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*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.

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:

During November, most of the region finished with below average precipitation for the month as a whole. This month will turn around considerably, and precipitation will likely be slightly above to above average by month’s end. Through the middle of the month, we firmly believe these systems will be predominantly or totally in liquid form, absent of wintry precipitation. Chances for snow and/or ice will have a higher chance of occurrence during the 2nd half of December, but time frames for exact wintry signals is unclear at the moment.

The first notable time period for an impactful storm will be Monday and Tuesday of next week, and with a warm southerly flow ahead of a system cutting into the Great Lakes region, we expect this system will be rain from start to finish everywhere across the coverage area. Significant rainfall will be possible with this system, which will see periods of rain on Monday as the system cuts, then rain showers with the associated trailing cold front on Tuesday.

We highlighted storm signal in the December 14-15th time frame, with favorable signals for a storm during that period. Storm signals are not necessarily a signal for a winter storm, but rather favorable periods that can produce an impactful weather event, whether small or large, to at least half of our coverage area. Too early for specifics at this time other than to outline the signal, and indeterminable with extent of wintry precipitation, if any, to our region at this time. The end result of precipitation types will be timing and track-dependent, and we will follow more closely next week. Guidance has at one time or another suggested there could be a wintry side for parts of the region in some of their individual model runs, but have shown no consistency or agreement. We’ll monitor closely.

The precipitation departure from average for the month of December we maintain at a slightly above average (+0.5″ to +1.5″) projection with moderately high confidence. Early look at the month of January we project near to slightly above average precipitation (+0.0″ to +0.5″) by months end, using a blend of ensembles, climate models, and our privately shared 2019-2020 Winter Outlook projections.

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

December 9th-December 15th:  Slightly above average

December 16th-December 22nd:  Near average

December 23rd-December 29th:  Near to slightly above average

December 30th-January 5th:  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 in the outlook is clickable for larger viewing

The next impactful system will affect the region Monday and Tuesday of next week. Periods of rain Monday as low pressure cuts into the eastern Great Lakes, then showers follow with the trailing cold front on Tuesday.

The next storm signal highlighted period is December 14th/15th, but with track and timing uncertain, precipitation types for this system are indeterminable at this range. We will monitor more closely next week.

Pattern:

The Madden-Julian Oscillation (MJO): The Madden-Julian Oscillation is currently in the circle of death, but the best tropical forcing is expected to re-emerge into phase 2 and 3 in the next 10 days. After that, they both indicate the eastward propagation of the MJO wave, but it is uncertain if this continues into the Maritime Continent, or re-enters the circle of death. The Maritime Continent is typically associated with milder temperature risks in our area unless mitigated by other factors. Through the next two weeks, there will be risks for above average temperature stretches, albeit in transient fashion, and mostly synoptically-driven.

Through the middle of the month, we face unfavorable teleconnections (+AO, +EPO, +NAO, -PNA) for wintry weather as a notable Pacific jet extension screams across the Pacific from Asia to North America, with little if any amplification. The Arctic Oscillation (AO) remains positive, limiting the cold air advection from Canada and the Arctic regions as reach the 2nd week of December. An expected lack of blocking (+NAO) over the next few weeks will also contribute to a higher height field along the East Coast, and milder risks come back into play weeks 2 and 3 of December at times. We do think during the 2nd half of the month and especially the last full week of the month between Christmas and New Year’s we’ll see more of a split-flow jet pattern, which will be accompanied by colder than average temperatures…and that likely continues into January. This also could result in the relative stormy pattern continuing.

At the time this outlook was written on Friday December 6th, average highs are generally in the lower to upper 40s across the entire region from north to south, so any “slightly above/below average” periods will be relative to time of year. Average highs on December 15th when we project slightly above average temperatures will likely still be in the 40s for most areas, and is relative.

The month of December we project we’ll see near to slightly below average temperatures (-0.0°F to -1.5°F) by months end with moderately high confidence. The month of December began on the colder side of average thus far, but we do expect some milder risks weeks 2 and 3 especially at different points in that two week span. A return to colder than average temps are expected to end the month. The month of January early outlook is for near to slightly below to below average temperatures (-3.0°F to -5.0°F) using a blend of long range ensembles/climate models, analogs, and observational trends.

Snowfall: After starting off the month of December with accumulating snow in northern and northeastern locations, we expect to have a break in the action for at least the next week, then we’ll watch the mid-month system closely for changes in track/timing. A better chance for accumulating snow for more areas exists during the 2nd half of December. January we expect will be active as well, but with above average snowfall for most of the region to coincide with the colder temperatures expected.

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

To coincide with a storm cutting into the Great Lakes region on Monday and Tuesday, a mild southerly flow ensues ahead of and during this system. This leads to a rain event across our area, and mild temps Monday-Tuesday.

Behind the aforementioned system, quite the shot of colder air will follow as another deep trough settles into the NE US and Mid-Atlantic. This likely results in below average temperatures in the December 11th-13th time frame.

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.

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Forecaster: EPAWA Meteorologist Bobby Martrich
Discussion last updated: Friday December 6th, 10:30am