textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Moderate QPF amounts expected along the TN border in association with the cold front crossing the area. Very light amounts expected elsewhere.

Warm and dry with gusty winds Wednesday.

Precipitation chances were removed from Thursday night into Friday morning, including the previous mention of a slight chance of light snow above 4000 ft in the western NC mountains. Any remaining snow potential is now very low and impacts would be minimal.

KEY MESSAGES

1. Dry and breezy through this evening. 2. Rain chances develop tonight into Wednesday morning before dry conditions return Wednesday afternoon. Well above normal temperatures and breezy winds stick around through Wednesday. 3. Temperatures moderate back toward seasonal levels late week and through the weekend, with lingering uncertainty tied to cold-air damming and cloud cover. 4. A widespread rain event is increasingly likely over the weekend; while flooding is not currently expected, locally heavier rainfall could lead to isolated hydro concerns if higher-end totals are realized.

DISCUSSION

Key message 1: Dry and breezy through this evening.

Cloud cover will gradually increase through late evening ahead of an approaching cold front. Gusty winds, well below advisory criteria, will continue across the area, with higher winds over the mountains.

Key message 2: Rain chances develop tonight into Wednesday morning before dry conditions return Wednesday afternoon. Well above normal temperatures and breezy winds stick around through Wednesday.

The aforementioned cold front will move across the area late tonight into Wednesday morning keeping gusty winds in place and bringing rain chances. Best forcing and deepest moisture will be across the mountains late tonight, then the Upstate and NE GA Wed morning. Highest QPF will be across the mountains where upslope flow will aid in wringing out some precip, anywhere from a tenth of an inch to upwards of an inch along the TN border. Unfortunately, amounts elsewhere look to be a tenth of an inch or less, with little to mainly a trace for the NC foothills and Piedmont.

A very dry airmass moves in behind the front with highs remaining above normal. This combined with gusty NW winds behind the front could lead to some fire danger concerns. That said, land managers indicate fuel moisture values are likely high enough to preclude any widespread problems.

Lows tonight be 15 to 20 degrees above normal. Highs around 15 degrees above normal.

Key message 3: Temperatures moderate back toward seasonal levels late week and through the weekend, with lingering uncertainty tied to cold-air damming and cloud cover.

After the current unseasonably warm stretch, a cold front will move south through the area Wednesday, ushering in northerly flow and a return to cooler conditions. However, the core of the arctic air mass will remain displaced well to the north across eastern Canada and the Northeast, preventing a true cold outbreak. As a result, temperatures are expected to trend back toward near normal for mid February, with highs generally in the 50s to near 60 degrees across the lower and southern Piedmont from Thursday through Sunday.

Low temperatures are more nuanced. With surface high pressure tracking just north of the area through the Great Lakes, Ohio Valley, and eventually the Mid-Atlantic and New England, a persistent pressure gradient may limit ideal radiational cooling on some nights. Sheltered locations may drop closer to climatological lows, while other areas remain several degrees above normal. In addition, increasing cloud cover and warm-air advection ahead of the next system will result in well above normal overnight lows Saturday night through Monday night, with departures of 10 to 20 degrees above climo possible.

High temperature confidence remains relatively good through Saturday, as reflected by a narrow NBM ensemble spread of only 2 to 5 degrees. Ensemble spread increases substantially by Sunday (8 to 12 degrees), driven by uncertainty in the northward extent of a warm front and the strength and persistence of a cold-air damming wedge. This wedge may be reinforced by evaporative cooling as precipitation falls into an initially dry boundary layer. Given the known challenges global guidance faces in CAD setups, forecast confidence is lower than normal. The deterministic NBM trended toward the warmer end of the envelope, so temperatures were tempered toward the cooler ensemble percentiles based on pattern recognition.

Key message 4: A widespread rain event is increasingly likely over the weekend; while flooding is not currently expected, locally heavier rainfall could lead to isolated hydro concerns if higher-end totals are realized.

A strong Pacific shortwave trough is forecast to move into the Southwest U.S. late this week, then track eastward along the subtropical jet across the southern CONUS over the weekend. This southern track favors efficient moisture transport from both the tropical Pacific and the Gulf of Mexico. As a result, precipitation is expected to overspread the region from the southwest late Saturday afternoon into Saturday night, with the most widespread and steady rainfall occurring from late Saturday night through Sunday afternoon as forcing strengthens.

The heaviest rainfall is expected to coincide with persistent isentropic lift north of a warm front stalled to the south, along with the development of a southerly low-level jet overrunning a shallow cold-air damming wedge east of the mountains. While surface winds within the wedge are northeasterly and not classically upslope for the Blue Ridge Escarpment, the rainfall signal does not appear to be driven by low-level mechanical upslope alone. Instead, ensemble guidance suggests that the higher QPF along the southern Blue Ridge Escarpment and adjacent foothills is more likely tied to enhanced ascent along the baroclinic zone marking the southwestern edge of the CAD wedge. This zone often focuses stronger warm-air advection, deeper saturation, and prolonged lift, which can effectively anchor heavier precipitation bands near the escarpment. While some upslope contribution may occur above the ridge tops within the southerly flow aloft, the primary signal appears thermodynamically driven rather than purely terrain forced. A shallower-than-modeled wedge would further support this enhancement closer to the terrain.

NBM 48-hour QPF probabilities reflect this signal, with a 50-70% chance of exceeding 1 inch across much of the area and locally higher probabilities near the southern Blue Ridge Escarpment. Probabilities of exceeding 2 inches generally remain in the 10-30% range, increasing to 40-60% in portions of the mountains, foothills, and adjacent Upstate and northeast Georgia. While exceedance probabilities for 3 inches are lower, localized higher-end totals are not out of the question if the baroclinic zone remains stationary for an extended period.

At this time, antecedent dry conditions and the expected rainfall rates suggest a low risk for flooding. However, should higher-end rainfall totals materialize, localized hydro impacts could develop, particularly in terrain-favored areas. This system will continue to be monitored closely as confidence in placement and persistence of heavier rainfall bands increases.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

At KCLT and elsewhere: Dry and VFR through late tonight. SW winds with low end gusts into the evening for all but KAVL where light SW wind this morning turns NW and picks up in speed this evening. Low VFR clouds increase late tonight ahead of a cold front. Precip chances increase as well...and have PROB30s for this and associated MVFR conditions. Stronger westerly low level winds increase as well, leading to the potential for LLWs at KAVL. By 15Z or so, the front moves out of the area ending the threat of precip and restrictions. Winds turn W to NW with an increase in speed and gusts. This also ends the LLWS threat at KAVL as the low level winds turn NW as well.

Outlook: Dry and VFR conditions continue into Thursday before precipitation chances and associated restrictions develop Friday into the weekend ahead of a low pressure system.

GSP WATCHES/WARNINGS/ADVISORIES

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