Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 191728 AAA
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1128 AM CST Thu Jan 19 2017

...ACTIVE PERIOD OF WEATHER EXPECTED THROUGH THE WEEKEND...

.UPDATE...
Updated for morning update and 18Z aviation update.

&&

.DISCUSSION...
Large swath of rain and some embedded thunderstorms are pushing
through central and eastern Mississippi this morning. A few severe
storms occurred earlier this morning, including a potential tornado.
This swath of rain will continue across the region today, which could
continue to lead to some localized flooding issues due to our
high precipitable water in place over the region. The severe threat
is waning given this morning`s activity. However, as better forcing
occurs this afternoon with the upper trough passage, any better
instability or heating could promote a strong storm or two especially
in the west. Will look at making adjustments to the HWO and graphics
for this afternoon. Think the biggest concern will remain flash
flooding. /28/

Prior discussion below:


Today and Tonight:

The main concern for today will be the potential for heavy rainfall,
as a stream of subtropical moisture surges over the region.
Widespread rainshowers and embedded thunderstorms will bring the
potential for localized flooding where training of storms occurs, as
well as a limited threat for severe weather. Details on both threats
are as follows. Looking at water vapor satellite imagery early this
morning, an upper low could be clearly seen spinning over Kansas,
with a plume of subtropical moisture extending from central Mexico
northeastward to the Great Lakes. The greatest lift and therefore
heaviest precipitation is focused just east of the upper-level jet
axis. As the low pulls northward today, a shortwave will rotate
around the low and push the deeper moisture east of the forecast
area by late tonight/early Friday morning. In the lower levels, a
decaying cold front will linger in central Louisiana. Short-term
model guidance indicates some lower-level response to the shortwave
as it passes overhead this afternoon, strengthening the low-level
jet and perhaps locally intensifying rain rates.

PWAT values ranging from 1.5 to 1.75 inches within this airmass are
near the climatological max for this time of year, and forecast
soundings indicate a saturated atmospheric profile can be expected
throughout the day. Some warming during the day should see around 500
J/kg of MUCAPE realized, making for efficient rainfall production.
Considering all factors, rainfall amounts of 2 to 3 inches can be
expected along a corridor from south-central Louisiana through
northeast Mississippi. Locally higher amounts will be possible.
Heavier rainfall may be more hit-and-miss for locations northwest
and southeast of this corridor (southeast Arkansas and southeast
Mississippi).

Regarding any severe weather potential, will keep mention of a
limited risk across the entire forecast area today. Afternoon
heating in combination with an extremely saturated atmosphere could
result in some stronger thunderstorms becoming surface based (albeit
with MLCAPE values struggling to break above 500 J/kg). Deep layer
shear around 40 kts will be supportive of some organization and
persistent updrafts. 0-1 km shear values of 20 to 30 kts, especially
enhanced in the vicinity of the low-level jet, indicate a potential
tornado threat as well. Already overnight, some cells on radar have
briefly taken on supercellular characteristics. Brief tornadoes will
be possible with these stronger storms. /NF/

Friday through Wednesday,

A stormy weather pattern will continue through the weekend with
greatest severe weather potential focused on late Friday night into
early Saturday morning and then again late Saturday afternoon
into the evening.

There is more agreement now in the guidance that deep convection
will erupt sooner rather than later Friday night as a strong Pacific
jet stream energy approaches the ArkLaMiss.  The combination of
anomalous low level moisture transport, steepening mid level lapse
rates, and approach of a shortwave trough may support explosive
convective development, most likely late Friday evening into the
early morning hours Saturday. Straight-line hodographs suggest that
organized storm clusters may contain splitting supercells with large
hail potential mainly for locations along/s of the I-20 corridor.
Initially, storms should be slightly elevated, but increasing low
level shear and warm advection should eventually result in sfc-based
thunderstorms with the potential for damaging wind/tornado threats
toward daybreak, particularly along the Hwy 84 corridor.

Expect the initial activity to move out quickly Saturday morning
with a lull in thunderstorm activity for most of the day. In the
wake of the morning convection, a pronounced elevated mixed
layer/cap will enhance mid level lapse rates and instability to
extreme values for January. As the next stronger shortwave trough
approaches late Saturday into Saturday evening, expect the potential
for additional supercell activity with large hail and wind damage
primary concerns, but there is some question regarding tornado
potential given relatively weak low level shear being forecast.

As the cold core begins to move over the area late Saturday night
and Sunday, better instability supportive of severe weather will
shift east, so while forcing will increase greatly resulting in
rain/tstms...the cooler thermal profiles should preclude much in the
way of severe weather potential beyond Saturday evening. Overall,
expect cooler and unsettled conditions from Sunday into Sunday night
followed by drier weather for Monday/Tuesday, and then returning
rain chances as the next front approaches Wednesday. While moisture
will struggle to return ahead of that front, it will be followed by
significantly cooler temperatures more typical of this time of the
year. /EC/

&&

.AVIATION...
18Z TAF discussion:
Main aviation concerns today will be from
showers and thunderstorms spreading into the forecast area through
this evening. IFR to MVFR ceilings will continue in this rain shield
this afternoon. A few storms could be strong with some gusty winds
possible. Expect lingering moisture to cause some low clouds and/or
patchy BR late in the period, but confidence is low as to exact
impacts given the ongoing precipitation and amendments will likely be
needed throughout the day. /NF/28/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       69  58  75  58 / 100  48   9  60
Meridian      70  59  74  59 / 100  72  17  65
Vicksburg     68  56  75  57 / 100  22   6  52
Hattiesburg   73  60  76  61 / 100  65  28  75
Natchez       68  58  76  60 / 100  24   7  62
Greenville    66  53  71  55 /  91  19   5  33
Greenwood     68  56  73  57 / 100  39   7  41

&&

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

&&


$$

28



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