Which Version Of WRF Has It Right?

Mike Leuthold has alerted me to the fact that the 12 UTC runs of the WRF model have quite different forecasts than does the 06Z early version of WRF-GFS (discussed in post below). The situation today and tonight is complicated by the fact that the western end of the frontal zone over central Texas extends westward into southeastern Arizona. This is a weak and dissipating feature, but it could possibly act to provide a zone of moisture convergence, which would serve to increase PW and CAPE. 

Above is the WRF-GFS forecast of composite radar echoes for 2 am tomorrow morning from the 06 UTC run..

However, the forecast above is also for 2 am tomorrow morning, but from the WRF-GFS 12 UTC run.

Finally, the above is the radar echo forecast valid at 3 am from the WRF-NAM 12 UTC run.


These differing forecasts provide a nice example of the dilemma that can face NWS forecasters who must maintain hourly forecasts for a high-resolution grid network (deterministic forecasts for every hour out to SEVEN days). These three model forecasts for 2 to 3 am are extremely different. Which one will prove to be the "best" forecast? Very hard to say 12 hours ahead of time. The storms from the 12 UTC model runs have propagated southwestward into Pima County from the White Mountains (a situation that does happen a couple times each summer). However, a more unstable air mass is usually present over the lower elevations when this happens.


If I were to assign a POP for rainfall here at the house for 2-3 am from each of these, I'd come up with:
0% for WRF-GFS run at 06 UTC; 20 to 30% for WRF-GFS run at 12 UTC; and a much more serious 100% for WRF-NAM run at 12 UTC. It appears that the current grid-point forecast for the house from the NWS is 10% POP and 10% chance of thunder - essentially slightly between the first and second WRF forecasts above.


Will wait and watch.