9:40 AM | *Drought conditions across the US – about as good as it gets*

Current US Drought Monitor map with only 1.60 percent of the nation experiencing D2 (severe), D3 (extreme) or D4 (exceptional) drought conditions; courtesy NOAA and National Drought Mitigation Center (NDMC) at University of Nebraska-Lincoln

Overview
It is not often that “severe”, “extreme” or “exceptional” drought conditions are limited to only 1.6% of the continental US, but that is exactly what is currently taking place.  Going back to the year 2000, only February and March of 2010 had similar limited drought conditions on a nationwide basis that we are enjoying today.  In fact, the news may actually get better with the next “drought monitor” update as the numbers cited in today’s posting reflect only precipitation data registered through last Tuesday, April 4th and does not include the substantial rainfall that fell late last week in California and across the southern and eastern US.
 

Western US drought conditions from one year ago (left) to current (right); courtesy NOAA/CPC

Discussion on current and recent conditions
In recent years, much of the western US was suffering through widespread and deep drought conditions, but that has changed dramatically in recent months; especially, in the state of California.   One year ago, much of California was in the midst of an “exceptional” drought – the worst category of drought as classified by NOAA - but all of that has changed dramatically this winter season with a tremendous amount of rainfall throughout the state.  In fact, drought conditions have improved to the point that nowhere is the state classified by NOAA/NDMC as experiencing “exceptional” (D4) or “extreme” (D3) drought conditions and less than one percent of California is currently experiencing “severe” (D2) drought.

Sierra Nevada Mountains provide more than 60% of California's developed water supply

In addition to the recent  rainfall in California, there has been an extreme amount of snow this winter season in the higher elevations of the Sierra Mountains across eastern California.  Snowpack in the Sierra Nevada region plays a critical role in California’s water supply as a natural form of water storage.  In fact, more than 60% of California’s water originates in the Sierra Nevada region.  There has actually been so much snow this winter in some of the higher elevation locations that the National Guard has been called out to help with the removal of the snow.  Another 3 or 4 feet of fresh snow piled up in the Sierra Nevada Mountains on Friday of last week in the latest major storm to affect California with significant rain and snow.

While not nearly as bad as the recent extended and deep California drought, much of the south-central and eastern US experienced dry weather during the fall and winter seasons and this led to the declaration by NOAA/NDMC of “abnormally dry” (D0) or “moderate” (D1) drought conditions in many areas.  Like California, recent significant rainfall events during a very active weather pattern have improved overall conditions in many regions across the south-central and eastern US. 

The Palmer drought index, sometimes called the Palmer drought severity index and often abbreviated PDSI, is a measurement of dryness based on recent precipitation and temperature. The Palmer Drought Index is based on a supply-and-demand model of soil moisture. Drought conditions were extremely widespread and severe in July 1934 during the midst of the “Dust Bowl” era. 

1930’s – about as bad as it gets in terms of drought (and heat)
Any drought talk of recent years really pales in comparison to what happened in this country during the decade of the 1930’s.  “The Grapes of Wrath” is a book written by John Steinbeck that was published in 1939 and it captured well the plight of millions of Americans whose lives had been crushed by what is referred to as the “Dust Bowl” era.  The 1930’s still ranks as the hottest and driest in US recorded history and the “Dust Bowl” was truly a significant event in our national history. 

The figure on the left shows the annual values of the U.S. Heat Wave Index from 1895 to 2015 for the contiguous 48 states. An index value of 0.2, for example, could mean that 20 percent of the country experienced one heat wave, 10 percent of the country experienced two heat waves, or some other combination of frequency and area resulted in this value.  Data source: Kunkel, 2016 (EPA).  The figure on the right shows the number of all-time maximum temperature records at USHCN weather stations that reached extreme heights in 1936 - far and away above any other year.

Conditions were so dry in such a widespread part of the country that dust storms formed numerous times in the Central Plains as loose soil turned to dust which the prevailing winds blew away in huge clouds that blackened the skies – even as far away as the east coast. The drought came in three waves during this decade, 1934, 1936 and 1939-1940, and tens of thousands of families had to abandon their farms.     

Yes, these are pretty fortunate times we are currently living through across the US when it comes to drought.

Meteorologist Paul Dorian
Vencore, Inc.
vencoreweather.com