Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
Issued by NWS New Orleans/Baton Rouge, LA
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963 FXUS64 KLIX 130513 AFDLIX Area Forecast Discussion National Weather Service New Orleans LA 1213 AM CDT Mon May 13 2024 ...New AVIATION... .SHORT TERM... (This evening through Monday night) Issued at 300 PM CDT Sun May 12 2024 Tonight through Tuesday morning, multiple rounds of showers and storms will move through the area. There is still quite a bit of uncertainty in the models regarding the timing of the bulk of the rainfall. But in general, a round of showers and storms will move through the northernmost areas overnight tonight into early Monday. These storms could be strong to severe. The risk of severe weather is a low confidence forecast, however. A lot will depend on the eventual mode of the storms and storm motion. The main threats, however, will be gusty winds 30-60mph and large hail. Flash flooding will be a concern with these storms overnight, especially for the S MS areas and northern Southeast Louisiana parishes. This area is outlooked in a Slight Risk of Excessive Rainfall (level 2 out of 4) through 7AM. While antecedent conditions are fairly dry overall, the rainfall rates are forecast to be quite high 2-3 inches per hour. The PWs are around 2.0 inches, which is approaching the daily max for SPC Sounding Climatology. A Flood Watch is in effect for our northern half of our CWA (north of I-10/12) starting tonight through 10AM Tuesday. So with these storm overnight tonight into Monday morning, the main threat will be flash flooding with a limited risk of severe weather in the form of strong winds (30-60mph) and large hail. A tornado or two cannot be ruled out for our northernmost areas. After 7AM tomorrow, scattered showers and storms will be likely during the morning hours across the area ahead of a strong line of storms that is expected to move into the area Monday night into Tuesday morning. The timing of the storms is still unusually uncertain as model consensus has been quite lacking between the CAMs and global models, and also from the model to model runs individually. The main timing for the line of storms for the morning model consensus was mainly from midnight through 8am. Recent trends in a few of the mid-day CAMs are indicating that the line could approach our area as early as 00z (7pm Monday night). We hesitate to put all our eggs in that basket unless the 00Z runs also show an earlier timing on the line. For now, we would say the main timing is generally 10pm to 7am on Monday night into Tuesday morning for our area with the potential for the system to be earlier than forecast. Regardless of the timing of the line, there will be an all-day threat for severe weather and especially for flash flooding. With decent lapse rates during the daytime hours tomorrow, good instability, decent shear, there could be some damaging winds and large hail possible inside of scattered storms during the daytime hours. The main question for the daytime storms (but not for the line) will be whether there is enough forcing for severe storms. The main severe weather threat with the line tomorrow night will be damaging winds, hail, and an embedded tornado or two cannot be ruled out. We are outlooked in a Slight Risk of Severe Weather tomorrow through 7AM Tuesday for our entire area. To summarize, inside of storm development there will be the potential for damaging winds and large hail and a tornado cannot be ruled out, especially inside the line(s) of storms. For areas north of I-10/12, this risk will be in place from tonight through Tuesday morning and for areas south of I-10/12, this risk will be in place from Monday morning ~7AM through Tuesday morning. Regarding the flash flooding threat, there will be abundant moisture, good instability, deep atmospheric moisture column, and warm rain processes in the model soundings. PW values are 2.0-2.1 inches, which is approaching the daily max for SPC sounding climatology for our area. As a result, the rainfall will be highly efficient with rainfall rates estimated to be around 2-3 inches per hour. This will be the case for the scattered storms as well as the line of storms. The other concern related to the flash flooding risk will be if storms occur over the same area repetitively, which is possible. We are outlooked in a Moderate Risk (3 out of 4) of Flash Flooding for the majority of our area. Generally, we are expecting 3-5 inches of rainfall for the total event with locally higher amounts in excess of 6 inches possible. And a Flood Watch is in effect for our northernmost areas tonight through 10AM Tuesday morning and for our southernmost areas (I-10/12 and south) from 7AM Monday through 10AM Tuesday. All this to say... There will be the chance for flash flooding inside of shower/storm activity from tonight through Tuesday morning. The most vulnerable areas and areas with the greatest potential for flash flooding will be places that see multiple rounds of rainfall as well as urban areas (New Orleans metro, Baton Rouge, Coastal MS). Be prepared in case a warning is issued, and stay alert to the weather. If you encounter flooded roadways, turn around, don`t drown. In Summary, severe weather and flash flooding are likely tonight through Tuesday morning. Flash flooding is the larger concern, especially Monday morning through Tuesday with 3-5 inches of rainfall total for the event forecast with locally higher amounts in excess of 6 inches possible and rainfall rates of 2-3 inches per hour expected. But the severe threat potential will be there inside any storm activity with the main threats being damaging winds and large hail, especially inside the line(s) of storms. A tornado or two cannot be ruled out. Stay weather aware over the next 24-36 hours, and have multiple ways to receive warnings, especially overnight. And if you encounter flooded roadways, especially at nighttime with the limited visibility, turn around, don`t drown. MSW && .LONG TERM... (Tuesday through Saturday night) Issued at 300 PM CDT Sun May 12 2024 By sunrise Tuesday, a cold front should be pushing east of the local CWA, although we may still have some lingering precipitation during the morning hours. The associated upper system will be moving through the Ohio River Valley during the day on Tuesday, toward the Virginia coast by late Wednesday. Drier air will be moving into the area briefly, but surface winds will regain a southerly component Thursday morning with moisture rebounding quickly. For instance, forecast soundings at Baton Rouge will be around 1 inch at 12z Thursday and increase to 1.8 by Thursday evening. Southwesterly upper flow will bring another shortwave across the area Thursday night into Friday morning. That will produce another round of showers and thunderstorms. Considering the moisture availability, if we see another round of 2+ inch rainfalls across the area, there will be potential for hydrologic issues, especially if the short term forecast amounts verify. Beyond Friday morning, forecast confidence decreases, as the global models come into disagreement regarding which stream, north or south becomes the predominant trough. The ECMWF focuses energy in the northern stream, while the GFS is on the southern stream. This will mean the GFS operational run brings another area of thunderstorms and heavy rainfall across the area Saturday, while the ECMWF operational is much drier. Will note that the 00z ECMWF ensemble numbers support the 12z ECMWF global PoPs. Will ride the NBM PoPs for the weekend for now, and acknowledge limited confidence int eh weekend forecast. Won`t make significant changes to NBM max/min numbers. The days with no precipitation will likely see high temperatures near 90 degrees. Overnight lows will continue to be near to above normal. RW && .AVIATION... (06Z TAFS) Issued at 1204 AM CDT Mon May 13 2024 Most terminals are in VFR status but a few are seeing some restrictions due to cigs falling into MVFR status. Low clouds will be the main concerns outside of any convection but timing convection is the key problem. Convection could move back in over the next 6 hours and if terminals do see convection both vsbys and cigs will fall. Outside of convection low cigs will lead to MVFR status at times or could be just above to get into VFR status. Right now the most likely terminals to see imapcts from convection between now and 12z are MCB and BTR. Followed by HDC and ASD shortly after. /CAB/ && .AVIATION... (00Z TAFS) Issued at 634 PM CDT Sun May 12 2024 Most terminals reporting VFR at issuance time. Convection has been weakening as it moves into our area over the last hour or two. With lightning activity diminishing, have removed it from KBTR in the near term, but will hold VCTS in KHDC and KMCB. Expect ceilings to fall into the MVFR range at most terminals beyond 06z, and perhaps the upper end of IFR. Quite a bit of uncertainty regarding convective development overnight, both in location and timing, but there is likely a warm front north of Interstate 10, with convection primarily on or north of the front. Expecting amendments will be necessary during the evening hours as convective processes reveal themselves. Least likely terminals for convection tonight into Monday morning will be KNEW/KMSY/KHUM. At this time the second round of organized convection will occur beyond 00z Tuesday, and may be addressed more fully in the 06z forecast issuances. && .MARINE... Issued at 300 PM CDT Sun May 12 2024 A system bring multiple rounds of rain and storms will be moving through the area tonight through Tuesday morning, which will cause strong (15-25kts) southerly winds and higher seas through Wednesday morning. Exercise Caution headlines are in effect through at least tomorrow and will likely need to be extended in time. Winds will ease shift northerly Wednesday into early Thursday behind the system. Another system will likely move through the area Thursday through Saturday morning, which will strengthen the southerly winds (15-20kts) and bring higher seas. MSW && .PRELIMINARY POINT TEMPS/POPS... MCB 65 84 62 86 / 90 40 0 0 BTR 69 89 65 91 / 80 30 0 0 ASD 68 88 66 90 / 90 60 0 0 MSY 72 87 71 89 / 90 60 0 0 GPT 69 87 68 89 / 100 70 0 0 PQL 68 87 66 90 / 100 80 0 0 && .LIX WATCHES/WARNINGS/ADVISORIES... LA...Flood Watch through Tuesday morning for LAZ034>037-039-046>048- 071-076-079>086. Flood Watch from 7 AM CDT this morning through Tuesday morning for LAZ056>060-064>070-077-078-087>090. GM...None. MS...Flood Watch through Tuesday morning for MSZ068>071-077-083>088. GM...None. && $$ SHORT TERM...MSW LONG TERM....RW AVIATION...CAB MARINE...MSW