PHILADELPHIA WINTER CLIMATE FORECAST

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 UPDATE

Sunday Morning Update
The NAM has joined the rest of the models with a continued chance of on and off light showers and drizzle through the evening.

I don’t recall any of the models showing the fog that has developed. With the fog and  heavy low cloud deck, it doesn’t look like the mid 60s that was heavily advertised will become a reality.  High temperatures now looking to be about 59.

Skies clear on Monday.   A period of cold weather for much of the upcoming week and weekend with rain rather than snow looking possible for end of next weekend.

From last night:

Tonight’s NBM (National Blend of Models) has rain tapering and ending about 2-3 pm on Sunday.  The NAM has it ending a bit earlier, the GFS has the chance of continued light showers into the evening. Either way, it will cloudy and mild. High 63.

Outlook- A winter-like broad dip in the jet stream will bring cold temperatures for the next week or so.  Stay tuned.

PHILLY WEEKEND WEATHER

Saturday Morning Update 8 AM
The forecast is on track with rain starting about 4-5 PM Saturday. High 44.

For Sunday, chance of showers in the morning, then cloudy with a chance of light showers (NBM and GFS) in the afternoon. The NAM continues with a mostly dry and cloudy afternoon. High 63.

Forecast from Friday night:

An approaching low pressure system in the west with it’s associated warm front will pass through our area late Saturday evening into Sunday morning.

Saturday will start chilly with a mix of sun and clouds with temperatures not warming to 40 until noon. Highs will be in the mid 40s during the late afternoon. Clouds move in during the afternoon Saturday and rain starts about 4-5 PM.  Rain will become moderate during the evening and night.

The warm front passes north of us early Sunday morning.  The GFS and the NBM maintain some showers lingering into the afternoon, while the NAM has the possibility of rain ending around noon.  It’s a tough call on whether we’ll have clearing in the afternoon, but I’m feeling the GFS may be holding onto the showers too long.  High temperatures 63-67.

WEEKEND WEATHER OUTLOOK

Weekend Outlook Update Thursday 7 PM
Weekend Update – Like last weekend, it appears that the rain will arrive sometime mid to late Saturday afternoon. High near 49. Heavy rain Saturday night.

Rain ends during the [late] morning on Sunday. High temperatures about 63 Sunday, but some statistical models are suggesting 67! Updates Friday evening.

The overall weather pattern for Philadelphia over the next two weeks is for below average temperatures (average high about 49) with at least one 3 day warmup occurring over the coming weekend.

Low pressure will bring a southwesterly flow of mild air for Saturday and especially Sunday.  The statistical EKDMOS has a high of 60 for Sunday while the NBM shows a high of 58!

Unfortunately, there’s a high probability of rain for Saturday, but Sunday afternoon may be dry. Too soon to be sure. Stay tuned.

Storm Forecasts & Other Things "up in the air".