textproduct: Raleigh

WHAT HAS CHANGED

As of 800 AM Thursday...

An Increased Fire Danger is now in effect for all of central NC until 7 PM EST this evening. Potential for accumulating snowfall on Sunday continues to increase across the area, but confidence in details and amounts remains low.

KEY MESSAGES

As of 800 AM Thursday...

1) Increased Fire Danger for central NC today till 7 PM EST.

2) Cold and blustery conditions are expected today with highs only in the mid 30s to lower 40s. Winds will gust to 20 to 30 mph and result in wind chill values in the 20s for most of the day.

3) Continued cold tonight and Friday morning with lows between 15 and around 20. Below normal highs in the lower to mid 40s are expected on Friday.

4) After one mild day on Saturday with a slight chance of light rain in the north, 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.

5) Below to well below normal temperatures return Saturday night through Wednesday.

DISCUSSION

KEY MESSAGE 1... Increased Fire Danger for central NC today till 7 PM EST.

Although temperaures are colder today, the combination of low relative humidity values near 25 to 30 percent, ongoing dry fuels, and wind gusts of up to 25 to 30 mph, will produce an increased fire danger across central North Carolina from late morning through the early evening. An increased fire danger may also be warranted Friday with continued very low relative humidity and some marginal gusty winds.

KEY MESSAGE 2... Cold and blustery conditions are expected today with daytime highs only in the mid 30s to lower 40s. Winds will gust to 20 to 30 mph and result in wind chill values in the 20s for most of the day.

The Arctic cold front was advancing east early this morning and was located just west of U.S. route 1 at 2am. The front should reach I- 95 by 5am and reach the coast just after daybreak. Winds will shift to northwest behind the front and become gusty with gusts of 20 to 30 mph. Colder and drier air will surge into the region during the day with temperatures steady or even slowly falling. Most locations in the Piedmont will have temperatures persist in the 30s throughout the day with temperatures in the lower 40s in the Sandhills and Coastal Plain Plain falling into the 30s during the afternoon. Daytime highs will range from the mid 30s in the Triad, to the upper 30s in the Triangle and the lower 40s in the Sandhills. These highs are 10 to 15 degrees below average.

The combination of the chilly temperatures and gusty winds will result in wind chill values in the 20s for much of the day with the wind chill possibly dropping into the teens at times across the Triad and near the VA border.

In addition, as drier air surges into the region it will be enhanced by a downslope flow and good mixing resulting into dewpoints dropping to between zero and 5 degrees this afternoon. These values result in RH values in the 20-30% range. While the low RH values and gusty winds raise a fire weather concern, prevailing temperatures in the 30s should preclude much in the way of adverse fire behavior.

KEY MESSAGE 3... Continued cold tonight and Friday morning with lows between 15 and around 20. Below normal highs in the lower to mid 40s are expected on Friday.

Chilly high pressure will be centered to our south tonight and Friday morning with low level thickness values ranging in the 1270s. This should support lows in the upper teens to around 20. There is a chance winds could decouple around daybreak on Friday allowing lows to fall into the mid and even lower teens as noted by the NBM 10th percentile.

It will remain chilly on Friday but winds will become southerly and temperatures will moderate. Sunshine will be muted by some mid and high clouds with highs in the lower to mid 40s which is about 4 to 8 degrees below average.

KEY MESSAGE 4... After one mild day on Saturday with a slight chance of light rain in the north, 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.

Within broad mid/upper troughing over the Great Lakes and Eastern US, a shortwave will move NE across the OH Valley on Saturday as the prefrontal surface trough crosses central NC. Can't rule out some light rain across northern parts of the area on Saturday, but given limited moisture and the best forcing well to our north, POPs remain only slight. Highs on Saturday will range from lower-50s to lower- 60s.

Behind a cold frontal passage on Saturday evening/night, a pair of shortwave will swing across the Southeast US and Carolinas on Sunday, then NE and offshore on Sunday night, inducing a surface cyclone that develops off the coast of the Carolinas and moves NE. This could result in some wintry precipitation across central NC, but there is plenty of uncertainty as this is not a classic setup with a surface high pressure system to our north continuously driving down cold air, despite a cold air mass being in place initially. Given this and the low taking a Miller A track vs Miller B, this does not appear to be a favorable setup for ice and it is more a question of rain vs snow. Frontogenesis on the NW side of the low will likely be the driver of much of the QPF, and given low confidence in the exact track of the low this far out, there is still a lot of uncertainty on how much precipitation falls and where. The 00z GFS continues to depict a sharper trough and surface low that hugs the coast compared to the 00z ECMWF which has the cyclone more offshore. Thus the GFS is quite a bit wetter than the ECMWF, which keeps the heaviest QPF to our east, but the GFS is also warmer. This illustrates the dilemma without a continuous cold air source, as the storm essentially has to "thread the needle" for significant snow across the area. Too far west and it would be a mainly rain event, too far east and we won't get any precipitation at all. If it does take a close to perfect track, guidance shows up to a few inches of snow will be possible, but it is way too early to predict amounts with any confidence. All that can be said is accumulating snow somewhere across the area appears likely. The other factor to keep in mind is it will be daytime and if surface temperatures are in the mid-to-upper-30s, snow would have a hard time sticking if rates aren't high enough. Any precipitation will come to an end and skies will clear on Sunday evening.

KEY MESSAGE 5... Below to well below normal temperatures return Saturday night through Wednesday.

The below to well below normal temperatures should return Saturday night/Sunday and continue through the middle of next week. While there is plenty of uncertainty with Sunday's temperatures as they will depend on the track of the cyclone, lows on Sunday and Monday nights should range from mid-teens to lower-20s, with wind chills as low as the upper single digits possible. Forecast highs are only in the 30s and 40s Monday through Wednesday, with Tuesday looking like the coldest day as the Arctic High moves overhead. Lows Tuesday night could be in the teens areawide.

AVIATION /12Z THURSDAY THROUGH MONDAY/

As of 630 AM Thursday...

* High confidence of VFR conditions over the next 24 hours. * Northwest winds are expected at 10 to 15 kts today with gusts of 20 to 25 kts expected through the late afternoon.

A cold front located across the Triangle and Sandhills just before daybreak today will move into eastern NC this morning. Behind the front winds will shift to northwesterly and increase with gusty winds developing. Winds will dramatically increase after the frontal passage with sustained winds of 10 to 15 kts and gusts of 22 to 28 kts for a handful of hours into the early/mid morning then relax slightly before another surge of gusts during the mid to late afternoon arrives. Wind gusts will begin to relax between 02 and 06Z. Winds will decrease overnight and back to west and even southwesterly by daybreak on Friday at around 5 kts.

VFR conditions are expected through the period with SCT to BKN clouds associated with the cold front from 4 to 8kft early this morning shifting east during the day. Some scattered strato-cumulus clouds are possible this afternoon with some high cirrus clouds expected tonight.

Looking beyond 12Z Friday, VFR conditions will prevail through Friday evening although mid and high clouds will lower and thicken on Friday night. A weak system will move across the area on Saturday morning bringing a small threat of some spotty rain and marginal MVFR conditions. There is a better chance of adverse aviation conditions late Saturday night into Sunday evening as a storm system may bring MVFR to IFR conditions with a chance for rain or snow. Blaes.

RAH WATCHES/WARNINGS/ADVISORIES

None.