Flash Flood Warning 89, NWS Jackson, MS

Area Forecast Discussion
National Weather Service Jackson MS
712 AM CDT Tue Aug 25 2020

.UPDATE...
Updated for 12Z aviation discussion

&&

.AVIATION...
12Z TAF discussion:

A mix of flight conditions are prevailing around the region this
morning due to mainly low CIGS associated with the remnants of
Marco. The CIGs are lower in the southern portions of the region
where low level moisture content is greatest. Coverage of showers
and storms will continue to increase over the next several hours
impacting several sites with better confidence at sites in the
south and east. Sites impacted by these showers and storms will
see brief reductions in visbys and increases in wind speeds.

&&

.DISCUSSION...

Today and Tonight...

As of the latest NHC update, Tropical Storm Marco is now a remnant
low positioned just off of the coast of Louisiana. It will
continue to track slowly west before finally opening up as a
trough this morning. Tropical showers rotating around the
northern side of this system will continue to stream into the
region this morning. Some gusty winds will be possible with a few
of these showers. NWS New Orleans has already issued one
tornado warning early this morning and there may be enough low
level wind shear to develop across our region over the next few
hours to support an isolated spin-up in the south.

As we get into the day on Tuesday, some instability will begin to
build over the ArkLaMiss. The building instability, combined with
steadily increasing tropical moisture(Pwats ranging from
2.2-2.5"), we will begin to see some more robust showers and some
isolated thunderstorms. Expect a lull in activity as we get into
Tuesday evening and night as surface weakness that once was Marco
lifts out of the region and what is expected to be Hurricane
Laura makes its approach towards the northern Gulf Coast.

Wednesday night through the weekend...

Tropical Storm Laura has a lot to say about the weather for the
early parts of the extended. Where it will track will play a lot
into what impacts we will see across the ArkLaMiss region. Early
this morning, Laura departed from its visitation with Cuba and will
be moving into the Gulf of Mexico through the day today. It has
become better organized as it encounters the deep, warm waters of
the Gulf stream. Due to this, it is expected that Laura will
strengthen into a hurricane during its journey across the Gulf of
Mexico. The latest thinking from NHC indicates that there should be
some rapid intensification across the Gulf, and coupled with some
weakening shear, that Laura should be a major hurricane as it nears
landfall. As for landfall, that remains the main question. Models
and the current NHC forecast indicate that Laura will track across
the Gulf and make landfall around southwest Louisiana and track up
through western Louisiana near the Texas border. The timing for this
would be a landfall around Wednesday night, and tracking inland
during the day Thursday. I will say that the latest 00Z guidance in
some of the global models does show a little more westward track of
Laura, more toward the Upper Texas Coast. If additional westward
movement occurs, this would spell better news for the ArkLaMiss
region, as impacts would lessen at that point.

At this time, the ArkLaMiss region does remain on the eastern side
of landfall and we could see some impacts from Laura in any outer
bands that move across the area. Laura will be different than Marco
in that it will be a more expansive system so some impacts will be
felt further from the center.

First, the tornado/severe weather risk. As Laura makes landfall,
there will be the potential for a few tornadoes in any rainbands
that move across the region. The best location for this will be
across the western part of the forecast area. A slight risk has been
introduced for the far southwestern part of the forecast area to
account for this risk, as well as any gusty winds associated with
rain bands closer to the center of circulation. As Laura tracks
north on Thursday, some of this tornado risk also is expanded
further north into the Delta, but is a marginal risk for now. The
main timing for this should be later on Wednesday night into early
Thursday morning, and continuing through Thursday as Laura tracks
north.

The wind and flooding risk are a bit more uncertain. As for rain and
flooding, with the track shifting just a little more west, the bulk
of the heavier rainfall also shifts west. The higher QPF amounts
remain across south and central Louisiana and there is somewhat a
sharp gradient across northeast Louisiana even from roughly
Shreveport to Monroe. In my forecast area, the best or highest
rainfall amounts are west of the Mississippi River. However, even
these totals diminished some on this forecast package with around
one to maybe two and a half inches being seen from roughly Wednesday
night through the day on Thursday. That being said, some adjustment
to the inherited flooding graphic will likely be needed. Initial
thinking is to reduce the area of the elevated before eliminating it
altogether.

As for wind, as the track continues to move west, so do the worse
wind impacts. I can't discount the potential for wind in the western
part of my forecast area. However the worse wind looks to occur
closer to the landfall in southern Louisiana. The best locations for
gusty winds will be again west of the MS River, closest to the track
of the storm. Some adjustment will likely be needed to the inherited
wind graphic. I am not totally sold on the elevated region as winds
look to be sustained around 20-35mph and gusts to near 40 mph.

By late Thursday, Laura should be entering southern Arkansas and
will continue to track north. An upper trough will be approaching
from the west, which will eventually pick up Laura and by mid-day
Friday this will help accelerate its departure from the Mid-South
region and whisk the remnants to the east. A front looks to drop
south into the northern parts of the forecast area. This will help
initiate additional showers and storms as we head into the weekend.
The weekend forecast looks wet as a tropical airmass remains in
place and should help initiate at least some diurnal showers and
thunderstorms. Dewpoints this weekend could remain in the mid to
upper 70s and even some lower 80s which will make conditions feel
miserable.

As a side note but still worth mentioning, as temperatures reach the
lower 90s on Wednesday and dewpoints will be in the middle/upper
70s, heat indices will be around 100-105 across the area. Some
locations in the west/Delta could see heat indices around 105-107
degrees. Given all that is going on with the tropics, I won't issue
any heat related graphics but something worth noting for those who
are working outside or have issues with higher humidity. /28/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       86  75  91  75 /  80  54  43  39
Meridian      86  74  92  74 /  80  45  34  28
Vicksburg     87  76  92  75 /  77  43  46  45
Hattiesburg   87  75  89  75 /  84  57  55  38
Natchez       86  74  90  75 /  81  60  56  55
Greenville    89  75  93  75 /  69  34  42  35
Greenwood     87  75  93  74 /  70  40  35  34

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...None.
LA...None.
AR...None.

&&

JPM3

Hazardous Weather Outlook
National Weather Service Jackson MS
553 AM CDT Tue Aug 25 2020

ARZ074-075-LAZ007>009-015-016-023>026-MSZ018-019-025>066-072>074-
261100-
Ashley-Chicot-Morehouse-West Carroll-East Carroll-Richland-
Madison LA-Franklin LA-Catahoula-Tensas-Concordia-Bolivar-
Sunflower-Leflore-Grenada-Carroll-Montgomery-Webster-Clay-Lowndes-
Choctaw-Oktibbeha-Washington-Humphreys-Holmes-Attala-Winston-
Noxubee-Issaquena-Sharkey-Yazoo-Madison MS-Leake-Neshoba-Kemper-
Warren-Hinds-Rankin-Scott-Newton-Lauderdale-Claiborne-Copiah-
Simpson-Smith-Jasper-Clarke-Jefferson-Adams-Franklin MS-Lincoln-
Lawrence-Jefferson Davis-Covington-Jones-Marion-Lamar-Forrest-
553 AM CDT Tue Aug 25 2020

This hazardous weather outlook is for portions of southeast
Arkansas, northeast Louisiana, central Mississippi, north central
Mississippi, and south central Mississippi.

.DAY ONE...Today and Tonight

The probability for widespread hazardous weather is low.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

Rain bands associated with Tropical Storm Laura will move across
the region late Wednesday and Thursday as it moves inland. Damaging
wind and tornadoes are possible Wednesday night through Thursday
across northeast Louisiana and portions of southern and
southwestern Mississippi.

(https://www.weather.gov/images/jan/graphicast/1.png)

Sustained winds of 25 to 35 mph with occasional gusts around
45 mph associated with Tropical Storm Laura may occur mainly over
the western portions of the area Wednesday night through
Thursday.

(https://www.weather.gov/images/jan/graphicast/2.png)

Rainfall of 2 to 4 inches with locally higher amounts associated
with Tropical Storm Laura will lead to the potential for flash
flooding across the western portions of the area Wednesday night
through Thursday.

(https://www.weather.gov/images/jan/graphicast/3.png)

.SPOTTER CALL TO ACTION STATEMENT...
The activation of storm spotters, HAM radio operators, and
emergency management personnel in support of severe weather
operations may be needed for portions of the region Wednesday
night through Thursday.

28

&&

...HAZARD LEGEND...

No short term hazards expected.

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