The days are
getting shorter, and the leaves on some of the trees are starting to change.
Fall kicks off on Tuesday September 22, at 9:30 am, EDT. But if any of Y’all
are waiting for those comfortable fall daytime temperatures and those cool
crisp fall nights; You might want to get comfy, because those kinds of
conditions aren’t going to show up for a while, at least in a long-lasting
matter.
Over the
last four to five years, fall has arrived late, with summer like temperatures
hanging around through September. That trend is looking to include this September
as well.
There is no
doubt that the entire Northeast and Mid-Atlantic have been hot this summer. In fact,
much of the CONUS into Canada has been very warm.
The El Nino
Southern Osculation (ENSO)
The ENSO is
going to be one of the major factors driving the fall pattern. The Madden Julian Oscillation (MJO) is going to be
another big factor.
The ENSO has
a warm (positive) phase El Nino and a cool (negative) phase La Nina.
La Nina is
when the East-Central equatorial Pacific is cooler than average. NOAA currently
has an enhanced La Nina watch in effect. With an La Nina looking increasingly likely we
can expect to see both short and long-term major impacts in the Northeast and Mid-Atlantic.
In the
Northern Tier of the CONUS, La Nina tends to bring a cooler and more active
storm pattern. This is due to the Polar Jet staying a little farther north.
This is especially true during the winter. But how much La Nina will impact the
Northeast will depend on its strength and severity, so the effect for this fall
into winter is going to be varied.
While Equatorial
Pacific SSTs anomalies continue to cool slowly but
neutral El Niño/Southern Oscillation (ENSO) conditions still exist though I
expect to see NOAA declare La Nina by this fall. Those SST warm SST in
the Gulf of Alaska, will bring a change later this fall as well. By promoting
more in the way of ridging in the West and more in the way of troughing in the Midwest
into the East. The SSTs in the Atlantic are also mostly above average, with the
SST along the East Coast well above average.
Years that
match up with the current global SST pattern are: 2010, 2013, 2017, and 1970.
With 2017 being the closest analog.
It's not unusual
for the Northeast to see hot temperatures and humid air during the
summertime. For the last 4 to 5 months, we’ve been in the same general pattern,
while stagnant atmospheric patterns are also not uncommon, the length of this
current pattern isn’t unheard of but it is more unusual.
Another
reason is those much warmer than average SST off the East Coast. They have helped
boost the daytime temperatures, and especially the overnight lows. You can
blame all that extra water vapor for that.
The Madden
Julian Oscillation (MJO)
This Summer
the MJO has been mainly propagating through phases
8, 1, and 2. MJO phases 8 and 1 typically place more in the way of troughing in
the Gulf of Alaska and ridging across the eastern 2/3rds of North America. During hurricane season phases 1 and 2 are when
conditions in the Atlantic Basin are most favorable. They also favor higher heights
and ridging over the Northeast. This is another reason we’ve been warm over the
summer. It is also the reason for all the tropical activity in the Atlantic
Basin. We saw the MJO in the tropical active phases as the MJO traveled through
phases 8 and 1, which resulted in Marco and Major Hurricane Laura in the Gulf
of Mexico.
Over the
fall we should be in La Nina, with the MJO circulating into a more amplified
phases 3,4, and 5. This setup will be with us as we transition through Fall
into winter 2020-2021.
September, I
continue to think we will see hotter than average temperatures overall. The
first half of the month could feature more 90+ degree days for some of us. During
the 2nd half of the month the odds for those kinds of temperatures does
fall off with respect to seasonal averages.
October, the
month as a whole should also see overall above average temperatures. But as we
get into the 2nd half the overall trend should be slightly cooler,
but still most likely slightly above average with respect to seasonal averages.
Here is a
look at the SST and surface temperature anomalies from the 4 years I’ve
indicated as analogs.
Current 2020
2017
2013
2010
1970
2020 has
seen the MJO act similar to what it did in 2010
So here is a
blend of temperature anomalies for 2017 and 2010
As far as
precipitation, that is going to be difficult to ascertain. But with the pattern
as it is. The Mid Atlantic and Northeast are still extra susceptible to
tropical impacts. So, I think overall precipitation
will end up average to above average by the end of November.
Snow will be
later than normal in showing up. But with the La Nina induced storm track, if
we see any polar or arctic outbreaks, those down wind of Lake Erie and Lake
Ontario could end up with some lake effect snow out of it.
Combining
the idea of a La Nina Fall and Winter, the MJO wanting to stay in those warm
phases, along with those warm waters off the East Coast. The idea of a warm
Fall and potentially warm winter is a good bet IMO. For October and November, the
La Nina could create an active storm track across the Midwest, Great Lakes into
at least part of the Northeast. All of
this will make many across our region feel like they’re on a rollercoaster as
we move though Fall. Over the late Fall into the winter the MJO is going to
want to try and stay in Phases 3,4, and 5. Which isn’t the greatest news if you
don’t like warmer winters. The Mid Atlantic tends to not see tons of snow during La Nina winters. But things can and most likely will change between now and December.
I will be
working on my winter outlook over the next 4 weeks. As I have in past years I
will most likely release it in 3 parts…..
No comments:
Post a Comment
Thank you for taking the time to comment, I will answer as soon as I can.