textproduct: Columbia

WHAT HAS CHANGED

Precipitation chances trending downward over the next few days ahead of a cold front this weekend.

KEY MESSAGES

- 1. Daily shower and thunderstorm chances continue through the week, with isolated flash flooding possible.

DISCUSSION

Key Message 1: Daily shower and thunderstorm chances continue through the week, with isolated flash flooding possible.

As the upper trough off the east coast begins to deepen, a back door front will sag southward into the FA later today. PWATs will still remain in the 1.5-2" range, but the rich moisture flow that was in place the previous few days has started to shift orientation further north and east as more southwesterly to westerly flow settles into the area.

The latest guidance has started to trend a bit drier as the front starts to push dry northwesterly downslope flow across most of the CWA Thursday afternoon. However, there is still a decent amount of instability and moisture in the air mass to warrant a concern of storms ahead of the front. Most CAMs show minimal activity in the latest 00Z run, but I would still expect scattered showers and thunderstorms to develop from the upstate and traverse into the midlands/CSRA during the afternoon and evening hours. Up to ~2000 J/kg of CAPE across the area may be enough for a storm or two to become severe. But, overall the threat will remain low. Downbursts with precip loading as well as damaging winds with the strongest storms are certainly possible, but flash flooding with training storms is the most likely threat given the amount of rainfall we have seen in places the past few days.

Friday through the weekend is more uncertain. Guidance is mixed on where this backdoor front ends up. There is a range of possibilities, from the RRFS-MPAS which pushes the front clear into central GA to the ECMWF which hangs it up in the western Midlands. This will mainly modulate rain chances Friday/Saturday as it is likely that this front begins washing out a bit and lifting northward over the weekend. Given our saturated soils currently, any areas that do see repeat rounds of thunderstorms this weekend will have a flash flood threat associated with them. PWATS greater than 2" will promote more efficient rainfall. While showers and storms are expected each day Fri- Mon, the best chances appear to be in the CSRA on Friday and then the central/southern Midlands and CSRA on Saturday with better chances overspreading the area thereafter. Models are suggesting Saturday to be more of a stratiform rain event. A more robust front will push through on Monday as guidance begins to suggest a prolonged period of drying into the middle of next week, giving us a break from the above normal rainfall. Temps will also trend downward a little below normal with dewpoints decreasing as well, giving us a bit more of a pleasant start to June.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Predominantly VFR conditions expected with brief restrictions possible each morning. Diurnal thunderstorms are expected to develop and may periods of bring heavy rain, reduced visibility and gusty winds.

Limited restrictions are expected early this morning. Guidance has been persistent showing no or very brief vsby/cig restrictions during the predawn hours. However with shallow low level moisture in place and some rainfall the previous day we have included a tempo group for vsby and/or cig restrictions during the 010z-12z time frame.

Any restrictions in the morning should lift by 15Z as winds pick up from the west around 6 to 10 knots ahead of an approaching backdoor front. Scattered convection will develop this afternoon ahead of the front and as the front moves through the Carolinas in the evening. North winds should develop tonight as the front moves south and drier air pushes into the region. Depending on the location of the front there could be fog or stratus early Friday morning. However confidence is low at this point so we have not included it in the TAFs for now.

EXTENDED AVIATION OUTLOOK...Shower and thunderstorm chances increase over the weekend as a front settles over the region. The greatest rainfall and early morning fog/stratus chances will be favored across the CSRA and southern Midlands.

CAE WATCHES/WARNINGS/ADVISORIES

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