496 FXUS64 KJAN 181133 AFDJAN Area Forecast Discussion National Weather Service Jackson MS 633 AM CDT Sat Jun 18 2022 ...HOT AND HUMID WEATHER WILL CONTINUE TODAY... .UPDATE... Updated for 12Z aviation discussion && .AVIATION... 12Z TAF discussion: Aside from a few patchy areas of early morning BR, VFR conditions will prevail today through tonight. A cold front pushing through the area this afternoon should help to initiate a few TSRA, especially for the southern half of the area. Otherwise, expect light surface wind to become northerly. /EC/ && .DISCUSSION... ...HOT AND HUMID WEATHER WILL CONTINUE TODAY... .DISCUSSION... Today and Tonight: The main focus today will be the continuation of hot temperatures combined with high humidity to result in heat index values of 105 to 109F again between the hours of 10AM and 8PM. In addition there will be the threat of isolated severe storms capable of damaging wind gusts and hail perhaps to quarter size mainly during the afternoon. Early morning satellite imagery showed the circulation around a large 593dam high centered over the central CONUS and a broad upper level trough centered over the eastern seaboard. This upper level trough was helping support a weak and nearly diffuse cold front to our northeast that will sag into our CWA during prime heating as a backdoor cold front and help set off at least isolated storms. The 06Z HRRR continued to depict very sparse coverage of storms in our CWA while other hi-res guidance suggests greater coverage. The hottest temperatures in our CWA are expected in the southeast where afternoon highs will top out near 100F while mid to upper 90s will be common elsewhere. Although the 00Z Sat JAN sounding had a PWAT less than an inch and a half, latest satellite derived total PWAT products suggests PWATS in excess of an inch and three quarters back across our CWA ahead of the approaching boundary. Convection is expected to initiate in our north along and ahead of the boundary this afternoon and develop to the south during the afternoon and into the early evening hours before dissipating. Considering the environmental parameters this afternoon during convection, wet microbursts look possible along with some hail. These rain cooled areas will provide some relief from the oppressive heat but the Heat Advisory will be in effect for the whole CWA again today. A distinct diurnal trend to the convection is expected this evening. Drier air in the wake of the backdoor cold front will knock dew points down into the 60s tonight with mid to upper 50 dew points in our northeast by morning. This will help contribute to cooler than normal morning lows in the mid 60s across the northeast third of our CWA. /22/ Sunday through Friday: the drier and milder air will continue into Sunday resulting in more tolerable levels of heat and humidity for the forecast area, but this will be temporary relief as the subtropical ridge is forecast to intensify again over the lower MS Valley region Monday into Tuesday. By later in the week, the low level thermal ridge is expected to peak with H850 T likely reaching the mid 20s C. These values are highly anomalous, and it is likely many locations will reach or exceed surface temperatures of 100 deg F in the Wednesday to Friday time frame. We'll likely need to begin advertising for this next round of heat in the HWO graphics as we go through the weekend. Otherwise, the hot anticyclonic flow will greatly limit diurnally driven convective rainfall as we go through the upcoming week. /EC/ && .PRELIMINARY POINT TEMPS/POPS... Jackson 96 70 93 69 / 26 8 1 0 Meridian 98 67 94 69 / 22 5 0 0 Vicksburg 96 72 92 69 / 26 11 3 0 Hattiesburg 99 72 96 70 / 25 20 2 0 Natchez 96 74 94 71 / 20 12 4 0 Greenville 95 67 89 66 / 24 7 1 0 Greenwood 96 66 92 68 / 25 3 0 0 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...Heat Advisory until 8 PM CDT this evening for MSZ018-019-025>066- 072>074. LA...Heat Advisory until 8 PM CDT this evening for LAZ007>009-015-016- 023>026. AR...Heat Advisory until 8 PM CDT this evening for ARZ074-075. && $$