Springlike Warmth in Southwest U.S., Southeast Europe; Sierra Snowpack Below Average

Some of the warmest temperatures on record for this early in the year are enveloping large parts of the southwestern United States and southeast Europe this week. The mildness will work its way across the U.S. as the week unfolds, displacing a stormy pattern that’s brought ice and snow to the mid-Atlantic and Northeast and severe weather along the Gulf Coast. NOAA’s Storm Prediction Center logged at least 20 preliminary tornado reports on Monday, mainly from southern Louisiana to the Florida Panhandle, with several injuries reported and several dozen homes, businesses and schools damaged or destroyed. More twisters were reported early Tuesday morning across southern Florida and the Outer Banks of North Carolina. One or more apparent tornadoes inflicted widespread damage to cars and trees across the highly populated area between Miami and Fort Lauderdale at rush hour Tuesday morning. A roundup on weather.com has more on the Monday and Tuesday twisters. The Gulf Coast states are highly prone to severe weather during El Niño, with Florida having double its usual winter risk of tornadoes.


FIgure 1. A mobile home that also served as a day care facility in rural Lincoln County, Miss., was destroyed by a suspected tornado on Monday, Feb. 15, 2016, as severe weather affected south Mississippi. Minor injuries were reported to the adults and children inside. Image credit: The Daily Leader, via AP.


Figure 2. A stormy sunset painted the skies over Ponchatoula, LA, on Mon., Feb. 15, 2016, as heavy thunderstorms moved out of southeast Louisiana. Image credit: wunderphotographer llpj04.


Figure 3. WU observations show the pockets of cold air still trapped in parts of eastern Massachusetts while much milder air was moving in at noon EST Tues., Feb. 16, 2016.


New England says farewell to Arctic air
As quickly as it arrived, the record-cracking Arctic air mass that invaded the northeast U.S. this past weekend is heading out. Temperatures were jumping dramatically on Tuesday as a strong warm front moved north into New England. Below-freezing air was trapped in some river valleys, with readings soaring above 50°F close by. The past day’s patchwork of snow, sleet, freezing drizzle, and freezing rain over eastern New York and New England will be washed away by heavy rain, with widespread 1-2” totals expected.

Despite the ferocity of the Valentine’s Day cold outbreak, temperatures are still above average for the month of February across most of New England and New York (see Figure 4 below). A study in local contrasts: last year Worcester, MA, saw its coldest February in more than a century of record-keeping, yet no daily record lows were set. This past Sunday was the coldest morning Worcester has seen in almost 60 years, with a daily record low of -16°F, and yet the city has a good shot at ending up warmer than average for this February as a whole.

Even with the record lows from Saturday and Sunday taken into account, the year to date has produced more than six times as many daily record highs as daily record lows across the contiguous U.S. (2071 to 335), according to NOAA.


Figure 4. Departures from average temperature (°F), generated from preliminary data for the period Feb. 1 - 15, 2016. Image credit: High Plains Regional Climate Center.


Figure 5. Snow water equivalent (the amount of water held in snowpack) in California’s Sierra Nevada on Tues., Feb. 16, 2016, as a percentage of the average amount observed by April 1 (left values) and by this point in the winter (right values). Image credit: California Department of Water Resources.

Sierra snowpack drops below seasonal average
An unsettling threshold has been crossed in California. After a promising start to the water year, the total amount of water held in snowpack across all three sections of the Sierra Nevada has dropped below the seasonal average (see Figure 5). This number should jump back above average later this week, as a moderately strong Pacific storm moves across California. During the two other El Niños since 1950 as strong as the current one (1982-83 and 1997-98), the Sierra snowpack ended up well above average. However, weaker El Niños have sometimes produced below-average seasonal snowfall. In a typical year, more than 35% of the Sierra snowpack arrives after mid-February, so there is still time for this El Niño to come through. Runoff from the Sierra snowpack produces about 30% of California’s water supply in a typical year.

It’s been an especially dry February thus far in California’s major cities, where moisture for the water year to date (October 1 - present) was running below average across the board as of Monday. This week’s storminess is unlikely to push these values back above average, and long-range models suggest that another warm, dry period in store for next week. The next four to six weeks will be critical in bringing much-needed moisture to Southern California, as precipitation typically tails off rapidly in April. As shown below, Portland and Seattle have been dramatically wetter than California cities relative to the water-year average--in startling contrast to the prototypical El Niño pattern.

San Diego: 6.06” (water year average to date = 6.24”)
Los Angeles Downtown: 4.20” (average 9.10”)
San Francisco Downtown: 13.70” (average 15.77”)
Sacramento: 8.92” (average 11.79”)
Portland, OR: 32.33” (average 20.98”)
Seattle, WA: 35.37” (average 22.91”)


Figure 6. Percent of normal precipitation for the period Feb. 1 - 15, 2016. Image credit: High Plains Regional Climate Center.

Here comes the warm
The mild, dry air mass about to sweep from California across the United States began generating record highs on Monday in downtown Los Angeles (89°F, breaking 88°F from 1985) and San Francisco (77°F, beating 76°F from 1930). A clutch of more impressive records is likely on Tuesday across most of California, and Phoenix may hit 90°F on both Tuesday and Wednesday. The earliest 90°F ever observed in Phoenix was on February 24, 1904. Swarms of record highs can be expected on Wednesday and Thursday as the air mass invades the central U.S., with 70°F air as far north as Nebraska and readings topping 80°F from parts of Kansas southward.

Unseasonable mildness over southeast Europe
Another relatively hot pocket this week is in Europe, where torrid southerly winds from Africa brought temperatures more typical of spring or even summer across eastern Mediterranean islands through the Balkans and beyond. On Monday, the city of Chania on the island of Crete reached a high of 29.2°C (84.6°F)--about the same as a typical day in August. The capital city of Albania, Tirana, reached 25.3°C (77.5°F), and Macedonia’s capital, Skopje (located near the latitude of Boston) reached 24.6°C (76.2°F), close to its monthly record for February. Even parts of eastern Ukraine topped 65°F, approaching 30°F above average. Thanks go to Maximiliano Herrera and Michael Theusner for these data.

Jeff Masters will be back on Wednesday with a full report on January’s global climate.

Bob Henson


Figure 7. High temperatures across Europe for Mon. Feb. 15, 2016. Image credit: OGIMET, courtesy Michael Theusner, Klimahaus Bremerhaven.