FXUS64 KJAN 160604

Area Forecast Discussion
National Weather Service Jackson MS
1204 AM CST Sat Dec 16 2017

Updated for 06Z aviation discussion


06Z TAF discussion:
VFR conditions will prevail through Saturday evening. Expect
lowering ceilings and increasing SHRA chances toward daybreak
Sunday in the GLH/GWO/JAN/HKS area. /EC/


Surface ridging will remain in place across the ArkLaMiss tonight
with a drier and cooler airmass in place. Efficient radiational
cooling is already underway across much of the area as the
boundary layer has already decoupled with calm surface winds. The
high cloud cover is slowly thinning out as drier air and
isentropic descent continue to move in and what cloud cover there
is hasn`t hindered the radiational cooling. In fact, some current
obs are already at or within a degree or two of the forecast lows,
therefore the main focus with this update was to lower min temps
in line with the low end of guidance and the latest trends. Also
adjusted the hourly diurnal temperature curve, otherwise no other
changes were needed. /TW/

Prior discussion below:

Tonight through Saturday:

A quiet period will ensue through the period as cold dry high
pressure will slowly filter through the region. Expect the pattern
to consist of a 1025mb surface high building towards the eastern
seaboard while better isentropic lift will continue to filter over
the region. This will lead to slow moist southerly flow developing
and PWs closer to a half inch or so along and south of the Highway
84 corridor. Expect the rest of the area strong ridging to be over
the eastern half of the area as a surface high builds to our east.
In addition, as the polar longwave trough digs off into the
Atlantic, the closed mid-level low near the Great Basin & western
Mexico will remain somewhat stretched out and phased across our
area. This will lead to continued isentropic subsidence overnight,
which will help clear out the clouds. We should be able to radiate
well below freezing, even into the mid-upper 20s overnight due to
better subsidence.

As a longwave trough digs down the eastern Pacific seaboard and
through the Great Basin, this will help kick out the closed low
stalled south of the Great Basin. This will gradually help mid-level
ridge axis to swing into the area on Saturday. As the surface high
builds off the Atlantic seaboard, expect west-southwesterly return
flow to only slowly increase moisture from the southwest. Due to
that, PWs will only slowly increase towards three quarters to around
an inch in the southwestern portions of the area (i.e. northeast
Louisiana into southwest Mississippi). Main thing will be there
should be enough isentropic lift in the 310-325K Theta E layers to
help some mid-high level clouds to move back into the area by mid-
afternoon on Saturday. In advance of that, thermal profiles warm a
few degrees, so expect near normal high temperatures in the upper
50s to near 60 degrees. If clouds move in quick enough, that could
hamper warming some, even with somewhat cool thermal profiles. /DC/

Sunday through Thursday:

A complicated weather pattern will set up on Sunday and push a
couple disturbances through our region throughout the week. To start
off with, as a shortwave moves through the TX/OK panhandles and into
the Plains Sunday morning, a front collides with a surge of
moisture out of the Gulf of Mexico. The moisture along with ample
forcing from the shortwave will provide our region with good rain
chances to start off the week. PWs will surge above 1.5" in south
MS Sunday morning, which is quite anomalous for this time of
year. Therefore efficient rainfall can be expected in a short
amount of time as much of the area could receive at least an inch
of rainfall Sunday morning when the front moves through. The
shear vectors over our central CWA and just to our west will be
substantial (values up to 40-60 kts of 0-3km shear). In the south,
the bulk shear will be closer to 30-40 kts. And while the
greatest CAPE values remain south of the coast on Sunday, the
instability will build into the afternoon and will be enough for
thunder and possibly a strong storm or two in the Pine Belt. The
front slows down in the afternoon and eventually will stall along
the coast.

After Sunday, the model patterns vary drastically. The Euro/Canadian
show a cutoff low ejecting out of the 4 corners region into Texas
and drawing up moisture from the Gulf and then bringing another
round of rainfall/storms to our region. Though, the two models
vary on timing. The GFS has a constant stream of moisture out of
the Gulf into our region along the stalled frontal boundary. A
similar cutoff low in the 4 corners region then ejects into the
southern Plains and kicks the moisture out of here late on Tuesday.
For the forecast, decided to go with a blend of the solutions
leaning more towards the Euro. All models seem to agree on a
quiet Thursday however. /10/


Jackson       26  60  45  65 /   0   2  37  83
Meridian      24  57  42  62 /   0   2   9  75
Vicksburg     24  60  45  66 /   0   2  72  77
Hattiesburg   28  57  44  70 /   3   2  10  81
Natchez       26  60  47  68 /   1   4  63  81
Greenville    26  58  43  61 /   0   1  84  65
Greenwood     26  59  41  61 /   0   1  66  79





NWS JAN Office Area Forecast Discussion