Late Monday temperatures were 30-50 degrees below normal in a widespread area from Dakotas to Texas and west to the Rocky Mountains. Map courtesy of weathermodels.com, NOAA
Guest contribution by Paul Dorian
While the tropical scene in the Atlantic Basin remains active, an explosion in the Arctic continues to bring record-breaking cold weather to parts of the western and central US, as well as some unusual snowfalls in the early season. In the meantime, tropical storm “Zeta” enters the Gulf of Mexico after a brief encounter with the region of the Yucatan peninsula in Mexico. It is very likely that it will return to hurricane status (Category 1) today and will land in southeast Louisiana tomorrow. The remnants of "Zeta" will combine with a strong low on the upper level over the US Southwest to create a significant rain event in the Tennessee Valley, the mid-Atlantic and the Northeast US from Thursday through early Friday. Enough cold air will be wrapped in the powerful system on Friday to cause a switch to snow so that parts of the northeastern US will accumulate snow for the first time of the season. All of this is followed by a cold Saturday Halloween, with temperatures in the mid-Atlantic / Northeast US about fifteen degrees below normal.
Numerous record or near record low temperatures on Monday October 26th in the central and western United States. The lowest temperature ever recorded for the month of October was observed in many places. Card courtesy of coolwx.com, NOAA
Some amazingly cold and unusually accumulating snowfalls
The Arctic cold has been historic in parts of the western and central US for the past few days, and some long-standing low temperature records have been completely destroyed. In fact, late Monday temperatures were up to 30-50 degrees below normal in a widespread area from Dakotas to Texas and in the west across the Rocky Mountains.
Numerous record or near record low temperatures on Tuesday, October 27, in the central and western United States. The lowest temperature ever recorded for the month of October was observed in many places. Card courtesy of coolwx.com, NOAA
An example of the extreme cold was in Denver, Colorado on Monday, where the high temperature was 15 ° F. Not only was this the coldest high temperature ever recorded in Denver in October, but it completely destroyed the previous daily record for October 26 by halving the comparatively “mild” 31 ° F set in 1923. The Denver records go all the way to 1872 (i.e. 142 years) and the previous coldest high temperature in October was 18 ° F. The low temperature in Denver this morning was a record 8 ° F. Another example of the extreme cold there was it in Bozeman, Montana, where earlier today a low temperature of -20 ° F was measured, which is 31 degrees below the previous record of + 11 ° F. After all, the amazing cold in the Rockies today had a low temperature of -26 ° F in Laramie, Wyoming which, if checked, would not only break the monthly record for the month of October by 8 degrees, but would also tie the coldest temperature would for every day in November.
In terms of snow, accumulations in parts of New Mexico and Texas will be significant over the next 36 hours, with more than half a foot in places on top of what has already come in. Up to a foot and a half were observed in some areas of the Colorado Rockies yesterday. Earlier in this extended cold spell, snow accumulated impressively in an area stretching from the inner northwest to the northern plains. For example, Great Falls, Montana experienced the snowiest "one-day" ever in October and also the greatest "two-day" snowfall of all time. In Alexandria, Minnesota, the snowfall this month has already made the largest snowfall for the month of October.
Tropical storm "Zeta" is likely to land in southeastern Louisiana tomorrow – perhaps as a Category 1 hurricane. Map courtesy of NOAA / NHC
Tropical storm "Zeta" … significant rain event … accumulated snow threat on Friday in the northeast of the USA
While the western and central US is experiencing unusual cold and snow, the Atlantic Basin is still tropical. "Zeta" is now classified as a tropical storm, having weakened slightly in the night hours when it struck the northeastern part of Mexico's Yucatan peninsula. This tropical system is now entering the Gulf of Mexico and is likely to return to Category 1 hurricane status later today if it moves over the still relatively warm water. By later tomorrow, "Zeta" will likely land in the southeastern part of Louisiana – likely a Category 1 hurricane. This will be the sixth direct hit of the tropical season in the state of Louisiana, and "Zeta" entered the 2020 record books by taking the 2005 season for the highest number of named storms in a given year. While the number of storms mentioned may be the same now, the strength of the storms in 2005 was significantly higher on average than this year. Of the 27 named storms in 2020, only four achieved major hurricane status (i.e., Category 3 or higher), while there were seven majors in 2005, also a record.
Thursday through Friday, a major rain event hits the Tennessee Valley, the mid-Atlantic and the northeastern United States with the combination of the remains of "Zeta" and a sharp low on the upper level. Map courtesy of NOAA / WPC
Upon landing, the remnants of "Zeta" will rotate northeast and connect to a strong low on the upper level over the US Southwest to create a strong storm system and significant rain event over the Tennessee Valley, the mid-Atlantic region and the Northeast the US generate Thursday through Friday. By late Thursday evening and early Friday morning, this powerful storm will likely be off the mid-Atlantic coast and a cold mass of air will be wrapped up. As a result, there is a good chance that some of the higher elevation, interior areas of the Northeast US (e.g., Poconos, Catskills, Hudson Valley) will see a switch from rain to snow, with piles certainly on the table. In fact, snow can accumulate as far as the coast in southern New England, and flakes are possible as far as New York City in the south and east.
In fact, in parts of the northeastern US, it is possible to accumulate snow on Friday, as shown here by the forecast of the 06Z Euro model. Map courtesy of Weather Bell Analytics, ECMWF
First freeze possible and a cold Halloween in the mid-Atlantic / Northeast USA
After the storm has departed, the mid-Atlantic and northeastern US will be pretty cold on Friday evening, with the first sub-zero temperatures possible – even in the corridor from DC to Philly-New York City. If Saturday actually brings the first freeze of the season, it marks the shortest growing season in some areas (e.g. Chester County, PA: Source Paul Callahan, Twitter) since 2002, with 174 days between freezes. On Saturday, mean temperatures in the mid-Atlantic / Northeast US could very well be fifteen degrees below normal, which means a pretty cold time for trick or treating as we close the month of October. In fact, temperatures could be in the single digits by early Saturday in southern New York state, where there could be a decent snowfall on the ground.
One final note: this is the weekend when the clocks will go back from early Sunday morning, November 1st.
Meteorologist Paul Dorian
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