Impacts of Tropical Storm Rachel

Tropical Storm Rachel is currently well off the coast of Baja California, but it and its remnants are expected to affect the southwest United States this weekend and Monday. 

The latest track and intensity forecast shows Rachel moving on a northeastward path, ultimately making landfall somewhere on the northwest coast of Baja or the California Coast near San Diego as a Tropical Storm.  By 5 PM Sunday, Rachel is forecast to be a post-tropical cyclone as it moves into Utah.  

Source: NHC

A post-tropical cyclone has lost its tropical characteristics, including its warm core and symmetrical storm structure, but maintains a low-level circulation and in some cases evolves into a mid-latitude frontal cyclone through a process known as extratropical transition.  In this case, Rachel is forecast to maintain a low-level circulation all the way to Utah because it is gaining the assistance of a strong upper-level trough that is digging down the Pacific Coast, as evident in the GFS forecast below, which is valid for 0000 UTC 12 November (1800 MDT Sunday).  At that time, the GFS forecasts the low center to be on the Utah/Nevada border.  

As discussed in the previous post (Rogue Shower, October Storm), Rachel is just one of many moving parts affecting Utah during this weekend and early next week.  Some periods of showers and maybe some t-storms are possible tomorrow and then precipitation odds and frequency pick up for Sunday and Monday across much of the region.  Exactly who will get it and when is still a little uncertain, but everyone will probably get something.  The Utah Snow Ensemble total precipitation forecast through 0000 UTC Tuesday (1800 MDT Monday) below includes the mean of the 82 forecasts at top right, min of the 82 forecasts at bottom left, and max of the 82 forecasts at bottom right.  Based on the minimum, all of northern Utah gets at least some precipitation.  The mean of all the forecasts suggests over half an inch of total precipitation for much of the area.  The max shows the potential for over two inches in some instances.  

That's model guidance.  The NWS forecast discussion issued this afternoon is calling for higher amounts in portions of Utah, although I'm not sure if that might include precipitation after Monday.  

Thus, the NWS infographic issued last evening still looks quite valid.  

A wise meteorologist once told me to beware when the atmosphere is in outlier mode.  That is definitely the case during this period.  Monitor forecasts and adjust plans accordingly.