-- Discussion containing changed information from previous version are highlighted. --
000
FXUS64 KMRX 202346
AFDMRX

Area Forecast Discussion
National Weather Service Morristown TN
746 PM EDT Sat Apr 20 2024

...New AVIATION...

.SHORT TERM...
(This evening through Sunday)
Issued at 242 PM EDT Sat Apr 20 2024

Key Messages:

1. Drier airmass bring drier weather tonight to northern portions
of the forecast area. Cooler temperatures expected tonight and
Sunday with troughing over the area.

2. Low pressure system south of our region will produce some cloud
cover and light rain showers Sunday morning, mainly for southern
counties.

Discussion:

Synoptic frontal boundary has continued south this morning with
drier and and clearing conditions across the region this
afternoon. Clouds will continue to clear out this afternoon and
evening. As a surface low moves eastward across southern
AL/GA/and the Carolinas late tonight, clouds and rain chances
will increase for our southern counties with highest PoPs near the
Georgia state line and southwest North Carolina through Sunday
morning. Total rainfall amounts would be very light.

By Sunday afternoon, this area of low pressure will be moving east
of our region with clearing conditions and drier weather area-
wide. Temperatures remain cooler than normal with longwave
troughing across the Southern Appalachians and Tennessee Valley.

&&

.LONG TERM...
(Sunday night through next Saturday)
Issued at 242 PM EDT Sat Apr 20 2024

Key Messages:

1. Patchy frost is possible Monday and Tuesday mornings, especially
in northeast Tennessee, southwest Virginia, southwest North
Carolina, and the Cumberland Plateau.

2. Warmer temperatures are expected Tuesday onward with low-end rain
chances Wednesday morning and again on Friday and Saturday.

Sunday Night through Wednesday

At the start of the period, deep upper troughing will be moving over
the region with surface high pressure expanding from the west.
Recent northerly flow and subsidence will have produced
significantly cooler temperatures in the lower levels, which is
illustrated by 850mb temperatures near to below freezing. These
values are near the daily minimum for this region for the time of
year. Based on how much the MSLP gradient is expected to weaken,
conditions do look favorable for light winds and radiational
cooling sufficient for frost development into Monday morning. This
looks more likely in the higher elevations of Tennessee and
southwest Virginia and into southwest North Carolina. Products
will likely be needed, and additional messaging will be utilized
in the HWO. During the day on Monday, troughing will shift off to
the east with high pressure moving towards the southern
Mississippi River Valley. This will begin a warming trend from the
near-term period with much of the area returning to the 60s.
However, additional subsidence and radiational cooling will be
sufficient for potential frost development again by Tuesday
morning. By this time, a system will be progressing along the
upper Great Lakes region with a frontal boundary extending towards
the Great Plains. This will put the region in a more southerly
flow pattern and further enhance the warming trend.

By Wednesday, upper troughing will amplify from the north with the
aforementioned frontal boundary from the northwest. This will lead
to a return in PoPs, especially earlier in the day. With 850mb
temperatures near or below 8 Celsius, any instability is likely to
be elevated and very limited, only sufficient for isolated chances.
Moisture will also be limited and short-lived as well, which will
keep rainfall totals fairly light.

Thursday through Saturday

By Thursday morning, the frontal boundary is expected to be south of
the area with high pressure expanding from the north. Accordingly, a
more northerly flow pattern is expected, which will moderate
temperatures back to below normal with a return of drier conditions.
Friday to Saturday, a more robust system is expected to develop and
progress towards the Great Lakes region. At this point, the upper-
level support and track of the system are far enough north that the
focus for more organized convection will be focused in the Midwest.
The pattern is supportive of broad southerly flow and a return of
rain chances. This system will still be something to watch, but the
current indications don`t suggest anything impactful in our area.

&&

.AVIATION...
-- Changed Discussion --
(00Z TAFS)
Issued at 739 PM EDT Sat Apr 20 2024

Showers expected to increase from the south overnight, with
no thunderstorms forecast. Guidance suggests CIGS will remain VFR
even with increase in cloud cover and eventual arrival of showers.
VSBY not expected to be of any concern either. By daybreak,
showers expected to move east and confine mostly along the
mountains before clearing later in the day, leading to increasing
CIGS heights. Winds will be light, generally <10 kt from a
northerly direction.
-- End Changed Discussion --

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             48  62  43  68 /  60  70   0   0
Knoxville McGhee Tyson Airport, TN  46  58  40  64 /  50  50   0   0
Oak Ridge, TN                       46  61  40  66 /  40  40   0   0
Tri Cities Airport, TN              42  56  35  62 /  30  50   0   0

&&

.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&

$$

SHORT TERM...JB
LONG TERM....BW
AVIATION...KS