I will add a bit more over the next few days.
2020-21 Original Forecast & Grade for Accuracy (Moderate Traditional La Nina):
Prediction in last Fall-Winter-Spring forecast
Grade.....What actually transpired.
1. Very warm, drier Fall 2021 with record warmth.
A+...Warm well through October & warmest weather so late in the year on record in November with dryness.
2. Overall warmer than normal winter with above normal precipitation & slightly-below normal snowfall. Not cold enough for peach die-off this year, unlike last winter.
B-...Warmer than normal winter, but normal precipitation & snowfall was above normal (due to snowy February). Not cold enough for peach die-off as seen at Wea Creek & Annie's Orchards with the peach harvest underway.
3. Coldest, snowiest weather late January to early February.
B...Snowiest weather was end of January through much of February with one of the snowiest Februarys since 2007 & the greatest snow depth. I did not expect it to get as cold or stay as cold as it did in February from Polar Vortex in the Plains. February was only one of two months averaging below normal mean temperature-wise since last November as of August 21, 2021.
4. Multiple icing events & one ice storm (especially in February).
A+...4 icing events with icing tree & powerline damage & 1-2 could be considered ice storms.
5. Early start to spring with very warm March-April period with vegetation advancement up to 2 weeks ahead of schedule.
A+...Earliest first 70, 75, 80 since 2010...earliest 85 since 2012. Vegetation advancement & heat accumulation was impressive at up to 2 weeks ahead of schedule.
6. Above normal rainfall & severe weather through spring, but planting window with drier spurt late April.
C...Rainfall was near normal & severe weather was lacking in spring. We did see nice planting window in mid-April for planting. I did not foresee such a freak snow in late April with 1-5" record-tying event to 1910. The lack of severe weather in spring was a surprise.
7. Late May dry spurt for planting with below normal temperatures initially becoming above normal with hot weather to end May. Less likelihood of damaging freeze in May unlike 2020.
B+...Highly-damaging hard freeze in our eastern counties in late April, but coldest in May was 35 on the 8th with lack of any damage.
8. Early start to summer heat with rapid crop growth.
A+...Hottest temperatures so early in May since 2018, so that early summer heat occurred. June 8-13 90s with peak of 98 (earliest temperature so high since 2011). May 17-27, overnight lows did not drop below the 60s.
9. Wetter early June, drier, hot latter June (hottest temperatures since 2012 with first 100 likely since 2012).
A+...First 100 since 2012 measured on June 18 at West Lafayette. Hottest June (mean temperature) on record. Very dry June with Moderate Drought (D1) until June 26 when "Ring of Fire" pattern set in with multiple rounds of storms. However, June still ended up drier than normal.
10. Higher risk of Serial Derecho here in Summer & over the Great Lakes to New England.
B...There have been a couple so far this summer, but none have impacted our area. They have all occurred in the "Ring of Fire" (Great Lakes to New England) with the extreme heat in the Plains, which was an expected Summer pattern. It has been a Summer of impressive damaging wind events with bows & derecho for the Mid-Atlantic & parts of the Northeast.
11. Overall drier, hotter July (hottest temperatures since 2012), but "Ring of Fire" & tropics being wildcards that could save us from drought impacts if we play our cards just right (especially during critical periods for corn pollination & kernal fill & soybean flower & pod development). Forecast period of extreme dew points of 80-83.
C...July saw the temperature being EXACTLY NORMAL for the month. The highest temperature for the month was 90 with many days 85-88. Early July was wet & stormy with severe weather in the "Ring of Fire" pattern, but mid-July onward was DRY. July ended up EXACTLY NORMAL for the month for rainfall due to wet start.
"Ring of Fire" pattern early in the month did indeed save us from drought just in time. June 26-early July saw 6-12" of rainfall over the viewing area with the greatest amount of severe weather in a year.
It did not get as hot as I expected in the month.
Period of dangerous dew points of 79-83 occurred
12. August drier than normal ("Ring of Fire" & tropics being wildcards). Hotter than normal first half, cooler than normal second half.
A (for now)....So far, August has been drier & warmer than normal. Much of the area is Abnormally Dry (D0) & headed for Moderate Drought (D1).
13. Original forecast from last year was cooler than normal & drier than normal September overall (tropics wildcard)
We will see.....(Based on the latest analysis, it looks warmer than normal for first half of September, cooler for second half with rebound back above normal by end of September. It still looks drier than normal with tropics as the wildcard for rainfall).
14. Period of at least Severe Drought in at least part of the area at some point Summer-Fall.
We will see.....
Overall good long-range forecast done late last summer, but the surprises were:
1. Such a cold & snowy February for such a duration.
2. The record snowfall event in late April & the record hard freeze in our eastern counties following the snowfall.
3. Lack of severe weather this spring with heavier rainfall.
4. I expected July to be hotter overall.
NOW ON TO 2021-22!
Seasonal forecasts takes into account a very complex interplay of numerous players on a team seemingly fightning for dominance. For example, if we take the 2021-22 Purdue basketball season, then take the 2021-22 Big Ten, then the 2022 National Tournament we would ask............what time will be dominant? Which player will be player of the year & why? What conference will be dominant? Who will win the Big Ten? As we know in basketball history, dominance can go in a lot of directions & forecasting is the same way. Who will emerge on Purdue the dominant force? What will be the dominant force in play that will be best against opponents? A combination of lots & lots of research & factors into these basketball forecasts would lead us to some predicted trends. To say that a La Nina will be here, so a La Nina pattern is dominant is like saying Duke will be #1 by February because of their history of dominance. No El Nino or La Nina or +PNA or -PDO or +NAO or -AO gives you the exact same results. It is the complext interplay of global factors that makes a local or regional forecast for a season or seasons. It is like changing up your Purdue basketball line-ups or changing line-ups on a Purdue AND IU team playing each other then you throw in assistant coaches doing the coaching.....followed by a slippery floor.....on a neutral court in a different state......or you do this at Mackey, then at Assembly Hall......to see the results.
Also, different interplays will exist at different times of year. At times, you will see La Nina or La Nina Modoki look exactly like a mean La Nina or La Nina Modoki, then another factor outflexes it. At times, two or three factors or indices may actually enhance another or vica versa. It may quell one factor's influence & increase the other's, which results in a pattern change. In fact, at one point last winter, it looked like that La Nina-La Nina Modoki hybrid split with TWO segments of coldest waters in the Equatorial Pacific.
Good example is last year's Polar Vortex down to Texas. It was extreme, record cold Kansas to northern Mexico. Why didn't it move farther eastward? The strong subtropical high caused by La Nina & MJO basically propped the record cold in the southern Plains & it stayed there. It was only enhanced because it didn't move & snow pack developed. Same pattern caused us to get caught in snowfall after snowfall, leading to the deepest snow pack here since the winter of 2013-14. We never got extremely cold here, but it was consistently cold. So, several factors worked to together to enhance one thing & save other areas from the extreme cold. That Polar Vortex event seems to be tied to ozone concentration changes in the stratosphere, but also Arctic warming. That overcame the tendency for strong Polar Vortex keeping worst of the cold locked up for 2020-21 winter. However, there was a window for that strength to be overtaken by the ozone & warming. So, as you can see, it is an complex interplay in a seasonal forecast. You have to look at how the atmosphere behaved under these conditions in the past decades, the past year & also what models are showing for the sea surface drivers.
As expected, a double-dip La Nina is ahead after a Moderate La Nina maxing out in late Fall of last year. The La Nina lasted until this summer & we have been neutral much of the summer. We are going back to La Nina quickly now.
Mean model data shows weak La Nina, however, I am going with MODERATE based on analog data.
HOWEVER, this will not be a traditional La Nina like last winter, but its colder sibling La Nina Modoki.
No La Ninas are exactly alike & there may be as many as 4 sub-types, but traditional & Modoki are the two main ones.
Modokis have different outcomes in El Nino as well. During normal El Nino, California tends to be wet, but in El Nino Modoki, drought tends to occur there.
The influences of Modoki events are also seen in tropical cyclogenesis, stratosphere warming of the Southern Hemisphere, What about stratosphere warming of Northern Hemisphere? Have to research & compare.
Modoki keeps the greatest cold surface water anomalies of a La Nina in the middle of the Equatorial Pacific, rather than the eastern part.
We see that just evolving now (dark blues in the middle of the 0C line in image below).
These are the sea surface temperature anomalies for December-January-February. The Modoki shows up well.
Unusually warm water is projected for the North Pacific, around Greenland & the North Atlantic & the middle of the South Pacific.
Cooler water is projected around Vietnam to Hong Kong to South Korea, while it will be much water around Indonesia to the Philippines.
Last winter looked like this overall with sea surface temperature anomalies. Note how many of the other anomalies look the same as last year, but the La Nina certainly looks different in where it is positioned.
So, a lot of similar drivers to last winter mixed in & a similarly hot, rather dry summer & an early start to the spring spells good analog to forecast Fall-Winter-Spring.
2021-22 September-May outlook:
September 2021: Warmer than normal first half, cooler than normal mid to late month before trending back to warmer than normal to end month.
Trend is drier than normal.
Tropics are a wildcard. If we can get a system this far to the north & northwest, we will see a good-soaking rain.
My analog data showed this for September: cooler than normal for Deep South & northwest U.S. & northern U.S.
I actually think that all of the heat the first half of the month overall will offset the below normal temperatures mid-month onward (before we warm up above normal to end September.
So, the anomalies map will likely look more like this:
Analog & overall thinking is drier than normal here (again....watching the tropics).
October 2021: Above Normal Temperatures, Below Normal Precipitation, No Snowfall
Warmer than normal, drier than normal October expected.
Tropics are a wildcard. If we can get a system this far to the north & northwest, we will see a good-soaking rain.
November 2021: Above Normal Temperatures, Near Normal Precipitation, Below Normal Snowfall
Sudden start to winter after a warm month in late November.
Fall 2021: Above Normal Temperatures, Below Normal Precipitation
Discussion: Looks like warmer, overall drier than normal Fall with sudden onset winter with cold by early December.
December 2021: Below Normal Temperatures, Above Normal Precipitation, Above Normal Snowfall
December looks quite a bit colder than normal. It also looks like a wet to snowy month with above normal precipitation & snowfall. We have a higher than normal chance of a White Christmas this year.
Thoughts are that the tide turns after Christmas or New Years toward bif thaw & warmer than normal conditions.
January 2022: Slightly-Above Normal Temperatures, Above Normal Precipitation, Below Normal Snowfall
Month looks warmer than normal until much colder weather arrives late month with snowfall. This should all even out to "slightly-above normal" temperatures. Precipitation looks above normal. Since much of the snow will occur late in the month, I kept it at below normal.
February 2022: Slightly-Above Normal Temperatures, Normal Precipitation, Above Normal Snowfall.
February looks colder than normal & snowy for the first half, then much warmer second half. Precipitation is above normal & the above normal snowfall looks to be confined to the first half of the month.
Winter 2022: Bit Below Normal Temperatures Overall, Above Normal Precipitation, Above Normal Snowfall
Overall, we should even out to below normal temperatures for the winter, but you can see there will be considerable, rapid fluctuation. It will seem when it is cold, it stays cold & get very cold, but when it swings the other way, it is quite spring-like. Above normal precipitation overall & above normal snowfall looks to be the mean.
October-April Snow Season: Above Normal Snowfall
The October-April snow season looks above normal with much of it falling in December & late January to early February.
March 2022: Above Normal Temperatures, Above Normal Precipitation,Below Normal Snowfall
March swings back to warmer than normal overall with below normal snowfall.
April 2022: Below Normal Temperatures
April looks cooler & drier than normal. We still still likely get a couple of severe weather events/outbreaks, however, given analog data.
May 2022: Above Normal Temperatures
May looks to go above normal with temperatures & precipitation.
There seems to be a higher likelihood of severe compared to this year.
Persistence forecast tells me that this spring has higher potential of severe weather compared to the last 3 springs, as it is extremely rare to have such a severe weather drought in the spring season extend beyond 2-3 years. This, especially given the La Nina (Modoki) influence.
Summer to Winter 2022-23 Sneak Peek:
El Nino looks to rapidly evolve in the 2022-23 Fall-Winter.
Looks like a cooler than normal September, October 2022 & even November 2022, then warmer than normal December 2022. Overall, January-February 2023 is trending warmer than normal with below normal precipitation & below normal snowfall.
El Nino years tend to be slow to go back to La Nina years, so we will likely go more neutral in the 2023-24 winter. That said, other factors will then be the drivers of our overall weather trends during that time.