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.
It’s that wonderful time of year…cool crisp mornings, mild, sunny afternoons, the smell of wood burning in fireplaces, honey crisp apples, Halloween just around the corner… and of course the first frost/freeze of the season is only several weeks away. Fall is without a doubt my favorite season.
Meteorological Fall begins September 1st and runs through the end of November. The Fall Equinox (first day of Autumn) this year comes Tuesday, September 23rd! The growing season will be coming to a close very soon. Happy Fall! The map above depicts when on average the first frost/freeze occurs here in the Washington Region. The further one goes from the warmth of the Chesapeake Bay and Tidal Potomac the earlier you can expect the first frost and or freeze as we head into the spectacular month of October.
High temperatures on Sunday will climb into the lower 70s with a light northwesterly breeze. Enjoy! Happy Fall!!
A strong cold front will approach the Washington Region on Thursday afternoon touching off scattered showers and thunderstorms. Some thunderstorms could contain damaging winds and hail. Highs on Thursday will climb into the lower 90s with a noticeable increase in humidity. The heat and humidity, and strong winds aloft will aid in the development of scattered strong to severe thunderstorms.
Behind the front, temperatures will begin to slide to well below normal levels as we head through the weekend and into the middle portion of next week. High temperatures will only rise into the lower to middle 70s with lows possibly dipping into the 40s in the suburbs and middle 50s in the cities!