HMT Forecast Discussion for 1/18/2008
A wave is expected to go over the HMT area 00 UTC 12/20. IWV values in the GFS are about 15 mm, and the system is moving out of the north at a rapid rate. Furthermore, the Pacific water vapor imagery does not show any swirls or convective activity with the potential to undercut the ridge. However, a really great atmospheric river extends from Hawaii to the Aleutian Islands.
A change in the large scale pattern is evident in many ensemble members at 7-8 days. The ridge in place over the Gulf of Alaska is forecast to retrograde in the 144-192 hour period. This occurs in concert with building heights in the western Tropical Pacific, as evident in the PSD reforecast ensemble. The pattern of troughs that will emerge from the regime shift is anyone's guess at this point. Ed Berry noted the timing of this pattern shift is roughly consistent with the briefing they gave last week.