More Rain for Texas

Location of Hill Country in Texas

Last week persistent torrential rain fell over the Texas Hill Country north and northwest of San Antonio/Austin causing record and near-record flooding on rivers and lakes in the area. This area is particularly susceptible to flash flooding and is known as Flash Flood Alley. It wasn't just the amount of rain, but the rainfall rates that helped cause the problems this week, as well as a record wet September.

The heaviest rain fell between October 14 and October 16, with lighter rain the remainder of the week. In those three days more than a foot of rain fell in the Hill Country, with 7 to 10 inches of the rain falling in the 24-hours ending at 7:00 a.m. on October 16. The CoCoRaHS stations shown below in Llano and Mason Counties tallied the highest totals during the three-day period and for the week.

The persistent rain last week over Hill Country and central Texas was caused by what is called an "overrunning" pattern. In this case a cold front, marking the leading edge of a large cold air mass that spread across the western two-thirds of the U.S., lie along the Texas coast. Warm, moisture-laden air from the Gulf rode up and over the dense, cold air in the lower layers of the atmosphere producing clouds and rain. In addition, several waves of low pressure moved along this frontal boundary enhancing the upward motion and the flow of air from the Gulf.

Surface weather map for Monday, October 15 at 10:00 a.m. CDT.

Here is the upper air sounding from Corpus Christi, TX the evening of October 15. You can see the cold layer of air near the surface and northerly winds, and the southerly winds aloft along with the warmer, saturated air. During the winter an overrunning setup like this could produce significant freezing rain.

Atmospheric sounding plot (Skew-T) for Corpus Christie, TX at 7:00 p.m. CDT October 15. The solid red line is the temperature plot, the solid green line is the dew point.

A wet September and rain earlier in October meant that any rain last week was going to run off into the rivers and streams. The rise on rivers in the Hill Country was spectacular, rising 10 feet or more in just a few hours. These tributaries eventually feed into the Colorado River (the Texas Colorado River, not the Colorado River). The Colorado River flows southeast through a series of lakes  used for flood control and recreation (Buchanan, Inks, LBJ, Marble Falls, Travis, and Austin) and eventually to the Gulf of Mexico.

Watershed of the Texas Colorado River.

Many of the tributaries to the Colorado River quickly flooded, with all of the water feeding into the Colorado River. The Llano River at Llano came close to setting a new record flood level but fell just short of the record of 41.5 feet set on June 14, 1935. Flood stage is 10 feet. The flooding washed out a highway bridge over the Llano River outside Kingsland, TX on Tuesday, October 16. Here is video of the bridge washing out. Damage to homes and other infrastructure was extensive.

Hydrographs for rivers in Hill Country during the flooding, compiled by NWS San Antonio/Austin.

Lakes Buchanan, Inks, LBJ, Marble Falls and Travis were closed to recreational use last week and were expected to remain closed until at least until today. On Monday, a boil order was issued by Austin Water for all of its more than one million customers due to elevated levels of silt from the flooding. The boil order is expected to be in effect until at least Sunday.


This week the remnants of Hurricane Willa, which made landfall on the west coast of Mexico on Tuesday, interacted with an upper level trough moving through central Texas triggering additional rain yesterday. The heaviest amounts fell between Galveston and Houston where 2 to more than 5 inches fell. Much of the Dallas/Fort Worth metroplex received 1 to 3 inches of rain. Most reservoirs in central Texas are now near or over capacity.

Texas reservoir status as of October 25, 2018.
Source: Texas Water Development Board

Rain is still needed in west Texas and in the panhandle, but much of the state could use a break for a while. Precipitation is much above normal since September 1, more than 20 inches above normal in some places.

So Much Weather...

Trying to decide what to write about is a difficult task this week because there is so much to talk about - summer-like heat in the east, hurricanes, snow in the Rockies and Plains, and heavy rain from Texas to Iowa. A number of , so Here is a quick summary of the significant weather events taking place across the U.S.

To start with, here is the latest watch/warning map for the U.S.to give you an idea of the variety of weather ongoing.

Watch /Warning/Advisory map as of 9:23 p.m. CDT 10/9/2018. The latest map can be found at www.weather.gov

Tropical Weather

The major news this week is Hurricane Michael, destined to make landfall along the coast of the Florida Panhandle on Wednesday. Dangerous winds gusting more than 100 mph and catastrophic storm surge are expected as Michael approaches and crosses the Florida coast. As I write this Michael is a strong Category 3 storm and is expected to reach Category 4 before landfall. 

Hurricane Michael as the sun was setting over the eastern Gulf of Mexico at 6:07 p.m. EDT.
Image from https://weather.cod.edu/

Infrared image of Hurricane Michael at 10:07 p.m. EDT. Image from https://weather.cod.edu/

Hurricane Leslie has been looping around the Atlantic for 17 days, and reached hurricane again tonight. I it expected to maintain tropical status as it moves east toward Africa this week.

This afternoon, Tropical Storm Nadine in the eastern Atlantic was named and is forecast to move northeast before weakening by Friday.

For the latest information on Hurricane Michael visit the National Hurricane Center web site.


Winter Weather

Snow has been falling on and off in the Rockies the past several days as cold air spilled into the region and a low spun up over the southern Rockies. Snowfall from Monday to Tuesday accumulated from Montana south through Colorado, and from Colorado northeast through the Nebraska panhandle and into the Dakotas. More than 5 inches of snow fell west of Denver in the 24 hour period ending Tuesday morning, and 6 to 8 inches accumulated northeast of Rapid City, SD. Tonight winter weather advisories extend from northern Minnesota south into western Kansas.

24 hour snowfall ending the morning of October 9, 2018.

Heavy Rain

It has been a stormy set up on the boundary of the cold air in the west and warm air in the east, and rain fell this week from Texas northeast to the Canadian border. Rainfall accumulations this week ranged from 7 to 9 inches in parts of Texas, 6 to 8 inches in western Oklahoma, and 7 to 10 inches in eastern Kansas and in the Kansas City metro area.

Big changes are ahead later this week. Hurricane Michael will make landfall, weaken, and move into the Atlantic. Cold air that has been pooling in Canada and the western U.S. will spread to the east and Gulf coasts bringing an end to summer-like weather for most.

CoCoRaHS Observers in Right Place, Right Time in Western NC

When I pull up the CoCoRaHS web site each day one of the first things I check is the national map for any unusually high values that might indicate an error.  On Sunday September 30 the first thing I noticed was that the scale showed a top value over eight inches. There was a red dot over western North Carolina. "Perhaps an observer entered observation time as precip or made a typo entering the amount", I thought. It's a very common error.

Zooming in, it was clear this was no error. The southeast corner of Buncombe County, North Carolina got a very large amount of rain, and heavy rain also fell in surrounding counties.

Rainfall amounts of 1 inch or more from Sunday morning, September 30.

The largest amount of 8.11 inches was recorded by the observer at NC-BC-115, Black Mountain 5.5 SE. The comments entered by the observer helped tell the story of what happened overnight. Comments are very helpful and important in events like this.

What was really interesting was that this was an isolated storm for the most part. Out of 33 CoCoRaHS observers reporting in Buncombe County that morning, 22 reported amounts of 0.10 inch or less, and about half of those reporting zero.

Radar showed a nearly station storm over southeastern Buncombe, western McDowell, and western Rutherford counties. The center of the white circle is the approximate location of NC-BC-115. The first image in the sequence shows two strong cells just to the south. The middle image is three hours later and the heavy rain has been falling for two hours.

Radar images from weather.us

The precipitation accumulation map from the NWS Advanced Hydrologic Prediction Service (AHPS)  indicates 6 to 8 inches over southeast Buncombe County, and just how small the area of heavy rain was.

The heavy rain resulted in flash flooding with debris flows, roads and bridges washed out in the affected counties. The National Weather Service issued an Areal Flood Watch at 4:46 a.m. EDT.

It is possible that that more than 8.11" of rain fell in the area near NC-BC-115, but were it not for that observation and that of the observer at NC-RT-6 Chimney Rock 0.3 with 5.01" there would not have been ground truth for this event. Right place, right time.

Tropic Thunder

The tropical Atlantic was fairly quiet this summer. Until last week there were only five named storms, only two of which reached hurricane strength.

Map showing first five tropical systems in the Atlantic in 2018

 
Tropical Storm Gordon made landfall in the Gulf last week and its remnants brought heavy rain to the Midwest and mid-Atlantic this past weekend.

Since last week, however, three new storms are churning way in the Atlantic, and one area of disturbed weather over the northwestern Caribbean Sea has a 60 percent chance of developing into a tropical system within the next five days.

The focus of all the attention the last few days has been Hurricane Florence. Florence started as an area of low pressure that moved off the African Coast 12 days ago on August 30. The depression became Tropical Storm Florence on September 1. Florence attained hurricane strength for the first time on September 4. The storm encountered an area of upper level shear as it moved west, which weakened Florence considerably and it was downgraded to a Tropical Storm late on September 7. All indications were that Florence would reach hurricane strength again, and yesterday morning it did. The storm underwent rapid intensification today, and as of this writing Hurricane Florence is a category 4 storm (maximum winds 140 mph) heading for the Southeast Coast of the United States. It's possible it could briefly reach Category 5 strength on September 11.

We are also keeping an eye on Hurricane Issac. As of this writing it is a Category 1 storm with top winds of 75 mph. Its projected path will take through the Lesser Antilles and to the south of the Dominican Republic by Saturday as a tropical storm. Its future beyond Saturday is uncertain, but it will be over the warmer waters of the Caribbean Sea.

Hurricane Helene is currently the last in line of the storms in the Atlantic right. This storm is expected to re-curve to the north and weaken by Thursday.

Meanwhile, in the Pacific Tropical Storm Olivia is heading for the Hawaiian Islands. A Flash Flood Watch has been issued for all the Hawaiian Islands though Thursday night. Olivia is forecast to produce total rainfall amounts of 10 to 15 inches. Isolated maximum amounts of 20 inches may occur along the windward sections of Maui County and the Big Island.

Forecast track for Tropical Storm Olivia

Back to Florence, though. The various forecast model projections were the subject of much discussion the past few days. There initially was a wide spread in possible tracks, including the possibility that Florence could re-curve north before reaching the coast. However, as the weekend progressed the models increasingly began to converge on a solution showing landfall somewhere along the Southeast Coast of the U.S. The current forecast (5:00 p.m. EDT 9/10) brings Florence ashore somewhere between Charleston, SC and Cape Hatteras, NC sometime on Thursday likely as a Category 4 storm.

The footprint of Florence is going to be very large, probably as big as South Carolina, North Carolina, and Virginia combined. While winds will certainly be a big concern especially close to landfall, the rain footprint of Florence is what is really scary. Indications are that Florence will stall over the Carolinas blocked by a strong ridge of high pressure over the northeast U.S. The storm's circulation will continue to draw moisture from the Atlantic into the Carolinas, Virginia, and northward. This will mean days of heavy, flooding rain. Here is the latest precipitation forecast for Florence from the Weather Prediction Center.

While the winds with Florence will be significant if the forecast holds, it is the  storm surge and the rain and resultant inland flooding that will make this a notable storm.


CoCoRaHS observers: If you are in the Carolinas and Virginia please remove the funnel and inner cylinder from your gauge as they can become projectiles in high winds. In heavy rain the outer cylinder alone will also be more efficient for catching heavy rain (no splashout from funnel). If you're given evacuation orders, please follow them. Your safety is our number one concern!

For the latest information on Hurricane Florence visit the National Hurricane Center website.

Evapotranspiration and Water Balance Maps Now Available

Atmometer (E-T Gauge)

About six years ago CoCoRaHS added measurement of reference evapotranspiration (ET0) to the phenomena observers can measure. Evapotranspiration is the sum of evaporation from ground surfaces and the transpiration of water to the atmosphere from plant leaves, and is a function of temperature, wind speed, relative humidity, and solar radiation. On average more than half the precipitation that falls is returned to the atmosphere through ET. There are about 120 observers across the the U.S. and in Canada currently measuring E-T using a special E-T gauge called an atmometer. You can read more background on CoCoRaHs E-T measurements in this blog post from 2013.

Recently the Midwestern Regional Climate Center (MRCC) in partnership with the National Integrated Drought Information System (NIDIS) developed are series of maps of E-T and water balance measurements using CoCoRaHS data. These maps can be found on the Midwest Drought Information page in the Midwest Climate Watch section of the MRCC web site.

There are maps of 7-, 14-, 30-, and 60-day accumulations of E-T for the Midwest region and for the continental U.S. and southern Canada. A second set of maps displays water balance calculations for the same periods as E-T. Water balance is the total precipitation minus the total E-T for a designated period. Water balance charts  are available on the CoCoRaHS web site and show the change in water balance over time at a location along with daily E-T and precipitation values. All the maps are updated each day.

Here is today's map of 7-day E-T for the U.S. and Canada. Note that only stations with 100 percent data completion in that period are displayed. E-T occurs every day, so stations with missing observations cannot be used to compare with other stations.

This is a 14-day water balance map. It's pretty clear where it's very dry and has been very wet.

An advantage to having this data plotted spatially is we can see where more E-T observations are needed. ET does not vary to the same extent as precipitation (it's more similar to temperature), so multiple measurements in the same general area are usually not needed, unlike precipitation. ET measurements are only made during the warm season, since freezing temperatures can damage the gauge. There a few stations in the south and west that measure E-T year 'round.

If you are interested in measuring E-T at your location contact CoCoRaHS headquarters for more information.

CoCoRaHS 36"+, 24-hour Rainfall in Hawaii Confirmed

Lost in the coverage of heavy snow in the Midwest and wildfires in Oklahoma this past week was an incredible rain event that occurred in Hawaii over the weekend. The rain fell beginning late on April 13 and continued through Sunday, April 15. In produced severe flooding over portions of Hawaii, particularly over east Oahu on Friday night and across Kauai from late Saturday through Sunday.




The entire island was under a flash flood warning on Saturday and Sunday.Here are the 24-hour rainfall amounts from Kauai on Sunday morning, April 15.

Throughout the storm on the night of April 14 until the morning hour of April 15, the CoCoRaHS observer at HI-KI-24 made several trips out to the rain gauge to measure than rain before it over-topped the gauge. Nolan Doesken from CoCoRaHS headquarters contacted the observer to get more details on this incredible event. Here is a timeline of what the observer measured and reported.

HI-KI-24 Hanalei 3.0 W (Wainiha)
Saturday, April 14, 2018

Time HST	Precip, in.	Duration (hrs)
7:30 a.m.	2.96	24
2:20 p.m	5.00	6.8
5:30 p.m	7.55	3.2
7:00 p.m.	7.33	1.5

Local damage began to occur. After this observation the observer evacuated the house and stayed in their car which was parked up the hillside from the house along the road.


Sunday, April 15, 2018

Time HST	Precip, in.	Duration (hrs)
1:30 a.m.	Gauge was nearly full. Observer did not measure precisely at this time, but conservatively estimated 10.00 inches of rain since 7:00 p.m.
6.45 a.m.	6.55	5.25

Monday, April 16, 2018

Time HST	Precip, in.	Duration (hrs)
6:30 a.m.	2.14	23.75

The total Sunday morning from the incremental measurements was 36.43 inches. The final total of 36.49 inches includes an estimate of what might have been lost during to spillage during the incremental measurements (the observer does not have an extra outer cylinder). He made the measurements with the help of a friend, wading out to the rain gauge for the measurements and making them in the rain. Nolan indicates the observation is fully valid and if anything may be a bit of an under-report.

The observer commented that based on the location of thunder and lightning, the heaviest part of the storm seemed to be a few miles east of his location. This observation seems to be borne out by the radar estimated precipitation. The maximum amount on the Storm Total Precipitation image below is 27.5 inches.We know that the total rainfall was considerably higher. The location of CoCoRaHS rain gauges are plotted on the radar image.

Radar estimated precipitation for the 50-hour period ending
at 2:13 p.m.HST April 15, 2018.

While the observer's house barely escaped flood damage, there was damage close by. One notable comment from the observer was that somewhere around 7:00 p.m. the roar of the nearby Wainiha River began dominating over the sound of thunder to the east.Two nearby houses were washed away, and a large 18-inch diameter log ended up in a neighbors living room. The road was washed out in three places. Roads and homes were flooded across much of eastern Kauai, and as of April 18 more than 425 people had been evacuated.

 U.S. Coast Guard video of overflight of area near Hanalei Bay, Kauai, April 15, 2018

What caused this heavy rain was the interaction of an upper level low and tropical moisture. On Friday a trough was crossing north of Hawaii, but the bottom of the trough cut off and became a closed low. This closed low then drifted westward across Hawaii, tapping into low level moisture fueling the storms.

Here is a three panel image that shows the 500 millibar analysis beginning at 2:00 a.m. HST on April 14 showing the low drifting west, followed by a chart of the total precipitable water.

Total Precipitable Water at 2:00 a.m. HST April 15. The Hawaiian Islands are circled.

The National Weather Service in Honolulu reported that the rain gauge in the town of Hanalei collected 28.15 inches of rain from early Saturday morning into Sunday morning (April 15) before the gauge stopped working at 2:00 a.m. HST. The 24-hour record for that location is 28.54" set on March 5, 2012. It's highly likely that this record was broken.

In Wainiha, where our CoCoRaHS observer is located, an automated rain gauge recorded 32.35 inches of rain for the 48-hour period ending at 6 PM HST on April 15, 2018. This rain gauge recorded 19.54" for the 24 hour period the previous record for a 24-hour total in Wainiha was 16.70 inches on January 6, 1969. The confirmed CoCoRaHS total more than doubles that record. The total rainfall for HI-KI-24 for the 72-hour period ending at 6:30 a.m. HST on April 16 was a whopping 41.59 inches.

The 24-hour record rainfall for Hawaii is 38.00 inches at Kilauea Sugar Co. Plantation (Kauai) on January 24-25, 1956. It is an estimate, but is listed as the record because it was obtained from a reliable rain gauge and is deemed conservative by an inch or more.

Tornado Detection by Radar Started 65 Years Ago Today

The first hook echo identified and photographed on radar.

Sixty-five years ago, out in the middle of central Illinois cornfields at the University of Illinois airport, electrical and radar engineer Don Staggs deferred shutting down a radar being used for rainfall research because he noticed something peculiar about the radar return he was seeing. That decision turned out to reveal the first detection of a tornado "hook echo" by radar. We have come a long way since then. The dual polarization Doppler radar now being used by the National Weather Service can detect rotation in storm before tornadoes develop, adding critical lead time for tornado warnings.


My blog post on April 9, 2013 relates the story behind the detection of the first hook echo on the 60th anniversary of the event. 

A Bullseye of Dry

The past winter season (December-February) was a little on the weird side. The west coast, which normally experiences it's wet season in the winter, was pretty dry. It was cold across the Plains and Midwest, but snowfall was way below average in many areas. Winter had a late surge in the northeast in late February and March. However, one aspect of the last five to six months that has been interesting to watch is the fairly rapid development of severe to exceptional drought in the panhandle region of Texas and Oklahoma and adjacent portions of Colorado, Kansas and New Mexico.

Here is the U.S. Drought Monitor as of today, showing parts of this area in Extreme Drought, compared to the Drought Monitor in early October.

Dryness expanded and intensified through November and December, and by early January the first depictions of Extreme drought were showing up on the U.S. Drought Monitor. 

By early March an area from the Four Corners region to the panhandles was painted with Extreme Drought, with a small area of Exceptional Drought in northern Oklahoma. That small area has doubled in size in the past two weeks.

The precipitation map for the past 6 months depicts the seriousness of the precipitation deficit.

This map from the Oklahoma Mesonet demonstrates the incredible precipitation gradient across Oklahoma the past four months, ranging from only an inch in the panhandle to more than 25 inches in the southeastern part of the state.

Then there was this note included in the Area Forecast Discussion by the NWS Amarillo office on March 28.

We have some dedicated CoCoRaHS observers that have been submitting daily observations, mostly zeros, throughout the development of this drought. Here is a list of CoCoRaHS rainfall totals under one inch from Texas, Oklahoma, Colorado, New Mexico and Kansas October 1 through March 28 for all stations which had observations for at least 90 percent (161) of the days in this period.
 

Station Number	Station Name	Total Precip	Total Snow
CO-BA-27	Stonington 8.6 SE	0.28	1.3
CO-LA-16	Kim 8.8 SSE	0.58	2.7
KS-HM-3	Syracuse 14 SSE	0.59	0.0
TX-LK-24	Ransom Canyon 0.4 ENE	0.64	0.2
NM-SC-26	Lemitar 0.7 NNE	0.67	0.0
KS-SV-18	Hugoton 0.6 NNW	0.69	0.0
NM-SN-39	Rio Rancho 3.3 ENE	0.73	0.0
NM-SN-62	Rio Rancho 3.0 WSW	0.75	0.0
KS-WH-9	Leoti 6.8 NNW	0.78	7.4
TX-LK-14	Lubbock 5.3 SSW	0.79	0.4
NM-SN-43	Rio Rancho 3.5 W	0.80	0.3
CO-OT-25	La Junta 1.0 S	0.82	1.8
NM-SJ-19	Farmington 3.4 WSW	0.83	0.0
NM-BR-205	Albuquerque 8.9 NW	0.83	0.0
NM-BR-36	Albuquerque 5.9 WNW	0.86	0.0
TX-LK-59	Wolfforth 4.6 S	0.86	0.5
TX-LK-7	Lubbock 6.7 SW	0.87	0.3
NM-BR-7	Albuquerque 7.1 SW	0.88	0.0
TX-LK-77	Lubbock 6.4 NW	0.89	0.0
CO-BN-8	Las Animas 8.1 NE	0.92	3.4
NM-BR-152	Albuquerque 2.9 W	0.92	0.0
CO-OT-28	La Junta 1.6 SW	0.93	1.5
NM-SJ-32	Kirtland 21.7 S	0.95	0.2
NM-TR-1	Mountainair 1.0 S	0.96	1.0
TX-LK-81	Lubbock 3.0 S	0.96	0.0
NM-BR-215	Albuquerque 5.3 W	0.96	0.0
KS-HM-19	Syracuse 3.1 NNE	0.96	0.0
KS-FO-23	Dodge City 12.7 S	0.98	1.2

The winds aloft, particularly in December and January, were west-northwest on average in this part of the country. Any moisture heading toward the Texas and Oklahoma panhandle region would get wrung out of the atmosphere as the air was forced up on the west side of the Rockies. Any low pressure systems that developed tended to be steered east before they started to develop. What the drought-affected area needed, and didn't get, were some strong low pressure system developing on the lee side of the Rockies that could tap into moisture from the Gulf of Mexico to produce precipitation.

These maps depict the average 500 millibar height pattern (~20,00 ft) for the months of December, January and February. Winds at this level blow parallel to the contour lines. The arrows show the general direction of the wind at this level.

Although this region did get a little rain this week, the operative word is "little". The latest forecasts keep the drought area dry for at least the next week or so.

Are You Up for a Spring Challenge?

Those of you in the Northeast might be saying "We've been challenged enough!" with the recent train of nor'easters passing thought, but this challenge will be less stressful.

NASA's GLOBE (Global Learning and Observations to Benefit the Environment) is running a spring challenge for cloud observations and is encouraging citizen scientists (that's you, CoCoRaHS observers) to participate.


From now until April 15th you can take part in the challenge by downloading the free GLOBE Observer app for iOS or Android. You can also submit you observations online through the web site. However, once you have the app, you can snap and send cloud observation photos directly to NASA using the app.

Participants are invited to enter up to 10 cloud observations per day from now to April 15. GLOBE and GLOBE Observer participants with the most observations will be congratulated by NASA scientists with a video posted on the NASA GLOBE Clouds website.

I spent some time on the GLOBE Cloud web site recently to find out more about what this entailed. There is plenty of training material available on cloud types and cloud observations, including a nice downloadable cloud chart as well as an online cloud chart, and a guide to Observing Cloud Types.

The optimal observation is one that coincides with a satellite pass over your location, and there is a tool on the web site where you can get these. There are at least five orbiting satellites that collect cloud data. you will need your latitude and longitude for this. The app will determine this if you have location services turned on on your phone or tablet. That's also available from your CoCoRaHS account if you don't have it written down somewhere. The app allows you to set an alarm to alert you to upcoming satellite passes.

Clouds are important to Earth's energy balance. They reflect, absorb, and scatter sunlight as well as infrared emissions from earth. The type of cloud, its height, and transparency all are factors that have to be addressed. Satellites can detect clouds, and while they are great tools, they have limitations especially when it comes to the details. For example, satellites see the tops of clouds, but not the bottoms. Satellites may also have a hard time differentiating high, wispy thin cirrus clouds (composed of ice crystals), from deep snow cover on the ground. So while satellites look down on the clouds, GLOBE cloud observers are looking up.

Altocumulus clouds.
Photo: Steve Hilberg

The app (available on iOS and Google Play) walks you through the steps of making an observation. The following information is required for each observation:

Date, time, location
SKY:clear, cloudy, obscured
COVERAGE: what percent is covered
TYPE:  cloud/contrail types
Visual opacity
Surface conditions
Photograph

One observation is allowed per time stamp, and it's recommended that you wait 10 to 15 minutes between observations so changes in the sky can be recognized.

Also, there is this important reminder:

"Reminder: This protocol includes a category of “No Clouds” which should be reported whenever there are no clouds visible in the sky. A “No Clouds” report is just as important as a “Clouds Observable” report in helping understand our Earth’s system. If “Clouds Observable” is reported, follow the observation hints located in the left navigation column."

Sound familiar, CoCoRaHS observers?? Blue sky (zero) is an observation.

You can also manually observe clouds and then enter the data into the GLOBE observer web site. A printable data entry form is provided for this.

I did try the app out and encountered a couple of hiccups. The data entry part, up to the photos, was quick and easy. However, there seems to be a little bugginess in the photo function. After messing with this a number of times I think I figured out how the app works with respect to taking photos (I could find no directions anywhere on how this works). So, you may want to hold on to these directions if you are going to use the app. I tested this on my Android phone.

 After your last entry of surface observations, you will see the photo screen.

If you want to take a photo using the app, select Take Pictures. A second screen will appear showing your camera view, along with N S E W Up Down on the bottom left, and a circle in the middle of the screen. 

IF the correct direction is showing for the direction you are pointing at (the "W" in this case), move the camera until the direction letter is lined up with the center circle. Once it is it will turn green and a photo will automatically be taken. Click DONE in the lower right of the screen and you will exit to the next screen, which will show your photo(s) at the bottom. this function, if it's working, is actually nice because by lining up the W with the circle it forces you to tilt the camera up at the correct angle

If you want to delete the photo, tap the photo thumbnail and select Delete. If everything looks OK, then click FINISH at the very bottom of the screen (you have to scroll down). The next screen will give you the option of reviewing and submitting your observation.

You can also add photos manually (second option). Selecting will take you to the Take Pictures screen. Tap the direction you are taking your photo. You have the option of taking a photo with your camera or choosing an existing photo from your photo gallery. If you are having issues with the first option the manual option is easier. 

The compass direction showing on my screen was off by 90 degrees for some reason (I was shooting north but it indicated west). There was some message about the phone's compass but it disappeared from the screen when I initially tried this and I couldn't seem to resurrect it. When I checked my phone with an independent compass app it was spot on. I don't know if the direction is determined by the internal compass or the GPS.

Also, once I took the photo in landscape mode the GLOBE screen would not return to portrait mode, and the camera was on in the background behind the menu. Even if I closed the app and reopened it it was still in landscape mode. Unfortunately there is no real app-specific help within the app itself to deal with these functions. Before you use the app to make an actual observations I would go through a few dry runs just to see how it behaves on your phone. None of the data is actually sent until you tell the app to send it. However, editing your observation is clunky. Editing takes you to the start of the data entry and you have to go through each screen again.

Once your observation is in the system, ground observations of clouds are matched with satellite observations. If your observation coincides with a satellite observation, you will received an automatic "match" email, which summarizes both your ground observation and the satellite observation. It takes anywhere from one to seven days to receive the satellite data, depending on the satellite. You can read more about the satellite comparison on this page.

This is a great opportunity to spread your citizen scientist wings in a weather-related way, and the data you collect may be used by NASA scientists for their research on clouds.

While this "spring challenge" only runs until April 15, cloud observations continue year 'round. Despite a few little glitches with the app, this is a worthwhile addition to your observation activities.