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OH: Drought Monitor

PA: Drought Monitor

NOAA Drought Monitoring Page

Otherwise known as the "creeping disaster," a drought does not start or end in a sudden fashion. There are no weather radio alerts, no winds tearing off roofs or knocking down trees, no rush of water with dramatic rescues to capture the nation’s attention. However drought impacts have a huge price tag. Just think of the damage to your lawn or garden? Multiply that by the thousands of other homeowners in the same situation. How about the farmers? The tourist industry? Water Departments? In fact, droughts rank second in types of phenomena associated with billion-dollar weather disasters during the past three decades. With annual losses over 5 Billion dollars per year, drought is a serious hazard with substantial socioeconomic risks for the United States.

As of July 17, much of Ohio was classified in the moderate category on the U.S. Drought Monitor (upper-left). Northwest Pennsylvania is considered to be abnormally dry (lower-left).

The area has been running around 70% of normal precipitation over the last 60 days preceding July 21 (below).

60-day percent of Normal Precipitation

USGS Map of 28-day average streamflow compared to historical streamflow for the day of the year.

28-day average streamflow compared to historical streamflow

While much of the local area has been running below normal, significant portions of the midwest, including northern Indiana and most of Illinois, have been experiencing a severe hydrologic drought with stream flows well below normal.

United States - Vegetation Health Index (VHI): Satellite observations are principally represented by the Advance Very High Resolution Radiometer (AVHRR) flown on NOAA Polar-orbiting satellites. The satellite global VH system is designed to monitor, diagnose and predict long- and short-term land environmental conditions and climate-dependent socioeconomic activities. For more on the vegetation health index click here.

vegetation health index

VHI is a proxy characterizing vegetation health or a combine estimation of moisture and thermal conditions. It is often used to estimate crop conditions. Indices below 40 (such as across extreme western Ohio and most of Indiana), then there is vegetation stress and potential loss of crop and pasture production.

What is drought?

Q. At what point does a precipitation deficit become a drought?

A. Droughts are measured by their impacts. A drought occurs when precipitation deficits cause negative impacts to occur. The impacts can vary from agricultural, hydrological, meteorological, or socioeconomical.

Q. How does the National Weather Service define a drought?

A. Establishing the presence of drought is both a science and an art. The NWS works with the National Drought Monitor to define drought. The National Drought Monitor (NDM) is a classification tool for drought in the United States. The Drought Monitor is updated weekly (usually Thursdays), and is a multi-agency effort (such as the USDA, NOAA, and the National Drought Mitigation Center).

Q. How is the National Drought Monitor made?

A. Quantifying a drought is not an easy task. Nearly 350 people from several different agencies provide their expertise into the severity of the drought in their region. The NDM uses this input in conjuncture with indices, indicators, and objective blends of data.

Q. How is the drought classified?

A. One of the keys to the success of the monitor is its use of a drought intensity scale similar to the Enhanced Fujita scale for tornadoes and Saffir-Simpson scale for hurricanes.

Drought Monitor Intensities

D0- An intensity level of D zero corresponds to 'Abnormally Dry'; conditions. At this level, an area experiences short-term dryness that is typical with the onset of drought. Such dryness can slow crop growth and elevate fire risk to above average. This level also refers to an area coming out of drought, with lingering water deficits and pastures or crops not fully recovered. D zero is noted when a convergence of indicators fall into the 30th percentile. In other terms, this equates to roughly a 1 in 3 year dryness. : Note that for the D0 level, the area in question is only considered to be dry, not necessarily in drought conditions.

D1- An intensity level of D1 corresponds to 'Moderate Drought'; conditions. At this level, some damage to crops and pastures can be expected. Fire risk is high, while stream, reservoir, or well levels are low. Some water shortages are developing or imminent and voluntary water use restrictions could be requested. In terms of percentile rankings, D1 is the first "drought" class and falls into the 20th percentile, or a 1 in 5 year type event.

D2- An intensity level of D2 corresponds to 'Severe Drought';. At this level, crop or pasture losses are likely, fire risk is very high, water shortages are common, and water restrictions are typically voluntary or mandated. This category is the 10th percentile, which roughly equates to a 1 in 10 year drought.

D3- An intensity level of D3 corresponds to 'Extreme Drought';. At this level, major crop and pasture losses are common, fire risk is extreme, and widespread water shortages can be expected requiring restrictions. Duration and impacts are critical in looking at D3 droughts, which fall into the 5th percentile, or a 1 in 20 year type of drought.

D4- The final intensity level, D4, corresponds to 'Exceptional Drought';. At this level, there are exceptional and widespread crop and pasture losses, fire risk, shortages of water in reservoirs, streams, and wells that yield water emergencies. Worst on the scale, D4 can loosely be likened to a "once-in-a-generation" type of drought noted by the 2nd percentile, or a 1 in 50 year drought.

Q. Why don’t they just use rainfall deficits to determine drought?

A. As an abnormal moisture deficit, drought is typically measured against a 'benchmark';, such as a thirty-year average of precipitation, or so-called normal. Using such benchmarks, it is clear that some areas of the United States are much drier than others. This means that the hurdle for reaching an abnormal deficit leading to the onset of drought differ substantially from one region to another. For example, 50 percent of normal rainfall over 6 months would be a notable drought in New Jersey, while the same percent of normal in Arizona might be only unusually dry. When considering the spatial extent of drought, it is important to recognize the wild variability in the severity of drought that can occur over a short distance, due to terrain, weather patterns, and other effects.

How long will it last?

Short-term Relief?

In order to break the drought the region would need to overcome our precipitation deficits, fill reservoirs, and recharge soil moisture and ground water. Rainfall deficits on average of 6 inches since April have been known to occur in one storm, however the result of such a rain would most likely be flash flooding with extreme runoff. This does little but briefly raise the rivers and provide short lived moisture for crops. The ground needs to be able to absorb the rainfall before it runs off into storm drains or rivers. For this to occur, it is more efficient if we have light rain over a widespread area for a long duration. Is this common in the summer? Not typically. Normal rainfall over the summer months comes from thunderstorms and showers, which are “hit or miss” in coverage and can bring varying amounts of rain.

Drought Begets Drought

When a drought area grows as large as the current one across the country, it can have negative feedback by reducing the chance of future rainfall. As moisture moves into an area, the very dry air near the surface can quickly erode the moisture needed to produce rain, or greatly reduce the potential rainfall amounts. The ground is so dry that there's not enough moisture in the soil to evaporate into the atmosphere to cause rainfall. And since drier air is easier to heat up, that means a higher likelihood of more hot days. For our region, the weather systems come from the west. As these areas are currently experiencing even more severe droughts, there is even less moisture for us to tap into.

Long-term Outlooks

The NWS Climate Prediction Center ( ) seasonal outlook for August through October shows that the region will have a high likelihood of hotter than normal temperatures. Much of the Midwest is likely to be drier than normal, too. It is unlikely that the region will see any improvement until at least past October. If El Nino forms as predicted this fall, it would result in even more dry weather next winter for the Ohio and northwest Pennsylvania.

3-month temperature outlook3-month precipitation outlook

How does this drought compare to past droughts?

Droughts differ greatly in their extent, duration, and severity. There is great difficulty when trying to compare and quantify different droughts and especially for different locations.

The four significant droughts that affected OH and northwest PA were 1930-1936, 1939-46, 1952-57, and 1975-77. As of mid-July the drought of 2012 had just cracked into the top ten list of worst droughts. The worst drought in Ohio history occurred from 1930 through late 1931. This enormous drought covered most of the Midwest from Iowa, Missouri, Wisconsin, Michigan, Ohio, Pennsylvania, West Virginia, Kentucky, Virginia, New York and Maryland. The 1931 drought saw only 53% of normal rainfall from July-August in Ohio, and 43% in Pennsylvania. Though no records exist on the extent of previous droughts, those that were comparable to 1931 include 1881, 1894-95, and 1910 when looking at rainfall deficiency and attendant heat. The dust bowl drought years of the southern plains in the early 1930s was so significant, that the excess dust reached Ohio in March of 1935.

The 1952-57 drought was the most severe in terms of streamflows and ground water at many gaging stations in the state. The drought of 1975-77 droughts was widespread but only marginal in severity when compared to the other droughts.

The 1988 was relatively short mainly lasting from March through July, but it produced severe impacts. The average precipitation for the state of Ohio in June was only 0.85 inches, the lowest on record. The spring of 1988 was also one of the driest on record. All time record minimum river levels were observed in many areas across the State. Many municipalities mandated water use restrictions as levels were critical. In 1986 Lake Erie water levels were near record levels, yet by the end of 1988 were near normal. Above normal rainfall in July-November relieved the drought for most of the state.

Ohio Historic Droughts 1895- July 2012

Ohio Drought: 2011-2012 Compared to Past Droughts

Related web sites

Additional information on current drought conditions may be found at the following web addresses:

U.S. Drought Monitor...
NOAA Drought Page...
Climate Prediction Center (CPC)...
Midwest Regional Climate Center...

Additional river information...

Local Climate Water & Weather Topics:
Current Hazards, Ohio Conditions, Pennsylvania Conditions, Radar, Satellite, Climate, Safety
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Page last modified: 15 APR, 2012

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