Scientific Forecaster Discussion
000 FXUS64 KMRX 250720 AFDMRX Area Forecast Discussion National Weather Service Morristown TN 320 AM EDT Wed Apr 25 2018 .SHORT TERM...(Today and Tonight)...Today, conditions have improved compared to yesterday but we will still be dealing with the affects from an upper low that is exiting east. We are now on the backside of the low and moisture is limited. With continued NW flow the best precip chances will be confined to favored upslope areas. Any precip that falls will be light. However, some valley locations could see a sprinkle here and there but most areas will stay relatively dry. The main thing we will be dealing with today will be the lingering cloud cover and the continued below normal temps. We could see a few breaks in the clouds this afternoon but mostly cloudy conditions will be the theme. Continued NW flow will keep temps in the lower to mid 60s for most places, which is 5 to 10 degrees below normal. Unfortunately, just as this system is finally exiting tonight another system quickly moves in from the west. Any breaks in the clouds we see this afternoon will quickly be replaced with more clouds as as this next area of low pressure pushes in overnight. Precip chances begin to increase from southwest to northeast after midnight, but chances are mainly confined to areas south of I-40. The reinforcing cloud cover moving back in will keep overnight lows mild with temperatures in the upper 40s to lower 50s which is a few degrees above normal. .LONG TERM...(Thursday through Tuesday)...At the beginning of this period another upper low will be approaching the area, with its associated surface low averaging its position in northern Mississippi Thursday morning. The surface low is forecast to track to the ENE, probably staying south of the area and keeping us in the cool airmass. However, the upper low will be very cold and will induce some instability. Will introduce slight chance of thunder into the widespread showers from 18z-03z. Thursday night the upper/surface low will go east of us, but a ridge doesn't have time to build as the next shortwave is racing at us, with its upper trough axis passing through the region on Friday. This trough is cold enough aloft to induce some instability during the day on Friday with 100+ J/kg CAPEs for the northern half of the area (and lesser CAPEs south), enough to keep the threats for showers lingering Friday through the area. After this shortwave passes, the area will finally undergo a pattern change with an upper ridge building into the region that will finally allow a warmer and drier regime. By Monday, the surface winds will veer to the south allowing the warm-up to get another boost. During the times of lift and precip, instability looks to be minimal, so except for the small area of slight chance thunder mentioned Thursday afternoon and evening, will be keeping thunder out of the forecast. Looks like no winds events either during this time, although the path of the stacked low on Thursday is worth watching--if it come farther north we could have a low level jet over the area, that might briefly get some gusty south winds either up the valley or in the mountains, but for now it looks like this low will be too far south for that scenario. && .PRELIMINARY POINT TEMPS/POPS... Chattanooga Airport, TN 68 53 61 49 / 10 40 100 50 Knoxville McGhee Tyson Airport, TN 65 52 62 49 / 30 10 80 70 Oak Ridge, TN 65 51 63 48 / 30 10 70 70 Tri Cities Airport, TN 63 48 65 48 / 50 20 60 70 && .MRX WATCHES/WARNINGS/ADVISORIES... NC...None. TN...None. VA...None.