Weather

090 
fxus64 kjan 060240 aaa 
afdjan 


Area forecast discussion...updated 
National Weather Service Jackson MS 
840 PM CST Monday Jan 5 2009 


Discussion...a few changes were needed to the forecast this evening. 
The boundary is currently located across the extreme southeast 
portions of the County warning forecast area...or stretched from just south of mei to just 
south of hez. Locations south of the front including mcb and hbg have 
seen decent warming the past couple of hours with middle to upper 60s 
seen over this area this hour. North of the boundary temperatures 
have been able to cool a little more than expected with some sites 
dropping below the forecasted low. The boundary is expected to slowly 
drift to the north this evening and during the overnight hours so 
temperatures should begin to warm through tonight. Based on current 
conditions have went ahead and updated lows and hourly temperatures 
to allow for a cooler start in the north. 


The weather grids through the remainder of the night look reasonable 
and do not anticipate any changes at this time. Widespread rain with 
an occasional embedded lightning strike will continue through the 
night. Little has changed to the current thinking of the flood 
potential. The bulk of the rain from today has fallen across the 
Flash Flood Watch area and the position of the heaviest rain should 
change little over the next 12-24 hours. So will continue the current 
Flash Flood Watch as it is. 


Otherwise no other changes to the going forecast is needed this 
evening. Updated products will be sent and posted to the web shortly. 


&& 


Previous discussion...tonight through Tuesday night...more active 
weather in the short term. Main focus continues to be on the upcoming 
heavy rain/flooding potential and severe weather risk over the 
southeast for the next 24-36 hours. The cold front pushed south of our 
area this morning but has since stalled and has drifted northward a 
tad. Latest surface analysis the stalled front between Hattiesburg and 
Pine belt stretching west to McComb and then southwest across south 
central Louisiana. Temperatures have been tough today and were 
running in the lower 60s around Hattiesburg but Natchez was still 48 
degrees at 3 PM and Greenville was 34 degrees. Widespread light to 
moderate rain was already spreading across the area this afternoon 
and more is on the way for tonight and Tuesday. Water vapor 
imagery/RUC analysis shows the approaching middle-upper trough over the 
Desert Southwest. Warm air advection will increase tonight and Tuesday ahead of the 
approaching trough. This and a surface low over the western Gulf that is 
expected to ride up the boundary tonight will cause the surface front to 
move northward a bit. The boundary is not expected to move quite as 
far north by Tuesday morning as previous model runs indicated and 
will likely remain south of a line from Meridian to Natchez. This is 
expected to help limit our severe weather threat Tuesday to a over 
the southeast. Heavy rainfall is still expected along and northwest of the 
surface boundary tonight and Tuesday. The amounts and axis of greatest 
rainfall has changed little from previous thinking...very near the 
Natchez trace. As the upper trough draws closer Tuesday a second 
surface low is expected to rapidly deepen and track along the stalled 
front into Tuesday afternoon. This feature is expected to enhance 
heavy rainfall potential over the central portions and severe storm 
potential mainly in the southeast. This second low is expected to be 
over the southern Appalachians by midnight Tuesday night. Shifting 
the focus for severe weather and heavy rainfall east of our County warning forecast area. The 
trailing upper trough will keep light rain chances in the forecast 
though until it passes Wednesday morning. /22/ 


Long term...things quiet down significantly Tuesday night after the 
front moves through. A drier air mass begins to move into the region 
but the driest air holds off until the second lobe of the surface low 
pivots through after midnight. Healthy low level cold air advection 
will result in a sharp 850 mb temperature trough that will trap low 
level moisture Tuesday night into early Wednesday morning. The deep 
long wave trough moves in late Tuesday night to maintain a good 
chance of rain...mainly over northern zones...through early Wednesday 
morning. Trended toward slightly cooler ensemble temperatures for Wednesday and 
Wednesday night due to strength of the long wave trough. Sunshine 
will return by Wednesday afternoon when the upper trough lifts out 
and the 850 mb temperature trough is eroded to allow moisture to mix out. 
Low level ridging will develop to maintain fair skies Thursday 
through Thursday night and allow warmer temperatures Thursday 
afternoon. Temperatures remain warm Friday in increasing low level 
southwesterly flow ahead of the next frontal system. 


Significant model differences continue for next weekend. The Euro 
remains the slower solution but GFS MOS was followed for Friday 
since it matches the lowest ensemble member and keeps Friday dry. 
Confidence is low for the weekend forecast at this time. The slower 
Euro solution looks more reasonable over the deeper faster GFS but 
the Euro remains the outlier among the extended models including the 
Canadian and ensemble solutions. The Euro is just beginning to 
advect a cooler air mass into the region Sunday while the GFS has 
shifted the cooler high eastward and is already setting up warm air 
advection at lower levels. Followed GFS MOS for now considering 
general extended model consensus and fact that its numbers generally 
coincide with the ensemble numbers favoring the slowest members 
solution. /03/ 




&& 


Aviation...rain will continue to impact all sites through most of 
the forecast period. LIFR to MVFR conditions can be expected for much 
of the period as well. Rain and fog will continue to reduce 
visibilities everywhere. The heaviest rainfall will be seen for sites 
mainly along and north of the Natchez trace corridor through Tuesday 
evening. Mainly light and variable winds can be expected through the 
night with winds picking up a bit after sunrise...especially for 
sites across the southeast. Strong to severe storms will be possible 
for the southeast...mainly impacting hbg and mei from 15-03z. The 
rain will slowly diminish through Tuesday evening with thunderstorm 
activity ending by around midnight Tuesday night. 




&& 


Preliminary point temps/pops... 
Jackson 46 58 41 53 / 100 100 94 12 
Meridian 56 65 43 55 / 96 100 100 21 
Vicksburg 38 55 41 55 / 100 100 78 8 
Hattiesburg 61 70 47 56 / 77 100 86 8 
Natchez 41 58 40 53 / 100 100 68 6 
Greenville 35 48 40 54 / 100 100 87 11 
Greenwood 42 53 41 50 / 100 100 97 17 


&& 


Jan watches/warnings/advisories... 
MS...Flash Flood Watch through Tuesday afternoon for msz018-019- 
025>045-047>050-053. 


La...Flash Flood Watch through Tuesday afternoon for laz007>009-015- 
016-023-025. 


Arkansas...Flash Flood Watch through Tuesday afternoon for arz074-075. 


&& 


$$ 


14 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)