San Diego’s Mission Valley can be quite a challenge during the winter. Most of the crossings of the San Diego River are low and not bridged. As a result, when it rains these crossings can be closed rather quickly. This greatly affects the ability to transect the valley along these roadways. The freeways, I-5, State 163, I-805, and I-15 are built with bridges and high enough to not flood. This is a guide to what is normally closed during storms.
From west to east:
Pacific Highway – Bridge – not closed
Morena Blvd – Bridge – not closed
Fashion Valley Road – closed more often than not during storms. This crossing has been rebuilt several times as well.
Avenida Del Rio – closed regularly during storms.
Mission Center Road – low crossing built a little higher than average. Still floods during major storms but is strong enough to avoid being damaged as a result.
Camino Del Este – Still low but built strong. Closes during major storms.
Qualcomm Way – Closes during very large storms. Built a little higher to help keep it open during major storms.
Ward Road – very low crossing and subject to closure during storms.
San Diego Mission Road – low crossing and subject to closure.
Friars Road (east) – Bridge – does not close.
Now, in the event all of these low-level crossings are closed, it is probably best to simply avoid Mission Valley in general. If you have to be there, I would suggest taking the 163 or 15 to cross the San Diego River. It may be a convoluted and circuitous route to use, but it is your only choice. Mission Valley circulation wasn’t designed with the river to flood in mind, unfortunately. Some developments, such as Fashion Valley Mall, was at least partly designed for flooding. The southern parking structure was built with the lower floor to be flooded and still allow for use of the rest of the structure. Even MTS built the San Diego Trolley Green Line with the floods in mind. Most of it is elevated through the valley.