The Washington Region will enjoy some mild temperatures during the last week of October with highs on Tuesday possibly nearing 80 degrees in the far southwestern exurbs.
Halloween may go off without a hitch across our area if the cold front waits to cross until the overnight hours on Friday. A coastal storm may form off of the Northeast coastline on Saturday and depending upon how close this system comes to coast, snow showers are possible across portions of interior Northeast.
After a cooler than normal summer and a very inactive Atlantic hurricane season what can we expect for the upcoming winter across the Washington Region? The latest climate models continue to suggest there is a 60 to 70% probability of a weak El Nino developing late this fall and continuing through the upcoming winter.
After researching historical analog years (historical climate data with similar conditions, etc.) I found eight weak El Nino winters and further drilled down to six years that had similar summer conditions (temperatures, inactive Atlantic hurricane season, active Pacific hurricane season and a developing weak El Nino).
Keep in mind that before you go and buy a snow blower these snowfall predictions are based on an average of the seasonal snowfall that fell during those six analog years. Some analog years featured below average snowfall and others well above average snowfall. The reason for wide variations in the six analogs has to do with the unpredictable nature of the North Atlantic Oscillation. If the NAO (North Atlantic Oscillation) does indeed remain mostly negative (increased blocking over eastern Canada & Greenland) during the upcoming winter, I would be surprised if the Washington Region didn’t receive at least one Nor’easter with heavy snowfall.
Northeast Winter Forecast (Washington, Baltimore, Philadelphia, New York & Boston) 2014 – 2015:
Analog Years (The historical climate data used to produce this snowfall forecast):
Upper Level (500 mb) Height (High & Low Pressure) Anomalies during the six analog years I chose:
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A strong cold front will approach the Washington Region Tuesday night passing through our area on Wednesday. A period of torrential rainfall, gusty winds and cloud to ground lightning are likely. Wind shear values will be running higher than usual for this time of year. The added spin (wind shear) in the atmosphere could produce isolated tornadoes. The models continue to slow the progress of the thunderstorms with each run, so if the morning rush hour is fine, the afternoon rush hour could feature torrential rain and severe weather… plan accordingly.
With less than two months (a little over 8 weeks) away from Meteorological Winter (December 1st through the end of February) I have updated my snowfall accumulation map format. This is NOT my winter forecast, I am simply showcasing what you can expect from my snowfall accumulation maps (colors, etc.) Always click on my snowfall accumulation maps for a larger view.
I will issue my Washington DC Area 2014 – 2015 Winter Forecast in mid October.
The latest climate forecast models continue to forecast a 60 to 75 percent probability of weak El Nino conditions developing later this fall and continuing through the upcoming winter.
El Nino conditions develop when the trade winds weaken causing warmer than average sea surface temperatures to develop across the Equatorial Pacific. When this occurs, the southern branch of the jet stream becomes more active directly impacting the weather across the United States during the winter months. For the Washington Area, the amount of snow or rain and winter temperatures depend on the strength of the El Nino (weak, moderate or strong).
There are other factors of course that impact our winter weather, one of the most prominent being the phase (positive or negative) of the North Atlantic Oscillation (blocking over eastern Canada & Greenland). Simply put, the more blocking you have in the upper levels of the atmosphere over the North Atlantic the higher the probability of low pressure systems slowing down along the Mid-Atlantic coastline (dumping snow). A weak El Nino and chronic negative NAO during the winter of 2009-2010 produced the snowiest winter since records have been kept here in the National Capital Region.
Let’s take a look at how temperatures vary (cooler or warmer than average during the winter months) during strong, moderate and weak El Nino Winters:
Let’s now take a look at how precipitation varies (wetter or drier than average during the winter months) depending up on the strength of the El Nino:
The stronger the El Nino (warmer the sea surface temperatures are off the Equatorial Pacific) the more noticeable the effects are on the continental United States. A strong El Nino can produce rainy, mild winters across the Mid-Atlantic states while a weak El Nino has a less noticeable impact.
If you like snow, weak to moderate El Nino winters are certainly more conducive in producing southern tracking storms while a strong El Nino (Winter of 1972-73 & 1997-98) produced two of the least snowy (mild winters) in Washington’s history when under a quarter of an inch of snow fell at National Airport. Those winters produced lots of rain as opposed to snow because the temperatures were too warm.
Latest Forecast Model Predictions:
The latest forecast from mid-September shows a slight uptick in probability that a weak El Nino may develop late this fall continuing into the Winter months.
I am a huge fan on the European Forecast Model. It is interesting to note that the European forecast model (ECMWF) is one of the more bullish models in predicting moderate El Nino conditions during the upcoming winter months.
The vast majority of forecast models currently do not suggest a strong El Nino developing. At this time, a weak El Nino seems likely, however if the European Forecast model is on to something and sea surface temperatures continue to warm… we may have a moderate strength El Nino on our hands.
I will be issuing my Washington Winter Forecast in mid-October as by then we should have more confidence in the strength of the potential upcoming El Nino. Stay Tuned.