Overall, no real surprises so far. The trough approaching from the west was originally part of an area of low pressure that just came onshore and is going to work its way across northern California. As is usually the case figuring out where that trough is located is a huge challenge. According to the National Weather Service, this morning at 4:30 am they had the trough on the Nevada/Utah state line. With the moisture plume ahead of the trough. They also said the following with regards to the precipitation: ”
“The large-scale forcing will be maximized later this morning through mid-afternoon as the trough progresses eastward. Therefore expect about a three to six-hour window for a majority of the precipitation to fall.”
This is in agreement with all of the models from yesterday and last night showing the heaviest precipitation falling between 5 am-11 am.
Well, I can see the moisture plume clearly exiting our area. on a couple of different views and I can see dry air getting entrenched to our west. Green is moist yellow and orange are dry.
WU is my preferred source of surface front data, however, every 3 hours or so they reset their map to the WPC map (NOAA’s Weather Prediction Center) which is frequently wrong. It appears they have just done that.
I have combined satellite and radar here. Even when I look at high-resolution satellite I am really struggling to see the trough at all (assuming it truly is in the middle of Arizona and Utah).
To further confuse the issue the NWS goes on to say this:
“Around midday a midlevel dry slot following the trough passage causes the low-level lapse rates to steepen and shallow convection to develop mainly in the higher elevations. Some of the convective allowing models show relatively modest instability within the trough axis with MUCAPE values of 50 to 200 j/kg, which could certainly support thundersnow and enhanced snowfall rates. By early afternoon the forcing for ascent crosses the divide leaving orographic lift and convection.”
When I look at the latest run of the HiRes WRF I do see the CAPE (instability) they are referring to. It peaks between 1-3pm.
The problem is the future radar does not indicate that the CAPE will trigger any enhanced activity at that time.
What I am taking a long time to tell everyone is I don’t have a great handle on this, and I am not sure anyone else does either. The future radar does show an uptick in activity between 9-11 am with a noticeable decrease after that.
I am anxious (and concerned) to see how this plays out! I hope the next pieces are easier to deal with.