Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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000 FXUS64 KMRX 031120 AFDMRX AREA FORECAST DISCUSSION National Weather Service Morristown TN 720 AM EDT Mon Aug 3 2020 .UPDATE... FOR 12Z AVIATION. && .SHORT TERM (Today and Tonight)... Current radar imagery indicates showers/storms to the east of the southern Appalachians in the Carolinas along on old frontal boundary. Current water vapor and RAP upper air analysis indicates a broad trough that extends from the Great Lakes southward into the Gulf of Mexico. Water vapor imagery indicates dry air extending from central Kentucky southward across Middle TN into the northwestern Gulf Of Mexico. Due to this dry air approaching, PW values vary a great deal across the forecast area from 1.7-19 inches across east Tennessee into southwest Virginia with values of 1.0-1.2 inches across the Cumberland Plateau. The RAP indicates that a couple of shortwaves will traverse the area today. This first is forecast in the 12-15z timeframe. The forecast area will also be in the favored right entrance region of an elongated 50-70 kt 300mb south to north jet streak. All of these factors, would support convective initiation some time around daybreak or shortly after for areas generally to the east of I-75. Due to the early natures of the CI, instability will not be overly impressive, somewhere in the 500-1000 J/Kg. However, 0-6 km bulk shear will be a respectable 35-45 kts due to the jet streak. Overall, expect most storms will remain well below severe limits this morning but could not rule out a stronger storm or two with gusty winds. This first shortwave trough should lift out of the area late this morning into the early afternoon before another races through the region in the 21z-00z timeframe. By this time, it appears the best jet dynamics will be a bit further to the north and east. However, SBCAPE values will be a little higher with daytime heating and once again could not rule out a stronger storm or two with gusty winds being the main threat. Overall, think temperatures will stay on the cooler side of guidance today with the early CI and persistent cloud cover from this activity early in the day. High temperatures will range from the low to mid 80s for most locations. Additionally, expect the PoP gradient will be tight today with much lower chances to the west of I-75 as drier air moves in from the west. Decreasing PoPs are forecast overnight as Isaias races northwards across the eastern Carolinas. A front will approach the area from the west as another shortwave trough dives into the Ohio River Valley by daybreak. The location of the upper level jet, subsidence around the outer edge of the tropical system, and low PW values will not be favorable for PoPs overnight. The southern Appalchians will be in the left entrance region of a 70-90 kt 300 mb south to north jet. The location of the jet will favor upper level convergence. PW values will drop down into the 1.2-1.4 inch range areawide. which is around to slightly below average for early August. Therefore, expect a decreasing trend in precipitation chances overnight. Overnight lows will generally be in the 60s. MA .LONG TERM (Tuesday through Sunday)... For the bulk of this forecast period the eastern U.S. will be under the influence of a broad trough. Expect diurnal showers and thunderstorms each day throughout this period. A few isolated stronger storms could produce strong wind gusts and locally heavy rain particularly on Tuesday afternoon. No widespread severe weather is expected for the remainder of the week/weekend. A pattern change begins to occur starting on Friday as the upper high begins building eastward -setting the stage for more much warmer daytime temperatures. AC && .AVIATION... 12Z TAF DISCUSSION. VFR conditions currently across the terminals. Current radar imagery indicates showers/storms along the spine of the Appalachian Mountains as the CAM`s forecast. These showers and storms will drift down into the valley later this morning. With the close proximity of TYS to the ongoing activity, went ahead and started with VCTS there. This first shortwave is forecast to move through the area this morning into the early afternoon. Expect the possibility of a break in the coverage late this morning into the early afternoon before the next shortwave trough rotates through later in the afternoon. Coverage with this shortwave may not be as widespread but kept VCTS in all the terminals to account for any activity. Convection should come to an end around 00z with patchy fog possible late in the TAF cycle. MA && .MRX WATCHES/WARNINGS/ADVISORIES... NC...NONE. TN...NONE. VA...NONE. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.