Area Forecast Discussion
Issued by NWS Jackson, MS

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154
FXUS64 KJAN 260220
AFDJAN

Area Forecast Discussion
National Weather Service Jackson MS
920 PM CDT Tue Apr 25 2017

...SEVERE STORMS EXPECTED WEDNESDAY NIGHT...

.UPDATE...
Updated for evening discussion.

&&

.DISCUSSION...
Another quiet evening is expected before storms move into our CWA
tomorrow night. Increasing winds from the south will be a hazard
tomorrow afternoon in the Delta as the front approaches from the
west. A Wind Advisory has been issued for this region from 11:00am
till 6:00pm; gusts of 45mph are expected. /12/


Prior discussion below:


Tonight through Wednesday,

Latest satellite imagery showed a flat ridge across the ArkLaMiss
region. Meanwhile our next storm system was over the four corners
region as it was pushing toward the Plains. Surface high pressure
was providing sunny skies across the region. Temperatures were in
the lower 80s as of mid afternoon. Latest gulf moisture analysis
showed 1.5 inches of precipitable water over the northwest gulf
waiting to be tapped with our midweek system with lower 70s
dewpoints.

For tonight low level moisture will increase from the west as 60s
dewpoints make their way to the I-55 corridor. So along with it
expect clouds to increase across the west half of the ArkLaMiss.
With the increase in moisture, temperatures will be milder for
tonight with lows from the upper 50s east to the middle 60s west.

For Wednesday the upper trough will track into the Plains as
surface low pressure along the front deepens. In response to this
the pressure gradient will tighten across the region as pressure
falls increase from the west. This will cause breezy conditions
across the region to develop from west to east during the morning.
The breezy conditions will continue through Wednesday evening. So
with this in mind expect winds to reach wind advisory criteria
with gusts to 45 mph across the western delta region, while the
rest of the forecast area will have gusts to 35 mph. Short Term
guidance shows winds gusts around 35 to 40 knots in the delta
region. A strong cap will be in place across the region as
dewpoints rise to the lower to upper 60s. This will help temps to
climb into the middle and upper 80s at most locations with some
upper 70s and lower 80s in the far west. A few locations may reach
90 under this cap. CAM guidance also shows some convective rain
chances across the far western area for Wednesday afternoon as the
cap weakens some there in the afternoon with height falls coming
in. Instability and shear will be on the increase as the storm
system closes in on the CWA for some late afternoon severe risk.
CAM guidance shows that a squall line will be pushing into our far
western areas by Wednesday evening. With mid level cap in place,
not expecting much in terms of prefrontal discrete storm activity.
/17/

Wednesday night through the weekend,

An active weather pattern is anticipated for later in the week
into the weekend. In particular, severe weather is expected
Wednesday night, and then a longer duration of severe weather and
heavy rain potential is expected this weekend.

A deepening northern stream upper level trough over the southern
Plains Wednesday will track northeast across the mid Mississippi
River valley Wednesday night while supporting a surface low that
will send a cold front across our CWA Wednesday night. WAA wl
increase significantly over our region Wednesday ahead of the
approaching cold front. This will result in a breezy south wind
across much of our CWA with the strongest winds northwest of a
Winnsboro Louisiana to Grenada Mississippi line where a Wind
Advisory will likely be needed from afternoon into the evening.
Anomalous moisture is expected to pool ahead of the cold front
with surface dew points in the upper 60s and PWATs in excess of an
inch and a half inch. Models still show a decent cap over our CWA
until late afternoon in the west just ahead of the cold front. A
squall line is expected to develop along and just ahead the cold
front and move into our western most zones before evening.

The initial environment over our western zones will feature 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. As the squall line
progresses across our CWA, severe storms capable of damaging wind
gusts, quarter sized hail and a tornado or two will be possible.
Considering the PWATs, locally heavy downpours will accompany the
strongest storms as well. The GFS is a little faster but consensus
places the line near I-55 by midnight and southeast of I-59 by
6AM. Over eastern Mississippi, there is a little more question
about the ability for large scale forcing to overcome the cap and
this makes the severe potential a little more conditional than in
the upper Delta region.

A weak surface high but much drier airmass will move over our
CWA Thursday in the wake of the front but a second shortwave and
associated surface low will move over the southern Plains and help
the cold front move back north as a warm front Thursday night.
Our CWA will be back in the warm sector Friday with rain chances
mainly across our north near the front.

The longwave pattern still looks to amplify sharply during the
weekend with a 591dam high developing just off the coast of the
southeast states while a closed low drops over the southern Plains
Saturday. Strengthening WAA ahead of this system looks produce
breezy to windy conditions across our CWA again by Saturday
afternoon. Model consensus has sped up the timing of this system
and are in better agreement with the potential for severe
thunderstorms over our CWA Saturday night into Sunday. In addition
to severe storms, models suggest potential for heavy rainfall
over a large portion of our area as well. This system is expected
to shift east of our area Sunday night with dry weather on Monday.
/22/EC/

&&

.AVIATION...
00Z TAF discussion:
VFR conditions will continue through the evening. Some low clouds
will move in later tonight affecting TAF sites mainly along and
west of the I-55 corridor, bringing MVFR to IFR category ceilings.
These should improve by late morning tomorrow back to VFR. Winds
will be gusty out of the south tomorrow with sustained speeds
around 15-23kts, gusting to around 25-33kts during the day. Storms
will move in around or after 21Z tomorrow afternoon and move
through the region from west to east. /28/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       61  87  58  80 /   1   6  78   3
Meridian      58  86  63  82 /   0   7  79   5
Vicksburg     64  85  56  79 /   1  13  79   3
Hattiesburg   60  84  64  85 /   0   6  67   3
Natchez       65  84  56  79 /   1  18  78   3
Greenville    65  82  54  76 /   2  37  82   3
Greenwood     62  87  56  76 /   1   8  80   3

&&

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

&&


$$

12



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