When major snow storms hit the central and northern Plains of the U.S., the blame can more than likely be placed on the occurrence of a 'Panhandle Hook Low.' These types of lows tend to be responsible for the heaviest snow events of the season each winter. The most epic snow events in history will oftentimes trace back to the passage of an intense Panhandle Hook Low. The famous Armistice Day Snow Storm, which will live forever in weather lore, was one of the most intense heavy snow and wind events that has ever occurred in the northern Plains. The track of this historic system is shown below. It depicts the characteristic 'hook' northward that these systems exhibit once they enter the southern Plains. This epic storm dropped two feet of snow on parts of central Minnesota. Due to sustained winds of over 50 mph at times during the storm, snow drifts of up to 20 feet were reported in parts of west-central Minnesota. Thankfully, most Panhandle Hook Lows are far weaker than this one that hit back in November of 1940. In this blog, I will take you through the development cycle of a typical Panhandle Hook Low, while giving you an understanding of what can be expected when one of these systems tracks in your direction.
The origin of most Panhandle Hook Lows can be traced far to the west, out over the Pacific Ocean. These systems will first be noticed in the U.S. when they push onshore along the West Coast. Depending on the orientation of the jet stream, these lows can make landfall anywhere from Washington State down through California. Gusty winds and soaking rains will fall in the valleys and coastal regions, while heavy snows occur in the mountains. As these systems progress eastward and run into the towering Rocky Mountains, they start to weaken and lose their structure. Once these systems reach the eastern range of the Rocky Mountains, they are oftentimes just a shadow of their former selves. At this point, the system has typically made it into central Colorado or New Mexico. As the low emerges in the western Plains, the low will often begin its reintensification process. This is when the low can be referred to as a lee-side low. Lee-side lows are called such because they develop in the lee (or downwind side) of the Rocky Mountains.
When the jet stream is oriented from west to east over the Rocky Mountains, lee-side troughing occurs. This occurs when the air is first forced up the mountains and then proceeds down the leeward side. The larger the drop in elevation is on the lee-ward side, the more enhanced this process becomes. Some of the most severe elevation drops in the lower 48 occur just east of the Colorado Rockies, making it a prime location for the development of lee-side low pressure systems.
Once the remnants of these Pacific lows reach eastern Colorado or the Panhandle region of Texas, they are essentially reborn. Thanks to the effects of lee-side troughing, the low starts to intensify into a stronger surface low as it heads into the western Plains. At this point, the low can now be referred to as either a Colorado Low or a Panhandle Hook Low. As the low circulation strengthens, warm and moist air from the Gulf of Mexico is driven northward. Meanwhile, frigid, arctic air masses are oftentimes looming to the north. These contrasting air masses act to further strengthen the low as it continues heading northeast across the Plains.
These systems can produce major severe weather outbreaks across the southern Plains, especially during the early part of the spring season. Meanwhile, heavy snows and blizzard conditions will reside on the north and west sides of these lows. There is also typically a transition zone with these systems, where a mix of sleet and freezing rain occurs. This is due to the fact that the warmer air arriving from the south rises over the dense layer of cold air that resides to the north. This layer of warmer air aloft is referred to as the inversion layer. Diagnosing these varied precip types can prove to be quite difficult, due to uncertainties involving the timing and eventual track of these lows. Once the low heads northeast of the Great Lakes, a strong southward surge of arctic air can be expected in its wake. Bitterly cold, arctic high pressure systems will often follow the passage of a hook low, bringing another added effect of these systems.
When folks in the Plains recount major snow events from past winters, it's likely that a hook low was to blame. These lows are not a common occurrence during most winter seasons, but when they do occur, they can be memorable. For those who are interested in maritime history, many shipwrecks over the Great Lakes can be blamed on the manifestation of an historic hook low. The Armistice Day Storm of 1940 was responsible for the sinking of 3 large freighters on Lake Michigan. 75 mph winds and wave heights of over 20 feet occurred during the peak of this storm, making it one of the most tragic days on record for Lake Michigan. Another notable Panhandle Hook Low was the infamous Halloween Blizzard, that occurred back in 1991. Once this epic storm was finished, residents of Duluth, MN, were given the formidable challenge of digging out from nearly 37 inches of snow. These historic storms are much more grandiose than most Panhandle Hook Lows. Nonetheless, when one of these systems heads into the Plains, be prepared for the variety of conditions they can bring.