232
FXUS64 KMEG 270529
AFDMEG

Area Forecast Discussion
National Weather Service Memphis TN
1229 AM CDT Fri Sep 27 2024

...New AVIATION...

.UPDATE...
Issued at 853 PM CDT Thu Sep 26 2024

We did our best to keep a rogue thunderstorm out of northwest
Tennessee but it managed to make it almost to Tiptonville before
our efforts were successful. Additional thunderstorms look
unlikely tonight, but showers should increase in coverage as an
upper level low moves south across west Tennessee into north
Mississippi. Thunderstorms can`t be ruled out tomorrow, but should
be isolated in nature with widespread rain that will be heavy at
times. No significant changes made to the forecast this evening.
Our rainfall totals over the next 24-36 hours are highly dependent
on the track of Helene. I would suspect that we will see a pretty
tight gradient from northeast to southwest across the region
with the highest totals over 4 inches in west Tennessee near
Paris, tapering off to about an inch in far northwest Arkansas and
southeast Arkansas.

&&

.SYNOPSIS...
Issued at 230 PM CDT Thu Sep 26 2024

Rain is expected to ramp up tonight and last through Saturday.
Rainfall totals will be higher with northern extent with anywhere
from 3 to 5 inches across west Tennessee, eastern Arkansas, and
the bootheel of Missouri. Portions of Mississippi could expect
around an inch to and inch and a half. Weather will calm down
Sunday and Monday with highs in middle and upper 70s. A cold front
passes through Tuesday, keeping highs in the 70s through the
middle of next week.

&&

.DISCUSSION...
(This evening through next Wednesday)
Issued at 230 PM CDT Thu Sep 26 2024

Weather in the Midsouth is likely to sour in the coming days. A
currently strengthening Hurricane Helene will make landfall and
pivot northwestward across the Ohio valley. The upper pattern
surrounding Helene`s entrance into higher latitudes currently
contains a cutoff upper low over MO/IL with amplified ridging in
the Western CONUS. Over the next two days, Helene will pivot
around the upper low in MO/IL and bring rain and winds to the
Midsouth through the weekend.

Impacts from Helene are expected to begin tonight as rain. A
flood watch already exists across the region, where rain totals
through Saturday are expected to be in the 3-5" range. PWATs in
the 1.5-2" range, deformation banding, and MUCAPE between 200-400
J/kg will promote locally higher precipitation amounts. The best
configuration of these ingredients appears to be across the
northern two-thirds of the CWA through Saturday afternoon. We have
opted to continue the flood watch through 12z Saturday.

Gusty winds are another concern on top of the rain. A strong
surface pressure gradient will set up as Helene forces her way
into established surface high pressure. Wrap-around winds from
within the tropical system will persist well inland at 925-850mb
with velocities anywhere from 45-60 knots. With some potential for
embedded convection and entrainment from continental dry air,
downward mixing of these winds are quite possible. Current
HREF/NBM75+/HRRR forecasts all show surface winds around 25 mph
with gusts up to, and potentially higher than, 40 mph throughout
along and north of I-40 through Saturday morning. Therefore, we
have issued a wind advisory for these areas from 12z Friday until
12z Saturday.

Medium range ensemble guidance has gained confidence that the
Helene-Upper Low system will generally advect east and deamplify
into Sunday, and leave the CONUS into the Atlantic on Monday.
Weather across the Midsouth is expected to become calm at the same
time. By Tuesday, a new shortwave is expected to dive into the
region, bringing a cold frontal passage overnight into Wednesday.
However, it is too far to tell if any precipitation will occur as
it passes through.

&&

.AVIATION...
(06Z TAFS)
Issued at 1148 PM CDT Thu Sep 26 2024

VFR conditions are expected to begin deteriorating to MVFR
conditions overnight, dropping to IFR conditions towards sunrise,
and persisting through the remainder of the 06Z TAF period.
Scattered showers will retrograde W/SW over the next few hours
with rain becoming more widespread as tropical moisture from
Hurricane Helene spreads further inland. Confidence remains low
with the potential for any thunderstorms to affect TAF sites
through the period with instability remaining limited at best.
Winds are expected to remain elevated with occasional wind gusts
at all sites, especially MKL and JBR.

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...Flood Watch through Saturday morning for ARZ009-018-026>028-035-
     036-048-049.

     Wind Advisory from 7 AM Friday to 7 AM CDT Saturday for ARZ009-
     018-026>028.

MO...Flood Watch through Saturday morning for MOZ113-115.

     Wind Advisory from 7 AM Friday to 7 AM CDT Saturday for MOZ113-
     115.

MS...Flood Watch through Saturday morning for MSZ001>009.

TN...Flood Watch through Saturday morning for TNZ001>004-019>022-
     048>055-088>092.

     Wind Advisory from 7 AM Friday to 7 AM CDT Saturday for
     TNZ001>004-019>022-048>051.

&&

$$

PUBLIC FORECAST...JDS
AVIATION...CJC