Area Forecast Discussion
Issued by NWS Jackson, MS

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476
FXUS64 KJAN 230302
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
1002 PM CDT Mon May 22 2017

.UPDATE...
Updated for evening discussion.

&&

.DISCUSSION...
As of 230z, a surface low was located near the MS/LA line just NE
of Baton Rouge with an inverted trough axis extending into central
MS and a baroclinic zone just inland separating a moist unstable
marine layer from cooler more stable air to the north. Meanwhile
aloft, broad troughing is located across the central US with a
coupled jet structure supporting upper level divergence across the
ArkLaMiss. Strong isentropic ascent above the baroclinic zone in
concert with the aforementioned coupled jet helped to support an
expansive area of moderate to heavy stratiform rain across a large
portion of the CWA this afternoon and is still ongoing, but lower
rainfall rates with this area of precip have precluded a greater
flash flooding threat so far. Latest RAP analysis also indicated
the presence of an internal diabatically enhanced potential
vorticity anomaly which has helped to strengthen the low level
flow and moisture advection into the area. For the remainder of
the evening, the heaviest rainfall is starting to edge into the
south central portions of the forecast area and will slowly spread
further north and east overnight. This is where the flash
flooding potential will be maximized mainly south of the I-20
corridor where 2 - 4 inches of additional rainfall with some
locally higher amounts will be possible. As such, the current
flash flood watch and limited/elevated areas in the HWO look well
placed and will let ride as is for now. The majority of the
lightning activity has been well offshore over the Gulf and with
little instability not expecting any severe weather so the
marginal risk was removed in accordance with the latest SPC
outlook. However, an isolated lightning strike or two cannot be
entirely ruled out as a few pockets of moist absolutely unstable
layers move through the area. Last, but not least, a few areas of
patchy fog are possible tonight mainly along the Hwy 84 corridor
and portions of the Delta as the rain moves off to the east. /TW/

Prior discussion below:

Rain has been slow to advance east today, but saturated lower
levels now are ensuring much more reaching the ground. Surface low
over southeast TX remains responsible for the widespread
isentropic ascent and should continue tonight as the low moves
along the baroclinic zone along the coast. Have some concern that
the low may shift a bit to the north as better baroclinicity
actually exits from west central LA into southwest MS. If this
occurs, heavier rainfall could develop further north than expected
right now. As of now, expect around 2 inches in the far south
with locally higher amounts.

Most of the heavy rainfall will depart into AL by 12Z Tuesday, but
digging mid level trough and at least a few breaks in the cloud
cover should be sufficient for scattered thunderstorms in the
afternoon. The best lapse rates will occur in the east during the
afternoon and with around 40 knots of deep layer shear, would not be
surprised to see some isolated severe storms here./26/

Tuesday night through Sunday...our winds aloft will remain out of
the southwest as a closed low drops south from the Upper to Mid-
Mississippi River Valley by Wednesday morning. A shortwave rounding
the base of the closed low will swing east across our CWA and help
support a weak cold front and another good chance of showers and
storms Tuesday night into Wednesday. Cooler and drier air will
filter into the CWA in the wake of the cold front but the closed low
will continue to drop southeast across northeast Mississippi and
maintain light rain chances over the northeast half of our CWA
during the day Wednesday. By Wednesday evening, dry weather is
expected and the skies will clear from the southwest. With mostly
clear skies and a drier airmass over the area, the coolest morning
lows of the forecast period are expected Thursday. Most sites will
bottom out in the lower 50s. Thursday and Friday will be dry with a
warming trend. Low amplitude ridging aloft will move over our CWA
while a surface high strengthens over the northwest Gulf and
ridges back to the west across the Gulf coast states. The
resulting southerly flow will slowly increase moisture back across
our area. Saturday mid level ridging will strengthen over the
Gulf and may limit convection across our southern zones but
elsewhere deep enough moisture will be back across our CWA to
combine with daytime heating to result in isolated to scattered
afternoon and early evening storms. Models differ on timing but
another closed low near the upper Plains and Canadian border will
deepen a trough over the central CONUS Sunday into Monday. This
will lead to increasing rain chances Sunday into Monday. /22/

&&

.AVIATION...
00Z TAF discussion:
A mix of VFR to IFR ceilings are occurring this evening as a large
swath of rain is ongoing over many TAF sites. This will continue
to reduce vis and ceilings through the rest of the evening. Some
heavier showers or storms could occur through the night. Overall,
not good flying conditions through daybreak. Conditions should
improve after 17Z Tuesday. /28/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       64  79  58  73 /  87  48  60  17
Meridian      64  80  60  74 /  91  81  58  32
Vicksburg     61  80  58  75 /  92  37  62  13
Hattiesburg   65  82  63  77 /  89  84  57  22
Natchez       62  79  58  74 /  85  34  62  10
Greenville    60  78  57  73 /  91  34  61  18
Greenwood     62  78  57  71 /  97  42  61  25

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Flash Flood Watch until 7 AM CDT Tuesday for MSZ052-054>066-
     072>074.

LA...Flash Flood Watch until 7 AM CDT Tuesday for LAZ024-026.

AR...None.

&&


$$

TW/22/26/28



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