2005-12-19 Wx Discussion (1945 UTC)
Visible image shows broken cloudiness over the ARB region this morning. A 500 mb height ridge has developed over the area in the wake of the active trough that passed through the area this weekend. The good news is that Sunday was very rainy. Reports of 24-hr precipitation totals (Sunday 12 UTC - Monday 12 UTC) are Blue Canyon 3.72", Sugar Pine 2.64", Greek Store 2.88", Auburn 1.88", Georgetown 2.44", Chico 1.69", Alpine Meadows 3.05", and Huysink 3.68". This morning's water vapor shows an area of ehanced water vapor moving toward ARB with ETA between Monday 22UTC and Tuesday 02 UTC. Visible imagery shows some cloudiness associated with it, but it is neither an extensive cloud shield nor vigorous as suggested by the absence of deep cloud tops. Precipitation is expected to be minimal with this feature, if any occurs at all. The next large wave is positioned near 32N, 144W in the GFS 500 mb 12 UTC analysis, which coincides nicely with its location in water vapor imagery. Also, water vapor imagery indicates the wave is beginning to take a more northward trajectory. It was noted that PW at Bagoda topped out at 30mm during Sunday's event.
Weather forecasters at Sacramento largely agree with the timing of precipitation of precipitation as discussed in what follows. Model guidance suggests the next opportunity for rainfall is Tuesday evening into Wednesday morning. (Why can't you fellas get a break and have a DAYTIME event?) Although the models (GFS ensemble, Candadian, MM5, RUC) closely agree on the position of the shortwave trough passing near California during this period, large disparities exist in QPF over the ARB, as the models are not in agreement concerning the inland penetration of a low-level front trailing the short wave. A couple of models suggest 12-hr accumulation ending 12 UTC Wednesday could be as large as 1-2". A couple of model forecasts contain no precipitation in the region. The majority of QPFs lie between these two extremes. Onset of precipitation, when it is forecasted to occur, is consistently between Tuesday 18 UTC and Wednesday 00 UTC. It was noted that PWs associated with this approaching trough is as high if not higher than what was observed during Sunday's events.
Chris Anderson