HMT Forecast 2/12/07
With the end of IOP 5 last evening I will focus on the outlook for the next possible event that looks to be well off into the future.
This morning a large Pacific ridge sits with a central high pressure at 143W 35N and continues to drive moisture plumes over its top. One main plume 150E has merged with another swept north in the E flow at 160W. This moisture will not play a role in the immediate future but may in about a week's time.
Meanwhile a rogue piece of disconnected moisture enters the ARB by 12ut on the 13th. The main moisture remains far offshore west of 130W. This bit of moisture might be responsible for light precip in the ARB forecast area by both the NAM and GFS, progged to occur early this week, but both models keep the total precip well under one inch through 12utc Sunday 2/18.
Meanwhile, the high pressure ridge progresses to 135W 35N on or about 16 Feb teasing the CA coast with some additional moisture but it appears to remain west of the ARB with the main plume intersecting the OR coast and then being driven NE away from CA with time.
Another surge is forecast to brush the coast in the 18utc 2/18 (Sunday) timeframe and this might be associated with the higher ensemble probabilities for precip at about this time.
Examining the GFS ensembles this morning we see a virtually dry ARB until a 75% chance of precip on or around Sunday 12utc 2/18 through 12utc Tuesday of next week. Then another possible precipitation event occurs around the 24th (Saturday). It is too early to tell whether the upcoming potential Sunday event will be associated with a good upper level moisture river from the tropics. We will keep an eye on this possibility throughout this week.
Dan Birkenheuer - ESRL/GSD