U.S. Severe Weather Forecast (Convective Outlook)

Day Three

acus01 kwns 211238 
Storm Prediction Center ac 211237 

Day 1 convective outlook 
National Weather Service Storm Prediction Center Norman OK 
0637 am CST sun Dec 21 2014 

Valid 211300z - 221200z 

..no severe thunderstorm areas forecast... 

numerous showers and possibly a few thunderstorms will occur over 
the northern half of Florida into southeast Georgia today and 

In middle-upper levels...series of shortwave troughs will contribute to 
development of synoptic-scale trough over central Continental U.S. By 
12z...with anchoring 500-mb low between vtn-mhe. By that 
time...associated belt of cyclonic flow will extend from central/southern 
rockies and northern mex to upper Great Lakes...Ohio Valley and southern 
Appalachians. Moisture-channel imagery indicates southern-stream 
shortwave trough over Rio Grande Valley of S Texas and adjoining 
portions of northestern mex. This perturbation is forecast to deamplify 
throughout rest of period...crossing la around 00z...and in 
much-weakened condition...Carolinas by 12z. 

At surface...wavy/quasistationary frontal zone was evident from off 
central Florida Atlantic coast southwestward across S-central Florida then westward over 
N-central/northwestern Gulf. Atlantic portion should move northward as warm front 
today...but remain offshore GA/Carolinas. Gulf segment should 
remain quasistationary or drift northward while gradually weakening. 

..sern Continental U.S.... 
isolated to widely scattered thunderstorms are expected to occur within 
broad swath of shallower convection and precipitation...generally north of surface 
frontal zone from central Gulf across central/northern Florida and southern Georgia. 
Convective intensity and depth will be limited by lack of more 
robust lapse rates and resultant restrictions on cape. Forecast 
soundings suggest elevated MUCAPE generally remaining below 400 j/kg 
over land...with only brief/marginal incursions of buoyancy into 
suitable thermal layers for lightning production. 

.Edwards/cohen.. 12/21/2014 

Mesoscale Discussion

acus11 kwns 170924 
sels mesoscale discussion 
Storm Prediction Center mesoscale discussion 170924 

Mesoscale discussion 1980 
National Weather Service Storm Prediction Center Norman OK 
0324 am CST Wednesday Dec 17 2014 

Areas affected...portions of coastal Southern California 

Concerning...severe potential...watch unlikely 

Valid 170924z - 171130z 

Probability of watch issuance...5 percent 

Summary...limited risk for a marginally damaging wind gust or two -- 
or possibly a brief/weak tornado -- is evident over coastal portions 
of Ventura/Los Angeles/Orange counties in Southern California early this morning. 
Ww issuance will not be required. 

Discussion...latest radar and lightning data depict a small cluster 
of thunderstorms crossing The Channel islands area and adjacent 
coastal Southern California at this time...coincident with a middle-level cyclonic 
circulation center moving east-southeastward across this area per WV loop. 

Despite surface dewpoints only in the low 50s...relatively steep 
lapse rates through the lower and middle troposphere are 
contributing to marginal cape /a few hundred j/kg per objective 
analyses/...thus fueling updrafts which are extending through the 
mixed-phase /-20 c/ layer. 

While area vwps depict relatively modest /20 to 30 knots/ swlys through 
500 mb...backed/sely low-level winds ahead of the storms seem to be 
aiding in occasional weak/short-lived low-level circulations in 
stronger cells -- as observed by kvtx /Ventura/ WSR-88D. Given the 
sustained/weakly rotating storms...a very isolated/low-end severe 
risk may spread onshore over the next couple of hours. With that 
said...any risk for strong winds and/or a brief/weak tornado should 
remain well below thresholds required to consider ww issuance. 

.Goss/Thompson.. 12/17/2014 

..please see www.Spc.NOAA.Gov for graphic product... 


Latitude...Lon 33831966 34421979 34531953 34431907 34101833 33781773 
33401780 33231830 33171948 33391973 33831966