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WHAT HAS CHANGED

As of 120 PM Thursday...

* A Special Weather Statement has been issued for the Triad counties for continued black ice concerns tonight into Friday morning.

* High confidence in strong and potentially impactful wind gusts on Saturday.

KEY MESSAGES

As of 120 PM Thursday...

1) Areas of patchy black ice possible tonight into Fri morning over the Triad region. Cannot rule out some isolated patchy fog as well, but confidence is low.

2) Light rain may mix with snow/sleet at times Friday evening. No accumulations are expected.

3) Strong winds should be expected on Saturday behind a cold frontal passage Friday night.

4) Fire danger concerns for Saturday are being evaluated and headlines may be needed after conferring with NCFS on Friday.

DISCUSSION

As of 120 PM Thursday..

KEY MESSAGE 1... Areas of patchy black ice possible tonight into Fri morning over the Triad region. Cannot rule out some isolated patchy fog as well, but confidence is low.

The mid-level trough continues to slide east and off the southeast US coast this afternoon. An area light snow and flurries continues to progress southward across the Triad and NW Piedmont into early this afternoon. Based on mesoanalysis, this light snow area seems to be driven by some low-level FGEN within the moist NE flow with high pressure to our north. No CAM guidance is having any good handle on the snow but feel given latest radar trends, the light snow in the NW should taper off within the next few hours. Little if any snow accumulation is expected as temperatures rise above freezing this afternoon.

Tonight, temperatures area-wide will drop into the upper teens to lower 20s under clearing skies and light winds. Snowfall reports from last night ranged from 0.2 to 0.5 inches across portions of the Triad. While it is difficult to tell how much of this may linger into this evening, an SPS will be issued for this evening into mid- morning Fri for patchy black ice in our Triad Counties of Forsyth, Davidson, Guilford, and Randolph. Some patchy fog could develop in this area and the western Piedmont early Fri morning. Some HREF members are showing the potential for fog, but confidence in this scenario is not great. If this were to form, some isolated freezing fog could develop.

KEY MESSAGE 2... Light rain may mix with snow/sleet at times Friday evening. No accumulations are expected.

A low-amplitude clipper wave embedded within northwesterly flow is expected to shift across the Ohio Valley Fri morning then push through VA/NC Fri evening, bringing 50-70m H5 height falls in 24 hours of synoptic forcing. This feature is now being more regularly modeled by hi-res guidance and is resulting in a slight, but noticeable, uptick on QPF (as much as 0.1 of an inch in spots).

To determine p-type, a top-down method and TRENDS nomogram analysis was applied. Partial thickness of < 1530m (850-700mb layer) and between 1310 and 1290 (1000-850mb layer) suggest Indeterminate and S (Snow) will be the dominate categories. This would suggest that the mid lvls will be sufficiently cold to produce snow, with sufficient saturation which point soundings support, but the primary driver in the resultant phase state once precipitation reaches the ground will be the surface temperatures and precipitation rates. Max wetbulb of 1-4C in lowest 500mb from 18-03z and surface temps in the low 40s to upper 30s will likely result in partial or perhaps complete melting to sleet or rain.

The sensible result at the surface will be mostly rain that may mix with or become predominantly snow at times given sufficient rate of precipitation Friday afternoon/evening. If a period of snow does occur, it will most likely be conversational and none impactful due to surface temperatures remaining above freezing until around 10 PM, after which time precipitation will have ended across central NC.

KEY MESSAGE 3... Strong winds should be expected on Saturday behind a cold frontal passage Friday night.

Behind the clipper wave, a highly amplified mid/upper level pattern is expected from the trough over and off the East Coast and the anomalous ridge over the Great Plains. At the surface, an area of broad low pressure is expected to rapidly deepen to a sub-990mb low just north of Bermuda, while at the same time strong > 1030mb high pressure over the Upper Great Lakes shifts into the Ohio Valley by Sat evening.

Strong subsidence on the backside of the slowly departing trough axis will result in mostly clear skies during the daylight hours and favor efficient momentum transfer through the boundary layer. Wind gusts should rapidly develop through the early morning hours as daytime heating mixes into the elevated mixed layer just above the surface from CAA behind the front. Widespread wind gusts of 25-35 kts should be expected. Clear skies and abundant insolation, should result in efficient momentum transfer from the top of the mixed layer and may result in infrequent gusts of 35-45 kts, strongest from the mid- morning to early afternoon.

KEY MESSAGE 4... Fire danger concerns for Saturday are being evaluated and headlines may be needed after conferring with NCFS on Friday.

In addition to the windy conditions on Saturday, very dry Arctic airmass will be in place behind the cold frontal passage Fri night into early Sat. Downsloping northwest winds will further warm/dry the boundary layer and combine with abundant dry air aloft mixing down to the surface. This combination of very dry air and windy conditions will met the meteorological criteria for at least an Increased Fire Danger Statement if not Red Flag Warning.

Collaboration with fire partners at NCFS will need to occur to assess the soil conditions, long-term fuels, and impacts temperatures in the 30s to low 40s would have, and if any of these parameters may mitigate otherwise favor meteorological pattern for erratic/dangerous fire behavior. Stay tuned for further updates.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

As of 120 PM Thursday...

Lingering low stratus behind a frontal system will gradually scour out later this afternoon and especially this evening. Most ceilings are ranging from 2500 to 5000 ft AGL across the terminals this afternoon. MVFR stratus will be a concern at GSO, INT, and FAY for the next few hours before scattering out by this evening. Some patchy MVFR may linger off/on at INT till 03z with the moisture boundary still across the western Piedmont. VFR should prevail through the rest of the period, though a few HREF members are indicating the potential for some patchy fog across the western Piedmont, perhaps clipping GSO/INT early Fri. Confidence in this scenario is not great, so decided to keep things VFR for now. Light NE winds this afternoon will switch around to SW Fri between 6-12 kt.

Outlook: A fast moving clipper system will bring a chance of IFR- MVFR conditions in light rain/snow Fri evening, mainly across the northern terminals. A brief period of LLWS is possible Fri night to early Sat. Otherwise, strong and gusty NW winds will develop and persist most of Sat, with gusts between 35 to 40 kt, which may cause mechanical turbulence. VFR should prevail Sat through Wed.

RAH WATCHES/WARNINGS/ADVISORIES

None.