275 FXUS64 KLIX 190931 AFDLIX Area Forecast Discussion National Weather Service New Orleans LA 431 AM CDT Thu Aug 19 2021 .SHORT TERM...A few nocturnal showers have developed along the coast and are moving inland but the deeper inland they continue to move they have slowly dissipated. Additional activity is struggling to develop in the coastal waters and this may be to slightly drier air indicated by GOES16 TPW sensor. As for temps, it is quite warm out there with much of the area still in the upper 70s to lower 80s by 8z and most if not all locations already at 95-100% RH so temps will struggle to drop much more this morning. Main focus in the short term will be on the potential for oppressive heat across the region. With morning lows struggling to even drop into the mid 70s across much of the area and a number of sites struggling to get below 80 conditions will already by rough this morning. Today may actually be the coolest day of the next 3-4 days but given highs climbing into the mid 90s across much of the area yesterday and LL temps not any cooler, maybe even a degree warmer, I see no reason to expect cooler temps today outside of one possible impact, convection. Right now we already have isolated showers across the coastal areas and this activity is moving north but the farther north it moves away from the coast it has tended to dissipate. CAMs actually has indicated this and shows most of this convection dying off around sunrise. This could actually have a negative result on cooling as any rain that falls is not really going to cool us off right now but it will just add more moisture to the BL and by 14-16z we could have a number of sites with upper 70s to near 80 dewpoints. Once we heat up the heat index values will climb and climb quickly with a good chunk of the area likely seeing heat index values over 100 degrees before 15z. So for today h925 temps will likely be around 25-26C and this mixed down should result in highs around 34-35C which is well into the mid 90s. Given the amount of moisture in the BL not anticipating that superadiabatic skin layer which could add another degree or two to the highs but that may not be the case Friday or this weekend. As mentioned there is one possible cog in the wheel. Guidance is actually quite high with PoPs in two areas, the northwest and coastal SELA. The nrothwest which includes southwest MS and adjacent LA parishes will have less impact from the building ridge to our east allowing the weakness to our west to aid in convection developing there. The other locations could be the southern half of the CWA where activity has already been developing and the seabreeze will have the best potential to really activate later today. That all said if scattered to numerous storms hold off till midday or even early afternoon then we will have already warmed up. Second looking GOES16 and that relatively drier air just off our doorstep to the southeast it could really put the hammer on convection across the south if it continues to slide to the northwest. PWs could drop to below 1.8 and that will absolutely hurt rain chances across coastal areas. So with respect to the heat, yesterday max heat index values were generally in the 107-111 range outside of a few that were cooler and that will likely be the case again today and with this being the second day we will issue a Heat Advisory for much of the region. Again, yes it is Summer and mid August is suppose to be warm and humid but that still doesn't mean the environment isn't oppressive, especially for the population who are unable to cool off or those who have not become acclimated, tourists or others from out of town. In addition school is back in session across the region and many schools have afternoon practice for various activities while conditions could be the hottest. It is that which has gone into consideration for issuing the heat advisory today and there is a good chance that additional adv's will be needed Friday and through the weekend with even an outside shot of an Excessive Heat Warning this weekend, especially Sunday. Using the WetBulb Globe Temperature it is in the extreme value for much of the area as well. The 2 locations we will not have in the heat advisory today will be the immediate coast of SELA and the northwest where it will have the best potential for storms and slightly lower afternoon highs. These locations will likely not be so lucky in the next few days. As for Friday and into the weekend, HOT, yes it will be hot. The mid- level ridge will continue to build west and by Friday will be centered over LA and east TX. The ridge will then be centered over the Lower MS Valley through at least Sunday. LL temps will climb another degree or two and could range from 26-28C this weekend. That mixed down to the sfc should easily lead to a few upper 90s across the area this weekend. The ridge directly overhead will also put the brakes on convection and that will not help in cooling things off. That said we will not be completely dry. Moisture will still be quite abundant and there is still a fetch that is on the periphery of the ridge and around the base of a developing trough which will be a key in steering Henri this weekend and into next week. PWs will likely range from near 1.8 Friday to back over 2" by Sunday. 2" PWs will be hard to keep convection at bay as we heat up. However, combine that with weak northerly flow Saturday and even more so Sunday, and convection will likely hold off till late in the afternoon but should still develop. This could lead to a few stronger storms late Sunday afternoon and evening across far eastern sections like coastal MS. With the lack of rain expected for most of the area Friday through Sunday, heat advisories are all but guaranteed and there could be a few locations that may need an Excessive Heat Warning this weekend if highs can truly get into the upper 90s. /CAB/ .LONG TERM...(Monday through Wednesday) Ridge will remain in place through early next week however a backdoor trough sets up over the northeast in the wake of hurricane Henri. This will bring a weak backdoor frontal boundary into the southeast early next week as we remain on the western side of the ridge. The boundary will be weak with no airmass change...however stalling and bringing an increase to afternoon convection by the Monday Tuesday timeframe. However...a sign that fall is approaching and the potential start of an early fall later next month could be in the making with multiple shortwaves riding along the northern tier of the country. A shortwave trough will swing through the northern Rockies on Sunday riding over the ridge on Monday and eventually moving into the Great Lake states by Monday. That trough weakens and lifts while another shortwave moves along the northern Rockies and plains through midweek. This trough axis will bring a cold front down through the Tennessee valley mid to late week eventually merging with the old boundary stalling over the forecast zones through the end of the week. Tropical waves will ride along from the southeast bringing a return to gulf moisture as the energy merges up with the stalled boundary. This will bring PW values back up to 2.00 inches plus by mid week thus increasing POPS and bringing an end to the excessive heatwave that is about to unfold. /GP/ && .AVIATION...12z TAF Package...All terminals will likely remain in VFR status until convection can become more scattered or even numerous which should be around 17-20Z. Outside of convection VFR conditions will persist but with storms look for both vsbys and cigs to be impacted with most likely terminals seeing this being BTR/MCB/HUM/MSY. Storms will still be around other terminals but will only show VCTS for now. Once convection starts to die off late this afternoon and this evening, VFR conditions will once again persist. /CAB/ && .MARINE...High pressure will dominate the coastal waters for what looks like pretty much the next week. Light and variable winds will be the bulk of the forecast with winds closer to the coasts being controlled by diurnal fluctuations. Also the typical nocturnal increase in winds east of the MS river during the Summer will develop each night, so in the Breton, Chandeluer, and MS Sounds, along with the open inner waters, winds of 10-12kts will develop between 3-12z each night. /CAB/ && .PRELIMINARY POINT TEMPS/POPS... MCB 93 75 94 74 / 70 40 30 0 BTR 94 75 95 75 / 70 30 20 0 ASD 94 77 96 77 / 60 10 20 0 MSY 96 82 98 82 / 60 10 20 0 GPT 92 78 94 78 / 50 10 30 10 PQL 94 77 94 77 / 50 10 30 10 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...Heat Advisory from 9 AM this morning to 7 PM CDT this evening for LAZ037-039-046>050-056>061-063>065-071-072-075>078. GM...None. MS...Heat Advisory from 9 AM this morning to 7 PM CDT this evening for MSZ077-080>082. GM...None. && $$