Dave Williams (to LAPS_Feedback)

 Hello,

        I know my name is 'mud' but I will continue to offer some feedback
[one-way as it is] on the models when I believe that some discussion
about them is worthy.

        I returned to shift on Saturday after 3 days off and was immediately
impressed by the cold pool that was over Victoria. It looked cold and
indeed was. However, the LAPS guidance badly under-estimated its
strength. This I noted on one of internal forecast products at the time.
The JMA was in broad agreement with the LAPS but the EC, UK and US were
not. They all had the thicknesses considerably lower, with the US going
for 5360 metres over us [YSCB], compared to the LAPS +24hr forecast of
5460 metres. Consistent with this under-playing of the thickness the
LAPS and Meso-LAPS under-played the weather associated with this system.

        The 00Z run was marginally better dropping the forecast thickness over
us in YSCB [+12hr] to 5410 metres but it still under-played the cold
nature of the system more than the other models. The analysis came in
with a considerable area of southeast NSW, upto 36S enclosed within the
5360 metre contour, whereas the +24hr forecast had the 5400 metre
contour just clipping the far south coast.

        Given the proximity of this cold air to the mainland and the relatively
short nature of the forecast, I must confess to being somewhat
disappointed with the model run in this instance. Fortunately I ignored
it completely and used the foreign guidance instead. [All of which had a
very strong thickness trough on their 12Z analyses incl. the JMA] I have
attached 4 GIF files that present the forecast for 12Z Saturday at the
time just prior to the update of the LAPS to the 00Z run. I didn't
capture the 00Z +12hr forecast from LAPS nor the analysis, maybe some of
you will have a chance to have a look at it later. It would be worth
some discussion as to why the model unde-played this system to the
extent that it did.

Dave

Attachments:

LAPS

US

EC

UK