textproduct: Raleigh

WHAT HAS CHANGED

* The Marginal Risk of severe storms today has expanded west to include the Triangle and along the US-1 corridor.

* Rainfall amounts are still expected to range from 0.25" to 1" across central NC. A localized swath of 1" to 2.5" is possible, with guidance suggesting the best chance along the US-1 corridor.

KEY MESSAGES

As of 108 AM Friday...

1) Showers and embedded storms will exist this morning through late afternoon, with the risk of a few severe storms.

2) A dry stretch returns after today, though a pattern change may be in the offing late next week.

DISCUSSION

As of 108 AM Friday...

KEY MESSAGE 1... Showers and embedded storms will exist this morning through late afternoon, with the risk of a few severe storms.

A cold front will be pushing through the region today and tonight as an area of low pressure tracks into the Lower Great Lakes. The main batch of showers and embedded storms will be tied to an effective pre-frontal moist axis. This boundary will track through during the morning hours across the Piedmont and mid-late afternoon across the Sandhills and Coastal Plain. The real cold front, bringing eventual lows tonight into the 40s to low 50s, will not arrive until overnight tonight.

Isolated showers and storms are present at the moment across the western and southern Piedmont. Coverage and intensity is expected to increase during the mid to late morning hours and continue into the late afternoon before exiting into eastern NC/VA by early this evening.

The severe weather threat today remains focused along and east of the I-95 corridor, along and south of the pre-frontal moist axis. The HRRR/RRFS suggest MLCAPE of 1000-1500 J/kg in this zone, within a band of 35-40 kts of deep-layer shear. SPC, however, has expanded the Marginal Risk to include not just the Coastal Plain and Sandhills, but also the Triangle. This westward expansion of the threat is likely tied to subtle variations in the position/timing of the moist axis, shifting the instability axis as far west as Wake County. Most guidance depicts the instability axis straddling the US Hwy 1 corridor by midday, thereby confining surface-based instability to mainly areas along/east of US-1. Proximity soundings from the RAP/RRFS indicate this same pattern, with more elevated storms along/west of US-1 and more surface-based convection east of that line. The main threats are damaging winds, though we certainly cannot rule out a few brief short-track tornadoes from transient supercells within line breaks, especially for areas along and east of I-95. The main timing for severe weather is between 10 AM and 4 PM, indicating a slightly faster trend in the latest 00z guidance.

There has been a notable trend in the QPF amounts and footprint in the last few runs of the HRRR/REFS. Rainfall totals are presently expected to range from a quarter inch to around an inch. However, localized totals between 1" and 2.5" will be possible, especially along the south and eastward moving moist convergence axis. The HRRR/REFS are painting this footprint along the US-1 corridor, including portions of the Triangle. This would be some very beneficial rainfall given the dry stretch we have had these past several weeks.

KEY MESSAGE 2... A dry stretch returns after today, though a pattern change may be in the offing late next week.

A dry stretch of weather is expected to return after today. Much of the medium-range ensemble guidance shows northwest flow at mid- levels into early next week. Cool high pressure building in this weekend could bring some patchy frost Sunday morning with middle to upper 30s expected. Thereafter, a warming trend looks to take hold with highs again some 5-10 degrees above normal in the upper 60s to low 70s come the early to middle part of next week.

While the dry stretch looks to hold into at least the middle of next week, ensemble guidance is highlighting a potential deep and potent trough digging into the OH Valley to Mid-Atlantic region Thursday into next weekend. There is presently large spread in the trough position, thereby leading to low confidence in precipitation chances. However, some AI-models are showing a more favorable storm track for rainfall. Some solutions also indicate 850-mb temperatures dropping below freezing late next week, favoring below normal temperatures.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

As of 108 AM Friday...

Ahead of a frontal passage later this morning through the afternoon, all of central NC should have some sort of flight restriction from rain and/or low ceilings. Coverage and intensity of rain looks to increase over the next few hours and through the night. This can be seen by the thunderstorm currently located north of CLT, which is moving towards the Triad region. Other cells such as this should continue to develop overnight and especially this morning. As we get into the afternoon, thunderstorm chances will further increase, bringing a risk of low visibilities, gusty winds, and lightning.

In terms of ceilings, MVFR to IFR and potentially LIFR low stratus has started overspreading the region. While probabilities have come down slightly, ceilings are possible at all sites and could prevail until after sunrise. MVFR ceilings will also accompany the rain/thunderstorms as they move through the region late morning through the afternoon. It looks like all sites should return to VFR by about 22Z Friday evening.

Outlook: Additional fog may be possible Friday night/Saturday morning, especially in the Coastal Plain. Otherwise, VFR conditions are likely to prevail beyond the risk for continued late-night/early- morning fog.

RAH WATCHES/WARNINGS/ADVISORIES

None.