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fxus64 khun 210245 
afdhun 


Area forecast discussion 
National Weather Service Huntsville Alabama 
945 PM CDT Sat Mar 20 2010 


Update...lower probability of precipitation for overnight and tweak temperatures 


&& 


Discussion...00z u/a soundings from bmx/ohx were very dry from 
around 7h and down to the surface. Also with surface high over a large 
portion of the southeastern US this evening...looks like precipitation will stay 
out of our County Warning Area until well after midnight. The new NAM and RUC 
data does show precipitation pushing into northwestern Alabama by 12z. Dont have any 
new GFS data yet...but the GFS usually will be quicker with precipitation 
timing than the NAM. So with all of the above in mind...lowered 
probability of precipitation to likely in the northwestern zones to chance probability of precipitation elsewhere. Will keep 
isolated thunderstorms and rain in for tonight due to increasing 800 mb low level jet towards 
sunrise. Also did some minor tweaking to temps/dewpoints. 


&& 


Previous discussion... /issued 705 PM CDT Sat Mar 20 2010/ 


Update...for 00z tafs 


Aviation...cold front extended from surface low over northestern Arkansas through eastern Arkansas 
and into western la...with a line of mainly showers/few thunderstorms and rain over 
Arkansas and la. Upper low now over southern OK will slowly move east 
overnight and will drag the cold front along with it. The cold front is 
expected to push out of the County Warning Area by early Sunday evening. Ahead of 
the cold front...the atmosphere over the County Warning Area is fairly dry. Based on 
model soundings...the atmosphere does not saturate until around 10z 
Sunday morning over northwest Alabama and by 12z in the hsv area. Will keep VFR 
conditions until around 18z for both taf sites...and MVFR conditions 
after 18z. There will some instability for a few thunderstorms and rain Sunday 
afternoon...but no severe weather is expected at this time. 


Previous discussion... /issued 313 PM CDT Sat Mar 20 2010/ 


Discussion... 
Spring has officially begun as of 1232 PM...and for the most part it 
feels like it outdoors. These Spring like temperatures however will come to 
an abrupt end during Sunday...as a developing storm affecting parts 
of the central and Southern Plains nears. This system was bringing 
increasing clouds...with virga noted along the Mississippi and 
Alabama border to west of Birmingham. Despite the clouds...3 PM 
temperatures across the area have warmed into the upper 60s/lower 70s with 
southeast-S winds 10-20 miles per hour. 


The above mentioned system...which brought accumulating snow over 
The Rockies and adjacent plains...and thunderstorms over eastern 
Texas had a surface low forming over the arklatex region. This low... 
moving to the NE will bring showers and isolated thunderstorms 
across the Tennessee Valley beginning late this evening across far 
northwest Alabama. This shower activity will affect the remainder of the 
region from SW-NE through the overnight. Have maintained categorical 
shower chances in for Sunday...with isolated storms. Convection this 
go around for the most part should not become severe...given weak 
instability. Strong lower level shear however will make up for the 
lack of instability...thus as is the case most of the time...cannot 
rule our one or two storms...with gusty winds and small hail the 
primary threat. Timing wise...the cold front with this system will 
move across northwest Alabama during the morning...reaching the i65 
corridor during the early afternoon and be east of this area during 
the early evening. 


Much colder air will move into the area Sunday night and Monday. 
This will provide another opportunity...possibly the last for a 
good while to experience early Spring snows across the Tennessee 
Valley. Have opted to go with a rain/snow shower mix...with very 
slim chances for any accumulations given a warm ground from the 
recent string of days above freezing. Boundary layer temperatures in the 
middle 30s after daybreak Monday argues for a rain/snow mix in through 
18z...afterward confined the mix to the higher elevations of northwest 
Alabama and Cumberland Plateau. The precipitation should wind down Monday 
evening from west to east...with clouds hopefully decreasing before 
daybreak Tuesday. Despite the abrupt sensible weather change...area 
wide temperatures for the most part will remain above freezing into Tuesday 
with this system. 


A warm up to more Spring like temperatures is expected for the middle week... 
as high pressure builds in from the west. Under sunny skies...temperatures 
should warm back into the upper 60s/lower 70s for Wed/Thu. 


Another system nearing will bring another chance for showers and 
storms for the latter part of next week. Thus far...dynamics and 
instabilities were inconsistent per the model output concerning 
strength and character of this convection. 


&& 


Hun watches/warnings/advisories... 
Alabama...none. 
Tennessee...none. 
&& 


$$ 




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