Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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744 FXUS64 KMRX 131148 AAA AFDMRX Area Forecast Discussion...UPDATED National Weather Service Morristown TN 748 AM EDT Mon May 13 2024 ...New AVIATION... .SHORT TERM... (Today and tonight) Issued at 324 AM EDT Mon May 13 2024 Key Messages: 1. Rain chances increase today and tonight as upper low slowly approaches from the west. 2. Mountain wave conditions develop today and tonight, with gusts to around 40 mph possible. Uncertainty high enough to preclude issuing an advisory though. Discussion: An upper low was moving into the central plains early this morning, while a southern stream disturbance was out ahead of it moving into Louisiana. The vertically stacked system is forecast to slowly shift eastward over the next 24 hours, perhaps making it to western Kentucky by the end of the short term period. Therein lies the uncertainty with the forecast, trying to get a handle on rain chances and expected rain amounts. Isentropic analysis shows the forecast area lying between two more pronounced areas of ascent, one focused just to our south with the southern stream disturbance and one to our northwest closer to the upper low. Regional radar imagery shows some weak returns spreading northeast across northern Alabama this morning, which is consistent with the leading edge of higher RH and ascent along the 305K surface. Most guidance brings this into the southern parts of the CWA by 12z-14z or so. Current radar imagery is less impressive than models would have you believe but it`s also still developing. Have a feeling that today is going to be more along the lines of a high PoP and low QPF type forecast. Tempered the NBM PoPs with a blend of various models, which lowered them significantly. This left some areas of likely PoPs in the mountains this afternoon, with chance values elsewhere. Rain chances and shower coverage should increase overnight as better ascent and forcing continue to inch closer. Another thing to note about today is that H85 flow becomes SSE today and increases to around 30kt. There`s plenty of support in various guidance for some mountain wave effects in the wind fields as a result of this pattern. Will hold off on a wind advisory with this forecast issuance. Have a few spots where advisory criteria is met in the forecast across the Smokies, but the stronger H85 wind field will remain to our northwest and even there its only 30-35kt so I`m not confident we`ll hit criteria over the TN mountains. Certainly we`ll see mountain wave conditions, just not sure we`ll hit advisory criteria. && .LONG TERM... (Tuesday through Sunday) Issued at 324 AM EDT Mon May 13 2024 Key Messages: 1. Showers and thunderstorms continue through Wednesday 2. After a brief break Thursday, another round of storms expected as we head into the weekend. Discussion: At the start of the long term Tuesday, the area`s active week will already be underway. A trough sweeping across from CO will send a low pressure center directly for the Tennessee Valley. Something different that stood out with this system, is maybe better chances for thunderstorms, as CAPE values are a bit more present than they have been previous model and forecast runs. New this morning, SPC has bumped the MRGL for severe a bit to the north which slices our area approximately north of Knoxville. Cloudiness and temperatures not all that warm may hamper things a bit, working in our favor. If we do get any strong to severe storms, damaging winds and large hail would be the main threats. But I believe the main threat of them all this week will be flooding, which WPC still hangs onto the MRGL for FF for parts of our area Tuesday into Wednesday. We will be seeing multiple rounds of showers and thunderstorms with varying intensity. Heavier downpours over a certain area will increase the flash flooding threat. Activity may wane some overnight into Wednesday, but categorical PoPs return Wednesday afternoon with increasing instability again. The slow moving low pressure center and associated upper low will move to our east switching flow to the northwest. Thursday will try to dry as high pressure and weak ridging try to build in, however, wrap-around from the low that just exited the area may send isolated precip chances to mountainous areas of SW VA and far NE TN. Elsewhere will be dry and warming into the low 80s. Come Friday through Sunday becomes a big question mark as agreement between models decrease with time. A similar tracking system may impact the area Friday with numerous showers and thunderstorms possible. Saturday and Sunday is a toss-up between activity from the Friday system still, additional low pressure development, or just ridging and drying out. Therefore, isolated to scattered showers and thunderstorms were kept in the forecast to end the week and long term period. && .AVIATION... (12Z TAFS) Issued at 744 AM EDT Mon May 13 2024 Expect ISOLD SHRA to spread northward across the forecast area later this morning. Coverage seems like it will less than previously thought so have trended TAFs towards high res guidance that suggests a 3hr TEMPO for SHRA should cover it at KCHA and KTYS. Doubt anything makes it as far north as KTRI. More widespread SHRA will move in towards the end of the period. Otherwise, continued moist southerly flow should lead to MVFR CIGS developing at KTYS and KCHA as well by this evening. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 71 63 78 63 / 40 70 90 70 Knoxville McGhee Tyson Airport, TN 74 61 76 62 / 30 60 90 90 Oak Ridge, TN 74 61 76 61 / 30 60 90 90 Tri Cities Airport, TN 76 58 76 58 / 20 50 80 80 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...CD LONG TERM....KS AVIATION...CD