Extreme Temperature Diary Monday May 4, 2020/ Main Topic: Update On Forecast Historic U.S. May Cold Outbreak

Monday May 4th… Dear Diary. The main purpose of this ongoing blog will be to track United States extreme or record temperatures related to climate change. Any reports I see of ETs will be listed below the main topic of the day. I’ll refer to extreme or record temperatures as ETs (not extraterrestrials).😉

Main Topic: Update On Forecast Historic U.S. May Cold Outbreak

Dear Diary. Over the weekend the cold outbreak, which I have been alluding to last week, became very apparent on meteorology models:

Since my last report on Saturday models have become faster, bringing cold air into the Midwest and Northeast on Thursday and Friday with the core of a strong vortex moving into the Northeast over this coming Mother’s Day weekend:

Our next questions are how cold will conditions get and how long will the dipole pattern last?

Another lobe of the eastern North American cold pocket could rotate into the Midwest by Tuesday of next week, reinforcing May chill:

There are signs, though, that a storm system, as noted by the cold pocket off of the Pacific Northwest Coast, will break down the western ridge and bust up the dipole. If this occurs typically warm but stormy conditions will return to the U.S. for the second half of May:

Jason Samenow of the Washington Post has just published an excellent article on what should be historic record cold for a good chunk of the United States east of the Rockies later this week. Here is his writeup:


Capital Weather Gang

Rare and intense May outbreak of Arctic air targets East for Mother’s Day weekend

Temperature difference from normal Saturday at 5,000 feet above the ground as a deep pool of cold air invades the eastern United States; simulation from European model. (The Washington Post)

By Jason Samenow May 4 at 11:39 AM

An unusually strong blast of frigid air for the month of May is set to crash into the eastern United States late this week, likely bringing record-low temperatures in some areas for Mother’s Day weekend. The blast of cold may even allow for some snow in parts of the Northeast and frost as far south as the interior Carolinas.

The weekend cold will be the second of two shots of Arctic air spilling into the eastern half of the Lower 48 this week as a chillier-than-normal pattern that began in mid-April shows little sign of relenting. This abnormally cold weather marks a major departure from January through March when temperatures were much warmer than normal.

“Temperatures may approach record cold levels for some areas with a late frost/freeze where the growing season has typically started,” wrote the National Weather Service in its extended forecast discussion.

Michael Palmer, a meteorologist at the Weather Company, described the incoming Arctic intrusion as “[o]ne of the coldest modified polar air masses on record so late in the season,” in a tweet.

The European model predicts that the intensity of the cold air mass in Pittsburgh on Saturday will be the most extreme recorded during May.

Just how cold and when?

An initial and less biting dose of chilly air will arrive in the Great Lakes on Tuesday into Wednesday and filter into the Northeast on Wednesday into Thursday. It will result in temperatures about 5 to 15 degrees cooler than normal. This means high temperatures mostly in the 50s instead of the 60s.

The second and stronger punch will hit the Upper Midwest and the Great Lakes on Thursday into Friday barging across the East Coast on Friday night. In cities such as Minneapolis, Chicago and Detroit, Friday is likely to be the coldest day, while the core of the Arctic air mass settles over cities from Washington to Boston on Saturday.

European model shows two shots of chilly air arriving in the eastern United States; the first Wednesday into Thursday, the second and more intense, late Thursday into late Friday. (The Washington Post)

Temperatures are predicted to be 15 to 25 degrees colder-than-normal because of this blast. This means highs only in the 40s from Minneapolis to Detroit on Friday, and over large sections of the Northeast on Saturday; mountainous areas may get stuck in the 30s.

Even along the Interstate-95 corridor, from Washington to New York, highs should only reach the 50s on Saturday. Some of these highs are likely to be the coldest on record for the date.

Predicted temperature difference from normal on Saturday afternoon from European model. (The Washington Post)

Freezing lows are likely through much of the Great Lakes region Saturday morning and much of the interior Northeast on Sunday morning; some of which may set records. Frost will be possible as far south as the interior Mid-Atlantic, even into the western Carolinas, on Mother’s Day morning.

Forecast low temperatures on Mother’s Day from the National Weather Service. Those circled indicate records. (WeatherBell)

The core of the cold will exit the Northeast on Sunday into Monday; however, cooler-than-normal conditions are likely to persist through at least the middle of the month.

As this forecast is still five to six days into the future, these predictions may change slightly over the coming days.


As chilly air in the wake of Friday’s Arctic front passes over the Great Lakes, lake-effect rain and snow showers are possible downwind Saturday, particularly over western New York and Pennsylvania. Some accumulation could even occur in hillier areas with a bit more elevation.

Snow could also fall in portions of interior New England on Saturday, especially in the mountains, as low pressure along the Arctic front barreling through draws moisture off the Atlantic Ocean.

Why so cold?

The configuration of the jet stream, the fast-moving air current along which storms track, is predicted to be ideal for the delivery of Arctic air by late this week. Due to zones of high pressure over both western North America and Greenland by the weekend (see the areas of the red on the image below), the jet will have no choice but to buckle southward allowing a frigid pool of air to drop into eastern North America (see the area of blue and green on the image below).

This pattern is likely related to the spring breakup of the polar vortex, which was unusually strong and undisturbed during the winter and mostly kept cold air locked up over the Arctic as a result. As the vortex is disintegrating, it is allowing some remnant lobes of Arctic air to escape into the mid-latitudes.

[How a record-strong Arctic weather pattern aided a troubled Arctic research expedition]

[The demise of the polar vortex could spell weather surprises this spring]


Here is the latest guidance for lows occuring Sunday Morning:

The above chart is more March-like than one we would expect in May. By this point many record lows will be reported across much of the eastern half of the United States, some below freezing as we can see. I’ll be reporting more on this cold outbreak going through next week.

More from Weather Underground:

Global warming has not quit, though, unfortunately. On the other side of the planet there has been record heat:

Now here are some of today’s articles and notes on the horrid COVID-19 pandemic. (As usual, the most noteworthy items will be listed first.):

Here is more climate and weather news from Monday:

(As usual, this will be a fluid post in which more information gets added during the day as it crosses my radar, crediting all who have put it on-line. Items will be archived on this site for posterity. In most instances click on the pictures of each tweet to see each article. The most noteworthy items will be listed first.)

Here are more hot West Texas “ET’s:”

(If you like these posts and my work please contribute via the PayPal widget, which has recently been added to this site. Thanks in advance for any support.) 

Guy Walton “The Climate Guy”

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