Area Forecast Discussion
Issued by NWS Charleston, SC
Issued by NWS Charleston, SC
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356 FXUS62 KCHS 050601 AFDCHS Area Forecast Discussion National Weather Service Charleston SC 201 AM EDT Sun May 5 2024 .SYNOPSIS... Atlantic high pressure will remain across the Southeast U.S. through much of next week. A cold front will approach the area on Friday. && .NEAR TERM /THROUGH TODAY/... The updated forecast will add SCHC PoPs across the Savannah River border counties late tonight, based on radar trends. Otherwise, shower activity should gradually increase across the SC waters and the Santee River basin. Temperatures are on track to cool to the upper 60s along the coast to the mid 60s inland. && .SHORT TERM /TONIGHT THROUGH TUESDAY/... Sunday: The mid-level weakness that was aligned along the Southeast U.S. coast Saturday will shift offshore as shortwave ridging builds in behind it. This feature will dominate for Sunday with forecast soundings and model time sections showing a distinct lowering of mean moisture values with quite a bit of drying occurring in the mid- levels. PWATs will lower about a quarter of an inch, but will still remain rather elevated with values holding around 1.50". Convection will be mostly driven by the afternoon resultant sea breeze along with mesoscale boundary collisions. Most of the convection looks to concentrate along the climatologically favored I-95 corridor and chance pops around 50% still look reasonable for the afternoon/early evening hours. Localized corridors of higher pops may eventually be needed as mesoscale trends become more apparent. Mid-level drying will help enhance the risk for gusty winds with modified soundings supporting DCAPE values around 800 J/kg. Although 0-6km bulk shear will be limited in the absence of any meaningful forcing mechanism passing by aloft, any convective updrafts that can be enhanced by mesoscale boundary collisions could yield a few strong to locally severe convective wind gusts. Freezing levels and WBZ heights look to remain seasonably high, but some small hail can not be ruled out. There will also be a potential for some localized flooding of low- lying and poor drainage areas with fairly weak steering winds in place. Convection will gradually wind down during the evening hours with the best focus for showers/tstms refocusing over the Atlantic overnight. Some of this activity could make a run for the coastal counties during the early morning hours Monday. Highs will warm into the lower-mid 80s with overnight lows ranging from the mid 60s well inland to the lower 70s at the beaches and Downtown Charleston. Monday: Monday could be a convectively more active day as shortwave ridge aloft dampens and shifts offshore as a modest southern stream shortwave crosses the Southeast U.S. during the afternoon hours. The pattern will favor yet another modest resultant sea breeze moving inland within a moderately unstable environment and fairly low convective temperatures. Convection could get going fairly quickly Monday morning, first initiating along the developing resultant then shifting and/or refocusing inland and potentially interacting with additional convection firing over the Midlands, CSRA and east- central Georgia. There are signals that a large amalgamation of shower/tstms will occur over inland areas mid-late afternoon as a number of significant boundary collisions occur within a warm/moist environment. With the approaching shortwave providing modest forcing for ascent during the diurnal maximum, a healthy coverage of showers/tstms is expected, especially away from the coast. Pops 60- 70% were held for now, but the introduction of categorical pops may eventually be needed as confidence on the placement/timing of mesoscale features increases. A few strong tstms could occur with wet microbursts if updrafts can become enhanced in the vicinity of boundary collisions. Convection will gradually wind down across the interior Monday evening with the focus for showers/tstms shifting into the Atlantic. A southwest steering flow should keep most of this marine-based convection over the Atlantic, possibly brushing the middle/upper Charleston County beaches early Tuesday morning. Highs will warm into the lower-mid 80s with lows Tuesday morning ranging from the mid 60s well inland to the lower 70s at the beaches and Downtown Charleston. Tuesday: Mid-level heights will begin to build Tuesday as Monday`s shortwave pushes offshore. Modified soundings show the atmosphere becoming increasing capped through the day in response to increasing subsidence aloft, but there may still be enough mixed-layer instability and convergence along the afternoon resultant sea breeze to initiate a few showers/tstms. Slight chance pops look reasonable for Tuesday afternoon. Highs will warm into the upper 80s/near 90 away from the beaches. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... *** THE FIRST HEAT WAVE OF THE SEASON TO BRING NEAR RECORD HEAT NEXT WEEK *** Subtropical ridging will dominate the Southeast U.S. for much of next week bringing with it a risk for building heat and the first real heat wave of the year. The NWS defines a heat wave as a period of abnormally hot weather that generally lasts for 2 days or more. As the heat builds next week, a number of record highs and record high minimums could be challenged. Forecast soundings show pronounced subsidence inversion just below 700 hPa prevailing for much of the period and while an isolated shower/tstm could still pop along the sea breeze each afternoon, the probabilities for anything measurable look to remain below 20 percent for both Wednesday and Thursday. The hottest day looks to occur Thursday as compression heating and deep westerly flow occur ahead of an approaching cold front prevails. 850 hPa temperatures could warm as high as 19-20C by this time with mid- level temperatures between 850-500 hPa running about +1 to +2.5 standard deviations depending on the layer. Highs look to warm into the lower 90s by Wednesday with mid 90s possibly by Thursday, which is about 12-15 degrees above normal. It will remain rather warm during the overnights with lows only cooling to around 70 well inland to the mid 70s at the beaches and Downtown Charleston. Although dewpoints will likely mix out into the 60s each afternoon yielding maximum heat indices in the mid 90s to near 100 (below the new Heat Advisory criteria of 108-112), the experimental NWS Heat Risk tool is highlighting much of the area in a "moderate (cat 2) heat risk" Wednesday through Friday given how abnormal this level of heat is for the time of year and the lack of any meaningful nighttime recovery. Precautions should be taken, especially given this will be the first real heat wave of the year. Rain chances could increase Friday as a cold front moves through the region. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... Prevailing VFR conditions are expected at CHS/JZI/SAV terminals through the 6Z TAF period. Scattered showers, possibly a thunderstorm, may develop just inland of the terminals early this afternoon. The convection should focus along a sea breeze and will track inland during the mid and late afternoon. Extended Aviation Outlook: Flight restrictions possible in overnight/early morning fog and stratus. Isolated to scattered showers and thunderstorms are possible Saturday through Monday. && .MARINE... Tonight: Quiet marine conditions are expected locally between high pressure across the western Atlantic and weak low pressure across southeast Georgia. Outside a few early morning thunderstorms, the surface pattern will yield southeast winds around 10 kt or less through the night. Seas should range between 1-2 ft across most nearshore waters and 2-3 ft across waters off the Charleston County coast and offshore Georgia waters. Sunday through Thursday: There are no concerns. Southerly winds will prevail through the period. While some nocturnal surging and sea breeze enhancements could occur each day, winds should largely remain 15 kt or less. Seas will average 2-4 ft. && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...None. && $$ NEAR TERM...NED SHORT TERM... LONG TERM... AVIATION...NED MARINE...DPB