2015-2016 WINTER FORECAST NY Metro Weather @NY_WX
DISCLAIMER: Seasonal forecasting is difficult and this is my first attempt at a Winter Forecast. I ve looked at all factors and put them together to create a forecast. Sometimes it all comes together as expected, and other times it doesn t. If one factor changes unexpectedly, it can cause parts of the forecast to be incorrect. use at your own risk...
FACTORS: There are many different variables that enhance the pattern of the winter. It appears the most commonly known factor is the El Nino, or ENSO, but of course, there are plenty of other factors that must be taken in consideration. (All of which I will be covering) I wish it was that easy just to base a winter forecast just off of the ENSO. Some factors that will influence the weather pattern over the winter include Pacific Ocean SSTs, (El Nino as well as PDO) Atlantic Ocean SSTs, and teleconnections*: The AO (Arctic Oscillation) and NAO. (North Atlantic Oscillations) *The term "teleconnection pattern" refers to a recurring and persistent, largescale pattern of pressure and circulation anomalies that spans vast geographical areas. (NOAA)
Pacific Ocean SSTs (Sea Surface Temperatures) (ENSO) ENSO The location of the warmest waters within the tropical Pacific has substantial interest for long range forecasts. El Nino (as well as La Nina) both largely effect the placement of sub-tropical jet stream. With this winter s El Nino expected to be western/central biased (Highest temperature anomalies being in Nino regions 3.4 and 4). Comparing this El Nino to 1997-1998, we can see that 97-98 was defiantly more eastern biased, which concludes that the current Nino is not exactly like 97-98. (97-98 El Nino shown below). Western and Eastern biased El Ninos provide completely different weather patterns throughout the United States as well as the rest of the world. The current status of the El Nino appears to be Central biased, with the highest SST anomalies being in Nino regions 3.4 and 4. Strong, eastern biased El Nino s usually develop a Gulf Of Alaska trough/low, with warm/mild temps in the northern United States (like 97-98).
FUTURE OF EL NINO (WILL/ WHEN WILL IT WEAKEN?) No doubt the El Niño will still be in place this winter, but it s a matter of how strong it ll remain and when/if it ll weaken. Model guidance suggests a steady weakening of the El Nino in mid November, which some obviously being earlier or later. A strong El Niño is extremely different from a weak or moderate El Nino.
NOTHERN PACIFIC SST (PDO) Here you can note the ring of warm water in the northern pacific, which is where the PDO (Pacific decadal oscillation) temperature anomalies are located. Along with the El Nino, the PDO also plays a big role in the upcoming weather pattern this winter. I m expecting the PDO to remain strongly positive for most of the winter. In general, a +PDO generally promotes ridging over western Canada/USA, which (along with other factors) could promote a trough in the eastern USA leading to below average temperatures, and along with the subtropical jet, lead to above average precipitation towards the second half of winter in especially February.
Atlantic Ocean SSTs (Sea Surface Temperatures) (HOW WILL THIS AFFECT TELECONNECTIONS?) NORTH ATLANTIC OSCILLATION (NAO) As much as the Pacific ocean SSTs are using for long range forecasting, the Atlantic SST s are equally important. Atlantic SST s can effect the NAO, making it positive or negative. The NAO is a measure of pressure anomalies (either positive, neutral or negative) in the northern Atlantic Ocean. When there s below normal heights over Greenland, it s a +NAO, and if there s Above Normal Heights over Greenland, it s a NAO. A NAO sometimes helps of the placement of a trough over the eastern USA, also possibly helping lead to below average temperatures, or a snowier pattern. I m predicating the NAO to be positive in the beginning of the winter, and trend negative towards the end of winter in especially February. A NAO also creates blocking over Greenland and traps storms. COLD POOL With a cold pool over the northern Atlantic, this creates divergence leading to High Pressure/Above normal heights, which could lead to a NAO in the second half of winter. However, the NAO will not be predominantly negative until the middle part of the winter. At this time, I favor a positive NAO to begin the winter from November into December. During the month of January, a gradually changing NAO (and AO) state is anticipated, with a NAO developing through February.
Atlantic Ocean SSTs (Sea Surface Temperatures) (HOW WILL THIS AFFECT TELECONNECTIONS?) (CONTINUED) ARCTIC OSCILLATION (AO) Just like the NAO, the AO (or Arctic Oscillation) is the pressure anomalies/patterns over the Arctic. During it s positive phase, low pressure prevails over the arctic, and does not any cold air to funnel down. And on the other hand, during it s negative phase, high pressure over the arctic allows cold air to funnel down into the eastern US with a trough. Even with the El Nino, the AO will be a significant factor this winter. Once again, just like the NAO, the AO will be positive in the beginning of winter, turning negative towards the latter half of winter. A AO features a weather pattern that support cold air, and snow, to the eastern United States.
NOTHERN HEMISPHERE SNOW COVER/GROWTH The more widespread the snow coverage/depth over Siberia & Eurasia, the higher the probability of the AO becoming negative. A -AO displaces the Polar Vortex from the North Pole southward towards Canada/USA, which would bring extremely cold temperatures into the area. Snow cover for these parts of the world are well above average, and will continue to greatly expand in the future. Although, these amounts aren t as high as they were at this time last year. Either way, with well above average snow cover, there s a higher chance of the AO sustaining itself in the second half of Winter in the latter half of January and in February (and possibly lasting into the beginning of March). 11/14/15 11/14/14
DECEMBER HIGHLIGHTS: +1-3 F Above Normal Slightly Above Average Precipitation A warm(er) start to the winter is expected during December. Without a AO or NAO, the weather pattern supports mild Pacific air into the USA. Multiple storm systems are possible, with any snow most likely being confined to inland/higher elevation areas. Overall, December will contain above average temperatures (.5-2.5 F above normal), with slightly above average precipitation.
JANURARY HIGHLIGHTS: 0 to -1 F Below Normal Above Average Precipitation January (and especially February) remain very uncertain. January (and February) will greatly depend on the factors previously mentioned. January will start off similar to December, with mild pacific air for the beginning of the month. A general retrogression of the Gulf of Alaska trough/upper level low will support more ridging on the West Coast of the United States, possibly leading to a trough in the east, bringing cold shots of air towards the end of the month. More wintry weather is likely during this time (second half of month) Overall, January will feature normal/ slightly below average temperatures (0-1.5 F below normal), with above average precipitation.
FEBRUARY HIGHLIGHTS: -1-3 F Below Normal Above Average Precipitation As mentioned earlier, February still remains significantly uncertain. In general, February will be the worst of the 3 months, with below average temperatures and above average precipitation expected. With increasing chances of a NAO and AO, below average temperatures would then be expected. In addition, the Subtropical jet will continue above average perception, similar to December and January. With all of these factors coming together, this could possibly lead to some bigger winter evens. A similar pattern may last into parts of March.
WHAT COULD GO WRONG?: I am expecting the El Nino to weaken, but it s worth mentioning if it doesn t weaken. If the El Nino does not weaken to forecast, and stays somewhat strong, this would lead to a very warm winter across the northern and eastern United States. The likelihood of this happening is very low at this time.