Technical discussion is below for advanced readers:

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 Discussion

OVERVIEW: Most areas within our region are generally between 1-2" above average month to date, thanks in large part to receiving nearly a month's worth of rainfall in just the first 4 days of April in a multi-day anomalous event. Going forward from this point through the end of April, it will be a relatively dry (overall) stretch with just a couple of fast-moving and limited moisture fronts moving through, most notably next Tuesday with a cold front passage. Despite the drier periods for most of the remainder of April, the precipitation departure is still expected to remain above average (+1.0" to +2.0") for the month as a whole, largely due to that very wet start in early in April. The month of May was adjusted this week for a near to slightly below average (0.0" to -1.0") precipitation departure with a zonal flow leading to more fast-moving systems and less in the way of extreme events like seen in early April. The presence of thunderstorms can skew monthly projections of rainfall on a hyper-local basis, and it is important to understand that the projections heading into storm season are a composite average based on synoptic events, not mesoscale-based activity. 

Shorter term, a warm front will cross through the region on Saturday afternoon and evening, and a few light rain showers will be possible with it as it moves through. Precipitation will be a bit more organized in our western areas in Central PA, then lessening in intensity as it moves farther east through early evening. Less than 1/10th inch of rain is expected, and areas close to 1/10th of an inch will be in those aforementioned western areas, and a couple hundredths of an inch farther east. After several very warm days in the warm sector, a cold front arrives late Tuesday with scattered showers and thunderstorms along and ahead of the boundary from Tuesday afternoon through early evening. Another cold front will follow next Friday with more scattered showers and thunderstorms possible ahead of that boundary, and a cooler airmass follows that front unlike the first front earlier in the week.

Our projection for the month of April as a whole was maintained this week for an above average (+1.0" to +2.0") precipitation departure along with below average snowfall…or for most areas, none at all. This already occurred in northern areas that saw minor snow earlier in the month, and none is expected for the remainder of April. The month of May projections were adjusted this week for near to slightly below average (0.0" to -1.0") precipitation departure for the month as a whole with a fast zonal flow leading to less precipitation overall, and climate models adjusted to the drier outlooks compared to this time a week ago. No snowfall projections are included between May and October since the occurrence of accumulating snow in any of those months is extremely rare.

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

April 27th – May 3rd: Slightly below average

May 4th – May 10th: Near to slightly below average

May 11th – May 17th: Near average

May 18th – May 24th: Near average

May 25th - May 31st: Near to slightly above average

June 1st - June 7th: 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 below is clickable for larger viewing  

Pattern Discussion

OVERVIEW: A back and forth battle of milder temperatures and cooler temperatures was seen for most of this month, which is typical pattern behavior for the month of April. Once we get into May, typically those cooler vs. warmer battles become less prevalent, especially after Mother's Day. It is for this reason that we recommend holding off with planting sensitive vegetation until that time since frosts and even freezes can occur overnight as we've seen on multiple occasions this week. Currently to this point of the month, most areas fall in between +0.0°F and +1.5°F in terms of cumulative temperature departures from average, and a warm end to the month over the last three days will allow the month of April as a whole to finish with a slightly above average (+1.0°F to +3.0°F) temperature departure. Our projections for the month of May was maintained this week for a near to slightly below average (0.0°F to -2.0°F) temperature departure for the month as a whole, but this will be relative to seasonal average at that time, and not cold by any means. Most notable "chill" in May will be found on either side of the middle of the month. See the average highs and lows chart below which provides some transparency of what average temperatures are for our major climate sites throughout the region going forward over the next 6 weeks. 

The Madden-Julian Oscillation (MJO) is currently straddling phase 3 and the Circle of Death, and is expected to move into the Maritime Continent phases 4 and 5 from late April through the first week of May before collapsing back into the Circle of Death for week 2 of May. Through much of May, the pattern is relatively zonal. This means temperatures shouldn't stray too far from average, and less in the way of extremes far above or far below average. The pattern does lean very slightly cooler than average overall, but this will be relative to average highs and lows at the time. Average highs for most areas are getting into the 70s in May, so even though it may be slightly cooler than average at times, mostly notably on either side of the the middle of the month, it certainly won't be cold. The zonal flow will also mean less-amplified systems and faster-moving, but frequency of fronts and events are generally higher. Although we limit the long range outlooks purposefully at a 5-6 week lead time with accuracy in mind, there has been a lot of questions regarding the Summer. While we don't engage in seasonal outlooks of any kind due to the lower probability of it working out as planned, we feel the transition from the current weak El Niño to ENSO neutral will be reached later in May, but is likely to remain in ENSO neutral territory for most of the Summer. There has been a lot of talk about the developing La Niña, but that isn't as likely to happen until late Summer at the earliest, and may end up waiting until the early Fall months to reach. So what does that mean for Summer? ENSO neutral Summers are typically warmer than average, which is similar to a La Niña Summer. The difference between the two (again typically) is that ENSO neutral favors more precipitation during the Summer months than a La Niña Summer. With this in mind, we personally favor the former... which is hotter than average, but not super hot like you would see in dry conditions typically in a La Niña, and also wetter than average.

Average high temperatures are currently in the 66-69°F range from north to south across our coverage region, which is about 3 degrees higher than at this time last week. Temperatures were climbing at a rate of a 3°F increase per week through this point of April, then it will slow down that rate of increase slightly in May to about a +2°F per week. 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 for the May 11th-17th period generally features highs in the upper 60s to near 70°F across the region, coming at a time when average highs are in the lower to middle 70s. 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, which is one of our warmest climate sites.

Our projection for the month of April is for a slightly above average (+1.0­°F to +3.0°F) temperature departure. As a regional average, we are currently sitting about +0.0­°F and +1.5°F month to date, but the expected warmer last couple of days of April should allow the monthly temperature departure to settle back into our projected +1.0­°F to +3.0°F range by end of month. The month of May was maintained this week for a near to slightly below average (0.0°F to -2.0°F) temperature departure expectation, using longer term climate guidance and global observation trends. Despite leaning to the cooler side of average, it will be relatively close to normal temperate conditions for May. Springlike. 

Note:  Any image below is clickable for larger viewing`

Long Range Outlook Table

 

Date(s)	Threats	Significance	Confidence
4/27	Temperature	Slightly below average	Very high
4/28-5/2	Temperature	Above to well above average	Very high
5/3	Temperature	Near to slightly above average	High
5/4-5/10	Temperature	Near to slightly below average	Moderately high
5/11-5/17	Temperature	Slightly below average	Moderate
5/18-5/24	Temperature	Near to slightly below average	Moderately low
5/25-6/1	Temperature	Near average	Low
6/2-6/9	Temperature	Near to slightly above average	Very low
4/27	Warm front	A few showers will be possible Saturday afternoon most notably in western areas with a warm front, and weakening as showers head east	High
4/30	Cold front	A cold front will cross the region next Tuesday evening with scattered showers/t-storms along and ahead of the frontal boundary	Moderately high
5/3	Cold front	Another cold front crosses next Friday with scattered showers/t-storms possible along and ahead of the frontal boundary	Moderate
April as a whole	Temperature	Slightly above average (+1.0°F to +3.0°F)	Very high
April as a whole	Precipitation	Above average (+1.0" to +2.0")	Very high
April as a whole	Snowfall	Below average or none	Very high
May as a whole	Temperature	Near to slightly below average (0.0°F to -2.0°F)	Moderately high
May as a whole	Precipitation	Near to slightly below average (+0.0" to -1.0")	Moderate

Climatology

Date	Average Hi/Lo (°F)	Current EPAWA projection
April 27th	69°F/48°F	Slightly below average
May 4th	71°F/51°F	Near to slightly below average
May 11th	73°F/53°F	Slightly below average
May 18th	75°F/55°F	Near to slightly below average
May 25th	77°F/57°F	Near average
June 1st	79°F/59°F	Near average
June 8th	81°F/62°F	Near to slightly above average

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.

Climate Prediction Center (CPC) Graphical Products

These products are from the NOAA Climate Prediction Center (CPC) and do not necessarily reflect the EPAWA forecast which is detailed above. All images below update automatically as the CPC releases new graphical products

U.S. Soil Moisture Anomaly

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.

US drought monitor (NE US)