Weather and Climate Data Analysis: Detecting Signals for High D.C. Snow Seasons

The goal was to compare global weather and climate data signals for years that Washington, D.C. experienced above average snowfall during meteorological winter months of December, January, and February. The years chosen were pulled from the following link that documents all D.C. seasonal snowfall from the D.C. area National Weather Service office. All maps were produced from NOAA/ESRL Physical Science Division, Boulder Colorado form their website at http://www.esrl.noaa.gov/psd/.

U.S. Winter Air Temperature Tendencies (NOAA/ESRL Physical Science Division)

The first map shows lower than average temperature anomalies for the D.C. area from December to February during years that D.C. experienced high snowfall years of at least 20".  The average seasonal snowfall in D.C. is 15".  These regional lower temperatures should be expected as a result of vast snow-cover reflecting solar radiation that would otherwise be absorbed by the Earth's surface as heat without the snow-cover.  Another interesting result is how most of the continental U.S. also tends to experience low temperature anomalies during D.C. high snowfall years.

 U.S. Winter Precipitation Rate Tendencies (NOAA/ESRL Physical Science Division)

U.S.Winter Soil Moisture Tendencies (NOAA/ESRL Physical Science Division)

The next two maps show that high D.C. snow years tend produce above average precipitation rates (top) and slightly above average soil moisture (bottom).  High precipitation rates also typically result in high concentrations in soil moisture.  Similar correlation over the Ohio Valley has interesting results that low precipitation rates tend to lead to low soil moisture during years that D.C. has high snowfall.

Northern Hemisphere Winter Sea Level Pressure Tendencies (NOAA/ESRL Physical Science Division)

 
Global teleconnection signals can also occasionally be linked to repetitive weather events and associated climatic trends.  The next map (above) shows the tendency for a negative North Atlantic Oscillation (NAO) during D.C. snow years with higher than normal sea level pressure tendencies over the arctic region.  This result verifies the many scientific studies that a negative North Atlantic Oscillation (NAO) correlates well with Eastern U.S. low winter temperature anomalies.  

 

Winter Tropical Pacific Sea Surface Temperature Tendencies (NOAA/ESRL Physical Science Division)

The final map generated shows a strong El Niño signal during high D.C. snow years.  Not only does the map generate an El Niño signal, but also a Modoki El Niño signal where the warm sea surface temperature anomalies are centered over the central Pacific basin rather than the typical East Pacific El Niño. 

The NOAA/ESRL Physical Science Division products are excellent tools for generating atmospheric signals that can be verified with past, present, or future conditions.  This analysis for D.C. high snow years can be reproduced for other locations and weather events over various time periods of interest.  

Documenting a Year's Worth of Local Weather

Celebrating a Weather Station's One Year Anniversary



Today (September 2014) marks the one year anniversary of collecting continuous data from a weather station located in Northern Virginia. The station is mounted atop a 10 foot wooden post to allow the wind vane minimal interference. A dark plastic disk-like cover that was previously used as a flower pot base shades the temperature sensor from having excess direct sunlight. Always consider minimizing direct exposure to the sun when positioning a weather station or temperature readings may often be too high! Reflective aluminum foil was sealed underneath the weather station's flower pot cover to minimize heat from the darker colored solid plastic.

Weather data over the last year will be detailed from the station that includes readings of temperature, humidity, and precipitation observations. The automated measurements that were collected will be compared to those of the official local weather readings for the Washington, D.C. area.

Connecting Local Weather to Washington D.C.

The following graph shows how local temperature readings (red line) compare to those recorded for Washington, D.C. (blue line). Shockingly, there appears to be relatively strong statistical correlation for maximum temperatures between the two weather stations that are located approximately eight miles apart. What should end up being the highest annual temperature of 99 degrees for 2014 was recorded on July 2 for both stations. The lowest temperatures for 2014 for both stations again fell on the same day on January 19 when temperatures never rose above 19 degrees thanks to the polar vortex strong dips in the Jet Stream into the Continental U.S.


Daily Maximum Temperature Comparison

Comfortably Uncomfortable Proximity to Saturation 

Multiple factors of the state of the atmosphere determine your outdoor comfort levels. Humidity and temperature are included within these conditions. As already shown, temperatures between the D.C. airport and Virginia weather stations have little variability, but the next graphs show different results. The top relative humidity graph values for the Virginia weather station (green line) almost always exceed those that are recorded for D.C. (burgundy line). This result is surprising, because the D.C. station is located where there are likely influences from the adjacent Potomac River.

Basic meteorology principles reveal how proximity to a water body can induce cloud development, but for some unknown reason, the relative humidity values from the top graph tend to be higher in the suburban Northern Virginia location about 8 miles west of the Potomac River. The precipitation comparison lower graph between the two stations does support the water proximity idea. D.C. precipitation (orange line) tends to often exceed Virginia's precipitation (purple line) from the weather station. Saturation occurs only when humidity rises to 100%. Soon after 100% humidity is exceeded, the atmosphere reaches supersaturation and precipitation will soon form. Typically, surface relative humidity values close to 100% can indicate precipitation is on the way, if not already falling.


Daily Maximum Relative Humidity Comparison


Daily Precipitation Comparison

Weather and Climate Data Analysis: Monthly Temperature Anomalies for Central Pacific Modoki and East Pacific El Niño Years

The goal was to compare monthly temperature averages in the continental U.S. to years that included a Modoki El Niño when above average sea surface temperatures were in the Central Pacific Ocean.  The years chosen were pulled from a publication in the Journal of the Meteorological Society of Japan, Differences in Teleconnection over the North Pacific and Rainfall Shift over the USA Associated with Two Types of El Niño during Boreal Autumn (Zhang et al. 2012).  East Pacific El Niño maps were also generated for comparisons.


The following graphics show U.S. monthly temperature anomalies (values relative to normal) compared to composite years that had El Niño conditions.  Meteorologists have continued to reiterate that a Modoki El Niño could develop later this year (2014), though the most recent trends have been toward a weaker event.
 

 

August Temperature Anomalies for years with Modoki El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

August Temperature Anomalies for years with East Pacific El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

September Temperature Anomalies for years with Modoki El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

September Temperature Anomalies for years with East Pacific El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

October Temperature Anomalies for years with Modoki El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

October Temperature Anomalies for years with East Pacific El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

November Temperature Anomalies for years with Modoki El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

November Temperature Anomalies for years with East Pacific El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

December Temperature Anomalies for years with Modoki El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

December Temperature Anomalies for years with East Pacific El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

 

January Temperature Anomalies for years with Modoki El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

January Temperature Anomalies for years with East Pacific El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

February Temperature Anomalies for years with Modoki El Niño (NOAA Earth System Research Laboratory Physical Science  Division)

February Temperature Anomalies for years with East Pacific El Niño (NOAA Earth System Research Laboratory Physical Science  Division)