National Weather Service
Area Forecast Discussion

1259 PM EST Sat Dec 15 2018
SYNOPSIS
A large, slow moving low pressure system will move from the Tennessee Valley into the Southern Appalachians this weekend. Widespread rain and mild conditions are expected into tonight. The rain will taper off early Sunday as the low moves off to the east coast.



NEAR TERM
UNTIL 6 PM THIS EVENING
Large band of rain will continue to pivot across the forecast area through the afternoon. Back edge is working into the southern counties, so rain will diminish there. Temperatures will remain nearly steady.



SHORT TERM
6 PM THIS EVENING THROUGH 6 PM SUNDAY
Large mid level low to track northeast through the TN Vly tonight and east into the Delmarva region Sunday. As the mid level low approaches - elongated surface low to pivot thru the Ohio Valley tonight. Favorable moisture and forcing will continue into this evening with the potential for localized flooding continuing. As the system pushes off to the east, rain will begin to taper off from west to east late tonight into early Sunday. Expect considerable cloudiness through the night with lows from the mid/upper 30s northwest to the mid 40s southeast.

Northwest flow develops on Sunday with a good deal of clouds early. Forecast soundings show moisture becoming more shallow as the day wears on. Therefore, expect a decrease in clouds Sunday afternoon. Sundays highs to range from the mid 40s northwest to the upper 40s southeast.



LONG TERM
SUNDAY NIGHT THROUGH FRIDAY
An upper ridge will travel from the Great Plains Monday to the Great Lakes Tuesday and then to the East Coast on Wednesday. Surface high pressure forming under the confluent northwest flow ahead the upper ridge will push across the Ohio Valley, resulting in dry weather conditions in the subsident anticyclonic circulation around the high.

An upper trough will be approaching on Thursday. As the upper trough deepens and a closed upper low and surface low develop, moisture and lift will increase rather dramatically, producing the likelihood for showers by Thursday night, with snow possibly mixing in Friday as colder air filters in toward the end of the event.

Temperatures will start near normal Monday and Tuesday, with highs averaging 40. Warm advection on a southerly flow will nudge readings up to the 40s and low 50s by Thursday, before a retreat back to the low 40s on Friday.



AVIATION
18Z SATURDAY THROUGH THURSDAY
Rain will continue to slowly move north which will result in precipitation ending at the terminals during the early part of the TAF period. Additional rain will develop tonight as low pressure moves by. This will most likely affect the central Ohio sites, although cannot completely rule out some light rain at other locations. MVFR to IFR ceilings will lower to IFR area wide with some locations dropping to LIFR. Visibility restrictions will persist until after 06Z and then improve. IFR ceilings will persist until very late in the TAF period when ceilings will lift to MVFR and clouds may even start to scatter in some places by 18Z.



OUTLOOK

MVFR/IFR conditions will be possible at times through Sunday.