Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN
Issued by NWS Knoxville/Tri Cities, TN
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101 FXUS64 KMRX 171419 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 1019 AM EDT Wed Jul 17 2024 ...New UPDATE... .UPDATE... Issued at 1009 AM EDT Wed Jul 17 2024 Regional radar and satellite imagery shows there`s very little in the way of convection and shower activity across the area this morning. Most all of the ongoing activity is situated in the southern Tennessee mountains, towards the Tellico Plains area. Updated PoPs to reflect this current activity, blending into the previous forecast for the afternoon hours. Still think that part looks ok, with numerous showers and thunderstorms expected later today. Other notable change I made was to up expected afternoon highs today. Plenty of sunshine has been seen this morning. The last three HRRR runs, along with NAMNest and other guidance was a little higher than the previous forecast for afternoon highs. Bumped those up a couple of degrees. && .SHORT TERM... (Today and tonight) Issued at 338 AM EDT Wed Jul 17 2024 Key Messages: 1. Patchy fog possible through the early morning hours, focused in locations that observed rainfall this past afternoon. 2. Multiple rounds of showers and storms are possible this afternoon through tonight. A few strong storms with locally gusty winds and heavy downpours are possible. 3. Ambient temperatures will be cooler but heat indices will once again approach the mid 90s to lower 100s thanks to increasing dewpoints. Discussion: Currently an upper level impulse is traversing mean flow across the lower Great Lakes region where a quasi-stationary boundary is draped southwest to northeast. Decaying convective activity well ahead of the front can be observed on regional radar over northern portions of Kentucky. Lightning activity over the last 2 hours has decreased significantly as the convection surges ahead of the primary forcing along with the loss of daytime heating. Satellite and surface obs show some clearing has occurred over our CWA as well. This will allow for patchy fog into the early morning hours, primarily focused in locations that experienced afternoon precipitation saturating soils and lower levels of the PBL. Best chance for early-late morning precipitation will generally be north of I-40 as the aforementioned activity continues to progress southeastward. However, as this will be moving through during most stable hours minimal impacts are expected. Additional energy aloft and increasing frontal forcing will allow for multiple periods of showers and thunderstorms this afternoon and tonight. Latest RAP model derived soundings suggest MLCAPE near 2000J/kg with a highly saturated vertical profile and PWAT encroaching on 2 inches. Bulk effective shear may even approach 20kts at times as shortwave energy translates aloft. If shortwave timing coincides with peak heating, stronger and more intense updrafts could lead to precip loading bringing gusty winds and locally heavy downpours with the strongest storms. Additionally, increasing dewpoints will allow for continued heat indices in the mid 90s to near 100 across central and southern portions of the East Tennessee valley. && .LONG TERM... (Thursday through Tuesday) Issued at 338 AM EDT Wed Jul 17 2024 Key Messages: 1. A frontal boundary will remain across the area on Thursday, allowing showers and storms to continue. 2. A break from the heat is expected behind the front, with slightly below normal temperatures throughout the long term. 3. POPs remain elevated throughout the long term due to higher than normal moisture content across the area. Discussion: Models seem to be in better agreement that the cold front will remain across our area early on Thursday. The front looks like it should push south of the area sometime Thursday afternoon/evening. With the front in place, we will see continued chances for showers and storms. The higher chances will remain south of I-40, closer to the location of the front, with lesser chances north of I-40. By Thursday evening we should be mostly dry as the front should be to our south by that point. NBM keeps slight chance to chance POPs in for most places on Friday. While I do think we will still see some isolated showers around, not sold on the coverage of the NBM. However, without knowing the exact location of the front on Friday will leave NBM POPs unchanged. Overall, drier conditions in place north of I-40. Better chances for rainfall across the southern TN valley and southwest NC, which will be closer to the front. Chances for rain and storms increase again over the weekend. This is as a shortwave to our southwest transitions the old frontal boundary into a warm front and lifts it north through our area. Thereafter, elevated POPs continue to remain in place through the remainder of the long term. This is due to a Bermuda high in place across the Atlantic and an approaching broad, longwave, trough to our west. This will allow Gulf moisture to freely flow into the area and keep moisture content higher than normal for this time of year. GFS and ECMWF ens show PWATs ranging from the 75th to the 90th percentile through this timeframe. && .AVIATION... (12Z TAFS) Issued at 723 AM EDT Wed Jul 17 2024 Unsettled pattern continues with med-high confidence in scattered to numerous showers and storms around at times. However, confidence is low in regards to best timing so the TAFs largely focus on vicinity activity with a prob30 for this afternoon, when the greatest coverage is expected to occur. Winds will be from the southwest around 10kts, but some stronger gusts cannot be ruled out at TYS/TRI. A front approaches the region overnight with continued precip chances. This may bring reduced flight categories in the from of low cigs and will be monitored over the next few issuances. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 93 73 89 70 / 80 50 70 30 Knoxville McGhee Tyson Airport, TN 92 71 85 68 / 90 60 60 20 Oak Ridge, TN 91 70 84 66 / 80 60 60 20 Tri Cities Airport, TN 89 69 80 64 / 90 60 50 20 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ SHORT TERM...CD AVIATION...KRS