Cooler than average conditions likely
dominate through end of November…

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 month of November had a bit of a reprieve in the overall abnormally dry conditions this past week with much needed rainfall in the form of a pre-Thanksgiving area-wide soaker. Despite the plentiful rainfall from that system, most areas are still on the drier side of average for the month as a whole. With minimal prospects for rain for the remainder of the month sans a system that brings showers Sunday evening and overnight, we are confident that the month will finish with at least slightly below average precipitation by month’s end. November typically doesn’t yield much in the snowfall department on average, so it is of course relative…but outside of very far northwestern areas, no snow is expected for the remainder of the month…at least not measurable. December projections were maintained this week for near to slightly above average precipitation, and a +0.0″ to +0.5″ precipitation departure overall for the month. With an El Niño background state, we can expect an uptick in precipitation departures heading into winter with a more active subtropical jet stream despite the overall dry Fall months prior. With temperatures very close to average in December, combined with the near to slightly above average precipitation expectation, the projected snowfall has been maintained this week at near average.

Shorter term, a weak coastal low will develop on Sunday near the Carolinas and quickly move northward along the coast ahead of an incoming trough. This will draw in just enough milder air to keep the precipitation type primarily rain showers Sunday evening and part of the overnight, but snow can mix in with the trailing trough/cold front in far northwestern areas Sunday evening. A more active pattern takes shape in the first week to 10 days of December, with a system cutting to our west dragging a warm front (and milder air, rain showers) through our region in the December 3rd/4th time frame…followed by a cold front around December 6th. With a blocking pattern (west-based -NAO) well established by this point and rising toward neutral in the December 7th-9th period, a storm signal was introduced this week which is common when there is a relaxation of an existing blocking pattern. Whether this (1) materializes and (2) has enough cold air in place to make this a wintry event is still unknown, but this can certainly transition from storm signal to winter storm signal in subsequent outlooks if the right conditions are met. A storm signal indicates a favorable period for a storm to occur, but is not a guarantee for rain (or snow) at any given location. Just a period of interest at present time, which will be monitored going forward.

Our projection for the month of November as a whole is for a slightly below average (-0.5″ to -1.5″) precipitation departure, and below average snowfall. For most of the region, no measurable snow will occur. Our projection for the month of December was maintained this week for a near to slightly above average (+0.0″ to +0.5″) precipitation departure for the month as a whole, along with near average snowfall using collective long range ensembles and global observation trends.

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

November 25th – December 1st: Slightly below average

December 2nd – December 8th: Near to slightly above average

December 9th – December 15th: Near to slightly above average

December 16th – December 22nd: Near average

December 23rd – December 29th: Near 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 below is clickable for larger viewing  

A weak coastal low will develop near the Carolinas Sunday and moves northward, drawing in air that is mild enough to keep this a mostly rain showers threat Sunday evening, and mostly east areas.

After a weak front moves through the region December 2nd, a more organized system arrives behind it in the 12/3-12/4 time frame that is most likely to draw in milder air and bring rain to the region.

Pattern:

OVERVIEW: For the month of November we maintained projections this week for a slightly below average (-1.0°F to -3.0°F) temperature departure for the month as a whole, and as a composite average for our coverage region. Through Thanksgiving, most areas are already within that temperature departure range, and several notably colder than average days are expected within the final days of November. Our December projections were also 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. This is in large part due to overwhelming ensemble support for a blocking pattern to begin the month, followed by a temperature relaxation before mid-month, then a slightly below average 2nd half of December…continuing into at least early January.

The Madden-Julian Oscillation (MJO) is currently found in phase 2, and is expected to spend a few days there before migrating into a brief stint in phase 3 to end November before collapsing into the Circle of Death (COD) around December 1st. Phases 1 and 2 are both support cooler than average conditions, and given the (approximate) week lag to feel the effects locally of any MJO phase, this is in large part why the cooler end to November is expected from Thanksgiving through very early December. The MJO becomes more critical to temperature and precipitation patterns on an intra-seasonal basis for the winter months. December won’t be a “torch” at all, and we actually project a fairly “normal” December this year with both temperatures and snowfall. The first half of the month is milder compared to the 2nd half in terms of departures from average, and we expect generally a near to perhaps very slightly below average December (0.0°F to -1.0°F) with near average snowfall. El Niño is strong and still east-based, there is currently a +IOD (Indian Ocean Dipole) that is muting equatorial convection somewhat. We don’t think the strong east-based El Niño lasts beyond December however. We are seeing observed Sea Surface Temperature (SST) data showing Niño regions 4 and 3.4 playing catch-up to the eastern regions (3 and 1+2) over the past several weeks, and we feel this catch-up will be completed in December. An interesting development this week is the sudden switch to west-based -NAO, or negative North Atlantic Oscillation. This is rather unusual given how strong the stratospheric polar vortex is recently in an El Niño and +IOD state. This isn’t your typical block that can been seen coming for over a week, instead it is the result of several amplified cyclonic wave breaks and troughs surrounding Greenland…essentially creating a traffic jam in the upstream pattern. The result is a blocking pattern that will be established in early December. When this blocking pattern relaxes and heads toward neutral/positive, a storm (perhaps wintry) often times accompanies this transition. Since we expect this to take place in the December 7th-9th period, a storm signal was introduced this week in that period.

Average high temperatures are currently in the 49-53°F range from north to south across our coverage region, which is about 2°F lower than at this time last week. Temperatures will continue to gradually drop off over the next two months heading into Winter. 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 below average temperatures listed for November 28th-29th period generally features highs in the 35-40° range, coming at a time when average highs are in the upper 40s to lower 50s across the region. 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 November is for slightly below average (-1.0°F to -3.0°F) temperature departure with the expectation of a notably colder than average final week of the month with very high confidence. Our projection for the month of December as a whole is for a near to very slightly below average (0.0°F to -1.0°F) temperature departure using longer term climate guidance and seasonal observation trends. The current thinking is the first half of the month to balance out fairly close to seasonal averages sans a few anomalous extremes, then a slightly cooler than average (overall) 2nd half of December follows. This trend may also continue into at least early January.

Note:  Any image below is clickable for larger viewing

A cyclonic wave break south of Greenland next week is likely to block up the pattern and create a west-based -NAO blocking pattern, leading to our storm signal introduced in the December 7-9 period.

Average snowfall for each month at our major climate sites within are region for November and December are below. November snow on average is minimal, but picks up a bit in December.

Outlook table last updated: Friday November 24th, 11:20 AM. Next scheduled update: Friday December 1st.

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.

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

CPC 6-10 day temperature outlook

CPC 6-10 day precipitation outlook

CPC 8-14 day temperature outlook

CPC 8-14 day precipitation outlook

CPC weeks 3-4 temperature outlook

CPC weeks 3-4 precipitation outlook

CPC next 3 months temperature outlook

CPC next 3 months precipitation outlook

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 November 24th, 11:20 AM