textproduct: Raleigh

WHAT HAS CHANGED

As of 300 AM Wednesday...

* While meteorological conditions are still expected to support Increased Fire Danger over the Piedmont and nrn Coastal Plain this afternoon, NCFS advised that snowmelt and related marginal fuel moisture values should mitigate the threat.

KEY MESSAGES

As of 300 AM Wednesday...

1) Rain will become likely across srn zones mid-morning through early afternoon; otherwise, it will remain unseasonably mild through this evening.

2) High confidence in a period of at least light to moderate rain late Sat night through Sun. Forecast details, such as amounts and areal coverage, remain uncertain.

DISCUSSION

As of 300 AM Wednesday...

KEY MESSAGE 1... Rain will become likely across srn zones mid- morning through early afternoon; otherwise, it will remain unseasonably mild through this evening.

A couple of shortwave perturbations, evident in GOES-E Water Vapor satellite data over the srn TN and lwr MS Valleys, will move generally ewd and across the Southeast early today. A trough in the nrn stream will amplify across and offshore the Middle Atlantic later today and tonight, at the base of a mid/upr-level cyclone forecast to track across srn QC and ME. Net, 50-80 meter mid-level height falls will result across cntl NC through early tonight, while a low-level warm air advection regime and associated maximum of moisture transport will be directed across and offshore the Carolinas through early this afternoon. The combination of the two will maximize related forcing for ascent over cntl and srn NC generally between 12-18Z, during which time around a tenth of an inch or so of rain will likely result across the far srn Sandhills and srn Coastal Plain, with just a few hundredths of an inch or less otherwise and elsewhere.

Meanwhile at the surface, a cold front now stretching from sern WV wswwd across Middle/wrn TN and the Mid-South, will progress sewd and across the nrn half of cntl NC this morning and srn half by early to mid-afternoon. The passage of the front will be highlighted by marked drying of the low-levels, characterized by a decrease of surface dewpoints through the 20s F and into the teens over the nrn Piedmont, after pre-frontal ones around 50F or so. Downslope flow will enhance that post-frontal drying and also delay any marked cooling of the compressionally-warm boundary layer, with well above average temperatures in the 60s today. Related afternoon RH will decrease to around 25%. Nwly, post-frontal surface winds will also increase and become gusty into the 20s kts and support meteorological conditions supportive of Increased Fire Danger, though the NCFS did not request any such statement owing to snowmelt and marginal fuel moisture values.

Colder air will not arrive until a lee trough and effective, secondary cold front lead post-frontal high pressure east of the Appalachians tonight. A combination of continued nwly stirring, and also what will probably be a thickening of orographic cirrus, will keep temperatures mostly in the 30s and with morning lows within a few degrees of average.

KEY MESSAGE 2... High confidence in a period of at least light to moderate rain late Sat night through Sun. Forecast details, such as amounts and areal coverage, remain uncertain.

A strong mid/upper level short-wave will move across the southern Plains/Deep South Friday/Saturday before moving across the southeast Sunday into Monday. This system will feature a swly surge of anomalous PWAT ( up to ~1 to 1.25 inches; ~200 to 250 % of normal) into central NC by Sunday afternoon. At the sfc, a slowly retreating high off the New England coast will extend lingering nely flow across central NC Saturday/Sunday. Further west a sfc low will develop somewhere over the TN valley before advecting east and transferring energy to an offshore low through Monday via Miller B style.

There remains disagreement with the evolution of the mid-level shortwave/low as the GFS/GEFS keeps the stronger forcing to our south (and consequently the max QPF footprint to our south). Conversely, the ECMWF/EPS/GEPS brings the mid-level features directly over us on Sunday, spreading higher amounts northward over us and off the Carolina coast. Will likely take a few more forecast cycles to dial in amounts, but after collaborating with WPC, the QPF forecast will take a "middle of the road" approach between these two diverging scenarios.

Despite continued disagreement wrt to mid/upper features, there does seem to be agreement wrt to the sfc low taking a path that at least keeps our climatologically favored CAD locations locked into cool nely flow. The GFS develops a weaker coastal low compared to the ECMWF, and shows perhaps some warmer temperatures creeping up into our southern areas. Conversely, the ECMWF locks in chilly CAD temps across the entire area. After collaborating with WPC, a blend of the 25th percentile will be applied to temperatures Sunday to better capture this CAD potential.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

As of 630 AM Wednesday...

TAF period: With the 12Z TAF package, there is higher confidence in all terminals remaining VFR through today's cold front passage, although a TEMPO group remains at FAY for potential MVFR cigs. Low- level wind shear will continue for a few more hours, coming to an end as a cold front moves through from northwest to southeast. The potential for a shower remains too low to include in the INT/GSO TAFs, while the MVFR ceilings were removed from the RDU/RWI TAFs. Continued with a few hours of prevailing rain at FAY/RWI. Wind out of the southwest will veer to the northwest after the cold front moves through. The atmosphere may remain mixed enough for gusts to continue this evening, but still did not have enough confidence to mention the overnight gusts at this time.

Outlook: Dry VFR conditions are expected until Saturday night into Sunday, when widespread rain and restrictions will move into the region from west to east.

RAH WATCHES/WARNINGS/ADVISORIES

None.