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Area Forecast Discussion
Issued by NWS Jackson, MS
Issued by NWS Jackson, MS
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631 FXUS64 KJAN 180702 AAC AFDJAN Area Forecast Discussion...UPDATED National Weather Service Jackson MS 202 AM CDT Sun Aug 18 2024 ...New AVIATION... .MESOSCALE UPDATE... Issued at 943 PM CDT Sat Aug 17 2024 Convective activity has shifted out of the forecast area and just some remnant convective debris is left across the south half. Several updates were made earlier to capture temps that were impacted by precip/cooler outflow so things are pretty much on track. Will updated to capture temp tweaks shortly. Focus will shift to Sunday, it will be HOT as we will reside in the lower level thermal axis. It sure looks like it will be the hottest day of the year for most locations with Highs peaking in the 98-102 range with some 100-105 very possible. As for storms, it`s not a slam dunk as the atmosphere, as often the case with volatile situations, will be right up to a point that could go either way. In the "either way" I`m referring to is just enough to convect and we get very windy storms which in-turn establish deep enough cold pools to develop additional cells and we ultimately get an organized cluster. The other way would be there`s too much dry air and limited lower level convergence that doesn`t overcome any capping resulting in few to no convective cells. While each scenario remains on the table, the latest 00z CAMs are favoring convection. While instability is not anticipated to be extreme, there`s other elements of the likely environment that are very rare for us. First will be storms developing in 98-104 degree temps. From this, there will be very steep lapse rates in the 0-3 and 0-4 km layers that will allow for efficient momentum transfer to the surface. Also between 700- 400mb there will be strong flow of 30-40kts. I`ll add in dry air in the mid levels as well which will all for more evaporative cooling as we should see Dcape values in the 1200-1600 j/kg range. So, with all that, the signal we see from the HRRR and NAM3km with strong downdraft wind signatures are very telling. Compiling all of this offers the potential for a more widespread wind event along with some potential for sig type wind gusts as well. Still more details to cover, but wanted to offer the potential and some background as to why. Lastly, timing looks to be later and main time window for this appears to be 4p to midnight. /CME/ && .DISCUSSION... Issued at 231 PM CDT Sat Aug 17 2024 Tonight through Monday... Tonight: Convection should persist through early evening, but wind down before midnight. In the wake, a quiet night will be in store, with some potential patchy fog in low-lying areas or locations that receive rainfall. With increased boundary layer moisture, persistence forecast, with seasonably warm lows in the mid-upper 70s (74-78F) are expected. Sunday-Monday: An active period of excessive heat & severe storms is expected Sunday, before a frontal zone moves through, finally breaking the grip of the heat & more seasonable & dry conditions move in next week. Synoptic & sfc pattern will consist of deep mid- level ridge centered over west TX to the southwest states while mean longwave trough persist east of the MS River Valley. This will keep perturbed northwest flow & a frontal zone is expected to sink southward into Sunday. Moisture & deep mixing is anticipated in advance of the frontal zone moving in. Guidance indicates efficient mixing up to 850-700mb layer. There are indications combined with this deep mixing, favorable thermo profiles (i.e. 28-30C vertical totals & DCAPE nearly 1800-2000 J/kg) & 25-40kt bulk shear in the mean 0-2 to 0-6km layer, southward moving organized convective clusters could contain some higher end gusts near 70mph at times & quarter size hail. Convective allowing models (CAMs) indicate some potential of gusts in excess of 50-60kts, so strong to severe storms remain a low-medium chance, where advertised "Slight" risk looks on track. The convective outlook area has been brought further southwards towards I-20, which seems to be in agreement with most guidance. With convective storm onset in the mid-late aftn timeframe, mainly between 2-4PM, high boundary layer moisture ahead of the boundary will lead to continued dangerous heat stress again into the aftn to early evening hours. With seasonably warm highs in the 98-102F range & excessive heat potential more expansive, the "Significant" area was expanded east along I-20 & southeast, with the "Extreme" taken out of the Delta, with less oppressive conditions today, while pulled eastward near east MS due to ongoing persistent dangerous heat & expected conditions Sunday. Heat headlines were maintained from mid-morning to early evening , with a heat advisory in east-northeast MS & a Excessive Heat Warning areal configuration with similar but slightly larger coverage. The Excessive Heat Warning may be able to be adjusted to the northeast but some earlier convective coverage makes this potential a low confidence forecast. Will led later shifts decide on any further adjustments. Expect storms to persist into the evening hours but could linger a little later closer to midnight. For now, timing looks mostly intact but may be able to be refined as confidence increases. Timing looks to be mid-late aftn & persist into the evening, with rain & storm chances in the isolated to scattered range (15-40%). As heights in the ridge to the west begins to fall, there will be continued surges of drier & less oppressive airmass beginning to move in the region into next week. This will help highs become more seasonable in the low-mid 90s & lows in the mid-upper 60s north of I- 20 to upper 60s to near 70F in the south into Tuesday morning. Some storms are possible but become more focused into the Hwy 84 corridor into Monday aftn to early evening. Can`t rule out an isolated strong storm in southwest MS & portions of northeast LA on Monday. /DC/ Tuesday through Friday... Post frontal passage will bring relief from the oppressive heat/humidity of the previous week. Upper/mid-lvl ridge will primarily encompass the Southern Plains/CO/NM area, placing the ArkLaMiss region on the periphery of the ridge. As a result, northwest to northerly flow allows for dewpoints to fall into the upper 50-mid 60s range across the area, lowering humidity for the area. Afternoon high won`t be as hot either, as upper 80s/lower 90s temps are expected. Low temperatures will more likely resemble early fall than summer, as low temperatures are expected to range in the 60s midweek to near 70 degrees by late week. /SW/ && .AVIATION... (06Z TAFS) Issued at 200 AM CDT Sun Aug 18 2024 VFR conditions should prevail at the TAF sites through the period, however the chance for scattered SHRA or TSRA mainly between 21Z today to 03Z Sunday does bring the possibility of variable ceilings, gusty winds, and reduced visibility near any stronger storms. Current confidence in impacts to any particular TAF site from thunder were too low to mention in the TAFs at this time. /NF/ && .PRELIMINARY POINT TEMPS/POPS... Jackson 74 92 69 92 / 20 10 10 10 Meridian 71 93 67 92 / 20 0 0 0 Vicksburg 74 92 69 91 / 30 20 10 10 Hattiesburg 75 95 70 93 / 20 20 10 0 Natchez 75 92 71 92 / 20 30 20 10 Greenville 72 90 66 89 / 30 10 10 0 Greenwood 72 92 66 91 / 20 10 0 0 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...Excessive Heat Warning from 10 AM this morning to 8 PM CDT this evening for MSZ018-019-025>029-032-034>037-040>044-047>066- 072>074. Heat Advisory from 10 AM this morning to 8 PM CDT this evening for MSZ030-031-033-038-039-045-046. LA...Excessive Heat Warning from 10 AM this morning to 8 PM CDT this evening for LAZ007>009-015-016-023>026. AR...Excessive Heat Warning from 10 AM this morning to 8 PM CDT this evening for ARZ074-075. && $$ CME/SW/NF