textproduct: Charleston

WHAT HAS CHANGED

A new Key Message for smoke generated by the Horse Island Wildfire was introduced. The Aviation and Marine sections were also updated.

KEY MESSAGES

- 1) Smoke from the Horse Island Wildfire will impact northeast Berkeley County tonight into Monday.

- 2) Hot and humid conditions are expected across the area into midweek. Heat Advisories could be needed.

- 3) A shift in the synoptic pattern will likely bring higher precipitation chances towards the end of the week.

DISCUSSION

KEY MESSAGE 1: Smoke from the Horse Island Wildfire will impact northeast Berkeley County tonight into Monday.

A Dense Smoke Advisory has been requested by the U.S. Forest Service for northeast portions of Berkeley County in response to the Horse Island Wildfire. Smoke in the vicinity of the fire is significant and conditions will deteriorate overnight as the nocturnal inversion develops. The latest Hysplit output shows the worst of the smoke will remain across northeast Berkeley County and extending across the Santee River into a small area of southwest Georgetown County. Visibilities may drop below 1/4 mile at times overnight, especially along parts of Highway 45. Road closures are possible. Smoke will likely remain an issue into Monday although visibilities should improve some by mid- morning as dispersion increases and mixing heights rise. Another dense smoke advisory may be needed Monday night as smoke settles during the overnight hours.

KEY MESSAGE 2: Hot and humid conditions are expected across the area into midweek. Heat Advisories could be needed. Very little change in the forecast is expect the next couple of days as the heat and humidity lingers through Wednesday. The overall players remain the same across the area with deep upper troughing across the Northeast, high pressure to our east over the Atlantic and a tropical depression over the northern Gulf. Monday and Tuesday, will see highs topping out in the low to mid 90s and dewpoints able to mix out into the low 70s. This should be enough to keep heat indices in the 100 to 105 range and while this is still hot, this is more in line with typical summertime conditions for the area. A few locations may be able to crack 108 to 110 along the immediate coastline especially across coastal south carolina as the seabreeze slowly moves inland. Confidence in reaching those values for a long enough period of time is too low at this time to support an advisory for tomorrow. Nonetheless, the difference between 104/105 and 108/109 is not that noticeable and the key takeaway is that conditions still remain on the hotter side.

The bigger questions come on Wednesday as dewpoints should gradually increase as better moisture arrives. This will be aided by the depression in the Gulf as it slowly tracks westward. The usual trouble areas behind the seabreeze could approach advisory criteria come Wednesday as dewpoints climb into the upper 70s to near 80 resulting in heat indices of around 108 to 110. This could require Heat Advisories across portions of the area. The biggest question for Wednesday will be if convective coverage will be enough to limit the heat across the area. With better moisture usually comes more storms and more storms earlier in the day could limit how hot we are able to get.

KEY MESSAGE 3: A shift in the synoptic pattern will likely bring higher precipitation chances towards the end of the week.

As a low pressure in the northern Gulf (TD2) slowly shifts westward through the mid-week, a high pressure will remain centered over the western Atlantic. Simultaneously, a mid-lvl trough will situate itself over the eastern CONUS by mid-week. At the surface, an associated cold front will approach the region on Wednesday, likely stalling in the vicinity of the forecast area into the end of the week. This stalled front will likely bring increased precipitation chances to the region. The Weather Prediction Center (WPC) has the entire forecast area outlooked in a Marginal Risk for Excessive Rainfall on Thursday, with a Slight Risk over northern Charleston and Berkeley Counties.

AVIATION /06Z MONDAY THROUGH FRIDAY/

20/06Z TAFs: Expect VFR conditions will prevail KCHS/KJZI/KSAV through the period. Light southwesterly flow overnight should strengthen this afternoon as the seabreeze shifts inland between 18- 19Z for KCHS/KJZI and ~20Z for KSAV. As the seabreeze shifts more inland, the winds should veer out more out of the south with gusts up to 20-21 kts noted. Gusts should subside after 00Z, although sustained south-southwest winds around 10 kts will continue through the end of the period. No mention of showers and thunderstorms as coverage remains rather limited.

Extended Aviation Outlook: Prevailing VFR through mid week. Chances of flight restrictions increase later this week with a greater coverage of showers/thunderstorms.

CLIMATE

Record High Minimum Temperatures:

July 19: KCHS: 79/1986 KCXM: 83/1986

July 20: KCHS: 79/2025 KCXM: 83/2000 KSAV: 79/1942

July 21: KCHS: 80/1986 KCXM: 83/1998

July 22: KCHS: 81/2011 KCXM: 83/2011

CHS WATCHES/WARNINGS/ADVISORIES

GA...None. SC...Dense Smoke Advisory until 10 AM EDT this morning for SCZ045. MARINE...None.