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HMT Forecast 2/4/2008 19:39 UTC

The current forecast problem is now the long range prospect of future precipitation events. This morning's water vapor satellite imagery shows a strong ridge building at 51N 142W and a closed circulation at 40N 166E. The ridge is forecast to progress over the CONUS this week basically suppressing short waves and potential moist surges.

The next possible plume of moisture has been forecast by past models and again appears to be associated with a short wave coming through the ridge by Wednesday 2/6. The SREF gives a very modest 35% probability of precipitation between 12-18UT 2/6. At the same time the GFS shows 0 precip (system brings precipitation to the north of the ARB only), and the NAM produces only a trace.

After this system passes, zonal flow dominates for some time. There is indication of some slight ridging in the pattern by Saturday 2/9. Over the weekend, the GFS (2/4 00ut run) deterministic model shows a possible 2/10 event bringing 1.17+ inches to the ARB, but the EC model does not have anything close to an event at this time. Therefore, I discount the possibility. However, all models do have an event on or about Wednesday 2/13. Looking at past forecasts, this date has been mentioned consistently since last week as a possible timeframe for something. The EC model starts precipitation over the ARB at 00UT on this date and has it continuing until the end of the run (at least until Thursday) with 1.82+ inches of precipitation. Since all models are showing something in this timeframe I will go with this as the next likely possibility of something in the ARB and will continue to monitor the potential the remainder of this week.

Dan Birkenheuer ESRL/GSD