Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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060 FXUS64 KMRX 170527 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 127 AM EDT Sat Aug 17 2024 ...New AVIATION... .UPDATE... Issued at 1040 PM EDT Fri Aug 16 2024 Additional isolated convection is possible tonight, but widespread or severe convection is unlikely. Mid-level lapse rates will steepen in response to the approaching shortwave, currently near Paducah, moving southeast. This amplified longwave troughing will be the primary influence of our scattered diurnal convection on Saturday afternoon. && .SHORT TERM... (This evening through Saturday) Issued at 231 PM EDT Fri Aug 16 2024 Key Messages: 1. Numerous showers and thunderstorms this afternoon and evening with a marginal damaging wind threat. 2. Quiet overnight but another round of scattered storms expected again tomorrow afternoon. Discussion: Upper heights will continue to fall across the region as an upper low over the Great Lakes deepens through the period and goes on to form a synoptic scale trough across the eastern CONUS leading into the long term period. Locally, shortwave energy is rotating through the Tennessee valley this afternoon and evening in the base of that developing trough/upper low to our north. In response, showers and thunderstorms firing along a line just coming off the Cumberland plateau area this afternoon, should continue to increase in coverage through the evening hours. Mesoanalysis shows somewhere around 1,500 J/kg of mixed layer CAPE in place across much of the CWA, along with strong low level lapse rates. Shear is lacking though, with effective bulk shear of 25kt or less...and that is maximized up closer to the TN/KY border. All things considered, expect much of the convection to be your run of the mill summertime thunderstorms. However thermodynamic profiles would support an isolated damaging wind gust this afternoon so I wouldn`t be surprised to see that occur. Would expect that to be more likely in the southern plateau and southern valley areas due to locally higher instability and downdraft CAPE values there. Expect convection to die off fairly quickly this evening, leaving mostly dry conditions in place. We will see increasing jet support aloft, with the forecast area lying beneath a strengthening right entrance region. Forecast soundings do show some meager elevated instability as well. As such, can`t completely rule out an isolated shower or two over our northern counties tonight. But I think that`s the exception to the rule though. Confidence isn`t the greatest in how Saturday plays out. We`ll be well ahead of a front that will push through during the long term period. So we won`t have that as a forcing mechanism. Thus convection during the day tomorrow will be largely diurnally driven, with any upper level forcing being subtle shortwave activity moving through. Current PoPs reflect scattered activity tomorrow afternoon, with a relative favoring of southern areas where instability will be greatest. But lack of a distinct forcing mechanism means this is somewhat of a low confidence forecast. In terms of severe weather threats tomorrow, the threat will be a little higher. Shear will be better, more along the 30-35kt range for effective shear versus today`s 20-25kt. So, a slightly better environment still favoring damaging winds, but still not a widespread severe weather type day. && .LONG TERM... (Saturday night through next Friday) Issued at 231 PM EDT Fri Aug 16 2024 Key Messages: 1. Shower and thunderstorm chances continue through Sunday, with a lower chance of showers in northern sections Monday. 2. Dry weather and near to below normal temperatures expected for much of next week. Discussion: A broad cyclonic flow will be over the eastern Conus at the start of the period, with the center of a closed low over the Great Lakes. Disturbances rotating around this low will keep PoPs in the high chance to likely range for Sunday, culminating in some categorical PoPs Sunday afternoon with the passage of an upper level trough axis and a surface cold front. Instability and shear look too limited to pose a severe threat. More stable conditions develop on Monday on the back side of the trough with a NW flow pattern through the column. However, some moisture wrapping around the closed low may bring showers to northern sections. The categorical NBM PoPs for Monday look way too high for this pattern and will be cut back significantly, to chance/slight chance. A large high pressure ridge will be developing over the Plains early in the week, with the surface high having a slow eastward drift to New England through the rest of the forecast period. This pattern will favor dry conditions with below normal temperatures. Expect highs on Tuesday in the mid 70s to mid 80s, with dewpoints dropping into th 50s on Tuesday. A slight warming trend can be expected for the rest of the week, but remaining near to slightly below normal. && .AVIATION... (06Z TAFS) Issued at 117 AM EDT Sat Aug 17 2024 Isolated to scattered showers and thunderstorms will continue throughout this forecast period. This activity will be hit and miss and timing is very uncertain, although it seems the best chances will be in the evening. Fog development early this morning is still possible near TYS and TRI with some clearing expected before sunrise but some uncertainty remains. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 94 70 91 69 / 30 50 30 0 Knoxville McGhee Tyson Airport, TN 91 70 86 67 / 30 50 60 20 Oak Ridge, TN 91 69 85 66 / 30 50 60 20 Tri Cities Airport, TN 87 66 80 64 / 20 70 80 40 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...CD LONG TERM....DGS AVIATION...McD