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).

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** 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.

 

astronomy, weather

The Moon and Venus are getting closer (H. Michael Mogil, CCM, CBM, DMS)

If you happened to look to the west-southwest tonight just after sunset, and the clouds didn’t get in the way, you got to see the Moon catching up to Venus. Venus is the brightest planet in the sky right now and continues to impress in the evening sky.

The other night, a faint waxing crescent moon appeared on the western horizon just after the sun set. During the past two nights, as the sky darkened, the moon has become more easily visible in a position higher in the sky. Tonight, it lies just beneath Venus.

Mars, a very faint, reddish, planet by Venus’ standards, sits well above and slightly to the left of Venus.

All of these celestial bodies are annotated in Fig. 1 (image taken in Naples, FL).

Tomorrow evening, according to Earth & Sky, the Moon will sit above Venus, but below Mars.

Hope the clouds don’t ruin an impressive New Year’s sky show for my readers.

Enjoy!

© 2017 H. Michael Mogil

Originally posted 1/1/17

weather

What a difference a wind direction makes (H. Michael Mogil, CCM, CBM, DMS)

The other day, I wrote about the arrival of a strong cold front in south Florida. That front arrived with a significant chill down. Low temperature readings, this Saturday morning (Dec. 31, 2016), were in the 40’s across many areas of southwest Florida. Even with relatively light north winds, wind chill readings dipped into the 30’s to the north of a Fort Myers-Lake Okeechobee line. Dew point readings tumbled into the teens and twenties in many areas (Fig. 1).

But, with brilliant sunshine and a wind shift to the southeast, temperatures soared into the 70’s across most of south Florida by mid-day Saturday (Fig. 2) and into the mid- to upper- 70’s across southwest Florida by Saturday afternoon. Of even more significance was that dew point readings jumped from the 20’s into the low and mid 50’s in most places (Naples shown in Fig. 3).

This transition was linked to a change in wind direction. During the day on Friday and into Saturday morning, winds arrived from the north and northeast (Fig. 1); this kept the trajectory of the arriving continental Polar air mass passing over land. On Saturday, the trajectory of air was from water first and over the Florida peninsula next (Fig. 2). The result was that a continental Polar air mass had been replaced quickly by a maritime Tropical one.

And the trend will continue. By today, New Year’s Day, highs across southwest Florida reached the low- to mid- 80’s. Morning lows only dipped into the mid 60’s to lower 70’s along the southeast coast and low 60’s in most other coastal locations. These warmer day- and night- time readings should be the rule (plus or minus a few degrees) for most of the upcoming week.

I hope to be writing, soon, about examples in which wind direction and/or variations in wind direction play a significant role in an evolving weather event. Other GWCC writers have already posted regarding lake effect snow showers and squalls. Stay tuned!

© 2017 H. Michael Mogil

Originally posted 1/1/17

climate, weather

View from the top of the world (H. Michael Mogil, CCM, CBM, DMS)

Santa has been in the news of late. So, I thought it might be fun to take a look at weather from Santa’s perspective. To do this, we’ll have to look at upper level and surface weather maps from a polar-centric perspective. Fortunately, NOAA’s National Center for Environmental Prediction (NCEP) produces forecast weather maps for many regions of the globe, including maps centered on the geographic North Pole.

I decided to use NCEP forecast upper level (Fig. 1) and surface (Fig. 2) maps for Jan. 7, 2017 (eight days into the future) just because the patterns on these maps would be the easiest to explain. There are three important observations that I’d like to share.

First, the jet stream (a long, thin ribbon of high altitude, high speed moving air), shown by shades of blue, extends in a more-or-less continuous band around the globe. However,

there are times when the jet stream exhibits a more broken pattern. In general, the jet stream separates colder air on its polar side from warmer air on its Equatorward side.

Second, the jet stream exhibits dips (troughs or low-pressure areas – shown by orange lines in Fig. 1) toward the Equator and bulges (ridges or high-pressure areas) toward the pole. Associated with these upper level features are matching surface features (typically displaced slightly to the east of their upper level counterpart). Most of the upper level troughiness and most of the surface low-pressure systems lie within the 45 to 60 degree North latitude band. This is slightly south of the climatologically-preferred latitude.

Third, the “polar vortex” is not a single upper level low-pressure system, but rather a large zone (covering much of the high latitude region) with many low-pressure systems within it. These low-pressure systems rotate in a counterclockwise sense (west to east) around the overall “vortex” center. Here, one larger lobe of the “vortex” covers much of Canada.

The troughs noted under item two above actually appear like spokes on a wheel, as they, too, rotate around the main polar vortex circulation center.

Given this “polar vortex” and jet stream pattern, northern states will continue to be ruled by cold air, while southern states will enjoy well-above average temperature readings. In between, warm and cold air will battle for control, with a much more changeable weather pattern.

NCEP’s eight- to fourteen-day forecast (Fig. 3) shows this overall pattern. The only exception is that below average readings should trend further southward thanks to more troughiness in the west, an expected slight jet stream dip southward, and the further southward displacement of cold surface air.

Finally, the storm track suggests that the Northeast will be the recipient of the most stormy weather action. Based on details of longer range model forecasts (not shown), more meteorological “bombs” (very rapid low-pressure deepening) are coming.

© 2016 H. Michael Mogil

Originally posted 12/30/16

weather, weather safety/preparedness

Chilly wind chills for south Florida (H. Michael Mogil, CCM, CBM, DMS)

Once a strong Pacific cold front barrels through south Florida later today, attention will shift to windier weather and much chiller temperatures. The combined effect of wind and temperature will contribute to unusually low wind chills for the area. Wind chill is a measure of heat loss from exposed skin.

For Friday morning, wind chills across south Florida will range from the mid 40’s in more northern inland locales to the lower 60’s along southeast and southern locations (Fig. 1).  By Saturday morning, wind chills from Collier County northward, along the west coast, will likely dip into the 30’s and lower 40’s. The combined effect of nearby warm Atlantic waters and a northerly wind flow across Lake Okeechobee (whose waters are still quite warm) will keep East Coast southeast inland locations mostly in the mid 40’s to near 60 degrees (Fig. 2).

Then the chill vanishes, almost as quickly as it came.  Winds will quickly turn to east and allow warmer, more humid air from over the Atlantic to move back into the area. Hence, by Saturday afternoon, many western areas of southwest Florida will see temperatures skyrocket into the mid 70’s.

As noted in yesterday’s post, for the fireworks and other outdoors activities on New Year’s Eve, look for temperatures across southwest Florida to fall back into the mid to upper 60’s with light (5 to 10 mile per hour) southeasterly winds.

© 2016 H. Michael Mogil

Originally posted 12/29/16

climate, weather

Record Precipitation for Minneapolis, MN in 2016 (H. Michael Mogil, CCM, CBM, DMS)

Throughout 2016, we heard a lot about California’s long-term drought and a short-term, evolving, drought across the southeast U.S. There were also a few heavy rainfall events. Now, as we approach year’s end, annual precipitation (and other weather) records are going to be making the news.

One of the first to cross my desk was from the National Weather Service (NWS) Minneapolis office. Through yesterday, a yearly record 40.32 inches of precipitation had fallen at the Minneapolis (MSP) airport (Fig. 1). This eclipsed a record last set 105 years ago. With weather records dating back to 1871, this takes on even greater weather significance.

Some may ask, “how can weather records at an airport date back to before we had aviation and airports?” This is a very good question with a very easy answer. Due to many factors, including urbanization, observing site relocation, and others, observing sites for most places have undergone some to many relocations during their lifetimes. Each NWS office keeps track of these. The focus is on keeping the weather record as uniformly-obtained as possible.

With that part of history behind us, let’s turn to the precipitation records themselves. Here are the top 5 annual numbers (although 2016 may change a little during the next few days):

2016 – 40.32”

1911 – 40.15”

1965 – 39.94”

1983 – 39.07”

1881 – 39.06”

Note that these totals are NOT for rainfall, but rather precipitation. Snowfall (and possibly sleet and/or hail) is transformed into liquid water content (i.e., melted) and then that water is counted in precipitation totals.

By-the-by, the 30-year precipitation average for MSP is 30.61”. So this year’s precipitation is nearly 32 percent above average!

© 2016 H. Michael Mogil

Originally posted 12/29/16

weather

Record Florida warmth comes to an end (H. Michael Mogil, CCM, CBM, DMS)

Last week, I reported on south Florida’s record warmth and indicated that more records were likely to be broken. This week, I get to report that several south and central Florida locales have again set some warm temperature records. A total of seven occurred in the three-day period encompassing Christmas. Here they are:

Dec. 24

…RECORD HIGH TEMPERATURE (88) SET AT FORT MYERS…THIS TIES THE OLD RECORD OF 88 SET IN 1981.

Dec. 25

…RECORD HIGH TEMPERATURE (88) SET AT FORT MYERS…THIS BROKE THE OLD RECORD OF 87 SET IN 2015.

Dec. 26

…FOR A THIRD DAY IN A ROW, RECORD HIGH TEMPERATURE (88) SET AT FORT MYERS…THIS BROKE THE OLD RECORD OF 87 SET IN 2015.

Dec 25

…RECORD HIGH TEMPERATURE (85) SET AT MIAMI…THIS TIED THE OLD RECORD OF 85 SET IN 1941.

Dec 26

…RECORD WARM LOW TEMPERATURE (75) SET AT MIAMI…THIS BROKE RECORD OF 74 DEGREES SET IN 1911.

Dec 24

…RECORD HIGH TEMPERATURE (85) SET AT TAMPA…THIS BROKE THE OLD RECORD OF 84 SET IN 2015.

Dec 25

…RECORD HIGH TEMPERATURE (86) SET AT TAMPA…THIS TIED THE OLD RECORD OF 86 SET IN 2015.

Note that for Miami, temperature records date back to 1895.

This will be the end of warm temperature records for 2015 as a trend toward significantly cooler temperatures has already begun and will intensify by tomorrow evening. A large, modified Pacific air mass will be pushing through the area, at that time, along with gusty northerly winds. Expect winds to get into the small craft advisory category in nearshore and offshore waters and possibly over larger inland lakes (including Lake Okeechobee).

Temperatures should tumble into the 50’s by Friday morning and only rise to the mid and upper 60’s Friday afternoon. Saturday morning will see the mercury dip well into the 40’s inland, with readings near 50 along the coast.

Then, as is typically the case, the arrival of cooler and drier air will be short-lived. Once winds become easterly on Saturday, Atlantic moisture will quickly return. By Sunday, the first day of the new year, daytime highs will again be rising into the lower 80’s.

For the fireworks and other outdoors activities on New Year’s Eve, look for temperatures across southwest Florida to fall into the mid 60’s with light (5 to 10 mile per hour) southeasterly winds.

© 2016 H. Michael Mogil

Originally posted 12/28/16