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

geography, weather

THEWEATHERMOGIL:: Latitudes and altitudes, Colorado style

Dateline: Vail, CO

This article, which addresses the effects of altitude and latitude on temperature, could be for most anyplace(s) in the 50 states. But the western U.S. (including Alaska and Hawaii), with incredibly wild swings of altitude across relatively small distances, offers some of the best settings. Since I am stationed in Vail, CO this week, the “Centennial State” will be my focus.

According to, Colorado’s elevation ranges from a low of 3,315 feet above sea level on the Arkansas River at the Kansas-Colorado border to a peak altitude of 14,440 feet atop Mt. Elbert. Pike’s Peak, the state’s most famous mountain, tops out at a scant 330 feet below Elbert’s. The state’s mean elevation of 6,800 feet makes it the highest state in the Nation.

Early morning temperatures today (Sun., Jun. 26, 2016), provide some insights into the effect of altitude (i.e. terrain) and latitude. For latitude, one only has to look across Kansas and Nebraska (Fig. 1). As is typically the case, from about 25 degrees latitude poleward, temperatures are lower the further one is from the Equator.Fig001-colorado-temps-160626-12Z

Across Colorado, latitude is partially masked by terrain effects on dew point and temperature. Dew points early on Jun. 26 were highest (mid-50’s) across the southeastern Plains (east of the Continental Divide – represented by the ochre colored line extending mostly north-south across the eastern part of the state). Dew points dropped into the 40’s across the northeast Plains. Across mountainous areas from the Continental Divide westward, dew points were mostly in the 30s.

When talking about low temperatures, dew point is extremely important. The dew point near the ground acts as a brake on nighttime cooling. It is hard for temperatures to fall below the air’s dew point temperature.

Since air temperatures normally drop off with increasing altitude, it is not a surprise that sunrise temperature readings were lower at higher mountain altitudes. The relationship isn’t one-to-one due to several reasons, including local terrain variations, geographic features (e.g., nearby river, nearby lake, nearby urban center) and the presence or absence of wind. Wind can mix the air near the ground and keep surface temperatures warmer.

Most notable is that the temperature at Craig (elevation 6,918 feet), in the northwest part of the state, dipped to 35 degrees. Eagle (elevation 6,547 feet), to the southeast of Craig only dipped to 46 degrees. But, Carol B., who works at a Vail timeshare resort, reported that at her home in Edwards, a community about 15 miles due east of Eagle, frost graced her windshield this morning.

While it may be summer, early on Jun. 26, there was a hint of cooler times across parts of Colorado.

© 2016 H. Michael Mogil

Originally posted 6/26/16


THEWEATHERMOGIL:: Fair weather funnel for Naples, FL

Typically seen in high wind shear environments, “fair weather” funnels are awesome things to encounter. They usually form through vortex stretching, are always short-lived, and shouldn’t ever touch the ground. They also form during “benign” weather scenarios.

Yesterday, I caught one, totally by accident (as is usually the case). I was observing the southwest Florida sea breeze (Fig. 1), which is marked by a distinct cloud-no-cloud boundary. The cloud-free zone is closest to the water (image was taken facing southwest).

Fig001-seabreeze-160622-IMG_2895  Fig002-003-fair-wx-funnel-160622-IMG_2900-2901

Then, I glanced up as the boundary oscillated overhead and saw a laminar tube-like shape within the overall puffy to ragged clouds. That visible difference in cloud shape is what caused me to think about something unusual. I quickly grabbed several pictures (Fig. 2 and Fig. 3, shown here) and then, as quickly as it appeared, it was gone.

If you haven’t seen a “fair weather” funnel yet, then keep an eye to the sky. Those funnels are out there!

© 2016 H. Michael Mogil

Originally posted 6/23/16



THEWEATHERMOGIL:: S marks the spot with this towering cumulus cloud

Early on Jun.14, 2016, I headed out to read my rain gauge (located on the 16th fairway of my community golf course). Looking up and to the west, I was treated to a spectacular cloud display (Fig. 1). One small cumulus cloud had managed to grow vertically thanks to a small, but relatively “strong” updraft. No other nearby clouds displayed such vertical development (Fig. 2). Fig. 3 shows the radar image at about the same time as the image in Fig. 1.


My wife immediately likened the shape of this towering cumulus cloud to a backwards question mark. Meteorologist Adam Caskey (KSAT-TV, San Antonio, TX) noted that the image actually “painted a picture of the updraft.”


And paint a picture it did. An examination of radiosonde (weather balloon) winds for nearby Miami, FL showed winds at different atmospheric layers (up to about 18,000 feet) were light and variable (Fig. 4). This likely allowed the updraft to assume its rather unusually contorted shape. Note that radiosondes at Key West, FL and Tampa, FL (not shown) both showed light low-level winds, but not the same variability as did the Miami radiosonde.


Later that afternoon, while driving across Alligator Alley (I-75) from Naples to Fort Lauderdale, I witnessed larger, more developed, thunderstorms, some of which had shapes similar to the morning “question mark” cloud (Fig. 5). The late afternoon Miami, FL radiosonde also showed a similar light and variable wind pattern at lower levels.

Fig004-MFL-sounding-160614-12Z   Fig005-cb-160614-0700pmEDT-Alley-IMG_2374

© 2016 H. Michael Mogil

Originally posted 6/17/16


THEWEATHERMOGIL:: Wet and windy weather upcoming for south Florida

For more than a week, computer models have suggested a developing rainy period for south Florida during the first part of June. Now, a tropical weather system may enter the equation. Computer models and National Hurricane Fig001-NHC-outlook-160603-160608   Fig003-QPF-160603-160610Fig002-upper-winds-160605 Center guidance suggest that a potential tropical low will develop off the Yucatan Peninsula and race northeastward to near Tampa by Tues., Jun. 7 (Fig. 1). The low will then track out into the Atlantic where it is expected to intensify further. If named, this tropical system will become Colin.

Aside from the tropical system, a very warm and moist air mass is currently in place

over the Florida peninsula. When the sub-tropical jet stream moves into the area and winds at higher altitudes become more southwesterly (Fig. 2), the ingredients will be in place for widespread shower and thunderstorm activity to develop and persist late into next week. National Weather Service forecasters are already anticipating up to half a foot of rainfall by next Friday across parts of the Florida peninsula (Fig. 3). As always, my rule-of-thumb is that local amounts can easily be double the overall forecast values, especially if successive thunderstorms move across the same area.

Some coastal and low-lying area flooding and wave action leading to rip currents and beach erosion on Gulf of Mexico-facing beaches (south of the Big Bend) is possible. Further, strong thunderstorms and possible tornadoes and waterspouts can’t be ruled out.

While rain and thunderstorms will be widespread and cloudiness extensive, there will likely be some periods during which the sun will peek through the overcast. The added solar input will just add extra heat to the lowest atmospheric levels…more fuel for thunderstorm development.

Meanwhile, heavy rain will be continuing across parts of eastern and central Texas, adding to the major flood event there. This flooding will be a subject for a separate post here at GWCC.

© 2016 H. Michael Mogil

Originally posted 6/3/16