WY/SD Takes Full Force Of 1st Blizzard, Midwest Tornado Threat, Karen Bears Down On Gulf Coast

Written by on October 4, 2013 in United States of America with 0 Comments

The much talked about storm that’s now pushing into the central Plains has already produced upwards of 20 inches of snow to parts of South Dakota with blizzard conditions closing I-90 in Wyoming and South Dakota. The low itself has a tight pressure gradient and is tightening as it draws warm, moist air up from the Gulf with cold, dry air gets pulled out of Canada.

Winds are cranking around the circulation, driving temperatures towards 80 over Kansas and SE Nebraska within the warm sector while a howling northerly gale and temperatures in the 20s and low 30s with snow is producing white out conditions on the backside.

Below is a smorgasbord of various watches and warnings issued by the National Weather Service. It includes a ‘blizzard warning’ in red while there’s a large ‘winter storm warning’ area marked in light pink with ‘freeze warnings’ in light blue. ‘High wind warnings’ are in orange and as well as it being issued for eastern Colorado and western Kansas, it’s also issued for Southern California due to a developing Santa Ana wind threat this weekend which poses the greatest wildfire risk to the region in 5 years according to the NWS.

US

The main headline grabber is of course the major storm system bringing heavy snow but also a major severe weather threat from Oklahoma up to Wisconsin with a likely bullseye over central and northern Iowa later this afternoon and evening as colder air rides over top of very warm, humid air and winds blow out of the south at low levels, SW within the low level jet while upper winds blow out of the NW. This increased lapse rate ( temperature difference with height) harnesses a thunderstorm producing and maintaining environment for thunderstorms and it’s the wind direction difference with height, which increases the risk of these storms becoming supercell.

Firstly, let’s take a look at the setup as of this afternoon (chart below) and note the tight pressure gradient and tightly wound circulation. NNE winds will be in the 40-60 mph range this afternoon and evening and so minor structural damage is possible as well as power outages even within the snow. Large amounts of precip can be seen wrapping into the cold air and that’s where the blizzard is currently raging over the Black Hills region of South Dakota and where greatest totals will be. Heavy pounding snow should continue through much of the day but should ease from central and eventually eastern Wyoming later tonight after dumping 1-2 feet.

Note the strong SOUTH winds to the south and east, this is the primed region for severe thunderstorms and also temperatures are soaring, likely into the low 90s across eastern Kansas this afternoon.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

By Saturday morning the system hasn’t moved too far east and so heavy snow, strong winds and blizzard conditions are likely to continue raging on with I-90 probably remaining shut.

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

2 Or More Feet Of Snow Expected Over South Dakota

The snowfall is already impressive with 24 inches recorded at in two western Wyoming counties as of this morning while 20 inches is down over parts of the Black Hills in South Dakota.

With an additional 6-12+ hours of heavy, windblown snow to come, it’s highly likely that some parts of eastern Wyoming and western South Dakota will exceed 30, perhaps 36 inches (3 feet) when all is said and down.

Here’s the latest GFS snow forecast over the next 36 hours. Just look at the large area of 2+ft. Incredible. New records are inevitable!

Courtesy/Owned by AccuWeather Pro

Courtesy/Owned by AccuWeather Pro

Check out a few traffic cams from this morning and it’s clear to see the kinds of conditions out there.

I-90 at Gillette, WY as you can see is in very poor condition and is currently closed.

I90GilletteEast

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An empty I-90 at Spearfish, SD

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Big Temperature Spread: Large Area Of 25-35F Below Normal

With all large and powerful spring or autumn storm system, a large temperature contrast is created across the country with abnormally warm air lifting north ahead of the cold front while abnormally cold air gets drafted in on the rear. Here’s the estimated temperature departures from normal based on forecasted highs according to weather.com. Notice the extreme cold vs unusual warmth.

Source: weather.com

Source: weather.com

We also often see a tight thermal gradient or temperature difference across a relatively short distance ahead and behind the cold front.

Here’s the current temperature difference as of early afternoon. This contrast will grow even larger in coming hours as the air heats further ahead of the front while temperatures stay the same behind the front.

Source: weather.com

Source: weather.com

Greatest Severe Weather Threat For Months

As for the severe weather threat mentioned above. Here’s the threat area in accordance with the Storm Prediction Center. Note the area of MODERATE RISK issued across Iowa. The Weather Channel has raised their ‘TORCON’ to 6, that means there’s a 60% chance of a tornado within 50 miles over central and northern Iowa this afternoon and tonight but that risk isn’t confined to just Iowa, it really stretches from eastern Oklahoma up to southern Minnesota and Wisconsin.

day1otlk_1300

Here’s AccuWeather’s graphic showing the big cities in the way of dangerous PM storms.

Source: AccuWeather

Source: AccuWeather

Karen Weakens To 50 mph, Sets Sights On SE Louisiana, Alabama

As for Tropical Storm Karen, the system has been struggling with an exposed low level center for quite some time now. The NHC has dropped winds to 50 mph as the system heads northward towards the central Gulf Coast. Though weakening and looking more likely to remain a fairly weak entity as it makes landfall later tomorrow, don’t underestimate the flooding rain threat and even strong, gusty winds along the coast as well as a 1-2 foot storm surge.

Here’s the system currently on visible satellite.

vis0

You can clearly see the exposed low level center with all the deep convection well to the east due to shear, perhaps dry air too.

Here’s the forecasted track from the NHC.

144417W5_NL_sm

Significant Santa Ana Wind Event This Weekend Presents Greatest Wildfire Threat In 5 Years to Southern California

An upper level ridge is strengthening on the backside of the Plains storm system and with low pressure off the Southern California coast, so strong northeast winds will be triggered. According to the NWS, winds are expected to gust to between 60-80 mph through the canyons and valleys linking the desert with LA basin presenting not only one of the stronger Santa Ana wind events in recent years but also raises the greatest wildfire threat in 5 years. With the downslope and compressional warming effect of these winds, temperatures are expected to soar well into the 90s this weekend across coastal SOCAL.

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