Area Forecast Discussion
Issued by NWS Jackson, MS

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FXUS64 KJAN 240409 AAA

Area Forecast Discussion...UPDATED
National Weather Service Jackson MS
1009 PM CST Thu Feb 23 2017

Updated for evening discussion.


Evening surface analysis had a 994mb low over the central plains
and a 1011mb high centered just off the Mississippi Gulf coast.
The pressure gradient between these two features will likely keep
the southerly wind up through tonight with the exception of our
southeast zones. Across our southeast zones areas of dense fog are
expected and a Dense Fog Advisory has been issued from 4am until
9am. The forecast was updated to reflect this change. Otherwise,
the remainder of the forecast was on track. /22/

Prior discussion below:

It`s been a nice and warm afternoon under the influence of the
shortwave ridging and Bermuda surface high wedging through the
Appalachians down into our area. Due to that, the low stratus
clouds have lingered most of the afternoon near Columbus, which
has kept temperatures down. Elsewhere, clear skies and warm
conditions in the upper 70s with some areas reaching the low 80s.

Expect warm conditions tonight as conditions begin to become warm
in advance of a cold front moving through the area Friday into
Friday night. Expect warmer lows, still some 10-15 degrees above
normal. We won`t have as much of an issue with crossover
temperatures tonight as we did the past few nights, but still have
some opportunity for lows in south Mississippi to get about 3-5
degrees below the afternoon dewpoints today. Based on the
placement of dense fog in the east and southeast last night and
gradual building of the shortwave ridging southeast, expect that
corridor of patchy dense fog to be confined to south of the I-20
corridor, mainly from a line from Brookhaven, MS to Quitman, MS to
south. The most dense fog will likely be near Hattiesburg but
could extend up to just south of the Jackson Metro and Meridian
area. Added a limited threat for patchy dense fog to the
HWO/graphics based on this thinking. Couldn`t rule out some of
these low clouds/fog could move into the I-20 corridor but best
confidence will be confined to the south.

As the upper trough deepens through the Rockies into the central
Plains, ~995mb surface low will be moving into the upper
Mississippi Valley and into the Great Lakes. This will help drag a
cold front into our area tomorrow. Anomalously warm boundary layer
temperatures, with us warming near 16 degrees C at 850 and 17-18
deg C at 925mb, will support a very warm afternoon tomorrow.
However, an increase in isentropic lift and cloud cover along the
front and any lingering low stratus could hinder some warming. Due
to that, didn`t go as warm as some MOS guidance but still warm
into the upper 70s in the northwest Delta to low 80s elsewhere.
Some areas along and south of I-20 could again reach near record
highs Friday. There are some decent lapse rates aloft but the
subsidence inversion/cap looks very strong just above 850mb and
this will limit much of any convection/showers until likely near
mid-afternoon when enough lift could weaken that cap. There also
looks to be limited moisture but there will be some shear around.
However, there looks to be enough subsidence to keep much of any
thunder chances low and only, if any, shower chances near mid-
afternoon or so, likely after 3PM along and just west of I-55
corridor. Hi-res guidance is really weak and unimpressive so for
now just kept slight chance POPs of showers in the mid-afternoon.

Friday night through Wednesday:

At the beginning of the period, southwesterly mid level flow
pattern will be in the process of ushering a shortwave across the
upper MS river valley while its attendant cold front moves through
the forecast area. Decent lapse rates, CAPEs and shear will be
available in the warm sector ahead of the boundary, but the
strength of the inversion above the boundary layer will be as such
to prevent convective development until right at frontal passage.
The majority of the CAM guidance is not impressed with the setup
either as these show no more than showers along and ahead of the
boundary mainly Friday evening.

A quick shot of more seasonable temperatures will overspread the
region for the weekend, but mid level zonal flow will quickly shift
surface high pressure eastward with moist southerly flow returning
Sunday afternoon. At the same time, a fast moving mid level
shortwave embedded in the southern stream will move out of the
southwest CONUS and into west TX. Model solutions vary with this
feature with the GFS being strongest and most aggressive with its
surface reflection low pressure area/front. Nevertheless, models
do agree that widespread isentropic/warm advection rains will
develop over the ArkLaTex region and spread into the forecast area
Monday/Tuesday. Depending on the eventual positioning of the
surface boundary, at present Wednesday looks to remain unsettled
as well. /26/


00Z TAF discussion: CLR skies noted on satl imagery at 00Z. VFR
conds will prevail areawide this evening but IFR/LIFR conditions
due to low stratus and some patchy dense fog wl move in from the
south toward 09Z. These IFR/LIFR conditions are expected
especially at HBG. Conditions wl improve to VFR areawide by 16Z.
Gusty south winds are also expected Friday. /22/


Jackson       55  82  46  61 /   1  15  22   4
Meridian      52  81  48  63 /   0   4  28   5
Vicksburg     56  82  44  60 /   3  16  19   3
Hattiesburg   55  81  51  67 /   0   4  24   3
Natchez       57  82  46  61 /   3  16  16   3
Greenville    56  77  42  55 /   3  15  11   4
Greenwood     56  81  42  56 /   2  16  17   5


MS...Dense Fog Advisory from 4 AM to 9 AM CST Friday for MSZ056>058-




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