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fxus64 kbmx 220545 
afdbmx 


Area forecast discussion 
National Weather Service Birmingham Alabama 
1145 PM CST Sat Nov 21 2009 


Update...for aviation. 


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Discussion... 


The latest water vapor imagery indicates the upper low spinning over 
southern Louisiana with a fairly weak surface reflection in the same 
general area. Airmass over central Alabama has moistened quite a bit 
since this morning and several locations have already had measurable 
precipitation this evening. The upper low will slowly migrate 
northeastward overnight and will be over west central Alabama by 
morning. Elevated instability in southern Mississippi near the cold 
core upper low generating a few thunderstorms this evening. Although 
a clap of thunder may be possible in south central Alabama after 
midnight...do not think the occurrence will be widespread. Will 
continue to monitor this development. Once the airmass saturates... 
expect a bit more rain amounts to add up. The areas far north and 
east will be the last to saturate with most of the rain after 
midnight. Therefore...made all areas categorical for rain chances 
tonight. Overnight temperatures will be tricky. If heavier rain can 
fall into dry low level air...temperatures will cool. Otherwise... 
quasi-stationary surface temperatures and dew points expected. Generally 
increased lows a degree or so area wide and tweaked the hourly 
grids. Updates on the way. 


75 




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Aviation...06z taf discussion. 


Rain finally beginning to make it to the surface. Already measured 
at all terminals...with bhm and anb the only exceptions. This will 
be changing within the next 2 hours as the bulk of rain continues to 
move north. Overall conditions are the best they will be right now 
over the next 24 hours. Expect conditions to degrade throughout the 
overnight hours. The main upper low will have a hard time clearing 
the area...and models are becoming more convinced that ceilings will 
remain low for a good portion of the day on Sunday...along with 
light rain or drizzle. With that being said...went ahead and took 
ceilings down to IFR and LIFR by 15z and will keep them there for 
the rest of the period. There will be some breaks but went for the 
predominate conditions and overall trends. May need to be refined on 
the timing with the next few updates. 


16 


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Bmx watches/warnings/advisories...none. 


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