U.S. Spring Flood Forecast: No Widespread Major Flooding Expected

By: Jeff Masters and Bob Henson , 4:35PM,GMT on March 20,2015

No widespread major flooding is expected this spring in the U.S., NOAA said on Thursday in their annual spring flood risk forecast. Rivers in western New York and eastern New England have the greatest risk of spring flooding because of a heavy snowpack of 3 to 9 inches of snow water equivalent, coupled with the potential for heavy spring rain to fall on the snow and cause a sudden melt-water pulse. Significant river ice across northern New York and northern New England increase the risk of flooding related to ice jams and ice jam breakups if there is a quick warm-up with heavy rainfall. The latest 16-day forecast from the GFS model does not call for any heavy rainfall events capable of triggering widespread moderate flooding through the end of March, though.

Areas at risk of moderate flooding:
Eastern New England and western New York
Lower Missouri River basin in Missouri and eastern Kansas
Lower Ohio River basin including portions of southern Illinois, southwestern Indiana, and western Kentucky.


Figure 1. The NOAA spring flood forecast shows about one-third of the country is at risk of minor to moderate flooding, but there are no areas at high risk of major flooding. Image credit: NOAA Spring Flood Forecast.

Flood categories are defined by NOAA as follows:
Minor Flooding: Minimal or no property damage, but possibly some public threat (e.g., inundation of roads).

Moderate Flooding: Some inundation of structures and roads near streams. Some evacuations of people and/or transfer of property to higher elevations.

Major Flooding: Extensive inundation of structures and roads. Significant evacuations of people and/or transfer of property to higher elevations.

Drought a bigger concern than flooding in the U.S. this year
Meanwhile, widespread drought conditions are expected to persist in California, Nevada, and Oregon this spring as the dry season begins. “Periods of record warmth in the West and not enough precipitation during the rainy season cut short drought-relief in California this winter and prospects for above average temperatures this spring may make the situation worse,” said Jon Gottschalck, chief, Operational Prediction Branch, NOAA’s Climate Prediction Center. El Niño finally arrived in February, but forecasters say it’s too weak and too late in the rainy season to provide much relief for California, which will soon reach its fourth year in drought. Current water supply forecasts and outlooks in the western United States range from near normal in the Pacific Northwest, northern Rockies, and upper Colorado, to much below normal in the southern Rockies, portions of the Great Basin and in California:

·      Columbia and Snake Rivers - Median forecast at The Dalles is 82% of average
·      Missouri River - Median forecast at Toston is 86% of average
·      Colorado River - Median forecast inflow to Lake Powell is 71% of average
·      Rio Grande and Pecos River – Median forecasts generally range from 60% to 105% of average
·      Great Basin – Median forecasts range from 35% to 75% of average for most locations
·      California - Median forecasts range from less than 20% to 50% of average


Figure 2. The March 19 NOAA drought outlook calls for drought to persist in California, Nevada, and Oregon through June with the onset of the dry season in April. Drought is also forecast to develop in remaining areas of Oregon and western Washington. Drought is also likely to continue in parts of the southern Plains and in Minnesota. Image credit: NOAA Climate Prediction Center.



WunderPoster of the week: Sundog!
Even though it’s unclear how they got their name, we do know what it is that produces sundogs (also written “sun dogs”), the phenomenon highlighted in this week’s WunderPoster (Figure 3, right).

Normally seen as a pair of bright spots, and sometimes referred to mock suns, sundogs occur in the presence of very thin ice-crystal clouds such as cirrus or faint cirrostratus. They form when sunshine is refracted horizontally through the sides of plate-shaped crystals that face upward and downward within the cloud. Each sundog is located 22° away from the sun, with a visible halo often connecting the sundogs.

All WunderPosters can be downloaded in formats suitable for posters or postcards. There’s also still time for you to provide photographic inspiration for a new WunderPoster, as part of the 20th anniversary celebration of Weather Underground. The deadline for submissions is April 2. Our “picture yourself here” website has all the details.



Figure 4. This pair of sunrise sundogs appeared above snow-covered fields on Feb. 5, 2014, near Seward, Nebraska. Image credit: wunderphotographer lindag47.

Have a great weekend, everyone!

Jeff Masters and Bob Henson