Category Archives: PHL Climate Forecasts

WEATHER OUTLOOK

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Two more rain storms forecast for this week –one Thursday (possibly missing us, staying to the south) and on Saturday.   The Saturday storm may be a nor’easter, but the lack of cold air makes this an atypical nor’easter for January.  It looks like rain!

The current weather pattern is quite anomalous for January.  There’s little evidence of deep intrusions of cold air into the  continental US for the first two to three weeks of January!

There will be short duration cold air intrusions  into the Northeastern US which will alternate with mild air and wet flows from the southwest.

The current climate model forecast captures this nicely:

CFS Forecast for the first week in January (areas in red/orange are above average upper air heights associated with above normal temperatures.)

What we need for winter to return is for the height contours (shown in black) to take the following configuration, (shown in blue.)

Blue line drawn shows typical configuration for cold air intrusion in January

Obviously, there  would have to be giant changes in the current weather pattern to support my early December climate forecast of significant cold weather and significant precipitation.  I’m not very confident about that forecast at this time.

So enjoy the relatively mild weather!

The current long range climate models show colder intrusions around the third to fourth week in January, a time when we usually get the “January Thaw”.

PHILADELPHIA WINTER CLIMATE FORECAST

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It’s about that time of year when I take a stab at the long range winter forecast. I always preface this with the disclaimer that predicting a seasonal trend is really climate science, not weather forecasting. Climate science isn’t as advanced as weather forecasting. That said, there’s always interest in this, so here goes:

Basically, the current pattern suggests colder than average temperatures this winter due to the nadir in the sunspot cycle and higher precipitation due to an El Niño.   Let me explain-

Climate forecasts boil down to temperature, moisture and jet stream position.

Regarding temperature, we are about to entering a solar minimum.The solar cycle is a regular, periodic change in sunspot number and the mimimum correlates with reduced total solar irradiance. The Lasco Project has shown that total solar irradiance drops almost 1 watt/m2 during solar minimums.

While not universally accepted, solar minimums allow for these colder conditions.

Global Temperatures
Current Global Temperatures Dark Violet -30-35 Degrees C

The current global models show very cold temperatures already developing in the polar region, Siberia and Greenland. The appearance now is similar to that seen in the middle of winter.

So we have one ingredient- very cold air this season. This winter will likely be colder than average in the Northeast.

Regarding the moisture component, an expected El Niño in the Pacific is developing – warm ocean temperatures that will provide a stream of moisture along what is referred to as the southern jet stream.

So we have a second ingredient- moisture picked up from the warmer Pacific ocean. Precipitation will likely continue above average in the Northeast.

Does that mean we will have more snow than average? Probably, but not necessarily. That depends on the jet position.

While TV forecasters often suggest the jet stream is moving in ways with a mind of it’s own, the jet stream really flows between boundaries of air masses. It’s the edge of the air masses that determine the jet position, not the other way around. Large cold air masses developing at the poles have to sag down and mix. In doing so, their boundary sags and dips, causing a dip in the jet. Warm air masses in the tropics push their edge north. The boundary is where jet stream is and where low pressure systems develop,

While it would make sense that we get more snow, the actual random shape of the cold air mass boundary (jet stream) might spin up storms to our east (snow) or to our west (rain).

One more thing— With plenty of warm air in the southern hemisphere from global warming, it likely that wide swings in temperature will occur, with extended below average cold periods interrupted by much shorter periods of warm temperatures. 

This is my best guess for Winter 2018-2019.

WEATHER OUTLOOK -COLD THANKSGIVING

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Monday Update 10:30pm
Tonight’s NBM model is showing a high temperature on Thanksgiving Day of 28 for Philadelphia!

A dip in the jet stream is predicted for the coming week, with  the coldest temperatures forecast for Wednesday night through Thursday night.

amplified jet
GFS Model Forecast for Thursday, (Thanksgiving) afternoon.

The extended range GFS and NBM (National Blend of Models) shows a high of about 32 for Philadelphia on Thursday!   Actually, that’s an improvement; the forecast dip was even more amplified just a few days ago.

A warm up and rain is expected next Sunday or Monday, then a return to colder conditions sometime during the following week.

I continue to feel we will have a colder than average winter due to the nadir in the sunspot cycle and a stormier winter as well, with plenty of moisture available in the southern jet stream from a developing El Niño in the Pacific.

I first made this preliminary climate prediction a few weeks ago.  Past information about the sunspot cycle’s influence on temperatures can be found here.

EARLY WINTER CLIMATE OUTLOOK

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I received an email from a follower of this blog asking for my thoughts regarding the upcoming winter.   Here’s what I replied:

Thanks for the confidence you expressed in my forecasts. Winter weather seasonal forecasts are more about climate than weather.  Even the National Center for Climate Prediction doesn’t do too well with these very long range forecasts.

That said, I usually take a stab at the Winter Weather Seasonal Forecast towards the end of November.  By that time, any pattern that may become established will have revealed itself.

But if you want an early sense of things, the nadir in the sunspot cycle suggests plenty of cold air.  The current dips in the jet stream suggest a stormy winter.   And an expected appearance of El Niño in the Pacific suggests plenty of moisture.

So expect a cold winter with plenty of storms and plenty of snow.   That’s my best bet right now.  But things could change if the jet stream dips change over to the western side of the US.