My Summer Outlook 2016 (VERIFICATION)

[Isotherm]

http://www.lightinthestorm.com/

 

Critical Variables

 

As we progress forward into meteorological summer, there will be significant alterations to the pattern of the previous 6-8 months. A super El Nino – arguably the strongest one on record as per certain metrics – will be collapsing rapidly over the next several months and subsequently reversing into a predominately cold ENSO state (La Nina). Significant cooling of tropical Pacific sea surface temperatures has already occurred with most ENSO regions now nearing neutral (SST anomaly close to 0). The haste with which the El Nino transitions into a La Nina regime will aid in determining the mean structure of the atmospheric circulation pattern.

 

Tropical easterly trade winds have intensified as a consequence of shifting pressure patterns and a reorientation of the walker cells. The former of which can be evidenced by the increasing frequency of positive Southern Oscillation Index (SOI) values, indicative of declining atmospheric pressure in the tropical Pacific and rising atmospheric pressure near Australia. This creates a large scale easterly flow in the Pacific. The latter of which (shifting walker cells) can be evidenced by the variation of the upper level atmospheric divergence, suggestive of the mean location of tropical convective forcing. An invaluable proxy for which is the 200hpa velocity potential – clearly translating westward with time. Model prognostications are suggestive of an increased proclivity for Indian Ocean and Western tropical Pacific upper level divergence, consistent with a La Nina regime.

 

Concomitantly, the atmospheric angular momentum will be decreasing over the next few months, reflective of an El Nino to La Nina collapse. The sensible weather consequences of such a shift will be widespread, with significant ramifications on the mean ridge/trough pattern over both the United States and northern hemisphere.

 

Given the likelihood of a developing La Nina for the summer months (probably further intensifying into a moderate La Nina for the autumn), the declining AAM, alterations of the mean Pacific tropical forcing and atmosphere pressure patterns, one can ascertain the likely mid/upper level result. However, specifics will – of course – be highly indeterminate due to the chaos of the system.

 

Other not insignificant variables under consideration are the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO). These indicators, particularly the latter, tends to influence and feedback on the large scale atmospheric circulation pattern more than it does during the cold season. The PDO has been strongly positive (positive for the past two years) and will continue to persist in a warm/positive state for the next few months at least.

 

Conversely, the Atlantic will not be as robustly warm/positive, but should still maintain a slightly warmer than normal state. The combination of the aforementioned variables are examined in conjunction with a survey of prior years in order to ascertain potential commonalities, from which clues can be derived for the future weather pattern.

Typical walker cell orientation in La Nina base state:

Summation of Indicators and Resultant Analog Years

 

As an aside, one may notice that analysis of northern hemispheric blocking potential was avoided. This is because – unlike the cold season – the correlation of indices such as the NAO/AO to the sensible weather pattern in the United States is not as strong. The East Pacific Oscillation (EPO), namely, the geopotential height anomaly pattern in the Alaskan, W Canadian, East Pacific region tends to be slightly more influential; however, even it, is not nearly as pivotal as in the winter. With that being noted, the northern hemispheric indices are still examined with moderate scrutiny as their effects can be crucial when coupled with other mechanisms.

 

The expectation for the meteorological summer in terms of the global regime is: 1) a transition into a weak La Nina ENSO state by mid-summer; 2) predominantly positive to strongly positive PDO; 3) slightly positive/warm AMO; 4) Declining AAM with its concomitant GWO impacts; 5) Negative EPO initially, transitioning into a predominantly neutral to positive EPO modality; and, 6) Negative AO/NAO initially, becoming increasingly positive for mid to late summer, thus averaging near neutral.

 

The resultant analog years, that is, seasons which featured the most commonalities insofar as many of the variables analyzed, are the following (in order of decreasing importance):

 

1) 1983
2) 1988
3) 1966
4) 1973

 

One must still adjust these analog years to correct for disparities in the present pattern; however, one can derive important clues pertaining to the evolution of the mean ridge/trough pattern.

 

500mb anomalies for the June-August period of the closest analogs – 1983, 1988, and 1966. 1983 and 1988 in particular, featured a collapsing El Nino transitioning into La Nina with the maintenance of a strong to strongly positive PDO. That combination is relatively rare in the available data, thus precluding a sufficient sample size of analog years. Nevertheless, one can see the following:

 

Mean ridging in the Mid-west with tendency for lower heights in the South.

 

A positive NAO during the summer yields a strong inverse correlation with respect to temperatures in the Southern US, implicating a +NAO should produce cooler temperatures relative to normal in the deep South. If a positive NAO develops, it will follow the general theme of the analogs with a warmer north / cooler South propensity.

The analog temperature pattern yielded a very warm result for most of the North, and cooler in the South.

 

The precipitation departures for the analog years are clearly reflective of the overall temperature pattern – cooler areas in the South wetter, while much of the North is drier.

 

 

The analogs are corroborated by several seasonal forecast models, which indicate the likelihood of widespread warmth or dual mid-level ridge centers inducing above normal temperatures – in the Western US and another in the Mid-west/East, with a weak trough in the central US.

 

Adjustments from analogs: 1) Less positive NAO; 2)Slightly less negative EPO; 3) More expansive warmth in the Southeastern US; 4) Stronger warmth in the Western US; 5) Wetter across the immediate Southeast US coast due to tropical cyclone activity in late summer.

 

Outlook and Favored Progression

 

Early season blockiness – particularly in the EPO domain – will destructively interfere with protracted heat spells in the Northeast, although, an overall regime of near to above normal temperatures is still anticipated. The residual hemispheric heat as a consequence of the collapsing super El Nino will make it exceptionally difficult to force a prolonged cooler than normal period over an expansive geographic area. Temperature anomalies in the South were adjusted upward versus analog years due to the background global / climate state and expected pattern progression.

 

The expectation is for progressively declining heights in the EPO domain as June nears its close, particularly for July and August. Geopotential heights should be higher relative to normal across the Northern US with closer to normal heights in the South, consistent with the analog package and the noted EPO / NAO / AO mean state.

 

July should be very hot relative to normal across much of the United States, potentially featuring severe, protracted heat waves, especially in the Mid-west, Southeast and East. The Pacific NW should see some heat as well. August may feature a subtle retrogression of the mean ridge/trough axes such that more transitional intervals are permitted in the Northeast. However, all three meteorological summer months are expected to finish above the normal, with July likely the hottest relative to normal (possibly around +2 in much of the I-95 corridor, with August potentially similar, and June closer to +1). The official forecast will focus specifically on the seasonal three month departure; however, as inter-monthly variability is such that it precludes one from deriving sufficient value from long range monthly departure forecasts.

 

The precipitation pattern should be wetter than normal in the Texas/Deep South and Florida/SE immediate coast, the latter due to tropical cyclone activity. Cape Verde activity should be suppressed while contemporaneously in-close cyclone genesis is heightened this year. I expect a fairly active Gulf of Mexico/Caribbean and W Atlantic cyclone season. Drier than normal conditions look likely over much of the rest of the United States, but that doesn’t preclude occasional outbreaks of strong to severe T-storms. Insufficient skill exists with respect to T-storm forecasting; however, if the mean mid-level ridge situates itself in the Mid-west, at times, there could be elevated mixed layer (EML) ejections eastward and into the Northeast (an important variable for strong convection). That is speculation, however.

 

 

Resultant maps are as follows:

 

 

 

 

 

-Tom
Trained SKYWARN Spotter

[winterymix]

Bummer.

[Stebo]

My concern with using 1988 as an analog is that there was a massive drought leading into that summer which had a positive feedback toward ridging in the Plains and into the Midwest. Right now we have the exact opposite going on with the Plains being more moist compared to normal with the excessive rains this spring.

[Isotherm]

My concern with using 1988 as an analog is that there was a massive drought leading into that summer which had a positive feedback toward ridging in the Plains and into the Midwest. Right now we have the exact opposite going on with the Plains being more moist compared to normal with the excessive rains this spring.

 

 

A couple points in response to that:

 

1. While soil moisture is definitely important in precluding protracted severe heat - the atmospheric pattern can evolve such that the ground rapidly dries out in the high sun angle months of MJJ. Additionally, the atmospheric circulation pattern is more important than the precursor soil moisture of May, IMO. For example, May 2010 drought index depicts a fairly wet picture across much of the Central US/Mid-west, yet the summer that ensued was very hot,

 

 

 

 

 

2. May has dried out significantly over much of the Mid-west, with below average rainfall MTD:

 

[Stebo]

A couple points in response to that:

 

1. While soil moisture is definitely important in precluding protracted severe heat - the atmospheric pattern can evolve such that the ground rapidly dries out in the high sun angle months of MJJ. Additionally, the atmospheric circulation pattern is more important than the precursor soil moisture of May, IMO. For example, May 2010 drought index depicts a fairly wet picture across much of the Central US/Mid-west, yet the summer that ensued was very hot,

 

 

 

 

 

2. May has dried out significantly over much of the Mid-west, with below average rainfall MTD:

 

Conversely though using 2010, the highest temperature anomalies was centered where there were drier areas in the east and south preceding the summer.

 

As for this year, yeah this month has been drier, but the next 10 days looks to change that with a prolonged southwest flow regime and an open gulf.

[Isotherm]

Conversely though using 2010, the highest temperature anomalies was centered where there were drier areas in the east and south preceding the summer.

 

As for this year, yeah this month has been drier, but the next 10 days looks to change that with a prolonged southwest flow regime and an open gulf.

 

 

I think the central/southern Plains will probably be wetter overall. I have the warmest departures relative to normal across the north/far north (generally N of a Lincoln-Springfield IL line) due to the consideration of a wetter central/southern Plains. 

 

Additionally, as I said in the outlook, I think June is probably the coolest of the three months relative to normal and may struggle to featured protracted robust heat. It will be important to monitor whether the pcpn distribution changes as we move through June, as I think the core heat months this summer are July-August. If the pattern transitions into one which featured increased dryness across the North/Mid-west for much of June, I think temperatures could respond fairly easily for July/August.

 

What are your analogs and/or forecast for the summer?

[Stebo]

I think the central/southern Plains will probably be wetter overall. I have the warmest departures relative to normal across the north/far north (generally N of a Lincoln-Springfield IL line) due to the consideration of a wetter central/southern Plains.

Additionally, as I said in the outlook, I think June is probably the coolest of the three months relative to normal and may struggle to featured protracted robust heat. It will be important to monitor whether the pcpn distribution changes as we move through June, as I think the core heat months this summer are July-August. If the pattern transitions into one which featured increased dryness across the North/Mid-west for much of June, I think temperatures could respond fairly easily for July/August.

What are your analogs and/or forecast for the summer?

1998

1973

1983

2007

2010

In that order. Like you mention all 5 of these analogs were warmer in the midwest in the back half of the summer. With August being much above normal for all 5.

[Powerball]

 

*snip*

 

That would be awesome.

 

But I'm still taking a wait and see approach at this point. 

[ohleary]

Crap I read "Isohume" as the OP and got excited, then came in and saw it was a real forecast.  

[Isotherm]

http://www.lightinthestorm.com/archives/1003

 

VERIFICATION:

 

United States Temperature and Precipitation Departures for JJA 2016

 

 

 

Select cities; June-July-August temperature departure:

NYC: +2.4

BOS: +2.6

DCA: +2.8

Chicago (ORD): +2.5

Houston: +0.8

Denver: +1.4

 

The idea of nationwide warmth with departures of > +2.0 across much of the Mid-west, Great Lakes and into the Mid-Atlantic/Northeast verified. Additionally, the forecasted progression of near normal June, and hot/very hot July-August, particularly centered in the Mid-west and East, worked out correctly. In fact, conditions were slightly hotter than expected overall on the East Coast. In terms of precipitation, the anticipated dry summer overall verified, with wetter conditions in the nation’s mid section. One flaw was that the wettest weather / above average pcpn departures were a bit further east than anticipated.

In summation, this summer of 2016 will go in the books as a very warm to hot one for the country, and an especially hot August for the Eastern US.

 

Forecast grade for summer 2016: A-

 

[Hoosier]

Your temperature forecast was much better than the precipitation forecast, as the 90 day maps show.  I feel like summer precip is often tough to nail down though as the numbers can really start piling up quickly with convective events, which is what happened around here in the Midwest. 

[Isotherm]

24 minutes ago, Hoosier said:

Your temperature forecast was much better than the precipitation forecast, as the 90 day maps show.  I feel like summer precip is often tough to nail down though as the numbers can really start piling up quickly with convective events, which is what happened around here in the Midwest. 

 

I completely agree. Summer precip is actually more difficult than cold season precip departures IMO, due to the convective nature of the pcpn, as you noted. In that way, I think more leeway should be given to the forecaster for summer precip patterns. Though I was glad to get the overall idea of a generally dry summer for the majority of the country. At least in the winter season, precip departures can largely be inferred through expected ridge/trough orientation and concomitant storm tracks.

[BlizzardWx]

You did good, as usual. Any thoughts on fall? 

[Isotherm]

10 hours ago, BlizzardWx said:

You did good, as usual. Any thoughts on fall? 

Thanks! To be honest, I haven't had an opportunity to look much beyond September, which I think will be much warmer than normal in the Eastern US, with troughiness attempting to develop in the C US by mid month. 

[WEATHER53]

For mid Atlantic and DC area it was a very good forecast 

+1 for June and +2 for July and August is how I read your prediction and that was B+ overall. Your narrative of hot to very hot was very good

rainfall I read as below average and it was more around average so a B- there 

 I think KA call of +1 to +3 for each month and overall was slightly better and his rainfall call the same as yours

overall grade B

 

[Isotherm]

 

For mid Atlantic and DC area it was a very good forecast 

+1 for June and +2 for July and August is how I read your prediction and that was B+ overall. Your narrative of hot to very hot was very good

rainfall I read as below average and it was more around average so a B- there 

 I think KA call of +1 to +3 for each month and overall was slightly better and his rainfall call the same as yours

overall grade B

 

 

Thanks for your feedback. I wish I had gone hotter in the East with an expansion of the > +2 departures, though I'm glad the favored progression worked out. I agree, rainfall was definitely more difficult. Dry worked for most of the Northeast, but south of PHL had quite a bit of convection this summer. Onto the winter outlook season soon!

[Roger Smith]

Not sure if this detail will help much, but on the west coast, the pattern shifted abruptly in early August from hot/dry to cool/wet and the core of the western heat shifted from about central WA to northeast WY for the last portion of the summer. At about that same time, the desert southwest went from rather warm to rather cool by their standards. 

However, as to precip, forecasting that in the west is almost pointless. We were just driving through Utah last week and saw two examples of 1-2 inch rainfalls on one side of a road and zero to 0.25 inch outcomes on the other side. It seemed orographic in one case but entirely random (cell movement) in another. Despite that, the farmers on both sides of the highway had similar looking crops but I imagine one will have to wait a week longer than his neighbor to get out into the fields to harvest it. 

[Isotherm]

On 9/7/2016 at 0:52 PM, Roger Smith said:

Not sure if this detail will help much, but on the west coast, the pattern shifted abruptly in early August from hot/dry to cool/wet and the core of the western heat shifted from about central WA to northeast WY for the last portion of the summer. At about that same time, the desert southwest went from rather warm to rather cool by their standards. 

However, as to precip, forecasting that in the west is almost pointless. We were just driving through Utah last week and saw two examples of 1-2 inch rainfalls on one side of a road and zero to 0.25 inch outcomes on the other side. It seemed orographic in one case but entirely random (cell movement) in another. Despite that, the farmers on both sides of the highway had similar looking crops but I imagine one will have to wait a week longer than his neighbor to get out into the fields to harvest it. 

 

Good point. In contemplation of this dilemma, I'm beginning to wonder whether forecasting precipitation departures in the summer months is utterly futile. Particularly in the West, where the nature of convection seems to be even more randomized than the C/E US. The predictability of pcpn departures may simply be insufficiently low to warrant any devotion to it in the summer, but I think general patterns can still probably be foreseen. It certainly didn't look like a wet summer for most of the country this year (to the extent that one can prognosticate macoscale tendencies), and that certainly verified. The specifics of anomalies on a mesoscale level are virtually impossible to ascertain though, I agree.

[40/70 Benchmark]

Great job, as usual.

[Isotherm]

18 hours ago, 40/70 Benchmark said:

Great job, as usual.

 

Thanks, Ray!