328 
fxus64 kjan 072120 
afdjan 


Area forecast discussion 
National Weather Service Jackson MS 
320 PM CST Wednesday Jan 7 2009 


Discussion...look for dry and clear conditions to last until midday 
Friday before things begin to change and moisten up ahead of our next 
weather system. Low level flow will generally be out of the S/SW 
until late Friday. The only exception will be for early Thursday when we 
will see a weak surface trough move just to our north and push a weak surface 
boundary into the north/NE County Warning Area. 


Solid warm air advection will develop by Friday afternoon as a surface low and healthy 
cold front take shape over the plains and push into the County Warning Area Friday 
night into Sat morning. Friday north/Sat are the main focus periods this 
forecast due to the mentioned cold front and associated precipitation 
chances. There are some minor timing issues with the models...but 
even the slower models are beginning to speed up and get more in 
line with the GFS...GFS ensembles...sref and Canadian. I will lean 
heavily with the faster guidance as systems moving through northwest flow 
patterns are nearly always faster. This will result in precipitation 
chances higher after midnight Friday north lingering until noon Sat. 


As for forecast elements...guidance temperatures look good tonight-Friday and have 
followed. The main adjacent were to lows Friday north and highs on Sat. The 
airmass that will be moving into the region will be quite cold. Look 
for lows Friday north to range from the lower 40s in the northwest to middle 50s southeast. 
The timing of the front will be critical over the southeast 1/3rd and will 
not get too aggressive at this point as a slight shift in timing 
will have huge impacts. As for highs Sat...strong cold air advection will keep 
temperatures from rising. Look for highs to occur early and hold steady 
with readings likely falling by afternoon. As for probability of precipitation...guidance values 
looked good Friday north. With the faster solution preferred...I have gone 
with less probability of precipitation Sat and have followed the 00z GFS probability of precipitation across the 
west/northwest half. I did increase probability of precipitation to 30-40% across the southeast half on Sat 
to match the latest guidance and timing of the front. Overall...not much 
rain with only .10 to .25 expected as totals. /Cme/ 


Previous long term...high pressure builds in Sunday and maintains 
through Monday. The next cold front drapes across the Midwest Monday 
dips into the northern zones around Tuesday. Looks like mostly 
clouds...but guidance came in with slight chance values...so went 
with the small values. The upper ridge builds into the Pacific 
northwest around Sunday/Monday...while the trough shifts into the 
northwest. The northwest flow will bring plenty of cold air into the 
region. Highs by Tuesday and Wednesday may struggle to get out of 
the 40s. Beyond Wednesday...models suggest an Arctic airmass will 
settle into the region suggesting lower teens/single digits for lows 
and 20s for highs. Will be interesting to see how the models evolve 
over the next week and what the cold air will look like on the next 
few runs. 


Went with guidance temperatures for the most part...lowered values several 
degrees around the end of the period to account for the colder air. 


&& 


Aviation...VFR conditions will prevail with SW to west surface winds. 


&& 


Preliminary point temps/pops... 
Jackson 40 59 39 69 / 0 0 0 0 
Meridian 39 62 34 66 / 0 0 0 0 
Vicksburg 41 60 40 70 / 0 0 0 0 
Hattiesburg 40 68 38 71 / 0 0 0 0 
Natchez 42 62 42 71 / 0 0 0 0 
Greenville 39 55 39 66 / 0 0 0 4 
Greenwood 39 54 37 66 / 0 0 0 0 


&& 


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


$$ 


Cme