9:41pm Wednesday 11/30/22 Forecast update from KSBY Chief Meteorologist Dave Hovde:
The new modeling is coming in tonight. Very little chance to timing and intensity is expected with the Thursday rainfall (which is detailed below in the earlier posting of this story).
What is new, and has been the big story of the day, is information relating to the second part of this 1-2 rain punch Thursday thru the weekend.
Today the story has been the increased speed and intensity of the 2nd system. Tonight's models back that up.
In fact, the American GFS speeds up the system even more than it already had. Most models are in agreement on the pieces and generally the timing. The Canadian and UKMet also like a fairly quick arrival, not as early as the GFS which is even bringing in rain Friday later evening. It really looks more like Friday night into Saturday for the beginning of part 2.
I think the big question tonight is how significant will storm 2 be. Of the 3 models with updates tonight. All like significant cumulative rain potential. My official forecast is back to .5-2" inches but I think the question is: does it need to be higher. 2 of the 3 models like 3+" potential for all the rain Thursday-Sunday night. The GFS today which suggested 4" in the afternoon run backed off a little but still likes up to and possibly more than 2".
Apologies, it can get technical but to simplify: essentially all models like an inch or inches of rain Thursday to Sunday (with a break much of Friday). If the UKMet is right and this becomes an atmospheric river event then we might need advisories at some point.
Due to the timing and intensity changes that arrived to this forecast today, I think the forecast is high confidence for Thursday and moderate about Saturday but there is certainly growing agreement on the timing with perhaps only intensity being something to figure out in refined detail.
The current atmospheric river element of the Saturday storm is 2 on a scale where 5 is the maximum.
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The headlines in the weather today are essentially: Thursday rain still coming, and rain is now likely Saturday into Sunday (rather than a Friday and Saturday break). Friday does look to be a gap between systems. I think the timing change is important with a number of holiday events planned for the weekend the Saturday rain could be very impactful for those events and people who plan to attend.
Already over the course of Wednesday, we witnessed an increase in clouds in the region. While a drop or two of rain is possible anytime now, rain is more likely along a frontal boundary which arrives Thursday morning. The front looks to drag its way across the area from northwest to southeast over the entire daytime hours Thursday. I think this initial rain will taper Thursday night and Friday looks dry. Rain with the first system alone looks to be lighter inland to as much as 1" near the coast.
This next part is where the forecast has made a significant turn: the second part of this 1-2 punch has sped up. Not only has it sped up but the meteorological set-up is more clear (more model agreement as well). Rain looks to resume by Saturday afternoon (models only disagree a little on timing now by a few hours here and there). The second rain event looks to be associated with another low dropping in from the PacNW and arriving at the same time another low comes up from the PacSW. The systems essentially merge. The impact of this is not only the earlier arrival but also the potential for another significant rain event. Models disagree on what the "hot spot" for this second phase of rain will be but most suggest another .5-2" could be possible for the area.
Cumulative rainfall could be impressive. The 18z is very bullish .5-4"! Even if it were only a fraction of that, it is very significant. This assumes the hot spot for accumulation Saturday into Sunday is on the west-facing Central Coast, that hot spot could be further south. However, anytime you see this kind of potential you have to consider what it would be like IF that happened. Flooding could be an issue.
Thus far there are no advisories. I do think wind advisories are possible Thursday. If we get some saturation Thursday, then I think we'll have to watch rain rates Saturday. Again, I think the key message today is that timing changes could be significant for Saturday's planned outdoor events.