Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 261447 AAA
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
847 AM CST Sun Feb 26 2017

.UPDATE...
Updated for morning discussion.

&&

.DISCUSSION...
Short term guidance is trending a little warmer today and with the
ample sun, relatively dry ground, and efficient mixing anticipated
through the day this seems reasonable and was incorporated into
the forecast update. The subtly increased temps will only work to
further lower afternoon RH values which has implications on the
fire weather situation, as discussed in the dedicated section in
this AFD. Otherwise, enjoy a pleasant Sunday with chances of rain
increasing greatly late tonight into tomorrow morning. /BB/

Prior discussion below:

Today through tonight....

A cool, clear morning is present throughout the ArkLaMiss. Morning
temperatures have fallen below average areawide, an uncommon event
this abnormally warm February. Below average temperatures this
morning will give way to above average temperatures by this
afternoon as the surface high shifts east of the area, setting up
return flow from the Gulf resulting in winds from the SE then S.
Upper level flow will be from the SW by this afternoon. Highs today
should reach mid to upper 60`s under sunny skies. The fire weather
threat will be more of a concern today as RH`s could fall below 20%
this afternoon before they begin to rise this evening. Winds should
peak near 10-12 kts, however if they overachieve the fire weather
threat will increase. Fire weather conditions will have to be
monitored throughout the day. A fire weather section is included
in the AFD.

Cloud cover will begin to increase this evening as moisture moves
into the area ahead of a weak disturbance embedded in SW flow. This
disturbance will also result in increasing shower/storm chances
overnight. PWAT`s will increase about 0.5"-0.7"areawide between
Sunday afternoon and Monday morning, reaching 1.2". Latest hires
guidance depicts showers/storms entering the region from the west
mainly after midnight, although some isolated shower activity
could enter the the counties and parishes along the MS River a few
hours earlier. The atmosphere will be supportive of some weak
elevated thunderstorms, but no strong or severe storms are
expected through 12Z. /jpm3/

Monday through the week...

Models are coming into better agreement for the active, yet complex,
weather pattern expected for this week. This will include potential
for severe storms.

After a rather dry airmass was in place over the weekend, moisture
will return to the region by Monday morning as southerly flow takes
place from Sunday onward. PW values will be around 1.3-1.5 inches
through the first half of the week as southwest flow aloft also sets
in. The first disturbance should move through Monday, beginning
early in the morning. Most models, including hi-res guidance, agrees
that there should be some kind of remnant MCS barreling through the
region that is a result of Sunday`s thunderstorm activity across
portions of Texas. This activity will enter western areas of the CWA
by 12Z Monday and continue through much of the ArkLaMiss during the
day Monday. The bulk of this activity should come through early in
the day while instability is not as high and exiting the southeast
by early afternoon, thus severe potential at least right now looks
low. The NAM seems to be more of the outlier in this scenario and
keeps much of the activity across the north, with some potential for
convection further south. There could be some afternoon convection
as afternoon heating occurs and creates decent instability, but
think that this will be much more isolated in nature after the
morning convective activity as well as increasing mid level heights
over the region by afternoon.

By Monday night, a warm front will make its way north across the
region. This will keep all convective activity confined generally
near the front with increased heights south of there(increasing even
more during the day on Tuesday). The upper jet will remain just to
our north and most of the area should remain capped through the day,
which will limit convective activity, though it won`t be out of the
question for there to be some isolated to potentially scattered
activity in the warm air advection regime, especially as afternoon
temperatures increase to the upper 70s and lower 80s across the
ArkLaMiss region. During the day Tuesday, a sfc low will develop
across Wisconsin and track east across the Great Lakes. As this
occurs, a cold front will drop south. When this front gets further
south, additional surface low will develop across the Mid-
Mississippi River Valley and track across the Ohio Valley Tuesday
night. As this occurs, the front will continue to drop south.
Showers and thunderstorms will develop along and ahead of this front
across portions of Arkansas and north Mississippi and Tennessee,
just to our north. Think that we should remain capped through much
of this time and most of the more potent activity will remain to our
north. However, it won`t be out of the question for there to be a
few storms in the north/northwest Delta Tuesday night.

The better chance for storms across the region and subsequently
severe storms will come Wednesday. The front will be just on our
northwest doorstep come daybreak Wednesday morning and should
progress southeast through the day. Ahead of the front, steep lapse
rates will be present as depicted by vertical totals around 27-30C
and 6.5-7C/km mid level lapse rates. Ample wind energy will be
present throughout the atmosphere as a 135kt upper jet rounds the
base of the upper trough. 0-1km wind shear will be around 30-40kts
with 50-60kts of deeper layer shear should be plentiful for damaging
winds as well as potential for tornadoes as well. 200-300 m2/s2 of
helicity should also be enough for tornadoes as well(though sig tor
parameters indicate better potential further north of our region).
Will continue mention of severe in HWO/graphics, especially for
Wednesday. There does remain a little bit of timing differences
between the GFS and ECMWF by roughly 6 hours or so, with the latter
bringing in storms closer to 18z. If this is the case, then
potential for severe storms should increased across the region.

In general, the front will pass through the region by evening and
storms will move out by then. Surface high pressure will move into
the region following the front. This will usher in more seasonable
weather with highs in the 60s and lows in the 40s through the end of
the week. /28/

&&

.AVIATION...
12Z TAF discussion:
VFR conditions will prevail through the day. Moderate winds from
the east will become more southerly as the day continues. Clouds
will begin to move into the area this evening. Chances of showers
will increase late in the period as a disturbance approaches from
the west.

&&

.FIRE WEATHER...
Fire danger will be a concern today as RH`s should range from 15
to 25 percent in the afternoon hours for a good portion of our
area. Winds will be moderate and from the south, maxing out at
near 10-12kts. The fuel moisture content will be below 10% for
most of the region. Conditions are expected to remain just below
red flag criteria with 20ft winds speeds being the limiting
factor. Still, we increased the category of fire danger this
afternoon from limited to elevated as open burning is discouraged
given the mentioned combination of factors. /BB/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       69  52  74  63 /   1  43  69  27
Meridian      68  47  70  61 /   1  21  61  28
Vicksburg     70  54  75  63 /   1  62  66  28
Hattiesburg   70  51  75  62 /   1  17  51  17
Natchez       71  57  75  65 /   1  42  64  21
Greenville    66  50  69  61 /   2  73  72  52
Greenwood     67  50  68  61 /   1  63  73  53

&&

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

&&

$$

JPM3/28/BB



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