HMT Forecast 2/1/2008 19:42 UTC
This morning we are seeing the tapering off of the event that began yesterday morning. As of 7am Pacific time, BLU had reported 1.72 inches, Huysink 1.92, Auburn 1.12, and Georgetown 1.04 showing a trend of higher totals in the north of the ARB over the south. This morning's NAM has the potential for additional accumulations of up to 0.4 inches with the event ending sometime around 15ut morning according the SREF ensembles, so I think the NAM might be over doing the precip on this. These moisture amounts were right in line with the HMT high res ensemble runs yesterday that showed the NAM to maybe be a bit high on the total precip side as well, and gives further credibility to the HMT project's high resolution ensemble forecasts.
This morning we have another moisture surge in the IR water vapor imagery nosing its way toward the coast located at about 44N 139W. This is the source for the next system that is still on track to start another precipitation event between 21UT 2/2 and 00UT 2/3. Today this event still looks to be fairly cold in overall character with freezing levels starting near 950 hPa (1960 ft), rising quickly to 920 hPa (2900ft) and then further lifting (gradually) to 900 hPa (3500ft) by 15UT 2/3 where it remains until the end of the event. The moisture plume dimensions as shown by GFS are broader (N-S) in nature over the current system with a TPW content of about 2.5cm and therefore should result in a longer lasting event for the ARB. This is corroborated by the appearance of the plume in this morning's satellite imagery, but the plume may change dimensions between now and Saturday evening, even so, it looks like the GFS is doing a good job on describing the areal extent of the moisture. As noted yesterday, the winds associated with this event remain stronger and more favorable than the current event with winds beginning at SSW at 30kts, increasing to SW at 50kts for a considerable timeframe (06UT - 15UT) 2/3 after which they drop at 15UT coinciding with a trof passage and the likely start of the end of the event with the winds going westerly to 30 and finally northerly at 15 near 00UT 2/4. The NAM produces 2.83 inches of liquid equivalent, while last night's GFS had 2.14 and this morning's GFS produced 2.25 inches. So the models are all pretty consistent with 2+ inches of precipitation. By all accounts this could be considered a favorable IOP candidate with the exception of the cold nature of the event with the freezing level staying at relatively low levels throughout.
Following this event there appear to be some minor precipitation opportunities, but nothing to get excited about yet. The 06UT 2/6 event is both weaker and faster moving than the "Saturday evening" event mentioned in the prior paragraph. Following this there appears to be another potential plume of moisture entering the vicinity of the ARB, on or about Wednesday 2/13.
Therefore, as things currently stand, after this next potential opportunity (Saturday evening local time) the ARB enters an extended period of minor to inconsequential events and possibly an extended dry period.
Dan Birkenheuer ESRL/GSD