textproduct: Columbia

WHAT HAS CHANGED

Update to Aviation.

KEY MESSAGES

1) A rain-snow mix is possible on Sunday but potential for significant accumulation is low.

2) Lows this morning and Sun night may approach Cold Weather Advisory, although confidence is trending lower for Sun night.

3) Dry weather and low afternoon relative humidity levels this afternoon.

DISCUSSION

Key Message 1: A rain-snow mix is possible on Sunday but potential for significant accumulation is low.

The overall synoptic forecast will continue to favor a deepening trough through the central CONUS with surface low pressure moving along the coast with overrunning leading to developing precipitation over the area late Saturday night into Sunday. Trends in the GFS and GEFS suite have brought it closer in line with EC and EC ensembles with a more progressive trough. Strongest warm advection and associated frontogenesis has generally shifted east, although again this can be a tricky feature to pinpoint as the previous discussion mentioned. Temperatures continue to appear marginal for accumulating snow and it is likely that any snow will struggle to accumulate outside of some stronger banding where snow rates would be able to overcome marginal surface temperatures. This appears to be less likely over much of the forecast area as the progged strongest warm advection has shifted east. Guidance continues to lower the ceiling of this snow event. Blended guidance probability of 1 inch or greater of snow is around 10-20% across the area, with a notable decrease among GEFS members in the last couple runs, indicating that the higher-end limit will generally be Winter Weather Advisory criteria but this potential remains low. While it will be worth monitoring how things may evolve as we enter into the timeframe for higher resolution model guidance, at this point it appears that the most likely scenario will be rain developing over the area late Saturday night with snow mixing in with rain during the day Sunday, which will likely struggle to accumulate. Drier air likely moves into the area Sunday afternoon into Sunday evening.

Key Message 2: Lows this morning and Sun night may approach Cold Weather Advisory, although confidence is trending lower for Sun night.

Temperatures are already firmly in the 25-30 degree range, with some light winds out of the west bringing apparent temperatures down to around 20 degrees. Winds will continue to diminish by sunrise, bringing better radiational cooling towards morning. So as temperatures drop into the lower 20s and upper teens by sunrise, without the winds, apparent temperatures will converge to what the actual temperatures are. ie what the expected morning lows will be for this morning. So do not anticipate the need for a cold weather advisory this morning.

The next chance for any advisory would be Sunday night/Monday morning, but the confidence in needing that is lower at this time. Radiational cooling conditions will not be as strong due to winds keeping up around 5 mph through the night, and this will help keep low temperatures closer to the middle 20s. With the winds added in, apparent temperature readings remaining above 15 degrees for the majority of the forecast area, so the current thinking would be that a cold weather advisory would not be needed for the Sunday night/Monday morning period.

Key Message 3: Dry weather and low afternoon relative humidity levels this afternoon.

Dewpoint readings will be back into the single digits through the daytime hours today. With afternoon temperatures from the middle 40s to around 50, this will bring minimum RH values down to around 20 percent for much of the area, which is below critical values. However, winds are not expected to be as strong this afternoon as what was observed on Thursday, with sustained winds of between 5-10 mph and gusts only up to 15 mph expected. This should preclude the need for another Fire Danger Statement for today, but conditions will continue to be monitored throughout the daytime hours.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

VFR conditions are expected throughout the period.

Winds will be more light and variable to calm towards through sunrise with low-levels mostly decoupled. After sunrise, expecting winds to pick up again from the southwest after about 15z, with gusts as high as 15 kts possible in the afternoon. With dry air in place, fog is not expected to occur and skies mainly clear. Thus vfr conditions through the period. There is a low chance for some low level wind shear to begin affecting the terminals between 17/00z-06z. Low-level jet may increase to between 30-35 knots around 2kft, but surface winds are currently forecast to be above 5 knots through the night. It will be a borderline situation, and can not rule out the need for llws being forecast later on if it looks like surface winds will become weaker, or the jet is stronger.

EXTENDED AVIATION OUTLOOK...The next system expected to impact the region over the weekend and some restrictions are possible.

CAE WATCHES/WARNINGS/ADVISORIES

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