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 around 2 inches 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. Despite the drier periods at different points 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 the very wet start and the multi-day system that affected the region early in April. The month of May was maintained this week for a near to slightly above 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, we have a cold front's pre-frontal trough bringing light showers Friday afternoon and evening with a quick-moving line, which won't yield much in terms of rainfall. The trailing cold front will move through early Saturday morning and clears the coast by the afternoon. There could still be residual (early morning) showers in eastern and coastal areas, most notably across New Jersey and Delaware until the front fully clears. The next system is another cold front that again will be fast-moving and have limited upside of quantitative precipitation, expected to move through next Wednesday. These fronts will be responsible for a transient up and down temperature periods within the upcoming week, where it turns cooler and below average for the day or two in the wake of the fronts, and then turns briefly milder ahead of the next one. This pattern likely continues over the next week before turning milder at the end of April. 

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 is not as likely for the remainder of April. The month of May projections were maintained this week for near to slightly above average (+0.0" to +1.0") precipitation departure for the month as a whole. 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 20th – April 26th: Slightly below average

April 27th – May 3rd: Near to slightly above average

May 4th – May 10th: Near average

May 11th – May 17th: Near average

May 18th – May 24th: Near to slightly above average

May 25th - May 31st: 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 below is clickable for larger viewing  

Pattern Discussion

OVERVIEW: A chilly start to the month over much of the first 6 days had been offset since with milder temperatures experienced last week, and since then we have been in an up and down pattern with some cooler temperatures at times following fast-moving cold fronts. We expect this general pattern to continue through the remainder of April with cooler risks in the day or two following each cold front passage, then some moderation ahead of the next front, then the process repeats...transient up and down pattern. The month ends on a milder note, but with a zonal flow expected for much of the month of April, there will likely be some cooler risks (relative to average of course) at times throughout the month. Not much in the way of extremes on either side (far above or below average) but the month as a whole leans very slightly cooler than average overall. The projection for the month of April as a whole is for a near to slightly above average (0.0°F to +2.0°F) temperature departure, with the expectation that current average temperature anomalies across the region (+2.0°F to +3.0°F)  will be offset somewhat with the cooler risk to end to end month. 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. 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 in the Circle of Death. and is expected to remain there through at least the middle of May. This means that tropical forcing in the equatorial Pacific will have little effect on the overall pattern, and other teleconnections run the pattern instead. For the remainder of this month, we'll still see a slightly negative Arctic Oscillation continue to influence the pattern at times with transient cooler shots and a general up and down pattern ahead of and following a couple of cold fronts this week. We do moderate to end April, then after that point 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, 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 (transparency: it's really a guess) the developing La Niña pattern expected this summer does suggest a hotter than average summer overall in the June through August period. The Climate Prediction Center (CPC) 3-month outlook for the May through July period (see image below) does suggest above average for that period. But keep in mind that this is grouping all three of those months together, and skewed by a likely warmer June/July. May is still near to slightly below average we project. 

Average high temperatures are currently in the 63-66°F range from north to south across our coverage region, which is about 3 degrees higher than at this time last week. Temperatures will continue to climb and maintains a 3°F increase per week through the end of April, then slows that climb slightly in May to about a 2°F per week increase. 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 to below average temperatures listed for the April 25th-27th period generally features highs in the upper 50s to lower 60s across the region, coming at a time when average highs are in the middle to upper 60s. 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 near to slightly above average (0.0­°F to +2.0°F) temperature departure. As a regional average, we are currently sitting about +2.0­°F and +3.0°F month to date, but the cooler risks at times (along with some colder nights) should allow the monthly temperature departure to settle back into our projected 0.0­°F to +2.0°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
4/20	Temperature	Near average	Very high
4/21-4/22	Temperature	Slightly  below average	Very high
4/23-4/24	Temperature	Near average	High
4/25	Temperature	Below average	High
4/26-4/27	Temperature	Slightly below average	Moderately high
4/28-4/30	Temperature	Slightly above average	Moderately high
5/1-5/3	Temperature	Near to slightly below average	Moderate
5/4-5/10	Temperature	Slightly below average	Moderate
5/11-5/18	Temperature	Near to slightly above average	Moderately low
5/19-5/25	Temperature	Near to slightly below average	Low
5/26-6/1	Temperature	Near to slightly below average	Very low
4/20	Cold front	A few showers will be possible early Saturday morning in eastern and coastal areas (NJ/DE) until a cold front fully clears the region	High
4/24	Cold front	Another cold front will cross the region next Wednesday with scattered showers along and ahead of the frontal boundary	Moderately high
April as a whole	Temperature	Near to slightly above average (0.0°F to +2.0°F)	High
April as a whole	Precipitation	Above average (+1.0" to +2.0")	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)	Moderate
May as a whole	Precipitation	Near to slightly above average (+0.0" to +1.0)	Moderate

Climatology

Date	Average Hi/Lo (°F)	Current EPAWA projection
April 20th	67°F/46°F	Near average
April 27th	69°F/48°F	Slightly below average
May 4th	71°F/51°F	Slightly below average
May 11th	73°F/53°F	Near to slightly above average
May 18th	75°F/55°F	Near to slightly above average
May 25th	77°F/57°F	Near to slightly below average
June 1st	79°F/59°F	Near to slightly below 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)