Moderate La Niña conditions continued over the equatorial Pacific (95 percent chance of persisting through the end of March 2021), with a potential transition to ENSO-neutral during the Spring 2021 (55 percent chance during April-June). Climate anomalies associated with the La Niña response will likely play the dominant role throughout the winter and early spring months.
As a result, both the CPC monthly (February 2021) and seasonal (February-April 2021) outlooks closely resemble composites of previous La Niña events.
During the past month, drought improved across the southern Plains, especially in Texas, as 30-day precipitation exceeded 150 percent of normal from central Texas northward into eastern South Dakota. Surplus precipitation also brought some relief to the Pacific Northwest, the eastern Gulf Coast, Tennessee Valley, and Northeast.
In contrast, subnormal 30-day precipitation enveloped the Southwest, central and northern High Plains, Ohio Valley, central Gulf Coast, southern Appalachians, and most of Florida. Surprisingly, 4-week deteriorations were limited to parts of California, the northern High Plains, upper Midwest, and southern Texas as much of the driest areas were already in D2-D4 drought, and mid-December to mid-January is climatologically dry in most of the Nation’s mid-section.
Overall, 44.85 percent of the contiguous U.S. was experiencing drought (D1-D4) as of January 12, with the greatest coverage and most intense drought conditions located in the Southwest. Some drought expansion also occurred in Hawaii and Puerto Rico during the past 30 days.
Since winter La Niñas typically result in above normal precipitation across the Northwest and north-central U.S. and below normal precipitation across the southern tier of States and central Plains, these conditions are expected to occur during the upcoming winter and early spring months.
Therefore, drought reduction is favored for the Northwest and northern Rockies, while drought persistence is likely for the southwestern quarter of the Nation. Drought development is favored over southern California, the south-central Plains, and along the central and eastern Gulf and southern Atlantic Coasts.
Additionally, the La Niña response shifts the favored winter storm track toward the Ohio Valley and interior New England, favoring continued drought improvements for the eastern Corn Belt and Northeast. While the climate signal favors above-average precipitation for the northern Plains, no improvements are expected as very dry and mild conditions the past 30-60 days have worsened conditions and greatly diminished the snow cover.
Additionally, February and March are climatologically dry, so even above-normal precipitation would most-likely not erase recent deficits or infiltrate into the frozen ground. Elsewhere, abnormal dryness and warmth have promoted drought expansion across much of Hawaii, but given the oncoming wet season and enhanced tradewinds in association with La Niña, drought improvements are forecast, especially across the leeward sides of the island.
Small D1 areas were present in north-central Puerto Rico, and with the dry season underway and some models forecasting below-normal Feb and FMA rainfall, some expansion of drought was forecast. No drought was anticipated to develop across Alaska during their frigid winter months as much of the state was in a deep freeze.
Forecast confidence is moderate to high for the Western region.
- The ongoing La Niña event unfortunately favors subnormal precipitation and above-normal temperatures across the southern tier of States where drought is currently severe to exceptional (D2-D4) levels.
- SNOTEL basin Snow Water Content (SWC) values are less than 75% of normal across much of the southern half of the West, and under 50% in southern Utah, Arizona, and New Mexico, including below 25% in most of Arizona and southwestern New Mexico.
- In contrast, where near to above normal precipitation and seasonable temperatures have occurred (Northwest), SWC values are better across the northern half of the West, with basins in Washington, northeastern Oregon, northern Idaho, western Montana, and northwestern Wyoming close to normal or slightly above.
- For the next 2 weeks, however, a change in the long-term weather pattern should bring welcome precipitation and subnormal temperatures to the West, including the Southwest, before the Week 3-4 and 1- and 3-month LLFs revert back to the “typical” La Niña anomaly pattern.
- This brief favorable weather pattern in the Southwest is likely not enough to make any significant improvements in the long run (end of April), thus persistence was made for much of the Southwest, with development in southern California.
- In contrast, the Northwest should continue receiving above-normal precipitation and (probably) seasonable temperatures, continuing a wet trend from this Fall for additional improvements in the Northwest.
- The improvement in northwestern California was based upon recent heavy rains the past 30-days, more heavy precipitation expected during the next 2-3 weeks, and a wet climatology with equal chances (EC) of below, normal, or above precipitation in both the 1- and 3-month precipitation LLFs.
Forecast confidence is moderate for the High Plains region.
- In the northern Plains, although the 6-10 day ERF, Week 3-4, and 1- & 3-month LLFs tilt toward above-normal precipitation, the past 30-60 days have been quite dry and very mild there, which has led to minimal or no snow cover.
- Plus, with climatology quite dry during February and March, any surplus precipitation in the Dakotas most-likely would not eliminate the accumulated deficits and impacts of the past 1-2 months. Thus, persistence (not improvement) is forecast for the northern Plains.
- In addition, development was not added in South Dakota since the forecasts showed potential for above-normal precipitation. Improvement might have been depicted if this SDO was for MAM or AMJ as the precipitation climatology is much wetter then.
- Farther south, with the ongoing La Niña, the 3-month LLF favors subnormal precipitation in Colorado, Kansas, and Nebraska, thus persistence for existing drought areas and some development along the eastern drought border (southern Kansas) was drawn.
Forecast confidence is moderate to high for the Midwest region.
- The past 30-days brought surplus precipitation to western parts of the Midwest, with subnormal totals in Wisconsin, Illinois, Indiana, Michigan, western Ohio, and Kentucky. Temperatures have also averaged above normal, leading to diminished snow cover.
- With the 7-day QPF limiting moderate precipitation to southern sections (Kentucky), only light amounts should occur for much of the region. The 6-10 day ERF favors above-normal precipitation, but by 8-14 days, the odds call for near to below-normal precipitation (with seasonable ERF temperatures).
- With the Week 3-4, 1- and 3-month LLFs favoring above-normal precipitation, improvement is expected in Illinois and Indiana and northern Minnesota.
- In western Iowa, with only a weak signal for improvement, a rather dry February and March climatology, and the drought being long-term, persistence was the safest forecast.
Forecast confidence is moderate for the South region.
- Surplus precipitation, including snow, has fallen on most of the South (Texas, Oklahoma, Louisiana, Arkansas) during the past 30-60 days, prompting drought improvement across most of Texas, Oklahoma, and Arkansas recently.
- The 7-day QPF continued the ample precipitation across central and eastern Texas, Arkansas, and most of Louisiana, Mississippi, and Tennessee, although drier weather is expected by 8-14 day ERF and into the Week 3-4 forecast. The upcoming rains should be enough to remove the small D1 areas in western Tennessee and northern Mississippi.
- The 1- and 3-month LLFs favor subnormal precipitation for southern and western sections of the South (and above-normal temperatures), with a southwestward dip of above-normal precipitation probabilities from the Ohio Valley into the lower Mississippi Valley in the FMA precipitation LLF.
- With subnormal precipitation expected in southern Texas and along the central and eastern Gulf Coast, development was depicted in these areas – but not along the western Gulf Coast where the precipitation outlooks are closer to normal.
Forecast confidence is moderate for the Southeast region.
- Mostly dry conditions have enveloped parts of the Southeast the past 30-60 days, namely the central and eastern Gulf and southern Atlantic Coasts and eastern Tennessee Valley, although a band of surplus precipitation did fall from Apalachicola, FL area northeastward into the Carolinas and southeastern Virginia. Currently, only a few areas of D0 were found on the Jan. 19 USDM in the Southeast.
- However, the 7-day QPF predicts heavy precipitation (1-4 inches) across much of the Southeast – except drier right along the Gulf Coast and Florida. Then, the extended range forecasts expect precipitation to gradually decrease, with the 8-14 day ERF favoring subnormal precipitation across the region.
- Similarly, the Week 3-4, 1- and 3-month LLFs also expect subnormal precipitation (thanks to La Niña) mainly along the Gulf Coast – thus, development is expected along (most of) the central and eastern Gulf and southern Atlantic Coasts (including all of Florida) by the end of April.
Forecast confidence is moderate to high for the Northeast region.
- A wet winter pattern has dramatically improved conditions and stream flows across New England, with only a few small D1 areas left.
- The 7-day QPF showed light precipitation, 6-10 & 8-14 day ERFs have a slight tilt toward below-normal precipitation, and temperatures will be seasonable out to 2 weeks. The Week 3-4 hinted at above-normal precipitation, while the 1- and 3-month LLFs favored above-normal precipitation in western areas and EC toward eastern areas (above-normal temperatures for both time periods).
- With minimal soil moisture loss during the winter (low temperatures, no evaporation, frozen ground) and future moisture infiltration (e.g. snow pack), most winter precipitation that occurs should contribute to decent spring moisture conditions by the end of April. Thus, the remaining D1 areas should be gone by the end of April.
Forecast confidence is high for Alaska and Hawaii, moderate for Puerto Rico.
- In Hawaii, a La Niña typically brings above-normal rainfall during their climatologically wet winter season, particularly later in the season (Jan-Mar), thus improvement is expected across the islands.
- In Alaska, no changes are anticipated during their frigid winter hibernation.
- In Puerto Rico, recent dryness in the north (D0 and D1) may expand somewhat by the end of April based upon some model guidances forecasting subnormal Feb and FMA precipitation; therefore some development was added in north-central sections.