I'll give the bottom line first...potential IOP is still there for early next week. An open wave solution looks likely, so not a prolonged event, and this means potentially marginal precipitation totals. But the amount of tropical tap is uncertain, so greater than 1 inch totals seem quite possible at least. Timing could be as early as precipitation beginning around 21z Monday or certainly Monday night, with things wrapping up late Tue to around 00z Wed at the latest the way it looks now. There was in general more optimism on the possibility of an IOP for this time frame among the folks on today's telcon. The gory weather details are below....
Took a look at the jet stream analysis at 12z this morning near and west of the Dateline over the southern latitudes near that blowup of convection discussed in our recent telcons. Not much difference between the 24-h forecast from the 00z/14 Mar GFS run and the jet analysis, but there is some difference between the previous 00z run (from 13 Mar, before the blowup) with the 48-h forecast jet not as far south as analyzed, especially near 155E. This jet has pushed eastwards from the upper low that had moved off of Asia in the western Pacific and with it is a strong upper level low at 500 mb currently near 170E/40N. Looking at the GFS on the U of Hawaii site, there is a small plume of moisture (model precipitable water) extending northeastwards from this tropical convection into this system near 170E. The upper low downstream from this system continues to weaken as it moves to the northeast, evolving into the deep upper low that extends into the Gulf of Alaska. There is a nice plume of moisture with all of this extending from east of Hawaii northward along 150W and then eastward mainly into Vancouver, south into northern Washington, with the downstream ridge building just off the California coast and downstream from this a trough deepening east of the Rockies. The strong wave near 170E/40N is the one that progresses across the Pacifc and provides an opportunity for an IOP early next week. Behind this wave a strong jet is forecast to emerge off of Asia early this coming weekend and the U of Hawaii site shows a much more significant moisture plume forecast to get involved in that system beginning tomorrow. This jet and associated wave remain quite strong as they progress across the Pacific, and this builds the ridge behind next week's system. In response the GFS and other models are forecasting a deepening of next week's system but after it passes the HMT area, so more over the intermountain west, by Wed-Fri/21-23 March. In the 00z GFS deterministic run the result was another ridge along the West Coast and dry in the HMT area almost through the rest of the month, although at day 15 in the GFS run there is a large system with a tropical connection lurking well off the West Coast. Variations, however, are found in the ensembles, discussed later.
As for details on the potential IOP next week, a review of the 00z deterministic runs indicates the forecasts continue to be split as they have been over the last couple of days, although big differences are dissappearing. The GFS remains the most progressive solution, with an open trough about onto the West Coast by 06z/20 March (Monday night), then the trough axis passing the HMT area 12 h later, with the precip diminishing on Tue afternoon (21 March). Total precipitation from the GFS is barely above 0.50 inches by late Tue. A second wave does follow this Tue night into Wed (20-21 March), but additional amounts are not great, into the 0.10-0.25 inch range. There is a rather weak tie to some tropical moisture, some of which is left behind by the current plume of moisture noted earlier near 150W. Other 00z model runs are somewhat more favorable, in that they are slower and some are deeper with the wave. This ranges from the ECMWF run, which is trending farther south (maybe a bit too far south for the HMT) and is about 12 h or more slower than the GFS. The UKMET has more of an open wave reaching the West Coast near 00z/Wed/21 March, so slower than the GFS. The Canadian run is a bit faster than the UKMET, maybe 6-12 h slower than the GFS, and with a little more precip than the 00z GFS. The NOGAPS is missing a critical time period but overall is also progressive, close to the Canadian run. The summary of the 00z runs is that this is a system we will have to watch, but at this point is still on the marginal side, for a quality IOP.
The 12z models are more encouraging, especially the GFS, in that while still an open and progressive wave, more precipitation is forecast, perhaps owing to a better tropical tap. Precipitation actually commences around 21z on Monday/19 Mar, and ends around 18z on Tue/20 Mar. Maximum is right in the HMT area and around 1.25 inches. Given orographic enhancement one could expect local amounts to be higher if this model solution verified. There is no secondary system right behind the main one in the 12z run, as a very weak shortwave stays well to the north on Wed. The 12z Canadian run is pretty close to the 00z GFS, and not quite as favorable as the 12z GFS. The 12z NOGAPS continues to be missing a key time, but appears to be a tad slower than the 12z GFS. Finally, the 12z ECMWF run, not quite fully in, is more favorable than the 00z run in that it has an open trough, deeper than the GFS, but not trending to quite as deep a southern portion as the 00z ECMWF run that would be too far south of the HMT area. Timing is a little slower than the GFS, maybe by 6-12 h or so.
Environment Canada has an interesting ensemble presentation that includes precipitation (at http://weatheroffice.ec.gc.ca/ensemble/cartes_e.html# ) for both the set of 00z Canadian runs and the 00z NCEP runs. They show a precipitation rate presentation at 24 h (valid at 00z) intervals and most of the members have the heaviest rate in the vicinity of the HMT 00z/21 March. A few still have something going on 24 h later, but they are certainly in the minority. As might be expected given we are not so far off into the future, the GFS 00z ensembles do not show a lot of variation with the system early next week, although there are a few members a little deeper and slower than the 00z deterministic run. There is a lot of variability into the following week, however, and this is true of the set of Canadian runs as well, with a number of members having potential for something into the HMT area rather than having the closed low staying well off the west coast. So at this point it would be impossible, it seems, to say that next week's system will be the last thing for March. The 12z GFS ensembles just coming in actually seem to have a little more spread for next week's system, with a few runs even a tad faster, but more of the runs slower and a little stronger than the 12z GFS deterministic run. And in the longer range, begining later next week, there is quite a lot of spread, similar to the 00z ensemble set, so lots of things open to possibility.
ed szoke NOAA/GSD