FXUS64 KMEG 171209
Area Forecast Discussion
National Weather Service Memphis TN
709 AM CDT Tue Jul 17 2018
Updated for the 12z Aviation Discussion.
.PREV DISCUSSION... /issued 453 AM CDT Tue Jul 17 2018/
Temperatures are steady in the mid to upper 70s across the Mid-
South this morning. A few light showers were noted on radar mainly
near the Tennessee River. Latest GOES East nighttime microphysics
RGB shows light patchy fog across the majority of the area.
.Short term...Today through Thursday...
Another hot and humid day on tap. A weak front is forecast to move
from north to south across the Mid-South today. Due to the
unstable airmass in place and available trigger, a few strong to
severe thunderstorms will be possible this afternoon and evening.
Latest Hi-Res models show convective initiation by late afternoon,
with the best coverage of storms along and south of I-40
corridor. Inverted V soundings will support a damaging wind threat
and the high PWAT air will support heavy rainfall as well. The
weak front is expected to sink into southern parts of the forecast
area by tonight. Slightly drier air will move into Tennessee
River Valley by Wednesday morning. Lows in that area will touch
the 60s, with lower 70s expected elsewhere.
The ridge of high pressure that has been over the Mid-South for
the past week will finally break down this week, as a large scale
trough builds in across the eastern half of the United States.
This will place the Mid-South in northwest flow aloft and support
an MCS pattern. POPs on Wednesday will depend heavily on a
forecasted ongoing MCS across Missouri early Wednesday morning. It
will weaken as it arrives in our area and may eject an MCV into
western portions of the area by Wednesday afternoon. This could
enhance thunderstorm activity across the area, and at the very
least cloud cover. Other than that, mostly dry and temperatures in
the lower 90s.
Another relatively cool morning is anticipated across the Mid-
South on Thursday with lows in the 60s and lower 70s. Shortwave
ridging over the Mid-South will keep the forecast mainly dry
during the day. High temperatures will be slightly cooler with
highs in the upper 80s and lower 90s.
.Long term...Friday through Early Next Week...
The aforementioned trough is expected to deepen this weekend with
appreciable heights falls to the east of our area. This will
help push a reinforcing front through the region on Saturday and
maybe knock high temperatures down a couple of degrees. Dry air
is expected to move behind the front and remain in place through
at least Sunday. By next week, the ridge will begin to build back
in and humidity levels will on the increase again.
VFR conditions will prevail through today, outside of any
convection. Scattered showers and thunderstorms should develop
later today and persist through this evening. Winds will gradually
shift to north, then northeast. Winds should diminish this evening
and become easterly later tonight into Wednesday.
AR...Heat Advisory until 8 PM CDT this evening for Clay-Craighead-
MO...Heat Advisory until 8 PM CDT this evening for Dunklin-Pemiscot.
MS...Heat Advisory until 8 PM CDT this evening for Coahoma-DeSoto-
TN...Heat Advisory until 8 PM CDT this evening for Dyer-Lauderdale-
FXUS64 KOHX 171124
Area Forecast Discussion
National Weather Service Nashville TN
624 AM CDT Tue Jul 17 2018
FOR 12Z AVIATION DISCUSSION.
Showers and a few thunderstorms ongoing at forecast time as Middle
TN remains entrenched in 70+ dew points and in turn, plenty of
overnight instability. These conditions will continue for about 24
more hours, where at least scattered coverage of thunderstorms will
be possible. Latest hi-res guidance shows this overnight activity
fading around sunrise with a lull in late morning hours, then a
slight uptick in coverage for the afternoon. While we still aren't
dealing with any shear, the instability is enough that any of these
storms could become strong with gusty winds and locally heavy rain,
but they all should remain sub-severe.
By late this afternoon, all indications are that we'll start to see
a northerly surface wind shift spread into the mid-state and this
will mark the beginning of at least one, and maybe two, drier days
across Middle Tennessee. Low 60s dew points that are currently over
northern Illinois, Indiana and Ohio will push southward into the
state tonight and provide us with a much different airmass than
we've been experiencing as of late. Actual temperatures will
remain around normal Wednesday and Thursday -- it is still
summer, after all -- but low to middle 60s dew points will flood
the area. It's a little treat for those of us who don't care for
the instant sweat when you step out the door. However...this will
be short lived....
By Thursday night, the region will recover back into a similar
airmass we have out there right now. Southerly return flow gets
going again, dew points get back into the low 70s and as this
occurs, a rather intense closed upper low amplifies and digs into
the Great Lakes region. By Friday, northwesterly flow aloft will
encompass the mid-Mississippi and Tennessee Valleys and we might
very well see a cold front approach the mid-state. With ample
instability already in place, the addition of 40-50 kts of deep
layer shear Friday evening, at least some strong, if not severe
weather might be in play. The window of opportunity has narrowed a
bit compared to last night's extended guidance, so I'm not going
to add it to the Hazardous Weather Outlook this morning, but if
these shear numbers hold steady, I'll likely add it in with
tomorrow night's guidance.
The upper low continues to dig southward Saturday leaving a chance
for scattered showers and thunderstorms over at least the eastern
half of the mid-state and that low isn't in a hurry. Sunday and
Monday could be similar as the low doesn't want to break down until
the start of next week. Will maintain at least a chance PoP over
the east with temperatures around normal through the first of the
12Z TAF DISCUSSION.
VFR conditions look to prevail this TAF period, with KCSV seeing
some MVFR fog/LIFR cigs this morning and KBNA/KMQY/KCSV possibly
seeing thunderstorms this afternoon. Have in VCTS mention for now
as short term models have mainly isolated to scattered coverage
during the afternoon. Winds will become more northerly after the
front passes today, with speeds around 5 to 10 knots. Winds should
calm down to around or below 5 knots later in the evening.
FXUS64 KMRX 171315
Area Forecast Discussion
National Weather Service Morristown TN
915 AM EDT Tue Jul 17 2018
.DISCUSSION...Current forecast in good shape for today with an
area of showers and thunderstorms moving steadily southeast
through Southeast Kentucky toward the forecast area. Instability
gradient just ahead of pre-frontal trough driving this convection
will slip south across much of the northern half of the forecast
area through early afternoon. Perhaps a few more showers and a
thunderstorm build in behind this action in association with the
trailing frontal boundary to keep probability of precip going late
into the day. Temperature forecast looks decent with warming
capped off to a small degree from frontal convection.