Geographic Centers: Comparative Weather and Climate (Reflection 1)

Comparative Weather and Climate of Duluth, Minnesota & Vienna, Austria

Vienna in wintertime.  Like Duluth, polar airmasses bring cold winters,
however, outbreaks of arctic air do not reach Vienna or bring the
extreme chill felt in Duluth.  In January, averages temperatures in
Vienna are 20 degress warmer than in Duluth. Image retrieved from:
 2005worldtrip.com/images/aus-wintervienna320.jpg

Vienna, Austria, blogged by Claire Brewer, is related to the the location of this blog primarily through a characteristic of geography.  Just as Duluth

falls near the geographic center of the North American landmass, Vienna is located near the center of the European landmass. 

While both regions experience a humid continental climate, there are many variations between the two.

Climatograph for Vienna, Austria showing several variables.  Note the low average sunlight received (Claire's blog noted persistent cloud cover in Vienna) and flat average wind speed curve. Retrieved from climatetemp.info.

Climate characteristics of Duluth, MN.  Note incresed wind speed during all but summer months.  Retrieved from climatetemp.info. 

The graphs above provide a basis for comparison of Duluth and Vienna.  An initial similarity between the two locations is found the black curve, relative humidity ranging from ~60-80%,  which is expected in a humid continental climate regime.  Also, both cities also fall within latitudes (~30-60 deg. N/S) that experience mid-latitude cyclones (See fig. below).  However, this is where the similarities end.    

A developing mid-latitude cyclone typical for Europe.  Convergence of cold dry cP air with warmer, moist mP air over the Atlantic sets up the systems which track eastward due to jet stream flow.  The heaviest precipitation falls in the British Isles where orographic influences exist.  Yet, an absence of north/south mountain ranges creates little impedement for a mid-latitude cyclone to move towards Vienna (approximate location shown on the image as a black star). 
 Image retrieved from: www.fas.org/irp/imint/docs/rst/Sect14/AAAMBHBA.jpg

Airmasses:
The airmasses which affects Duluth and Vienna are the main cause of variation, continental polar (cP) and maritime polar (mP), respectively   The climatographs show that Vienna experiences a milder winter in comparison to Duluth likely because of the influence of mP air, which is warmer than cP air, since the ocean will retain a higher surface temperature than that of a continental landmass.  Just as summer heat is mellowed by cool wind from Lake Superior, Vienna's summers are mild as a result the cool marine influence (mP), brought in by prevailing westerly winds.


Precipitation and Severe Weather:


Surface heating in both locations leads to summer showers and thunderstorms, yet Duluth experiences a greater spike in summertime precipitation.  Considering the East-West trend of topographic features, the Swiss Alps squeeze out the moisture moving from Mediterrean, which leaves the Altlantic-based mP airmass as Vienna's source of precipitation.  Far inland, Vienna receives little of the moisture and experiences a drier summer in comparison.  In Duluth, evaporative processes over the Great Lakes combined with the northward advance of mT air from the Gulf results in moister conditions and more precipitation.  For example, in June, Vienna receives 10" whereas Duluth doubles the figure with 20".



Devastation of August 1969 tornado near Duluth.  A reported 15 people were killed.  Retrieved from: hill.areavoices.com/files/2010/09/boulderlake1-1024x715.jpg


Both locations are susceptible to tornadoes, especially Duluth which lies on the northernmost extent of North America's "Tornado Alley."  Moist Gulf air will contact the cold, dry cP airmass that affects Duluth, however, the occurrence rate is significantly lower than the annual state average of 27.  On the other hand, only 1.2 tornadoes occur per year in the greater Vienna region as cyclonic conditions are rare. 




Sources:


Airmasses Over Europe: http://meteorologytraining.tpub.com/14312/css/14312_104.htm


Minnesota Tornado History and Statistics: http://climate.umn.edu/doc/historical/tornadic.htm


Tornado Climatology of Austria: http://tordach.org/at/Tornado_climatology_of_Austria.html

Weather and Climate Playmakers (Blog 2)

Duluth's Weather and Climate Playmakers: Air Masses, Fronts, and Unique Factors

• Air Masses

The air mass which has the greatest effect on the weather and climate of Duluth, MN is cool, dry Contintental Polar air that is present year-round.  The much colder and very dry Continental Arctic (cA) air mass often pushes southward into Duluth during the winter, however, the mass quickly receeds due to summertime insolation of the northern latitudes.

Duluth lies well within the exent of the cP air mass which brings cool air that mollifies
the summer heat; a buldging of the the cA in the winter months brings bitter cold.

Occasionally, summer heatwaves can occur when warm Marine Tropical (mT) and Continetal Tropical (cT) airmasses push northward into the region.  A late season push of mT air has the potential for early snowstorms as was seen in 1991 (See figure below).

The Halloween Blizzard of 1991.  A warm, moist mT front swept north from the
Gulf of Mexico that pounded Duluth with 36.9" of snow.

• Fronts and Mid-Latitude Cyclones

Although mid-latitude cyclones often mature further south, Duluth is still affected by these cyclones.  The diagram below shows Duluth in the center of the the occluded low pressure, just at the tail of the cold occlusion.

This low pressure "land-bomb" late October, 2010 was touted as stronger
than the historic storm that took the Edmund Fitzgerald.

Mid-latitude cyclone with occlusion and low pressure system near Duluth.

The "Current Fronts" map shown below indicates a cold front moving towards Duluth. With no warm front visible in its path, it is unlikelythat an occluded front will form and spawn a mid-latitude cyclone. This will likely push through bringing cooler temperatures in the next few days.

Weather Underground Front Map shows advancing cold front.

• Unique Factors

In addition to the topographic and other factors introduced in the previous blog, there are several others worth mentioning: 

 -Ice Storms:  Related to the topography, the lake provides frequent, near-freezing but moist easterly winds that when forced to rise over Duluth's topographic barrier drop below freezing.  Advection of cold air from the lake bolsters the process and the city freezes over.

Iced branches near Lake Superior's north shore

-Alberta Clippers: Fast-moving low pressure systems that form in the Canadian Rockies then cut across the upper Midwest.  The clippers bring bitter cold to Duluth and drive engine block heater sales.

"Exact Storm Track Uncertain;" clippers are small and fast which complicates forecasting

-Colder by the Lake:  As stated in the previous blog, Lake Superior helps keep Duluth cool in the summer, but when the head of the lake freezes in winter cold air sinks to lower elveation and pools at lake level.

During the winter, locations on Duluth's western ridge are often several
 degress warmer than those along the shore where cold air is occluded from interaction with the
warmer water by a layer of ice and snow.

-Thundersnow Captial of Upper Midwest?: Cloud to ground lightning alongside snowfall can be seen in Duluth on rare but instances; on Jan. 1, 2005 the national Weather Service recorded 6" of snow in two hours.  Over data ranging from 1960-90, the Duluth region led the Middle and Upper Mississippi Valley in frequency of thundersnow storms.



Sources:

"Air Masses."  http://www.srh.noaa.gov/jetstream/synoptic/airmass.htm.

"An Immaculate Mid-Latitude Cyclone and its Decay." http://www.washingtonpost.com/blogs/capital-weather-gang/post/an-immaculate-mid-latitude-cyclone-and-its-decay/2011/09/27/gIQAEaTt1K_blog.html.

"Duluth (Orographic City) Local Influences." http://snincr.net/duluth_local_effects/duluth_local_effects.php

"Duluth Storm Tracks." http://snincr.net/winter_profiles/DuluthMN.html.
"General Climate Description of Minnesota." http://climate.umn.edu/doc/online_resources.htm

"20th Anniversary of the Halloween Blizzard."  http://climate.umn.edu/doc/journal/halloween_blizzard_20th.htm.

 "Weather and Climate - Cyclone Image." http://www.mrsciguy.com/weather.html.