Addressing the Stagnation of U.S. Operational Numerical Weather Prediction

U.S.  operational numerical weather prediction has stagnated.

• For decades, the skill of the U.S. global model has lagged those of leading international weather prediction centers
• U.S. operational numerical weather prediction (NWP) has fallen behind the state-of-the-science in other areas as well, even though the U.S. is the leader in meteorological research.
• Regional prediction, particularly ensemble-based probabilistic forecasting, is lagging far behind where it should be.
• And as easily demonstrated, U.S. operational weather prediction is not catching up.

But why the stagnation?

It is not for lack of resources.  It is not for the lack of sufficient personnel.  It is not because NOAA/National Weather Service meteorologists or leadership lack interest, knowledge, or motivation.  It is not because the research community does not want to assist.

It is because the structure of research, development, and operations in the U.S. is essentially broken and dysfunctional.  Divided and inefficient, with poor organization.  Lack of strategic planning. And because the operational and research communities are not working together effectively.

The cost of inferior weather prediction to the nation is immense.  Property and lives lost unnecessarily due to poorly predicted storms.  Economic loss and inefficiency resulting from weather prediction errors that could be substantially reduced.

The bottom line of this blog:

U.S. weather prediction will never become state-of-the-art until the U.S. governmental weather prediction enterprise is totally reorganized.

And in this blog I will describe how it could be reorganized to address the inherent problems, allowing U.S. operational prediction to be the best in the world within a few years.

The opportunity

Today there is a great opportunity to fix the problem.  The first thing needed to address a problem is to know that it exists.  The public knows, because there have been many stories in the national media on the trailing U.S. weather prediction enterprise.  Congress knows, and even passed a bill (the U.S. weather research and innovation act of 2017).  NOAA/NWS management knows and have started some well-motivated, but ineffective measures.   Private sector forecasting firms know and have pushed for reforms.  One U.S. National Academy of Sciences report after another has called for change.

Today we have new and highly able high-level managers in NOAA  (administrators Neal Jacobs and Admiral Tim Galludet) that understand the problems and would like to fix them.  We have an administration that wants "to make America great again."

 Incremental changes that leave current structures in place will fail.   After decades of talking about the problem, can we finally take the substantial measures that will make a real difference?

The warning signs

I have published at least a dozen blogs documenting U.S. inferiority in operational numerical weather prediction, the foundation of all weather forecasting in the U.S.  Others have described the problems as well.  But let me show you a few examples that demonstrate the problems.

Consider the 5-day forecast over the Northern Hemisphere for a typical level aloft (here, 500 hPa, about 18,000 ft, half the atmosphere is above and below this level).  Consider a measure of forecast error (root-mean-square error, RMSE) for the U.S. model (the GFS, red line) and the top world model (the European Center, ECMWF, black).  The  top plot below shows the forecast errors from 1996 to today, while the bottom one displays the difference between U.S. and European Center errors.

Note that the U.S. model (red line) has a higher error that the ECWMF at all times.  And the U.S. is not catching up.  In fact, our standing compared to ECWMF has worsened in the past few years.

 Another sign of NOAA/NWS problems is inferior statistical post-processing of model forecasts, a step in which several model forecasts can be combined, biases removed, and the other improvements.  The U.S. private sector uses much more sophisticated approaches (which they secured though cooperation with the university research sector, including the National Center for Atmospheric Research, NCAR). 

Here is an example of forecast accuracy from Chicago from the forecastadvisor website (virtually every other city shows a similar situation).  Major private sector firms (e.g., the Weather Channel), using some of the same model inputs, have much better forecasts that the NWS.

One national academy report after another (e.g., this one) has recommended the U.S needs a convection-allowing, high-resolution ensemble system that is large enough and designed sufficiently well to provide useful forecast uncertainty information.   The NWS has lagged in this area and has only created a kluged a small ensemble (the Storm Scale Ensemble of Opportunity, SSEO, now HREF).  Not good enough.

During the past several years, the NWS Short-Range Ensemble Forecast System (SREF) has stagnated in resolution and design.  Same with the Global Ensemble (GEFS).  The seasonal forecasting system (CFSv2) has remained basically unchanged for years, with no plans for upgrading for many years.

The only exception to this dismal situation is the excellent work done by the NOAA ESRL rapid refresh team  for frequently updated, short-term forecasts (RAP, HRRR).

The NWS is developing a new global modeling system (FV-3), but there is no evidence that it will significantly improve forecasts without better data assimilation and physics (see figure below for comparison of the 5-day forecast).

I could list a dozen other examples of ways U.S. NWP has fallen behind, and virtually everyone who knows the situation would acknowledge that U.S. numerical weather prediction is woefully lagging where it should be.

Poor Coordination and Lack of Cooperation, Coupled with Insufficient Planning and Organization

So how does a nation with leading weather scientists, leadership in computer science and information technology, and substantial vulnerabilities to storms and other weather features (e.g., hurricanes, windstorms, severe thunderstorms, wildfires) end up with second rate forecasting capabilities?

Poor organization, lack of cooperation, acceptance of inferiority, among others.

You can think of U.S. numerical prediction as an old tree that has been left without pruning, trimming, or planning:  its eventually becomes very overgrown and unhealthy over time.

A visual metaphor of U.S. operational NWP

Consider the poor organizational structure of U.S operational numerical weather prediction.  Keep in mind that the National Oceanographic and Atmospheric Administration (NOAA) is part of the Dept. of Commerce, and that the National Weather Service is part of NOAA.

Operational weather modeling is the responsibility of the Environmental Modeling Center (EMC) of the NWS National Centers for Environmental Prediction (NCEP).  But they don't run the models--they let another group in NCEP do it (NCEP Central Operations, NCO).   Now, although EMC is responsible for the weather modeling, they don't develop most of their own models.   That is done by a number of other centers, some in the NWS and some not.  GFDL in Princeton develops some (hurricane models, new global model), NOAA ESRL (not in the NWS) develops others (e.g., rapid refresh models).  The statistical postprocessing is developed outside of NCEP in MDL (Meteorological Development Lab).  Decision making for new models (and the financial management) is done by different folks outside of NCEP  (Office of Science Technology Integration, OSTI).  No one individual or group is responsible for U.S. operational weather research, operations, and research.  It would be hard to make up a more ineffective approach to managing such a complex task.

Even more inefficient, consider that other agencies (like NASA, the Navy, and the Air Force) are all running their own (and different) numerical weather prediction systems, with independent development groups.

Not bad enough?   The research community through the National Center for Atmospheric Research (NCAR) has developed a separate suite of weather and environmental modeling systems, from the global to local scales. 

Worse?   A NOAA Office of Water Prediction and a National Water Center was set up in Alabama to take on the nation's water prediction (and hydrological forecasts), as if that should be separated from the rest of water prediction (this boondoggle was the result of a Senator wanting some pork for his district).

Vast sums are spent on uncoordinated weather forecasting research by the National Science Foundation, NOAA, DOD, NASA and others, much of redundant or never destined to assist operational capabilities.

And did I mention that there is no concrete strategic plan in NOAA/NWS for the development of U.S. environmental prediction?   Just vague platitudes.   This is in stark contrast to the detailed planning by NOAA/NWS's big competitors (e.g., the European Center, the UKMET office, etc), which as extensive, detailed, and coherent planning processes.

The bottom line:  we have a disastrously inefficient system of developing, running and post-processing numerical weather prediction guidance for the U.S., with agencies doing their own things, disorganization growing, and U.S. capabilities stagnating.

Most decision makers are thinking about protecting their own turf and resources, and few high-level NOAA administrators have known enough to see the problem or were willing to take the heat for the necessary changes.  Numerical weather prediction is technically very challenging and few in Congress has sufficient background to revamp the organization of U.S. weather forecasting.

The latter point is worth repeating:  numerical weather prediction is perhaps the most complex activity of our species, involving billion dollar satellites, global data collection, running complex models that encompass molecular to global scales, and that use the largest computers on the planet.  You can't do this in a haphazard, uncoordinated away as done in the U.S. and expect to be state-of-the science.

The current NOAA/NWS response will not solve the problem

NOAA/NWS management know there is a big problem, and to be honest, some things have improved.  A few years ago, there was outright tension between model developers in NOAA ESRL (Earth System Research Lab in Boulder) and the NWS EMC folks.  That is much better now.  The NWS is putting more funds into extramural research in the academic community and is holding workshops and meetings to gain input.  Recently, the NWS begin developing a new global model (based on the GFDL FV-3 system) to replace the hoary old model (the GFS).

NOAA/NWS has not dealt with the central problem of poor organization, coordination and planning.

They have not created a structure to develop actionable strategic plans.  Different folks are responsible for model development and operations.  The  NOAA extramural funding has often not been well spent.  The University community is drifting away, with nearly all using the NCAR models.  There is  insufficient computer resources to support weather prediction and weather prediction research that the nation requires. And there is little evidence that the new global model will improve verification scores very much, since the real problems are in data assimilation, physics, ensembles, and post processing.

The National Center for Atmospheric Research Mesa Lab

The NWS has held workshops and organized all kinds gatherings to garner support, but these have led to long laundry lists, with little ability to lead to actionable, organized efforts.

And let me be clear that I am not singling out NOAA management for this problem.  It is difficult for a line manager in NOAA to visualize and change a complex organizational structure.   Important partners (like NCAR, DOD, NASA) have often shown little interest in working with NOAA, wanting to maintain their own modeling sandbox. Congress has not been sufficiently attentive to the dysfunctional structures they have created and maintained.

How to fix the problem of U.S. numerical weather and environmental prediction

The key is reorganization, coordination and planning.  The best possible circumstance would be to bring all environmental prediction activities of NOAA into one group-- research, development, operations--with one individual responsible for the whole operation.  We are talking about combining the NWP activities and responsibilities of NWS NCEP, NWS MDL, NOAA ESRL, NOAA GFLD, the National Water Center, and NWS NCO (and others) into one group.  Even better would be to create a truly national center, and bring in the NASA and DOD components--but that is a heavy lift.

But let's imagine something that is smaller lift, that might be a good first step.  Leave responsibility for running the weather/environmental prediction models in the National Weather Service, but move all model development and testing to a new integrated entity within NOAA:  The National Environmental Prediction Research and Development Center (NEPRDC).  A schematic of the organizational structure is shown below.  It would include a chief scientist to help organize and lead the scientific work, with a strong scientific advisory committee.

One organization in NOAA would be responsible for research, development, and testing of the nation's environmental models (weather, ocean, hydrological, coastal, etc.)  The center would have ample supercomputer resources for model testing (which does not exist now) and control of extramural funding, which would help support university (and other) researchers working in research that will directly address current and future modeling problems.

An ideal location for the center would be in Boulder, Colorado-- the center of U.S. weather research, with both NOAA ESRL and NCAR (the university community's center) located there today.   The Developmental Testbed Center (which can provide extramural support for U.S models and help evaluate the new ones, is already in Boulder). Some  NWS EMC personnel (who are now in DC) could work as a satellite center in Boulder.  Bringing NCAR  (also in Boulder) and NOAA together through such a center is critical, and Boulder is a far more central venue than DC for combining the nation's modeling efforts.

Improvements in environmental prediction will only come from sustained, coordinated hard work in physics, data assimilation, and other key areas.  This requires coherent planning and the coordination of the vast scientific and technical resources of the U.S.  The current system is incapable of such effort, the proposed one will be up to the task.

As a first step in fleshing out this proposal might be a national workshop on U.S. environmental prediction, bringing together the entire environmental prediction community, with a detailed white paper coming out of it.  And with so many changes in the bureaucratic structures, Congress will have to be involved.

But in the end, it is clear that the current structures, the result of legacy and administrative drift over decades, are failing.   Only major restructuring and reimagining of U.S. environmental prediction can result in the necessary changes.    The U.S. can easily regain leadership in weather prediction if we only have the will to acknowledge the current failed structures and replace them with something better. 

The U.S. has fallen behind in so many areas due to complacency, poor leadership, self-interest, and loss of energy.  Can we do better in weather and environmental prediction, rebuilding our capabilities when we still have the resources to be the best and give the American people state-of-science forecasts?   I hope so.

Smoke Reaches Western Washington

The smoke is back over western Washington and it is about to get worse, as California wildfire smoke pushes northward over our area.

This morning's sunrise clearly showed a smoke layer, with the reddish glow so familiar from last summer's sunrises and sunsets.

The view of the mountains from Seattle's SpaceNeedle Panocam shows a progressive loss of visibility over the past six days from July 25th to yesterday (all at 5:10 PM).

July 25

July 27

July 29

Most of the of smoke has not been local, but rather came from huge fires over Siberia!   Here is a satellite image from five days ago, showing the smoke moving southwards towards us.  Perhaps Trump can talk to Putin about it.

In a similar image yesterday afternoon, you can just make out the Siberian smoke (particularly north of us), if you look carefully.  There is also one fire in eastern Washington (Chelan Hills) and a few in southwestern B.C. that are contributing a bit as well.  You see all the smoke in California, particularly from the Redding fire?  That is coming our way.

Last nights run of the NOAA HRRR-smoke forecasting system predicted that a significant slug of California smoke will soon reach us.  Here are the smoke forecasts for 7 AM and 5 PM today--substantial smoke is moving northward--particularly bad in Oregon, where sunsets will be very red.

The latest (6:45 AM) visible satellite photo shows the "smoke front" clearly (I put an arrow in to show the leading edge).   Something to look forward to.  Smoke will be worse over eastern WA than over the West.  

Want some good news?  The smoke may knock a degree or two off the high temperatures.

Talking about temperatures, yesterday was a very warm day, getting into the lower 90s from Puget Sound southward and into the 100s in eastern WA.   But perhaps the most unusual aspect were the temperatures in the mountains, where some pass locations got into the upper 80sF and higher (see below, click to expand).  Stampede Pass at 4000 ft maxed out at 88F and mid-90s reached the eastern slopes of the Cascades.  We had very warm air aloft, that approximately tied long-term record values.

Today will be smoky and warm away from the coast, but tomorrow we will start transitioning to cooler, onshore flow.   Relief is only 24 hour away.
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Update at 3 PM.  Here is the MODIS visible image around noon...the smoke moving through Washington State is obvious.

And the solar radiation is clearly being reduced based on measurements here at the UW....will cool us down by 1-4F I suspect...

After A Benign Start to the Wildfire Season: Washington State Must Be Vigilant

As of today (July 28th), the wildfire season has been extremely benign over Washington State,  with few fires and very little smoke--in stark comparison to summer 2017.   Right now, there are only two very small fires burning in our state, and one is contained (see map).  The main locus for Northwest fires today is southwest Oregon.

The fires so far this year have been mainly grass/brush fires--flashy, quick growing, but quick to die and relatively accessible to attack.

The visible satellite imagery yesterday showed a relatively smoke-free Washington, with the only apparent smoke from a grass fire southeast of the Dalles.

Why are we in better shape than last year?   A key difference is less lightning.   Last yeas there were more weather disturbances coming through that produced thunderstorms, whose lightning can initiate fires in difficult to access locations.   June was also very dry and warm in BC. In 2017 there was a large collection of lightning-induced fires in British Columbia in early July, which resulted in numerous fires in lots of smoke reaching our region.   Much less lightning this year.

But things are starting to change.   During the past several days we have seen an increase of cumulus and cumulonimbus activity over the Cascades...something that has been very obvious from Seattle ( see below)

The 24h lighting totals for Thursday and Friday (from the National Lightning Detection Network) shows a cluster of hits on Thursday and more scattered strikes yesterday.

I hope none of them started a fire.

The region is now becoming hot and dry enough to sustain major fires, and it will only get worse during the next month, so great care is needed to prevent human-initiation of fires. 

During the last 60 days, the Cascades and western WA have been drier than normal, bt close to normal in the Columbia Basin.

Over the same period, temperatures have been warmer than normal over western WA,  with the northeast part of the state and the central Cascades below normal.

But the key issue is the recent warmth, with the last two weeks being 2-6F above normal over much of the state.

These temperature and precipitation anomalies from normal are not extreme, but recent warmth and typically dry conditions have left fuels (grass, bushes, etc) quite dry.  The most anomalous region is the western slopes of the southern WA Cascades.

The USDA Forest Service has an integrated assessment of fire danger, showing Oregon to be in much more immediate danger than Washington, with the southern Cascades and eastern Cascade slopes being the most threatened in our state.

But it is possible to get a more nuanced view of the fire threat by looking at the Forest Services analysis of the amount of moisture in various dead "fuels."  For "10-hour" fuels (mainly grasses and very small vegetation), the dead fuel moisture percentage is VERY low (3-4 %) over the inland west and California (red colors).  Small fuels are ready to burn...that is why we are having so many grass fires.

100-h fuels (1-3 inch diameter, large bushes and small trees) are better (less dry), but still below 5% in eastern Oregon and portions of eastern WA.  Dry enough to burn.

 The 1000-hr fuels (3-8 inch diameter, getting into small trees) are shown next.  The lowlands of western Washington are in good shape (green), but deal fuel moistures are 6-10% in eastern WA and Oregon, at dangerously low levels. 

Sunday will be dry and warm over the region, but there will be a continued threat of scattered thunderstorms in the Cascades.  The big issue will be mid-week when an upper trough will approach, enhancing the changes of thunderstorms over the Cascades and British Columbia (see upper level map below for Wednesday at 2 PM).

The cumulative precipitation through next Saturday show lots of precipitation in BC (and most of that will be thunderstorms, and some precipitation (again thunderstorm over the Cascades and Rockies. Not much over Oregon.

So the fire season is upon us and the potential for fires will increases progressively during the next month.  Western WA will cool down substantially mid-week, reducing, but not eliminating the west-side threat temporarily.  But folks will have to be very careful from the Cascade crest eastward--both in preventing fire and dealing with fires that are started by some scattered lightning strikes and human initiation.

The Seattle Tacoma Airport Temperature Sensor is Running Too Warm: Again

There appears to be a problem with the temperature sensor at Seattle-Tacoma Airport:  it seems to be running several degrees too warm.

This is not the first time this has happened.   And excessively warm temperatures at airport stations seems to be a growth industry around here.   In a previous blog I talked about the problem at Yakima--which has been fixed.   Ellensburg is running too warm as well.

But this blog will be about Seattle-Tacoma Airport, whose official NWS/FAA temperature sensor is located between two of the runways.

Why should you care about this?  Because the official records will be wrong and all kinds of records could be broken because of the bad sensor.  And since Sea Tac is the most cited temperatures around here, you will think it is a warmer than it really is.  You might even buy an air conditioner.

Let me show you why several of us  (including Mark Albright, past state climatologist, and Justin Shaw, proprietor of the Seattle Weather Blog).are worried.  First, here is  a comparison between Sea-Tac's high temperatures and those of a very close station (SEAT6, located 10 blocks away) for days Sea-Tac got to 90F or more this month (see below).  So far this month, Sea Tac got to 90F five times, while SEAT6 did not do it once.   On average, SeaTac is 3-5 F warmer than SEAT6 and other neighborhood stations.

 A plot of temperatures around Sea Tac at 5 PM this afternoon indicates a problem.  Sea Tac's temperature (92F) is a clear outlier.

There is another way to show the Sea Tac warming--a longer term comparison to another station.  Let's compare Sea Tac against Boeing Field.  You would expect Boeing Field to be warmer, since it is in the middle of a more urbanized area, within the Seattle Urban Heat Island, and at lower elevation.

Let's first do the comparison for July 1-25, 2014, after the sensor was replaced following the last warm period.  Boeing Field was warmer than SeaTac on most days for the highs and nearly all the time for the lows.

This year?  Very different.  SeaTac generally has higher maximum temps than Boeing Field and the lows are similar...something has changed.

I could provide more evidence...but there appears to be a problem, with Sea Tac being too warm...probably a bad temperature sensor.

Have you noticed that when there are sensor problems, the result are temperatures being too warm?  Often that is due to a broken fan, which is supposed to bring fresh air into the sensor unit.  If the fan slows or is broken, the enclosure heats up.

Now, an error of several degrees can result in Sea-Tac breaking daily records, or monthly records, or record number of days about 90F, etc.   Then the media will headline the records and talk about global warming being the cause. 

Don't think this scenario is plausible?   It happens all the time--let me give you an example.

Earlier this year, the Yakima airport temperature sensor failed and provided temperatures roughly 3F too warm...which is a lot.   The national media noticed.  An AP story by Seth Bornstein and Nicky Forster headlines about 30 years of global warming and cites the Yakima warm anomaly as proof of anthropogenic global warming.   But it really was only a bad temperature sensor.

Anthropogenic global warming IS warming the planet, but the effects are muted here in the Pacific Northwest.

How much have we warmed ?  Let's take a look at the mean daily temperature for July for the NOAA/NWS climate division encompassing the Puget Sound lowlands (see below).  Around 62.5F before 1980 and warming to around 64 F the last decade (smoothing out the annual ups and downs)-- so about 1.5F over the past 90 years--and a lot of the change occurred between 1975 and 1985.  So July's are warming around here. 

Some of this probably was the result of human-caused global warming, but not all.  Of particular interest is the major warming during the late 1970s, when circulation patterns were shifting as the Pacific Decadal Oscillation (PDO) moved into its warm mode (the PDO is a mode of natural variability).  Human caused global warming is occurring, but it does not explain periods like this week, when we are 10-15F above normal.

The media is already talking about Seattle having the warmest July on record (see below), based on the Sea-Tac Airport temperatures, but is it really?

I called a colleague at the Seattle NWS office and he said they will check out the SeaTac temperature sensor.

Few Air Conditioners in Seattle (and western Washington): The Dry Facts

Today, one of my favorite Seattle Times writers (Gene Balk) had a fun story about the lack of air conditioners in Seattle.  Turns out that our ownership of air conditioners is noteworthy:  no major city has less AC per capita.

Much of the article is fine, noting our mild temperatures, proximity to water,  and cooling at night...all important factors in our modest AC count.

But there is an critical fact that he doesn't mention.   Our low humidities.   Whenever it is hot around here our air is dry.  Which makes us far more comfortable.

The relative humidity of the air is critically important for comfort because evaporation of sweat is an enormously effective way to lose heat.

Humans are unique in our ability to sweat from our skin.  No other mammal other than horse can do so effectively....and according to what I read, horses sweat differently than us (mainly in their armpit area).   Even our closest relatives (the great apes) use another mechanism...panting....as do our pets.   With millions of sweat glands and naked skin.....we are the superstars of sweat.  And evaporation of water requires huge amounts of energy (heat), and thus is an enormously effective cooling mechanism.  So if a human has a large supply of water, he or she can handle very warm temperatures....but there is a catch.

For sweating to be effective the water must evaporate from our skin and that only occurs when the relative humidity is below 100%.  The drier the air, the better we can evaporate and cool.  So 85F and 35% relative humidity is far more comfortable than the same temperature and 95% relative humidity.  The National Weather Service even has an equation to express this, which they use for their "Heat Index" (see below)

The southeast U.S. is miserable during the summer, not because they are crazy warm (it rarely gets above 100F there) but because the humidity is so high.  Why?  Because the air had been over the warm Gulf of Mexico and the amount of water vapor air can pick up depends on temperature of the water and the adjacent air.  And the Gulf is very warm (80s to 90F)

Here is Seattle, our summer air is nearly always quite dry.  Most of the time, our air is coming off the cool Pacific Ocean.  That keeps the temperatures moderate, but also prevents the air from picking up a lot of moisture--since cool air, even if it is saturated, can't pick up a lot.

The number one measure of moisture content of the air is dew point, the temperature to which air must be cooled at constant pressure to produce saturation.  Drier air has a lower dew point.   Our summer air typically has dew points in the lower 50s... over the eastern U.S. dew points in the 70s are common.

Dogs pant, we sweat

And when this relatively dry (low dew point) air moves inland it warms, and the relative humidity plummets.  Why?  Because relative humidity is the ratio of the amount of water vapor in a volume of air, divided by the max. water vapor that volume can hold--and that depends on temperature.  Warmer air can hold more water vapor than cooler air.  So warming air, allows it to hold more, which makes relative humidity plummet.

Our warmest temperatures...our real heat waves... occur when air comes from the east.  That is when we get into the mid-90s and more.  But that air is very dry.  First, there isn't much of moisture source east of the Cascades...the land is arid.  And as the air descends the Cascades, it warms by compression, which causes the relative humidity to fall.

Enough theory, let's check out what happened the last three days on top of my department!  (see plot below, time increases to the right).  The third panel shows temperature (black line) and dew point (red line).   Our dew point was very modest....around 50F...about the same temperature as the ocean offshore.   Temperatures swings up and down each day, with a slow overall rise as we have warmed.

But look at the fourth panel...relative humidity.   Huge gyrations... very low (about 30%)when it is hot later in the afternoon , but 70-80% when the air temperature is lowest at night (55-60F).

And the low humidities have another benefit...they allow our nights to cool.  Water vapor is the most potent greenhouse gas, which means it traps and reradiates infrared energy....slowing down the night time cooling.  That is why deserts can get cold at night, even when they are hot boxes during the day.

Want proof?...Here are the minimum temps last night. In some lowland locations temperatures dropped into the upper 40sF!  Those folks needed a blanket.

So sweating is virtually always effective around here, unlike for those poor folks in the SE U.S.  Just make sure you stay hydrated.   Don't sweat enough?  Take a cold shower or run through a sprinkler.  A wet tower in front of a fan can cool things down.  And air out your home or apartment at night to prevent the place from progressively warming up.

"The S is for SuperSweat"