Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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656 FXUS64 KMRX 140232 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1032 PM EDT Sat Jul 13 2024 ...New UPDATE... .UPDATE... Issued at 1004 PM EDT Sat Jul 13 2024 Inherited forecast has verified well so far, so nothing needing to be drastically changed in the nearest term. Temperatures earlier did end up a couple of degrees warmer at our climate sites than forecast, so will take that into account for tomorrow and the days following. BNA this evening captured 850 mb temps around 20 deg C and expecting that to be a degree or so higher for tomorrow if that`s any indication of what`s to come. Flow aloft will continue to be weak out of the west into tomorrow, perhaps sparking a shower/storm over the higher terrain. KS && .SHORT TERM... (This evening through Sunday) Issued at 300 PM EDT Sat Jul 13 2024 Key Message: 1. Hot and mostly dry weather continues. Discussion: Upper-level ridge continues across the Southeast CONUS with weak troughing across the Mississippi Valley. Low-level 850mb ridge remains centered across the Midsouth with 21C to 23C temperatures across the Tennessee Valley and Southern Appalachians. This is also limiting northward moisture transport across the region which is keeping RH values lower and limiting convection each afternoon. This will produce mostly dry weather across the region with some low 10 to 20 percent chances of weak diurnal convection across the higher terrain. This is a pretty consistent persistence pattern for the next couple of days. && .LONG TERM... (Sunday night through next Saturday) Issued at 300 PM EDT Sat Jul 13 2024 Key Messages: 1. Dangerous, near record heat is expected Monday and Tuesday with temperatures near 100 degrees and heat index values reaching around 105 degrees, especially on Tuesday. 2. Rain chances are limited until late in the week, which will also be when temperatures cool off significantly. Sunday Night through Wednesday At the start of the period, quasi-zonal flow will be in place aloft with anomalously high 500mb heights around 5,920 meters. At the surface, high pressure will be in place across much of the eastern U.S. Very impressive warming in the lower levels is indicated by 850mb temperatures of 21 to 22 Celsius to begin the period, values that are just below daily maximum high values. As such a dry and mild night will begin the period with similar conditions remaining in place for the day on Monday. Overall moisture will still be fairly limited with efficient mixing likely dropping dew points to around 60 degrees, which will limit how high heat index values reach. However, the continued dryness and impressive low-level heat strongly suggest dangerously high temperatures, possibly to the highest that we`ve seen since the record heat wave of 2012, i.e. 100 degrees through the southern and central Valley. A stray shower or storm can`t be ruled out, but the chances are certainly very limited. On Tuesday, a very weak closed low is noted to our southwest that will move towards the area with surface high pressure starting to break down to our south, producing a more southerly shift in winds. 850mb temperatures will remain similarly near record high values with an increase in humidity from Monday. This means temperatures will likely stay just below Tuesday`s, but the increase in humidity will produce equally dangerous heat with heat indexes upwards of 105 degrees. With this increase in moisture, chances for convection will increase but still be limited outside of the higher terrain. On Wednesday, we continue to see a breakdown of high pressure and upper level ridging with a cold front approaching from the Ohio River Valley. There are still timing differences, but the trajectory and height falls certainly suggest more substantial convection chances, especially further north. This will hopefully provide some relief to the extreme heat, as well as much needed rainfall. Daily Record High Maximum Temperatures Date Chattanooga Knoxville Tri-Cities Oak Ridge 07-14 103(1954) 101(1954) 98(1954) 101(1954) 07-15 103(1977) 98(1995) 96(1995) 100(1980) 07-16 105(1980) 100(1980) 100(1988) 103(1980) 07-17 103(1980) 101(1980) 94(1980) 103(1980) Thursday through Saturday Late in the week, the region will remain in a troughing pattern with the main question being how far south the aforementioned frontal boundary reaches. It could get hung up across the area or possibly even move further to the south. This will keep continued chances for much needed rain, but this will certainly depend on where the frontal boundary ends up and how much moisture remains in the area. In any case, temperatures will certainly be a lot cooler than the days before heading into the weekend. The worsening drought may continue to limit development, especially after the extreme heat. && .AVIATION... (00Z TAFS) Issued at 749 PM EDT Sat Jul 13 2024 Persistent high pressure, relatively light winds, and thus VFR expected for the updated TAF period. Mid to high level FEW-SCT-BKN at times. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 73 99 75 100 / 0 20 0 20 Knoxville McGhee Tyson Airport, TN 72 96 73 98 / 0 10 0 20 Oak Ridge, TN 71 96 72 98 / 10 10 0 10 Tri Cities Airport, TN 66 93 69 95 / 0 10 0 10 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...JB LONG TERM....BW AVIATION...KS