textproduct: Raleigh

WHAT HAS CHANGED

As of 230 AM Thursday...

* No appreciable changes.

KEY MESSAGES

As of 230 AM Thursday...

1) A strong cold front will bring widespread showers today, with the possibility of a few strong to severe thunderstorms primarily south and east of Raleigh late this morning.

2) Another strong cold front will shift across the region Monday and bring a low-predictablity risk for severe weather, primarily in the Sandhills and Coastal Plain.

DISCUSSION

As of 230 AM Thursday...

1) A strong cold front will bring widespread showers today, with the possibility of a few strong to severe thunderstorms primarily south and east of Raleigh late this morning.

Water vapor imagery this morning depicted a strong vort max moving across and triggering convection over the Gulf states. A few weaker perturbations were also evident stretching light to moderate rainfall north into the southern Appalachians.

At the sfc, latest analysis depicted the strong cold front just west of the NC mountains pushing into far eastern TN. Dew points across central NC this morning aren't overly impressive, largely in the mid 50s to lower 60s with higher dew points locked ahead of the advancing squall line in the Deep South. However, with time, expect some of that deeper moisture to advect north into our area ahead of the advancing cold front. As strong mid-level height falls spread across the southeast this morning, the line of convection will push east across central NC through mid afternoon.

Strengthening flow aloft will increase bulk layer shear upwards of 60 kts during this time. As such, if any instability can be realized later this morning/early afternoon a low-end severe threat will be possible. The 00Z HREF updraft helicity swaths were largely clustered along the NC/SC border up into the Sandhills and Coastal Plain which generally aligns with latest upstream radar and observational trends. Forecasted hodographs largely indicate strong mid/upper-level shear, with weaker lower-level shear. As such, think that any organized storms would largely favor a severe wind gust threat via mixing of stronger winds aloft to the sfc and a lesser hail threat. While an isolated tornado can't be ruled out, the better instability/kinematic combo for tornadoes will be to our south.

The severe threat should largely end by ~19Z as the cold front quickly sweeps east of our area. Although lingering light precipitation will be possible through ~21Z. Some CAMs are trying to generate snow on the back-end of the exiting precipitation along the NC/VA border. However, looking at forecast soundings in this vicinity, saturation in the DGZ is limited, and dry air quickly advects in from the west. As such, while there could be a few flakes that mix in across the NC/VA border no accumulation nor impacts would be expected.

Rather anomalous warm temperatures this morning should drastically cool with frontal passage this morning/early afternoon. Overnight temps tonight will drop into the lower 30s.

KEY MESSAGE 2... Another strong cold front will shift across the region Monday and bring a low-predictablity risk for severe weather, primarily in the Sandhills and Coastal Plain.

Overall there is reasonably good confidence in the evolution of the mid/upper level pattern within the medium range. A more highly amplified system is expected to develop over the northern/central CONUS Sun and progress eastward into the Great Lakes into the TN Valley by Mon. At the surface, this will result in a stationary boundary over the Carolinas to lift northward as a warm front Sun into Sun evening as surface high pressure strengthens off the Northeast coast while at the same time low pressure deepens over the OH Valley. Strengthening southwesterly flow will result in a narrow window of moisture return into the region ahead of yet another strong cold frontal passage.

The overwhelming trend within the ensemble guidance is a slightly slower and more amplified trough as it progresses through the Midwest, Ohio Valley and Great Lakes. This has resulted in a roughly 6hr-12hr delay in the cold fropa among mean MSLP fields, with the most likely timing now centered in the 15z Mon to 00z Tues; which is diurnally favorable for severe weather. A complication to the convective risk appears to be a signal for morning stratus layer, especially in the initially upslope region into the Piedmont. Instability still appears to weak overall (500 J/kg or less and maximized over the Coastal Plain) and result in a highly conditional high-shear, low-cape setup that will need to be watched closely. Mostly straight hodographs with 40-60 kts of deep layer shear oriented parallel to the cold front will favor strong to severe winds to be the primary severe hazard if a severe threat were to develop. Low-level shear of > 20 kts and 0-1 SRH of > 100 m2/s2 also suggests a low-end tornado threat can't be ruled out.

AVIATION /06Z THURSDAY THROUGH MONDAY/

As of 116 AM Thursday...

06Z Update: Gusty sswly flow under VFR conditions persist early this morning. After assessing latest high-res guidance, the timing of showers/impacts and other details from the previous discussion below appear to be still valid at this time.

Previous discussion:

VFR conditions are expected to start the TAF period. South to southwest winds continue to prevail across the terminals this evening and this is expected to continue prior to a cold frontal passage Thursday morning. Once the front moves through, gusts will remain, but switch to be out of the northwest between 25 and 30 kt, with an infrequent gust to 35 kt certainly possible as well. With the front approaching, restrictions with showers will promote MVFR conditions. The heaviest period of showers looks to move through between 14 and 21z, earliest in the west at GSO/INT and latest at RWI in the east. Associated with these heavier pockets of rain will be the potential for IFR and perhaps brief LIFR. Instability may favor a low-end storm threat, most favored at FAY, where a TEMPO for TSRA was introduced. VFR should return by the tail end of the TAF period, though gusts should continue from the NW before diminishing Thu night.

VFR returns Fri into Sat. Increasing moisture return followed by another cold front will bring a return to sub-VFR conditions and showers on Sunday and Monday.

RAH WATCHES/WARNINGS/ADVISORIES

None.