textproduct: Columbia

WHAT HAS CHANGED

Isolated shower and storms expected this afternoon with additional activity with a frontal passage tonight. Also lowered high temps today slightly due to prolonged cloud cover. Aviation discussion for 18z TAF issuance updated.

KEY MESSAGES

- 1. Chances for showers/storms continue into Tuesday before drier conditions begin to move in. A strong storm cannot be ruled out into this evening.

- 2. Below normal temperatures Tuesday behind a front before a warming trend is expected into this weekend.

DISCUSSION

Key Message 1: Chances for showers/storms continue into Tuesday before drier conditions begin to move in. A strong storm cannot be ruled out into this evening.

Some isolated showers and storms are possible this afternoon ahead of a frontal boundary moving through later this evening. An ongoing MCS moving through the Tennessee Valley is bringing thunderstorms to that area. It does not appear that this activity will make it to our CWA, but guidance hasn't been handling this feature well thus far. So, it can't be ruled out that this activity does make it. In addition, typical summertime showers/storms are beginning to develop over the mountains in the Upstate and are expected to move toward our forecast area over the next few hours. Overall, the environment this afternoon/evening is expected to be characterized by PWAT's near 1.70-1.90", increasing deep layer shear near 20-30 kts, and MLCAPE values around 1000 J/kg. As a result, any activity this afternoon could produce a stronger cell with strong winds.

An upper trough over the Great Lakes is expected to sharpen and dig through the eastern US. An associated front is expected to accompany this sharper trough, passing over the area tonight into Tuesday morning. This is expected to bring another round of convection to the area later is evening. The overall flash flooding risk is lower than previous day's as storm motions are expected to increase to between 15-25 kts. A storm on the strong side with the main risk of strong to damaging wind gusts cannot be ruled out with this activity as well, but overall severe risk is quite limited.

This front moving in from the northwest should bring cooler/drier air into Tuesday, though it may stall out near the southern FA, bringing continued scattered rain chances through at least the first half of the day. PWAT's then likely drop to under 1" Tuesday evening as a surge of dry air moves, leading to drier conditions that likely hold the remainder of the week.

Key Message 2: Below normal temperatures Tuesday behind a front before a warming trend is expected into this weekend.

Temperatures have risen to around 80 across the forecast area, but I did lower the high temps for the afternoon a couple of degrees because of the prolonged cloud cover. Temperatures are then expected to fall below normal Tuesday as a push of CAA moves in behind the front. Current NBM guidance has high temperatures Tuesday in the mid to upper 70s, but depending on how far south the front pushes and the timing of the onset of 850mb CAA, temperatures, could trend toward somewhat lower than currently forecast. There is limited change in the temperature outlook through this weekend. The latest LREF cluster analysis remains is decent agreement that the upper ridge currently over the Central US will shift overhead with surface high pressure building in as well. This should bring temperatures that remain below normal Wednesday, but begin steadily raising closer to normal Thursday and into this weekend.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Restrictions will ease through the afternoon with VFR conditions returning.

A mix of MVFR/VFR CIGS should continue early this afternoon, but are expected to return to predominately VFR closer to 21z. As another front drops into the area late this afternoon into evening, isolated to scattered showers and thunderstorms will develop and move from northwest to southeast through the terminals. There is potential for two rounds of storms, one early this evening and another closer to 04-06z tonight. Brief decreases in CIGS/VSBYS are possible with the stronger storms, along with wind gusts around 30-35 kts. Outside of convective gusts, surface winds SWLY to NWLY less than 10 kts can be expected. Guidance indicates additional low CIGS may develop after sunrise Tuesday morning, with mainly MVFR restrictions occurring. Additionally, winds will become more NELY behind the front at around 10 kts.

EXTENDED AVIATION OUTLOOK...Restrictions east late Tuesday morning or early afternoon. Drier air returns to the region mid to late week with mainly VFR conditions expected.

CAE WATCHES/WARNINGS/ADVISORIES

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