Area Forecast Discussion
Issued by NWS Columbia, SC
Issued by NWS Columbia, SC
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100 FXUS62 KCAE 261831 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 231 PM EDT Sun May 26 2024 .SYNOPSIS... Isolated to scattered thunderstorms possible today in a moist and unstable air mass. A more organized system is expected to cross the eastern US Monday and Tuesday with additional chances for thunderstorms. Drier weather will return for Wednesday through Friday with the next chance of showers and thunderstorms returning Saturday and Sunday. && .NEAR TERM /THROUGH TONIGHT/... A series of shortwave troughs and associated MCS`s will push through the area over next 18 hours or so ahead of the deepening low over the central US. Ridging aloft remains in place over much of the eastern US, with the primary axis sitting just to our northwest, so northwest mid-level flow is present over SC and GA. The first of these MCS`s that will come at least close to our area is developing over TN as 18z and will steadily slide east before turning southeasterly this evening as it rounds the ridge axis. Ahead of this, a generally unstable airmass will develop with somewhere between 1500-2500 j/kg MU CAPE will develop, but only around 1000 j/kg ML CAPE thanks to pervasive dry air at low-mid levels. The tightening height gradient aloft as the primary trough axis pushes southeast will increase mid-level flow (40-50 knots at 500mb) enough to provide modest deep layer shear this afternoon and into the evening. But given the lack of forcing, mid-level entrainment, and noticeable dry air below 700mb, airmass thunderstorms this afternoon will remain very isolated with only a few expected to initiate prior to 22-23z; however, any deep convection that does develop and become established will have a fairly high probability of producing severe weather given the dry mid-levels and modest shear. Convective coverage will likely increase somewhat, especially across northern SC, this evening as the first of the MCS`s moves it way southeast out of the Appalachians. The environment will still remain favorable for severe thunderstorms given the diurnal timing and any organized cold pool should be plenty to trigger convection until diurnal instability wanes. Hi-res guidance is mixed on exactly how far south the convection will make it (mostly staying over NC) but most of the HREF members have any at least some thunderstorm activity moving across northern SC between 23-02z. So PoP`s increase, mainly from Columbia north into the northern Midlands, during this timeframe. The next MCS in the series is progged to push towards the region late tonight into Monday morning. Again most of the HREF members develop this MCS within the prefrontal trough of the primary trough and then send it southeast over the Appalachians between 06-10z. The severe threat with this MCS would be very limited given the diurnal timing, but some gusty winds and heavy rain would remain possible. This MCS however will play a role in complicating the severe threat for the rest of the day Monday. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... The active weather pattern will continue Monday into Monday night as low pressure tracks through the central Great Lakes and pushes a cold front through the SE US. Although there is high confidence the front will be moving through the region confidence is currently low as to storm development and coverage with much surrounding the convection and movement of the MCS tonight. The MCS is expected to be moving toward Upstate SC tonight however models continue to weaken the remains as it crosses the mountains. Model soundings indicate some CIN in the area Monday morning along with low level lapse rates under 5.5 C/Km and 850 mb winds turning more westerly. Even though thunderstorms may not form in the morning and early afternoon hours the front will still be west of the area and act as a focusing mechanism for convection during the late afternoon and evening hours as it crosses the region. CAPE during the afternoon and early evening ahead of the front will be around 2000 J/Kg or higher with pwat values aoa 1.75 inches and DCAPE around 1000 J/Kg. Divergence aloft during the late afternoon and evening will be weak with winds at 35 kft expected to be a maximum of 60 knots. With the potential for damaging winds and hail SPC has expanded the slight risk to include the entire forecast area tomorrow. High temperatures tomorrow will be in the upper 80s to low 90s with lows Monday night in the mid 60s to around 70. Tuesday and Tuesday night are expected to be convection free as the front will be offshore and high pressure along with drier air will be building into the region. The upper level trough will remain over the eastern US however with pwat values dropping to under 1 inch by midday and 850-500 mb lapse rates under 6.0 C/Km do not expect much in the way cloudiness and any cumulus which develop will be vertically limited. Highs Tuesday afternoon will be in the upper 80s to low 90s with lows in the low to mid 60s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... The upper level pattern will remain highly amplified and progressive through the long term with changing conditions across the region. Upper level trough will remain over the eastern US through Friday while the surface will be controlled by high pressure and drier air. This will keep partly clear skies over the area with increasing clouds Thursday as a mid level disturbance moves through the region. This feature will be quickly ushered offshore as the upper level trough axis swings through the region Friday afternoon. High pressure will be moving across the region Saturday with increasing moisture Saturday afternoon as return flow from the Gulf begins. By Sunday the high will be east of the region with a trough of low pressure moving into the area and possibly becoming a focusing mechanism for convection. Temperatures through the long term will be near to slightly below normal. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... VFR conditions expected outside of any shower-storm activity this evening and overnight. Relatively dry air over the region will help limit how dense the cu field will develop this afternoon and evening. Winds will continue to remain weak this afternoon, from southwest up to 10 knots. Shower and storm potential will slowly increase after roughly 21z with a few pop up thunderstorms possible, but not enough confidence for a TAF mention at this time. More organized convection is possible closer to 00z at CAE and CUB as a system slides to our north, but again confidence is still too low for a direct mention so only went with VCSH at those sites for now. There will be a lull in shower- storm activity after roughly 03z across the area before another wave of showers-storms possibly moves through between 06-12z Monday. EXTENDED AVIATION OUTLOOK...Restrictions possible Monday afternoon in scattered thunderstorms as a cold front approaches. Otherwise, significant restrictions not expected. && .CAE WATCHES/WARNINGS/ADVISORIES... SC...None. GA...None. && $$