FXUS64 KJAN 261127 AAA

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
627 AM CDT Wed Apr 26 2017


Updated for 12Z aviation discussion.


12Z TAF discussion:

VFR conditions were observed at all TAF sites at 1030Z but
satellite imagery suggests MVFR to IFR category ceilings will
spread north mainly along and west of the I-55 corridor 12Z-15Z
before improving to VFR conditions areawide by around 17Z. Strong
gusty south winds will develop today with sustained speeds around
15-25kts and gusts to around 25-35kts into the evening. A squall
line is expected to move in vcty of GLH around 23Z and continue
across the area overnight. The line of TSRA should shift SE of
HBG by 10Z. /22/



Today and Tonight: Early morning water vapor imagery showed the
circulation around a potent shortwave over northeast New Mexico
that will track east today and deepen a surface low over east
Texas before tracking northeast tonight across the mid Mississippi
river valley. The deepening surface low and increasing WAA ahead
of the approaching system will result in windy conditions across
our western zones and breezy conditions across the remainder of
our CWA. A Wind Advisory is in effect from later this morning into
early evening, generally northwest of a Natchez to Grenada Line
where occasional southerly wind gusts to 45 mph are expected.
These gusty southerly winds will help contribute to a deep
moisture increase ahead of the approaching cold front that will
move into our northwest most zones early this evening. Confidence
has increased that a squall line will develop along and ahead of
the cold front today. Model soundings still indicate a stout cap
over our CWA that should limit convection until the squall line
arrives at our northwest most zones around 5 pm by model
consensus. Overall, environmental parameters over our western
zones at the time the squall line arrives hasn't changed much from
previous runs. Anomalous moisture with surface dew points in the
upper 60s and PWATs in excess of an inch and a half inch will pool
ahead of the cold front. Steep mid level lapse rates >7.5c/km,
MLCAPEs near 2000j/k, deep layer shear of 50-55kts and 0-1km
helicity 200-300 m2/s2 will contribute to severe storm development
capable of damaging wind gusts, large hail and tornadoes. SPC has
outlooked our southeast Arkansas counties and a portion of our
northeast Louisiana Parishes in a Moderate Risk with an Enhanced
Risk east to the I-55 corridor. A Slight Risk remains over east
Mississippi as the line is expected to slowly weaken the later
into the night and farther east into Mississippi it pushes.
Considering the PWATs, locally heavy downpours will accompany the
strongest storms as well but, the progressive nature of the line
should limit duration. Model consensus moves the line southeast of
our CWA before sunrise with cooler and drier air back across our
CWA in the wake of the cold front. /22/

Thursday through Tuesday Night: Rain should be clear of the
forecast area by sunrise on Thursday, with clearing skies and
lighter winds expected throughout the day. Temperatures will
quickly rebound to around 10 degrees above normal for Friday as
southerly winds return. Parts of the area could reach 90 degrees,
which combined with humidity could lead to heat index values
approaching 95 degrees. Capping should keep convection from
developing on Friday, but a few isolated showers or storms can't
be ruled out with daytime heating. Saturday will see a
continuation of hot and humid weather, increasing southerly winds,
and a low end chance for showers or storms across the area as the
next upper-level low pressure system swings from New Mexico
toward the Panhandle of Texas. Tightening pressure and height
gradients ahead of this system could see near wind advisory
conditions develop across portions of the ArkLaMiss region.

The main period of concern with this approaching weather system will
be late Saturday night through the day on Sunday. Model guidance is
in fairly decent agreement on an organized line of thunderstorms
approaching southeast Arkansas and northeast Louisiana by around
sunrise on Sunday and reaching the eastern edge of Mississippi by
Sunday evening. Modest amounts of instability and deep layer shear
will support at least a Slight Risk for severe thunderstorms during
the day on Sunday. Moisture will also be concentrated ahead of the
line of storms, and forecast PWAT values approaching 2 inches would
place the system near the climatological maximum for this time of
year. Therefore we will also continue to highlight a limited risk of
flash flooding during the day on Sunday due to the potential for
heavy rainfall. Quieter weather is expected for the early part of
next week, though rain chances look to increase ahead of another
possible low pressure system by midweek. /NF/


Jackson 85 56 79 63 / 6 84 2 5
Meridian 85 59 81 62 / 2 79 11 7
Vicksburg 84 55 78 61 / 16 90 2 5
Hattiesburg 86 62 84 64 / 3 67 10 7
Natchez 84 55 79 62 / 10 86 2 5
Greenville 81 55 75 60 / 47 90 2 5
Greenwood 84 55 75 60 / 7 90 3 5


MS...Wind Advisory from 11 AM this morning to 9 PM CDT this evening
for MSZ018-019-025-034-035-040-041.

LA...Wind Advisory from 11 AM this morning to 9 PM CDT this evening
for LAZ007>009-015-016-023>026.

AR...Wind Advisory from 11 AM this morning to 9 PM CDT this evening
for ARZ074-075.



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