732 
fxus64 kjan 210944 
afdjan 


Area forecast discussion 
National Weather Service Jackson MS 
406 am CDT sun Mar 21 2010 


Short term...a cold front was moving across the forecast area this 
morning and was producing a large swath of precipitation across the region. 
A cold upper low was approaching from the west and precipitation upstream 
had switched over to snow at many areas across eastern Texas and western la. We 
will see a light rain/snow mix...possibly periods of all light 
snow...develop over northwestern/west-central sections of the arklamiss this 
morning. A rain/snow mix can be expected eastward later this morning in 
to the afternoon as the cold core shifts into the region. No snow 
accumulations will occur because the ground has not cooled enough 
and a shallow layer near the surface will remain above freezing as 
the cold core moves through. The surface pressure gradient will 
increase in the wake of the cold front...which will exit eastern zones 
this afternoon. A lake Wind Advisory has been issued for western zones 
for today and the lake Wind Advisory issued earlier for areas lakes 
remains in effect. 


Weak forcing will continue across the region in the wake of the 
primary cold front. A secondary surface trough will gradually pivot 
around the surface low into northwestern zones tonight and weak isentropic 
lift develops in response to warming that occurs as the cold core 
shifts to the east. A forecast concern for tonight involves lows for 
the region. MOS has been consistent in keeping relatively warm 
temperatures...especially for western zones...for tonight as the cold 
core moves out. Will cut lows slightly considering the colder air 
mass that will move in behind the front but cloud cover and light 
wind will persist to prevent optimal radiational cooling. 


Rain chances finally end from the west Monday as heights and surface 
pressure increase from the West. Flat ridging develops from the west 
Monday night and clouds are forecast to clear. The surface ridge 
line shifts into the forecast area by sunrise Tuesday and once again 
MOS low temperatures look a bit warm. Wind calms and skies clear so MOS 
lows have been cut to keep Monday night temperatures from the middle 30s to 
near 40 degrees. 


Long term...Tuesday through Saturday...the sref...Canadian...UKMET 
and the GFS as well as GFS ensembles were in general agreement with 
the upper pattern with some minor timing differences. Flat upper 
ridging develops by Tuesday with surface ridging into the area by 
early Tuesday. 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 by Wednesday night in developing 
southerly flow ahead of a cold front that will shift into the arklamiss 
Thursday night. There will be enough instability lapse rate wise and 
some cape for showers and mostly elevated thunderstorms with this 
system for Thursday through Friday. The rains will end from the west 
by Friday night. Another shortwave will approach the region from the 
plains on Saturday. This will send a cold front and isolated 
thunderstorms into the region for Saturday night. See no strong 
storms with any of these systems at this time. 


Went close to mostly ensemble guidance as the upper flow flattens out 
for the period until a confluent system comes for Thursday into 
Friday. Went close to ensemble temperatures for the weekend system as well. 
Made some downward adjustments to MOS probability of precipitation for Wednesday night as 
the system approaches. Also increased probability of precipitation slightly for Thursday 
night into Friday. Otherwise went close to mex probability of precipitation for the rest of 
the period./17/ 




&& 


Aviation...a cold front will push east through the area...exiting 
eastern zones around sunrise. A large swath of showers will swing across 
the area...decreasing in coverage from the SW today although 
scattered showers will continue through the afternoon. Periods of 
light snow will become mixed with rain over northwestern/west-central zones this 
morning with a chance of rain and snow mixed spreading across eastern 
zones today. Widespread MVFR ceilings are expected with occasional IFR 
ceilings/visibility in precipitation and fog. 


&& 


Preliminary point temps/pops... 
Jackson 44 37 50 38 / 52 41 18 0 
Meridian 47 36 51 38 / 57 35 19 0 
Vicksburg 42 37 51 39 / 53 46 15 0 
Hattiesburg 54 37 54 37 / 37 19 10 6 
Natchez 44 36 51 38 / 41 34 6 0 
Greenville 43 38 53 40 / 68 61 27 0 
Greenwood 44 36 51 39 / 69 53 30 0 


&& 


Jan watches/warnings/advisories... 
MS...lake Wind Advisory until 7 PM CDT this evening for msz018-019- 
025-026-030-031-034-035-040>043-047-049-052-053-059-060. 


La...Lake Wind Advisory until 7 PM CDT this evening for laz007-008- 
015-016-023>026. 


Lake Wind Advisory until 7 PM CDT this evening for laz009. 


Arkansas...lake Wind Advisory until 7 PM CDT this evening for arz074. 


Lake Wind Advisory until 7 PM CDT this evening for arz075. 


&& 


$$ 
03/17