textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Lowered temperatures today with cloud cover being more persistent than previously forecast.

KEY MESSAGES

1. Cold air damming weakens today but looks to keep temperatures relatively cool. Abundant surface moisture may allow formation of dense fog tonight that could impact the Wednesday morning commute. 2. Well above normal temperatures and mostly dry conditions through the weekend with rain chances possible by Sunday.

DISCUSSION

Key message 1: Cold air damming weakens today but looks to keep temperatures relatively cool. Abundant surface moisture may allow formation of dense fog tonight that could impact the Wednesday morning commute.

Late-stage cold-air damming persists over the region, with parent high still strong at ~1040mb but now centered over the Atlantic, off the New England coast. Moist southerly flow is occurring over the wedge, which produced low stratus over much of the area early this morning. Wedge inversion is shallow, below 3000 ft AGL across NC/SC and NE GA, with northeasterly flow occurring up to around that level. The stratus are trapped under the inversion, proving stubborn. As long as they persist, the wedge likely will as well, although the chance of precip is minimal. Seeing some thin patches south of I-85 near the Savannah River and in the northern NC foothills. That could lead to holes forming, which would be expected to expand at least slightly with time. Higher cloud cover should diminish with 850mb RH decreasing this afternoon, allowing insolation to warm the cloud layer as well. All these noted, per short-term model progs, these developments look unlikely to occur early enough in the day to allow our previous fcst max temps to be reached. Those values have accordingly been lowered; maxes are now at or below 60 in most of the Piedmont. The lower parts of the French Broad and Little TN valleys, near the TN border, look to be the warmest parts of the CWA today.

The afternoon cloud cover forecast also makes tonight's forecast more challenging. Even the more wedge-sensitive guidance has winds turning southerly (but remaining light) this afternoon as the parent high loses influence. The southerly flow likely will be associated with near-surface moisture advection, and potentially areas of fog developing overnight, toward daybreak Wed. However, the persistence of stratus could keep sfc temps elevated and inhibit the decoupling necessary for dense fog; most guidance with fog tonight does so where skies manage to clear in the late afternoon or evening. Thus the most likely location of any dense fog currently looks to be areas south of I-85, where the wedge has least influence, as well as the northern foothills due to the aforementioned thinning.

Though a moist boundary layer will remain in place Wednesday, 925mb thermal advection turns neutral and the parent high even more distant, so we will advertise scattering clouds and warming reflective of the spring or early-summer like pattern, with max temps in the lower-mid 70s.

Key message 2: Well above normal temperatures and mostly dry conditions through the weekend with rain chances possible by Sunday.

A strong Bermuda High, a pattern generally typical in the summer months, remains fixated off the Carolina coast and well over the region through at least Monday. Current guidance retains weak southerly/southwesterly flow and very slow moisture return through the end of the forecast period. The persistent high pressure keeps temperatures well above normal everyday and rain chances away until the weekend. Guidance has trended drier, but depicts an eastward shift of the high pressure. If this occurs, more moisture could advect into the region along the western fringe. This has the potential to increase rain chances on Saturday, though confidence remains low. By Sunday, model guidance lifts an area of low pressure across the northern Plains and drag a weak cold front towards the area, also increasing rain chances. Additionally, depending on when/if this front can make it into the CWA, there could be a low chance for thunderstorms. Will continue to monitor.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

At KCLT and elsewhere: Cold-air damming hanging on by a thread across the region, but with inversion remaining strong and moist over all sites except KAVL, restrictions will continue into the afternoon. KAVL will see a few clouds at MVFR to low VFR level though they are likely done with restrictions for today. Elsewhere the existing stratus should gradually lift back to VFR and partially scatter by late aftn or early evening. Winds generally will be somewhat VRB as the shallow NE flow near the surface mixes with light S to SW winds above the inversion, but SW sfc winds should prevail by late afternoon, remaining there if not going calm/VRB overnight. Not expecting moisture to completely mix out, and as the SW winds will be associated with near-sfc moisture advection, some areas of fog and low stratus remain possible overnight; cigs likely to form at low VFR to MVFR level. Not confident enough to go with IFR at KCLT or the SC sites due to that stratus looking more likely than ground-based fog, although it cannot be completely ruled out. KHKY is the exception with clearer skies going into the night and potential for IFR radiation fog and/or stratus. Expecting faster erosion of low clouds after daybreak Wed than what was seen today, and winds to come up from the SW.

Outlook: Springlike weather pattern over the next several days. Cannot rule out patchy overnight fog/stratus. Another cold front may bring showers and associated restrictions for the weekend.

CLIMATE

RECORDS FOR 03-05

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 78 1955 20 1960 60 2004 5 1960 KCLT 84 1955 31 1960 62 1955 12 1960 1880 KGSP 80 1976 31 1960 61 2004 12 1960 1905 1976 1961

RECORDS FOR 03-06

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 78 1908 28 1960 58 1961 5 1960 KCLT 80 2022 33 1901 62 1961 10 1960 KGSP 79 1974 37 1948 63 1961 16 1960 1915 1901

RECORDS FOR 03-07

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 82 1974 23 1920 61 1956 15 1960 KCLT 85 1974 30 1899 63 2022 14 1899 1956 KGSP 83 1974 36 1920 62 1961 13 1901 1901 1956

RECORDS FOR 03-08

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 81 1974 23 1996 57 1921 8 1920 KCLT 84 1974 36 1989 59 1946 16 1920 KGSP 84 1974 35 1899 56 1921 14 1901 1899

RECORDS FOR 03-09

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 80 1974 22 1932 57 1964 8 1996 KCLT 83 2009 30 1960 62 1925 16 1996 1974 1921 1925 KGSP 85 2009 29 1960 60 2009 16 1996 1921

RECORDS FOR 03-10

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 76 1974 29 1932 58 1903 10 1996 1932 KCLT 82 1974 36 1924 59 1903 17 1932 KGSP 84 1974 39 1924 58 2009 17 1932 1997

GSP WATCHES/WARNINGS/ADVISORIES

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