Area Forecast Discussion
Issued by NWS Knoxville/Tri Cities, TN

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FXUS64 KMRX 240727

Area Forecast Discussion
National Weather Service Morristown TN
327 AM EDT Wed May 24 2017

.Short Term (Today and Tonight)...An active day across the
Tennessee Valley and southern Appalachians. A deep upper trough
will dig southeast into the Tennessee Valley with jet dynamics
moving across the Region. First wave of energy is currently moving
across northern Alabama. This wave will move northeast across the
area this morning with showers and embedded thunderstorms. As
another jet streaks moves across the Region late this morning and
afternoon, pressure falls are expected across the lower
Ohio/northern Tennessee Valleys with a surface low moving
northeast into east Kentucky/southern Ohio.

The pressure falls will help induce a boundary layer jet of 35kts
across the Region improving the shear profile. A surface boundary
will move across the area late this morning and afternoon with
moist and unstable air ahead of the frontal boundary. Main
question is if there will be enough breaks in the cloud cover
today allowing the low-level airmass to destabilize. Latest high
resolution models, such as the HRRR model do show individual
strong convection developing. Due to the expected shear, low-
topped supercell structures are anticipated later today with the
SPC HRRR Browser depicting good updraft helicity for the storms
across the eastern/northern counties between 16-20Z.

Given the above isolated tornadoes are a concern Today for areas
mainly along and east of interstate 75. Besides the tornado
threat, cold air aloft and low-level jet may produce hail and
damaging winds with the stronger storms.

Frontal boundary will move east of the area by early evening with
shower coverage diminishing for tonight. A cool night is in store.

.Long Term (Thursday through Tuesday)...
Confidence in forecast through Saturday is fairly high with models
in good agreement on a largely amplified wave pattern aloft.
GFS Ensemble as well as GFS and ECMWF begin to diverge slightly
Sunday through Tuesday as next fairly broad 500 mb low begins to
drive SE across the Great Lakes area.

By Thursday morning, 500 mb low over central Ohio extends trough
axis south over East TN. As trough axis swings eastward through
Friday morning expect to see some showers and thunderstorms
particularly over the northern half of the area that will diminish
with sunset Thursday night as a broad ridge builds over the area on

Shortwave trough is fcst to move across the broad ridge on Saturday.
With it, expect chance for some showers and thunderstorms Saturday
afternoon. Greatest threat for strong storms on Saturday will likely
lie in SW Virginia and NE Tennessee where nose of 300 mb jet pushes
across the ridge axis late Saturday.

Next front approaches the area Sunday before moving through on
Monday. Digging 500 MB trough coupled with surface dewpoint climbing
back into the upper 60s across a large portion of the area, will
result in greater coverage of showers and thunderstorms on Sunday
with potential for more strong to severe storms by afternoon.

Broad trough aloft dominates the eastern third of the US on Monday
into Tuesday with instability on Monday holding up chance POPs into
Tuesday before significant dry air aloft lowers chances on

Thursday`s temperatures expected to be on the cool side with cloudy
skies and the upper trough swinging over the area. However,
temperatures will rebound nicely on Friday to near seasonal norms
through the remainder of the forecast.


Chattanooga Airport, TN             72  55  75  56 /  90  50  30   0
Knoxville McGhee Tyson Airport, TN  73  54  70  54 /  90  40  50  10
Oak Ridge, TN                       72  54  71  55 /  90  40  40  10
Tri Cities Airport, TN              73  53  64  52 /  90  60  70  30



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