Fall 2014: Polar vortex to visit Northeast; South at risk for tropical hit
AccuWeather Global Weather Center -- 6 August 2014 --AccuWeather reports as fall 2014 takes form, no relief is in sight from the historic drought and the raging wildfires in the West.
While the West undergoes another period of heat and dryness, the Southwest, South and Texas will experience a soggy end to 2014. For the Northeast, blasts of winterlike air will arrive early this fall, serving as a reminder of last winter's brutality.
As wild weather unfolds across the nation, the tropics will also ramp up, putting the eastern coast of the United States at the highest risk for a direct impact.
Polar Vortex to Return Early in the Northeast
While the fall will kick off with days of sunshine and temperatures above normal in some of the region's largest cities, including New York City and Philadelphia, the polar vortex may make its return for short, sporadic periods in September.
"The vortex could slip at times, maybe even briefly in September for the Northeast," AccuWeather Lead Long-Range Forecaster Paul Pastelok said. "There could be a significant shot of chilly air that comes across the Great Lakes region and into the interior Northeast sometime in mid- to late-September."
As conditions in northern Canada begin to set up similar to last fall, getting colder and unsettled quickly, it is likely that this pattern could become a source for colder air to make its way down at times into the United States, inducing a drop in temperatures for the interior Northeast during mid-fall.
"Temperatures will not be as extreme in November when compared to last year, but October could be an extreme month," Pastelok said.
After short-lived days of the polar vortex in September, the weather should turn a bit warmer in November as rain ramps up across areas from New York City to Boston and Portland, Maine, as well as the rest of the region.
"We will see some dry weather in the Northeast, barring any tropical systems, in September and October but in November it will get wet," Pastelok said.
Following a soaking November for Northeastern residents, El Niño will make its debut early this winter, fueling early winter snow across the area.
"December could get kind of wild due to the very active southern jet stream that is going to provide the moisture for bigger snowstorms," Pastelok said. "The Northeast could have a couple of big storms in December and early January."
Winterlike Cold, Snow to Blast Plains to Rockies
Unlike the Northeast, the trend for the northern Plains and northeastern Rockies will sway more winterlike, as early snow and cold air blast the area this fall.
"October could be a month of snow and cold weather across the northern Plains and in parts of the northeast Rockies," Pastelok said.
While it's not uncommon for this area of the country to receive snowfall in the fall, areas from Bismarck, North Dakota, to Miles City, Montana, will be more vulnerable this fall to an increased number of snowstorms.
Aside from the snow, temperatures are expected to be near or below normal for most of the region with some parts of the southern Rockies experiencing temperatures 2 to 4 F below normal.
"Some areas of the southern Rockies will start out in a hole 2 to 4 degrees below normal and never recover from that," Pastelok said. "The northern Rockies and the Plains will get colder as the season goes on."
As the cold grips areas from the Colorado Rockies to the Sierra, the cold may even expand southward into the central Plains and portions of the Midwest, including Chicago and Milwaukee and Green Bay, Wisconsin.
While the cold and snowy weather will create ideal early-season conditions for ski resorts and avid winter athletes in the eastern Rockies, Colorado, those in the western Rockies, the Sierra, will not be as lucky.
"The dryness in the West is going to hamper any early significant snowfall in the western Rockies from Lake Tahoe to Bend, Oregon," Pastelok said.
Severe Storms, Flooding to Unfold Across the South
With the heart of hurricane season in the early fall, September is predicted to be an active month in the Atlantic.
"We are looking at a low number count for the tropics in the Atlantic, but we may have a couple more storms on the way," Pastelok said. "We've seen September in past years as an active month during past El Niño years, so don't count the season out yet."
As the Southeast coast, from Florida up through North Carolina, is most susceptible for a direct impact from a tropical system this fall, areas farther north, including Boston and New York City, could experience rain from a tropical system as well.
"September is an active month and there could be some impacts, especially from Cape Hatteras, North Carolina, down through Daytona Beach, Florida," Pastelok said.
Regardless of tropical activity this season, the Southeast will feel the effects of El Niño with an increase in stormy weather and rain.
Areas from New Orleans to Jackson, Mississippi, and Atlanta will see above-normal rainfall for the season, while areas closer to the southeastern coastline such as Pensacola, Florida, will likely break both daily and perhaps even yearly rainfall records this fall due to the immense amount of rain that fell during spring.
Likely to drench the region further, a busy secondary severe weather season may transpire late in the fall from mid-October to November across portions of the South.
Based on the weather patterns so far this summer, the lower Mississippi Valley and the Gulf Coast, specifically the central and western Gulf Coast, will be most vulnerable for a late severe weather season, according to Pastelok.
Generating strong and even tornadic thunderstorms, the fall's secondary severe weather season can prompt heavy rain, damaging winds and produce flash flooding.
"We've seen in past years like 2009, 2004 and 2002, years with patterns similar to this year, that there have been several tornadoes that have broken out during the fall season," Pastelok said. "Back in 2004, there were over 150 tornadoes that broke out in the month of November."
Among the highest risks for autumn severe weather in late October and November are some of the Southeast's major metropolitan cities, including New Orleans, Jackson, Mississippi, and Little Rock, Arkansas.
"Some smaller risk in November may also be in the mid-Atlantic and parts of the lower Northeast, including Washington, D.C., Philadelphia and even New York City," Pastelok said.
Battle to Ensue Between Flooding and Drought Relief in the Southwest, Texas
Following periods of extreme heat and dryness this summer, the onset of El Niño this fall will supply moisture for communities in the Southwest and Texas.
"We are looking at an increasing wet period for areas like the Four Corners region, New Mexico and southern Arizona, with that wetness working its way gradually into Texas," Pastelok said.
Amid drought in most of New Mexico and Arizona, as well as northwestern Texas, the much-needed autumn rain will help improve drought conditions.
"All places in Texas will get wet at some point over the course of the fall season, probably lasting into the winter season, too," Pastelok stated. "In fact, we may see some places get four or five months in a row of above-normal rainfall."
While the rain may be welcomed in drought-stricken communities, heavy rain falling over extremely dry terrain over short periods of time could prove to be dangerous and detrimental.
"When you go from dry conditions to heavy rains and monsoons, the rain can cause mudslides and major flooding," Pastelok said.
Western Drought to Hold, Wildfire Threat to Persist
Following the driest year on record and a parched summer for the Golden State of California, the fall season will not provide any drought relief for the region.
With a weak El Niño predicted this year, it is likely that the state will not receive enough rainfall to break the ongoing drought.
"We've noticed that weak El Niños don't always bring beneficial rains to southern California," Pastelok said. "They probably are not going to get enough rain at this point to deal with the drought; they will get some but not nearly enough."
As the drought holds in southern California, from Los Angeles through San Diego, northern California will also have some water troubles.
"Northern California will have a tough time," Pastelok said. "Fronts will tend to weaken heading into the West Coast so they might not get the full blast of moisture."
The Northwest region will also remain fairly dry this fall due to the split of the jet stream, a byproduct of El Niño.
"We may see a split jet stream where one jet goes way up into western Canada and that will leave dryness across the Pacific Northwest compared to normal," Pastelok said.
Expected to be warmer than normal this fall, the weather pattern will yield no assistance to the wildfire threat in the Northwest.
"From Portland, or just east of Portland, over the Cascades to Spokane on southward, temperatures will be 2 to 4 degrees above normal for the three-month fall average," Pastelok said.
As the summer heat and dry weather sparked multiple blazing fires across the Northwest, burning thousands of acres, forcing hundreds to evacuate and ruining tens of homes, the region will have to wait a little while longer for the fire danger to subside.
"There will be some relief but it is going to be a gradual transformation, so it's going to take some time," Pastelok said. "The fire danger is going to still be severe into the early fall."