Warm/dry conditions remain in place,
but abrupt change is on the horizon Get The Forecast!

*Indications of above or below average temperatures in the table above are relative to what is considered “normal” using data collected over the long term for a particular date. This is collected and maintained by the National Climatic Data Center in conjunction with the National Weather Service actual data from previous years collected at official ASOS/climatology stations across our coverage area. Also note that as time moves forward into a different period as shown above, average temperatures for those dates will also change. See the example below using Philadelphia, PA as the climo station:

The departure from normal uses the average temperature for the date, averaging temps over 24 hours for any given location, using both high and low temperatures hourly during any particular day. This outlook determines warm vs. cool periods relative to normal temperatures.

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Precipitation:

We have been in the midst of a long dry stretch over the past week or so, and that trend is expected to continue through this weekend and Monday of next week. A slow-moving cold front will propagate eastward on Tuesday and will bring periods of rain to the region for the majority of Tuesday, tapering to showers overnight Tuesday night. Low pressure is projected to form along the frontal boundary during its slow eastward progression, which could for a time enhance rainfall rates on Tuesday afternoon and evening for at least parts of the region. Early rainfall estimates are for between 0.5″ and 1.0″ of rain for most areas, with higher amounts possible on a hyper-local basis.

Behind this front, a transient shot of cool air settles in for a few days, and then will lift out as the next cold front approaches over the course of next weekend. Timing differences exist with this feature, which the progressive GFS suggests will arrive later Saturday and Saturday night, while the ECMWF/Euro suggests a slower approach and a Sunday frontal passage. Showers will accompany this 2nd front, and another trough settles in behind the front, although not as anomalously cool as the first trough expected midweek of this week.

Breakdown of precipitation departures from normal over the next several weeks:

October 21st-October 27th: Slightly above average

October 28th-November 3rd: Slightly above average

November 4th-November 10th: Slightly below average

November 11th-November 17th: Near average

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Note:  Any image in the outlook is clickable for larger viewing

A cold front moves through on Tuesday with moderate rainfall along the front, with possible heavier rain for some areas due to low pressure enhancement along the frontal boundary later Tuesday/Tuesday night.

Another cold front is projected to move through with showers next weekend, but timing is uncertain between the faster GFS (pictured) and the slower ECMWF, which suggests a Sunday frontal passage.

Pattern:

A warmer than average pattern has been the story of October, with many places running 7-9° above average. This is certainly not unprecedented by any means, but the anomalously warm Octobers have become commonplace over the past couple of years in this region, and many Fall lovers are disgruntled about the lack of a true Autumn feel for yet another year. We are currently too late in the month for a saving grace so to speak, but there will be cooler shots in the next 10 days or so. This will likely skew the average temperatures for the month as whole downward some, but still likely finishing well above average by month’s end.

Many have been speculating about a pattern change toward the end of the month, but as I write this Friday morning, October 20th, I don’t see it. A deeper trough than what we’ve seen so far this Fall will arrive on Wednesday behind Tuesday’s cold front, aided in part by a recurving typhoon in the Pacific temporarily altering the jet stream/pattern. This trough will be relatively transient, and provide a teaser of Autumn weather for just a few days. Some moderation is expected in the few days prior to the next front next weekend, before another trough settles in for the following week. This trough is not modeled to be as strong as its predecessor, but near average temperatures can be expected to begin the month of November.

We still think that around the 4th/5th we see a long stretch of slightly above average temperatures returning through at least the middle of the month, and a more zonal pattern. This is in large part due to the continued eastward progression of the MJO into milder phases. After that point, there are signs of the AAM anomalies progressing poleward with time, and the ENSO is showing a weak La Niña that is focused on the central and eastern basins at the moment. These two features combined suggest more frequent cold shots into the NE US moving toward the middle of November onward. This is also supported by our analog choices for Autumn – and November specifically.

October as a whole we project will finish well above average in most locales (+5.0°F to +7.0°F) when the dust settles October 31st, with very high confidence. The November outlook suggests a below average month as a whole as suggested by our leading analogs chosen for Autumn 2017, but some long range mixed signals exist with how the month plays out as a whole, so lower confidence for now with that monthly projection. We decided to keep the near to slightly above average temperature outlook (for now) for the month of November with higher confidence in slightly above average temperatures occurring in the first half of the month.

Note:  Any image in the outlook is clickable for larger viewing

The GEFS shows the trough and transient cool shot expected to arrive midweek next week, which will at least temporarily bring slightly below average temperatures to the region after warmer than average prior.

The ECMWF Madden-Julian Oscillation (MJO) projection showing the best forcing returning to the Maritime Continent which leads to cooler risks, but eastward progression propagates into warmer phases with time.

Images below are clickable for better viewing

Days 1-5 outlook – confidence VERY HIGH:

Days 6-10 outlook – confidence HIGH:

Days 11-15 outlook – confidence MODERATELY HIGH:

Days 16-20 outlook – confidence MODERATE:

Below is a look at the latest soil moisture anomaly, which is an integral part of drought outlooks. Reds and oranges represent below normal soil moisture levels, greens represent above normal values.

This image will automatically update daily.

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Forecaster: EPAWA Meteorologist Bobby Martrich
Discussion last updated:  Friday October 20th, 11:00am