The U.S. Spring Outlook: Wet Central U.S.; Warm East
Executive summary: The Climate Impact Company month 1-3 ahead forecast valid for meteorological spring (MAR/APR/MAY 2019) is updated. The forecast is based on climate diagnostics the next 2 months with some recognition of the NCEP CFS V2 and ECMWF climate models and a consensus between the 2 sets of models for May. There are no satisfactory analog years. The ENSO outlook is neutral phase although forecast models continue to claim El Nino risk will re-emerge during spring. Some of the forecast highlights include:
Wetter-than-normal spring Great Plains, Ohio and Tennessee Valley(s).
A cooler revision Interior West to North-central U.S. in March.
Anomalous warmth Southeast in March and the Northeast in April.
No “surprise” early season heat in May.
Climate discussion: Not recommended is using ENSO analogs to generate climate forecasts in this topsy-turvy and somewhat difficult to explain climate pattern. As an example, we’ve just seen a historical bitter cold arctic outbreak into the Midwest U.S. and more recently that same bitter cold and snow back into the West U.S. Normally, arctic air of this magnitude is caused by sudden stratospheric warming events such as the February 1989 outbreak (Fig. 1). However, February 2019 produced one of the coldest stratospheric analysis on record (Fig. 2) and speculated is a piece of the high latitude polar vortex broke apart and descended into the lower atmosphere toward the U.S. to cause that cold. It’s tough to analog first-ever climate events.
Fig. 1-2: Depiction of upper air features over the northern hemisphere for the past 90 days (left) and past 30 days (right).
So for the spring outlook we’ll rely on what we know and to a certain extent allow the NCEP CFS V2 and ECMWF “monthlies” to help to update the spring 2019 outlook. Taking a look at the 90-day and 30-day 500 MB anomaly analysis (Fig. 3-4) we find that an expected ridge area over Greenland (A) this winter has been present with varying intensity. The ridge in this area was expected due to the anomalous warmth emitted into the upper atmosphere caused by ice free water north of Europe. Of course, with a Greenland high pressure block upper troughs will form in the middle latitudes lead by an expanding trough in Europe and the Western U.S. plus the Kamchatka Peninsula (B). Upper ridge areas are usually present where large areas of warm SSTA are present. The “ridge bridge” extending across Alaska is present due to warm northeast North pacific SSTA while a formidable upper ridge was also present over warm SSTA off the U.S. East Coast (C).
Fig. 3-4: Depiction of upper air features over the northern hemisphere for the past 90 days (left) and past 30 days (right).
The SSTA patterns are normally very slow to change so the correlation between the Alaska ridge and warm SSTA in the northeast Pacific and the upper ridge over warm SSTA east of the U.S. are likely to persist into spring 2019 (Fig. 5). Also re-emerging recently is an upper ridge pattern over the warm SSTA southwest of California. Given the likelihood of the upper ridge positions listed the risk of a wet/cool upper trough for much of the spring season in the Central U.S. is likely.
The expansive West U.S. snow cover lends support for lingering cold in the West to last into spring. The projected upper trough will be biased toward the snow cover for early spring and may ease eastward by mid-spring. The NCEP CFS V2 is not an exact match to this forecast philosophy but is closer than the ECMWF “monthlies”. The forecast is generated based on the theory defined and persistence (previous forecast).
Fig. 5: The weekly global SSTA analysis provided by NCDC/PSD.
March 2019: Favored is a semi-permanent upper trough over mid-continent with cold weather beneath the polar vortex in northeast Canada and lingering cold across expansive snow cover in the western U.S. Presence of the upper trough mid-continent favors a wetter than normal regime affecting the Great Plains, central Rocky Mountains (mostly snow) and the Ohio Valley. Precipitation amount could be higher in this zone if the Madden Julian oscillation is active. The upper ridge pattern off the East Coast holds bringing anomalous warmth especially in the Southeast U.S. The Northwest forecast is adjusted considerably cooler.
Fig. 6-7: The Climate Impact Company month ahead forecast for March 2019. The previous forecast is below.
April 2019: A Northwest U.S. and East Coast upper ridge pattern is confidently forecast lending support for a warmer than normal pattern in each region. That leaves the Central U.S. susceptible to an upper trough which causes a wetter than normal pattern Great Plains to the Mid-Atlantic.
Fig. 8-9: The Climate Impact Company 3 months ahead forecast for April 2019. The previous forecast is below.
May 2019: The late spring outlook is not quite as warm in the East but remains warmer than normal across the northern U.S. and possibly very wet in the Great Plains. The forecast is based on agreeable NCEP CFS V2 and ECMWF “monthlies” solutions and persistence with the previous CIC forecast. Forecast models are somewhat El Nino-biased and CIC is doubting any return of warm ENSO. Therefore the May forecast is susceptible to change.
Fig. 10-11: The Climate Impact Company 3 months ahead forecast for May 2019. The previous forecast is below.
