HMT Forecast 2/5/2008 19:35 UTC
Yesterday's forecast can be repeated today with confidence. Today we see 2 closed circulations in the Pacific, one at 52N 132W and the other further west at 47N 172W. Between them is probably the most moisture over the mid latitudes upstream of the CONUS at 43N 161W. Unfortunately, the near term forecasts do not show much hope in bringing this moisture to the ARB.
Last night's 06UT GFS run looked a lot like the 00UT EC run with minor precipitation entering the ARB (0.5 inches) on or near 2/13, the date we have been mentioning in discussions for the past several days. However, this morning's 12UT GFS run is now looking even more pessimistic for any chance of precipitation in the ARB on that date. The upper air pattern in the latest GFS run appears to stay more zonal and the cutoffs in earlier runs now appear as open progressive waves that traverse the CONUS rapidly. This mornings GFS basically has the system going even further north than prior runs and leaving the ARB dry on the 13th. Anything really beyond this point in time is highly speculative, since after 216 hours, the GFS ensembles produce some forecasts with precipitation; most of the ensemble members remain dry. The ensemble spaghetti plots also diverge rapidly after 216 hours leading me to think that we can't really say much beyond this timeframe.
As of this morning, the forecast for the ARB is to remain dry for at least the next 216 hours with possibly showers at times well under IOP threshold criteria.
Dan Birkenheuer ESRL/GSD