Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 300558 AAA

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1258 AM CDT Thu Mar 30 2017


Updated for 06Z aviation discussion


06Z TAF discussion:

Expecting a good deal of MVFR flight cats around the region
(mainly due to ceiling reductions) late tonight through tomorrow
morning. Flight category reductions associated with heavy rain and
thunderstorms will be most pronounced over the next several hours
at JAN and HKS. Tomorrow the thunderstorm impact will be more
questionable and likely more brief. Confidence in impact is
highest in the midday through afternoon hours around CBM/GTR where
there is a decent chance of severe weather and hail. Elsewhere
severe weather cannot be ruled out for tomorrow. Active weather
should be moving out of all areas by tomorrow evening. /BB/



Midnight update:

Threat for severe storms and a few embedded tornadoes continues
for portions of the forecast area near and just west of the I-55
corridor in central and southern MS. Other areas will be canceled
shortly. Thinking is still that waning instability east of I-55
will contribute to convective weakening and a slowing in eastward
advancement, thus the watch is not expected to be extended further
east through the remainder of the night (although severe weather
cannot be completely ruled out in most of those areas not
covered). /BB/

Evening update:

Tornado watch #101 was issued a bit ago for mainly western zones
until 3 AM CDT. Numerous thunderstorms initiating late this
afternoon near the east TX/southwest LA border have gradually
evolved into two separate areas of convection this evening; one
area progressing northeast into the Arklamiss Delta and another
area hugging more closely to the LA coast. Relatively broad
forcing helping trigger these storms could set off more in the
watch area through late evening and the combination of wind shear
and instability is enough in the watch area to be concerned about
tornadoes. 00Z JAN sounding revealed steep lapse rates, but plenty
of dry air and capping above the surface to provide an impediment
for potent storms to easily transition east past the I-55
corridor. Activity has developed eastward into the region a little
faster than anticipated and our forecast and graphics have earlier
been updated to reflect observations and thinking through the
night. /BB/

Prior discussion below:

Tonight through Thursday night: The next 24-30 hours are expected
to be quite active across the region with multiple rounds of
severe weather possible. The main culprit will be an upper trough
currently over the Southern Plains swinging eastward into the mid
MS River Valley through the day tomorrow. The associated surface
low is currently situated over south Kansas and will track ENEward
into the Ohio Valley through tomorrow, dragging a cold front
across the region tomorrow. Two rounds of severe weather are
expected with this system - one late tonight through early
tomorrow morning and another from around midday tomorrow into the
early evening.

The initial round of storms, currently over the TX/LA border, is
being kicked off by a spoke of PVA/upper height falls pivoting
around the main upper low. Ahead of these storms across northeast
Louisiana, a rather favorable environment is expected to exist
later this evening, with deep layer shear of up to 50 kt, a 40-50
kt low level jet, mid level lapse rates around 7 C/km, 0-1 km SRH
of up to 100 m2/s2, and sufficient surface based instability with
SBCAPE of 500-1000 J/kg. Ongoing convection and available high-
res guidance suggests decent potential for supercells evolving
into more of a QLCS as they advance E/NE into the Delta later
tonight. Given the favorable environment in the western portion
of our forecast area, we have relatively high confidence in
severe weather overnight, with some potential for some instances
of sig severe (2"+ hail, a strong tornado) as well. Forecast 0-3
km shear vectors suggest the greatest damaging wind potential with
any bowing segments moving in a more SW to NE direction during
this time frame. This convection should lose steam by around
daybreak as it begins to outrun the best low level forcing and as
instability reaches it`s nocturnal minimum.

A bit of a lull is expected during the mid/late morning hours as
remnant storms from overnight continue slowly eastward. This,
along with any significant development of coastal convection, will
present a potential limiting factor for redevelopment of storms
later in the day tomorrow. Nevertheless, new convection is
expected to initiate around midday somewhere between the MS River
and the I-55 corridor as renewed upper forcing moves across the
region and deep layer shear increases. It is possible these storms
will not initiate until the boundary reaches the I-55 area, so the
threat for additional severe weather west of this area (and
especially back into AR/LA) is very questionable tomorrow. Farther
south, instability may be increasingly limited by convection
earlier in the day, so uncertainty increases south of the I-20
corridor. The storms that do develop with likely need some time to
percolate before reaching severe thresholds as they move
eastward, suggesting the greatest potential for severe storms in
our CWA with this second round will be around the Golden Triangle
area (with perhaps greater potential north and east of the area).
Once again, relatively steep mid level lapse rates are forecast
across much of the area, suggesting the potential for large hail.
In addition, weak to moderate instability and a respectable low
level jet portends the potential for damaging winds. The greatest
low level helicity is forecast to pull out of the area by early in
the afternoon, so the window for greater tornado potential may be
somewhat limited with the second round of storms.

To reiterate, there is considerable uncertainty surrounding the
second round of storms, and there`s a decent chance that some
parts of our area may not be impacted. However, it is worthwhile
for everyone to keep checking the latest forecasts, because there
is the potential for a significant severe weather threat where
storms do develop.

Storms are expected to exit the area by mid evening, with rain
mostly out of the forecast area by midnight. Somewhat cooler air
will filter in overnight. /DL/

Friday through next Wednesday:
As Thursday`s system pushes off to the east, quiet weather will
prevail as surface high pressure builds over the region on Friday
and Saturday. High temps will return into the 80s while lows
increase again into the 60s.

During the weekend timeframe, a trough over the Four Corners region
will travel eastward and into the Plains. As a surface low begins to
deepen Sunday, impulses of energy rotating around the closed low
will begin to affect our region beginning on Sunday. Surges of
moisture associated with a low level jet may bring inches of
rainfall to southern Louisiana and Mississippi Sunday into Monday.
Models are in a bit of disagreement about the total rainfall amounts
but agree that there will be plenty of moisture being pushed into
the region. PW values increase to 2+ inches. Dewpoints will be in
the upper 60s Sunday night into Monday. WPC has QPF amounts as high
as 5.5 inches bullseyed in south Mississippi in the day 4/5
timeframe. A limited risk, therefore, has been added to the HWO for
flooding and in order to keep things simple in light of the current
severe risks, just a note about flooding has been added to the
Graphicast. This will certainly need to be adjusted as time
approaches. As to severe weather, a limited risk will remain
possible with strong winds aloft and favorable instability profiles
suggesting organized severe storms.

This system will push out gradually late Monday night through
Tuesday. A closed low sweeping through the plains next Wednesday
will drag a cold front through our region. This will bring another
round of storms to part of the area. /10/


Jackson       53  79  54  84 /  34   3   2   1
Meridian      54  80  52  84 /  60   3   2   1
Vicksburg     52  81  55  85 /  14   2   1   3
Hattiesburg   55  82  54  86 /  45   2   1   1
Natchez       54  81  56  84 /  12   1   1   7
Greenville    50  76  54  82 /  12   3   2   2
Greenwood     50  76  53  83 /  21   3   2   1





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