Update to the Long-Range Pattern: Heat Not Out of the Question, but Less Likely

After yesterday's blog post on the "potential" for heat in the medium and long-range, I'd like to issue an addendum to that post, summarizing what the latest models have changed in regards to the time period in question; 120-168 hours out.

The latest models have shifted westward in regards to the placement of the upper level ridge. Yesterday, the 00z and 12z runs of the ECMWF were indicating that an amplified upper-level ridge would shift eastward with time, shifting the heat dome eastward into the region.

Today's model runs have shifted the dome westward, with the area on the periphery of a sharp [yet very "shallow"] trough over the East and Appalachians. This will cause a sharper temperature gradient between temperatures in the 90's to our West and 70's/80's to our east. What's very likely to happen here is that the area has temperatures "juggling" between 85-90, and then possibly a few days with temperatures exceeding 90. It will all depend upon the axis of the upper-level ridge, which at this time appears to set itself up across the Northern Plains.


Here's a look at the ensemble consensus and the ECMWF from the WPC:

For the next few days, the upper level height pattern will flatten, allowing clouds and the upper-level cold pool to clear out of the area, as well as allow for warmer temperatures. In fact, within the next four days or so, we could hit the lower 90's [if enough insolation is realized].

On the otherhand, a shortwave trough dropping out of Canada will amplify the ridge, and cause it to retrograde. It's entirely plausible that with the very moist and unstable air mass in place that we see numerous showers and thunderstorms from this shortwave. Even so.. It's influence will be minimal on the area and for a short period of time. After it shifts east, the ridge will attempt to edge eastward, but very slowly. It will not be until the next shortwave trough shifts out of the Western trough, and causes the ridge to amplify that we get a chance with the heat. If this does not happen, then its not likely at all that we see any kind of marginal "heat" [90+].

I'll continue to monitor the situation for now.. More details will either come early tomorrow morning, or it'll have to wait a week. I'm going to be gone for most of next week and the following weekend, so don't expect any updates.

Have a great evening!

The Possibility of Heat Returns; Mundane Warm and Humid Pattern in the Short-Range

Before I get to the longer-range forecast and its implications for the rest of July, let's look over the details of the shorter-range forecast, and what it means for the next several days.

First and foremost, the Bermuda high is "attempting" to push westward from the Western Atlantic on to the East Coast. At the same time, this Bermuda high is pumping extremely warm and moist tropical air into a large portion of the Eastern United States. Because of this warm, moist, and at times, unstable flow, the mundane pattern of warmth and humidity will continue for at least the next 3-5 days, with the possibility of daily thunderstorm activity in the tropical air mass.

The Bermuda high is being forced westward because of the breakdown of the "split" trough that has been sitting over parts of the East and Midwest for days, bringing heavy showers and thunderstorms at times. This pattern will end soon, giving way to diurnally-driven showers and thunderstorms, and then to a drier pattern in the long-range.

As for now, expect increasing humidity and day-time temperatures in the coming week, with high temperatures averaging around 85-90 with dew points in the low to mid 70's. This will allow for isolated thunderstorms to develop each day in the unstable air mass.

As for the long-range, there is some model disagreement, but the overall consensus is as follows:

1.) The Bermuda High begins to shift back east, and causes the height pattern at 500 millibars to flatten out across the United States.

2.) At the same time, a shortwave ejects from the main Alaskan vortex [which is trying to hold together], and flattens the Western ridge, while sending a surge of warmth eastward [about mid-late next week; possibly allowing temperatures to hit 90].

3.) The shortwave then deepens weak troughing in the far East along Maritime Canada and the East Coast. This causes a re-amplification of the upper level pattern, and causes the ridge out West to strengthen.

4.) By late next week, and the weekend, a secondary stronger wave ejecting from the main Alaskan vortex [and subsequently weakening it as well] will force the ridge to move eastward, and amplify. This will cause mid-level subsidence to strengthen, with compressional heating, daytime clearing, and thus much warmer air temperatures.

At the same time, ridge heights may build as high as 5940 meters or more according to the ECMWF, which could allow 90+ surface temperatures. Even then, the humidity levels will linger, with dew points well above 70 likely.

Even in this case, we still have model disagreement. Some of the ensemble members have a much flatter height pattern in the long-range, and thus, not as warm of surface conditions [but still rather warm]. I will continue to monitor this to see how the models change their forecast in coming days, but I do think its becoming apparent that a much warmer pattern is headed our way for many areas west of the Appalachians.

The trend in the PNA index indicates that a warmer pattern is a possibility later next week.

Upcoming Pattern; Heat on the Horizon?

The beginning of summer has know passed, and we are entering into the middle period of summer. Even so.. We have seen very little heat, but longer periods of cooler, wetter weather. This summer/late spring has been quite unusual in this regard.. In fact, June ended as one of the wettest Junes on record, with nearly six inches of rain.

Even so.. It has been rather cool ever since a strong cold front pushed through. In the wake of the cold front, a closed upper level trough formed, and closed off from the main flow over Canada, allowing a highly anomalous pattern for this time of year. It was something that was VERY unusual.

So what is likely to happen over the next several weeks? Well, models have remained fairly consistent in bringing in a warmer, but more zonal pattern to the United States. For the beginning of next week, both the ECMWF and GFS indicate that a strong ridge will form over the East Coast [594 dm+], allowing 850 temps to soar passed 18-20 degrees Celsius. This indicates that surface temperatures will likely exceed 85-90 a few times next week. But at the same time, due to an incredibly saturated ground, very high dew points are likely, with dew points possibly exceeding 75 next week. This allow for the development of daily showers and thunderstorms as well.

After this, the models show somewhat of a "flattening" of the Eastern ridge, which will give way to a pattern more favorable for MCS thunderstorm complexes. I also believe that with this flattening, the Midwest/Rockies ridge may surge eastward once again, and allow for a period of well above normal temperatures [temperatures possibly exceeding 95 for a few days]. If this does not happen, I would expect the continuation of a warm, and very humid pattern, with the possibility of numerous thunderstorms.

More details about the medium and long-range coming tomorrow...