Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 202249
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
449 PM CST Tue Feb 20 2018

...WET PATTERN IN ORDER FOR THE REMAINDER OF THE WEEK...

.DISCUSSION...

Tonight through tomorrow...

An active period of weather will commence during the short term as
a surface front that stretches from SE Canada through South Texas
continues to slowly approach the region. South of this front,
warm and muggy conditions will continue to exist as tropical air
is advected into the region. Maximum-minimum temperatures records
will fall at almost every climate site tonight with some records
being broken by nearly 5 degrees. Lows tonight will be so warm
that they`ll be about 4-7 degrees warmer than the normal highs for
this time of year.

A few WAA showers will be possible overnight with the best chances
occuring in the Pinebelt. Scattered showers ahead of the front
will begin to spread into the region from the NW after midnight as
the slow moving front continues to approach the region. A strong
isolated thunderstorm or two can`t be ruled out tomorrow with
better chances of this occuring in the western portions of the
region where slightly better height falls will exist and combine
with an unstable prefrontal atmosphere. The main threat with any
storms will be straight line winds and hail. A flash flood threat
will begin to develop tomorrow afternoon in our Delta parishes
and counties as rain rates increase and the front slows.

Temperatures will once again rival their daily highs in areas
southeast of the front with readings in the low 80`s expected
once again.

Wednesday night through Tuesday...

An active period of weather will persist through much of the period
with flash flooding and severe weather possible. The synoptic
pattern over the CONUS will feature subtropical ridging off the
southeast coast with a deep mean longwave trough over the Rocky
Mountains. This pattern will help maintain deep moist southwesterly
flow with substantial and anomalous moisture transport into the
region. There will be two main time frames of interest for hazardous
weather during the forecast period. The first will be Wednesday
through Thursday as a slow moving cold front edges into the
northwest Delta as multiple shortwave troughs propagate through the
southwesterly flow. Convection will already be ongoing Wed night as
multiple composite outflow boundaries from upstream convection
interact and help focus heavy rainfall. These rounds of storms are
expected to continue through Thursday morning with the highest
rainfall totals across the Delta. 3-5" of rain will be possible
across portions of Ashley, Chicot and Bolivar counties so went ahead
and added a flash flood watch and increased the HWO/graphics to
include an elevated area for those locations. The limited area
remains the same and extends from near Vicksburg to Grenada where 2-
4" of rain will be possible. The exact location of heaviest rainfall
will be dependent on how the aforementioned outflow boundaries
interact and where training convection becomes focused, so further
changes and expansion to the watch and/or graphics is possible,
especially for parishes in northeast Louisiana. In terms of severe
weather, latest hi-res CAM guidance is in fairly good agreement that
any storms Wed evening will be elevated on the cool side of the
remnant outflow boundaries which will greatly preclude any severe
potential.

By Thursday afternoon into Friday, the stalled frontal boundary is
progged to lift back northwest into Arkansas and will provide a
brief relief from the heavy rainfall and storms as the next storm
system becomes more organized over the Great Basin. This more potent
shortwave trough will eject out of the Four Corners region and into
the Central Plains on Saturday and will bring a much stronger cold
front into the area. The stubborn subtropical ridge will also weaken
and become more suppressed allowing substantial height falls to
overspread the region. Sufficient deep layer shear of 50-60kts
combined with upwards of 1000 J/kg of SBCAPE will support a threat
for severe thunderstorms late Saturday afternoon through early
Sunday morning as the front moves through. The main threat will be
for damaging winds and a few tornadoes. Went ahead and added a
slight risk to the HWO/graphics to highlight this potential as the
GFS and ECMWF are both in good agreement on the severe potential.

Following the cold frontal passage, the subtropical ridge will
become centered more over the central Gulf of Mexico with zonal flow
across the Deep South. There is some uncertainty as to whether the
front will clear the area or stall over the south. If the front
hangs up there will be the potential for rain to continue south of I-
20 early next week as disturbances move through the zonal flow
aloft, however too much uncertainty exists to speculate on any given
solution. /TW/

&&

.AVIATION...
18Z TAF discussion:
VFR, MVFR, and IFR flight conditions are possible through the
region over the next 24 hrs due to low CIGs. MVFR CIGs will be
apparent arewide wide today as moisture continues to advect into
the region from the Gulf. A few breaks in the cloud deck may
result in CIGs becoming SCT but this should be short-lived. Winds
will be strong and from the south with gusts up to 25kts expected
in the Delta. The best chances for showers will exist near KHBG
today. CIGs will lower to IFR levels tonight as wind speeds
lessen. Rain chances will begin to increase late in the TAF
period.

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       66  82  66  80 /   9  48  61  33
Meridian      65  82  68  80 /  21  30  38  19
Vicksburg     67  80  64  78 /  13  80  98  79
Hattiesburg   66  84  67  81 /  24  33  38  16
Natchez       68  81  67  79 /  15  68  67  69
Greenville    64  69  53  69 /  25  88  99  85
Greenwood     66  75  59  75 /  11  83  98  83

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Flash Flood Watch from Wednesday morning through Thursday
     morning for MSZ018.

LA...None.
AR...Flash Flood Watch from Wednesday morning through Thursday
     morning for ARZ074-075.


&&


$$

TW/JPM3



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