FXUS62 KCHS 270720 AFDCHS
Area Forecast Discussion National Weather Service Charleston SC 320 AM EDT Mon Mar 27 2023
.SYNOPSIS...
A cold front will slowly advance into the region later today and tonight. This front will stall as low pressure crosses the area Tuesday, then will push south of the region Tuesday night. High pressure will prevail for the rest of this week. Another cold front will cross the area Saturday, followed by high pressure into early next week.
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.NEAR TERM /THROUGH TONIGHT/...
Today: The stationary front has begun to retreat north as a warm front this morning and has been pushed towards the SC/ GA/ NC border. On water vapor, the MCV over GA/ AL can be seen with the back edge now over MS. Along coastal SC, a stratus deck has remained over Charleston county, but looks to be advecting northeast as low clouds have cleared from Hilton Head. Convection continues to train across central SC, and this will continue through the early morning hours as the MCV approaches from the southwest. Around, or just after sunrise, the MCV will exit the NC coast with a brief period of subsidence, or DAVA, taking over. Convection will likely initiate over GA/AL just after the wave passes though and slowly ooze southeast. This movement southeast with the convection is thanks to an area of mid-level low pressure across WY and CO heading east and then south around a potent closed upper level low over the Hudson Bay. This will create just enough of a push to cause the warm frontal zone to again stall and then turn around and head southeast this afternoon.
By late this morning, weak PVA will move back across the area with the upper level jet being in a slightly more favorable position. Ongoing convection across GA will advect southeast over our GA and SC zones early afternoon and then slowly sink south through the afternoon. Previous model guidance had been very bullish with widespread rainfall today, but latest guidance has started to cast doubt on this. In particular, ACARs soundings show a persistent mid-level dry slot in place this afternoon and with little in the way of large scale forcing for ascent, significant modification looks not likely. The question remains, will the modification that does take place be enough. The general thinking is that the TriCounty down towards Jenkins might be in a QPF minimum with the highest totals today being along and south of I-16. Our QPF is presently up to 1/4 to 3/4 inches.
There is again another chance of severe weather today as bulk shear values are forecast to be in the 40 to 50 kt range with MLCAPE around 1000 J/kg. The highest threat area for severe weather seems to be displaced down towards GA or near the I-16 and south region as this airmass will likely be untainted from morning convection and resultant outflows. The primary hazards will be damaging winds (supported by mid-level dry air) and large hail (ample CAPE in the hail growth region). An isolated tornado can't be ruled out where boundary interactions occur if outflows merge and/or the resultant sea breeze gets involved.
This afternoon will once again be warm with highs in the low 80s across SC and even upper 80s possible towards southern GA. Afternoon temps will likely drop into the 70s if not the 60s where the more intense thunderstorms and resultant cold pools form.
Tonight: Showers and thunderstorms will slowly decrease in coverage this evening as daytime heating is lost. A cold front will then enter the northern zones late tonight/ early Tuesday morning bringing drier air across the TriCounty. There is a chance of some patchy fog right ahead of front, but confidence is low at this time and we've decided to leave it out of the forecast for now. Expect low temperatures in the upper 50s for inland SC and mid 60s forecast along coastal GA and SC.
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.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
Tuesday: Weak low pressure will track east along a surface boundary. After a relative lull in precipitation coverage to start the day, another surge of moisture transport should translate to increasing coverage of showers. Highest PoPs, likely to categorical, should occur across the southern half of the forecast area. Coverage of showers farther north remains uncertain, so PoPs are capped at 50 percent there. Also of note, instability could persist across southern counties, along/south of the surface boundary which should reside between I-16 and the Altamaha River. Thus, we maintained a mention of thunderstorms in this area, and an isolated severe thunderstorm cannot be ruled out. Otherwise, highs in the mid to upper 70s should be common away from the immediate coast.
Tuesday night: Low pressure will move into the Atlantic will push cold front south of the region. A few showers could linger near the coast in the evening, then high pressure will push cooler/drier air into the region. Northwest winds will veer toward the north/northeast, and cold air advection should push temperatures into the upper 40s well inland and into the lower to middle 50s elsewhere.
Wednesday will start with elevated north/northeast winds, then winds should diminish as high pressure settles over the region. Sunshine could remain somewhat limited as high level clouds should persist most of the day and decent cumulus field could also develop. Expect the coolest day of this week, as temperatures are expected to top out in the middle to upper 60s north and around 70F south. Low Wednesday night should dip into the 40s at many locations away from the immediate coast, perhaps into the lower 40s well inland. On the beaches/islands, temperatures will remain in the 50s.
Lake winds: A surge of north to northeast winds Tuesday night into early Wednesday could produce a few gusts to 25 knots on Lake Moultrie. The latest forecast hold winds just below this threshold, but we will continue to assess the potential for Lake Wind Advisory conditions.
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.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
Thursday through Saturday will feature another warming trend, with highs in the 70s Thursday increasing into the 80s Friday and Saturday. Ahead of an approaching cold front, Saturday temperatures could warm into the middle to upper 80s. Instability/shear could then support some showers/thunderstorms Saturday pm before cold front pushes through the area Saturday night. The front could stall just south of the region, and showers could linger Sunday into early next week. temperatures should remain above normal for early April.
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.AVIATION /07Z MONDAY THROUGH FRIDAY/...
CHS/ JZI are IFR currently thanks to a marine stratus deck with the stationary front stalled across the middle of SC. Convection remains ongoing towards Columbia, but has remained clear of the TAF sites. This looks to continue through the overnight/ early morning hours, as the convection is forecast to amalgamate into an MCV and exit the NC coast around sunrise Monday morning. The marine stratus deck will then likely start to lift not long after sunrise.
As the convection from overnight/ early morning exits the coast of NC, there will likely be a very brief break in the precipitation on the back side of the wave. Another round of showers and thunderstorms will then develop across GA and slowly sink east/ southeast. By late morning/ early afternoon showers and thunderstorms will slowly sink south as the stationary front begins to ooze south. Have kept the VCTS in for all TAF sites with tempo groups likely being needed by the 12z TAF issuance.
Extended Aviation Outlook: Flight restrictions are likely at KSAV and could also occur at KCHS/KJZI as low pressure crosses the region Tuesday. VFR should the then prevail through late week.
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.MARINE...
Today and Tonight: Southerly winds will persist through the day today and then veer around from the southwest tonight. Expect seas 2 to 4 ft. A cold front will then approach the waters tonight. There also will be patches of stratus and potential sea fog this morning until convection moves over the waters.
Tuesday through Wednesday: Winds/seas will remain below SCA levels Tuesday, although thunderstorms could produce locally hazardous conditions especially across GA waters Tuesday afternoon/evening. Then, in the wake of cold fropa Tuesday night, north to northeast winds will surge as high pressure builds into the region. As a result, Small Craft Advisory winds/seas should develop in many areas, especially later Tuesday night and Wednesday.
Wednesday night through Friday night: Winds should diminish, but SCA seas could persist in some areas, especially within AMZ374. Otherwise, late this week high pressure will shift offshore, and a cold front will approach from the west. Winds will shift to the S/SW, and SCA conditions could redevelop Friday night into Saturday.
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.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None. SC...None. MARINE...None.
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NEAR TERM...Haines/PJM SHORT TERM...SPR LONG TERM...SPR AVIATION...Haines/SPR MARINE...Haines/SPR