You may have heard of the Pineapple Express, which is the tremendous atmospheric river (river of deep moisture, originating in the tropics near Hawaii) that brings flooding rainfall to the West Coast. However, there is the other Express……….the Mayan Express. This brings flooding rains to the Tri-State, usually in the cool-season. It work in tandem with the MJO (Madden-Julian Oscillation) & occurs as a stream or river of very deep moisture through the atmosphere from the northeast Pacific to the Ohio Valley, even New England. They can be forecast up to two weeks out & have brought historic flooding in winter.
Its flooding occurs usually with a blocking Bermuda type high funneling usually high PWAT (Precipitable Water) values through the low-levels of the troposphere. The ridging through the southeastern U.S. blocks movement of an upper trough in the Plains, while a surface front stalls Arkansas to the Northeast. Waves of surface lows ride the front, enhancing the rainfall. Not only is the rainfall enhanced by this, unusually deep moisture of the Bermuda high & the atmospheric river from the tropics, but the lack of movement of the axis of moisture keeps it raining heavily over the same area for up to 30 hours.
With this usually occurring in the winter to very early spring, when plant uptake of water is low & soils are typically, seasonally wet, flooding risk is high. Flash flooding usually transitions to a river flooding event.
The biggest cool-season flooding events in our region have occurred in this situation like March 1997, March 2008…………even February 1882, 1883, 1884, February 1904….etc.
December 1846-January 1847 & December 1847-January 1848 saw event indicative of “Mayan Express” events with widespread flash, then river flooding.
IMAGES COURTESY OF NOAA:
FIGURE 1: MAYAN EXPRESS PATTERN
FIGURE 2: PINEAPPLE EXPRESS
FIGURE 3: EXAMPLES OF THESE ATMOSPHERIC RIVERS
Early December 1847 saw heavy rainfall in a 30-hour event with 6″ rainfall reported in parts of western Kentucky atop wet soils. The heavy rainfall was reported as far north as Quebec with unusually warm weather & the St. Lawrence River in Quebec completely free of ice & flooding in mid-December. Most river systems from the St. Lawrence to the Connecticut to the Schyullkill to the Miami to the Ohio, White & Wabash Rivers were in significant flood by mid-December of 1847. Many bridges were washed away & many towns were completely submerged.
A similar event occurred in December 1846-January 1847, too. What is interesting is that like these two years, multiple consecutive Februarys saw significant floods 1882, 1883, 1884.
On a side note, which will be another entry, a significant snow storm hit the Ohio Valley to Northeast during this river flood in mid-December 1846. 16″ fell at Owensboro, 18″ Cincinnati, Ohio, 14″ Columbus, Ohio.
Another storm in late December dumped 6″ of snow in parts of South Carolina & +8″ in parts of North Carolina.
This was a vast supply of moisture!
The melting of this snowfall in the Ohio Valley & Northeast kept rivers above flood stage into January.