2007-01-07_hmt_forecast
Not a lot of substantial change from yesterday's discussion for the upcoming week. Bottom line is that unless something changes substantially we are looking at a cold event with low snow levels for Wed night into early Friday but with very marginal amounts of precipitation, probably below what the HMT thresholds are. The trough of interest is currently heading into the Gulf of Alaska where it is phasing with an upper level low over Alaska. The trough then will move down the west coast of North America as a high-amplitude upper level builds behind it and pushes well north across Alaska. There will be good precipitation in the Pacific Northwest Tue/Wed as the trough digs down the coast, but then the trough starts to head inland, with a substantial decrease in precipitation forecast for the HMT area. The current GFS 12z run, which is in good agreement with the 00z ensembles and pretty much all the other deterministic runs, moves the base of the trough across the HMT area on Thursday and then shifts it east and south. Precipitation with low snow levels is forecast by the GFS from very late Wed into early Friday, but it is fairly scattered looking in nature and the maximum amounts are barely over a quarter of an inch for a storm total. Again, there is good agreement on this scenario. Only a 00z run of a version of the Global Canadian model
is different, dropping the trough more off the coast and actually producing quite a bit of precipitation for the HMT area. However, there is no ensemble member from the 00z Canadian ensembles that supports such a solution, so it is a predominant outlier. The latest ECMWF and 12z GFS ensemble runs are also in good agreement with the forecast outlined above.
Beyond this system the deterministic runs of the Canadian, ECMWF, and GFS are not optimistic for action in the HMT area even for days 10-15 (out to 23 Jan), as the models maintain a high-amplitude upper level ridge off the West Coast, effectively blocking any oncoming systems. A few of the ensemble members are a little more optimistic after day 10, but today it seems that more members support maintaining the upper level ridge. The ECMWF by day 10 (17
Jan) also is trying to break a rather weak system into the ridge with some potential (this system is more just inland in the GFS). Apparently there will be some discussion how this could be in error given some action in the tropics that will be posted on Monday, so perhaps one would want to put even less confidence in this solution at this time.
ed szoke