textproduct: Raleigh

WHAT HAS CHANGED

As of 1005 AM Friday...

* The Dense Fog Advisory has expired across central North Carolina.

KEY MESSAGES

As of 310 AM Friday...

1) A pre-frontal trough/confluence axis and focus for scattered showers and perhaps an isolated storm will move across cntl NC today. Meanwhile, a dryline will likely move across wrn NC and into the srn and wrn NC Piedmont by late afternoon. Critical fire weather conditions may briefly result over the wrn/srn Piedmont Fri afternoon.

2) A couple rounds of stratiform rain appear likely Saturday and again on Sunday. Some wet snow may mix in Sunday evening into the early overnight hours near the NC/VA border, but confidence in any accumulation is low.

3) Below normal temperatures expected early to middle of next week, with low confidence in a cold front bringing rain late week.

DISCUSSION

As of 310 AM Friday...

KEY MESSAGE 1... A pre-frontal trough/confluence axis and focus for scattered showers and perhaps an isolated storm will move across cntl NC today. Meanwhile, a dryline will likely move across wrn NC and into the srn and wrn NC Piedmont by late afternoon. Critical fire weather conditions may briefly result over the wrn/srn Piedmont Fri afternoon.

The stalled boundary has migrated a bit further south into the northern/central Sandhills early this morning according to latest sfc analysis. Just south of the boundary, warm sly flow persists with temperatures in the mid 60s. Locations north of the boundary have dipped into the mid 40s across the NC/VA border to mid to upper 50s down in the northern Sandhills. Areas north of the boundary, especially up across the NC/VA border will continue to see areas of dense fog through a little after sunrise coinciding the boundary's northward retreat into VA.

Regional mosaic radar depicted a thin line of pre-frontal convection extending from central Mississippi northeast through western TN/central KY/southern WV. As we progress into the morning hours, this line will largely wash out over the higher terrain to our west. However, guidance is still bullish on sending a pre-frontal dryline across central NC this afternoon ahead of a cold frontal passage tonight. Upper forcing will largely maximize north of us, and as such, lift will largely be confined to the dryline and developing pre-frontal trough. As such, scattered showers are possible, but overall coverage should be limited as should amounts (pockets of a few tenths possible, but largely a few hundreds here or there most likely). Increasing theta-e behind the retreating boundary embedded within deep southerly flow will allow for upwards of 500 J/kg of SBCAPE to develop later this morning into the afternoon. As such, can't rule out some isolated thunder with this passing scattered convection.

In addition to the passing convection, strong swly sfc gusts of 25 to 35 mph are likely this morning into the early afternoon period especially across the Sandhills/Coastal Plain. Equally as strong wly gusts are then likely across western/southern Piedmont post dryline passage. Temperatures will rise to near- record levels in these areas, and as a result, critical fire weather conditions may develop across western areas for a few hours this afternoon.

Any lingering convection should move east of central NC by late afternoon. Overnight lows will remain mild in the lower 50s tonight under mostly dry conditions till closer to sunrise Saturday.

KEY MESSAGE 2... A couple rounds of stratiform rain appear likely Saturday and again on Sunday. Some wet snow may mix in Sunday evening into the early overnight hours near the NC/VA border, but confidence in any accumulation is low.

A rare dryline is expected to settle across southern NC into central GA by Sat morning with considerable low-level drying and minimal cooling behind the front, resulting in 15-30 degree dew point depressions. This will set up the potential for an insitu CAD regime that will be highly dependent on the amount of rainfall on Sat that can lock-in a cooler/denser airmass at the surface via diabatic cooling. Overall the rainfall amounts are expected to be light and not impactful, but this results in low forecast confidence for temperatures on Sat with a 10-15 degree range in high temps in the latest guidance, especially across the Piedmont.

After a brief lull in stratiform rain Sat evening, initially weak low pressure is expected to develop along the main baroclinic boundary loosely around SC, but is expected to rapidly deepen Sat night into Sun as it moves over the Gulf Stream and experiences intense synoptic forcing (H5 height falls on the order of around 300m in 24 hrs) via the approaching shortwave from the Ohio Valley. Minor timing differences in its intensification and east-west wobbles as occlusion occurs is resulting in large differences in the rainfall footprint and magnitude (EPS/AIGFS/AIFS on the lower side with GEFS/GEPS showing higher amounts) especially over northeast NC and southeast VA. Latest forecast suggests most locations should see 0.25 to around 0.5" from 06z Sun until precip exits early Mon morning. Amounts could be as low as less than 0.1" in the western Piedmont and as much as 1.25" in the northern Coastal Plain.

Wet snow may mix in with the rain as early as Sun afternoon, but more probable after sunset into the overnight hours when a brief transition to all snow may be possible. Using local TRENDS database and nomogram analysis for p-type forecasting, the primary categories will be either "Snow" or "Indeterminate" with a shallow warm layer near the surface delineating between rain or snow. These categories are also very susceptible to rate-driven p-type changes, which will certainly be possible given the strong DPVA potentially overlapping H850 convergence on the backside of the low. The best overlap in forcing appears to be after 18z through roughly 00z, but this is when surface wet-bulb temperatures will be warmest, and above freezing, and not falling below 32F until after 00z, resulting in mostly the potential for conversational snow and not impactful as far as accumulation and travel conditions are concerned. The time period of concern may be after 00z as wet-bulb temps drop below 32F and lingering saturation and weak low-level forcing underneath the core of the mid/upper trough may allow snow to stick to elevated surfaces and perhaps even untreated roadways; however, confidence in this solution is low given minor changes to the low track/strength will have a large effect on where these conditions will overlap, if at all.

KEY MESSAGE 3... Below normal temperatures expected early to middle of next week, with low confidence in a cold front bringing rain late week.

As the surface low continues to move northeast out of the area, below normal temperatures will return to central NC as surface high pressure moves to our south. Temperatures should fall below normal on Sunday and last through mid-week. Monday will be the coldest day of the period, with highs in the 40s and lows in the mid 20s to around 30. This will be up to 15 degrees below normal. Temperatures should slowly moderate each day through mid-week as high pressure passes to our south. Temperatures on Wednesday look to be back to near normal. The next chance for rain will be Thursday into Friday as a cold front looks to move through the region, but high model spread leads to low confidence in the timing and amount of rain that is expected.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

As of 635 AM Friday...

12Z Update: Northern terminals remain LIFR and socked in this morning. The stalled boundary is slowly moving north, so should see some lifting of ceilings to IFR/MVFR this morning. Any lingering dense fog should lift by ~14 to 15Z. Otherwise, the previous discussion below remains valid at this TAF update.

Previous discussion:

The northern tier of terminals have all socked down to LIFR conditions (combo of low ceilings and visibility) this morning as they remain near or just north of a stalled frontal boundary. Expect these conditions to persist through at least day break, before a gradual lifting to MVFR and eventually VFR occurs through this afternoon.

A dryline front is expected to sweep across central NC later today. Out ahead of the front, swly gusts of 25 to 30 kts will be possible at KFAY/KRDU/KRWI starting ~14Z through 18Z. Then post- frontal wly winds (20 to 30kts) will pick up at KINT/KGSO early this afternoon and persist through sunset. Winds will shift to wly at KRDU/KFAY/KRWI as well, but may only gust in the 15 to 25 kt range during and after this shift. A cold front will then sweep across central NC tonight, but winds should weaken overnight despite its passage.

A broken line of showers and perhaps a few weak thunderstorms may accompany the dryline passage later this morning/afternoon but should push east of central NC by mid afternoon. Any lingering sub- VFR conditions should sweep out through the early afternoon, and VFR conditions are otherwise expected to persist through the end of the 24 hr TAF period.

Outlook: A cold front will move across cntl NC Fri night and stall over SC by early Sat. That front will be a focus for the development of a couple of areas of low pressure and associated periods of rain and additional flight restrictions over the Carolinas this weekend.

CLIMATE

Record High Temperatures:

February 20: KGSO: 74/1922 KRDU: 75/1939 KFAY: 82/2014

Record High Minimum Temperatures:

February 20: KGSO: 56/1939 KRDU: 62/1939 KFAY: 60/1939

RAH WATCHES/WARNINGS/ADVISORIES

None.