US Drought Monitor November 7, 2017.

West Drought Monitor November 7, 2017.

Colorado Drought Monitor November 7, 2017.

Click here to go to the US Drought Monitor website. Here’s an excerpt:

Summary

A vigorous Pacific storm system and a series of low pressure centers traversing along a semi-stationary front in the eastern half of the Nation brought moderate to heavy precipitation to portions of the Northwest, the Ohio and Tennessee Valleys and eastern Great Lakes region, and parts of the lower Mississippi Valley and west-central Gulf Coast. With subnormal temperatures present, heavy snows fell on higher-elevations of the Cascades, northern Sierra Nevada, and northern and central Rockies, producing an early Water Year to Date (WYTD; Oct. 1-Nov. 7) basin average snow water content (SWC) much above normal across the northern half of the West, along with above-normal basin average precipitation. Unfortunately, the WYTD basin average SWC and precipitation values were below to much below-normal across the southern third of the West. In the East, strong upper-air energy and low-level moisture produced widespread showers and thunderstorms, including some that were severe, in the Ohio Valley. In contrast, little or no precipitation fell on Southwest, southern Rockies, much of the Plains, western Corn Belt, the Southeast, and along coastal New England. Temperatures averaged below normal in the Pacific Northwest, northern Rockies, northern half of the Plains, upper Midwest, and Florida while above-normal readings occurred across the Southwest, southern Plains, Southeast, Ohio Valley, East Coast, and Alaska. Drier weather returned to both Alaska and Hawaii after several weeks of ample precipitation while light to moderate showers fell across Puerto Rico…

High Plains

Cold weather and light precipitation (about 0.5 inches or less) occurred across most of the High Plains region, including light snow blanketing parts of the Dakotas and northern Nebraska. The combination of subnormal temperatures and light precipitation was enough to keep conditions from deteriorating, but not enough for improvement, thus no changes were made. The exception to this was some improvements made in southeastern Wyoming and adjacent southwestern Nebraska where short-term surpluses existed and most indices were normal or wet, even out to 1-2 years. Accordingly, D0 was removed in southeastern Wyoming and D0 and D1 slightly trimmed in southwestern Nebraska. The D0 and D1 remained where long-term indices were still negative. In South Dakota, winter wheat conditions continued to be poor, with the USDA condition index reported as the second lowest in the last two decades. Causes included the ongoing long-term drought impacts, and most recently the sudden cold spell…

West

This week’s weather pattern produced a story of the haves (northern half) and have nots (southern half) as a strong storm system brought plentiful precipitation to coastal and mountainous areas (including high-elevation heavy snows). Along coastal Washington, Oregon, and northern California, 1-4 inches of rain fell while the Cascades, northern Sierra Nevada, and northern Rockies reported 1-5 inches of liquid equivalents. After a rather wet September in Wyoming, Idaho, and Montana (although precipitation is normally low) and a wet October is Washington and Oregon, November has also started out wet in the Northwest, leading to favorable WYTD basin average precipitation and snow water content (SWC). Since October 1, the basin average precipitation was between 100-150% of normal across the northern half of the West while recent colder conditions have increased basin average SWC from 100-900%, although it is early in the season and normal SWC values are low. However, with the recent wetness across much of the northern half of the West, and since the abnormal dryness and drought were short-term in western and southern sections (e.g. Washington, Oregon, Idaho, southwestern Montana), it was easier to justify improvements across this area as compared to long-term drought in northern and eastern areas (e.g. northern and eastern Montana, the Dakotas). Accordingly, with most short-term deficits nearly erased or some areas now with surpluses, most USGS streams have risen to near or above normal levels, including western Montana’s Clark Fork, Bitterroot, and Blackfoot River basins that indicate they have recovered from the dry summer, and SPEI values during the past 2-3 months have been positive (wet) across most of Washington, Oregon, Idaho, and the southern half of Montana. The 2-month SPEI values, however, have remained negative (dry) across northern Montana but not as significant as earlier (thus less or no improvement here), but SPI values depicted significant improvements nearly statewide. Soil moisture continued to show low values along the U.S.-Canada border and northeast Montana, and it may be a while (spring thaw?) before we know if the soil moisture has truly improved. Large precipitation deficits remained in northeastern Montana, and stock ponds have water quality issues or no water currently. Unfortunately, cattle pregnancy terminations are likely due to the high nitrates in the feed due to the drought.

Further south, the opposite is true of the WYTD conditions, with subnormal basin average precipitation and SWC, including no snow at some Utah, Arizona, and New Mexico basins. But the majority of the cold season precipitation normally occurs later in the winter here, so there is still plenty of time left. However, due to a weak summer monsoon and early withdraw, 90-day deficits existed in northwestern and southeastern Arizona, southwestern Utah, and extreme western New Mexico, thus D0 and some D1 was added to these areas.

Click here to read the discussion:

NSO Alert System Status: La Niña Advisory

Synopsis: La Niña conditions are predicted to continue (~65-75% chance) at least through the Northern Hemisphere winter 2017-18.

During October, weak La Niña conditions emerged as reflected by below-average sea surface temperatures (SSTs) across most of the central and eastern equatorial Pacific Ocean. The weekly Niño indices were variable during the month, with values near -0.5 C during the past week in the Niño- 3.4 and Niño-3 regions. Sub-surface temperatures remained below average during October, reflecting the anomalously shallow depth of the thermocline across the central and eastern Pacific. Also, convection was suppressed near the International Date Line and slightly enhanced over parts of the Maritime Continent and the Philippines. Over the equatorial Pacific Ocean, low-level trade winds were mainly near average, but the upper-level winds were strongly anomalously westerly and the Southern Oscillation Index was positive. Overall, the ocean and atmosphere system reflects the onset of La Niña conditions.

For the remainder of the Northern Hemisphere fall and winter 2017-18, a weak La Niña is favored in the model averages of the IRI/CPC plume and also in the North American Multi- Model Ensemble (NMME). The consensus of forecasters is for the event to continue through approximately February-April 2018. In summary, La Niña conditions are predicted to continue (~65-75% chance) at least through the Northern Hemisphere winter (click CPC/IRI consensus forecast for the chance of each outcome for each 3-month period).

La Niña is likely to affect temperature and precipitation across the United States during the upcoming months (the 3-month seasonal temperature and precipitation outlooks will be updated on Thursday November 16th). The outlooks generally favor above-average temperatures and below-median precipitation across the southern tier of the United States, and below-average temperatures and above- median precipitation across the northern tier of the United States.