I-95, with a chance of a rain/snow mix west of I-95. Cannot rule out some rain/snow hanging around Halifax or Edgecombe counties Sunday evening, but all precipitation should move east by midnight.

Liquid precipitation totals will be the lowest in the Triad (as low as 0.05 inches) and the highest across Sampson County (up to half an inch). Skies should clear rapidly Sunday night, and that will allow temperatures to tumble anywhere from the mid teens to the mid 20s. Any rain or snow that falls Saturday night and Sunday will be likely to freeze on roadways Sunday night.

KEY MESSAGE 3... Cold early next week with temperatures in the teens -- 10 to 15 degrees below normal -- for consecutive mornings.

Minor air mass modification is expected on Mon behind the cold fropa from Sat night ahead of a reinforcing cold front, which will bring cold and very dry conditions to central NC. There is good agreement within the model guidance that an Arctic airmass will emerge from Alberta/Saskatchewan on Mon and settle directly over the Carolinas by Wed morning. Wed morning will likely be the coldest for most across central NC as the surface high will be centered overhead and high temperatures on Tues will only peak in the 30s. Next precipitation chances come as the southern stream becomes more active with several ejecting waves of energy mid-late week, but confidence in timing/intensity is low.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

As of 100 PM Friday...

VFR conditions are expected to start the TAF period and persist into this evening. Increasing warm advection will bring a period of mainly MVFR ceilings to GSO/INT and perhaps briefly at RDU, Sat morning. A band of light rain may accompany these sub-VFR ceilings, most favored at GSO/INT. Low-level wind shear and/or mechanical turbulence will develop tonight and continue into mid-morning Sat tied to a developing strong LLJ. VFR is favored to develop Sat afternoon across the Triad terminals, with some gustiness developing out of the southwest in the lower 20s kt at all terminals.

Outlook: Another area of precipitation, including some snow over the Piedmont, will overspread cntl NC late Sat night through Sun, when additional flight restrictions will be likely area-wide. VFR should prevail Mon-Wed.

RAH WATCHES/WARNINGS/ADVISORIES

None.