522 FXUS64 KTSA 122317 AFDTSA Area Forecast Discussion National Weather Service Tulsa OK 617 PM CDT Tue May 12 2020 .AVIATION... CONCERNING TAF SITES KTUL/KRVS/KBVO/KMLC/KXNA/KFYV/KFSM/KROG. Widespread IFR conditions are expected to develop/continue tonight with a general lowering trend in both vis and ceilings resulting in a period of LIFR conditions late tonight into early Wednesday morning as a warm front lifts north. This will also result in scattered showers or drizzle, with a few thunderstorms likely developing across NE OK early Wed morning. Winds will increase out of the south after 18z Wed, with at least some improvement in flight conditions after that time. && .PREV DISCUSSION... /Issued 217 PM CDT Tue May 12 2020/ DISCUSSION... A very active weather pattern is expected through the weekend as multiple waves of showers and thunderstorms (some severe) will be expected. The flooding threat (both river and flash) will increase through the week with each passing wave of showers and storms. What’s left of the shower and storm activity will continue to move eastward through the afternoon and evening hours. A warm front will begin migrating through the area late this afternoon and will continue northward through the evening and overnight hours. The warm front is currently analyzed along and just south of the Red River at this time with Mesonet data starting to show dew points rising along the southern tier of Oklahoma. Showers and thunderstorms are expected along the advancing warm front this evening and overnight. Conditions will be marginal, but increasing MUCAPE and limited shear along and just ahead of the warm front may promote a strong thunderstorm overnight with gusty winds and small hail being the main threats. An isolated storm could briefly pulse to severe limits, but this does not appear to be too likely. Wednesday will finally bring May-like temperatures to the area as we will be fully in the warm sector. A subtle short wave will eject out of the Rockies late in the day tomorrow and will generally add to the large scale ascent that will aid in thunderstorm development across the OK/TX panhandle late in the day Wednesday. As for us, highs tomorrow will reach into the mid to upper 70s with dew points well into the low to mid 60s. This, in turn, will promote a fairly unstable environment characterized by MUCAPE values between 2000 to 2500J/kg. We will lack a concrete trigger for thunderstorms to focus on tomorrow and we will lack elevated bulk shear (due to a weak flow regime) which will still be well west of the area through the afternoon, evening, and most of the overnight. The dryline will be well to the west as well and will act as the main trigger for severe weather expected for W OK and N TX. With that said, tomorrow should be fairly dry overall minus the shower/storm activity during the morning hours mentioned earlier. Pops were maintained through the day from about I-40 and northward due to the potential of a compact short wave and associated jet streak embedded within the large scale flow that may allow for a cluster of showers and storms to develop. Opted to only go with chance PoPs (might be too optimistic) as this seems reasonable given a moisture rich warm sector environment. The storms to the west of the area will gradually weaken due to storms out pacing the best available shear (bulk shear will only be around 20 to 30kts in and around E OK and NW AR) as they move into our area, but strong to severe storms will remain possible from about US Hwy 75 and points westward. Severe threats should be on the marginal side with damaging wind gusts with hail potentially up to quarter size. Another threat to consider, especially given the relatively weak flow and deep moisture, will be the flooding threat. This will not be a huge concern for Wednesday, but any rainfall on Wednesday will help elevate the flood threat all the more as we progress through the week. Weak overall shear will hinder severe storm organization Thursday, but given temps in the 80s and dew points in the mid 60s to near 70 MLCAPE values will rise between 2500 and 4000J/kg during the afternoon and early evening hours aided by steep mid level lapse rates on the order of 7.5 to 8.2C/km. With all this said, Thursday morning and afternoon may see various outflow boundaries from previous night storms across E OK and NW AR. These boundaries will act to locally enhance shear in an overall weak shear environment expected through the day which could locally enhance the severe risk. Forecasting the exact locations of the boundaries at this time is very difficult. The mesoscale details will continue to be ironed out over the next few days. Guidance has continued to show a cold front advancing toward NE OK but stalling at or just north of the OK/KS border. This area will be the focus for strong to severe thunderstorms during the evening and overnight hours. Storms would be possible over NE OK and far NW AR as a result of the influence from this frontal boundary. Storms will likely train along the boundary during the evening and overnight hours and given deep moisture in place and weak shear aloft, torrential downpours are likely. Flooding, both river and flash, will become an increasing concern Thursday evening and overnight. Storms will continue to fire along this stationary boundary on Friday with the boundary, more or less, over SE KS allowing all of E OK and NW AR to be within the warm sector. Again, shear is expected to be weak given the relatively weak flow regime despite a 500mb trough moving into the region. Friday’s severe threats will basically be a repeat from Thursday with really no change. Heavy rainfall from thunderstorms is expected to continue over much of the area with the northern half likely seeing the best chances for heavy rainfall. This will continue to increase the threat for flooding. The weekend (especially Saturday) will continue to see an influence from the near stationary boundary generating thunderstorms across the area. Some of these storms could be strong to severe. These storms will also continue to bring heavy rainfall to the area increasing the flooding concerns. The boundary will finally start to exit the area by Sunday. Storms will continue to be a possibility over NW AR and far E OK on Sunday as the boundary and associated showers/storms move out of the area. Monday shows rising heights associated with a building ridge across the area which will finally bring a period of dry and likely much warmer weather to the forecast. The ECMWF and GFS are continuing to show hints of a cutoff low spinning across the southern plains by the early to middle part of next week which would likely increase our storm and shower chances. Will opt to keep precip chances out of the forecast for now given low confidence, but will evaluate the potential in future forecast updates. Overall, the main forecast concerns this week will be the threat for severe weather (albeit a limited threat at this time) Wednesday through Saturday and heavy rainfall which could lead to flash or river flooding. When it is all said and done, 2.5 to 4” of rain will fall across the area with locally higher amounts very possible where storms train over the same area. River and flash flooding will be an increasing concern with each passing wave of showers/storms. The river basins of greatest concern will be the Neosho, Illinois, and Spring. With that said, all interests near rivers, creeks, or streams should continue to monitor the forecast closely as any small shift in track or expected rainfall could greatly influence other rivers in addition to the aforementioned basins. Low lying areas and areas already prone to flash flooding should remain alert through the week for rapidly rising waters, especially toward the latter part of this week. A Flash Flood Watch could be needed by the end of the week. Remember to Turn Around, Don’t Drown if you encounter a flooded roadway. Snider && .TSA WATCHES/WARNINGS/ADVISORIES... OK...None. AR...None. && $$ AVIATION.....14