textproduct: Columbia

WHAT HAS CHANGED

Minimal change to Key Messages. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Above normal temperatures likely continue this week as heat indices exceed 100F multiple days.

- 2. Chances for scattered diurnal showers and thunderstorms continue into the work week. Strong to marginally severe storms possible the next couple afternoons.

DISCUSSION

Key Message 1: Above normal temperatures likely continue this week as heat indices exceed 100F multiple days.

As has been advertised for the last handful of days, this prolonged period of heat is expected to continue into the work week. Temperatures are already in the mid 90s for much of the FA and are expected to top out in the mid to upper 90s in the coming couple hours. Dew points in the upper 60s to low 70s are bringing heat indices up to 105F. A couple spots nearing 106-108F will be possible, but showers/storms this afternoon may keep indices a bit more in check. The stage for the first half of the week is already setting up with the axis of the upper ridge shifting a bit offshore in response to the trough currently extending from the northern Great Lakes toward the lower Mississippi Valley. This pattern will allow warm/moist advection from the southwest, keeping 850mb temps near 20C and generally keeping 1000-850mb thickness values above 1425m. Temperatures in the mid to upper 90s remain likely with LREF probabilities for max temperatures above 95F between 40-60% through the midweek before increasing toward 50-70% late this week. While generous mixing is expected each afternoon, 925mb dewpoints are expected to creep toward 19-21C, maintaining moist conditions with surface dewpoints sticking to the upper 60s to low 70s. This combination brings high LREF probabilities (above 60-70%) for heat indices to exceed 100F each day this week. As has been discussed, scattered diurnal convection that is expected each day complicates this a bit, but if drier conditions trend for any one day, additional heat products could be needed.

Due to the prolonged nature of this heat, be sure to check on those without adequate indoor cooling and take heat safety precautions this week.

Key Message 2: Chances for scattered diurnal showers and thunderstorms continue into the work week. Strong to marginally severe storms possible the next couple afternoons.

As expected, convective temperatures are being attained early this afternoon, leading to a cumulus field that has been quick to become agitated and the development of a couple storms. Scattered coverage is expected to continue as MLCAPE sits around 2000 J/kg, DCAPE values approach 1000 J/kg, and TEI values approach 25C. It is also worth noting that microburst composite values per the SPC mesoanalysis are between 3-5 across the FA. Overall, the main hazard with this convection will be isolated strong to severe pulse storms with the risk of damaging downburst winds from precip-loaded downdrafts.

A similar strong to severe pulse environment is expected the next 2-4 days, but weak synoptic forcing in the form of pieces of shortwave energy that move over the FA as we remained wedged between the trough and the upper ridge could aid in initiation. The latest EC Ensemble mean solution keeps MUCAPE over 2000 J/kg in the area through at least Tuesday, and high atmospheric moisture content combined with generous mixing should yield impressive DCAPE values. As has been discussed, damaging downburst winds in the strongest storms will be the main risk considering the environment and the latest CSU ML probabilities maintain this elevated risk. The most recent NBM run and global models show slightly "drier" air (PWAT's near 1.60-1.80") could push into the region during the midweek, possibly limiting convective coverage a bit, but there remains some uncertainty in this. Overall, expect a couple strong to severe thunderstorms or two the next couple days across the area with diurnal convection chances continuing into the mid to late week, but with a bit more uncertainty at that point.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Afternoon convection will lead to brief periods of mvfr or even ifr restrictions in heavy rain. Gusty winds between 20-30 knots will also accompany stronger storms this afternoon. With expected coverage, will include a tempo group at all sites for restrictions from 18z-22z, and adjust as necessary through the afternoon.

Outside of any convection, expecting vfr conditions with cu and strato-cu, along with cirrus from decaying thunderstorms. Winds this afternoon will be more out of the west or southwest at 5-10 knots, then returning to light and variable late this evening. For Monday, should see winds pick up once again out of the southwest by mid-morning, with speeds between 5-9 knots.

EXTENDED AVIATION OUTLOOK...Daily rain chances and possible restrictions continue through at least midweek.

CAE WATCHES/WARNINGS/ADVISORIES

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