905 FXUS62 KCHS 121517 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 1017 AM EST Sun Jan 12 2020 .SYNOPSIS... A cold front will stall over the area today, before shifting back inland as a warm front tonight. The front will linger over or near the region through the middle of the week. Another cold front will cross the area on Thursday, followed by high pressure late week. && .NEAR TERM /THROUGH TONIGHT/... Update: Radar and surface observations indicate shower coverage/intensity is a bit greater/heavier than anticipated at this typing. We tinkered with the POPs/Weather to capture the location of the banding and it's anticipated movement. Also, plugged in the latest temperature/dew points observations and blended into the afternoon. More significant updates are possible depending on how things evolve over the next few hours. A strong mid and upper level anticyclone off the southeast part of the nation will nudge back to the west and northwest. This will halt the progression of a cold front that caused severe weather just outside the forecast area last night. That front will lie near the northwest tier of the area throughout the day, with some minor fluctuations in it's position to occur. This feature will be the main focus for convection, where PWat is still abnormally high around 1.75 inches. We have a high chance and likely PoP far inland, with a slight chance and low chance PoP closer to the coast this morning, with decreasing coverage this afternoon. There remains quite a bit of shear, but instability is extremely limited and lapse rates are poor, so we don't foresee anything more than a little thunder and lightning across a few far inland sections. Any severe potential is virtually non- existent. The day begins with temps that are already some 6-10F above the normal high, and with 850 mb temps reaching as high as 14-15C, or about as warm as it can get in this part of the country for January, it's suggests another abnormally warm day despite considerable cloud cover. Not quite at record levels, but lower and middle 70s will be common away from the beaches, with even a few upper 70s in locations closer to the Altamaha River basin. Also, winds will finally start to relax as a 35-45 kt low level jet lifts away this morning. Despite the elevated winds, all coastal sites and various webcams depict low stratus and patchy fog. This will continue through at lest the morning hours, if not into the afternoon. Then as winds slacken off even more this afternoon, the coverage of sea fog will increase across the nearby Atlantic, and at some point either later today or tonight will spread back onshore. That fog has the potential to become dense with a favorable light southerly flow. Dense fog advisories seem a certainty, especially tonight, due to the advection of the sea fog and/or the build down of stratus. There isn't much probability of any convection through the bulk of the night, except for maybe isolated or scattered showers from off the ocean late across the coastal corridor. Lows tonight will again be far above normal, averaging at least 20-25F above climo. && .SHORT TERM /MONDAY THROUGH WEDNESDAY/... The forecast area will be positioned in between high pressure over the Atlantic and a stalled front well inland through mid week. Southwest flow aloft on the western periphery of a mid level ridge will gradually flatten out and become zonal by Wednesday. The best coverage of rainfall appears to be on Monday, with the highest PoPs shifting from the coast to inland through the day. Model soundings do indicate some marginal instability so a mention of thunder has been maintained. Thereafter, isolated to maybe scattered activity is possible, but the highest rain chances will be inland of the area, in closer proximity to the better forcing. The stretch of warm and muggy conditions will continue through the period. Highs will generally peak in the mid to upper 70s each afternoon, with temperatures overnight only falling to the low 60s. For reference, these low temperature values are generally near or slightly above our normal highs for this time of year and will be within range of record high minimums. See climate section for more information. The other forecast issue revolves around fog potential. Conditions are favorable for at least patchy fog each night. In addition, any sea fog that develops could drift onshore and impact coastal locations. && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... A change in the stagnant weather pattern will finally arrive on Thursday as a cold front crosses through the area. Some showers could accompany the front, but overall models hint that activity will be decreasing as it moves through. We have maintained low-end rain chances. High pressure will then build into the region Thursday night and will prevail through late week. Another cold front could approach the area on Saturday. While temperatures are not expected to be as warm as the first half of the week, they are still forecast to be above normal. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... KCHS: Due to a nearby cold front, numerous SHRA and maybe a TSRA will impact the terminal this morning, resulting in MVFR and possible IFR conditions. Convection will diminish in coverage this afternoon, but considerable moisture remains in place beneath the low level inversion and held in place by the front. As a result MVFR ceilings are still expected. The lowering of stratus and the advection of sea fog will lead to conditions becoming IFR and perhaps even LIFR the second part of tonight. KSAV: A nearby cold front will contribute to numerous SHRA and even some TSRA at and near the terminal this morning, with the end result of MVFR or IFR conditions. Convection will diminish in coverage this afternoon, but considerable moisture remains in place beneath the low level inversion and held in place by the front. Thus we still anticipate MVFR ceilings. Stratus will lower across the area tonight, leading to MVFR or IFR weather. But if sea fog impacts the terminals then LIFR conditions could also occur late. Extended Aviation Outlook: Periodic flight restrictions are expected in fog and stratus, especially during the overnight and early morning hours. && .MARINE... Today and tonight: Small Craft Advisories are in effect for some of the coastal waters. Marine Dense Fog Advisories are in effect for some of the coastal waters. The cold front inland over the Southeast will not make it into the coastal waters, as strong high pressure both surface and aloft blocks it's movement. The pressure gradient will slacken and a low level jet will pull away late this morning or early afternoon. This still allows for S and SW winds as high as 15 or 20 kt, before they drop off 5 or 10 kt this afternoon. It'll take time for the already large seas in the Atlantic to subside, but we do anticipate seas falling under 6 ft on the southern South Carolina waters by early afternoon, when the Small Craft Advisory for the AMZ354 waters will come to an end. The Small Craft Advisory for AMZ350 will take until late tonight to expire, while the outer Georgia waters will still have advisories beyond the tonight tonight period. The biggest concern across the coastal waters will be the formation of sea fog, which will eventually become widespread and dense. We're already experiencing fog on the nearshore waters this morning, despite winds the elevated winds. With the drop off winds this afternoon and tonight, and given a favorable southerly flow within the already warm and humid air mass, we expect fog to increase in coverage and become dense. After coordination with WFO and JAX, and with an attempt to be proactive, we have opted to issue a Dense Fog Advisory beginning at 1 PM for all waters out 20 nm, which will continue into tonight. If winds are slower in decreasing and/or convection continues longer into the afternoon, the dense fog would be delayed in developing. No advisory just yet for Charleston Harbor, since this will likely not happen until tonight. Not yet sure if the fog will spread into the outer Georgia waters, but it does remain possible. Mariners should be prepared for navigation problems and the possibly closures of the Port of Charleston and the Port of Savannah, especially tonight. Monday through Friday: South to southwest winds will prevail through mid week, with speeds around 10 knots or less. Seas will remain below Small Craft Advisory levels, with the exception being across the outer Georgia waters where the ongoing advisory will persist through Tuesday as 6 foot seas linger. A cold front is progged to cross the waters on Thursday, with high pressure to build in its wake. Winds and seas will increase as a result and a portion of the marine zones could need a Small Craft Advisory. Sea fog: The main marine forecast concern remains the potential for fog. Once fog develops, it will likely linger for an extended period of time since there won't be anything to change the overall setup. The current forecast features areas of fog Monday into Monday night, and then patchy fog through Tuesday night. It is likely that fog will become much more widespread at times and dense. Dense Fog Advisories will likely be needed at various times, and the potential for fog could persist until a cold front moves through on Thursday. && .CLIMATE... Record high min temperatures for January 12: KCHS: 61/1972 KSAV: 63/1972 KCXM: 60/last set in 1972 Record high min temperatures for January 13: KCHS: 62/1972 KSAV: 65/last set in 1972 KCXM: 63/1932 Record high min temperatures for January 14: KCHS: 62/1995 KSAV: 63/1932 KCXM: 62/1950 && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Dense Fog Advisory from 1 PM this afternoon to 1 PM EST Monday for AMZ350-352-354. Small Craft Advisory until 1 PM EST this afternoon for AMZ352. Small Craft Advisory until 7 PM EST Tuesday for AMZ374. Small Craft Advisory until 1 AM EST Monday for AMZ350. && $$ NEAR TERM... SHORT TERM... LONG TERM...ETM AVIATION... MARINE... CLIMATE...