North American Monsoon Archives

The North American Monsoon (NAM) – Posted on April 27, 2024

By Sig Silber April 27, 2024ClimateNo Comments

In this article, I am presenting information from the National Weather Service and some other parts of NOAA on the North American Monsoon (NAM) which really is the Sonoran Monsoon but we wanted to have our own so we appropriated it. When the Sonoran Monsoon leaks into the U.S. it is called the NAM. The quoted material is indented and my comments are in boxes.

Yes and no. Yes, it is a season not a single storm. Tucson NWS is Monsoon Headquarters and they had criteria for determining when the Monsoon started and stopped but it was felt that these were too complicated for Americans so they changed to a calendar start and stop time which works well.

The starting point for understanding the NAM or pretty much anything in Meteorology is to think about the time of the year. In the winter, the prevailing westerlies and the jet stream dominate weather in the CONUS. In the summer they still have an impact but other mechanisms can come into play. No time in this article to explain it but the ITCZ moves to the north.

I would like to add that the differential heading of land and water in Mexico causes moist air to rise creating thermal low which kind of shoves the high north of it to the north. The mountains also play a role in sometimes blocking air flows and uplifting air masses which causes precipitation. It is quite complex but we are going to simplify it a bit in this article.

This map shows the percentage of annual precipitation that arrives during the Monsoon Season. You can see that the NAM is very important to Arizona, New Mexico, Kansas, Western Texas, and the small part of Southeast California. But it is important to many other states as well. It may not provide a disproportionate part of their annual precipitation but a good monsoon versus a poor monsoon has an impact on many states. As you can see, it is even more important to Mexico.

There are more than four types but these are the main ones. We will go into detail on each of them in the body of this article. But it is really simple when you think about a high being clockwise and a low being counterclockwise. Where you have a low west of a high, the air will be shuttled to the north from Mexico. So first look for the position of the main high-pressure area. Then look for where the low is. You will be able to figure out which way the wind will be blowing. If it is coming from where moisture is, it is likely to rain.

Some readers will need to click on “Read More” to get to the body of the article.

NOAA Updates it’s Four-Season Outlook On February 16, 2023 – Potential El Niño impacts were considered in the outlooks for autumn 2023 and next winter

By Sig Silber February 17, 2023weatherNo Comments

Updated at 3:05 p.m. EST February 17, 2023 to incorporate information on the latest Sudden Stratospheric Warming (SSW) event

On the third Thursday of the month right on schedule NOAA issued what I describe as their Four-Season Outlook. The information released also included the MId-Month Outlook for the single month of March plus the weather and drought outlook for the next three months. I present the information issued and try to add context to it. It is quite a challenge for NOAA to address the subsequent month, the subsequent three-month period as well as successive three-month periods for a year or a bit more.

It is very useful to read the excellent discussion that NOAA issues with this Seasonal Outlook. The CPC/IRI analysis suggests that ENSO will very soon return to Neutral with a La Nino bias and gradually transition to true Neutral, Neutral with an El Nino bias, and then solidly El Nino. Confidence in the first part of that sequence of transitions is higher than in the latter part of the sequence.

September 2, 2022 Looking Ahead 28 Days Plus our usual 48-hour report.

By Sig Silber September 3, 2022weatherNo Comments

Updated at 7 pm Saturday, September 3, 2022 to include a comparison with the Monthly Outlook Issued on August 31, 2022

Southern Tier to be wet; the Northwest starts warm but the warm anomaly rapidly moves to the East with the Northwest experiencing some cold air intrusion.

NOAA updates many of its weather outlooks daily or even more frequently and in many cases issues a discussion with those outlooks. We provide a daily report which focuses on the shorter-term predictions but has links to all the partial-month outlooks. One of the reports issued by NOAA only gets updated on Fridays and since this covers weeks 3 and 4 it is very important. The discussion that gets issued with this week 3-4 NOAA report is often where possible changes to the weather pattern are first identified.

So we have decided to issue a special report on Fridays in which for a subset of the information we show the actual forecast maps not just provide the links. This makes it easier for the reader. We will also include at the end of the article the other information from the daily article

When the Week 3-4 Outlook is issued on Friday, we have a 28-day view of the future. It is important to recognize that the forecasts do not always work out as predicted. But in the article, there are links to obtain updated forecasts. This is important because it appears that changes are happening and the current view of the next 28 days differs substantially from the Monthly Outlook issued just a few days ago.

NOAA Updates their September 2022 Outlook on August 31, 2022

By Sig Silber September 1, 2022weatherNo Comments

Wildland Fire Risk Maps updated at 10:04 pm EDT on September 1, 2022

Short-term improvement in drought for September. It is more than previously forecast.

At the end of every month, NOAA updates their Outlook for the following month which in this case is September. They also issue a Drought Outlook for the following month. We are reporting on that tonight.

There have been some significant changes in the Outlook for September and these are addressed in the NOAA Discussion so it is well worth reading. We highlighted some of the important changes within the NOAA Discussion.

Of significant interest is the Drought Outlook for September. It is again a big improvement but unfortunately, it probably is a one-month event. We have also included four months of Wildland Fire Potential Outlooks and also a map showing the year-to-date precipitation in the West. We also included a Monsoon Update.

NOAA Issues Four-Season Outlook on August 18, 2022

By Sig Silber August 20, 2022weatherNo Comments

Preparing to Say Goodbye to La Nina Early in 2023

Today is the third Thursday of the month so right on schedule NOAA has issued what I describe as their Four-Season Outlook. The information released also includes the Early Outlook for the single month of September plus the weather and drought outlook for the next three months. I present the information issued and try to add context to it. It is quite a challenge for NOAA to address the subsequent month, the subsequent three-month period as well as successive three-month periods for a year or a bit more.

“The La Niña signature is likely to fade during FMA and MAM 2023, given that La Niña and ENSO-neutral are about even odds”

You can take La Nina out of the forecast, but the warming trend continues. But the Outlook is for a wetter CONUS starting in AMJ 2023. For many parts of CONUS, 2023 will be wetter than 2022. At least that is what NOAA is predicting right now.

August 14, 2022 Looking Ahead 28 Days Plus a Review of State Temperature and Precipitation Rankings

By Sig Silber August 14, 2022weatherNo Comments

Northern Tier from Great Lakes West Predicted to be Hot and Dry

NOAA updates many of their weather outlooks and in many cases issues a discussion with those outlooks. On Fridays, they issue a week 3 – 4 outlook which is farther out than the typical 10-day forecast and the discussion is excellent. So we have decided to issue a weekly special report on Fridays.

When the Week 3-4 Outlook is issued, we have a 28-day view of the future. It is important to recognize that the forecasts do not always work out as predicted. But in the article, there are links to obtain updated forecasts. Since we are publishing this article on Sunday we only have a 26-day view of the future. Sorry about that.

We have also taken a look at the state temperature and precipitation rankings for July and Year to Date (YTD). It is not a surprise that they differ. We provided that information in a recent article but thought it useful to repeat it here for those who did not happen to read the other article. There is value in relating the future outlook to the prior month and to the YTD.

Friday Looking Ahead 28 Days July 22, 2022

By Sig Silber July 23, 2022weatherNo Comments

First half of 28-Day Forecast Period is wetter than the second half. But it is hot throughout the 28-Day Forecast Period.

When the Week 3-4 Outlook is issued, we have a 28-day view of the future. It is important to recognize that the predictions do not always work out as predicted but in the article, there are links to obtain updated predictions.

It is somewhat surprising that there is as much difference between the first 14 days and the second 14 days of the 28-Day Forecast Period. The North American Monsoon is strong throughout the 28-Day Forecast Period. It is stronger at the beginning and slowly returns towards what is a normal Monsoon. Heat will be a hazard.

NOAA Issues Four-Season Outlook on July 21, 2022

By Sig Silber July 22, 2022weatherNo Comments

Preparing to Say Goodbye to La Nina, but Not Quite Yet

Today is the third Thursday of the month so right on schedule NOAA has issued what I describe as their Four-Season Outlook. The information released also includes the Early Outlook for the single month of August plus the weather and drought outlook for the next three months. I present the information issued and try to add context to it. It is quite a challenge for NOAA to address the subsequent month, the subsequent three-month period as well as successive three-month periods for a year or a bit more.

The three-month period Jan/Feb/Mar next year seems to be when the overall precipitation situation improves but for some reason the temperature situation does not and may be worse for several months along parts of the Southern Tier. You can take La Nina out of the forecast, but the warming trend continues. For many parts of CONUS, 2023 will be better than 2022. At least that is what NOAA is predicting right now.

Daily Short-Term and Intermediate Term Weather Forecast – July 4, 2022

By Sig Silber July 4, 2022weatherNo Comments

This is still an experimental article so it has some problems that need to be worked on especially the tropical section.

Here is what we are paying attention to this evening and the next two days from this afternoon’s NWS Forecast.:

...Excessive Rainfall and Severe Thunderstorms possible across northern
tier...

...West cools down as Great Plains into Midwest warm up...

...Critical fire weather conditions to persist across the Great Basin this
weekend...

NOAA Updates July Outlook – June 30, 2022 – Not Much Change – Some Ocean Indicators are Surprising

By Sig Silber July 1, 2022weatherNo Comments

Updated at 2:30 am EDT July 2, 2022 to incorporate the Week 3 – 4 Outlook which suggests that the second half of July will not be as cool in the Northwest but perhaps less warm elsewhere and the Monsoon may be less robust but some other areas will be less dry.

At the end of every month, NOAA updates their Mid-Month Outlook for the following month which in this case is July. They also issue a Drought Outlook for the following month and update the three-month Drought Outlook. We are reporting on that tonight. The updated Outlook is very similar to the Mid-Month Outlook. This is surprising since the Mid-Month Outlook was issued two weeks ago and there usually are more changes in that period of time.

For temperature, the shape and location of the large dry anomaly have changed a bit. The cool anomaly in the Northwest is now slightly larger. For precipitation, the area where an above-average Monsoon is forecasted is a little larger and shifted a bit to include more of New Mexico. there is a new small dry anomaly

We provide partial-month Outlooks for the first 22 days of July which allows us to somewhat assess if the Monthly Outlook is consistent with the partial-month Outlooks and it generally is. But we will not be able to answer that question definitively until the Week 3-4 Outlook is issued tomorrow. We will provide an update at that time.

We also provide enough information for readers to understand any changes from the Mid-Month Outlook and we try to figure out why these changes were made. Many of the changes are explained in the NOAA discussion which is included in the article. The partial-month forecasts that we have provided show how NOAA thinks this will play out as the weather pattern evolves during July.

There is also a discussion of the ENSO condition which is ever so slightly different than what NOAA used to develop the Mid-Month Outlook. But there is a fairly strong signal that this La Nina will end in late winter 2022/2023. The impacts on weather may not be noticed until Spring. But that is just the current forecast and can change.

We have also begun our tropical storm coverage. Yes, it is that time of the year. We are also providing special coverage of the Monsoon by providing the links to those daily updates.