Preliminary 2014-15 Winter Weather OutlookCreated by: Christian Walker

Forecast Valid: August 31, 2014 ***PRELIMINARY***

Forecast Thru: March 15, 2014

Overview

• 50% chance of above average precipitation and below average temperatures

• 20% chance of near average temperatures and slightly below average precipitation

• 15% chance of average conditions• 10% chance of above average temperatures and

slightly below average/average precipitation• 5% chance of above average temperatures and

below average precipitation

El Nino Watch

• 65% chance of a weak to moderate El Nino• Warming of sea-surface temperatures in the East-

Central Pacific likely through the next 3-4 months • Pattern similar to 2009-10 winter• El Nino could be an important driving factor of

more snowfall and colder temperatures in the Mid-Atlantic, however an El Nino alone, especially a weak one that we are likely to see, will not bring us a snowy winter.

Other Driving Factors

• Jet Stream Positioning• MJO (Madden-Julian Oscillation) Where are the

low-level Westerly bursts? Where is tropical convection entering the high-level (jet stream winds) that push into the Northwestern U.S.?

• PDO (Pacific Decadal Oscillation) Long-term negative phase trends in the 2000s increase the chances of a snowier winter this year.

• Moisture Availability (Sub-Tropical Flow and bodies of water)

All of that science jibber-jabber explained in English

• Continue to the next page. That way

What is El Nino?

• an irregularly occurring phenomena in which ocean waters in the equatorial Pacific gradually increase in temperature, causing climatic changes in parts of the Pacific Ocean, South America, North America, and other regions that typically occurs in late November through early January; the opposite of La Nina

• typically characterized by 5 consecutive three-month periods of Pacific oceanic temperatures at or above the +0.5°C threshold ONI (Oceanic Nino Index)

Why is El Nino Important?

• The change of temperatures at the surface of the Pacific Ocean (SST’s) can impact the climate here in the U.S. in the winter and spring. Depending on the location and intensity, El Nino can cause a warmer than usual winter, or a colder and snowier than usual winter. In addition to El Nino, there must be other conditions such as a persistent jet stream dip, high moisture availability, and MJO favorable trends.

El Nino Regions

Due to the positioning of the jet stream, typically we see a warm and drier-than-usual winter when ocean temperatures are warmer in the1+2 and Eastern part of the El Nino 3 region. Why is this? When we havean El Nino in the 3.4 and 4 region (near/at the Int’l Date Line), there is a betterchance that deep tropical convection and atmospheric circulation will be pushedinto our jet stream. Eventually, that convection and circulation will travel along the jet stream into our area and then we could have a major snowstorm on our handswith a lot of moisture and cold air available.

El Nino “Modoki”

• El Nino Modoki refers to an El Nino occurring nearing the International Date Line in the 3.4/4 region.

• Typically (depending on strength), El Nino Modoki causes a colder and snowier winter for our region.

• El Nino only projected to be weak this Winter (currently a 65% chance of El Nino)

• However, deep tropical convection traveling through our jet stream could “boost” the weak El Nino .

Why is this tropical convection (thunderstorms) important?

• If deep tropical convection and atmospheric circulation enter our jet stream, this can cause a “blockage” in the atmosphere at the high latitudes (U.S./Canada border in the Northwestern corner of the U.S.)

• This blockage would push the jet stream south into the middle/southern portion of the U.S.

• This would cause a surge of cold air (polar vortex) to drop into the East Coast and Midwest.

Why is this tropical convection (thunderstorms) important? (cont.)

• When those areas of tropical convection/moisture and atmospheric circulation finally travel along the jet stream across the U.S., it could produce a major snowstorm for our area.

• Why? Not only would there be a surge of cold air blasting into the region, the approaching storm system would collect moisture from the Pacific (zonal flow), Gulf of Mexico, and the Chesapeake Bay/Atlantic Ocean. Those are perfect ingredients for a very cold and snowy winter.

• This is an effect of the MJO (Madden-Julian Oscillation)

El Nino Area65% chance of WEAK El

Nino

MJO + PDO EFFECTS

Dip in jet stream

SURGE OF COLD AIR

MOISTURE PUSHES TOWARD THE COLD AIR

Zonal FlowL L

Areas of tropical convection travel along jet stream.

Moist air

Cold air

Jet Stream

***Area of Interest***Potentially favorable conditions for cold, snowy winter.

Evidence of El Nino (CFS Model)El Nino 3.4 Region (Modoki, which typically brings our region favorable conditions for snow/cold.)

FORECASTMODEL #1

Credit to the Climate Prediction Center: cpc.ncep.noaa.gov

Evidence of El Nino (CFS Model)El Nino 3.4 Region (Modoki, which typically brings our region favorable conditions for snow/cold.)

FORECAST MODEL #2

Credit to the Climate Prediction Center: cpc.ncep.noaa.gov

Evidence of El Nino (CFS Model)El Nino 4 Region (Modoki, which typically brings our region favorable conditions for snow/cold.)

FORECAST MODEL #1

Credit to the Climate Prediction Center: cpc.ncep.noaa.gov

Evidence of El Nino (CFS Model)El Nino 4 Region (Modoki, which typically brings our region favorable conditions for snow/cold.)

FORECAST MODEL #2

Credit to the Climate Prediction Center: cpc.ncep.noaa.gov

Evidence of El Nino (CFS Model)El Nino 1+2 Region (Typically brings our region unfavorable conditions for snow/cold and a warmer, sometimes drier winter weather-wise.)

FORECAST MODEL #1

Credit to the Climate Prediction Center: cpc.ncep.noaa.gov

Evidence of El Nino(CFS Model)El Nino 1+2 Region (Typically brings our region unfavorable conditions for snow/cold and a warmer, sometimes drier winter weather-wise.)

FORECAST MODEL #2

Credit to the Climate Prediction Center: cpc.ncep.noaa.gov

Analysis (El Nino 3.4 Region)

• Both computer model graphs show water temperatures solidly above 0.5°C , with some forecast members even showing water temperatures around 1.5°C.

• Water temperatures between 0.5 and 1.5°C could warrant an active winter. However, if water temperatures stay mostly around 0.5°C, it would likely keep snowfall at a reasonable number.

Analysis (4 Region)

• Both computer model graphs are consistently showing water temperatures between 0.5-1°C. However, there are a few forecast members under 0.5°C. This “modoki” region El Nino looks weak.

• However, if water temperatures stay consistent around 1°C in both the 3.4 and 4 region, an active winter could be on hand.

• If water temperatures hold around 0.5°C in both the 3.4 and 4 region, El Nino would not be a significant factor in this year’s winter.

Analysis (1+2 Region)

• Water temperatures look to stay at or below 0.5°C for the first half of the winter, and at or above 0.5°C the second half. Whether it is above or below could be a huge factor in what happens this winter in the Mid-Atlantic.

• Everything is situational. If the water temperatures stay just a tad bit warmer in the 3.4 and 4 region and a tad cooler in the 1+2 region we could see a very active winter (and vice versa). That is why it is very difficult to forecast the winter this far out.

SON

Cooler water temperatures approx. halfway up the Northern Hemisphereat the International Date Line.

Warmer water temperatures in the GulfOf Alaska.

Warmer water temperatures at the Equator spread West to theInternational Date Line.

Warmer water temperatures in the GulfOf Alaska.

Cooler water temperatures approx. halfway up the Northern Hemisphereat the International Date Line spread slightly further East.

Warmer water temperatures at the Equator spread West to theInternational Date Line. Water temperatures continue to become warmer, possibly warranting an El Nino (modoki).

The warm water temperaturesat the equator in the 3.4/4 region andin the Gulf of Alaska and the cooler water temperaturesin the Northern Hemisphere at the International Date Linehave been a common sign of colder and snowier winters in the Mid-Atlantic.

CFS model projections alone are not showing awetter winter than average.

CFS model projections alone are not showing acolder winter than average.

CFS Model Pitfalls

• Tends to overestimate strength of El Nino• Does not take into account forcing factors such as

tropical convection, zonal flow, jet stream positioning, upper latitude blockage, etc. on the precipitation/temperature maps.

• Seems to handle Nino conditions better when it is a La Nina (opposite)

• El Nino Modoki is harder to predict due to the differential of water temperatures between the 3 and 4 region compared to the 1+2 region.

Additional Factor: Solar Activity

• Less solar activity such as sunspots are expected this winter.

• On average, winters with more solar activity experience less snow, but with less solar activity experience more snow.

• Solar Activity Scale for November-February 2014/2015: 1.7/10

• This is another factor that could indicate a colder and snowier winter this year

Snowfall Predictions

Winter 2014-15 Forecast

Winter 2013-14 Average

0

5

10

15

20

25

30

18-24"+12-18"

8-12"4-8"

Less than 4"

18-24"+12-18"8-12"4-8"Less than 4"

This chart shows we could still go well above average in snowfall this year, just not as above averageas last year. We should anticipate at least one “big one”, as well as several snowstorms of up to 8”.

For the entire Mid-Atlantic.

Notice

The snowfall prediction chart was for the entire Mid-Atlantic. The numbers were so high because to calculate the totals from last year, I took the amounts from every state in the Mid-Atlantic. Therefore, your location could have seen 3”, while fifty miles away 15” fell. That would be counted as “less than 4” and “12-18”. The totals came from each individual snowstorm, with Winter Storm Pax dropping overall the highest amount last season.

Winter Forecast Map

Summary

• There is a generally solid chance of a colder and snowier winter than average.

• Weak El Nino could bring more tropical convection and cold air into the region from many different driving factors.

• There are still many variables and conditions that are uncertain.

• Overall, there is a 50% chance of a wetter and colder winter than average.

Thanks for reading!

The final outlook will be issued November 15, 2014. If you have any (appropriate) questions or comments, please follow the contact information that is listed on the next page. I hope you enjoyed reading the forecast; hopefully you will get the winter you are hoping for, whatever that may be.

Have a great day!-Christian

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