Another Cold and Wet Sunday?

The top figure shows the NAM 500 mb forecast from 12 UTC this morning valid at 84-hours, which is 5 pm Sunday afternoon. The model forecasts a very sharp S/W to be moving across Arizona on Sunday. The wavelength is quite short, having been pinched down by the S/W to its northwest, and to some degree by this morning's S/W which has moved out to Illinois and become nearly a mesoscale feature. The bottom panel shows NAM 84-hour SLP, 1000-500 mb thickness and 6-hour accumulated precipitation - so yes, the NAM says cold rain on Sunday. However, timing may be a crucial issue for this feature, since the ECMWF has been consistently slower with it. The very cold air at 500 mb leads to a fairly large area over AZ with thicknesses below 540 dm. This needs to be monitored, since thicknesses this low would bring the snow level down quite low (need 534 dm or a bit lower to see snow here at the house but we're one of the lowest elevations in the metro area). As the system digs down the coast in the model forecast an area of thicknesses less than 528 dm makes it far south down the California coast. The final question with this system concerns the subtropical moisture to the south - at least three of the GFS ensemble members seem to pull this air into the system and predict much larger precipitation areas on last evening's runs. So, lots to watch as the synoptic pattern rapidly evolves over the next three days!