Area Forecast Discussion
Issued by NWS Jackson, MS

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527
FXUS64 KJAN 260226 AAA
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
826 PM CST Sun Feb 25 2018

...MORE LOCALLY HEAVY RAIN AND EMBEDDED THUNDERSTORMS TONIGHT...

.UPDATE...
Updated for evening discussion.

&&

.DISCUSSION...

Evening update discussion:

Rainfall rates are increasing across southwestern LA and now
extending into the southwest portion of the forecast area along
and north of a lingering frontal boundary stalled across the
region. Uptick in precipitation is tied to the arrival of a decent
piece of shortwave energy aloft into the Lower Mississippi Valley
with associated synoptic lift enhanced by warm air and moisture
advection just east of a surface low developing along mentioned
stalled front. Expecting this surface wave to transition east-
northeast-ward down the stalled front through the night with
locally heavy rains and even embedded thunderstorms moving through
the heart of the region in tandem. The going advertisement of a
LIMITED flash flood risk in the graphics and HWO is certainly
valid, especially over southwestern zones where already saturated
ground will lead to flooding issues more easily. For this update
we also introduced a MARGINAL risk of severe thunderstorms through
the night in far south-central and southeastern zones. These areas
have a chance to access surface-based instability as the stalled
frontal zone buckles north a bit just downstream of the incoming
low pressure wave. While thunderstorms are possible well north of
the boundary it will likely only be where storms are rooted close
to the surface (like potentially in the latter case) that severe
weather has some opportunity to occur. The main risk with any
severe storm will be damaging wind gusts, although a brief tornado
cannot be completely ruled out.

Otherwise, expect the bulk of the rain to be starting to move out
of the region from west to east after midnight through just after
daybreak. Temperatures will actually have a chance to cool down
into the 40s in northwestern zones by daybreak, but elsewhere
expect lows generally in the 50s. /BB/

Prior discussion below:

Rest of Today through Monday...Shower activity continues to increase
in both coverage and intensity across the forecast area this
afternoon as anticipated.  Through this evening and overnight, the
once stalled front is expected to begin lifting north in response to
a shortwave swinging east into the Mid-South region.  Areas of
ascent ahead of this trough, will lift northeast in the vicinity of
the front and across the ArkLaMiss this evening into tonight.  This
will set the stage for a good coverage of moderate, to occasionally
heavy, rain likewise shifting east northeast through the region.

Rainfall amounts on the order of one to two inches will be possible
through early Monday morning with this scenario.  This could
potentially lead to some localized flash flooding, as well as
further aggravate ongoing river flooding, or just further add to
some already high river levels across the region. Thus, I`ll
maintain a "Limited" risk of flash flooding in the HWO.

A few thunderstorms will be possible with this activity, primarily
south of the Interstate 20 corridor, in the warm-sector.  That said,
this area has been worked-over pretty good today by ongoing light
shower activity.  However, due to just enough deep-layer wind shear
and instability being advertised over mainly far southern portions
of the CWA late tonight, I can`t rule out a stray strong storm over
mainly Southeast Mississippi.  Also, while confidence is quite low,
a stray storm could perhaps briefly reach severe limits over mainly
Southeast Mississippi as well late tonight, with gusty winds being
the primary concern with any such storms.  Again, because of the
current low confidence in this, I`ll not introduce the mention of
severe storms into the HWO on this afternoon`s package.

Activity will come to an end from west to east across the forecast
area through the course of Monday morning.  High pressure will build
into the region, with some slightly cooler drier air advecting south
into the forecast area.  By mid-afternoon, highs will be topping out
from the middle 60s to the lower 70s, with a good bit of sunshine
being observed across the region. /19/

Monday night through Sunday...Come Monday evening wl still have a
dry airmass over our CWA with PWATs less than a half inch north
of Highway 84. This will be due in part to a 1028mb surface high
centered over the Ohio valley and ridging back across the
southeast states. This high will shift to the mid Atlantic
seaboard by Tuesday morning as our winds aloft back more to the
southwest downstream of a closed low dropping over southern
California. Monday night will be dry but rain chances will
increase from the southwest Tuesday as WAA increases back over our
region ahead of the approaching upper level low and disturbances
rounding its base. The old cold front will lift back north through
our CWA during the day. Models are in good agreement that it will
take until noon to get measurable rainfall in our CWA. Despite
the increasing rain chances and associated cloud cover,
temperatures will top out well above normal in the lower 70s at
most locations. Mild temperatures will continue Tuesday night as
overcast skies and WAA hold temperatures in the 60s. A shortwave
within the southwest flow aloft will enhance convection along the
warm front Tuesday night. Model consensus suggests one to two
inches could fall Tuesday night over our northwest and northern
zones where recent heavy rainfall occurred. Rain chances and
amounts will lower Wednesday as the shortwave departs the region
but closed low will be opening up over the Southern and Central
Plains Wednesday night and lead to another round of heavy rainfall
of one to two inches across our northern zones. There will also
exist a limited threat of severe storms over our Delta Wednesday
evening as well. Considering the recent heavy rainfall over the
area, a Flash Flood Watch may be needed by Wednesday night lasting
into Thursday morning before the associated cold front swings
through and ends the rain. Cooler and drier air is expected back
over the whole CWA by Thursday evening. Morning lows Friday will
be more seasonal in the 40s. Dry weather and slightly above normal
temperatures are expected Friday through the weekend. /22/

&&

.AVIATION...
00Z TAF discussion:

Not a terribly great night for flying across the region as a
frontal boundary and incoming disturbance create widespread rain
showers and MVFR to IFR ceilings. Rainfall rates should pick up in
many areas through the evening hours with embedded thunderstorms
as well. Some locations (such as HBG) are mainly VFR currently,
but expect conditions and flight cats to go downhill pretty
rapidly later on this evening. Winds will be variable from the
east through north tonight. Clouds and ceilings will attempt to
gradually improve from northwest to southeast tomorrow morning
through tomorrow afternoon with precipitation generally ending
well before flight cats improve to VFR. /BB/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       54  69  46  73 / 100  12   2  28
Meridian      56  69  43  72 /  97  19   2  12
Vicksburg     52  68  47  72 / 100   7   2  41
Hattiesburg   61  73  52  75 /  92  39   4  23
Natchez       53  68  50  73 /  98   8   4  46
Greenville    45  65  42  68 /  81   5   0  30
Greenwood     49  67  41  71 /  94   7   0  18

&&

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

&&

$$

19/22/BB



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