textproduct: Columbia

WHAT HAS CHANGED

Aviation updated for 12Z TAFs.

KEY MESSAGES

- 1. Significant and beneficial rainfall expected later today through Saturday.

- 2. Cooler than normal temperatures this weekend followed by a significant warmup next week.

DISCUSSION

Key Message 1: Significant and beneficial rainfall expected later today through Saturday.

Radar tonight shows a few showers developing across the Midlands as a cold front moves through the region. Additional rain is possible today prior to the arrival of the main batch of rain for the evening and the overnight hours, with the highest probabilities along and south and east of I-20.

The weather pattern continues to favor the potential for the most significant rainfall event in over a month starting later today and continuing into Saturday. Northern stream energy digging into the Midwest is forecast to phase with southern stream energy moving across the Southern Plains into the Gulf Coast states by this evening. NAEFS IVT reaches the 97th percentile with strong moisture advection into the region Friday night through Saturday. Ensemble forecasts of PWATs show a strong gradient across the region with values ranging from 1.7 inches in the southeast Midlands to 1.2 inches in the northern Midlands at 12z Saturday, which likely would favor higher precipitation amounts in the southeast Midlands with lower values north. This looks to be a strong overrunning event with a surface low developing along the Gulf Coast and moving off the Carolinas coast with little to no instability available. The eventual rainfall totals and axis of highest precipitation will ultimately be dictated by when the phasing occurs and and if there is any amplification of the trough. However, overall rainfall trends have continued to improve with LREF probability of 1 inch of rain increasing over the past 3 model runs, especially across the southeast Midlands and lower CSRA. NBM also continues to increase in rainfall totals with the 50th percentile values now well over an inch across the entire area. However, the NBM continues to show a large range in values with the 25th percentile ranging from around 0.4 inches north to 1.25 inches south and the 75th percentile ranging from around 1.5 inches north to 2.4 inches south. Regardless, this should be the ideal way to help improve drought conditions with a long duration soaking stratiform rainfall event rather than strong thunderstorms with lots of runoff from dry hard surface conditions.

Key Message 2: Cooler than normal temperatures this weekend followed by a significant warmup next week.

Temperatures this weekend expected to be well below normal with extensive rainfall on Saturday and continued below normal on Sunday behind a cold front as high pressure builds over the region. Temperatures may be nearly 20 degrees below normal for highs on Saturday with highs in the lower 60s as NAEFS 1000mb and 850mb temperatures are at or below the 10th percentile. Temperatures will gradually warm early next week as surface high pressure shifts offshore and a return southerly flow develops. Highs expected to rise back into the 80s by Tuesday and mid to upper 80s by Wednesday ahead of the next approaching system.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Periodic MVFR ceilings to start the TAF period at most locations transitioning to VFR by midday. MVFR to potentially IFR conditions return late in the period.

A pocket of MVFR ceilings has been reported around the TAF terminals and is anticipated to continue through about 14z-15z. Ceilings at CAE and CUB could stay at lower end VFR, however. One shower is showing up near OGB at the time of this writing, but will likely move away from the terminal by the start of the TAF period. East to northeast winds between 7-10 kts are expected this morning, with a few gusts around 15 kts or so. These winds are forecast to diminish through the day, shifting to more southerly by this evening. An approaching system brings rain showers and lowering ceilings tonight, likely after 03z-04z, as winds shift more westerly. Ceilings are expected to lower to MVFR as the rain moves in, potentially dropping to IFR.

EXTENDED AVIATION OUTLOOK...Periods of restrictions likely continue into Saturday as widespread rain overspreads the region. Drier conditions then are expected Sunday and into the early week.

CAE WATCHES/WARNINGS/ADVISORIES

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