Summerlike Warmth Returns for First Days of June

I'm expecting summerlike warmth to come back for the first week or so of June.

The image above shows projected 500mb height anomalies over the northern hemisphere. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. In the image above, if we look towards the Bering Sea, we can see a very strong ridge of high pressure, seen by the splotch of red around the Aleutian Islands. This image is valid for May 13-14, and if we extrapolate it out 2-3 weeks using the Bering Sea Rule, we can expect high pressure and warm weather to appear in the East US.

If we look at another 500mb height anomaly forecast graphic, this one valid on May 19th, we now see that our strong ridge has shifted west into the middle of the Bering Sea, with cooler, stormier weather now protruding into western Alaska. This tells us that we can expect warm temperatures in the first several days of June in the middle of the country, with cooler conditions along the Eastern Seaboard.

This warmth is supported by long range modelling of enhanced tropical convection around the central Pacific, which is typically associated with warmer than normal weather in the Central and East US in the May-June-July time period. The bottom panel in the graphic above demonstrates the enhanced convection (blue) present in the Central Pacific.

Andrew

May 21-25 Potential Storm System & Severe Weather

I'm analyzing the May 21-25 time period for a substantial storm system to bring cool weather and possibly some severe weather to the nation.

Tropical Tidbits

The image above shows projected 500mb height anomalies over the western Pacific. We can signify the blues with negative height anomalies, which indicate the presence of cooler and stormier weather, while reds denote positive height anomalies, which allow for warmer than normal and calm weather. Looking towards Japan on this forecast graphic, valid on May 15th, we see a substantial closed low approaching Japan, bringing in cooler than normal and unsettled weather for the area. If we utilize the Typhoon Rule, we can expect this storm system to impact the United States 6-10 days after this storm affects Japan, which would give us a May 21-25 time period.

Indications I am getting from this graphic tell me much of the United States may be impacted by this cooler than normal weather, and while I do believe severe weather is possible, I'm currently thinking any severe weather will be limited due to the lack of a powerful ridge advecting north over Japan prior to this closed low hitting the country.

Andrew

Preliminary 2014-2015 Winter Analogs

After some consideration, I've decided to create a set of analogs for the upcoming winter, using the same parameters that gave me such high success this past winter.

This post will be divided into two sections of analogs. We will begin with the analog years that matched any two of my five parameters I set forth for this winter.

The image above shows 500mb height anomalies across the northern hemisphere, where cool colors signify stormy and cool weather. Warm colors define the presence of warm and quiet weather. In this image, which shows 500mb height anomalies averaged out across these 9 analog winters, we see significant negative height anomalies across the western coast of North America, defining a textbook negative-Pacific North American index (PNA) pattern. In negative PNA patterns, low pressure dominates the West US, leading to warm weather in the Central and East US. We see ridging in southern Canada, spilling over into the northern United States. There is no clear blocking pattern over the Arctic Circle, meaning cold weather may be even more difficult to come by.

The temperature composite for these same analog years confirms this assumption. We see warm weather dominating the northern United States, maximized in the northern Plains. This sort of temperature pattern is typically associated with an El Nino, where we see warmer than normal weather in the Northern US, with cooler than normal weather in the South or West US.

The precipitation anomaly for these same years confirms the textbook El Nino set-up, as we see below normal precipitation affixed over the southern Ohio Valley down towards the Gulf Coast, and the Southwest US along the Gulf Coast experiencing above normal precipitation. This belt of above normal precipitation looks to be due to the abnormally active subtropical jet stream, another characteristic of an El Nino. We also see a stripe of wetter than normal conditions along the East Coast, which can be attributed to that El Nino-induced subtropical jet stream.

Let's now go over my preferred analogs, which match three of the five chosen parameters that fit the upcoming winter.

Looking at the 500mb height anomaly composite for the four years that match three of my five parameters, we see a much different story than we saw with the less-preferred analog set we just went over. We now see a well-defined blocking situation over the Arctic Circle, with strong positive height anomalies in Greenland and into Canada. This exemplifies the negative phases of the North Atlantic Oscillation (NAO) and the Arctic Oscillation (AO). The negative phases of these indexes both allow cold air to push into the United States, and the negative NAO permits the storm track to push north and threaten the East Coast with more coastal snowstorms.

The temperature composite for these four choice analog years is also a change from the other analog set. Rather than most of the United States being warmer than normal, the negative AO and NAO seem to influence temperatures to be well below normal across much of the nation, maximized in the southern Plains. We still see warmer than normal conditions in the upper Midwest, but these warm anomalies are more restricted than they were in the first analog set. Unfortunately, this could mean the second straight colder than normal winter, as I place more trust in this analog set than the one we first analyzed.

The precipitation composite for these four analog years shows a very stormy East Coast, with anomalies anywhere from 4 to 6 inches above normal, most enhanced in the Southeast. This precipitation pattern is still somewhat aligned with a typical El Nino pattern, though the dryness in the Southeast argues against this somewhat. I'm not as ready to accept this precipitation composite, considering how dominating the El Nino may be this winter, but as always, the analog set will be refined in coming months.

Andrew

JMA Model Predicting Strong El Nino to Develop for Winter 2014-2015

The Japanese Meteorological Agency's long range climate model is predicting a strong El Nino to develop in time for the upcoming winter.

Shown above we see the predicted sea surface temperature (SST) anomalies in the yellow squares from present day to about October 2014, with observed SST anomalies in the red circles on the left side of the graph. We see that the JMA model is predicting a rather linear rise in sea surface temperature anomalies into this summer and fall, reaching El Nino territory by late spring. The shaded red region in this graph indicates the threshold and SST anomalies that define an El Nino (+0.5 degrees C or above), while the blue shaded region defines official La Nina SST anomalies (-0.5 degrees C or below).

The Climate Prediction Center (CPC) here in the United States makes its own climate model as well, named the Coupled Forecast System model (CFS). The CFS model above shows a linear increase in SST anomalies as well, maxing out at around 1.5 degrees Celsius for November-December-January in 2014-2015. The 1.5 degrees C above normal benchmark is also the threshold for a Strong El Nino, meaning such an El Nino of that strength is still possible (though in my personal opinion, not as likely). The general gist of these two models is that we can expect an El Nino to develop later on this summer, likely to strengthen through the fall and into this winter.

Andrew

Cool, Stormy Weather To Give Way to Summery Warmth by Late May

I'm expecting some cool and stormy weather in mid-May to eventually give way to a shot of above-normal temperatures, before a cool spell returns for late May.

* A quick note, I have had at least 8 comments telling me that my late April-early May forecast was wrong, with more than a couple of these comments delivered with a less-than-enticing attitude. I've been receiving these comments for 2 weeks now- enough is enough. I don't expect myself to be correct 100% of the time, and I certainly hope no one else expects that of me, either.

Tropical Tidbits

The latest GFS Ensemble forecast above, valid on the evening of May 6th, shows troughing and cool weather present over Japan. By using the East Asia / Typhoon Rule, we can estimate that cool and stormy weather is can be expected around May 13-17th or so. Judging by the weak negative 500mb height anomalies, I'm only expecting a weak chill in the US, with the strongest cold weather allocated further north.

Tropical Tidbits

By the morning of May 9th, we see that the western portion of that elongated trough, seen in eastern China on the first image we analyzed, as now become a closed low and is progressing through Japan. If we once again apply this correlation, it is understood that a strong closed low may traverse the United States between a May 15-19th period. When this low comes through, I'm estimating we see it hit primarily the northern and central thirds of the nation, if you were to slice the US into thirds, horizontally. Cooler than normal temperatures can be expected with this, as well.

Tropical Tidbits

We finally do get relief in mid-late May, we a massive ridge of high pressure pumps up over Japan on May 11th, sticking around for a little while. This tells me we can then anticipate a period of anomalously warmer than normal weather in the United States around May 16-22nd or so.

Tropical Tidbits

Unfortunately, long range ensemble guidance supports the return of troughing and associated cold weather in Japan by May 16th, leading to potentially cooler and stormier weather in time for Memorial Day weekend.

Andrew