Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Nashville Tennessee
1125 PM CST Sat Dec 27 2014
Aviation 06z discussion...
inverted surface trough to continue pushing slowly eastward across the
middle state tonight. Plenty of moisture...both in advance and behind
the trough...will allow for a continuation of rainfall through the
taf period. As a result...low ceilings and visibilities will persist. Rainfall
coverage will let up after 18z. By 00z should just be looking at
vcsh across the bna and ckv areas. Ceilings will remain low through
the taf period.
Previous discussion... /issued 732 PM CST Sat Dec 27 2014/
inverted trough axis approaching western middle Tennessee at this time. A
marked decrease in coverage is noted across western portions of
the County Warning Area. However...latest radar trends and the hrrr information
both suggest that precipitation coverage will fill in along and west of
the advancing trough. A closer look does reveal some appreciable
separation in regard to the 850 mb and surface front.
Furthermore...the greater low level forcing resides along the 850
mb front where the angular convergence is greater.
For the forecast...despite the current decrease in coverage...will
continue with the categorical probability of precipitation as was mentioned earlier...the
coverage should fill back in.
No changes for now to the forecast.
Previous discussion... /issued 510 PM CST Sat Dec 27 2014/
Aviation 00z discussion...
inverted surface trough to push slowly eastward across the middle state
tonight. Plenty of moisture...both in advance and behind the
trough...will allow for a continuation of rainfall through the taf
period. As a result...low ceilings and visibilities will persist. Rainfall
coverage will let up some as we approach the end of the taf
period...between 18z and 00z.
Previous discussion... /issued 304 PM CST Sat Dec 27 2014/
local and regional radar imagery show widespread rain shower
coverage stretching from middle Tennessee back to the Louisiana-
Texas border...and south to the Gulf Coast. These showers are
associated with an area of low level convergence...which as it
approaches the middle-state will become aligned with an upper level
jet streak. Lightning coverage has diminished...and with forecast
models showing laps rates below 6 degrees have removed it from
the forecast. After the steady rain moves through tonight...a
brief period of little if any shower activity is expected for
Sunday...mainly in the afternoon hours and especially across the
For Sunday night shower activity is expected to return...with
another shortwave tracking from the Louisiana- Texas border to
North Carolina by Monday morning. The better moisture axis and
upper level support...while minimal...favor the southern and
eastern areas. The northwest counties will just have slight to low
chance probability of precipitation for Sunday night...and may even be completely dry.
This southerly track will bring storm total rainfall amounts for
areas mainly along and south of I-40 to around an inch to an inch
and a half by Monday morning.
A secondary front with much more notable cold air advection pushes
through the middle-state Wednesday...and lingers through Thursday.
The long-range models indicate a much stronger shortwave
developing over Texas by Saturday morning...and tracking through
the Ohio River valley by Sunday evening. The warm front surge out
ahead of it arrives Thursday night...so with the aforementioned
cold air in place some mixed precipitation is possible...even a
period of snow during the overnight hours...mainly over the
southwestern counties. By Friday morning...temperatures warm above
freezing and steady rain is expected to linger through Friday
night and possibly into Saturday per the European model (ecmwf).
Preliminary point temps/pops...
Nashville 45 45 36 49 / 100 80 70 10
Clarksville 41 42 33 47 / 100 60 20 10
Crossville 47 51 40 49 / 100 100 90 20
Columbia 46 47 37 51 / 100 80 70 10
Lawrenceburg 47 49 37 51 / 100 80 90 10
Waverly 42 43 33 48 / 100 80 50 10