textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No major changes to overall thinking.

KEY MESSAGES

1. The severe threat remains low through Monday before increasing ahead of a cold front Tuesday afternoon and evening, possibly lingering into Wednesday. A warming trend is expected through Tuesday, with slightly cooler highs and lower humidity Wednesday into next weekend.

DISCUSSION

Key message 1: The severe threat remains low through Monday before increasing ahead of a cold front Tuesday afternoon and evening, possibly lingering into Wednesday. A warming trend is expected through Tuesday, with slightly cooler highs and lower humidity Wednesday into next weekend.

Surface front looks to be oriented NW-SE across the CWA early this morning, extending upstream into the lower Ohio Valley. Aloft, a full-latitude trough is in place over the Eastern Seaboard and Great Lakes, with a deep, broad upper anticyclone situated over the Rockies/Plains. This pattern will leave us in a persistent NW flow regime aloft through the first half of the week, and multiple subtle embedded shortwaves or ripples of vorticity are expected to dive through the trough and over the southern Appalachian region, potentially enhancing the development of convection, some of which may be nondiurnal in nature.

Today and Monday, forcing is rather ill-defined overall; drier air will gradually filter into the area and should push the frontal zone southward. Ridgetop convergence, and/or a lee trough at the surface, potentially will fire a few storms this afternoon even if the shortwaves aloft aren't a factor, so we retain 20-40% PoPs over much of the area downstream of the Blue Ridge Escarpment. 0-6km shear will be high for this time of year, 30-40 kt, with 0-3km shear 15-25 kt. Any storms that do fire may form into clusters, and if so they could pose a risk of damaging wind. The 00z NAM develops convection over the area after sunset which could be partially due to one of the embedded ripples aloft, but confidence is low on where that might happen if at all. The continued drying leaves behind dry and slightly capped profiles in place for Monday, which results in only 10-20% PoPs at best. Shear parameters will be similar but the severe threat during the afternoon would appear to be lower on account of lower instability. A few models have been hinting at a possible MCV or cold pool arriving Monday night from an upstream MCS, but even if that were to occur it would appear unlikely to survive over the Appalachians with the unfavorable thermodynamic profiles. SPC does hint at the possibility of an MCS reaching the far northern or western portions of the CWA before falling apart, by including those areas in a marginal risk on Day 2. Currently can't advocate for any more of the CWA being included than those areas.

A better defined shortwave will rotate into the trough on Tuesday and will bring a cold front southward toward our area. Assuming we are not still stabilized by a cold pool or debris cloudiness from Monday night, our MCS potential still looks greatest late Tuesday into Tuesday night: WAA ahead of the front should promote warmer daytime temps and deeper mixing which should overcome the cap, so we will see instability return to values more typical of a hot July afternoon, still with favorable shear and sfc-midlevel delta-theta-e values suggesting easy cold pool formation ahead of the front. Timing of the front suggests convective/severe threat could be greatest after peak heating, well into Tuesday night particularly in the southern CWA. Confidence is still limited partly due to not knowing how any cold pool from Monday night come into play. Day 3 outlook is not out as of this writing, but based on yesterday's Day 4, we are likely to be included in a marginal or slight risk for Tue/Tue night. Temps Tuesday will be the warmest of the week, mostly in the lower to mid 90s across the Piedmont; heat index is likely to exceed 100 and may reach 105 in the urban areas in the I-85 corridor or southeast.

Temps trend back to near or slightly below normal Wed-Sat in the wake of the front, but perhaps of more interest humidity should be much lower with dewpoints falling into the lower 60s each afternoon. The ridge-trough pattern across the CONUS does not break down, however. The front will stall north of the Gulf Coast and potentially will be reactivated by the next shortwave or low diving past the anticyclone. A few diurnal showers/storms appear possible by Friday with chance PoPs for all areas on Saturday with the activating front.

AVIATION /07Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Broad area of low VFR to MVFR stratus extends along a stalled front over the Carolinas early this morning. A few SHRA/TSRA will be possible beneath this cloud deck. Northwest downslope flow over the Appalachians has led to some breaks in the deck at times; thinking is that where the stratus scatters, with light winds and lack of higher cloud decks areas of LIFR stratus and/or fog could form. Confidence is limited on where this may occur so TEMPOs were used near daybreak for that possibility and/or for vsby restrictions in precip. Restrictive cigs are expected to linger through late morning before scattering. With warmer temperatures returning spotty development of diurnal SHRA/TSRA this afternoon warranted inclusion of a PROB30 at all sites except KAVL, which only receives a VCSH due to storms being more likely to form to the east or southeast and propagate away from the terminal. Low confidence for timing/placement of restrictions tonight/early Mon though sfc will remain moist and cloud cover expected to be SCT at best. Will be evaluating that more closely for 12z issuance.

Outlook: Only isolated TSRA expected Monday afternoon/evening. Strong to severe thunderstorms, as well as, breezy SW winds are possible Tuesday afternoon/evening ahead of a cold front. The severe storm threat could linger into early Wednesday, but confidence is low at this time. Low stratus and/or fog will be possible each morning, mainly in the mtn valleys.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.