Area Forecast Discussion
Issued by NWS Jackson, MS

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000
FXUS64 KJAN 190340
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
940 PM CST Wed Jan 18 2017

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

.UPDATE...
Updated for evening discussion.

&&

.DISCUSSION...
A mid/upper-level low is currently located over the south central
High Plains with a weak sfc low centered over the ArkLaTex with an
associated stalled frontal boundary across north central LA and
central MS and a cold front to the south across far east TX. As of
320z, an area of ongoing showers with some isolated thunder is
located across the majority of the CWA. Latest CAM guidance is in
agreement on scattered showers persisting through 9z mainly along and
northwest of the Natchez Trace before activity begins to ramp back up into
the early morning hours. The aforementioned stationary frontal
boundary across the ArkLaMiss will begin to lift north as a warm
front during the overnight, which will keep the majority of the CWA
in a weakly unstable moist warm sector characteristic of low to mid
60s dewpoints and a few hundred J/kg of MUCAPE. Renewed convective
activity is expected to develop by 9z across the SW portion of the
forecast area as a 30-35kt LLJ pivots into the ArkLaMiss. While
marginal, a sufficient combination of CAPE and low/mid-level shear
and 100-150 0-1km SRH will be enough to maintain a low end severe
threat through the early to mid morning hours. The main threat will
be for isolated damaging wind gusts, however an isolated tornado
cannot be ruled out either, especially with any low topped supercells
with sustained updrafts. The HWO graphic has also been updated to
reflect the current forecast. Severe storms also remain possible
during the afternoon hours tomorrow, please see the previous
discussion below/check back tomorrow morning for the last info for
the afternoon potential. Otherwise, kept overnight min temps on the
warmer side of guidance due to plenty of cloud cover and southerly
winds across the area. /TW/

Prior discussion below:

Tonight through Thursday:

Mild spring like anomalous conditions will continue through Thursday
with well above normal temperatures. The primary concern will be a
progressive storm system coming through late tonight into Thursday.

Latest satellite imagery shows the region under southwest flow with
an approaching storm system coming through the Southern Plains. Area
radars were picking up some scattered showers across our western
areas. A quasi-stationary surface boundary was observed across the
region. Mid afternoon temps were from the middle 50s northwest to
the middle 70s southeast.

For tonight showers and scattered thunderstorms will spread from
west to east as the storm system approaches. The frontal boundary
will push to the north as a warm front as a surface wave with an
associated front will approach from the plains. Shear profiles will
strengthen some after midnight across Northeast Louisiana into
Southeast Arkansas in response to the upper trough pivoting in the
Southern Plains. Short term convective models shows some possible
strong embedded convection moving into this area after midnight with
some locally heavy rainfall potential.

By early Thursday there will be widespread showers and thunderstorms
across the region with locally heavy rainfall possible. This will
occur as the upper trough becomes negatively tilted over the region.
The widespread rain coverage will limit instability with weak mid
level lapse rates, but there will be enough layered shear, and
forcing for a low end severe risk. The primary risks will be
damaging winds, hail up to quarter size, possible tornado, and
locally heavy rainfall. Short term convective models shows a broken
band of strong cells moving through the region during the day. The
approaching cold front will weaken across Southeast Arkansas and
Northeast Louisiana during the day as the associated surface wave
pulls to the northeast.

As far as heavy rainfall is concern this seems to be such a
progressive system that WPC has only a marginal risk of flooding
across the region. QPF looks to be around one to two inches with
locally three inch amounts possible. So with pwats around 1.6 inches
have kept the locally heavy rainfall wording in the grids.

As far as temps are concerned lows will range from the upper 50s
northwest to the middle 60s southeast. We could be breaking some
warm low temps records by early Thursday morning. Highs on Thursday
will range from the middle 60s northwest to the lower 70s southeast.
/17/

Thursday night through Wednesday morning:

An active period of weather is expected over the next several days as
we go into the weekend. By Thursday night, the cold front will have
moved through the region. A chaotic upper pattern will be ongoing as
the shortwave will have moved through into the mid-Mississippi valley
while another stronger trough will be diving into the Desert
southwest. Strong upper level jet energy will be moving into the
eastern Pacific into Mexico, near 150kts at 300mb. As that shortwave
over northern Mexico ejects northeast, broad surface cyclogenesis
will be taking place over the central Plains with ~992-995mb surface
low. At the surface, we will be under weak ridging moving in for
Friday afternoon. Dewpoints may temporarily fall into the upper 50s
Friday. We should be able to warm into the low-mid 70s Friday.

As a strong upper low and ~992-995mb surface low swings into the
northern Plains into the Great Lakes, a cold front will be moving
into the southern Plains. In addition, a strong shortwave will help
move moisture back in by Friday night into Saturday. More active
inclement weather is expected Friday night into Saturday as
increasing moisture transport moves 60s dewpoints back into the area.
The strongest push of lapse rates and shear will be after midnight
Friday through Saturday morning. Sufficient mid-level lapse rates
near 6-7 deg C/km and instability ~1000 J/kg will be present.
Sufficient low-mid layer shear (40-50kts at 0-3km bulk shear) will
be present as well. There is enough low level boundary layer
moisture, height falls, forcing and favorable jet dynamics (upper
diffluence/left exit region) as the upper jet moves through the
central-northern Gulf. This will help increase thunderstorm
development after midnight, mainly south of I-20 and especially in
the Highway 84 corridor. In addition, there is enough significant
hail parameter near 2-3 and large hail parameter approaching 20s or
so in the south to warrant potential for large hail. Wet bulb zero
heights are low around 7,000-8,000 feet, which will help large hail
potential. There is some issues with capping that could limit some
potential but does not seem to limit it much. The QPF field seems to
focus on that midnight to early Saturday morning timeframe. Some
supercell structures, including splitting cells, with large hail and
damaging winds are possible. Tornadoes are also possible if storms
can become surface based as effective helicity seems to approach 200
SRH m2/s2. There may be a lull in activity early Saturday afternoon
as the shortwave ejects to to the east before better height falls
will come with the strong deep closed low diving into the southern
Plains Saturday evening. Mid-late Saturday afternoon to evening, a
very unstable atmosphere, with some 1000-2000 J/kg of instability,
and unidirectional low-mid layer shear will continue to favor severe
weather. Updated graphics/HWO to focus more on Friday night/Saturday
and the afternoon. There is a possibility these outlooks could be
upgraded so keep a close eye on for any future updates.

More severe threat will linger into Sunday as the closed low (very
low heights near 540DM), dives into our area. There is some
uncertainty as the closed low moves over as temperatures will cool
down into the 60s but very steep lapse rates and extremely low
freezing level/wet bulb zero heights will favor potential for some
wind and hail, with most of it being very small. This type of
environment could be very shallow showers/cells that could
efficiently produce small hail. For now, left it in the HWO but
removed from the graphic as Friday night through Saturday looks to be
the higher end threat. Will still have to monitor that as we get
closer.

Drier air and more moderating temperatures will move back Monday
through mid week in the wake of the frontal passage. Upper ridging
and surface high build through the area before more rain chances may
move back in mid-late next week as a cold front approaches the area.
/DC/

&&

.AVIATION...
00Z TAF discussion:

Flight conditions will be deteriorating in all areas tonight with
showers and embedded thunderstorms moving into at least central and
western areas (GLH/GWO/HKS/JAN) as the night wears on. IFR conditions
will be increasingly likely in these areas but even locations to the
east (GLH/CBM/MEI/NMM/PIB/HBG) will have potential for showers moving
in tonight with also patchy fog not impossible. Tomorrow the stalled
front over the region will combine with an incoming disturbance to
generate rather widespread showers and storms and ceilings remaining
quite low (IFR). A few of the storms could be rather potent with
gusty winds and perhaps some hail. Otherwise, anticipate increasingly
southerly winds will some gusts up to or over 20 mph possible late
tonight into tomorrow. /BB/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       66  69  56  76 /  72  96  23  10
Meridian      64  70  57  75 /  41  83  61  17
Vicksburg     64  69  55  77 /  95  90  14   3
Hattiesburg   66  71  58  76 /  50  79  53  18
Natchez       66  69  58  78 /  93  94  14   4
Greenville    56  66  55  72 /  88  77  14   5
Greenwood     60  69  57  75 /  84  90  30   8

&&

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

&&


$$

TW/17/DC/BB



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