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    Jesse Ferrell

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    Chesapeake, Pontchartrain: Lake-Effect?

    February 20, 2007; 9:07 PM ET

    UPDATE: Blog reader John noted that Long Island Sound sometimes has lake-effect too, and I'll link to this page which explains it more. Blog reader Justin sent in a link to a snow event in eastern Florida that was caused by the Atlantic Ocean in 2003 and I have added that link below. Other readers also submitted some stories of Chesapeake Bay-Effect Snows from their recollections:

    Gordon: January 1994: "Local weathercaster said winds were blowing straight down the bay, causing it"
    John: 1994-1996? "10 inches when the local mets were predicting flurries"
    Samuel: "Virginia Beach & lower eastern shore have reported bay-effect over the past few years"


    I have received a few interesting emails from very inquisitive blog readers this month regarding Lake-Effect snow, and I'd like to respond to them.

    1. Could Lake-Effect Snow Occur From The Chesapeake Bay?
    2. Could Lake-Effect Snow Occur From Lake Pontchartrain in Louisiana?
    3. Could Lake-Effect Snow Occur In the Southeast From The Gulf of Mexico or Atlantic?
    4. Could Lake-Effect Rain Happen?

    First, in regards to #1 and #2, there's nothing special about the Great Lakes, except that they are great, meaning large, and located far enough north that they see frequent cold outbreaks. So Lake-Effect Snow could occur anywhere, provided the air is cold enough and the lake is warm and large enough.

    #1: Chesapeake Bay Effect: That said, research has been done on Chesapeake Bay's probabilities for lake-effect and this page proves that it should be possible As the page points out, there are no hills to provide additional ("orographic") lift for a lake-effect event, so the meteorological requirements would have to be more stringent here. Add that to the fact that the bay is barely big enough to support the phenomenon, and the fact that the area is less likely to suffer cold outbreaks because it is further south and next to the Atlantic Ocean, and you begin to realize that, while it is theoretically possible, it would be quite rare. However they do have an event, in 1999, documented with a radar loop (still image shown at right). COMET says that it has occurred there, and it has occurred on Delaware Bay and this page quotes it happening in 1996.

    #2: Lake Ponchartrain Lake-Effect: Lake Pontchartrain is much smaller, just over 30 miles across at its maximum width (per a map on WikiPedia). The article mentioned above quotes the minimum documented fetch for lake-effect to occur as 40 km (25 miles), sighting Lake Tahoe, Nevada, from which lake-effect snow has been observed. ("Fetch" is the length of water over which the cold air can flow before hitting land). Wikipedia claims that the maximum length of Lake Tahoe is 35 km (22 miles) but close enough. So, in theory it is possible. Only one lone post I could find on Google claims that it did happen, in December 2003. The author of the site has no valid contact information and all attempts to contact him have failed. An email inquiring about the possibility of Lake-Effect snow on Lake Ponchartrain that I sent to the NWS office in New Orleans earlier this month has gone unanswered. So for the moment I'm calling this one "Plausible" (but unproven).

    #3: Gulf-Effect (or Ocean-Effect) Snow in the Southeast: Could it snow in the Northwest corner of Florida as a result of cold air moving over that corner of the Gulf of Mexico? The previously mentioned post again claims it is so, as does an uncited reference in the WikiPedia entry for Florida. The fetch is certainly sufficient, if the winds came from the Biloxi area into West Florida. UPDATE: Blog reader Justin gave me this URL where ocean-effect snow is documented -- and on the East Coast of Florida nonetheless.


    #4: Lake-Effect Rain & Lake-Effect Shadow: Lake-Effect rain does happen and has been documented by The NWS [JessePedia] in Buffalo, as has the elusive "Lake Oasis Effect, a type of "lake-effect shadow" where cloud formation is discouraged (see illustration above).

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