Area Forecast Discussion Issued by NWS Knoxville/Tri Cities, TN
000
FXUS64 KMRX 171736
AFDMRX
Area Forecast Discussion
National Weather Service Morristown TN
136 PM EDT Sun Mar 17 2024
...New AVIATION...
.UPDATE...
Issued at 1121 AM EDT Sun Mar 17 2024
Temperatures for most locations were a little warmer than forecast
this morning, so blended in some MOS guidance to bring hourly
temperatures and the max temperature for the day up slightly.
Current visible satellite shows a mix of sun and clouds across the
region, with some locations cloudier and some sunnier. Dewpoints
have been a couple degrees higher than forecast as well,
indicating the front has been slower to cross than thought.
Otherwise today is still on track for dry and pleasant weather.
&&
.SHORT TERM...
(Today and tonight)
Issued at 239 AM EDT Sun Mar 17 2024
Key Messages:
1. Dry today as moisture-starved cold front and upper disturbance
cross the region this morning.
2. Much colder and drier air build into the area tonight.
Discussion:
A weak southern stream shortwave trough will spread mid to high
level clouds across the area through today. Radar is showing
precip in southern West and Middle TN, but obs show light rain
staying south of the TN/MS border. As this spreads east, the
precip falling from midlevel clouds will encounter dry low level
air with the chance of measurable precip at the ground being low.
Meanwhile, a cold front located across KY this morning will push
SE through our area during the late morning and early afternoon.
The main impact with this front will be an increase in winds to
10-15 mph and dry air advection. Dewpoints will be falling through
the afternoon behind the front. Tonight, there will still be
quite a bit of cloud cover in the evening, eventually clearing out
after midnight as drier midlevel air builds in. Some wind and
mixing will prevent temperatures from plummeting, but northern
sections may see sub- freezing lows tonight.
&&
.LONG TERM...
(Monday through Saturday)
Issued at 239 AM EDT Sun Mar 17 2024
Key Messages:
1. Much colder temperatures Monday through Tuesday with area-wide
hard freeze Tuesday morning and very cold wind chills in the higher
elevations. A warming trend follows Wednesday.
2. Very dry conditions are also expected Monday and Tuesday.
3. Rain chances return late Thursday into Friday with only
light precipitation totals expected.
Monday through Wednesday
At the beginning of the week, upper low over the northeast Canadian
coast with deep trough to the southwest extending all the way to the
mid Mississippi Valley Monday morning. A much colder airmass will
begin to move in Sunday night with this colder and drier airmass
taking over the forecast area. Winds will increase from the NW
during the day Monday and the cold air advection will continue all
day and overnight Monday night. The strong NW flow and the packed
surface pressure gradient will cause gusty winds as high as 30 mph
in the valleys and up to about 40 mph in the higher elevations for a
few hours late Monday and Monday evening. Possibly borderline wind
advisory criteria in the higher mountains. Highs Monday will be 10
to 15 degrees below normal, 40s to lower 50s. Also minimum relative
humidity levels will be as low as 30 percent Monday afternoon. Lows
Monday night/Tuesday morning will be much below freezing, a hard
freeze across the region. Actual frost formation may be limited by
the strong northwest winds. No freeze warning will be issued based
on climatology but the limited growing vegetation...early flowers
and blooming trees may be affected. Wind chills in the higher
elevations will stay below 20 degrees much of the day and then drop
to 0 to 10 Monday night and Tuesday morning. Even lower elevations
will drop to 10 to 20 degree wind chills overnight Monday night.
Tuesday a warming trend begins as heights rise and an increasing
southerly flow develops as the pronounced eastern trough shifts east
northeast. Temperatures will still be below normal, in the 50s but
winds shift to the southwest. High pressure becomes centered farther
south. Subsidence continues and afternoon RH`s will likely drop
about 5 percent lower than Monday, approaching 20 to 25 percent.
Wednesday more warming but also increasing low-level moisture, which
will allow relative humid values to be around 10 percent higher.
Temperatures will warm to near normal 60s with height rises and more
southerly flow.
Thursday through Saturday
Wednesday night and Thursday southerly flow continues with more
moisture increasing and a weak shortwave approaches from a cut off
low over Texas and western Oklahoma. A weak front that is moisture
starved moves through Wednesday night and Thursday but no
precipitation. The GFS model shows the cutoff low approaching the
Mississippi Valley late Thursday and Thursday night with the upper
flow switching to the southwest and brings a chance of light showers
to the eastern Tennessee Valley Thursday night and especially
Friday. More significant precipitation will track eastward along the
Gulf coast. The latest model guidance is drier with the ECMWF versus
the GFS with this system. It keeps most of the precipitation along
the Gulf Coast Thursday night and Friday. With the surface low
pressure center expected to track south of the area, the better
moisture and instability are expected to be well to the south. So
confidence in any significant rainfall is low. Rainfall amounts look
to be very light and impacts with the system limited. Saturday high
pressure rebuilds over the region.
&&
.AVIATION...
(18Z TAFS)
Issued at 131 PM EDT Sun Mar 17 2024
VFR and dry through the TAF period, gusty winds this afternoon at
TRI will lighten after 00z, all sites will pivot their winds to
more northerly by 03z as a front crosses the region. High and
midlevel clouds will dissipate tonight. Tomorrow, gusty winds and
midlevel scattered clouds possible again late in the period at
TRI.
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 38 52 29 58 / 0 0 0 0
Knoxville McGhee Tyson Airport, TN 34 49 27 55 / 0 0 0 0
Oak Ridge, TN 34 50 26 56 / 0 0 0 0
Tri Cities Airport, TN 31 47 26 50 / 0 10 10 0
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$
SHORT TERM...Wellington
LONG TERM....TD
AVIATION...Wellington