Some changes in my Outlook are in store for the beginning of my third decade of season outlook forecasting. They include an even more thorough analogue chart including previously mentioned patterns in the past such as: Arctic Oscillations, Solar and QBO cycles along with Siberian/Eurasia October snow cover (available since 1998) during the previous analogue winters. This in turn is compared to the upcoming Winter of 2017-18's observed or projected patterns. Therefore, much of the information discussed is there for the reader to quickly scan on the chart. I still will provide a brief summary of each indicator but limit the amount of description, while still occasionally connecting the reader to the corresponding website. The overall, Winter Outlook format remains the same as presented in the past. Now on to the Outlook...
Winter Outlook for the Winter of 2017-18
Occasionally in my past Winter Outlooks, I've eluded to Mom Nature 'tipping her hand' as to what the upcoming winter will bring. This appears to be the case this time as one casts one eye on the recent autumn pattern change and the other eye on this winter's analogues and general upper and surface weather pattern - which actually agree strongly with computer guidance. Of course, sometimes even though the overall general pattern verifies well; the final winter statistics may differ from the forecast - this too I could easily see being the outcome with this winter's projected pattern with the wild fluctuations.
Local Data Suggests
Temperatures: Normal to Below
Because of the parade of conflicting air masses diving in from the north and west, with temperature variability and associated storms and storm tracks ignited; above normal precipitation is likely for the Winter of 2017-18. This trend is supported by many of the analogue winters, along with model output for the winter and recent autumn trends. With the discussed storm tracks below; mixed precipitation is at a higher risk this winter. I do look for the alternating extended wet and dry periods to persist into the winter from the autumn.
Snowfall: Around Normal to Above
The especially tricky part of this forecast is how much of the expected precipitation will be snow and/or mixed precipitation? In the analogues: snowfall in the winters ranged widely from above normal to below. This would be expected since the variance of temperatures hint at the variability of the upper atmospheric patterns and storm tracks. Therefore, pinpointing the perceived prevailing storm tracks this winter will make a significant difference in regard to seasonal snowfall. This is similar to last year's La Nina and is strongly suggested in model output. Remember; an above normal precipitation winter does not necessarily mean above normal snow...even with a colder winter! It's been awhile since we've had a cold winter but with below normal snowfall. The state of the atmosphere when the precipitation becomes available is the key and this looks especially relevant this winter. Leaning on the analogues; I look for generally normal, or an average winter's snowfall (+/- 5" of the norm) across much of extreme Southeast Lower Michigan. This is a winter however where below normal snows could certainly occur especially in this area if the storm track rides further north. The better chance for above normal snow expected further west and north away from that region. Therefore; best chance for above normal snow will lie in an arc from the Brighton/Howell area /I-96 area/ east northeast across Flint and Port Huron /I-69/ and points north/northwest into the Saginaw Valley/Thumb Region.
Below Normal snowfall; less than /- 5.0"/ of the winter average snowfall
Normal snowfall; +/- 5.0" of the winter average snowfall
ENSO Regions in the Pacific
Current ENSO SST anomalies as of mid November
Current ENSO map conditions as of mid November
North Atlantic/Arctic Oscillation - NAO/AO
Snow-cover as of Nov 20th 2017
Pacific Decadal Oscillation /PDO/ and associated subset EPO
The previous warm phase Pacific Decadal Oscillation recently switched to a cool phase this year. A cool phase of the PDO is represented on the right of the following example and compare it to the current state.
SOLAR CYCLE /SC/
Solar cycle actual effects on short term weather and longer term climate variability remain a controversial subject. I've read several articles which support or are against their shorter term winter relevancy. Some theorize that both natural solar cycles and man's influence affect our climate. I am in favor of the solar cycle being somewhat relevant and sometimes giving the present winter cycle a "little kick" in regard to hemispheric wind flow patterns and resulting temperatures. Numerous recent studies for example, do in fact make the connection to our climate and solar activity including wintertime effects. One of the studies stated the following:
Sirocko et al. (2012) recently reached the same con-
Recent Sunspot chart since the new millennium
THE QBO INFLUENCE
WINTER 2017-18 ANALOGUES - SOUTHEAST MICHIGAN
CLICK ON TO ENLARGE
Some additional category explanations in the analogue chart from left to right
AO - The predominant phase of the Arctic Oscillation during that winter. AO- (negative), AOn
(neutral) or AO+ (positive).
SC - position of the solar cycle during that winter. Breaking it down (see solar cycle chart):
SC-- (opposite high cycle compared to the present, least similar) SC+/- (sunspots
waning but not near minimum or 2017 low level. Finally, S++ where solar sunspot cycle is
at or very close to the low cycle of 2017 and/or is at the same decline with 2017...the
best comparison and likeness.
QBO - W=West wind prevailed that winter or E=East wind prevailed. Trends: -/- (weak and
weakening trend), -/+ (weak but strengthening), s (steady trend, no change) +
moderate and strengthening +/- strong but weakening. Note that the trend now in the fall
of 2017 is E/+, a moderate east wind and still strengthening. This fits with all the winter's
that contained a easterly QBO. Those winters were the Winter of 1917-18 (also
increasing), 1950-51 (weak and weakening further), 1984-85 (strong but weakening),
WINTER ANALOGUE SUMMARY
One of the first things one notices about this winter's analogues is the wide-ranging temperatures and snowfalls. That is clearly NOT surprising; one look at the dominant atmospheric players for the winter, the subsequent jet streams and storm tracks explains exactly why the variable analogue results, in spades. This winter will not be a clear-cut La Nina influenced; mainly because of the influential strong Pacific jet tempering results at times. This shows up mainly in the variable jet stream/storm tracks, temperature patterns and resulting snowfall amounts. As an example; though on average Decembers averaged below normal, there were still a notable amount above /Detroit; 4 out of 14/ all in the later years since the 1970s. At the same time; if the Decembers were mild, then the Januarys were generally cold or below normal. Looking across the board at the three cities, there were a predominance of normal to below normal winters (also my forecast) with a few above normal. Generally; these winters were early to middle loaded with the preponderance of storms roughly from mid December into mid February with later winter, average to below. However; colder weather tended to hold on into at least early spring...not surprising in these parts. By the way; severe weather buffs should note that the spring looks to be busier than the past several years.
Total precipitation and snowfall also widely ranged from below to above. However; a definite trend was seen in normal to above precipitation (matching well with all guidance, La Nina winters on average and recent trends) while a dry winter was least likely. There again though, there were enough drier winters that made a showing not to eliminate that possibility. With the storm tracks created this winter (see below); the risk of mixed precipitation is higher. In other words: a normal to below normal temperature winter with below normal rain and snow is not out of the question reflecting back in previous analogue years...and it's been a while since we've had a "cold but relatively dry winter".
The snowfall category by itself is quite interesting with a wide amount of snow totals and where those snow amounts fell. First off; it was close to an even split for below, normal or above normal snowfalls across the Southeast half of our concerned region. This area extends from the Flint to Port Huron area; south to the Ohio border. There were significant below normal snows ranging in the 20s (inches) across Detroit and 20s and 30s into Flint, constituting a good third of the sample. On the higher side of normal; there were just as many above normal snowfalls into the 50s and 60s around the Detroit region and 50s to even a few in the 70s across the Flint region. I'm sure the reader here can see why snowfall for a season can be such a tough call...and where.
The only region where snowfall truly showed a trend (above) was across the northern third of Southeast Michigan; the Saginaw Valley and Thumb region. This are had 7 above normal snow winters and 4 normal - there were no below normal. Above snowfalls ranged from around 50" into the 70s. In fact; the average snowfall for the analogue winters at Saginaw was a foot above normal. Where as Detroit and Flint settled in the normal range.
Below are the maps from the analogue winters for Temperature departures, 500MB Low placement and subsequent likely storm track placement (Dec-Mar). Note the time period encompasses March also (still a winter month in my book)
500 MB LOW PLACEMENT
STORM TRACK PLACEMENT
Latest Model Output for the Winter of 2017-18 with a few surprising models.
Look for more write-ups through the winter involving notable weather events, major storms and comparing the Winter Outlook trends and actual weather trends!Making weather fun while we all learn,
Bill Deedler - SEMI_WeatherHistorian