Holiday weekend starts off unsettled,
but ends with clear skies/warm temps

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: The wetter than average start to May continues to carry the above average anomalies to this point of the month. With two cold fronts expected to be the only remaining threats this month, May projection of slightly above average precipitation (+0.5″ to +1.5″) with this week’s outlook, with very high confidence. Long range climate guidance continues to suggest a near to perhaps very slightly above average precipitation departure in June, and with the increase in temperatures and humidity that comes with the transition from late Spring to Summer, thunderstorms and localized heavy rainfall that can accompany them will become more prevalent with time. It is important to note that while localized heavy rainfall from thunderstorms can skew monthly averages on a local level, the monthly projection will be variable across the region and not indicative of an active precipitation pattern overall during the month of June.

Shorter term, the next chance for precipitation is the current system, which is a cold front that will work through the region on Friday. Scattered showers and thunderstorms, some with locally heavy rainfall will pass through the region over several rounds today. As the front clears overnight, a trailing upper level low will move through the region on Saturday, and after leftover morning showers for the interior, the upper level low could spark isolated to widely scattered showers or a thunderstorm in spots, but more of the hit-or-miss and pop-up variety for the remainder of the day. After a dry stretch Sunday through Wednesday of next week, the next cold front arrives next Thursday with scattered showers and thunderstorms.

The month of May we project will finish with slightly above average (+0.5″ to +1.5″) precipitation departures for the month as a whole with very high confidence. Looking ahead to the month of June suggests a near to slightly above average (+0.0″ to +1.0″) precipitation departure for the month as a whole using longer term climate models and global observation trends. July precipitation projections will be included with the next scheduled long range outlook update on June 10th.

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

May 28th – June 3rd: Near to slightly below average

June 4th – June 10th: Near average

June 11th – June 17th: Near to slightly above average

June 18th – June 24th: Near average

June 25th – July 1st: Near average

July 2nd – July 8th: Near to slightly above 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  

An upper level low will pass through the region on Saturday, and after morning showers in interior areas, it could spark a few pop-up showers or perhaps a thunderstorms in spots, but very hit-or-miss.

Next chance for precipitation after a 4-day dry stretch arrives on Thursday with the next cold front. Scattered showers and thunderstorms likely accompany the boundary as it moves through.

Pattern:

OVERVIEW: The first ten days of May were slightly below average as a whole. Since then, there have been several notably warmer periods mixed with some rather refreshing and springlike days over the past few weeks. After a near to slightly above average Saturday/Sunday, hotter and more humid conditions move into the region  beginning on Memorial Day Monday, lasting through midweek next week. A cold front expected Thursday will likely lower temperatures to slightly below average levels between the 3rd and 9th of June. The month of June overall continues to favor near average temperatures, with a slightly below average start, followed by temperatures that largely favor the near to slightly warmer side of average for much of the remainder of the month.

The Madden-Julian Oscillation (MJO) is currently in process of re-entering phase 6 in the Western Pacific via the Circle of Death (COD) and is then expected to progress through phases 7 and 8 is projected through June 10th or thereabout before again collapsing into the COD. A propagation through phases 6-7-8 that is expected will likely keep temperatures in a very familiar up and down transient pattern. It will prevent most likely long stretches of above or below average temperatures, and most likely not too far removed from either side of normal, and reinforces the expectations of a slightly cooler than average period in early June once the MJO reaches phase 8. Moderation likely occurs as the CCKW collapses back into the COD on or around June 10th for the remainder of June.

Average high temperatures are currently in the 75-77°F range from north to south across our coverage region, which is about 2°F higher than last week at this time. Average highs and lows will maintain a steady rise over the next several weeks throughout the remainder of May and June by about a 1-2°F per week gain in climatological high/low averages. 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, the slightly below average temperatures listed in the 6/3-6/9 period will generally feature highs in the 70s from N-S across the region, at a time where 80° or above is considered normal. Use the average highs/lows chart below that provides a point of reference for what average is for each corresponding date, with the examples used for the Philadelphia region.

The month of May we project will finish with near average temperatures (-1.0°F to +2.0°F) when the dust settles May 31st with very high confidence, largely due to the cooler first half of the month already observed balancing a relatively warmer 2nd half of the month. Early look at the month of June we project a near average (-1.0°F to +1.0°F) temperature departure for the month as a whole, using longer term climate guidance and seasonal observation trends. July projections will be included with the next scheduled long range outlook update on June 10th.

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

An upper level low exits the region on Saturday, which is followed and replaced by ridging into our region. Most notable time frame for above average temperatures will be Monday-Wednesday.

A cold front on the lead of the next trough arrives Thursday of next week, followed by a long stretch of slightly below average temperatures between June 3rd-9th with widespread 70s common.

Outlook table last updated: Friday May 27th, 11:00 AM. Next scheduled update: Friday June 10th. There will be no long range update on June 3rd – forecaster vacation.

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/mpm/ 

*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 27th, 11:00 AM