Strong ridging builds in by midweek
leading to summer temps for awhile

Technical discussion below will feature two (2) subcategories: Precipitation, and Pattern Discussion. Storm possibilities will be discussed exclusively in the Premium Forum with intense model analysis leading up to any major snow, ice, or rain events, not publicly. To join this discussion and hear the updated thoughts from our team, visit The My Pocket Meteorologist Page by clicking HERE and select the “Premium Weather Forum” option.

Precipitation:

OVERVIEW: For the first half of May, precipitation varies from near to slightly above average in NW areas to near to slightly below average in SE locales, while areas in the middle are generally near average. Going forward through the remainder of May, we expect precipitation chances to drop off further, and high pressure will likely dominate much of the 2nd half of the month. By month’s end, we expect slightly below average precipitation anomalies across the region, and have adjusted our monthly projection accordingly. Using global models and observational trends, the month of June we will maintain a near average precipitation projection for the month.

Very limited precipitation chances exist in the next 7-10 days, as high pressure will be in control of our weather through at least midweek, if not longer. A series of mid-level shortwaves cross the region this weekend, but with high pressure still overhead, coverage of showers will be limited, especially on Saturday. A stray shower chance is maintained Saturday afternoon that will be diurnally and instability driven. Same situation Sunday afternoon, but with a slightly stronger (albeit still rather weak overall) shortwave in the vicinity, a better chance for isolated to widely scattered showers and perhaps thunder is possible. We now project a frontal wave will remain south of the region Monday and Monday night due to the high pressure influence, but the high/ridge may shift east late in the week, allowing a similar frontal wave to reach our area in the Thursday-Friday time frame. We will monitor in the week ahead and update the local forecasts and daily forecast video accordingly and as needed.

The month of May we project will finish with slightly below average (-0.5″ to -1.0″) precipitation departures for the month as a whole with higher confidence, with the 2nd half looking drier than the first half in comparison. Early look at the month of June we project a near average precipitation (-0.5″ to +0.5″) anomaly for the month as a whole, using long range climate guidance and global observational trends.

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

May 15th – May 21st:  Below average

May 22nd – May 28th: Slightly below average

May 29th – June 5th:  Near average

June 6th – June 12th:  Near average

June 13th – June 19th:  Near to slightly above average

June 20th – June 26th:  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  

Using the 3km NAM, instability-driven showers will be possible (stray) on Saturday afternoon with a weak shortwave sliding through, but a better chance for thundershowers exists Sunday afternoon.

Parts of our area, most notably East-Central PA, are being monitored for potential drought conditions. This image released Thursday from the US drought monitor shows abnormally dry in that area.

Pattern:

OVERVIEW: As we expected for quite some time, the first half of May has been cooler than average, and now we have seen a transition back to near average temperatures. We expect to remain that way through early next week, then the remainder of week 3 moderates to slightly above average levels. After beginning week 4 at near to slightly above average, a warmer turn is expected during the last week of May leading into Memorial Day weekend. June we continue to project will finish slightly above average for the month as a whole, with the middle two weeks likely to be the warmest relative to average at that time. The Madden-Julian Oscillation (MJO) is currently straddling phase 2 and the circle of death, and is expected to quickly migrate through phase 3 early next week, then into the Maritime Continent to begin the 4th week of May. This time of year the Maritime Continent forcing typically yields warmer than average conditions.

Temperatures begin to lean on the warmer side of average for the 2nd half of the month, but it will be a gradual process. We expect to maintain at near average temperatures through the weekend and early next week, with a late week spike in temperatures and ridging in the center of the country shifts eastward. A slight step back between the 21st-25th, but still near to slightly above average at that time, then another surge beginning May 26th or thereabout that leads us right into Memorial Day weekend. Early thoughts on June increase temperatures to slightly above average levels with the potential for more summerlike ridging with time. Early projections are for weeks two and three of June to be the warmest relative to seasonal averages at that time.

Average highs and lows are continuing to slowly rise approximately every 3 days, and normal high temperatures are currently in the 70-74° range from north to south across our coverage region. Any above or below average stretches listed in the outlook will be relative to seasonal norms at that time, and it is important to note that cooler/warmer periods will be relative to the time of year we are talking about. For example, slightly above average temperatures listed between the 26th-30th of May likely results in high temperatures in the 78-84° range (north to south) with respect to the normal/average highs at that time. Use the average highs/lows chart above that provides a point of reference for what average is for each corresponding date, with the examples used for the Philadelphia region.

For the month of May, we expect near to slightly below average temperatures (0.0°F to -1.5°F) when the dust settles May 31st with high confidence. This is a largely due to a cooler first half that will skew the monthly mean, but the 2nd hald leans slightly above average going forward. Early look at the month of June as a whole suggests a slightly above average month (+1.0°F to +3.0°F) using long term climate models and seasonal/global observation trends.

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

The week ahead will see temperatures near average over the weekend and to begin next week, then moderation occurs to slightly above average mid to late week, with some areas reaching the 80° mark.

We reload between the 21st-25th, the signals are for another warmer than average push after that point, and extending into most of the Memorial Day holiday weekend, with 80°F+ temps possible.

Outlook table last updated: Friday May 14th, 11:25 AM. Next scheduled update: Friday May 21st.

This is a weekly updated public long range guidance product from EPAWA. For daily long range updates and more detailed updates M-F, please join the EPAWA forum. More information/sign-up at: http://epawaweather.com/my-pocket-meteorologist/ 

*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.

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.

Forecaster: EPAWA Meteorologist Bobby Martrich
Discussion last updated: Friday May 14th, 11:25 AM