textproduct: Columbia

WHAT HAS CHANGED

Lower rain chances this afternoon into tonight. Aviation discussion updated for 18Z forecast.

KEY MESSAGES

- 1. Diminishing flooding threat into Sunday with continued below normal temperatures.

- 2. A return to a more summer like pattern next week with increased strong to severe storm threat mid week.

DISCUSSION

- 1. Diminishing flooding threat into Sunday with continued below normal temperatures.

Atmospheric environment continues to be favorable to support a heavy rain and flooding threat with PWATs around 2.2-2.4 inches and MUCAPE values between 1000-3000 J/kg across the forecast area. However, a shortwave trough that supported earlier convection in moving through the Carolinas now and should be east of the forecast area by this evening with subsidence in its wake. Current radar showing generally very isolated showers across much of SC with heavier rains shifting to the NC coast where the best forcing ahead of the shortwave exists. Expect limited rain chances through the afternoon and evening with mainly isolated showers and a possible thunderstorm. Chances of rain increase late tonight into Sunday morning associated with the next shortwave moving through the developing upper trough, downstream from a building upper ridge over the Southern Rockies and Plains states. Drier air, especially in the mid levels is expected to move into the forecast area beginning tomorrow which will help to lower the flood threat. Below normal temperatures continue with extensive clouds and light northerly winds as the stalled frontal boundary becomes more diffuse.

- 2. A return to a more summer like pattern next week with increased strong to severe storm threat mid week.

LREF clustered ensemble guidance in reasonable agreement with the overall pattern for the upcoming week featuring a strong upper ridge centered over the southern Rockies and Plains states resulting in downstream upper troughing across the eastern third of the country. This pattern should support a drier air mass over the region early in the week with downsloping northwesterly flow and deeper mixing. There also is likely to be a series of smaller difficult to time disturbances moving through the flow which may add to or enhance normally diurnal convection. The increased mid level dry air may support a slightly higher chance of strong storms and lower flooding threat than we have recently experienced. Temperatures are expected to also warm back to near or above normal early in the week with Tuesday being the warmest day most likely with highs in the mid to upper 90s.

Stronger shortwave energy is forecast to dig through the base of the upper trough into the Mid-Atlantic by late Tuesday pushing a front into the region by mid week. Increased mid level flow and 850mb winds combined with moderate instability should yield increased threat of strong to possibly severe storms Tuesday into Wednesday. SPC continues to carry a 15% risk area across the Mid-Atlantic into North Carolina while CSU ML guidance continues to show a similar signal across the Carolinas on Tuesday and Wednesday. Damaging wind gusts would be the primary threat with any severe threat that may develop.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Gradual return to VFR conditions this afternoon outside of any isolated showers and storms. Restrictions may return tonight into Sunday morning.

The surface boundary has shifted slightly toward the far southeastern Midlands with light winds at the TAF sites more westerly to northwesterly. Stratus has continued to slowly mix out, but brief periods of MVFR ceilings could remain for the next hour or so before becoming VFR. As a shortwave moves into the region, a few showers/storms have developed in the Coastal Plain, but little activity is seen in the FA. OGB's proximity to the frontal boundary could possibly bring some of this activity here, but confidence remains fairly low seeing current radar trends. This evening, another shortwave currently near western Tennessee is expected to move into the region, possibly sparking a batch of showers mainly near the CSRA. This is supported in the mean 12z HREF solution and multiple CAM's, so have added a PROB30 group generally from 03z-09z to account for this. Outside of any rain chances overnight, LAMP and HRRR guidance indicate more stratus could be possible into early Sunday morning. Confidence is a bit higher toward CAE/CUB than the other terminals and potential showers in the early morning could complicate this a bit. For now have introduced periods of IFR to MVFR ceilings between 09-10z that gradually improve to the end of the TAF period, but adjustments to this may be needed in coming forecasts. Winds tonight become light and variable before picking up around 4-8 kts out of the west to northwest late Sunday morning.

EXTENDED AVIATION OUTLOOK...Drier weather and lower chances for morning restrictions expected early this coming week. By late Tuesday and into Wednesday, rain chances begin to increase again with associated restrictions possible.

CAE WATCHES/WARNINGS/ADVISORIES

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