743 
fxus64 khun 041959 
afdhun 


Area forecast discussion 
National Weather Service Huntsville Alabama 
259 PM CDT Friday Jul 4 2008 


Discussion... 
main forecast focus for the short term revolves around the obvious 
potential for ongoing convection tonight...where and when. Have 
weighed forecast heavily towards latest radar/Sat trends...which suggest 
large scale convective development continuing from the central Tennessee 
Valley wwrd towards the middle-miss valley. Considering movement of 
activity will generally be east-southeast per corfidi vector/mid-lvl steering 
analysis...much of the ongoing activity to our west should primarily 
affect the southern half of the hun County warning forecast area. Another area of convection 
which is already initiating in the lower Ohio Valley is ahead of an 
upper-level short wave which will move quickly ewrd ahead of the main 
short wave impulse still further northwest. Right now...am expecting the 
bulk of this activity to pass by to our north...but couldn't rule 
out the southern flank of this spreading into our northestern areas later this 
evening. For now...have painted a northwest to southeast gradient west/respect to 
probability of precipitation with slightly higher values in the southeast per the reasoning above. 
The result is likely probability of precipitation for the southeastern half of the area...with 
chance probability of precipitation northwestern half. Of course...this type of convection along 
weakly defined boundaries always presents a large degree of 
uncertainty...so further updates to the forecast may be necessary later 
this evening. Essentially...I would like to express low to moderate 
confidence in the forecast for tonight which is the unfortunate 
consequence in these cases. Considering the Holiday at hand and the 
abundance of outdoor activities tonight...feel it necessary to 
specify the weather threats...which as stated in previous forecasts will still 
consist of strong wind gusts and freq lightning. 


Another short wave noted on water vapor imagery is giving rise to 
convection in portions of Arkansas/OK this afternoon. As this pivots 
ewrd...this may present convective opportunity especially for 
western/southern portions of the area later tonight...but feel that most of 
this activity may actually shift to our south. Nevertheless...some 
uncertainty remains regarding exact timing/movement of this 
convection...so it will be important to pay attention to any further 
updates later this evening. 


For Saturday...feel that the main focus for convection will shift to 
our south and northeast with separate low-level confluent boundaries 
noted in strmline forecasts. This is likely due to the effects of the 
stalled front to our north...and convergence to the south along the 
edge of the outflow boundary from overnight convection. 
Anyway...think that chances for convection will decrease a little 
tomorrow now...and have left chance probability of precipitation in for all areas and 
tailored to show higher values in the east...where better 
thermodynamics will exist. 


For Sunday...main upper level short wave will traverse the 
region...with much of the differential positive vorticity advection actually occurring during 
the morning hours to early afternoon...per the best timing available now. 
This may help alleviate any sig threat for widespread activity which 
wouldn't be bad if we didn't need the rain. Nevertheless...have kept 
in chance probability of precipitation but have skewed to show higher values (40s) in the 
east...with near 30s in the west. So for now...would expect the bulk 
of any activity that develops on Sunday to be in the east. 


Monday through Friday...expecting isolated/sctrd primarily afternoon/evening 
convection each day through this period. Longer range guidance is 
suggesting low amplitude troughing in the east around middle/late week. 
Teleconnection patterns are favoring a ridging pattern beginning in 
the eastern Continental U.S. By late in the week. So...am a little reluctant to 
follow any guidance now that would suggest otherwise. GFS ensembles 
are rather split but some are certainly indicating a very quick but 
subtle trough passing through the eastern Continental U.S. ~Wed-Thu. This may 
represent the last vestiges of short wave energy passing around the 
larger scale trough that has dominated eastern North America as of 
late...just before the pattern makes a shift to western Continental U.S. Trough/eastern 
Continental U.S. Ridge pattern. Thus...chances for rain showers/thunderstorms and rain may be higher on 
Wednesday/Thursday as compared to earlier in the week. But...counting on a 
slightly slower evolution of events which is usually a safe bet this 
time of year may put any weakening trough through the Tennessee Valley late 
week...with ridging building in and a return to typical hot Summer 
weather beyond that. 


&& 


Aviation... 
convection developing rapidly across northwestern Alabama/northestern MS is presenting 
some challenges to say the least for khsv/kmsl tafs. Tafs will 
display best timing attainable at this time regarding thunderstorms and rain onset at both 
locations. Have only lowered visible to MVFR at both locations (3-4sm) 
because convective heavy precipitation will generally be of short 
duration...with longer period moderate/light rain and associated br being more 
representative. So...any lower visible experienced British Columbia of heavy 
rain should be less than ~15 mins with any storms. Have kept thunderstorms in the vicinity 
in at kmsl through 00z...then removed but appended cumulonimbus to low cloud 
layer after that to suggest ongoing threat. But not confident 
enough to put in actual timing of convection at this point. For 
khsv...have left in thunderstorms in the vicinity until 0400...given backbuilding tendency 
on radar/Sat suggests convection may linger in north central/northestern 
Alabama longer. Also...have included mention of light fog for now with 
MVFR visible after 09z at each location British Columbia of precipitation expected today. 
However...if precipitation amounts/duration become stronger/longer lived 
then these may need to be lowered in later tafs. 




&& 


Preliminary point temps/pops... 
Huntsville 68 87 69 88 / 60 50 30 40 
Shoals 68 87 68 88 / 50 40 30 30 
Cullman 68 86 69 87 / 60 50 30 40 
Fayetteville 67 86 68 86 / 50 50 30 40 
Albertville 68 86 69 88 / 60 50 30 40 
Fort Payne 65 85 67 88 / 60 50 30 40 


&& 


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


$$ 


Forecast and aviation...kdw 

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