Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

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.

National Weather Service Glossary of Abbreviations