Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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421 FXUS62 KCHS 261651 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1251 PM EDT Wed Jun 26 2024 .SYNOPSIS... High pressure will remain over the western Atlantic while weak cold fronts linger near our area through the end of the week. && .NEAR TERM /THROUGH TONIGHT/... At the surface a stationary front will meander across the SC Upstate. Aloft a larger scale trough will be positioned over the Great Lakes, with the forecast area in the vicinity of the southern periphery. Temperatures this afternoon have already reached into the low 90s across many locations, with dew point observations in the mid to upper 70s across the coastal counties. Further inland dew points have been able to mix out, resulting in observations reporting in the mid to upper 60s. The Heat Advisory is verifying already across the coastal plain, with KJZI and KNBC reporting heat index values of 108F. No changes were made to the areal extent of the Heat Advisory. Ample instability will be present this afternoon across the forecast area, however a forcing mechanism will be lacking. Therefore, afternoon convection will be driven by the inland pushing sea breeze and any outflow boundaries that develop. Isolated to scattered showers and thunderstorms will be possible this afternoon, likely dissipating by sunset. With the instability in place, a strong to marginally severe thunderstorm cannot be ruled out. Tonight: Diurnally driven convection will run its course through the evening hours. As mentioned, upper level troughiness will edge into the southeast region through the course of the night with enhanced QG-forcing for ascent working across the Appalachians and into the western Carolinas. It does appear at this juncture that any associated shower activity will remain well upstream through the night and plan to maintain a dry forecast. Low temperatures once again will only dip into the middle 70s to around 80. && .SHORT TERM /THURSDAY THROUGH SATURDAY/... Thursday: Mid-level longwave troughing initially over the East Coast will gradually shift offshore as time progresses. More notably, a shortwave embedded in the overall flow is expected to move over our region during the late afternoon or evening, then stall overhead overnight. A cold front located to our northwest at daybreak should very slowly move into our area late in the day, likely stalling across our area overnight. There will be a plume of deep moisture ahead of the front. PWATs could exceed 2.25", which is above the 90% mark for CHS per SPC Sounding Climatology. The heat will be the main concern due to 850 mb temperatures, low-level thickness values, and compression near the front. Highs are expected to reach the mid to upper 90s across most of our area, except cooler at the beaches. Dew points well into the 70s near the coast will cause heat indices to rise to 108-110 degrees. So Heat Advisories may be needed, most likely for our coastal counties. Forcing from the front, the afternoon sea breeze, and the shortwave will generate convection in the afternoon. The synoptic models and long range CAMs are in good agreement, indicating scattered to numerous coverage. MLCAPEs should approach 1,500 J/kg across portions of our area with some shear. With DCAPEs exceeding 1,000 J/kg, a few marginally severe storms with damaging winds are possible just about anywhere. Hence, the SPC has our area under a Marginal Risk for severe thunderstorms, which seems reasonable. Additionally, there will be the potential for locally heavy rainfall underneath the thunderstorms due to fairly weak steering flow and the potential for training. Convection should gradually decrease during the evening. But isolated remnant convection should persist everywhere overnight. Lows will be in the 70s. Friday: The mid-levels should consist of a shortwave hovering over our region in the morning. It is expected to dissipate into the afternoon, followed by weak zonal flow during the evening and overnight. At the surface, a stationary front should be spread across our area in the morning. It`s expected quickly lift north as a warm front into the afternoon, becoming located well north of our area by the evening hours. Deep moisture will persist across the region. PWATs should stay ~2.25", which is well above normal. Similar to Thursday, high temperatures are expected to reach well into the 90s for most areas. Dew points well into the 70s near the coast will cause heat indices to rise as high as 108-110 degrees, which would prompt Heat Advisories, most likely for our coastal counties. Forcing from the remnant shortwave, departing front, and the afternoon sea breeze will generate convection. Models point to another round of scattered to numerous coverage, especially in the afternoon. Instability should be similar to Thursday. However, shear and DCAPEs appear to be lower. This would lower the severe risk. But given the atmospheric setup and time of year, a strong or marginally severe storm with damaging winds is possible just about anywhere. There will also be the potential for locally heavy rainfall underneath the thunderstorms due to weak steering flow and the potential for training. Convection should gradually decrease during the evening. But it`s most likely to persist closer to the coast overnight. Lows will be in the 70s. Saturday: Weak mid-level zonal flow will initially be over our region, with broad High pressure building later into the day. Surface High pressure will be in the western Atlantic, while weak troughing develops over the Southeast U.S. later in the day. Deep moisture will continue to prevail across the region. Similar to the previous two days, high temperatures are expected to reach well into the 90s for most areas. Dew points well into the 70s near the coast will cause heat indices to rise as high as 110 degrees along the coast. So more Heat Advisories may be needed. Instability from the afternoon heat and humidity will generate convection along the sea breeze as it moves inland during the afternoon. Strong or marginally severe storms are possible. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... Surface troughing or weak fronts will be impacting the Southeast U.S. during the long term, while High pressure is located in the western Atlantic. Expect the typical diurnal convection with the highest POPs each afternoon and evening, then trending lower overnight. High temperatures will be well into the 90s each day. Additionally, heat indices could approach 108 degrees along the coast through Monday. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... KCHS/KJZI: Scattered showers and thunderstorms are possible this afternoon into early evening. However, indications are that most of the activity will occur a bit inland from the Charleston County coast and may not impact the terminals. Still too much uncertainty to include an explicit mention in the terminal forecasts, but will carry VCSH at KCHS during the afternoon. KSAV: A similar story, with showers and thunderstorms possible this afternoon into early evening. Recent guidance trends suggest KSAV will have the higher probabilities for showers and storms. 18Z terminal forecast will carry VCTS at the terminal during the mid to late afternoon period. Extended Aviation Outlook: Mostly VFR. However, convection could bring brief flight restrictions, mainly each afternoon and evening. && .MARINE... Persistent southerly flow lingers across the coastal waters through tonight, generally 10 to 15 knots with some gusts to around 20 knots. Seas 2 to 3 feet through today building to 2 to 4 feet tonight. Extended Marine: A typical summertime pattern is expected with High pressure in the western Atlantic and occasional surface troughing or fronts over the Southeast. Each day, expect gradually backing winds. They`ll be strongest along the land/sea interface and across the Charleston Harbor with the formation of the afternoon sea breeze. Each night, winds will gradually veer, possibly surging closer to the coast. Seas will be 2-3 ft. Rip Currents: Today, increasing 1-2 foot swell energy to around 9 seconds is expected to begin impacting the South Carolina beaches later today and into the southeast Georgia coast tonight. With that, internal guidance suggests a moderate rip current risk developing along the coast, particularly the South Carolina beaches as we go through the day. Thursday a 1-2 ft SE swell around 7 seconds and another SE swell around 9 seconds will be impacting the beaches. Per internal calculations, this would increase the rip current risk. We opted to maintain a Low risk for our SC beaches, but added a Moderate Risk at our GA beaches, where rip currents are most likely at Tybee Beach. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Heat Advisory until 7 PM EDT this evening for GAZ101-116>119- 138>141. SC...Heat Advisory until 7 PM EDT this evening for SCZ043>045- 047>052. MARINE...None. && $$ NEAR TERM... SHORT TERM... LONG TERM... AVIATION... MARINE...