textproduct: Columbia

WHAT HAS CHANGED

Lake Wind Advisory is now issued for Thursday from 8 AM until 5 PM. Besides this, minimal change to the forecast. Aviation discussion updated for 00z TAF.

KEY MESSAGES

- 1) Breezy conditions expected on Thursday. Rain chances increase tonight with rain possible Thursday and Friday.

DISCUSSION

KEY MESSAGE #1: Breezy conditions expected on Thursday. Rain chances increase tonight with rain possible Thursday and Friday.

The main change to the forecast at this time is issuing a new Lake Wind Advisory for Thursday from 8 AM until 5 PM as gusts up to 30-35 mph will be possible across the area. A very strong 40-50 kt LLJ sets up ahead of the cold front tomorrow and even weak mixing under cloudy skies/stable conditions should yield these breezy conditions. Any deeper mixing could aid in mixing down gusts a touch higher than currently forecast.

For rain chances, not much change has occurred as the strong southwesterly LLJ will pump moisture into the region with PWAT's approaching 1.25" Thursday morning. This along with subtle forcing from a weak shortwave could bring isolated showers late tonight and into Thursday morning before the cold front begins sagging into the area during the afternoon and into the evening. Moisture convergence along the front seems fairly meager but shower coverage should increase through the afternoon with a line of heavy showers moving through the FA during the late afternoon and into the evening from NW to SE. Recent guidance, especially the HRRR/RAP, are showing 100-500 J/kg of MUCAPE developing ahead of the front with 40-50 kts of deep layer shear and up to 35-40 kts of 0-3km shear thanks to the robust LLJ in place. Due to this, a couple embedded thunderstorms in the line of showers cannot be ruled out as the front moves through, but severe weather chances remain low. The front should slow as it moves through the region, aiding in becoming an axis for locally heavy rainfall and higher amounts, especially toward the southeastern Midlands. Rain chances slowly decreases from NW to SE Thursday night and into Friday and there continues to be a signal for diminishing rain chances on Friday as the front pushes south of the FA. Overall, a widespread 0.50-1" seems possible from this event but a swath of amounts over 1" could be possible in the southeastern Midlands mainly as the front slows and becomes a focus for persistent moderate to heavy rainfall before clearing the region.

AVIATION /00Z THURSDAY THROUGH MONDAY/

VFR conditions exist right now, with MVFR ceilings likely to develop sometime after 06z and then overspread the northern four TAF sites.

High clouds have been common across the area throughout the day as a deep trough slowly digs into the eastern CONUS. Westerly flow aloft has yielded moisture advection aloft and southwesterly flow at the surface has led to a slow increase in low-level moisture. This is expected to continue through the night tonight, with moisture advection likely resulting in some low clouds developing between 06z and 10z at the Augusta and Columbia sites. Guidance is in good agreement on this, with HREF and REFS probabilities increasing markedly in ceilings <2kft in this timeframe. It will likely be accompanied by light showers as isentropic lift increases across the area. In general, the heaviest rain is expected to hold off until 18z or later, which is why prob30/TEMPO groups cover the bulk of the rain chances ahead of the main front. There is still a surprising amount of spread within the guidance about the overall timing of this line of showers tomorrow. In general, no guidance is faster than 18z with the line and a select few are much later even at the Augusta/Columbia sites. If a convective line develops, it'll likely be a bit faster than the front itself so leaned into that solution.

The main problem for the TAFs may actually be the low- level winds ahead of this system. A low- level jet at 2kft on the order of 40-50 knot is expected to overspread the area. Even with meager mixing, surface wind gusts of 25 knots or more are expected beginning mid morning and continuing through the afternoon hours ahead of the front. LLWS is possible given the robust low-level jet but it seems that gusts will be strong enough to offset that. If the gusts don't materialize, we will absolutely need LLWS in future issuances. MVFR cigs are possible through the afternoon though guidance is more mixed on how long they hang around into the evening. Behind the front, in-situ wedging looks likely to set up tomorrow night but that is beyond the scope of this forecast. EXTENDED AVIATION OUTLOOK...Widespread restrictions and rain expected Thursday night and into Friday as a front moves through the area.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Lake Wind Advisory from 8 AM to 5 PM EST Thursday for SCZ016- 018-020>022-025>031-035-037-038-041-115-116-135>137. GA...Lake Wind Advisory from 8 AM to 5 PM EST Thursday for GAZ040- 063>065-077.