textproduct: Columbia

WHAT HAS CHANGED

Confidence in above normal temperatures increasing for next week. Aviation discussion updated for 06Z TAF issuance.

KEY MESSAGES

- 1. Diurnal thunderstorms expected through the weekend with the main threat of locally heavy rainfall. Drier conditions and above normal temperatures are expected next week.

DISCUSSION

KEY MESSAGE 1: Diurnal thunderstorms expected through the weekend with the main threat of locally heavy rainfall. Drier conditions and above normal temperatures are expected next week.

Persistent troughing is expected to linger across the region today and into Saturday. This should yield deep southerly to southwesterly moisture advection, bringing PWAT's between 1.90-2.20" across the FA. A weak frontal boundary sinking out of the Tennessee Valley should stall in the area today, possibly allowing a more focused area for convection by the late afternoon, but scattered to numerous showers/storms seem likely again today. The overall severe risk is limited with poor lapse rates, but around 35-45 kts of cloud layer shear is noted in modeled soundings, possibly allowing maintenance of any more robust updraft and the marginal risk for a couple strong to damaging wind gusts from precip loaded downbursts. The main risk will be localized instances of heavy rainfall and flash flooding. Profiles are nearly saturated throughout the atmospheric column with long/skinny CAPE profiles and deep warm cloud layers around 13,000 ft. This environment should make for efficient rain rates in excess of 2-4"/hr (as was seen yesterday) and slow storm motions or training near the front could lead to these spots of flash flooding. Due to this, the CWA remains in WPC's Slight Risk for excessive rainfall.

Continued troughing should yield one more day with scattered to numerous diurnal storms Saturday before the advertised upper ridge slowly works in to end the weekend, bringing more isolated to scattered chances on Sunday. Ensemble guidance and LREF cluster analysis remains in fairly good agreement that the upper ridge will shift overhead and strengthen through the early to mid week with 500mb heights approaching the NAEFS 99th percentile by Tuesday to Wednesday next week. This should bring temperatures back above normal (around 5-10 degrees), especially with diurnal convection likely being suppressed with strong subsidence under this ridge. Seasonable moisture is expected to remain in place, likely aiding in bringing back heat indices above 100F through the week with LREF probabilities peaking Tuesday through Thursday near 60-80%. This anomalous heat is also supported in the EC EFI with values between 0.70 and 0.80 seen by the mid week.

AVIATION /06Z FRIDAY THROUGH TUESDAY/

Another round of stratus and patchy fog is expected to develop overnight and into the morning, with cig/vsby restrictions. Additional showers/storms are possible by this afternoon and evening.

High low level moisture is expected to yield another round of low stratus and some patchy fog, especially where rain fell. Should start to see low mvfr stratus developing around 06z, becoming more widespread by 08z. This may be slowed slightly by some broken cirrus tracking across the region, but still somewhat confident that the low stratus will eventually materialize by 08z at all sites. Overall, IFR to periods of LIFR cig and/or vsby restrictions will be possible, continuing through 12-14z before gradually lifting through the morning and into the early afternoon. Winds light overnight, then pick up some late morning to around 5-8 kts out of the south. While an isolated shower is not out of the question through the morning, greater rain chances occur by early afternoon as another round of scattered convection is expected after 17-19z, which have continued with a PROB30 group at all sites for now.

EXTENDED AVIATION OUTLOOK... Restrictions possible from showers and thunderstorms into this weekend. Drier conditions expected early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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