geography, weather

A Look at GOES Water Vapor Imagery (H. Michael Mogil, CCM, CBM, NWA-DS*)

This feature is about GOES (Geostationary Operational Environmental Satellite) Water Vapor (WV) imagery. This type of satellite imagery (just one of many) is based on a specific band of data within the infrared radiation (IR) spectrum. It is collected from a geostationary satellite positioned roughly 22,000 miles above the Equator near the longitude of Florida and a longitude just west of the U.S. West Coast. With the satellites racing around their larger orbit path at an angular speed that matches that of the Earth’s surface, the satellite never sees the earth moving (hence, geo- or Earth- stationary). As a result, animations show cloud and/or moisture movement only. These two U.S.-operated satellites are part of a global network of satellites supported by several Nations and/or organizations.

I’m a big fan of WV imagery because it allows meteorologists and others to see the motions (called animations) of clouds and locations of moist/dry areas. Even when the image is not color-enhanced, the various white to black grey shades provide important discrimination. Thunderstorms, with cold, high, cloud tops appear as the brightest white; cirrus (ice crystal) clouds are white, but typically not as bright. Moist areas are generally grey; dry areas are black (see scaling, warm to cold, at lower left of Fig. 1). It would be easy to see this representation as something similar to a topographic or relief map, with thunderstorms representing the mountains and dry zones representing dried lake beds.

In this image (Fig. 1) and associated animation, there is a lot to see. For example, there is a bright area that develops across eastern Oklahoma and moves into southeast Missouri. To its north, it is easy to see a small-scale swirl in the clouds and moisture areas. Further northwest, a larger swirl (the center of the main storm system) was moving into southwestern Minnesota.

Since the WV imagery is based on IR (temperature) data, it is easy to ascertain ground-based features when very dry air covers a region (such as west Texas, New Mexico, Colorado, and western Kansas). Notice the roughly north-line that separates a light grey region to the west and a dark area to the east. This marks the front-range of the Rocky Mountains, with snow-covered, colder mountains to the west and low-altitude, warmer, plains to the east (Fig. 2).Near the end of the animation, a cloud rapidly develops over far west Texas, just to the northeast of El Paso. The western edge of the cloud stays locked in place, as nearby clouds continue to move by from the west. This cloud feature formed as moist air bumped into the Guadalupe Mountains (and Guadalupe Peak, 8751 feet elevation) and was forced to rise (Fig. 3). Rising air cools by expansion (lower pressure as one goes up in the atmosphere) and this often leads to condensation and cloud formation. Since the feature causing the cloud to form doesn’t move, the cloud feature continually reforms on its western edge. From the ground, this would likely appear as a standing wave cloud,

Finally, across New Mexico, notice that some grey clouds move over the snow-covered, colder ground areas. These clouds are warmer than the underlying ground and provide some information about the vertical atmospheric temperature profile in the area.

The bottom line to all of this is that GOES weather satellite imagery allows meteorologists and others to view larger geographic regions and both large- and small-scale weather features.

And this limited perspective of satellite capabilities is just with current GOES capabilities and just one IR channel. Wait until GOES R, launched last November, gets fully checked out and starts to deliver operational data and images. The WOW factor will likely be incredible!

© 2017 H. Michael Mogil

Originally posted 3/1/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.

weather, weather safety/preparedness

The winds win! (H. Michael Mogil, CCM, CBM, NWA-DS*)

Today through tomorrow evening, large areas of the Nation and some nearby ocean water areas are under various types of wind warnings. From hurricane-force wind warnings in New England’s offshore waters (large-scale winter storm and intense pressure gradient) to Santa Ana (canyon-channeled) winds in southern California (Fig. 1), the winds win!

In New England, for added measure, heavy snow and bitter cold will add to the misery. Across parts of west Texas, a wintry mix will develop. In the mid-Atlantic, it’s a combination of large-scale vertical mixing (high speed winds from higher altitudes mixed down to the ground) and the effects of downslope winds.

In all of these land areas, winds will be high enough to affect the travel of high-profile vehicles and even passenger cars. Offshore from New England, waves will build to heights of more than 30 feet. As noted in National Weather Service marine warnings, “seas are given as significant wave height…which is the average height of the highest 1/3 of the waves. Individual waves may be more than twice the significant wave height.” Hence, if a 60-foot wave does form, it would take on the scope of the self-proclaimed “George Clooney Memorial Wave” in “The Perfect Storm” movie.

Winds will die down in many locales by Tuesday, as a more tranquil weather pattern establishes itself. Until then, drive safely, act cautiously, and stay in safe places.

© 2017 H. Michael Mogil

Originally posted 2/12/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.

weather, weather safety/preparedness

One New England Blizzard…Two New England Blizzards… (H. Michael Mogil, CCM, CBM, NWA-DS*)

On Feb. 9, 2017, southeastern New England experienced a significant snowstorm. Within the storm’s circulation, blizzard conditions lasted for some three to almost six hours and affected many areas. The National Weather Service (NWS) Office in Taunton, MA summarized the storm in a lengthy weather release on the evening of Feb. 9, 2017. Excerpts from that release have been provided here (all times Eastern Standard Time).

The storm responsible for the blizzard (Fig. 1 – left) was a “meteorological bomb,” a storm that undergoes rapid pressure falls (or “explosive deepening”) of at least 24 millibars (0.71 inches of mercury) in 24 hours. Bombs typically contain some “thundersnow,” which often means locally heavier snowfall. This bomb was no exception.

First, it’s important to reiterate what a blizzard actually is. According to the NWS, a blizzard involves falling and/or blowing snow, sustained or frequent wind gusts of 35 miles per hour or more and visibilities frequently reduced to less than a quarter of a mile. All of these conditions must last for three hours or more.

For purposes of this summary, the NWS meteorologists used only official airport reporting stations (since all of the above weather conditions are routinely reported at these). For visibilities, they decided to use reported values of one-quarter mile or less since, “…that is quite low for an automated sensor to detect.” Obviously, blizzard conditions occurred elsewhere across the area.

  • Providence, RI wins the competition with 5 hours and 18 minutes of blizzard conditions (10:51 a.m. to 4:09 p.m.).
  • Hyannis, MA was a close second with 5 hours and 4 minutes (12:56 p.m. to 6:00 p.m.).
  • Boston, MA netted blizzard conditions for 4 hours and 34 minutes (12:20 p.m. to 4:54 p.m.).

Other locations reporting blizzard conditions (in decreasing length of time of blizzard conditions) included Martha’s Vineyard, MA; Block Island, RI; Beverly, MA; Marshfield, MA; New Bedford, MA; and Westerly, RI.

As the region digs out, another storm system looms on the western horizon. This one, much like its predecessor, promises to involve “explosive deepening” as it passes by the region from late Sunday into late Monday (Fig. 1 – right). However, its movement will be significantly slower, allowing heavy snowfall and blizzard conditions to last longer. Already, local snowfall forecasts are pegged at approaching two feet.

This will be a “hunker down” storm. So stay home, dress in layers if you venture out, and, unless you have a snowblower, consider letting a local teenager shovel your driveway.

© 2017 H. Michael Mogil

Originally posted 2/11/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.

photography, weather

Nephelococcygia from space (H. Michael Mogil, CCM, CBM, NWA-DS*)

On Sat., Feb. 4, 2017, I gave a talk to the Friends of Barefoot Beach. The talk centered on “Celebrating The Weather.” I decided to use cloud photography to focus the talk on the sky.

As part of the talk, I shared some cloud photography of things familiar to us. One image was a happy dog (ground perspective); another was a flying goldfish (taken from an airplane window over London).

Last evening, I was perusing some GOES (Geostationary Observational Environmental Satellite) images and came across an interesting cloud pattern, one the showed a smiley-faced storm just offshore from Washington State (Fig. 1). I’ve rotated the image clockwise 90-degrees to make the image easier to view (Fig. 2).

The term for viewing shapes in clouds is “nephelococcygia.” Loosely translated from Aristophanes’ play, “The Birds,” it means “cloud cuckooland.” Since Aristophanes lived around 400 B.C.E., I am 100 percent certain that he never considered cloud watching from some 22,000 miles above the Earth in his literary repertoire. However, interpretations from his writing indicate that Nephelococcygia was a utopian city in the clouds.

Stay tuned for more nephelococcygia stories.

© 2017 H. Michael Mogil

Originally posted 2/5/17

climate, humor, weather

Southwest Florida winter to continue (H. Michael Mogil, CCM, CBM, NWA-DS*)

BULLETIN: Four Naples groundhogs spied their shadows early Thursday morning. Hence, look for six more weeks of south Florida winter. Yahoo!

Punxsutawney Phil does not have a sterling record of furcasting the weather for the last six weeks of winter, even though the official Punxsutawney web site says otherwise. I know because an intern and I analyzed about 100 years of Phil’s forecasts in the late 1990’s. During our research, we discovered that, at best, Phil was accurate only about 10 percent of the time. Phil just kept getting it wrong…and getting it wrong…and getting it wrong, much like Bill Murray did in the movie, Groundhog Day.

Phil’s forecast accuracy is far below chance and offers stark testimony to the inability of the Groundhog legend to really offer any hint about upcoming weather. Still, the legend is fun and offers a great escape for mid-winter blues. And even with a spate of Johnny-come-lately Marmota Monax’s (Phil has many ancestors and bretheren), groundhog weather prediction simply doesn’t cut it.

One reason these groundhogs keep getting it wrong is because of media coverage. No, the furry critters aren’t creating fake news. Rather, as Al Roker noted on the Today Show, Thursday morning, there are simply too many camera lights. Hence, the only forecast possible is ongoing winter. Not surprisingly, even with cloudy skies (Fig. 1), Punxsutawney Phil saw his shadow on Thursday (Fig. 2). I didn’t even bother to see what the other nationally known groundhogs predicted. I knew the answer.

Instead, my focus was on four Naples groundhogs. Okay, so they are Ty babies™. They are still groundhogs! And I can report, unequivocally, that no camera lights were at play. It was pure sunshine that allowed these marmots to see their shadows (Fig. 3).

While folks in northern climes are dreading six more weeks of winter, we in Naples are thrilled about winter’s continuance. The reason is that in southwest Florida, winter means lovely weather. Average daily climatological temperatures start in the mid-60’s in early February and only rise into the lower 70’s by the end of March. The daily range spans about ten degrees above and below these values. In short, it’s almost like late Spring in northern states. With minimal rainfall chances, it’s the weather southwest Floridians crave.

The only drawback to the lovely weather is that southwest Florida could use a few days of steady rainfall. Southwest Florida and much of the Florida peninsula, according to the National Drought Mitigation Center, has been (and is expected to continue to be) abnormally dry.

Wherever you may live, and whatever the weather brings, please, enjoy. Summer heat and humidity, for most of us, are just over the distant horizon.

© 2017 H. Michael Mogil

Originally posted 2/4/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.

weather, weather safety/preparedness

Long duration lake-effect snow event underway (H. Michael Mogil, CCM, CBM, NWA-DS*)

The National Weather Service has issued “lake effect” snow warnings and advisories for areas to the east of Lakes Erie and Ontario through Sunday evening (Fig. 1). These forecasts call for locally heavy snow and wind-blown snow with associated hazardous driving conditions. Forecasts for areas in New York State downwind of these lakes indicate that snowfall amounts will be within a 15 and 40 inch range (locally higher amounts expected) along with wind gusts to 45 miles per hour. The heaviest snowfalls are expected in the Tug Hill Plateau area (downwind from Lake Ontario, near Watertown and Montague, NY), with 12-hour snowfalls, throughout the period, frequently in the six to 12 inch range. Already, early this Friday morning, Watertown reported wind gusts in excess of 40 miles per hour.

While not yet issued, look for similar forecasts to be posted for other downwind areas of the entire Great Lakes region during the next several days.

This entire weather scenario is linked to a quasi-stationary surface and upper air low-pressure system across eastern Canada (Fig. 2). The system’s counter-

clockwise circulation will send winds across the Great Lakes, mostly from a west to northwest direction.

With the Great Lakes mostly ice free (Fig. 3), colder air, moving over relatively warmer water, can gain heat and moisture. This allows clouds (often low-topped) to develop in bands across the lakes (Fig. 4). As these bands make landfall, the air they are riding on experiences increased frictional drag

(friction is higher as winds blow over land than water). The result is a low-level convergence effect, adding uplift to the clouds. In areas where terrain increases inland, there is an added orography-lift effect (e.g., the Tug Hill Plateau area). In a snowfall event earlier this winter season, parts of the Tug Hill Plateau were targeted with over four feet of snow in a three-day period.

Due to the nature of “lake effect” snow events, the National Weather Service in Buffalo, NY noted early this Friday morning that, “…in lake effect snow, the weather can vary from locally heavy snow in narrow bands to clear skies just a few miles away. If you will be traveling across the region, be prepared for rapid changes in road and visibility conditions.”

© 2017 H. Michael Mogil

Originally posted 1/27/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.

weather, weather safety/preparedness

Enhanced severe weather threat for southeast U.S. (H. Michael Mogil, CCM, CBM, NWA-DS*)

Batten down the hatches (and be prepared to take shelter today and tonight) if you live or are traveling across the southeast U.S. The Storm Prediction has issued a highly unusual severe weather outlook for the region – calling for a moderate to high severe weather risk for South Carolina, Georgia, a small part of southeast Alabama and much of northern and

central Florida (Fig. 1). According to news reports, the storm system behind today’s severe weather threat has already claimed the lives of at least six people across Mississippi and Georgia.

Fig. 2 and Fig. 3 show the radar and satellite images, respectively, late this Sunday morning. What is most telling is that the current strong thunderstorm activity is occurring in a region of dry air aloft (the oranges and blacks on the water vapor satellite image – Fig. 3). This means that rising air

inside the thunderstorms must be moving at very high velocity to counter this dryness. Hence, many of the stronger thunderstorms are already likely acting as “supercells (isolated storms ahead of a line of storms).” Two apparent supercells can be seen in the northern Gulf of Mexico (Fig. 2).

As a new low-pressure system develops across the southeast today, and moves to northern Georgia and eastern Tennessee by tonight,

(Fig. 4), a very strong jet stream aloft (winds greater than 130 miles per hour) and a very warm and unstable air mass (dew points above 70 degrees F) will all be factoring into the storm evolution as the day and night progress.

The local storm potential graphic (Fig. 5) indicates just how strong the storms may be, even removed from the main threat region.

As the newly forming low develops, it will move to the northeast and spread a large shield of rain along the entire east coast during the next several days. Except for parts of New England, the atmosphere is just too warm for snow.

Although winds will be strong across the southeast today, coastal wave action, higher than average tides,

rip current danger and other coastal and boating dangers (including offshore gale warnings in the Gulf of Mexico) will be the watchwords across the west coast of the Florida peninsula into the Gulf beginning tonight and continuing until Tuesday (Fig. 6). That is because strong west and northwest winds will arrive once the cold front clears the area (Fig. 4).

Although skies may be sunny to partly cloudy across much of the Florida peninsula now, conditions will rapidly deteriorate during the latter part of the calendar day and early Monday morning.

Stay tuned to the National Weather Service, local broadcast media outlets and any tailored private weather subscriptions you may have for watches, warnings and advisories.

If you have loose objects outdoors, consider bringing these inside before the storms arrive.

© 2017 H. Michael Mogil

Originally posted 1/22/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.

climate, weather

Sierra Nevada snowpack increases dramatically; drought conditions wane (H. Michael Mogil, CCM, CBM, NWA-DS*)

When the computer models started to forecast incredible precipitation amounts for the Sierra Nevada Mountains of California and Nevada earlier this month, I thought the numbers were somewhat exuberant. After all, California has been in the throes of an extensive and hard-hitting drought for several years. However, this storm event (and the one on the western horizon) are welcome news for a state that lives in drought.

According to the National Weather Service (NWS) Forecast Office in Reno, the early January stormy period (Jan. 2 – 13, 2017) transformed the Sierra snowpack from a sub-average value to one that is pushing 200 percent of seasonal average (Fig. 1). This snowpack provides California’s dry season river runoff, water for agricultural and human uses and other aspects of California’s existence. The snowfall is also helping to boost ski resort business (at least, once folks can get to the ski areas).

It’s easy to see the impact of this precipitation on the California drought (Fig. 2). Note that the data cutoff for Drought Monitor maps is each Tuesday at 7:00 a.m. E.S.T., even though the maps are published each Thursday at 8:30 a.m. E.S.T. Hence, next week’s maps will likely show a further reduction in drought coverage across California.

Observations indicate that the high Sierra received between 9 and 15 feet of snow since the start of 2017. In the Tahoe Basin, within the “rain shadow”** of the Sierras, 2 to 5 feet of snow fell, except for the west shore of Lake Tahoe which received

between 6 and 8 feet of snow. For the Virginia Range (located just east of Lake Tahoe), reports indicated over 2 feet of snow had fallen, while along Highway 395 between Bridgeport and Lee Vining (on the east side of Yosemite National Park) between 1 and 4 feet of snow was reported.

Forecasters see a brief break in the stormy weather pattern through early next week. Then, more valley rains and mountain snows are on the menu (Fig. 3).

–  –  –  –  –  –  –  –

** The “rain shadow” lies downwind from a mountain range. It typically receives lesser precipitation amounts because upslope winds on one side of the mountain receives the heaviest precipitation, while downslope winds on the rain shadow side receive less precipitation. For the Sierra’s, west winds provide the upslope across much of California; as the winds cross over the mountains, lighter precipitation occurs across western Nevada and the Lake Tahoe Basin.

© 2017 H. Michael Mogil

Originally posted 1/14/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.

climate, weather

A Significant Dixie chill (H. Michael Mogil, CCM, CBM, NWA-DS*)

 

Across the South, this Sunday morning, Jan. 8, 2017, folks were pulling out their winter clothing. Temperatures that plunged to below freezing levels across Texas and much of the Gulf Coast east to the western Florida Panhandle on Saturday morning did so again this morning. However, today, the sub-freezing chill also made it nearly as far south across Florida as a Tampa-Orlando line. Even in parts of far south Florida temperatures in the upper 30’s and lower 40’s led to highly unusual wind chill readings that dipped to near 32 degrees. It’s easy to see the expanse of the cold weather by viewing this National Weather Service (NWS) “watch-warning” map (Fig. 1). Wind chill advisories and freeze and hard freeze warnings covered the entire Gulf Coast from the Rio Grande Valley in south Texas to Naples and nearby locales in southwest Florida. In south Florida, palm trees were shivering (swaying) in the cold winds!

                             T

There are several culprits at work, here. First, a significant upper level trough (Fig. 2) has allowed northwesterly winds to drive a surface level high-pressure system southward. This high-pressure system, an unusually strong one, had a central pressure of 1043 millibars (30.80 inches of mercury) near Dallas, TX early this morning (Fig. 3). The record high-pressure reading at Dallas (records dating back to 1898) was 31.06 inches during an extreme arctic outbreak on Dec. 24, 1982. The record high pressure in Dallas during January was 31.05 inches in 1962.

As northerly winds blew south from the Plains into Texas yesterday morning, and over the entire Gulf Coast today, the trajectory involved passage over an extensive snow cover. Hence, air that would have normally passed over warmer ground did not. This allowed cold air to penetrate much further southward than expected. Early on Jan. 7, snow was observed on the ground in every one of the 48 contiguous states except Florida (Fig. 4).

In short, this has been a highly unusual, but not unprecedented, arctic outbreak.

The good news is that the high is moving to the east and warmer air is slated to return to many south and southeastern locales fairly quickly.

© 2017 H. Michael Mogil

Originally posted 1/8/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.

weather, weather safety/preparedness

Ground fog! (H. Michael Mogil, CCM, CBM, NWA-DS*)

Dense fog advisories (Fig. 1) as well as the fog they describe (Fig. 2), covered southwest Florida early this Friday morning (Jan. 6, 2017). Some places had 0-0 visibility (that is, zero feet both horizontally and vertically); other places had visibilities of several miles horizontally and several hundreds of feet vertically (Fig. 3). Visibility is defined as how far one can see cloud bases (vertically) or known ground-based objects (horizontally).

   

It is the variation in fog thickness horizontally (and associated visibility) that came to the forefront this morning as I walked my dog, Pepper, around our southwest Florida neighborhood.

  

First, looking up my street, visibility was about a half mile, the measured length of my street (Fig. 4). As soon as Pepper and I walked onto the golf course, fog density increased and visibility decreased (Fig. 5). As we approached the location of my COCORAHS (Community Collaborative Rain Hail and Snow Network) rain gage, which is adjacent to a large pond, the fog density increased further and visibility tumbled down to a few hundred feet (Fig. 6). All images were taken within 10 minutes of one another.

These three scenarios are described in the table below:

Location Fog density Visibility
Street light ½ mile
Golf course dense ~ ¼ mile
Near pond very dense few hundred feet

For the street, warmer air temperatures resulted in less dense fog. Over the golf course, temperatures were slightly cooler, allowing for somewhat dense fog to develop. In the pond area, cooler air temperatures and higher atmospheric moisture contributed to the densest fog.

Note that these conditions contribute to the formation of fog. But, local winds, drainage winds, and other factors can allow fog areas to move. Not surprisingly, this can result in highly variable fog density along roadways. Common sense dictates that motorists of all types of vehicles (cars, buses, trucks) drive more slowly and pay even greater than average attention to potentially rapidly changing visibility.

While the dense fog has lifted already, it will be back again, especially during the upcoming winter months.

– – – – –

© 2017 H. Michael Mogil

Originally posted 1/6/17

* The National Weather Association Digital Seal (NWA-DS) is awarded to individuals who pass stringent meteorological testing and evaluation of written weather content. H. Michael Mogil was awarded the second such seal and is a strong advocate for its use by weather bloggers.