textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated aviation discussion for the 00Z TAFs.

KEY MESSAGES

1. Scattered showers and isolated thunderstorms possible tonight into Tuesday. Near-record warmth returns Tuesday. 2. A strong cold front arrives Wednesday night into Thursday morning, producing widespread showers and embedded thunder, with a very limited severe weather threat. Cooler and drier conditions develop behind the front on Thursday and Friday. 3. Dry conditions persist the first half of the weekend before another cold front arrives Sunday into Monday.

DISCUSSION

Key message 1: Scattered showers and isolated thunderstorms possible tonight into Tuesday. Near-record warmth returns Tuesday.

Split-flow regime will remain in place through Tuesday; ahead of the deep cutoff low near Baja California, heights will rise as southwesterly flow occurs out of the western Gulf, promoting an increasingly warm and humid airmass across the lower MS Valley. The front which effectively reached our CWA and stalled late Sunday will be reactivated across the TN and lower OH valleys, leaving a NW-SE oriented gradient of moisture/instability from TN to SC through tonight.

MCS continues to steadily approach out of the west this evening. With the loss of daytime heating and a rather stable air mass in place across the GSP CWA ahead of the system, the severe threat should remain very low. A few strong, sub-severe storms cannot be entirely ruled out, mainly over NE GA and the western SC Upstate as these areas have the best potential to see the stronger part of the MCS track overhead. Showers are likely across the southern NC mountains. Some showers may reach as far north as the central and northern NC mountains, but confidence is lower on this potential and will depend on how far south the MCS ends up tracking. Shower chances will be lower the farther east you go as the system will continue weakening as it pushes eastward tonight into the early morning hours Tuesday. Prog soundings remain marginally favorable for convection through the end of the day Tuesday, though with the shortwave moving east of the CWA by early afternoon, the better chance is probably during the morning. Can't rule out isolated redevelopment over the mountain ridges which then could propagate eastward.

Cloud cover from the MCS or morning convection currently look to advect out Tuesday morning, but that does lower confidence slightly in max temps Tuesday afternoon, which otherwise should be warmer than Monday. The current forecast high at CLT and AVL does break the daily record, with GSP falling a couple degrees short--perhaps reflecting guidance that hangs onto the cloud cover longer. Record warm min temps are also likely to be broken Tuesday night.

Key message 2: A strong cold front arrives Wednesday night into Thursday morning, producing widespread showers and embedded thunder, with a very limited severe weather threat. Cooler and drier conditions develop behind the front on Thursday and Friday.

By Wednesday morning a remnant cutoff low over western Texas will be in the process of interacting with a low-amplitude trough extending along the Rocky Mountain front range...and should begin opening into the mean flow by late in the day, resulting in an elongated trough axis spanning the entire Mississippi Valley and progged to arrive in the Appalachians by late Wednesday night. At the surface, a low pressure center will follow the trough axis northeastward from the lower Midwest into New England through late Wednesday night. Recent operational runs depict slower phasing of the upper low and trough and weaker steering overall. As a result, progression of this frontal boundary occurs more slowly than it did in previous forecast cycles, and much better dewpoint pooling is depicted ahead of the front for Wednesday night and Thursday morning. Long-range ensembles seem to favor this idea as well, with over half of LREF membership trending toward a slower solution.

The thinking remains, therefore, that the severe risk will be nonzero but limited. It still appears as though instability will be severely constrained by the late night / early morning timing when deep synoptic forcing is expected to peak. Whatever narrow ribbon of DPVA and associated frontal uplift push across the area ahead of the trough axis will do so in the middle of the night, absent much surface-based instability. After 06z Thu, models depict a narrow tongue of 50-100 J/kg sbCAPE dipping out of the mountains and into the NC Piedmont/SC Upstate...paired with some 50-65kts of deep layer shear...enough to organize whatever storms develop. Given such scant instability, it's hard to imagine more than a a few isolated storms will develop, but those that do will have the capacity to become strong to severe.

Strong postfrontal CAA will set up on the leading edge of a cooler continental air mass on Thursday, as the front departs to our east. This will provide a narrow window on Thursday and Thursday evening for gusty winds across the mountains as well as light NW flow snow showers, and perhaps even some accumulation at higher elevations. By Thursday night, however, ensembles are in good agreement that a developing low over the Midwest will become the dominant feature, allowing the Carolinas to quickly toggle back to a southerly moist return flow...so cold, near- or even below-normal conditions on Thursday night will already be trending warmer by the end of the week.

Key message 3: Dry conditions persist the first half of the weekend before another cold front arrives Sunday into Monday.

A weak reinforcing cold front may cross the area with little fanfare on Friday, but by the time of its arrival most guidance suggests it'll be fading to obscurity. Thus, we can expect to more or less remain within a weak return flow through the weekend. This will result in the return of at least low-end PoP by Sunday afternoon...confined mainly to the NC mountains...and a warming trend that will persist through the end of the seven-day forecast.

Rapid cyclogenesis will take place in the lee of the Rockies on Sunday as well. Operational models are in remarkably good agreement that this feature will track into the lower Midwest and eventually the Allegheneys by Sunday night, driving another cold front across the area into Monday. The potential for convection associated with this front will depend heavily on its timing and the availability of decent instability and shear; right now, there's too much uncertainty to make much of a solid assessment.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Mostly dry and VFR through the 00Z TAF period, outside of the potential for brief -SHRA developing tonight at KAVL and across the SC terminals as a decaying cluster of storms approaches out of the west. Confidence on whether this activity will hold together all the way to KHKY or KCLT remains low so went with dry conditions across these terminals. Cirrus will gradually increase in coverage from west to east this evening into tonight, but restrictions should be limited to areas that see -SHRA develop. Brief LLWS may develop at KGSP and KGMU from 06Z-10Z. Cloud cover will gradually thin throughout Tuesday, with VFR cumulus developing during the afternoon hours. There is the potential to see MVFR cumulus develop Tuesday afternoon but confidence is low at this time. Isolated SHRA or TSRA may return Tuesday afternoon (mainly across western North Carolina), but confidence on whether activity will track directly over a terminal remains very low. Thus, went with dry conditions towards the end of the TAF period. Wind direction will be SW east of the mountains through the period, with low-end, intermittent gusts possibly developing Tuesday afternoon. Lighter wind speeds can be expected at KAVL through the period. Wind direction at KAVL should go light and VRB later this evening into Tuesday morning before picking up out of the W/WNW Tuesday afternoon.

Outlook: Mostly dry conditions linger through Wednesday before SHRA/TSRA chances, as well as associated restrictions, return Wednesday night into early Thursday. Gusty winds develop Wednesday into Thursday. Dry conditions return late Thursday into Friday.

CLIMATE

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.