A generally warm and drier pattern is
expected for remainder of September 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:

Not much if any at all in the precipitation department to speak of this week much like last week, and the longstanding below average precipitation projection we’ve had in place since the end of July projecting ahead to this month still looks to be on point. The only chance will be Monday with a weak cold front moving through the region, which will be very moisture starved as it does so. A few isolated showers are possible Monday afternoon/evening in a few spots, then the front moves through overnight. Precipitation amounts are under 0.20″ and some areas see much less than that or nothing at all from this frontal passage.

The remainder of the 7-10 period is modeled to be completely dry, and dominated by high pressure and ridging, which also leads to above average temperature stretches. At present time, there is NO CREDIBLE THREAT from any tropical systems to our area, whether direct or indirect with remnant rainfall within the next two weeks. We will continue to monitor closely, but the expectation is through the period, there will be no threats to local interests.

Precipitation for the month of September we continue to expect will finish below average (-1.0″ to -2.0″) by month’s end, with extremely limited (at best) chances for precipitation expected through the end of the month. The early look at the precipitation outlook for the month of October we project to be slightly below average for the 2nd straight month (-0.5″ to -1.0″) with moderate confidence, based on a combination of analogs and monthly climate ensembles. Tropical systems or remnants thereof are always caveats to a monthly precipitation projection, and we will adjust as needed if necessary.

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

September 23rd-September 29th:  Below average

September 30th-October 6th:  Slightly below average

October 7th-October 13th:  Near average

October 14th-October 20th:  Near to slightly below average

Public/free available maps will be updated when a threat is imminent for significant weather on the weather alerts page throughout the year:  http://epawaweather.com/weather-alerts/

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

With what is modeled to be the only precipitation chance here locally in the next 7-10 days, a weak cold front will move through the region on Monday night, and could have some isolated showers ahead of it Monday PM.

The lone hurricane in the Atlantic currently is Hurricane Jerry, but it is expected to recurve this week harmlessly out to sea. We will monitor closely in the week ahead, but NO CREDIBLE THREAT exists locally at this time.

Pattern:

The Madden-Julian Oscillation (MJO): The Madden-Julian Oscillation is currently in phase 8, and both GEFS and EPS guidance suggest a longer term continuation of the best tropical forcing to remain in phases 8/1. Typically this will open the door to colder intrusions in the northern US near the upper midwest and Great Lakes region especially, but guidance has been too quick with this feature, and instead a positive arctic oscillation (+AO) will continue to prevent the cooler anomalies from occurring through much of the first week of October.

A combination of the MJO in octants 8/1, a positive global AAM, and a mostly negative SOI supports the cooler temperatures across the Midwest and Great Lakes region, however it is clear that virtually all guidance suggests a continuation of the +AO or at least neutral through the first 4-5 days of October. With this specific teleconnection present, it will likely force the cooler anomalies to the Western US, and ridging is likely to continue across the Eastern US. There are signs that the cooler intrusions may have some influence beyond the 5th of October, but the latest Euro weeklies would suggest temperature anomalies will still remain largely on the warmer side of average through the middle of the month. At the time this outlook was written on Friday September 20th, average highs are in the 70s across the entire region, so any “above average” periods will be relative to time of year. Both this weekend/early next week we will likely see temperatures well into the 80s, and then 80° or above during the late September through early October stretch.

The September temperature outlook we continue to project will be an above average temperature month (+3.0°F to +5.0°F) as a whole by month’s end with very high confidence. Using a blend of leading analogs from our privately shared Summer Outlook and extended range climate and ensemble guidance, the month of October we project will be a slightly above average temperature month (+1.5°F to +3.0°F) by months end.

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

Ridging will be present this weekend/early next week, which leads to above average temperatures well into the 80s, and a continuation of the summer-like weather. A cold front late Monday temporarily suspends the heat.

After a transient midweek trough moves through the region behind Monday’s front, another strong ridge builds in and above average temperatures return to our region from late September through at least early October.

Images below are clickable for better viewing

Days 1-5 – confidence VERY HIGH

Days 6-10 – confidence HIGH

Days 11-15 – confidence MODERATELY HIGH

Days 16-20 – confidence MODERATE

Below is a look at the latest Soil Moisture Anomaly for the Contiguous United States. This is used by NOAA/CPC for the purpose of drought monitoring and drought outlooks.

This image will automatically update daily.

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Forecaster: EPAWA Meteorologist Bobby Martrich
Discussion last updated: Friday September 20th, 10:30am