textproduct: Columbia

WHAT HAS CHANGED

Potential for heavy rainfall increased in the upper CSRA this afternoon. Aviation discussion updated for 18Z TAF.

KEY MESSAGES

- 1. A typical summer pattern expected this week with increasing moisture.

- 2. Warming temperatures during the mid to late week time frame may lead to a period of dangerously hot temperatures.

DISCUSSION

Key Message 1: A typical summer pattern expected this week with increasing moisture.

Shower and thunderstorm has developed this afternoon as a shortwave propagates around an upper ridge over the area. Much of this activity has stayed in the Upstate so far, but some showers/storms have shown up in the upper CSRA. PWATs in this area have increased to near 2", leading to an increased chance of locally heavy rainfall, which could cause ponding in the roads. While high pressure works to limit convective coverage, elevated atmospheric moisture, generally 110-130% of normal PWAT values and strong heating are still expected to lead to isolated to scattered afternoon showers and thunderstorms elsewhere as a few very weak shortwaves move through. The summer-like pattern persists into this weekend as PWAT values approach 2" and upper level support becomes stronger, leading to increasing confidence in organized convection for the weekend.

Key Message 2: Warming temperatures during the mid to late week time frame may lead to a period of dangerously hot temperatures.

Anomalously strong ridging over the area late this week is expected to lead to 850 mb temperatures near 20C, or about 4-6C above normal Thursday through Saturday during peak daytime heating. At the surface, this should bring well above temperatures to the area reaching the mid to upper 90s, or 10-15F above normal. A few locations could see the 100F mark on Friday. At the same time, surface dewpoints remain in the generally in the 65-70F range in the afternoons. The combination of heat and above normal moisture could result in heat index values reaching the into the 100s Thursday and Friday for many locations. Although heat index values may not reach criteria for a Heat Advisory (108F), we continue to evaluate the need for an Advisory given that this is the first major heat the year.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

Isolated showers/storms this afternoon into the early evening then VFR conditions expected.

SCT to BKN mid and high level clouds continue across much of the region with a developing cumulus deck seen on regional satellite. Southerly to south-southwesterly winds have been picking up toward 5-8 kts as well and should continue into this evening. A couple showers have been noted just north of AGS/DNL, and this activity should continue through the afternoon, but coverage should remain isolated with chances of impacts at the terminals fairly low due to the limited coverage. Tonight, high clouds should continue to stream in as light and variable to calm winds develop. While low level moisture should linger, high clouds should help limit the overall threat for fog/stratus development. The 12z HREF and LAMP guidance indicate spotty stratus or fog could develop in any pockets of clearing, but confidence in restrictions at the TAF sites is fairly low. As deeper mixing ensues later Wednesday morning, 7-9 kt southwesterly winds develop as another cumulus deck forms into the early afternoon.

EXTENDED AVIATION OUTLOOK...Isolated to widely scattered diurnal showers and storms possible each afternoon this week into the weekend.

CAE WATCHES/WARNINGS/ADVISORIES

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