Weather Risk - US Rough Around the Edges

Similar to April 2003 and April 2004, the Northeast quadrant of the Nation is being victimized by the remnants of the Winter Season, with unseasonably cool nights, windy days and even some April snows.  Most computer models and popular outlooks consistently painted a very warm April 3-10 picture for the Eastern Great Lakes, New England and the Mid-Atlantic, where it has been quite the opposite for reasons we outlined in previous commentaries.

We are beginning to see the early hints of our Summer outlook pattern, which we visually have described as an "Omega" or "Horseshoe" shape of warmth overlaid on the contiguous U.S.  As a preview to the Summer Season, warmth/heat continues to emanate out of the Central U.S. propelled by ridging, subsidence and drought, contrasted by the much cooler/raw weather for the Pacific Northwest and New England (which will be a large reversal from their Summer 2005 results).

As we progress through the Spring months, certain Hemispheric tele-connections which were prominent in Winter become less influential in favor of others.  While the North Atlantic Oscillation [NAO] remains a key player throughout the entire calendar year, the PNA pattern takes a back seat to the NP, EP, WP and to a lesser extent, Scandanavian patterns.  It also should be reminded that ENSO Status [El Niño/La Niña] plays an insignificant role in U.S. Summer weather, outside of the influences on the Hurricane Season and the Southwest Monsoon Season, so any ENSO-attributed Summer outlooks should be viewed with scientific skepticism.

Forecasting the Forecast [04/06]:

NWS outlooks should continue their trend towards lower confidence with the prevailing transient flow across the U.S. being very Spring-like.  Cooler patterns in the West should begin to relax in the 8-14 day outlook and the warmth across the East should be reduced starting in New England and stretching down to the mid-Atlantic.

From previous discussion, re-included for pertinence:

Today will mark the first day of spring-like above-normal readings in Chicago following 16 consecutive days of below-normal temperatures.  Spring is definitely emerging across the U.S., but sizeable negative temperature departures are quite feasible over the next 4 weeks for a few key regions which we will touch on:

New England and Coastal Mid-Atlantic:  Pattern retrogressions, back-door cold fronts and on-shore flow could still plague these areas for a while.  Consequently, a pleasant Spring day breaking 70°F in Boston or New York, could be followed by afternoon highs 20-25° colder just a few days later (as we'll see over the next week).

Upper-Mid-West and Great Lakes:  With some residual snow-pack lingering across the Northern Tier, and Great Lakes water temperatures at their chilliest levels of the year, locations downstream(wind) of Canada or the Lakes will have to contend with occasional raw and chilly weather during this Spring.

West and Rockies: with lagged Seasons compared to most of the U.S., April is still very much a Winter month for the Rockies and the Western U.S., so warmth or cool should be viewed as variations of winter weather.  Outside of the Southwest, Heating Degree Days predominate over Cooling Degree Days for several more weeks.