HMT Forecast Discussion for Tuesday 26 Feb 08 (entered 2000z)
As noted yesterday, quite active across the Pacific but an upper level ridge has built along the West Coast behind the weekend storm and this is forecast to be a long-lived feature that could keep the Pacific systems north of the ARB for an extended period. The next system in line is the big one that built the upstream ridge for our weekend storm. It is now splitting with the main energy heading far north while the much weaker southern portion separates and drifts eastward. Currently the southern portion is near 35N/142W with a nice tap into moisture east of Hawaii. However, the system is quite weak when it comes onshore late tomorrow with little of this moisture remaining. Another strong system is behind this and also has a nice tap into tropical moisture, and it does squash the ridge some as it hits late Friday into Saturday, but most of the energy rides to the north. It is a close call and could see some precip into the ARB on Sat/1 Mar, but both the 00z ECMWF and 00z/GFS and in fact all the other 00z models keep most if not almost all of the precip north of the ARB. The latest 12z GFS is maybe a tad farther south and predicts ~0.25" at KBLU on Sat/1 Mar. The 12z/ECMWF just in is also a little further south with up to 0.30" at KBLU and almost 0.40" over higher terrain to the east on Saturday. On the same vein, the 12z/Canadian Global model also is a tad further south with ~0.3" of precip in the higher elevations of the ARB. It is a close call on a good number of the 00z ensemble members, with a few of the Canadian ensemble members and a couple of the GFS members bringing more substantial precip into the ARB, but still with a fast-moving system. Some of the 12z/GFS ensemble members also have some precip now sinking south into the ARB, but all keep the maximum to the north more over far Northern California and in OR/WA. It would take a farther south track to probably make this storm anything of interest, and even then it is still a fast-moving system. The one thing to keep in mind though is the current strong connection to tropical moisture stretching currently all the way back to the sw Pacific.
The next wave is not as strong as the Saturday system and there is good agreement that the precip with this open wave stays north of the ARB on Tue/4 Mar. This wave then drops into the central CONUS and phases with energy rotating around a cold Hudsons Bay vortex to form a big trough over the mid-CONUS by the middle of next week, with a high-amplitude ridge building along the West Coast behind this system. There continues to be very good agreement in the 00z ensembles on this evolution in both the Canadian and GFS ensemble systems, as well as in the 12z/GFS ensembles. As discussed yesterday, the Pacific remains quite active through early March and some of this energy finally breaks into CA by the second week in March. This is seen in a number of the 00z Canadian ensemble members with the first potential event on Sat/8 Mar and then continuing till the end of the forecast (12-13 Mar). The 00z GFS ensembles are largely dry although the deterministic run of the 00z/GFS does bring some precip into the ARB by Wed/12 Mar. The 12z/GFS deterministic run is more aggressive and has the first chance of precip by 8 Mar followed by other potential events through the end of the run on 13 Mar, and the 12z/GFS ensemble also have several members with periods of precip beginning near 8 Mar or during the next week. So at this point it still looks like a potentially active week by the second week in March, but baring some turn of events, probably not much before then.
ed szoke NOAA/GSD/CIRA