November 25, 2021

Another Drenching For The Pacific Northwest, Heavy Snow Headed For Northeast

It's been a remarkably quiet Thanksgiving across most of the United States. There are no severe thunderstorms to worry about. No massive nor'easters threatening to disrupt every major hub on the East Coast. The tropics are blissfully quiet. The only worrisome weather this holiday weekend seems confined to the two northern corners of the country, with another atmospheric river in the Pacific Northwest and heavy snow in interior New England.

Pacific Northwest Drenching

Yet another atmospheric river has its sights set on the Pacific Northwest over the next couple of days. It's already raining over much of western Washington and southwestern British Columbia, and there's plenty more on the way over the next couple of days.

We've heard a lot about "atmospheric rivers" lately. An atmospheric river is an area of elevated moisture in the upper atmosphere that usually flows from the tropics to the mid-latitudes. These features act like reservoirs that storm systems and thunderstorms can tap into and wring out tremendous amounts of moisture.

A recent atmospheric river event brought catastrophic flooding to parts of British Columbia and Washington, the damage from which essentially cut off access to the Vancouver, B.C., metro area by land. The current bout of heavy rain and gusty winds won't be nearly as prolific as the recent storm, but lots of rain is on the way and the added stress will exacerbate the damage and effects.

The heavy rain will wash over Washington and British Columbia in several waves. The first wave is ongoing tonight through Friday. The next round of heavy precipitation will move ashore late Saturday and stick around through Monday. A third batch of heavy rain will follow soon after and arrive by the middle of the week.

The Weather Prediction Center calls for hefty rainfall totals across the region, especially at higher elevations. 5-10 inches of rain could fall along the Cascades and Coastal Range, which is likely going to compound the damage in hard-hit areas, especially in British Columbia. Lower rainfall totals are expected in the big cities.

Wintry New England

The opposite northern corner of the United States is the other area expecting the week's most active weather. A winter storm moving across Eastern Canada will bring heavy snow to parts of the interior Northeast through this weekend.

Several inches of snow are likely in higher elevations across much of New York, Vermont, New Hampshire, and Maine, with an inch or two likely at lower elevations. The heaviest totals are likely in northern Maine, where some communities could wind up with double-digit snowfall totals by Sunday. Bands of lake-effect snow will also beef up totals along the eastern shores of Lake Erie and Lake Ontario.

[Satellite Image: NOAA]

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November 10, 2021

Season's First Big Snowstorm Set To Hit Northern U.S. Plains, Canadian Prairies

It was a sunny 77°F here in beautiful central North Carolina today, and we're staring down the season's first major winter storm up north. (Sorry.) 

Some areas are on track for legitimate blizzard conditions once the snow arrives on Thursday and Friday. The heaviest accumulations will fall near and north of the border, where some areas are on track to see double-digit snowfall totals by the end of the storm on Friday. 

The impending winter storm is winding up this evening as a low-pressure system moves into the Upper Midwest. The system will strengthen in a hurry as it treks into Minnesota during the day on Thursday, producing heavy snow on the cold side of the low and heavy rain on the warm side to its south.

For areas expecting snow, conditions will deteriorate during the day on Thursday and likely peak in intensity Thursday night into Friday morning. Precipitation will taper off through the day on Friday as the system weakens and pulls out of the region.

The best chance for shovelable snow will follow close to the U.S./Canadian border, where some communities straddling the international line could see as much as a foot of snow by the end of the storm. Farther south, a few inches of snow is possible throughout much of eastern North Dakota and western Minnesota, with the chance for a dusting pushing into the Minneapolis/St. Paul area.

My map uses the National Weather Service's snowfall forecast as of Wednesday night, which is why Canada is sadly excluded from all the fun. The Weather Network calls for a widespread swath of 8-16 inches of snow across southern Manitoba and northern Ontario. (Full disclosure—I occasionally contribute to TWN.)

Gusty winds are going to be a problem, as well. High wind warnings and wind advisories are in effect for much of the northern Plains as winds could gust 60+ MPH during the height of the storm. The combination of high winds and accumulating snow could lead to a period of blizzard conditions in northeastern South Dakota overnight Thursday into Friday.

[Model Image: Tropical Tidbits]

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November 5, 2021

A Pesky Coastal Storm Will Drench Parts Of The Southeast This Weekend

A developing nor'easter will bring dreary conditions to the coastal southeast this weekend, with cool temperatures, pouring rain, and driving winds making things miserable from northern Florida to eastern North Carolina.

The storm is already in its formative stages over northeastern Florida this evening. It's not all that impressive on satellite imagery—unless a bland deck of stratus clouds is your thing, then more power to you—but it's going to slowly grow more organized over the next day or so as it meanders up the coast.

The system and its worst conditions will peak during the day on Saturday, slowly winding down on Sunday as the system pulls away from shore.

This will be a nor'easter that doesn't affect the northeast. Nor'easters get their name from the northeasterly winds that buffet the coast. There's going to be plenty of that over the next few days. Winds could gust as high as 40-50 mph in parts of South Carolina and North Carolina.

Strong and persistent onshore winds will lead to widespread coastal flooding from storm surge, especially around high tide. Coastal flood warnings are in effect from Jacksonville, Florida, to southeastern Virginia through the next couple of days.

Heavy rain is going to be a problem near the track of the storm. The bulk of the heavy rain will stay juuust offshore, but a few inches of rain are likely throughout coastal counties from northeastern Florida to eastern N.C.

These totals could inch higher if the storm tracks a little farther west than currently predicted. Any amount of heavy rain is a headache if it falls too quickly, but leaf-clogged gutters and storm sewers will increase the risk for street and parking lot flooding in some areas.

Saturday is going to be a raw and gloomy day for much of the southeast. Northeasterly winds will lead to cold air damming, a phenomenon where cold air pools up at the foot of the Appalachians because it's too dense to flow up and over the other side. Widespread high temperatures in the 50s are likely as far south as northern Florida. Conditions will warm up a bit on Sunday as the storm moves away.

[Satellite Image: NOAA]

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October 19, 2021

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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October 12, 2021

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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October 9, 2021

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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October 4, 2021

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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September 27, 2021

Hurricane Sam Remains A Powerful Major Hurricane Over The Open Atlantic Ocean

Hurricane Sam spent more than 24 hours as a powerful category four storm this weekend as it churned out in the open Atlantic Ocean. The system was an absolute powerhouse for much of Saturday and Sunday, flirting with scale-topping category five intensity before the hurricane's structure stumbled on Sunday evening.

The latest update from the National Hurricane Center reported that Hurricane Sam's maximum sustained winds had dropped a bit to 145 mph by 11:00 p.m. on Sunday night, down from a maximum intensity of 150 mph earlier in the day. It's likely weakened some more since then given its ragged appearance on satellite imagery.

Hurricane Sam was a textbook example of rapid intensification if there ever was one. The system grew from a newly formed tropical storm to a hurricane in just about 24 hours.

The storm underwent another period of explosive intensification that began Friday evening and didn't finally level out until Saturday night when the storm reached solid category four intensity.

One of the great ironies of powerful hurricanes is that they're incredibly fragile systems. One hiccup can send them spiraling into a mess (can't we all relate these days?). That's what happened to Sam on Sunday night.

It's likely that Sam is undergoing an eyewall replacement cycle (ERC) right now, which occurs when the storm's eyewall degrades and is replaced by another, larger eye.

An ERC weakens a storm's winds and allows its minimum pressure to rise, all while redistributing its energy farther out from the center of the storm. This allows the hurricane to grow in size before potentially restrengthening once a new, stable eye emerges.

Hurricane Sam is one of the most impressive storms we've seen in the Atlantic Ocean in quite a while, and that's saying something given all the nonsense we've been through recently. It's a guilt-free gawk fest, one of the rare hurricanes in recent years we can admire without immediately cringing in fear.

Sam was a picturesque hurricane at its peak. The storm had a clear, bold eye that was surrounded by a dense core of ferocious thunderstorms fueling the system's immense power.

The near-symmetrical core of the storm vented into the upper levels of the atmosphere with a healthy outflow adorned by a beautiful plume of cirrus clouds that radiate clockwise from the eye of the storm. A hurricane's outflow exhausts air away from the eyewall so the storm is free to gather as much instability as it can from the warm ocean below.

The hurricane doesn't look that impressive anymore. Between the eyewall replacement cycle and possibly some wind shear throwing it off balance, Sam looks a little worse for wear tonight. Despite the storm's appearance, it remains a major hurricane.

Hurricane Sam is traveling around a large ridge of high pressure parked over the central Atlantic Ocean. It's crawling at just 7 mph, a relatively slow speed that's the result of weak steering currents hustling the storm along. 

Forecasters expect Sam to continue slowly lumbering along a northwesterly path that takes it safely clear of the Leeward Islands over the next couple of days.

While the storm will miss the Caribbean and likely won't have any direct impacts to the U.S. East Coast, this predicted path would bring the hurricane close to Bermuda by next weekend. We also have to watch where it goes from there for potential impacts in Atlantic Canada by the first week of October.

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