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afdjan 


Area forecast discussion...update 
National Weather Service Jackson MS 
950 am CST Monday Nov 23 2009 


Discussion... 


Update: the forecast is in good shape for today as stratus is slowly 
eroding from the southwest. Made minor adjustments to today's 
temperatures based on the current trends...but the thinning nature 
of the stratus on visible satellite imagery brings a lot of 
potential for a busted forecast. If the stratus breaks up more than 
depicted...then skies will become sunny and temperatures will warm 
well into the 60s and perhaps approach 70 in some cases...but if it 
stays cloudy...temperatures will struggle to reach 60. Have stuck 
with a more pessimistic solution for now and kept the cooler 
temperatures in the NE where it is more likely that skies will 
remain cloudy under the feeble late November sun. The updated 
aviation discussion is below. /Ec/ 


Previous discussion... 


Short term...today through Tuesday night...upstream trough diving 
into Wyoming will cross Kansas tonight and swing through MO on Tuesday. The 
associated surface frontogenesis this afternoon over the Central 
Plains sweeps southeastward tonight and through the lower MS valley Tuesday 
afternoon/evening. The boundary will have access to very little 
moisture and should only produce a minimal band of broken rain showers/light 
rain as it moves through our County warning forecast area mainly between noon and midnight 
Tuesday. 


Currently in the short term...stubborn stratus deck is trapped under 
a subsidence inversion across the Gulf states from about the Sabine 
River eastward. Patchy drizzle also noted along with some mostly light 
fog. Temperatures remain stuck between 52-56f and probably will be 
slow to rise after daybreak this morning. Will keep nearly all 
locations cloudy through early afternoon before breaks begin to 
slowly advance from the SW to NE in the afternoon in weak downglide 
regime. We should manage to get some broken layers by early tonight 
but not looking for a complete clearing out of the low level 
moisture probably until the frontal passage Tuesday night. 


High temperatures this afternoon will be controlled by the amount of 
sunbreaks at any one location. Expect most areas only to peak at 
58-66f with most of the m60s over southern sections of the area. A light 
southerly surface breeze sets up for late afternoon through tonight and 
will help keep lows in the M-u40s except over eastern MS where lower 40s 
are possible. Locations in the Highway 84 corridor will especially 
be susceptible to patchy/areas of fog late tonight if prior clearing 
skies occur. 


The prefrontal air mass on Tuesday will remain quite stable as a 
weak axis of near 5.5c middle level lapse rates...315k 850mb Theta-E... 
near 20 k indexes...and +2 showalter indexes push across our County warning forecast area 
with minimal moisture convergence. That axis exits southeastern MS by about 
midnight Tuesday night followed by modest cold air advection heading into Wednesday. 
/40/ 


Long term...Wednesday through next Monday...quiet weather through 
much of the extended forecast. Following the front on Tuesday...the 
upper trough moves across the region and brings a reinforcing shot of 
cold air to the region Wednesday night into Thursday. This will make 
for dry but chilly conditions for Thanksgiving with modest cold air advection in 
full force. Look for lows in the upper 30s on Thanksgiving morning 
and highs in the upper 50s north and warmer into the 60s further 
south. Conditions will be chillier for those shoppers waiting outside 
their favorite store on Friday morning with lows looking to flirt 
with the freezing mark in the east(but staying just above that) and 
into the upper 30s across the west. 


A 1026mb surface high over southeastern Texas Friday moves east 
along the coast and takes residence generally over the region(1022mb 
by this time) for Friday night into Saturday with ridging aloft. 
This should make for a nice weekend for family gatherings/travel. 


By Saturday night...light return flow resumes with some weak warm air advection. 
During this time...the surface high moves off to the east and the upper 
flow becomes more zonal with a slight southwesterly tilt. The next 
system begins to take shape as an upper trough out west over The 
Rockies starts to dig further south. In response to this....a surface 
low/trough starts to develop across southern parts of Texas on 
Sunday. As this system moves closer to the region Sunday night into 
Monday...rain chances begin to return to the arklamiss. At this 
point in time...both the European model (ecmwf) and the GFS agree that it could be a 
wet last day of November. 


No major adjustments made to mex MOS as it seems models continue to 
remain rather consistent with each other and from run to run. 
Residents will enjoy a pleasant Thanksgiving Holiday week free of 
severe weather(which is unusual for this region this time of year). 
/28/ 


&& 


Aviation...hbg was still reporting LIFR conditions at 15z with a 
ceiling at 400ft but IFR cloud decks continue across most of the 
area with bases 600-800ft. Visibilities of 3-5sm in patchy light 
drizzle was also being observed. Visibilities and cloud bases should 
gradually lift from the southwest as weak high pressure strengthens 
across the region. Visible satellite imagery was showing a few 
breaks developing over southern Louisiana already but any cloud 
decks that persist...primarily northern/eastern zones...should become broken 
around 2k feet 19-23z as much of the cloud cover thins by sunset. 
Areas of light fog will be possible later tonight with local dense 
IFR fog over southern sections 07-13z Tuesday. Look for more broken 
stratus to develop Tuesday ahead of the frontal system arriving for 
Tuesday night. /22/ 


&& 


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


&& 


$$