Rocktober Is Coming

Wow, what a forecast.  Buckle up as a lot is going to be happening through Sunday.  Things get exciting around here when the mid-latitude storm track phases with monsoon moisture and we will have both in spades this weekend.  

I'll start with the GFS forecast valid 1200 UTC 11 October (0600 MDT Saturday).  A deep trough sits along the Pacific coast and monsoon moisture is streaming into the four corners area, producing the Predecessor Rain Event (PRE) discussed the the previous post in advance of the remnants of Hurricane Priscilla over northern Arizona, southeast Utah, and southwest Colorado.  In addition, a strong cold front sits over eastern Nevada.

By 0000 UTC 12 October (1800 MDT Saturday) that strong cold front is over northern Utah and lighting up parts of northwest Utah.  

I'm not sure how Saturday is going to play out in the Salt Lake Valley ahead of the front.  There will be southwest flow ahead of the front but it's hard to say if we might get showers and thunderstorms from the monsoon moisture or if we might be "dry slotted" in an area of dry air that has wrapped round the trough.  We shall see.

By 0300 UTC 12 October (2100 MDT Saturday), the front is pushing across the Salt Lake Valley bringing rain and possibly thunderstorms.  This is a strong front and a deep trough, expect a big change overnight.  

By 1200 UTC 12 October (0600 MDT Sunday) we are post-frontal, with unstable northwesterly flow.  700-mb (crest-level temps) at this time are -5.6°C, compared to 6.8°C just 12-hours earlier on Saturday afternoon.  Snow levels will be a dropping with the front.  

Expect some adjustments in timing and details as the event approaches and consult forecasts, not only for the Salt Lake area, but especially if you are adventuring in southern Utah over the next few days.  The NWS currently has a flood watch up for that area starting this afternoon.  

Source: NWS; Snapshot from 1:06 PM MDT 9 Oct 2025

More mountain snow in the central Wasatch?  You betcha'.  Snow levels will be high Saturday, but they will be crashing down Saturday night if the forecast frontal timing is accurate.  Accumulations will depend strongly on how much precipitation falls during and after the frontal passage.  Through 0000 UTC 13 October (1800 MDT Sunday), the median downscaled GEFS and European ensembles are generating about 1.5" of water, but the former is around only 4" of snow whereas the latter is closer to 7".  Much is going to depend on details that are tough to anticipate now.  Stay tuned.

I'll add that median wet-bulb zero levels drop to as low as 6600 feet on Sunday morning.  It's not out of the realm of possibility to see some flakes down to bench levels.  

Buckle up.