A Rough Wednesday in Store

After tornadoes have already struck early this week in places like Oklahoma, another storm system will be swinging into the mid-section of the country with another bout of severe weather on the way for Wednesday and Wednesday evening.  The Gulf of Mexico is now open for business, pushing dew points above the 60-degree-mark all the way up the southern Mississippi Valley, and more moisture is slated to crawl northward.

US Surface Dew Point Map, Image: Unisys Weather

The dew point is the measure of moisture in the air and it is this moisture that drives thunderstorms.  Once the dew point exceeds 60, in combination with several other factors, the atmosphere is generally primed for thunderstorms and just waiting for a system to move in.

US Infrared Satellite Image, Image: Unisys Weather

It is the system circled above that will be that next system on Wednesday.  Therefore, the Storm Prediction Center has extended an area of slight risk of severe weather all the way up the lower Mississippi Valley and into the mid-Mississippi Valley.  The main threats are damaging winds, hail, and isolated tornadoes.

Severe Weather Outlook Wednesday-Early Thursday, Image: NOAA

Television meteorologists are talking about this elevated threat of severe weather in places like Mobile, New Orleans, and Little Rock.

Spring Has Sprung in the East For Now

After record setting snows and unseasonable cold across the eastern 2/3 of the United States this winter, the table have turned, at least temporarily.  This weekend, sunshine is the main player across much of the East as fair-weather high pressure retains control, meaning a well-deserved respite with highs ranging from the pleasant 50s in the Northeast to near 70 degrees across the Gulf South!  Place seeing the beautiful weather include Philadelphia, Raleigh, and New Orleans.

National Weather Service Advisories Map, Source: NOAA

Meanwhile, the “trough,” or dip in the jet stream, that was plaguing the East with precipitation and cold weather, has shifted to the West Coast, allowing in storm systems and markedly colder air.  Here, one cold storm is expected to swing across the Pacific Northwest allowing for snow as low as 1,000 feet around the Medford, OR area d0wn to northern California on Monday.  Here, Winter Weather Advisories are posted above 2,000 feet for up to 4″ of snow.  Another storm is rotating through the Southwest, affecting high elevations above 5,oo0 feet around Flagstaff and Tucson, AZ with up to 14″ of snow through Monday.

Satellite & Surface Map, Image: Unisys Weather

Snow-pack, Continuous Cold Set Stage For Spring Floods

The National Weather Service has released its spring flood outlook, and once again the Red River Valley in North Dakota is threatened.

National Snow Depth, Image: NOAA

The snow-pack is approaching record levels and a cold, cold winter has limited melting and evaporation. The frozen soil in North Dakota will eventually melt, causing streams and rivers to swell.

1997 Red River Flood, Image: NOAA

In 1997, major flooding along the Red River near Grand Forks led to the evacuation of 50,000 people. The river inundated areas 2 miles away.

River Flooding, Image: NOAA

You can keep track of river stages online at the National Weather Service website.

-Dawn Brown

Gulf Coast Seiche

The recent Chilean earthquake at a magnitude 8.8 had some pretty far reaching effects and we’re not just talking about across the Pacific!  Some effects were actually felt as far away as the Gulf Coast of the United States.  Something called a seiche was actually observed in Lake Pontchartrain.  What is a seiche? According to the American Meteorological Society Glossary, a seiche is an, “oscillation of a body of water at its natural period.”  In other words, it is some additional amount of water, or a “standing wave,” on top of the normal tidal cycle or water level.  In this case, this additional amount of water was caused by the seismic waves of Chilean earthquake 4,700 miles away traveling through the earth’s crust!  It was actually measured that tides were running 5″ above their predicted levels in Lake Pontachartrain 11 minutes after the earthquake occurred.  Seiches are nothing new.  The term was coined in 1955 and the phenomenon has been observed as far back as 1755 in England.

In fact in history, due to the massive Alaskan earthquake of 1964, seiches also occurred in the Gulf Coast area; some reported as high as nearly six feet!  This extreme height was probably aided by surface seismic waves that were in sequence with those moving through the earth’s crust.  The same earthquake caused bodies of water as small as home pools to overflow as far away as Puerto Rico.  Other seiches occurred in north and central New Mexico, eastern Kansas, and the region at the southern tip of Lake Michigan.

The occurrence of seiches seems to be more due to the make-up of the land that the seismic waves are traveling through, rather than the radial distance from the epicenter of the earthquake.  The density of seiches appears to be roughly proportional to the thickness of surface sediments.  For example, where there’s more opportunity for seismic waves to resonate through plenty of “loose” sediment and “rattle” bodies of water, like the Mississippi Delta region, there will be more seiches.  In places like the New England where the surface is more stable, there will be far fewer or no seiches.

More on seiches can be found on the USGS site.

1960's Seiche in Baraga County, Michigan, Image: Baraga County Historical Museum

Unbelievable and Unusual Northeastern Snowstorm

After seeing several inches (and in some spots even up to around a foot) of snow over the past few days from one coastal storm, parts the Northeast are getting yet another behemoth helping of heavy, wet snow from yet a second, much more unique system.  This storm, also a coastal storm, is not like the typical Northeast snowstorms which ride the jet stream quickly up the coast and then speed out into the North Atlantic, taking a day or less in any one spot to dump snow and then move on.  This system is actually running into, what we call in the weather world, a block.  In other words, the highway of air that the storm usually would travel on has become bottled up.  Therefore, the storm has virtually stopped in its tracks near Cape Cod, MA and is slowly plodding back westward toward New York City, getting prepared to meander around the New England through the weekend.  Unfortunately for folks in the Northeast, the storm will also be at its most intense point over the next 12 hours as it is lollygagging.  The silver lining is, though, thereafter it will be gradually weakening.

The strange and very sluggish movement of the storm, along with its tropical moisture connection have made for a very unusual pattern of weather across the entire Northeast.  For the time being, with the storm barely moving and basically at its strongest point, its counter-clockwise circulation has  had plenty of time to drag warm air from the south up on its eastern, and now also northern, side and on its western and southern side, colder air has had ample time to filter in from the north.

This means, as opposed to a typical East Coast snowstorm, where areas north and west, primarily inland, typically get the heaviest snow, places up north like Boston, MA and well-inland in the mountains like Albany, NY, Springfield, MA, and even Burlington, VT have been seeing mainly just a cold, soaking rain.  Head farther south and places like New York City, Binghamton, NY, and Atlantic City, NJ have been getting pasted with very heavy amounts of wet snow with Winter Storm Warnings extending as far south as the Delmarva!

National Weather Service Advisories Map, Source: NOAA

As the storm wraps in more cold air around its southern and eastern side, many locales seeing rain will finally transition to snow from southwest to northeast on Friday!  Fortunately, though, the storm should be weakening at this point, meaning lesser snow totals, but folks seeing all snow for this one, with nearly two feet of freshly-fallen white stuff already on the ground, will be measuring it with a yardstick by the time the snow gradually tapers off Sunday.

Storm Total Snowfall Forecast For New York City Area, Image: NOAA

Northeast Pummeled By Snow

National Forecast, Image: NOAA

TV forecasters in Philadelphia and Scranton, Pennsylvania, New York City, Binghamton, Buffalo, and Rochester, New York are preparing viewers for another winter storm that could dump another foot of the white stuff in some locations.

It’s been a messy winter for the Northeast. Washington D.C. was shut down for almost an entire week because of the amount of snow on the ground in the nation’s capital.

Snow Forecast, Image: NOAA

Storm after storm has been forming in the Gulf of Mexico, picking up moisture from the tropics and directing it toward the East Coast of the United States. Yesterday, I talked about the two weather patterns that have been colliding over the United States this winter: El Nino and the Arctic Oscillation. See yesterday’s MYL blog for more information on that.

Meanwhile, tune in to your local TV forecasters across the US for your latest winter forecast.

-Dawn Brown

Weather Patterns Collide

Texas Snowfall Totals, Image: NOAA

It’s snowing again in Texas! Snow showers have been falling all day in the Lone Star State. Dallas, Texas has very few accumulations (snow on the ground), but hill country areas such as Waco have 3 inches of snow on the ground.

The National Weather Service has issued Winter Storm Warnings for Texas, California, New York and other parts of the Northeast.

US Watches and Warnings, Image: NOAA

Two weather patterns are colliding over the United States this winter to produce storm after storm for the southern Gulf Coast and the Northeast. The El Nino Southern Oscillation is a weather pattern that causes a warming of the Pacific Ocean off the coast of Central America. This winter, El Nino is being credited with the surge of moisture and added rainfall/snow events in California, Arizona, New Mexico, Texas, and the Gulf Coast.  At the same time El Nino is occurring, scientists are also examining the effects of a Negative Arctic Oscillation. The NAO is associated with cold winters across the Northern Hemisphere, as more cold air descends from the Arctic to the nearby continents of North America, Europe and Asia.

Arctic Oscillation, Image: NOAA

The above graphic is data taken from the entire month of December 2009. What this graphic shows is average temperatures across Asia, Europe and North America have been substantially cooler than normal, whereas temperatures in the Arctic, Africa and parts of the Mid-East have been warmer.

Forecasted Lows, Image: NOAA

Take a look at the large dip of cold air across Minnesota, Iowa and the Dakotas. Once again, folks in Minneapolis will be waking up to below freezing temperatures. Look at the forecast lows across Louisiana… below freezing. If you add the extra moisture coming in from the Pacific due to El Nino and the cold air due to the Arctic Oscillation, you have the perfect recipe for snow.

TV forecasters in Shreveport and New Orleans, Louisiana are reporting once again on the unusual snowfall events.  In the Northeast, where snow has caused massive transportation problems, another round this week is expected.

-Dawn Brown

Line of Storms Threatens East Coast

National Radar Imagery, Image: NOAA

Click for the latest radar imagery.

A line of heavy rain and thunderstorms is converging on the Mid-Atlantic region this Monday. No major weather warnings are associated with the system that is affecting coastal Georgia and the Carolinas.

National Satellite Image, Image: NOAA

You can see from the latest satellite imagery, the line of heavy rain and thunderstorms on the East Coast stretches from the Florida Panhandle to Upstate New York.

Back out West, a storm system churning over the Rockies has triggered winter storm warnings just north of Phoenix, AZ, as well as New Mexico and West Texas.

-Dawn Brown

Less Confusing Saffir-Simpson Scale Released

Hurricane Ike, Image: NOAA

When Hurricane Ike slammed into the Texas coastline in September 2008, hurricane forecasters rated it a category 2 hurricane on the Saffir-Simpson scale with maximum sustained winds of 110 miles per hour. The storm surge associated with Ike topped 15-20 feet. If you used the Saffir-Simpson scale as a guide, the storm surge associated with Ike should have been about 6′. (See the graphic below.) The mismatch between the wind speeds generated by the storm and the associated storm surge have led the National Hurricane Center to drop storm surge from the widely used scale.

Old Saffir-Simpson Scale, Image: NOAA

The Saffir-Simpson scale was developed in 1971 by engineer Herbert Saffir and National Hurricane Center Director Bob Simpson to help forecasters explain the potential damage from a hurricane to the public. It was mainly designed as a way to explain what damage would occur to structures if a hurricane hit with 75 mile per hour winds, 95 mile per hour winds, 110 mile per hour winds, etc.  After the scale was developed, forecasters realized storm surge was a significant part of the damage from a hurricane, and they tried to come up with the height of the storm surge associated with different wind speeds. Unfortunately, it has led to errors in forecasting and misleading the public. The effect of storm surge on a coastline depends on the strength of the winds, the direction of the storm, the topography of the coastline, and the bathymetry (or topography of the coastline under the water.) Now, individual weather service offices, as well as universities, produce individual storm surge forecasts for each storm depending on the strength of the storm and its track. Here are the guidelines given today by the National Hurricane Center for the now called Saffir-Simpson Hurricane Wind Scale:

El Nino Making For Some Strange Weather

After causing a quiet Atlantic hurricane season, El Nino has been up to its old tricks again for the winter season.  El Nino has been causing tons of rain and storminess across California in places like Sacramento and down to Los Angeles, making for flooding and landslides.  Up to the west coast of Canada, its been warmer and drier than average.  This has been causing big problems for hosting the skiing events at the winter Olympics.  All the way from the mid-Atlantic to the Deep South, frequent arctic outbreaks have been pushing through and we’ve seen snow in places like Jackson, MS and Atlanta, GA.  We’ve even seen record amounts of the white stuff in places like Baltimore and Washington, DC.

An Average El Nino Winter, Image: NOAA

El Nino occurs when the waters of the western equatorial Pacific warm above normal.  This causes adjustments in large-scale seasonal weather patterns.  We’ve been in a moderate El Nino over the past couple of months with the central and western Pacific running at least 1.0 degree C above normal.

Latest Sea Surface Temperature Anomalies, Image: NOAA

ElNino, although it is forecast to be gradually weakening, is predicted to stick around through spring.  That means if you haven’t liked the weather you’ve been seeing, you might have to get used to it a little longer.

3-month Precipitation Outlook, Image: NOAA

On the image above, green denotes probability of wetter than normal and brown denotes probability of drier than normal weather.

3-month Temperature Probability, Image: NOAA

On the image above, red denotes probability of warmer than normal and blue denotes probability of cooler than normal weather.