Severe Thunderstorm Warning 40, NWS Morristown, TN

Area Forecast Discussion
National Weather Service Morristown TN
310 PM EDT Mon Jun 17 2019

.SHORT TERM...(Tonight Through Tuesday Night)...

The pulse convection will weaken quickly after 01Z as diurnal
cooling takes place and much of the area becomes convectively
overturned. Kept chance pops for showers and a few rumbles of
thunder through tonight as the shortwave approaches from the west,
with the best chances being over the plateau and central/southern
valley later tonight. Convergence will slowly be increasing ahead of
a weak surface frontal boundary, likely reinforced by convective
outflow, and MLCAPE across the central and southern valley will
remain above 1000 J/Kg in this moist airmass overnight. Stayed above
MET and MAV guidance for lows due to increasing clouds tonight on
top of this muggy airmass.

The above mentioned shortwave will cross east TN, southwest VA, and
southwest NC during the day Tuesday. A weak surface low will move
northeast through KY, and the NAM is stronger with this surface low
than the GFS and ECMWF. Suspect that the NAM solution is due to some
convective feedback, but either way, a weak frontal boundary looks
to cross from west to east between 18 and 02Z. Large scale ascent
from the upper wave and frontal convergence will lead to greater
convective coverage Tuesday, so have likely pops from mid morning
through the day. Severe weather potential will be low overall, but
slightly higher than the past couple of days. SPC has the entire
region in a marginal risk, and this is reasonable since 1500-2000
J/Kg of MLCAPE will once again develop along with a few hundred
joules of DCAPE during the afternoon as low-level lapse rates
steepen with afternoon heating. The main threat will be damaging
winds in convective downdrafts. Limiting factors continue to be poor
mid level lapse rates of only 5-6 C/Km and weak 0-6 Km and effective
shear values of 15-30 kts. This will keep any strong wind threat
isolated since strong convective updrafts will have a hard time
sustaining for a long period of time. An additional limiting factor
will be morning clouds and showers that will delay stronger surface
heating. With all of this being said, torrential rainfall and
localized flash flooding will be the bigger impact from any
convection since PWATs will continue to be 1.50 to 2.00 inches
(locally higher) with high freezing levels for warm rain processes.
Storm motion will also be slow due to the weak deep layer wind
fields. CAMs offer varying solutions for tomorrow, but thinking is
that an initial round of showers and some embedded thunderstorms
will move through between 10 and 16Z followed by some redevelopment
in the afternoon. Kept a heavy rain mention in the HWO for Tuesday.
High temps Tuesday will be slightly cooler than today due to the
clouds and widespread convective activity.

Much of the convection will move east of the region after 00Z
Wednesday as the shortwave and weak front exit to the east. Have
chance pops through Tuesday night since we do not see a change of
airmass and remain on the southern fringe of a convectively active
quasi-stationary front beneath a fast mid level zonal jet around the
OH valley. Convective complexes moving along this corridor north of
our region will occasionally send outflow boundaries into our
area, which warrants keeping chance pops through the night. Lows
will remain warm and humid.

.LONG TERM...(Wednesday through Monday)...

By 12Z Wednesday, the upper levels will feature a rather low
amplitude pattern with several disturbances moving through weak
cyclonic flow. A stronger shortwave trough/PV anomaly will be moving
through the central plains Wednesday. At the surface, an area of low
pressure will move through the central plains and into the Ohio
valley by 12Z Thursday. A subtle PV anomaly moving through the area
Wednesday afternoon and evening combined with differential heating
will likely be enough to generate TSRA especially with a moist and
unstable airmass as CAPE values climb upwards of 1500 j/kg.
Afternoon convection will decrease in coverage by Wednesday night
with the loss of solar heating.

The aforementioned shortwave trough will deepen as noted by
increasing cyclonic flow as it begins to approach from the west. A
trailing cold front will be aligned NE/SW from the parent low into
the Arklatex. Increasing forcing for ascent underneath height falls
along with low level convergence should increase SHRA/TSRA chances
through Thursday morning. Additional chances of precipitation are
expected immediately along the front through the day Thursday with
TSRA expected as CAPE values increase.

The area will see a short break on Friday as increasing heights
aloft and surface high pressure underneath the descending branch of
the h50 shortwave lead to increasing subsidence and dry weather. An
upper level ridge axis will be situated across the GoM northward
into the Great Lakes over the weekend. Both the GFS and EURO
indicate the ridge breaking down enough a few disturbances to rotate
around the ridge axis. Expect increased SHRA/TSRA chances through
the weekend as a result. Closer to early next week, the upper level
pattern will feature large scale troughing out west with ridging
along the east coast. This places the region under southwest flow
aloft. Increasing moisture along with several upper level
disturbances will keep chances of SHRA/TSRA in the forecast for
Sunday through Tuesday. Temperatures through the extended will be
near to slightly above seasonal averages.

&&

.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN             72  82  71  87 /  70  80  50  40
Knoxville McGhee Tyson Airport, TN  70  81  69  85 /  50  70  50  50
Oak Ridge, TN                       71  81  70  86 /  60  80  60  50
Tri Cities Airport, TN              69  81  68  82 /  50  80  40  50

&&

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

RG/AD

Hazardous Weather Outlook
National Weather Service Morristown TN
248 PM EDT Mon Jun 17 2019

NCZ060-061-TNZ012>018-035>047-067>074-081>087-098>102-VAZ001-002-
005-006-008-181900-
Cherokee-Clay-Scott-Campbell-Claiborne-Hancock-Hawkins-Sullivan-
Johnson-Morgan-Anderson-Union-Grainger-Hamblen-Northwest Cocke-
Cocke Smoky Mountains-Northwest Greene-Southeast Greene-
Washington-Unicoi-Northwest Carter-Southeast Carter-Roane-Loudon-
Knox-Jefferson-Northwest Blount-Blount Smoky Mountains-
North Sevier-Sevier Smoky Mountains-Sequatchie-Bledsoe-Rhea-Meigs-
McMinn-Northwest Monroe-Southeast Monroe-Marion-Hamilton-Bradley-
West Polk-East Polk-Lee-Wise-Russell-
248 PM EDT Mon Jun 17 2019 /148 PM CDT Mon Jun 17 2019/

This Hazardous Weather Outlook is for portions of southwest North
Carolina...east Tennessee and southwest Virginia.

.DAY ONE...This Afternoon and Tonight

Scattered thunderstorms will continue into early this evening. A
few isolated severe storms remain possible with strong winds and
hail, but widespread severe weather is not expected. Localized
flooding is also possible.

.DAYS TWO THROUGH SEVEN...Tuesday through Sunday

Scattered thunderstorms will develop during the afternoon and
evening hours each day. The greatest coverage of thunderstorms
will be Tuesday and Thursday. Any thunderstorm will be capable of
producing torrential rainfall, so there will be the potential for
localized flash flooding in areas that see repeated thunderstorms
this week. A few severe thunderstorms are possible Tuesday with
hail and strong winds, but widespread severe weather is not
expected.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not anticipated, but any reports of flash
flooding or rainfall amounts will be appreciated this week.

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