Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 180342 AAA
AFDJAN

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
942 PM CST Sun Dec 17 2017

...DENSE FOG WILL BE A CONCERN THROUGH THE NIGHT...

.UPDATE...
Updated for evening discussion.

&&

.DISCUSSION...

Mid evening update:

The previous forecast update remains pretty much on track.
Guidance has trended less bullish with potential for showers
coming back into southern zones late tonight into early on Monday,
although at least some isolated showers should occur. This only
increases potential for continued worsening low ceiling and fog
situation as solid areas of rain would tend to disperse the fog a
bit. Dense fog is not widespread at this juncture but confidence
is rather high the overall situation will continue to worsen due
to cool ground temps instigating a build-down of very low ceilings
toward the surface with time. Expecting fog could hang on quite a
while into the morning tomorrow in some areas but will hold on to
the 9 am expiration time for now with the thought that truly dense
fog will be mostly gone by that time. /BB/

Prior discussion below:

Early evening update:

Visibilities were already dropping to a quarter mile or less in a
few spots over southeastern MS by 5 pm and latest guidance
suggests widespread low ceilings will have a tendency to build
down toward the surface through the night owing to relatively cool
ground temperatures. Went ahead and hit fog a lot harder in the
forecast and included elevated and significant fog hazard areas in
the latest HWO and related graphic. Dense fog advisory has been
issued through 9 am tomorrow morning for much of southern and
eastern MS but there is certainly potential the advisory may need
to be expanded to cover more (if not all) of the area later this
evening, depending on how things trend. Finally, the potential for
showers and embedded thunderstorms coming back into southern zones
from the west late tonight into early Monday morning may help
break up the fog a bit, but that detail will be handled later
into the night. /BB/

Tonight and Monday:

A 594dam high nearly centered over the Bahamas will remain in
place through Monday while a weakening 557dam closed low over the
desert southwest tracks east into west Texas. This will maintain
southwest flow aloft across our CWA and atop of a nearly
stationary surface boundary across our southern zones. This will
lead to deep moisture increasing across our region and the
redevelopment of showers and a few thunderstorms mainly after
midnight tonight then continuing through Monday. Local radar still
had light rain tracking across our southeast most zones at mid
afternoon. This activity is expected to shift southeast of our CWA
by evening. A lull in precipitation is expected most of this
evening but hi-res models show redevelopment from the southwest
toward midnight. After midnight patchy fog development is expected
over most of our area with some dense fog possible in the east.
Showers and a few storms may help break up the dense fog prior to
sunrise so an Advisory is not anticipated at this time. Inch and a
half PWATs and lower 60 dew points are expected to surge north to
Interstate 20 Monday. Most of the convection Monday is expected
along and south of I-20. Temperatures will continue to moderate
tonight and bottom out well above normal. Despite the cloud cover
and rain Monday afternoon highs will top out above normal as
well. /22/

Monday Night through Sunday:

As an upper-level low pressure system swings out of the American
Southwest on Monday night into Tuesday, expect a stream of
atmospheric moisture to continue being lifted over our region as
we are positioned between the upper low to our west and a ridge of
high pressure to our southeast. The primary focus for rain chances
will shift to northern Louisiana, southern Arkansas, and northern
Mississippi by Tuesday night as a developing surface low lifts
from the TX coastline toward the ArkLaMiss Delta. Forecast
soundings indicate a mostly saturated column with lapse rates
nearly moist adiabatic during the overnight period, however warm
advection at the surface could be enough to generate modest
instability in the warm sector. Decent deep- and low-level shear
does suggest that showers and any storms could become organized.
At this time, the conditional threat is too low to highlight in
our Hazardous Weather Outlook products.

Warm weather then expected to continue through the remainder of
the week as southerly winds quickly return ahead of the next
developing low pressure system. Model guidance continues to waiver
on the exact details for the closely-watched Christmas holiday
weekend, with any trends in guidance difficult to discern at this
time. In general, the ECMWF and GFS increase rain chances across
our area Friday and into the weekend as a deep upper-level trough
sets up over the northern CONUS. Latest operational runs show warm
weather and some chance for rain (especially north) on Christmas
Eve and Christmas Day, however one only needs look back at the
previous run or two to find cold weather with rain to our east on
those 2 days. So the official forecast for the weekend is an
attempt to smooth out the possibilities and stick near a consensus
of current and recent solutions, while not going toward one
extreme or the other. Stay tuned for updates to the forecast for
both midweek and late-week as details come into better focus.
/NF/

&&

.AVIATION...
00Z TAF discussion:

IFR to LIFR conditions are expected to be quite widespread across
the region tonight through 14 to 15 UTC tomorrow morning due to a
combination of low clouds and occasionally thick fog. The chances
for showers and isolated thunderstorms will increase along and
south of I-20 late tonight through the morning tomorrow. Expect
heavier showers might actually tend to improve flight cats in
some areas as visibilities increase and ceilings lift a bit. Regardless,
the potential for VFR conditions at any sites through tomorrow
afternoon is low although anticipate true LIFR conditions should
relent in all areas by 10 am or so tomorrow. Winds will be light
and variable at the surface. /BB/

&&

.PRELIMINARY POINT TEMPS/POPS...
Jackson       55  66  57  74 /   9  24  30  48
Meridian      52  64  55  72 /  13  29  24  39
Vicksburg     52  65  57  75 /  13  21  40  60
Hattiesburg   59  67  60  75 /  11  48  20  24
Natchez       56  67  59  76 /  26  47  33  49
Greenville    46  63  52  69 /   9   9  54  79
Greenwood     48  64  52  71 /   9   9  49  74

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...Dense Fog Advisory until 9 AM CST Monday for MSZ018-019-025>066-
     072>074.

LA...Dense Fog Advisory until 9 AM CST Monday for LAZ007>009-015-016-
     023>026.

AR...Dense Fog Advisory until 9 AM CST Monday for ARZ074-075.


&&

$$

NF/22/BB



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