Prognostic Discussion for Week 3-4 Temperature and Experimental Precipitation Outlooks
NWS Climate Prediction Center College Park MD
300PM EST Fri Jan 11 2019
Week 3-4 Forecast Discussion Valid Sat Jan 26 2019-Fri Feb 08 2019
A host of well-defined teleconnection modes and centers of action are currently in play, and could continue to influence the Weeks 3 and 4 outlook. Over the past week the Madden-Julian Oscillation (MJO) pushed across much of the Western Hemisphere, and is currently approaching the Prime Meridian. Historically, the lagged response to MJO Phases 8/1 tend to be more of a transitional mode for the U.S., with anomalous troughing building over the West and ridging along the Canadian border. The Arctic Oscillation (AO) has flipped to negative, in line with past observations of the MJO crossing the Pacific during boreal winter. Model guidance supports the AO remaining negative during the next two weeks, despite the MJO reaching the Indian Ocean typically supporting a return to AO+ conditions. Some of this influence in the model guidance could be tied to the recently observed split in the stratospheric polar vortex, although models are notorious for how poorly stratospheric/tropospheric exchange is handled, so this should be taken with some caution. Yesterday (10 January) CPC officially extended its El Nino watch another month, with a coupled tropical response remaining unobserved over the tropical Pacific, leading to concerns about any substantial extratropical response for North America despite the persistently warm sea surface temperatures (SSTs) over the Central Pacific. On the whole, model guidance is fairly consistent with an amplified wavetrain emerging from the Central Pacific and resultant ridge-trough pattern over the CONUS, despite statistical guidance supporting a less robust trough-ridge that would be more in line with the MJO pushing towards the Indian Ocean. The resulting temperature and precipitation outlooks are rooted primarily in this dynamical model guidance, although resulting probabilities are damped somewhat given the empirical expectations from the statistical tools.
Dynamical model guidance is remarkably consistent in depicting an amplified wave train emanating from the Pacific during the Weeks 3 and 4 period, resulting in a ridge-trough dipole across the CONUS. Unsurprisingly, this supports elevated chances for above-normal (below-normal) temperatures from the Pacific Coast through Great Plains (approximately the Mississippi River through Eastern Seaboard). Highest confidence for each respective region is associated with the primary anomalous ridge and trough axis, centered over the Pacific Northwest and Central Appalachians. Substantial decadal warming trends over the Southern Plains tilt the official outlook towards equal chances, rather than the slight increase in below-normal temperature odds that dynamical guidance would support. The MJO response for Phases 8/1 would suggest increased chances for below-normal (above-normal) temperatures focused on the Great Basin (Northern Tier), that damp the out of phase dynamical model guidance probabilities that form the basis of the forecast. Anomalous troughing forecast over the Aleutians would support enhanced southerly flow and increased odds for above-normal temperatures for much of Alaska, with the highest probabilities closest to the Gulf of Alaska.
The anticipated ridge-trough dipole is supportive of a fairly dry pattern for the CONUS, with the primary storm track in the Norhteast Pacific shifted north into Alaska and Canada, in addition to increased chances for continental polar air masses to intrude into the East. Highest confidence for below-normal precipitation exists over the West, in association with the anticipated anomalous ridge axis, and over the western Gulf states that are likely to see the import of Gulf moisture limited by the anomalous northerly flow. Above-normal precipitation is favored across a portion of the High Plains tied to shortwave activity potentially diving into the longwave trough, and across Florida where guidance suggests the mean frontal zone becomes established downstream of the anomalous trough. Anomalous southerly flow forecast for Alaska leads to increased (decreased) chances of above-normal precipitation across the southern portion of the state (interior and western mainland).
SSTs surrounding Hawaii remain above normal, and the bulk of dynamical model guidance depict enhanced chances for above-normal temperatures. Dynamical model precipitation forecasts tilt towards below-normal odds, which are also consistent with the low-frequency oceanic warming being observed near the antimeridian.
| Temperature | Precipitation |
| FCST | FCST |
| Hilo | A80 | B70 |
| Kahului | A80 | B70 |
| Honolulu | A80 | B70 |
| Lihue | A80 | B70 |
Forecaster: Daniel Harnos
The next week 3-4 outlook will be issued on Friday, Jan 18, 2019
These outlooks are based on departures from the 1981-2010 base period
These are two category outlooks and differ from official current three category outlooks currently used for the monthly and seasonal forecasts.
The shading on the temperature map depicts the most favored category, either above-normal (A) or below-normal (B) with the solid lines giving the probability ( >50%) of this more likely category (above or below).
The shading on the precipitation map depicts the most favored category, either above-median (A) or below-median (B) with the solid lines giving the probability ( >50%) of this more likely category (above or below).
In areas where the likelihoods of 2-week mean temperatures and accumulated precipitation amounts are similar to climatological probabilities, equal chances (EC) is indicated.
As of May 19, 2017, the temperature outlook is operational, while the precipitation outlook is still experimental