December 19, 2002
Generally, not being one that places much trust in guidance past 5 days,
I have not taken a very close look at this storm that many folks are talking
about during the Christmas Day time frame until this morning. After seeing
several posts on the ne.weather group regarding rain/snow lines, 850 temps, track,
etc. I feel the need to play a bit of Devil's Advocate (even though the
bashing will commence thereafter).
In all seriousness, there are implications in the medium range (22nd?)
that will have a large impact on the Xmas System. In the east, we have the
appearance of a weak Rex-type suppressing the elongated PV farther to the
South. With spokes of energy pinwheeling around this feature, the
development of any weak surface feature in response may have implications
later on in the period regarding structure and positioning of the PV.
The biggest factor, IMO, with the development of this *potential* system
around the holiday is the vortex relative to the Southern Jet crashing
onshore in California in roughly the 60 hour time frame.
This piece of energy headed into Southern California is what the EC,
GFS, and NGP are keying on for development.
The other large key around 60 hours is the re-emergence of the Gulf of
Alaska low. This feature should pump the heights in the Western US and will
play a factor in the vortmax in the SW undercutting the developing upper
ridge. How strong this ridge gets will play a role in how much energy gets
ejected from the upper low early next week. All of these features are what
guidance have been struggling with for the past 3-6 days in the long range
with regards to a shift in the pattern (PNA/NAO configuration).
In my experiences past, I have found that this is a tough geographical
area in the Pacific and the SW for guidance to get a good handle on until
the energy actually comes onshore. I'm not saying this holiday system will
or will not happen, but I am urging caution to those already calling for a
sure system and penciling in rain/snow lines and placement of secondary lows
and where the upper low will capture the surface low.
Again, I don't mean to ruin anyone's day, but this is something we go
through at least 10 times each winter. It's best to wait until at least the
weekend and see what happens before cancelling the trip to grandmother's
house for the holiday.
S.B.
