textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated for the Aviation Discussion.

KEY MESSAGES

1. A line of thunderstorms may organize over Tennessee Saturday afternoon and reach the mountains of North Carolina before weakening late Saturday evening. There is a Marginal Risk of severe thunderstorms over the mountains and foothills through Saturday night, with the main threat being damaging wind gusts. 2. Warm and well above normal with mainly diurnal convection each day through the middle of next week. The potential for organized convection increases Thursday into Friday in association with a cold front, with cooler weather following.

DISCUSSION

Key message 1: A line of thunderstorms may organize over Tennessee Saturday afternoon and reach the mountains of North Carolina before weakening late Saturday evening. There is a Marginal Risk of severe thunderstorms over the mountains and foothills through Saturday night, with the main threat being damaging wind gusts.

Our recent late-spring-like pattern will relent somewhat over the next 24 hours, to the extent that the upper anticylone/sfc high off the Southeast Coast flattens and moves east, but in the meantime a S/SW low level flow ahead of an approaching front will continue to bring warmth and humidity into the region. The balance of Saturday is expected to be not as eventful as Friday. Lingering cloudiness in the morning should prevent temps from warming up quite so fast, thus the record highs are not as likely to be broken. We should also get a later start toward convective initiation, so precip chances are pushed out more into the late afternoon.

The main concern will be storms that develop along/ahead of the approaching cold front in the afternoon out over TN. The CAMs suggest a line of storms that would organize over middle TN in the late afternoon and then plow eastward toward the mtns in the evening before the front slows down as the pattern becomes more zonal. The environment ahead of the front/convective line looks rather modest with muCAPE no better than maybe 1000-1500 J/kg and shear on the order of 25-30 kt. This, being a somewhat limiting factor, is what is probably keeping the convective outlook set at a Marginal Risk for the area basically N and W of I-85 thru daybreak Sunday. Still, the output of the 00Z HRRR and NAMNest look interesting enough to support the idea that there would be some wind gust potential with the storms as they reach the mtns Saturday evening. The convective environment looks more unfavorable east of the mtns early Sunday morning. As to the forecast, the precip probs ramp up to the likely and categorical ranges over the mtns Saturday evening, but will stay more in the chance range over the east. Note that if the available 00Z CAMs are correct, the remnants of the convective line will be passing off to the east by daybreak Sunday, and thus the precip probs seen in the model blend at 12Z Sunday would be way overdone. Don't be surprised to see some downward adjustment later today.

Key message 2: Warm and well above normal with mainly diurnal convection each day through the middle of next week. The potential for organized convection increases Thursday into Friday in association with a cold front, with cooler weather following.

With a region of dampening height falls passing north of the area...a weak cold front is expected to be draped across the forecast early Sunday. The latest Convection-Allowing Models suggests showers and storms will be few and far between early in the day, but coverage should blossom throughout the late morning into the afternoon as the boundary layer warms/modestly destabilizes. Morning cloud cover is expected to limit the degree of instability to the tune of 500-1000 J/kg, but improved deep layer shear of 30 to 40 kts will increase the potential for organized convective structures. Nevertheless, the shear/buoyancy combo will support a marginal-at-most risk of severe storms.

Frontal boundary will push east of the area by late Sunday, generally bringing an end to convective chances. Having said that, any air mass change will be subtle (a slight drop in dewpoints), with upstream height falls flattening the upper air pattern over the northern half of the country, while a strong upper low is expected to settle over the Baja. A warm and humid warm sector regime will return to our area by Tue, with mostly diurnal convective chances returning through mid-week. Daily high temp and maximum low temp records will be in jeopardy each day Mon->Wed.

Toward mid-week, an area of height falls making landfall in the Pacific NW is forecast to kick out the Baja upper low over the Four Corners, with phasing of the northern and southern stream into an anomalously deep trough likely occurring across the Great Plains and Miss Valley by Wed night. Associated cold front will likely march across the Southeast and Mid-Atlantic Wed night into Thu. A consensus of model guidance indicates the potential for a well-forced front interacting with an unseasonably warm and humid air mass, and thus at least some potential for organized/perhaps severe convection and locally heavy rainfall. Forecast temperatures finally return to values more sane for the first half of March Thu into Fri.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Once again we look to the south for the development of a low cloud deck and/or fog that has moved over our area with the continuing light SLY flow. The boundary layer should be moist enough that the development of a cig restriction by mid-morning is a decent bet for most terminals. By mid-aftn, the boundary layer should deepen enough to lift cigs to VFR, if it hasn't already scattered out. The S to SW flow will continue with some gusts possible this afternoon. The latest guidance con- tinues to suggest a better chance of shower/thunderstorm activity this evening and into the overnight as a front approaches from the west. Thus, I have PROB30s for -TSRA at all sites during this time window with prevailing showers and/or thunderstorms at most sites just after 00z.

Outlook: The spring-like weather pattern will continue for the next several days with patchy fog/low stratus possible each morning.

CLIMATE

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

RECORDS FOR 03-11

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 79 1967 29 1924 55 2016 14 1934 1925 KCLT 83 2015 37 1960 60 1986 22 1969 2009 1934 1990 KGSP 84 2009 34 1960 60 1986 17 1969

GSP WATCHES/WARNINGS/ADVISORIES

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