Memorial Day weekend is coming fast,
and indications are it’ll be very warm 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:

The period for the next week to 10 days looks relatively dry – but not to suggest it will be entirely dry, but drier than what is considered average, and certainly drier than it has been so far this month. The timing is ideal heading into the Memorial Day holiday weekend, when most would agree it is more fortuitous to see dry rather than wet conditions. We’ll have a few fronts to deal with this week, but none have more than scattered thunderstorms associated with them, and sun is found on every day in the next 10 days. So no total washout days expected.

The first activity will be along a pre-frontal trough axis on Sunday late afternoon and evening, and favoring interior locations NW of I-95. Most of the day is dry and very warm with sun prior, and then the trailing cold front arrives later Monday after another very warm day, and a more isolated chance for a thunderstorm with the actual cold front.

Next chance(s) for any precipitation will come Wednesday night into Thursday morning as a warm front is forced northward by a building strong ridge in the SE US. A few showers may accompany that front as it pushes northward through the region. Finally, as the ridge begins to break down over the holiday weekend, a cold front may move through at some point with a line of scattered thunderstorms associated with it. It doesn’t ruin the day for the most part, but models favor Saturday to be the day to see the cold front as of now. Timing and impacts are subject to change at this range, and we’ll have a better look at this next week in the local forecasts and daily forecast videos as we near the holiday weekend.

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

May 20th-May 26th: Slightly below average

May 27th-June 2nd: Slightly above average

June 3rd-June 9th: Near average

June 10th-June 16th: Near 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

The NAM shows the scattered thunderstorms threat late Sunday for the interior locales along a pre-frontal trough axis, but the storm activity comes in late during the evening hours, rendering most of Sunday dry and warm.

A warm front is forced northward through the region Wednesday night and Thursday morning by a strong ridge that will be building at the time in the SE US. A few scattered showers will be possible along the front.

Pattern:

The Madden-Julian Oscillation (MJO): The Madden-Julian Oscillation is currently in phase 8, and will likely see a progression of the MJO wave through phase 1 briefly before collapsing into the circle of death. At that point, tropical forcing will be more variable, and other factors will contribute more to the overall pattern.

Blocking (-NAO) has been a big story for the middle 1/3 of the month, where cooler, rainy days were common. Despite the cooler days, the entire region is above average by generally 1-3°F for the month as a whole. With the NAO now returning to neutral, and warmer anomalies expected much of the rest of the month, we expect projections of +3° to +6° above average to come to fruition by the end of May. Currently we have a favorable Pacific jet bringing colder than average anomalies to the Western US, and a resultant -PNA trough keeps those cooler temperatures there and well north of our region. The SE ridge will flex several times between this weekend and the holiday weekend, and will likely become quite dominant across the SE US during this period. Our area will be on the NE periphery of that ridge, just enough to promote warmer than average temperatures, but also keeps the precipitation to a minimum. We do think this ridge eventually breaks down the week after Memorial day weekend, in large part due to SOI changes and recent pressure rises in Darwin, Australia. This allows for cooler, but still seasonable temperatures very late May and early June, but also a wetter pattern possible at that time.

The May temperature outlook we continue to project will be an above average month (+3.0°F to +6.0°F) as a whole by month’s end with high confidence, and the majority of the region is currently above average in the temperature department despite the ups and downs. Ups and downs aside, the warmer than average days are outperforming and outweigh the cooler/cloudy days, and that likely continues going forward. Using a blend of leading analogs from our privately shared Spring Outlook and extended range climate and ensemble guidance, the month of June early projections are for a slightly above average temperature month (+1.0°F to +4.0°F) by months end.

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

The ensembles show a strong ridge building into the SE US heading into the Memorial Day holiday weekend, and while we’ll be on the NE periphery of the ridge, it means warmer than average temps through the period.

The aforementioned ridge will begin to break down after the holiday weekend, and much of the week after returns to normal/average highs for this time of year. Precipitation also increases during this period.

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 May 17th, 10:30am