The first of several troughs arrives on
Thursday, cooler temperatures follow

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:  There is still a considerable spread in precipitation departures across the region through the first three weeks of July, most notably due to the haves and have nots with thunderstorm activity. For this reason, some areas have seen average precipitation while other areas have been inundated with heavy rain in slow-moving thunderstorms and flash flooding on several occasions. In addition, Tropical Storm Elsa paid a visit to eastern areas earlier in the month. Going forward, we remain in a rather inactive pattern for the remainder of July aside from a few cold front passages, and perhaps a mid-level disturbance or two in an expected northwesterly flow aloft next week. August we maintained slightly above average precipitation projections for the month as a whole with this update.

Shorter term, an overall drier picture for the remainder of dry will be interrupted in the Sunday-Monday time frame with the passage of a weak cold front, one which could touch off isolated to widely scattered thunderstorms Sunday PM for interior locales, and isolated thunderstorms Monday PM along and SE of I-95 until the front fully clears. A northwesterly flow aloft develops next week which typically promotes very fast-moving systems on the outer periphery of strong ridging found over the Plains and Rockies. These types of setups are not conducive to heavy rain/flash flooding, but a mid-level disturbance may traverse the Great Lakes and our region on Wednesday, followed by a cold front next Thursday. Confidence is lower for the mid-level disturbances in terms of areas affected and timing, and will be monitored on a shorter-term basis next week.

The month of July we project will finish with near well above average (+0.0″ to +4.0″) precipitation departures for the month as a whole with very high confidence, with a vast spread due to areas that have been hit with more frequent thunderstorm activity and flash flooding events vs. others. Early look at the month of August we project near to slightly above average precipitation (+0.0″ to +1.0″) 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:

July 24th – July 30th:  Slightly below average

July 31st – August 6th:  Near average

August 7th – August 13th:  Near to slightly above average

August 14th – August 20th:  Near to slightly above average

August 21st – August 27th:  Near average

August 28th – September 3rd:  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  

A warm front crosses the region Saturday night, followed by a cold front on Sunday. Scattered showers and t-storms for the interior Sunday PM, then isolated along and SE of I-95 Monday PM.

A NW upper air flow develops over our area next week, which promotes disturbances locally rounding the outer periphery of Central and Western US ridging Wednesday-Thursday.

Pattern:

OVERVIEW: An active precipitation pattern over the first 3 weeks of the month has led to up and down temperature spreads thus far, and most areas are fairly close to average temperatures for the month. We begin the period with a trough in place and slightly cooler than average temperatures, which will moderate over the weekend. As a northwesterly flow aloft develops next week, the surface flow will become more westerly, which encourages slightly warmer than average temperatures due to the westerly downsloping effects, but humidity is mitigated somewhat by that westerly surface flow. So bottom line is hotter temperatures, but not with oppressive humidty. Ridging in the Plains and Rockies will eventually transition to SW US ridging as we head into the first week or two of August, keeping temperatures locally relatively close to seasonal average through that period…perhaps near to very slightly above average during week 2. A warmer than average period is expected to end August and begin September.

The Madden-Julian Oscillation (MJO) is currently in phase 6 and will remain there in the nearer term, and as we move into very late July and August, a collapse into the Circle of Death is anticipated. As we progress through Summer, MJO waves are monitored for possible favorable periods of tropical cyclone development in the Atlantic. In part, phase 6 is not as conducive for Atlantic tropical cyclone development, and why we’re not projecting much noise from the tropics over the next two weeks or so.

Average highs and lows are now at annual climatological maximums. Normal high temperatures are currently in the 85-88°F range from north to south across our coverage region, which is the peak averages of any point during the calendar year. 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 next week will be generally in the upper 80s to lower 90s for most areas. 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.

For the month of July, we expect near average temperatures (-1.0°F to +1.0°F) when the dust settles July 31st with very high confidence. Looking at the month of August as a whole suggests a near to slightly above average month (+0.0°F to +2.0°F) using long term climate models and seasonal/global observation trends.

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

Slightly cooler than average temperatures currently to begin the forecast period will progressively transition to slightly warmer than average next week until a cold front arrives mid-late week.

A northwesterly flow aloft develops next week that keeps this area on the outer periphery of ridging in the Plains/Rockies, and a warmer pattern with westerly is expected with downsloping effects.

Outlook table last updated: Friday July 23rd, 11:00 AM. Next scheduled update: Friday July 30th.

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 July 23rd, 11:00 AM