234 
fxus64 kjan 200118 aaa 
afdjan 


Area forecast discussion...updated 
National Weather Service Jackson MS 
818 PM CDT Friday Mar 19 2010 


Update...only change made this evening was to decrease cloud cover 
through the night and update hourly dew points based on latest ob 
trends. Latest satellite imagery shows clear skies developing with 
the loss of sun...and expect mostly clear skies to prevail through 
sunrise. Updated products are out...updated aviation discussion 
below. /Bk/ 


&& 


Previous discussion... /issued 250 PM CDT Friday Mar 19 2010/ 


Short term...tonight through Sunday night...NAM and GFS in pretty 
good agreement today with the evolution of middle/upper level system 
currently gaining strength over The Rockies. This system will 
continue to deepen tonight as 300 mb 110+ knot jet rounds the base of 
the cold core. Other than a modest cold front...surface features 
look rather benign with no lows assicated with the frontal boundary 
as it moves out of the plains and into the Red River valley 
overnight tonight. One other aspect Worth noting for tonight is the 
middle/upper level potential vorticity maximum embedded in the jet axis 
and its potential impact once it reaches the baroclinic zone. 


Moving into Saturday/Saturday night...as the upper level jet axis 
and associated potential vorticity maximum begins to encounter the 
low level baroclinic zone...surface cyclogenesis increases rapidly 
over Arkansas/la with a low forming over this region by 00z Sunday. It 
then lifts up into east central Arkansas overnight and occludes as 
potential vorticity maximum overtakes the low. Although instability 
in the warm sector will be low (capes generally less than 50 
j/kg)...strong warm advection in response to deepening low should 
force thunderstorms (k index values 30-35 all through this area) to 
develop along the cold front. With such low instability...do not 
expect any severe storms...but some could become strong in the far 
southeast closer to somewhat more unstable air. Main threat in those 
areas will be wind gusts. 


Occlusion does not last long as new surface low looks to form on the 
front over Kentucky due to proximity of high pv air and upper level jet 
axis having now rounded the base of the system and pulling into the 
Carolinas by Sunday evening. Meanwhile...cold air will build into 
the region as middle level cold core slowly pushes across north MS. 
Isentropic lift assoicated with the advancing cold core and residual 
moisture will produce intermittent rain across the region...but 
mainly in the north. It is also in the north where a few flurries 
may mix in with the rain as model soundings show all below freezing 
except in shallow layer right near the ground. /26/ 


Long term...Monday through Thursday...the upper low lifts out 
Monday and weak surface troughing over the area washes out. Flat 
upper ridging develops by Monday night with surface ridging into the 
area by sunrise Tuesday. Forecast soundings show clouds clearing 
with the possibility of shallow fog developing Monday night. Weak 
high pressure continues Tuesday before shifting east of the area 
Tuesday evening. The first in a series of shortwaves lifts into the 
area in developing SW flow Wednesday. Moisture will be on the 
increase Wednesday night in developing southerly flow ahead of a surface 
trough that will shift into the arklatex Thursday. 


MOS guidance has been persistent in keeping Sunday night low 
temperatures on the warm side considering the degree of cold air 
advection expected. With a slowly decreasing surface pressure 
gradient...cloud cover and precipitation chances...will follow MOS guidance 
for now but with limited confidence. However...MOS low temperatures were 
cut for Monday night considering decreasing clouds and diminishing 
winds. MOS temperature guidance followed otherwise. 


&& 


Aviation...VFR conditions will persist tonight across the area as 
high and middle clouds increase from west to east through the overnight 
hours and into Saturday. Low level moisture will also gradually 
increase through the day Saturday...but again VFR conditions will 
persist. Southerly winds on Saturday will also increase between 
10-15 knots...with a few higher gusts around 20 knots possible 
across the Delta Region...kglh and kgwo. By late Saturday 
afternoon...as a storm system approaches from the west...some 
scattered showers...and perhaps an isolated thunderstorms...could 
affect far western portions of the area...kglh and kgwo. However... 
any prevailing shower activity that's expected will affect taf sites 
late Saturday night into early Sunday morning. /Ac/ 


&& 


Preliminary point temps/pops... 
Jackson 46 71 41 46 / 0 17 100 53 
Meridian 40 72 49 53 / 0 10 100 58 
Vicksburg 46 71 39 45 / 0 33 100 53 
Hattiesburg 44 73 50 55 / 0 10 100 28 
Natchez 47 73 38 46 / 0 40 100 42 
Greenville 48 69 39 45 / 0 36 100 70 
Greenwood 48 72 43 46 / 0 20 100 72 


&& 


Jan watches/warnings/advisories... 
MS...none. 
La...none. 
Arkansas...none. 
&& 


$$ 


Bk/ac