Mark’s Nightmare Weather Pattern

May 30, 2006

TI think I mentioned earlier this spring that there is one weather pattern that I hate forecasting for…an upper level low sitting offshore with waves rotating out of it and into the Northwest.  2 reasons for that:  one is that models don’t handle the individual shortwaves well.  The other is that the periods of steady rain are usually quite short, followed by hours of sunshine if the onshore flow isn’t too strong.  So what starts out as a rainy day forecast could be wet until 8am, mostly sunny from 9am-4pm, then rain again after 5pm.  Viewers think we don’t know what we’re talking about and can’t forecast the weather…ugh!

What sticks out tonight is the good plume of moisture across the Eastern Pacific.  Models show precipitable water well above 1.20" the next 2 days as several waves move inland.  No big onshore push though until Friday, which leaves us increasingly warm & humid.  One wave moves into Wednesday evening, and another later Thursday/Friday AM.  With high freezing levels (10,000’+) and good subtropical moisture feed, we could get a good soaking.  Maybe .50"-1.00" in the lowlands.

As for the chances for thunder tomorrow & Thursday?  Tough one.  Our RPM (rapid update precision model) model here at the station seems to indicate some convection just ahead of the main line of rain tomorrow evening, and the same thing Thursday afternoon.  It’s tough because solid cloud cover (with surface cooling) ahead of both waves could cancel out the lifting effects of the approaching wave.  We’ll see.  Flow is southwest, which IS a similar setup to our convection about a week and a half ago.