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fxus64 kbmx 180321 
afdbmx 


Area forecast discussion 
National Weather Service Birmingham Alabama 
1021 PM CDT Wednesday Mar 17 2010 


Discussion... 


Afternoon forecast is looking good...and no major changes are 
expected as light showers continue to rotate around the slow 
moving upper low that is parked just to our east. Just made slight 
adjustments to the hourly temperatures and dewpoint to match 
observation...otherwise...on track for the remainder of the 
overnight. 


&& 


Previous discussion... /issued 642 PM CDT Wednesday Mar 17 2010/ 


Update...aviation discussion. 


Discussion... 


No significant changes in the overall forecast package this 
afternoon. The morning package fell victim to abundant cloud cover 
across the area. High temperatures are currently topping out in 
the low 50s at most locations several degrees below forecast 
values. With no appreciable advection and only slight height 
rises...that trend will likely continue tomorrow. Therefore 
decided to undercut guidance a bit. Gut feeling is to 
significantly undercut MOS...but strong statistical agreement in 
ensembles made ME think twice about being so bold. Nevertheless I 
am slightly cooler than even the coolest member. 


Rain chances tomorrow are only slightly less foggy. The second upper 
level disturbance currently over western Oklahoma valley will 
track into southern Louisiana...then shift eastward along the 
northern Gulf Coast. As seen today in association with the first 
system...limited moisture will likely result in only light rain 
and minimal accumulations. Rain will only act to limit 
warming...so maybe my gut feeling about temperatures is on track. 


Moving on...Friday may be the first day in recent memory that much 
of the area receives a decent duration of sunshine. With such a 
cool day today it may seem outlandish that readings may climb into 
the 70s but a high sun angle under clear skies can result in 
significant warming. 


Moisture will return Friday night into Saturday resulting in 
progressively increasing cloud cover. The next forecast challenge 
comes Saturday night into Sunday. The largest forecast uncertainty 
at the moment seems to be dew points...with timing coming in at a 
close second. Return flow is routinely under-forecast by models so 
decided to use the moistest model...the European...as a starting 
point. However admittedly this basis results in unintended timing 
issues. With widespread thunder in the forecast and even a low 
confidence mention of severe storms in the severe weather potential statement...felt we needed to 
include at least some middle 50s dew points in the forecast. My hunch 
is that dew points will trend moister in subsequent runs and it 
would not surprise ME a bit to see readings approaching 60 degrees 
before all is said and done. 


As a direct reflection of low dew points across the area 
instability also looks to be limited. Likewise...expect those 
variables to trend more convective over the next couple of days. 


Dynamically the storm has potential...nothing to get overly 
excited about...but surely something to watch. Details should come 
more into focus over the next 24 to 48 hours. 


12/sirmon 


Aviation...00z taf discussion. 


Upper low which affected central Alabama today is currently rotating 
eastward...moving off the Carolina coast as the second upper low is 
moving southward across OK/AR. This second upper low will rotate 
across the northern Gulf Coast tomorrow. Between these two 
systems...cloud cover remain across the area...generally hovering 
between MVFR and IFR ceilings. Expect ceilings to fall overnight to 
around 1500ft. There is a small chance that isolated areas of IFR 
ceilings/fog could develop across the far south and east after 06z given 
these areas received light rainfall today. 


There is a small chance of light rain tomorrow with the second upper 
low...but chances are too small to include at this time. As the low 
moves to the east...some clearing is expected tomorrow afternoon 
across the west. 


14 


&& 


Bmx watches/warnings/advisories... 
none. 


&& 


$$