288 
fxus64 kjan 041451 aaa 
afdjan 


Area forecast discussion...update 
National Weather Service Jackson MS 
945 am CDT Sat Jul 4 2009 


Discussion... 


Update: the low-middle level ridge is centered over the forecast area 
this morning keeping the area sunny and this has allowed 
temperatures to rise a little faster than forecast...but afternoon 
forecast highs are in good shape. Latest NAM and local WRF guidance 
indicate a few showers could develop during maximum heating along the 
Highway 84 corridor in response to a subtle upper level shear axis and 
may need to add mention of this to grids. Otherwise...all is on 
track with the forecast and the heat advisory is in good shape. /Ec/ 


Previous forecast... 


Short term...we will have another day of above normal temperatures 
to deal with for Independence day throughout the County Warning Area with a strong 
ridge of high pressure nosing in from the Southern Plains. It 
should also be another dry day with plenty of subsidence and the 
storm track remaining well north of the area. There will be an 
increase in humidity compared to yesterday as winds turn to a more 
SW direction...especially west of I-55. This will make for quite an 
uncomfortable day to be outdoors...especially during the afternoon 
hours. A heat advisory has been issued for areas west of a line 
from Greenville...to Vicksburg...to Hattiesburg for expected heat 
indices of 105 degrees and overnight lows in the middle 70s. Guidance 
temperatures looked good for most places...except for the hbg 
vicinity where values were raised a few degrees given the recent 
stretch of very hot weather there. By Saturday night...a frontal 
boundary will begin moving closer to the northern County Warning Area border with 
slight chance probability of precipitation during the overnight period...but most central 
and southern zones should remain dry. 


By Sunday...rain chances definitely increase over the County Warning Area as the 
boundary moves further south. All models show this...and the best 
chances are for the northern 2/3rds of the area. Storm Prediction Center has even 
highlighted a slight risk of severe weather for Sunday given that we 
will be in the right entrance region of an 80kt 250mb jet...30kt 
850mb winds...and lower 70f dewpoints near a low level convergence 
zone. This potential will be mentioned in the severe weather potential statement. Mav temperature 
guidance seemed a little on the low side this run...especially 
across the northern half...so highs were raised several degrees for 
highs to be more in line with the higher NAM values. Overnight lows 
appeared good and no significant changes were warranted 
there...except for hks where lows were raised a few degrees to 
account for the urban heat island effect. /Dh/ 


Long term...models seem in decent agreement that the longwave pattern 
will finally retrograde for the Monday through Friday time frame. The 
recent upper ridge builds westward into nm by middle week which allows a 
stalled surface frontal zone to remain in place along the Gulf Coast 
for at least the first half of the week. This boundary will have 
daily interactions with any sea breeze action and a weak upper trough 
axis also lingers across the lower MS valley which should provide the 
additional cloud cover we need to hold temperatures closer to normals for 
this time of year. Both the European model (ecmwf) and GFS runs support 1 to 2 inch 
rainfall totals for locations S of Interstate 20 by the end of the 
week which would be very much welcomed. There are also some hints at 
a cutoff upper low center forming in southeastern la by either Thursday or 
Friday on the operational model runs. However... there is less 
support for this idea in the GFS ensemble means so we'll have to 
monitor future runs. 


The tropics appear to remain quiet for the upcoming week with any 
potential development confined to the epac. At any rate...the best 
probability of precipitation will be held over the southern portions of the County warning forecast area during the entire 
week with a push northward by Friday. Temperatures should return closer to normals 
at locations with the best rain chances... especially during the 
first half of the week. Have made slight upward adjustments to 
maxes/mins at locations with lower probability of precipitation as mex ensemble mean numbers 
above the operational run values./40/ 


&& 


Fire weather...the long stretch of hot and dry weather has kept an 
increased fire danger in place across the forecast area. While some 
areas saw brief relief with rainfall last weekend...most areas have 
seen very little rain in the past 6 to 8 weeks. Local fire agencies 
caution that an increase in aggressive fire behavior is possible and 
anyone setting off fireworks should be especially vigilant. Burn 
bans continue in several south MS counties...including Hinds County. 
Check the mfc website at www.Mfc.State.MS.US for the latest./40/ 


&& 


Aviation...only high cirrus and a few afternoon cumulus clouds are 
expected across all taf sites through today along with light winds. 
Thus...have maintained VFR conditions through 00z Sunday for all taf 
sites. Beyond the taf valid period...periods of rain showers and thunderstorms and rain will be 
possible during the day on Sunday...with the highest coverage in the 
vicinity of glh...gwo...and gtr. /Dh/ 


&& 


Jan watches/warnings/advisories... 
MS...heat advisory from 10 am this morning to midnight CDT tonight 
for msz047-053-054-059>064-072>074. 


La...heat advisory from 10 am this morning to midnight CDT tonight 
for laz007>009-015-016-023>026. 


Arkansas...heat advisory from 10 am this morning to midnight CDT tonight 
for arz074-075. 


&& 


$$