Weather Watch, 11/12/23

Dr. Daniel Swain noted later this morning:

Update on CA storm scenario next week:
“An active weather pattern still likely Tue-Sat, but details have changed considerably from last week. Storm now looks much warmer, w/strong subtropical influence. Hence, freezing line will be high & mountains may see rain vs snow.”

As NOAA/NWS says, the forecasts models are almost outrageous for these upcoming storms with their wide spreads, so much so, that they are almost unusable. For what it is worth, here it is:

“Significant uncertainty remains in the exact rainfall totals through the week. The current forecast calls for rain to begin late Monday and continue through Friday, with roughly 2-3 inches for most areas. More rain is expected in the coastal mountains with less in any valleys with terrain shelter to the south. While the forecast hasn`t changed significantly, the ensemble guidance continues to indicate a wide range of possible outcomes. In fact, the NBM 90th and 10th percentiles were almost outrageous, with over 10 inches on the high end and only a trace on the low end. While that`s a safe range, it`s not very useful. The GEFS and ECMWF EPS are more reasonable, but still show an equal potential for 1/2″ or 4″. Normally this spread would be tighter by now, but the fact that the main driver is a quasi-stationary low makes the forecast more uncertain that a typical fast moving cold front, for example. One look at the deterministic GFS vs ECMWF show that by Friday the low could still be spinning in the waters off the Bay Area, or making landfall as an open trough in Southern California. Without much steering flow, it`s difficult to pin down the details and the uncertainty will likely remain high even as the event begins.”