2006-01-11 WX Discussion and Forecast
Zonal flow over the Pacific is in the process of breaking down. Major troughs will be impacting the ARB over the next week.
The Wednesday event panned out with precipitation underway today. The first burst of action from the radar looked to be Tuesday evening (11/03GMT) . A series of surges continued throughout the night with Blue Canyon recording 0.46 by 8am. Rainfall looks to be lighter than expected with rates this morning in the ARB at about 0.1/hr. High Resolution WRF (clickable on HMT web page) shows a total for the event ( 11/12-12/00GMT) of close to an inch before the event ends by late afternoon. The model supports rain rates of .08 to .1 inch per hour up until noon then tapers off to less than 0.05/hr till about 4pm PST (12/00GMT). This compared favorably to observed rain rates this morning at Duncan and Forest Hill. In evaluating the models the NAM 12 appeared to move things in too early with too much rain; the GFS model was better on timing and intensity.
Big question now is the event for Saturday. There is no doubt a major trough will move through the ARB. The precipitation with the event will be in the post-frontal, cold-advection regime. A moist plume is present but weaker than previous events with 20-24mm maximum upstream of the ARB. This moist plume rapidly dissipates with the intensification of the surface low. Moisture moves into the area Friday night with a freezing level of about 8000ft. the freezing level drops throughout the event reaching 4000 ft by Sunday morning. The GFS begins the precipitation Friday night (14/03GMT) with maximum activity early Saturday (14/06-12GMT). This rain band is likely to have imbedded convection with low static stabilities likely. Other models support the general evolution of the rain but have differing opinions on its initiation. Both Etas and MM5 are looking at Saturday morning (14/12-18GMT); CMC and NOGAPS like the GFS timing.
Half of the GFS ensemble members start the precip off between 14/00-03; almost all have precip underway by 14/12GMT. So a consensus would point at late Friday for a start (14/06GMT). Amounts for the event look to be about 1-2 inches. Very strong SSW winds will accompany the storm.
The next situation looks to be late Tuesday-early Wednesday, probably another cold-advection dominated event, and another major trough.
John McGinley