Published : Monday, March 19, 2018 | 2:58 PM
The National Weather Service warns of a strong storm system that is coming in from the Pacific Ocean that brings the potential for a very wet and long duration storm event for Southwest California Tuesday through Thursday night.
The NWS calls this an “atmospheric river event” that is likely to bring the highest rainfall totals to Pasadena and most of the region so far this season.
Atmospheric rivers are “relatively narrow corridors or filaments of concentrated moisture in the atmosphere,” says the NWS. When atmospheric rivers make landfall, they often release the water vapor in the form of rain or snow.
The NWS said a prolonged period of moderate to heavy rainfall could occur with this system, with the highest rainfall intensity expected to occur sometime between late Tuesday night and early Thursday.
The weather service also said isolated rainfall rates as high as one inch per hour could be possible, especially as the storm system`s cold front moves in, between Wednesday night and Thursday morning.
“In addition to the flash flooding and mud and debris flow risk in recent burn areas, there will be flooding threats in non-burn areas due to the long duration and intensity of this storm,” said the NWS.
“Widespread urban roadway flooding is possible as well as rockslides and mudslides, especially near canyon roadways. As a result, there could be significant travel delays and road closures across the region between Tuesday and Thursday night.”
By Friday, the storm system is expected to exit the area, and skies should clear as the drying process begins.
Tuesday will see a 20 percent chance of rain after 11 a.m. and will be mostly cloudy, with a high near 71. Tuesday night the chance of rain jumps up to 50% percent, with a low of around 54 and a calm wind.
Rain could be heavy Wednesday. The highs will be near 66, with a southeast wind around five mph. Wednesday should see more rain and lows around 55.
Rain continues on Thursday, with highs near 63. Thursday night should see rain tapering off a bit with a chance of showers and a low around 49.
Friday should be mostly sunny, starting a warming trend with a high near 63. Friday night should be mostly clear, with a low around 46.