376 
fxus64 khun 180124 aab 
afdhun 


Area forecast discussion...updated 
National Weather Service Huntsville Alabama 
824 PM CDT Wednesday Mar 17 2010 


Update...to tweak hourly temperatures and pop 


&& 


Discussion... 
a low pressure system continues to develop and move northeast just 
off the Georgia and eastern Florida coastline. Energy and moisture 
continue wrapping around the back side of this low...producing 
some light rain in southern DeKalb and Marshall counties at this 
hour. This activity will continue pushing west into Cullman County 
through midnight...before slowly diminishing. Elsewhere...mainly 
north of the Tennessee River...mainly some scattered scattered light 
sprinkles are expected. 


Temperatures have changed very little due to cloud cover...remaining 
between 45 and 51 degrees. Persistent cloud cover will keep 
temperatures higher than guidance. The ongoing low temperatures in 
the middle 40s look good. Overall...only slight changes were made to 
probability of precipitation...wx...and hourly temperatures in the forecast package. 


&& 


Aviation... /unchanged from 00z tafs/ 


VFR conditions seen in most of the observation across the area at this 
time. Expect this to continue...as some -shra pass to the north 
and east of the taf sites before 06z. Could see some brief MVFR 
conditions...as some pockets of ceilings between 2000 and 3000 feet 
are still upstream. Ceilings should be solidly VFR around 06z...and 
continue to increase on Thursday. 


&& 


Previous discussion... /issued 343 PM CDT Wednesday Mar 17 2010/ 


Another cool and cloudy day was the main weather story today as 
temperatures only reached the lower 50s with still no sign of the 
sun. Precipitation has remained southeast of the forecast area 
with a few sprinkles also observed across middle Tennessee. This 
trend should continue tonight with most locations across the 
Tennessee Valley remaining dry overnight...however...a few light 
showers may move into northeast Alabama later this evening. As a 
result...kept a slight chance of showers for these areas 
overnight with sprinkles mentioned elsewhere. With cloud cover 
continuing...lows will once again remain in the low to middle 40s. 


The big weather question for Thursday will be if and/or when the 
cloud cover will break up and the sun returns. At this point...the 
longwave upper trough will finally begin moving east as the two 
upper level lows within this trough slowly exit the area. Current 
thinking is that cloud cover will hold strong for most of the day 
Thursday with possible clearing occurring during the late 
afternoon hours. Any precipitation that develops will be light 
with mainly sprinkles possible...especially south of the 
Tennessee River. Think the clearing...if it does occur...will be 
too little too late as highs once again struggle to reach 60 
degrees. However...if cloud cover dissipates sooner than expected... 
highs may be able to reach the middle 60s. 


By Thursday night...the upper trough will have moved well off to 
the east allowing skies to finally begin to clear across the area. 
As a result...think temperatures will be able to fall into the 
lower 40s. High pressure will briefly build over the region on 
Friday as a warm and mostly sunny day can be expected. By Friday 
night...this high shifts east allowing warm southerly flow to 
develop. As a result...lows will not be quite as cool as the previous 
night with lows in the middle to upper 40s expected. 


The next low pressure system and cold front will begin to approach 
the region on Saturday bringing showers and thunderstorms to the 
entire area Saturday night. There are some timing differences 
within the models...especially with the European model (ecmwf) as it is much 
slower than the favored GFS/Gem/sref solutions. However...the 12z 
European model (ecmwf) looks more reasonable than the 00z solution and is at least 
trending more towards the favored solutions. Current thinking is 
the precipitation will move into northwest Alabama late Saturday 
afternoon and evening. Feel pretty confident that all areas will 
see showers and thunderstorms Saturday night as the cold front 
sweeps through the area. The best upper support/dynamics will 
likely remain north of the forecast area...but still think strong 
thunderstorms will be possible with gusty winds being the main 
threat. This cold front will be fairly fast moving with most of 
the precipitation exiting the area by midday Sunday as colder and 
drier air filters in behind the cold front. 


High pressure will begin to build over the region Sunday night and 
into Monday as mostly clear skies can be expected. The threat for 
freezing temperatures seems less with the model solutions 
today...although not ruling out the possibility for rural 
locations Monday morning...especially if clear skies develop 
faster than expected. The surface high will quickly move east of 
the area Tuesday as southerly return flow develops over the region 
allowing temperatures to moderate back above seasonal normals 
Tuesday and Wednesday with dry conditions continuing. 


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


$$ 


Discussion...20