textproduct: Columbia

WHAT HAS CHANGED

Updated thinking for Saturday forecast and 06z aviation discussion.

KEY MESSAGES

- 1. Only a few storms expected mainly in the northern Midlands and Pee Dee, late this afternoon and evening, but these storms could be strong-severe.

- 2. Well above average temperatures expected to continue through Monday before a front moves in next week.

DISCUSSION

KEY MESSAGE 1: Only a few storms expected mainly in the northern Midlands and Pee Dee, late this afternoon and evening, but these storms could be strong-severe.

A low amplitude 500mb shortwave, currently visible in the water vapor across the central US, will dive through the northwest flow in the ridging aloft and into our area this afternoon. At the surface, strong ridging to our southwest and a weak trough to our north will help produce some convergence across SC this afternoon and will serve as a subtle initiation mechanism for convection. While low level dry air is pervasive, enough surface heating, and favorable lapse rates aloft thanks to the 500mb shortwave, will produce a swath of mixed layer instability between 500-750 J/kg across central and northern SC. With this meager instability, forcing that is not remarkable, and dry air below 700mb, convective coverage is expected to be limited; the best confluence of surface convergence, moisture availability, and instability is generally along the NC-SC, so this is where the highest likelihood of a few thunderstorms is between 400-900pm, albeit still fairly low. The 00z HREF which lines up better with current obs, has steadily weakened and slowed the approaching shortwave and therefore reduced convective coverage. While coverage will not be widespread, the inverted V soundings below 700mb, mid- level moisture that should prevent over- entrainment, and notable unidirectional cloud layer northwesterly shear around 30 knots, does suggest that any individual storm could produce a severe wind- hail threat, hence the Marginal risk outlook.

So, only a few storms are likely, north of I-20 towards the NC- SC border, but these storms will have an increased severe potential from roughly 400-900pm.

KEY MESSAGE 2: Well above average temperatures expected to continue through Monday before a front moves in next week.

No notable changes in the forecast for late weekend and early next week with high confidence in the well above average temperatures Sunday-Monday as upper ridging strengthens over the area. NAEFS mean continues to indicate 850mb temperatures rise to above the 97.5th or 99th percentile. While not expected to reach daily records through Sunday or Monday, blended guidance indicates highs will be 15 to 20 degrees above seasonal average, generally in the mid to upper 80s. A mostly dry front will move in late Monday, leading to temperatures closer to seasonal average for the middle of next week, although not a particularly cold air mass is expected behind the front with frost or freeze not expected through the end of next week.

Given the persistent low level dry air and northwest winds, we are entering a period of increasing fire danger concerns given the lingering drought conditions. Wind speeds however are expected to remain below critical thresholds, with max wind gusts around 20 mph Sunday-Tuesday.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Generally VFR conditions expected through the 24hr forecast period.

Satellite imagery showing high clouds spilling down the east side of an upper ridge into the area which should continue through the period. Bufkit time height show a solid low level jet around 35 knots which should provide marginal LLWS so included LLWS at CAE/CUB where confidence was highest. Otherwise southwest winds around 5 knots expected overnight before picking up from the west at around 10 knots with some gusts up to 20 knots possible after 15z all terminals. Some late afternoon convection is expected to develop across western NC and in the Upstate associated with a weakening shortwave moving through the northwesterly flow aloft but it appears most of this convection should remain north of the terminals so left out any mention at this time until confidence increases. Winds should subside to 5 knots or less after 00z.

EXTENDED AVIATION OUTLOOK... A more significant cold front will move through on Monday, with a slightly better chance for restrictions. Overall, conditions will be most likely VFR for the next several days.

CAE WATCHES/WARNINGS/ADVISORIES

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