Multiple Rounds Of Heavy Rain Heading For The West Coast Through Early Next Week

An active pattern will send multiple waves of drenching rain into the West Coast this week, bringing measurable rainfall from the central California coast straight up through coastal British Columbia. The heaviest rain will fall at higher elevations—with heavy mountain snow likely in California—but just about everyone from Santa Barbara to Seattle has some much-needed rain on the way.

The impending bouts of heavy rain will be the result of several atmospheric rivers, or bands of enhanced upper-level moisture that flow from the tropics to the mid-latitudes. Atmospheric rivers act like reservoirs that can boost rainfall rates.

The latest 7-day precipitation forecast from the Weather Prediction Center shows 5+ inches of rain falling across a huge portion of the West Coast. As usual, higher terrain near the water will see higher totals, while cities at lower elevations or in rain shadows will see lower rainfall amounts. High elevations are going to get thumped with a decent amount of snow by this time next week.

This is going to be a long-duration event with the potential for three or four rounds of precipitation through early next week.

The first wave of precipitation is arriving in northern California this evening, and it'll sweep through the Pacific Northwest throughout the day on Wednesday. The second round, associated with a front extending off a low heading into British Columbia, will arrive overnight Thursday and taper off through Saturday. A third big wave of precipitation, which is likely going to be the most significant of the bunch, will hit on Sunday and last through early next week.

Make sure wireless emergency alerts are activated on your smart phone in case flash flood warnings or evacuation orders are issued for your location. Stay mindful of the threat for landslides and mudslides. If you come upon a flooded roadway, it's not worth trying to drive across. It's impossible to tell how deep the water is before it's too late, and it only takes a few inches of moving water to lift up a vehicle and carry it downstream.

A couple of crummy days on the West Coast are certainly more than worth it after such a hot and dry summer. 

A huge swath of the western United States remains mired in a significant drought. Last week's update of the U.S. Drought Monitor found that 87.18% of the entire state of California in an extreme or exceptional drought, the two highest categories on the scale. The impending rains and mountain snow will bring some beneficial relief to these areas. It won't erase the drought or undo the damage, but anything helps.

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A Hurricane's Remnants Could Bring Flash Flooding To Texas This Week

Tropical Storm Pamela will make landfall on Mexico's West Coast as a hurricane late Tuesday night and quickly push inland over the next few days. Mexico's rugged terrain will tear the storm to shreds in a hurry, but the system's remnant moisture will continue into the south-central United States and bring a threat for flash flooding to Texas over the next couple of days.

The National Hurricane Center expects Pamela to regain hurricane strength before making landfall near Mazatlán overnight Tuesday into Wednesday morning. The system will quickly fall apart as it grates up against the steep mountains of central Mexico. However, a deep reserve of tropical moisture will continue flowing into Texas on Wednesday and Thursday.

Pamela's remnant moisture will reach central Texas at the same time as a cold front sweeping in from the west. Add in even more moisture flowing in from the Gulf of Mexico, and additional upper-level lift from the jet stream, and it sets the stage for very heavy rainfall across the region.

The latest forecast from the Weather Prediction Center calls for widespread rainfall totals of 2-4 inches for much of central Texas on Wednesday and Thursday, with the possibility for 5+ inches of rain in some areas. This may not sound like much, but the ground here is much more impermeable than in places like Alabama or Virginia. 

The WPC issued a moderate risk for excessive rainfall (in other words, flash flooding) across the areas expecting the highest rainfall totals. A moderate risk is usually a decent signal that widespread flash flooding is likely.

As such, flash flood watches are in effect for a wide swath of Texas and a portion of southeastern Oklahoma. The watches include San Antonio, Austin, Dallas, and Fort Worth. Flash floods are dangerous no matter what, but they're especially dangerous when they occur in heavily populated areas.

Driving through floodwaters is never worth it. It's impossible to tell how deep the water is until it's too late—or if the road is even still there under the water—and it only takes a small amount of moving water to lift up a vehicle and carry it downstream.

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Tornadoes Possible Sunday As Severe Weather Threat Targets The Southern Plains

A potent risk for severe weather will cover parts of the southern Plains on Sunday as a low-pressure system develops and moves across the area. It's been a relatively quiet year across the region as far as tornadoes go, but Sunday's threat could change that in a hurry. Make sure you're prepared for severe weather and have a way to receive warnings if you're in the area this weekend.

A low-pressure system will develop over western Texas during the day on Sunday and push across Oklahoma through the evening hours. Warm, humid air will provide plenty of fuel for thunderstorms to bubble up, while ample wind shear will give those storms the kick they need to turn severe.

The Storm Prediction Center issued an enhanced risk for severe weather for a large portion of Oklahoma, including the Oklahoma City and Tulsa metro areas. Sunday's severe risk also extends outward to include Dallas-Fort Worth to the south and Joplin to the north.

Any of Sunday's severe thunderstorms could produce tornadoes, large hail, and damaging winds. The greatest threat for tornadoes and large hail will occur in and around the enhanced risk area during the afternoon hours as the storms first develop. This initial batch of discrete thunderstorms will be able to maximize their interaction with instability and wind shear.

As the evening progresses, we'll likely see thunderstorms evolve into squall lines and bow echoes. The damaging wind threat will take over as the main risk when that happens, along with a threat for spin-up tornadoes along the leading edge of any of the lines.

The threat for severe thunderstorms will continue after dark for many areas at risk on Sunday. Given that we tend to tune out after sunset, it's more important than ever to get severe weather warnings the moment they're issued. 

If you live in the region (or if you're visiting for the weekend), take a look at your phone's settings and ensure that wireless emergency alerts are activated for tornado warnings and flash flood warnings. 

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A Stormy Pattern Will Bring Heavy Rain To The Southeastern U.S. This Week

Bouts of heavy rain will envelop parts of the southeastern United States over the next couple of days as a pokey upper-level low hangs around over the region. While we shouldn't see any organized severe weather, any of the thunderstorms that bubble up in the soupy airmass could produce heavy rainfall, leading to a risk for flash flooding in some spots.

The big weather story for most of the country this week is that the weather is going to be relatively boring. A huge upper-level ridge parked over the U.S. and Canada will keep things pretty warm for the next week, with high temperatures in the 60s and 70s reaching as far north as Hudson Bay. (That's toasty for October!)

However, an upper-level low over the southeast will keep things interesting through the end of the week. This cutoff low will linger for the next couple of days, providing the lift needed to kick off several rounds of showers and thunderstorms from Alabama to Virginia.

The Weather Prediction Center's latest rainfall forecast through next Monday shows a widespread region of 2-4 inches of rain falling from the northern Gulf Coast up the Appalachian foothills into Virginia. Some areas will see higher rainfall totals, especially if any productive thunderstorms park over one area for too long.

Flash flood watches are in effect for parts of Alabama and Georgia ahead of the heavy rainfall. It's already raining pretty hard in spots. A heavy storm delayed a race at Talladega earlier this afternoon, and we had one of the year's better storms today here in central North Carolina.

The rain is a welcome sight. It was a pretty dry September for much of the southeastern and Mid-Atlantic states, with many areas coming in several inches of rain below average over the past 30 days. 

[Satellite Image: NOAA]

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