textproduct: Raleigh

WHAT HAS CHANGED

As of 100 PM Thursday...

Potential for accumulating snowfall on Sunday continues to be possible, but plenty of uncertainty remains.

KEY MESSAGES

As of 100 PM Thursday...

1) Increased Fire Danger in effect until 7 PM EST this evening. Cold overnight lows in the middle teens to around 20 by Fri morning.

2) Marginal fire weather concerns Friday with continued very dry conditions and a light breeze.

3) A cold front will move through on Saturday night. Behind this front, a surface cyclone will develop and deepen off the Southeast US coast, potentially resulting in light snow and/or rain across central NC on Sunday, but plenty of uncertainty remains.

DISCUSSION

Key MESSAGE 1... Increased Fire Danger in effect until 7 PM EST this evening. Cold overnight lows in the middle teens to around 20 by Fri morning.

An increased fire danger statement remains in effect until 7 PM EST this evening. Gusts from the WNW will continue to reach values of 25 to 30 mph at times through this evening. As the pressure gradient relaxes by late tonight and overnight, we should start to see a gradual diminishing of the wind gusts, becoming light toward daybreak Fri. Relative humidity values will bottom out in the 20s this afternoon before recovering tonight.

Although the high is not the most favorable for radiational cooling, that parent high will shift toward northern FL overnight tonight. That along with low pressure near ME should allow winds to diminish with ridging building in aloft. Low temperatures will be quite cold, some 10 to 15 degrees below average in the upper teens to near 20, with the coldest spots near the mid teens in outlying areas.

KEY MESSAGE 2... Marginal fire weather concerns Friday with continued very dry conditions and a light breeze.

Very dry and slightly warming conditions are expected on Friday within the modifying Arctic airmass. Daytime heating will mix down drier air aloft with the departure of mid/high clouds by the afternoon hours. This will result in relative humidity values dropping into the teens to around 20 after noon and persisting throughout the daylight hours. A gradually tightening pressure gradient should increase sustained winds to 10-15 mph and gusts 15- 25 mph. This will result in marginal fire weather concerns from 17z until 22z, with higher confidence across the western Piedmont. Any headlines will likely be driven by NCFS assessment of soil conditions and their expected stress on fire suppression personnel.

KEY MESSAGE 3... A cold front will move through on Saturday night. Behind this front, a surface cyclone will develop and deepen off the Southeast US coast, potentially resulting in light snow and/or rain across central NC on Sunday, but plenty of uncertainty remains.

A cold front will move through on Saturday night, with a minimal chance of precipitation along the front itself. However, after the cold front moves through, a deep upper level trough is expected to swing across the eastern third of the United States, and this will help to form a coastal low along the cold front after it has moved offshore. There are still many uncertain pieces to the forecast. One is the amount of cold air that will be in place. The current forecast calls for temperatures primarily in the 50s in central North Carolina on Saturday, and lows ranging from the upper 20s to the mid 30s Saturday night. Sunday's highs are forecast to range from the mid 30s to the mid 40s. High pressure will be to the west of the area instead of north, which is not a climatologically favored location for accumulating snowfall. How much of a time period will there be that temperatures are cold enough to support snow? A second uncertain piece is where the surface low will form off the coast. The 12Z NAM shows a coastal low developing much closer to Cape Hatteras than the 12Z GFS, with the 00Z ECMWF even farther offshore. A third uncertain piece is how much phasing will occur between the surface low offshore and the upper level trough remaining inland. Will the precipitation shield with the two features remain continuous or will there be a gap between them? It's just too early to know with certainty how all of these pieces will continue together. At this point, the forecast has at least a slight chance of snow in all locations, but the highest chance of precipitation should remain along the I-95 corridor, where temperatures should remain warm enough that a rain/snow mix will occur.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

As of 100 PM Thursday...

There is high confidence in VFR conditions through the 24-hour TAF period. WNW winds will continue to gust to 25 to 28 kt into the evening hours, before slowly diminishing by late tonight and becoming light overnight. The high to our south will shift toward the SE coast Fri afternoon, favoring a return SW flow, which could gust in the 20 to 24 kt range.

Outlook: A weak system could bring a brief period of sub-VFR early Sat, mainly across the GSO/INT terminals. A strong storm system and cold front will bring a chance of rain or snow Sunday. Confidence on impacts and resultant aviation conditions is currently low at the moment. VFR should prevail Mon through Tue.

RAH WATCHES/WARNINGS/ADVISORIES

None.