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Area Forecast Discussion
786 FXUS62 KCHS 250438 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1238 AM EDT SAT JUN 25 2016 .SYNOPSIS... A cold front to the north will approach tonight, stalling across the region Saturday and dissipating Sunday into Monday. Another front will impact the area beginning on Tuesday and will become nearly stationary in the vicinity through the middle of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Conditions will remain relatively tranquil, albeit unseasonably warm and humid the remainder of the night. A little ground fog where it rained last evening, but no significant visibility restrictions will occur. Skies will average out to be partly cloudy ahead of a cold front to the north, with a south-southwest synoptic flow to produce lows only down into the mid and upper 70s for most of us. && .SHORT TERM /6 AM THIS MORNING THROUGH MONDAY/... Saturday...The day will start off fairly warm with a west/northwest downsloping wind that helps keep a seabreeze pinned near the coast. Strong sfc heating along with deepening moisture ahead of an approaching cold front from the north/northwest should support heat index values between 105-108 degrees over most areas. A Heat Advisory is now in effect from 11am-7pm on Saturday for southeast Georgia and a few locations in coastal South Carolina where afternoon temps peak in the mid to upper 90s. Some questions in regards to cloud cover and peak temps will keep the rest of southeast South Carolina out of the Heat Advisory for now. However, should convective activity and cloud cover hold off until early afternoon hours, a Heat Advisory will likely be needed for much of southeast South Carolina as well. As we head into early to mid afternoon hours the main weather concern will be the possibility of severe weather from pulse type thunderstorms. Mid-lvl ridging will gradually retreat to the deep south as a series of h5 shortwaves rounds its eastern periphery over the southeastern United States. The setup will favor an unstable atmosphere along and ahead of a sfc cold front approaching from the north/northwest during the afternoon. Although shear is marginal, SBCAPE ranging between 1500-2500 J/kg, DCAPE between 1200-1600 J/kg, lifted index values between -6 to -8 C along with modest mid lvl lapse rates and PWATS around 2.0 inches support scattered to numerous thunderstorms, some of which could produce strong and damaging wind gusts. At this time, strong to severe thunderstorms are possible beginning early afternoon in southeast South Carolina and mid/late afternoon in southeast Georgia as the cold front shifts slowly southward over the region. Sunday and Monday...A cold front will drift southward over parts of southeast Georgia before stalling and gradually dissipating early next week. However, the atmosphere will remain fairly unstable where deeper moisture and strong sfc heating coincide along and south of the weakening front. For this reason, a slight chance to chance of showers and thunderstorms will remain in the forecast on Sunday with highest chances in southeast Georgia. By Monday, mid lvl energy appears to shift south of the area and a lull in moisture is apparent, thus only a slight chance of showers and thunderstorms will remain in the forecast. Overall high temps should be slightly cooler than previous days to start off the week. In general, afternoon temps should peak in the upper 80s to lower 90s each day. Overnight lows should range in the mid to upper 70s. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... The main forecast feature to watch in the long term period will be a front currently progged to approach the area from the west/northwest on Tuesday and then become nearly stationary in the vicinity of the forecast area through Thursday. This set up, especially with the gradual breakdown of the eastern extent of the upper ridge, will favor increased diurnal convective activity through the middle of the week. For now pops are generally advertised in the 40 percent chance range, but this may increase as the time approaches and confidence grows in which particular forecast periods could be the most active. Temperatures will remain nearly steady state featuring low 90s for highs and mid 70s for lows. && .AVIATION /05Z SATURDAY THROUGH WEDNESDAY/... Periodic flight restrictions are possible Saturday afternoon at the CHS terminal and Saturday evening at the SAV terminal for showers/thunderstorms, but confidence is too low to include in the tafs at this time. Extended Aviation Outlook: Flight restrictions are possible with Sunday afternoon/evening showers and thunderstorms at the CHS and SAV terminals. Flight restrictions possible again on Tuesday. && .MARINE... Tonight: The waters will be positioned between Atlantic high pressure and a cold front approaching from the north. The front is expected to remain north of the waters through sunrise. A tightened pressure gradient and developing low level jet will keep southwest winds in the 15-20 kt range, 15 kt or less in Charleston Harbor. Seas of 3-4 feet. Saturday through Wednesday: A cold front will approach the waters from the north on Saturday and slowly shift southward before dissipating late Sunday into Monday. The strongest winds through the period are expected to occur Saturday and Sunday along and ahead of cold front. Southwest winds up to 15-20 kt will be possible on Saturday with another period of modest flow on Sunday during fropa. For now it does not appear that conditions will warrant any Small Craft Advisories, but we could potentially see wind gusts around 25 kt in northern SC waters and offshore GA waters until fropa occurs. Thereafter, south to southwest flow will prevail with winds no stronger than 15 knots through early next week. Seas will be highest over the weekend, generally 2-4 feet which will then diminish to 1-3 ft for early next week. && .CLIMATE... Record High Minimum for June 24th... KCHS...79 set in 1998. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for GAZ087-088-099>101-114>119-137>141. SC...Heat Advisory from 11 AM this morning to 7 PM EDT this evening for SCZ047-048-051. MARINE...None. && $$ SYNOPSIS... NEAR TERM... SHORT TERM...DPB LONG TERM...BSH AVIATION...DPB MARINE... CLIMATE...