climate, weather

More heavy rainfall for southwest Florida (H. Michael Mogil, CCM, CBM, NWA-DS*)

Rainfall for June (now almost only half over) is already at rarified levels. Many locations across southwest Florida have logged 15 to 20 inch values. And more rainfall is anticipated.

In fact, for the Naples area (my home base), the official National Weather Service (NWS) forecast is calling for 50 to 70 percent daytime rainfall probabilities each day for the next week.

And, no wonder. The atmosphere above the now, so-called “Sunshine State,” is overburdened with moisture (Fig. 1). According to NOAA’s (National Oceanic and Atmospheric Administration)’s Storm Prediction Center (SPC), precipitable water (PW) was at 1.92 inches at Miami, FL early this Thursday morning. PW is the measure of all water vapor in a column above a radiosonde (weather balloon) sounding location. For Jun. 15, the climatological average PW at Miami, FL is 1.66 inches and a 90 percentile PW is 2.00 inches. In short, if all the water vapor above a point could be condensed into liquid water and then squeezed out (like a sponge), and no water vapor moved in or out of the atmospheric column, 1.92 inches of rain would result.

Further, winds throughout the atmospheric column from the ground to some 50,000 feet above ground level are less than 15 miles per hour. That means that any storms that develop will not move very fast.

While outflow boundaries (areas marking where low-level winds blowing out of thunderstorm areas meet the environmental air mass) may interact with other outflow boundaries and sea breezes to enhance thunderstorm formation or localized movement, most storms will be slow-moving, prolific, rainfall producers. Many locations could see short-period downpours of one to two inches or more during the upcoming week or until the weather pattern changes.

© 2017 H. Michael Mogil

Originally posted 6/15/17

* 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, 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.

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.

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

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

climate, geography, weather

A real cold front is heading to Florida (H. Michael Mogil, CCM, CBM, DMS)

South Florida experiences “cool front” passages fairly often during the chillier months of the year. These bring wind shifts (winds northerly and northwesterly, quickly turning to northeasterly), and a modest drop in temperatures and a more significant drop in dew point temperatures. In summer months, very weak “cool fronts” occasionally reach as far south as places like Tampa and Orlando, and even less frequently to Naples and Fort Lauderdale.

fig001-sfc-fcst-161209-12zNow, a bona fide arctic cold front is enroute to the sunshine state and should pass by the Naples area on Thursday evening and be fully in control by Saturday (Fig. 1). No, arctic temperatures won’t reach this far south, but the temperature drop will be substantial. From daytime highs in the low to mid 80’s, temperatures in the Naples-Fort Myers area will tumble into the upper 60’s to near 70 by Friday. Overnight lows, which have remained in the uber-humid low to mid 70’s, will dip into the upper 40’s inland and lower 50’s in coastal population centers. This means that the Naples area will transition from temperatures that have been running about 6 degrees warmer than average so far this month to some 10 degrees colder than average by Friday and Friday night. That’s a 16-degree swing! For this time of year, the average high and low temperatures in Naples are 78 and 58, respectively.

Gusty winds will make the chill feel worse than it really is.

Although rain chances for the next several days are only 20 to 30 percent, once the initial non-arctic front passes through the Naples area by tonight, cloudy skies will rule until the arctic front sweeps things clear by Saturday.

Then, as quickly as it came, the cold air will be replaced by moderating temperatures and humidity as winds swing to the northeast by Saturday.

Keep looking to the northwest, though. Given the evolving upper level flow pattern, a string of Pacific weather systems, and periodic southward pushes of the polar vortex, additional cold air outbursts may be heading our way soon. Regardless of how the temperature evolves, dry weather should dominate for the next several weeks.

© 2016 H. Michael Mogil

Originally posted 12/6/16

climate, weather, weather safety/preparedness

Fiona fades; Gaston grows; but there is another tropical system (99L) on Florida’s horizon… (H. Michael Mogil, CCM, CBM, DMS)

Fiona (the sixth Atlantic tropical cyclone of the 2016 season) recently passed. In her wake, Gaston briefly reached hurricane strength far out in the Atlantic. Another tropical system (99L) near the Bahamas is still showing signs of intensifying this weekend as it approaches the Florida Straits. And, more African waves seem ready to exit the west African coast and join this Atlantic train of tropical weather systems. All this as the peak of hurricane season (Sept. 10) looms.

For obvious reasons, the potential system nearing the Bahamas brings the greatest concern. During the past two days, National Hurricane Center (NHC) forecasters have begun to downplay chances for tropical storm or tropical depression formation (although, anytime a system like this is near the U.S., it warrants close scrutiny).

However, the bigger threat seems to be heavy rainfall and rip currents. The persistent strong easterly wind flow (and the expected elevated wind speeds as the system approaches later this weekend) will allow for rip currents to develop along east-facing beaches across much of the so-called Sunshine State. I say, “so-called,” because extensive cloud cover and widespread precipitation areas (filled with heavy showers and thunderstorms) will make folks wonder if the sun even exists. The Naples area forecast, for example, keeps mostly cloudy skies as the main sky condition until next Thursday. If the sun does peak out of thick, multi-layered clouds, it will likely be for very short periods, at best.

Fig001-seven-day-qpf-thru-160902NOAA’s Weather Prediction Center (WPC) has issued its latest quantitative precipitation forecast (QPF) for the seven-day period ending next Friday. This places much of Florida in a five to seven inch rainfall zone (Fig. 1). As always, local amounts can often be double the expected general rainfall numbers.

Fig002-pct-annual-rainfall-FL-thru-160825Much of the southern half of Florida is already reporting above average yearly rainfall (Fig. 2). Some places are as much as fifty percent or more above average. Fort Myers, for example, is already nearly 12 inches above its yearly average rainfall of 36 inches through Aug. 25. Additional rainfall will only add to water management issues across the southern part of the state, including increased agricultural and fertilizer runoff (which contribute to the development of algal blooms in near-shore Gulf waters).

Since sand is the dominant ground material in south Florida’s (not clay soil like Louisiana), any localized heavy rainfall will not likely generate massive flooding. However, normally poor drainage areas, places with storm sewer gratings filled with leave sand twigs and even some urban areas can expect ponding of water on roadways and in low-lying areas. Coastal urban flooding will be exaggerated if heavy rain falls during the time of high tides.

The best advice for now is to keep up-to-date on the tropical activity near Florida, and be very cautious of any heavy rainfall and localized ponding water, especially while driving.

© 2016 H. Michael Mogil

Originally posted 8/26/16

climate, weather

The next hurricane…

Fig001-tropical-storm-day-of-year-climatologySeptember 10 marks the average day of peak tropical cyclone activity in the Atlantic Ocean basin (Fig. 1). As we approach that day, the atmosphere is delivering. Early this Monday morning (Aug. 22, 2016), there were three tropical systems at play in the Atlantic – Tropical Depression Fiona and two tropical convective areas (Fig. 2). All of these systems started their lives as tropical waves coming off the west coast of Africa. Note that there is another thunderstorm cluster getting ready to exit Africa. So, all eyes across the eastern half of the U.S. are turning to the east.

Fig002-Atlantic-satellite-160822-1030amEDTThe media is showing spaghetti plots and folks in Florida are starting to talk about these weather systems. Fortunately, the bread, water and toilet paper are not yet flying off supermarket shelves.

Successive runs of various computer models are showing an ever-evolving set of potential atmospheric solutions. The other day, one of the tropical systems was expected to pass over southwest Florida enroute to Louisiana. The model run six hours later had the storm in the Atlantic completely missing Florida. The solution set continues to grow. Several things are important to note:

(1)  Official National Hurricane Center (NHC) center position forecast errors (based on 2011-2015 data for the Atlantic basin) are about 272 miles at day five (120-hour forecast). We are currently at day 7 or 8 before the storm might affect the U.S. If forecasts were made this far ahead, errors would be expected to be even greater.

(2)  Longer-term forecast errors in storm strength are about 15 knots (17 miles per hour), roughly equivalent to one storm strength category.

(3)  Nearby weather systems (and sometimes systems far removed from the tropical cyclone) can affect the cyclone’s formation, development and movement.

(4)  Computer models are based on past computer model outputs and updated observations. Missing or incorrect data, model boundary conditions, and even the thermodynamics and physics built into the model can all generate errors or incorrect outcomes.

So, this far ahead, it just pays to watch the tropics and know what thenext named storm might be called. Keep up-to-date on any storms that have or may form and monitor official forecast tracks. As any storm gets closer to the U.S. (if one does), NHC forecasts and discussions (plus information here at GWCC, and on local and national media) will help guide our readers to risks and any needed safety actions.

© 2016 H. Michael Mogil

Originally posted 8/22/16

climate, geography, weather

THEWEATHERMOGIL:: Colorado’s summer monsoon begins

Dateline: Vail, CO

During the months of May and June, in many parts of the Nation, you might start hearing talk about the soon-to-arrive, “monsoon.” But, do you really know what the monsoon is?

The North American Monsoon provides summer thunderstorms from California to Colorado and from Mexico to Montana. The area of coverage is basically the southwestern U.S. and Northwest Mexico.

It is sometimes referred to as the Southwest monsoon or the Mexican Monsoon.

Not to be excluded, Florida experiences a similar monsoon.

When it comes to describing a monsoon, a lot of people tend to think about the torrential flooding rains that typically occur in India and Southeast Asia each summer. The U.S.’ summer monsoon is not quite as dramatic, but it does provide lots of precipitation. Flooding rains, due to slow moving thunderstorms and/or repeated thunderstorm transits, are often part of the “wet” monsoon season.

Yet, the word monsoon (Arabic origin) simply means a seasonal wind reversal. Rainfall is not the driver for the monsoon; rather, it is the result!

Hence, what starts as a “wet” event (linked to a certain wind flow pattern), ends with the onset of a “dry” event (with a different wind flow pattern). Both are monsoon events, even though most folks key on the “wet” portion only.

Fig001-seasonal-SLP-wind-patternsFigure 1 can be used to describe all three of the above-mentioned different geographically-based seasonal monsoon patterns. Note how the locations of pressure systems flip-flop between land and water locations based on solar heating variations and land-water differences. This, in turn, results in significant wind direction shifts seasonally (even if not day-to-day). Wind shifts allow different types of air masses to move into or away from certain areas.

Fig002-US-radar-map-160630-early amLinked to all these ground level (or “surface”) wind patterns, there are accompanying upper level pressure and wind patterns. For example, consider the upper level high-pressure system (5 to 10 miles above the Earth’s surface) that had parked itself across Arizona, Nevada and California for much of June. That high has now shifted eastward, allowing the upper level monsoonal wind circulation to transition. In the case of Colorado, my home base this week, the high’s movement to a location south of Colorado has allowed thunderstorms to finally develop across western parts of the state as well as much of the intermountain western states (Fig. 2).

Fig003-upper-winds-160630-21ZAccording to Julie Malingowski of the National Weather Service’s Grand Junction Forecast Office, “Synoptically, the classic monsoon pattern in Colorado is defined with high-pressure over the Southern Great Plains. This allows a clockwise/southeasterly tap from the Gulf of Mexico.” Then, moisture-laden easterly waves on the south side of the high ride the high into the Four Corners. This week, there is no closed high-pressure system, but the upper level ridge has moved to the south of Colorado. This is allowing Pacific moisture to move into the southwest U.S. and Colorado (Fig. 3).

Fig004-7-day-qpf-thru-160706-12ZThunderstorms are now mentioned in statewide forecasts for the southwest U.S. for most of the next four days. Then, the monsoon is expected to relax somewhat next week. However, the 7-day quantitative precipitation forecast map clearly shows that the upper high will be relocating even further to the east (Fig. 4), suggesting a quick return to monsoonal conditions.

Since the “wet” monsoon is summer-season based, it is not unusual for record-breaking heat to herald its arrival. Such was the case across much of the southwest U.S. earlier in June. Places like Denver and Grand Junction, CO, Flagstaff and Phoenix, AZ, Albuquerque, NM and Los Angeles, CA all reported very hot days just before the onset of the monsoon.

However, even with media hype about the excessive, sometimes record-breaking, warmth, temperature averages for the first 28 days of June, at all of the above inland locations, were only in the 3.7 to 4.7 above average range. Both Los Angeles airport and downtown locations reported readings only a couple of degrees above average.

Now that the monsoon has begun in many locations, temperatures have dropped to near to just slightly above seasonal averages.

© 2016 H. Michael Mogil

Originally posted 6/30/16