textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation forecast was updated to reflect the impending 06z TAF issuance.

Rainfall totals for today (Sunday) were refined, but the forecast has not changed significantly in most locations. Some areas across the I-77 corridor can now expect higher rainfall totals than in previous forecasts.

KEY MESSAGES

1. Widespread precipitation develops across the western Carolinas tonight through Sunday night, bringing a spell of much-needed rain to the area. 2. Dry with a warming trend next week, perhaps warming to near record temperatures by Thursday and Friday.

DISCUSSION

Key message 1: Widespread precipitation develops across the western Carolinas tonight through Sunday night, bringing a spell of much-needed rain to the area.

Already seeing light radar returns making their way into the Upstate and southern Blue Ridge tonight as moist upglide, already well underway upstream, begins to blossom across along and just east of the Savannah River Valley. What real-time profile data is available suggests there's still quite a bit a dry air in the mid- to low-levels, and this is supported by 03z METARs still boasting 20+ degree dewpoint depressions...so it'll be a while yet before we start to see more than a stray sprinkle here in the Carolinas.

The overnight hours will feature the steady march of a mature surface low, presently analyzed over extreme eastern Texas and Oklahoma, into the Mississippi Valley. Operational guidance still depicts the low actually occluding as its upper-level reflection begins to outrun it, and beginning to weaken around and after daybreak as it pushes into northern Alabama and Georgia. This looks like it'll take place too late, however, to stop ample moisture from making it into the Carolinas...resulting in PWs well above normal for February and some 2 to 3 standard deviations above NAEFS climatology. So, despite the cyclone's weakening, there'll be a period from mid-morning through late afternoon today during which significant synoptic forcing associated with the the upper wave and supplemented by the subpolar jet will drive widespread efficient rainfall and resulting in a weak in situ CAD wedge developing east of the NC mountains.

Impact-wise...this still looks like it'll produce QPF of 1.1-1.5" across most of the area along with isolated higher values across the Blue Ridge Escarpment. The 00z HREF depicts probability-matched mean values in excess of 1.5" across parts of the southeastern Upstate and NC I-77 corridor, which may be due in part to the potential for some erosion of the in situ wedging during the afternoon. Both the 00z HREF and the 00z REFS depict 40-50% probability of appreciable surface-based instability developing along the extreme southern and eastern tier of the forecast area as a result, which could produce localized higher rainfall rates in these areas during the afternoon and early evening should any convective towers develop.

Sunday night, operational models still depict secondary cyclogenesis somewhere between the NC Sandhills and Outer Banks, which should effectively push a backdoor cold front across the Carolinas overnight, eroding the wedge and bringing an end to precipitation by early Monday morning.

Key message 2: Dry with a warming trend next week, perhaps warming to near record temperatures by Thursday and Friday.

Cold Air Damming wedge will be quickly to break down Sunday night into Monday as the parent surface high shifts off the New England coast and the upper shortwave trough slides off the Carolina coast. This will allow for a return of above average temperatures with highs climbing into the low to mid 60s beneath mostly sunny skies. Heading into mid week, global models and their respective ensemble members paint a coherent picture with a flat and broad upper ridge extending from Mexico across the Gulf. On the poleward side of the ridge, a belt of westerlies is progged to extend from the Desert Southwest to the Appalachians. Rising heights and warming low-level temperatures within an expansive warm sector will promote a continued warming trend with highs soaring to the upper 60s and low 70s on Wednesday with low to upper 70s common by Thursday and Friday. Temperatures late week may challenge daily record highs. Most of the forecast will remain dry with a couple isolated to widely scattered showers on Thursday. Rain chances may increase by Friday as an upper trough axis swinging across the Great Plains into the Mississippi Valley helps to finally push a stalled frontal boundary towards the area. Guidance diverges by this point, however, with respect to timing of the boundary into the area and coverage of any associated showers.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Murky, murky, murky, in store for Sunday. It's presently VFR at all terminals circa 0530z, and upstream METARs suggest it'lll likely remain that way through daybreak or so, as rainfall gets only a slow start ahead of an aproaching cyclone. Retained the previous TAFs' PROB30s for -RA leading up to daybreak. Guidance is in good agreement that while restrictions develop and conditions crash after 12z, they'll crash HARD, with deterioration from VFR to MVFR to IFR or worse taking place in just 2-3 hours Sunday morning, as rainfall quickly intensifies across the terminal forecast area. Expect widespread LIFR ceilings for much of the day Sunday, and periods of heavier precipitation accompanied by IFR to LIFR visibility. Some locations - best confidence is at KAVL - will see 25-35kt LLWS during the day today also. Winds will be light and out of the SE, becoming NE by mid- to late-morning. Quick improvement is expected after sunset as dry air begins filtering in behind this system...with a rebound to at least MVFR by midnight, and VFR likely at all the TAF sites after midnight.

Outlook: VFR returns by Monday morning and dry conditions persist through the end of the week.

GSP WATCHES/WARNINGS/ADVISORIES

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