NOAA Updates The Outlook For July 2020 – Southwest Monsoon Delayed

Written by Sig Silber

At the end of every month, NOAA issues an update to their Early Outlook for the following month, in this case, July 2020, which was issued as usual on the Third Thursday of the month. Today, twelve days later, NOAA has issued their Updated Outlook for July. The changes are very significant. One major change relates to a delayed and weaker onset of the Southwest Monsoon. But there are many other changes. Everything is connected and these changes appear to be related to the development of La Nina but NOAA is not quite ready to announce that yet.

Some housekeeping: On June 18, 2020, we published Part I of our analysis of the NOAA and JAMSTEC Three- to Four- Season Outlook and that can be accessed here. In that report, the July 2020 Early Outlook was issued. This article presents the NOAA update of their Early temperature and precipitation Outlook for July and the most recent Drought Forecast update for the month of July.

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Now let us address the NOAA Update of the July 2020 Forecast.

We do not usually start with the NOAA Discussion but the changes are so significant and are well explained in the NOAA Discussion released today so we are presenting it first.

30-DAY OUTLOOK DISCUSSION FOR JULY 2020

The updated outlook for July 2020 utilizes the most recent dynamical model guidance across time scales and any change to the land surface state to modify the mid-month outlook release. For temperature, most of the forecast domain remains favored to see above-normal monthly mean temperatures for July 2020, although the probabilities in some areas required adjustment as well as a small region of elevated odds for below-normal temperatures was included in the update in the Pacific Northwest. Current troughing in proximity to the Far West and West coast decreases odds for above-normal temps for areas in California, the central Great Basin, central and southern Rockies and the Southwest, while introducing the small region of below-normal temperatures referenced above.

Probabilities for above-normal temperatures are increased in the northern Plains, Great Lakes, Ohio Valley and Southeast from the mid-month outlook due to expectations of ridging during much of the month. Forecast coverage and in some areas probabilities for above-normal temperatures are decreased for Alaska as a result of the latest forecast guidance showing greater uncertainty in this area as compared to earlier in the month.

Favored above-normal monthly total rainfall for parts of the lower Mississippi Valley, Southeast, lower Ohio Valley and lower Mid-Atlantic remains unchanged from the mid-month outlook. Elevated odds for below-normal rainfall originally focused in the north-central Rockies has been shifted southward and and expanded to include much of the central Great Basin, central and southern Rockies and Southwest. This area stretches eastward to include parts of the central Plains. Forecast troughing along the central West coast is not conducive for the climatological development of the Southwest monsoon ridge and so odds for a delayed and weaker onset of the Southwest U.S. monsoon are elevated and so favor enhanced odds for below-normal rainfall in this region for July.

The main core of the westerlies are forecast to run across the northern Rockies and northern Plains which favors modestly increased odds of above-normal rainfall in this region. Downstream of the central CONUS ridging favors a likely mean relatively dry zone to the east which is supported by most dynamical model guidance and so favors below-normal rainfall for parts of the Great Lakes northern Ohio Valley eastward to parts of the Northeast and New England.

Figure 8 suggests that the summer precipitation regime over the conterminous United States is characterized by coherent phase relationships between rainfall over the southwest and rainfall elsewhere. Over the Great Plains and along the northern tier, the rainfall decreases between June and July by roughly the same amount as the rainfall increases in the southwestern United States. Along the eastern seaboard and portions of the Gulf Coast, there are rainfall increases between June and July. Previous studies have linked the onset of summer rains over northern Mexico and the southwestern United States to a decrease of rainfall over the Great Plains (e.g., Mock 1996; Tang and Reiter 1994; Douglas et al. 1993; A. Douglas 1996, personal communication) and to an increase of rainfall along the East Coast (Tang and Reiter 1984). In section 5a, lagged composites of the observed precipitation field are used to explore how these phase relationships change during the evolution.

Now, we will compare the NOAA Early Outlook for July 2020 with the newly issued update.

Early Outlook Temperature

Updated Temperature Outlook

Early Outlook Precipitation

Updated Precipitation

Visual Consistency Testing.

It is useful to see how the full-month forecast fits with the set of partial-month forecasts that we have. These will continue to update in this article. It is important to remember that with the partial-month forecasts, we generally have about 25 days of the subsequent month to look at when we do this at the end of the month as we are doing now. It depends on what day of the week the month ends. So this month, which ended on a Tuesday, we are missing a forecast that includes the last seven days of the month. So we are in decent shape for the visual consistency testing this month.

First Temperature

The new monthly forecast is to the right. Does it appear to be reflective of the four parts of the month for which we have forecasts? →			↑ ← The Week 3 – 4 forecast was updated Friday, June 26 so we may want to update the commentary when the Week 3 – 4 update is reissued on July 3, 2020. But that probably will not be necessary. At this point, we have forecasts for 24 days of the 31 days in July and the fit looks pretty good except for Alaska.

And Precipitation

The new monthly forecast is to the right. Does it appear to be reflective of the four parts of the month for which we have forecasts? →			↑ ←The Week 3 – 4 forecast was updated Friday, June 26 so we may want to update the commentary when the Week 3 – 4 update is reissued on July 3, 2020. But that probably will not be necessary. At this point, we have forecasts for 24 days of the 31 days in July and the fit looks pretty good except for New England

Because the end of the month forecast was issued on a Sunday, we see no point in publishing the prior Week 3 – 4 Discussion as the monthly discussion is a lot more current.

Sometimes it is useful to compare the three-month outlook to the forecast for the first of the three months. It shows how much the pattern changes over the three-month period.

One can mentally subtract the First-Month Outlook from the Three-month Outlook and create the Outlook for the last two months in the three-month period.

And with respect to drought, this was also issued on June 30, 2020.

Latest Monthly Assessment – Drought intensification and development occurred during May across the central to southern Great Plains due to insufficient rainfall coupled with periods of above normal temperatures. According to the U.S. Drought Monitor valid on May 26, drought coverage across Kansas increased from 6.85 to 27.46 percent since late April with Oklahoma experiencing an increase from 3.94 to 14.44 percent. Additional development is likely across the central to southern Great Plains during early to mid-June with the combination of above normal temperatures and below normal precipitation. Development is also favored across parts of New Mexico and Wyoming. Much of the eastern U.S. remains drought-free, but development is forecast across parts of New England where short-term precipitation deficits are increasing and the updated June outlook calls for elevated probabilities of above normal temperatures and below normal precipitation.

Heavier rainfall during mid to late May resulted in improving drought conditions across southern Texas along with much of the Gulf Coast and Florida. Continued improvement or removal of drought is forecast for these areas, based on the likelihood of above normal precipitation through at least the first half of June. Meanwhile, drought persistence is most likely across ongoing drought areas of the West and North Dakota. Persistence is also favored for drought across Puerto Rico and Hawaii, while Alaska is likely to remain drought-free through the end of June.

Looking back on June to relate the forecast for July to the actuals in June

First June Temperature (29 out of 30 days).

And then June Precipitation (29 out of 30 days).

We then show the new forecast and the prior month actuals (less one day) side by side.

Conclusion

The purpose of this article was to present the updated Outlook for July 2020 and compare it with the Early Outlook. It is not to critique the updated Outlook for July based on our opinions but we point out possible inconsistencies if we find them. We have assessed the extent to which the monthly outlook seems to fit with the other forecasts provided by NOAA. In reality, all forecasts are obsolete when issued as the situation changes day by day or six hours by six hours i.e. each new model run. In our other articles, we continually examine the current forecasts from NOAA including Day 1- 5, 6-10, 8-14 and Week 3 and 4. So we are continually looking at approximately 25 days into the future.

On July 9, 2020, IRI/CBC will issue their ENSO forecast (and we expect them to declare that we are in La Nina Conditions) and we will present that and critique it. It is an ongoing process and we attempt to provide our readers with the best current assessment of the next approximately 25 days (except when we cover the Four-Season Analysis or medium-frequency cycles such as ENSO), so our analysis is pretty much ongoing. We also publish a “LIVE” Weather Article which updates in real-time to reflect NOAA Weather Headlines and for those interested provides detailed information down to current warnings in place. All of our reports including past versions of these reports can be located via the Directory/Archive which can be accessed here.