textproduct: Columbia

WHAT HAS CHANGED

Storm chances remain low today with only isolated activity anticipated. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Isolated diurnal storms possible each day this week, with diminishing chances midweek. A strong storm cannot be ruled out.

- 2. Increasing heat and humidity is expected next week.

DISCUSSION

- 1. Isolated diurnal storms possible each day this week, with diminishing chances midweek. A strong storm cannot be ruled out.

Satellite imagery shows some fair weather cumulus developing across the forecast area, but thus far they aren't looking too agitated. The most agitated cumulus thus far are from the upper CSRA into the PeeDee. Hi- res guidance from this morning does suggest some isolated storms developing this afternoon, but most of the activity is expected to remain near the coast and in the mountains. SBCAPE values range from 2200 J/kg to over 3000 J/kg per the SPC Mesoanalysis page, which could result in a stronger storm as we head into the afternoon. However, the severe threat is low.

Southerly to southeasterly near surface flow is expected to continue today and into early next week, before becoming a bit more southwesterly to westerly late in the week. Overall, with the region remaining between the upper ridge over the western US and the strong area of high pressure off the East Coast, seasonable moisture should persist through the forecast period with surface dewpoints likely remaining in the low to mid 70s much of the forecast period (as well as PWAT's near to just below 2"). This moisture combined with strong heating should bring SBCAPE values greater than 2000 J/kg most days but with lacking upper kinematics, creating an environment conducive for spotty to isolated pulse convection each afternoon through the the first part of the week, though the latest NBM guidance continues to come in drier than previous runs for the midweek timeframe. As is typical this time of the year, a strong storm or two cannot be ruled out with the risk of strong downburst winds, but widespread severe weather is unlikely. A bit more uncertainty in terms of precip chances enters late this week into the weekend. This is driven by greater spread amongst global deterministic and ensemble guidance with the strength of a shortwave moving out of the northern Great Lakes and thus it's ability to push a surface front near the region. A more amplified solution could bring increased rain chances/coverage, but details still need to be sorted out, while a less amplified solution would lean more to lower, more typical summer time spotty storms.

- 2. Increasing heat and humidity is expected next week.

The 500mb heights are expected to gradually rise through the week, peaking near the NAEFS 90th percentile by the late week. As this occurs, 850mb temperatures currently near 18C should rise to between 20-23C by the mid week. With these warming low level temperatures, rising mid level heights, and the expected spotty nature of afternoon convection, high temperatures are progged to peak in the mid to upper 90s Tuesday onward. Due to the uncertainty in potential troughing by this weekend discussed in Key Message #1, larger NBM IQR spreads exist, but near normal to just above normal temperatures still seem likely. Surface dewpoints remaining in the low to mid 70s through the period bring increased confidence in heat indices rising back above 100F with LREF probabilities reaching above 70% by Tuesday with probabilities for indices above 105F between 30-50% Thursday and Friday. Overall, confidence in reaching Heat Advisory criteria is low, but spots of 105-108F could be possible mainly between Wednesday and Friday so be prepared for returning hot/humid conditions this week.

AVIATION /18Z SUNDAY THROUGH THURSDAY/

VFR likely Sunday afternoon into early Monday, outside of some isolated storms. Some morning stratus-fog possible Monday, but less widespread than previous days.

Typical summer conditions out there this afternoon with a broad cu field around 3500 feet. Convection should remain across the Upstate and coastal plain through late afternoon, with some increasing chances for storms at the TAF sites. Confidence is only high enough for a prob30 TAF mention at this time however. Morning stratus-fog Monday looks less likely than the last few mornings especially with a lack of widespread rainfall.

EXTENDED AVIATION OUTLOOK...A seasonal pattern of early morning restrictions and diurnal thunderstorms is likely through much of the extended.

CAE WATCHES/WARNINGS/ADVISORIES

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