Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 231439
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
939 AM CDT Sun Jul 23 2017

.UPDATE...
Updated for morning discussion.

&&

.DISCUSSION...
As of 1430z, ridging remains in place over the Desert Southwest
through the Southern Plains and into the western fringes of the
Deep South with an upper-level low slowly drifting west along the
northern Gulf Coast beneath the ridge. A complex of thunderstorms
is ongoing along the Louisiana coast residing along the coastal
instability gradient and deep moisture axis in the vicinity of the
upper low. Further north over our CWA, a low cloud deck has been
stubborn to erode this morning thanks to wet soils from more
widespread rain yesterday and sufficient low level flow. Expect
this cloud cover to continue to lift and dissipate over the next
few hours. A few showers were also noted in the Delta in areas
that have already seen more sunshine this morning, but expect this
activity to remain more isolated through the morning hours. For
the remainder of today, the ongoing heat advisory in the northwest
Delta looks to be on track with heat index values reaching the 105
degree range, although any convection and lingering cloud cover
could help to limit the degree of heating in a few locations.
Diurnally driven afternoon thunderstorms are expected again today,
especially in the southwest closer to the upper low. The main
hazards with any convection will continue to be lightning,
torrential rainfall, and isolated gusty winds. Isolated
microbursts and flash flooding cannot be ruled out, but widespread
severe weather is not expected. Storms and showers should
dissipate after sunset during the early evening hours, although a
few isolated showers could linger through the overnight. /TW/

Prior discussion below:

Today and tonight:

A weakness in the SW/S CONUS upper ridge will remain over the
region today as a subtle upper low persists over LA and a
shortwave upper trough swings across the NE states. This pattern
will continue to provide somewhat better than climo rain chances
over the area today, though development will still be mostly
diurnal in nature. Guidance is hinting at the best chance of rain
being across the SW portion of the CWA, closest to the weak upper
low feature.

Otherwise, another humid day is on tap as we remain quite moist in
the low levels (dewpoints mid 70s in many areas). Forecast temps and
dewpoints suggest the greatest levels of heat stress will exist over
parts of the Delta, where a Heat Advisory was posted for this
afternoon. Outside of the advisory area, heat indices in the triple
digits are possible, but reaching advisory criteria is less certain,
particularly given the greater rain chances in some areas. /DL/

Monday through next weekend:

The juxtaposition of a weakness in the subtropical ridge and high
atmospheric moisture (precipitable water values around 2 inches)
will result in above average shower and thunderstorm activity
Monday and Tuesday. Most of the activity should be diurnally-
motived, and thus exhibiting the best coverage in the afternoon.
However, it is certainly possible to have some convection around
even through the night in many areas Monday night and then maybe
in southeast zones Tuesday night. Torrential downpours will of
course be possible in this environment but any flooding threat
should be relatively minor and very localized. Conditions will
continue to be very humid over this span but heat index values in
most locations should struggle to peak above 100 degrees
considering all the clouds and precipitation around the region.

Rain chances will be decreasing from the west Wednesday and
Thursday as the expanding eastern extent of the subtropical ridge
("heat ridge") squeezes the previous overhead upper level
weakness to our east. The highest rain chances these days will be
focused in eastern MS, but even here a subtle drying trend will be
evident. With the reduced overall clouds and precip expect a
daytime warming trend as well with potential for highs in the mid
90s in far northwest zones on Wednesday expanding further east on
Thursday. Plenty of humidity will remain in play and this should
raise heat stress levels back up some and more heat advisories
cannot be ruled out (especially in the Arklamiss Delta). This
resurgence of heat stress will be mentioned in the HWO.

On Friday our focus will turn to our north as a solid cold front
should be headed our way. Model consensus regarding this front has
continued to increase from last night with it now looking likely
this front should eventually progress most (if not all) of the way
through the region sometime over the coming weekend. General
consensus has sped up some with the front`s arrival into our
neck-of-the-woods, but the most reliable Euro model remains a bit
slower than consensus and its timing was leaned on for the
official forecast. Considering the latter, heat stress could
continue to be an issue for many areas on Friday as the associated
good coverage of showers and storms associated with the front
should likely wait until late in the afternoon (at the earliest).
Regarding storms, there is non-negligible potential of some semi-
organized and potent convection along and ahead of the front late
Friday and into Saturday and this will be monitored closely in
later forecasts. However, at this point uncertainty regarding
timing is too high to consider including in the HWO.

Finally, if this front can indeed manage to clear south of the
region over next weekend we may be looking at some below normal
temperatures and humidity values for at least a few days in its
wake. This potential evolution of conditions would feel pretty
great considering all the recent heat and humidity. Cross your
fingers! /BB/

&&

.AVIATION...
12Z TAF discussion:
A few patches of IFR stratus have developed across the area this
morning. These should quickly erode after sunrise. Otherwise, VFR
conditions prevail across the region. Scattered to numerous
SHRA/TSRA are expected to develop later today, possibly resulting
in brief visibility/ceiling reductions. Most of this activity
will taper off by shortly after sunset. Otherwise, VFR conditions
will prevail through the remainder of the period. /DL/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       90  73  90  74 /  40  21  62  45
Meridian      91  73  90  73 /  28  16  60  38
Vicksburg     90  74  90  74 /  48  23  60  38
Hattiesburg   90  73  89  73 /  46  26  59  46
Natchez       87  73  89  73 /  60  25  58  39
Greenville    91  74  92  74 /  35  21  55  30
Greenwood     92  75  91  74 /  32  19  58  34

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Heat Advisory until 7 PM CDT this evening for MSZ018-019-025-026-
     034.

LA...None.
AR...Heat Advisory until 7 PM CDT this evening for ARZ074-075.


&&


$$

TW/DL/BB



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