11:30 AM (Wednesday) | *Very active weather pattern to persist as cold air outbreaks continue through the month of April*

Colder-than-normal weather will dominate the scene in the central and eastern US for much of the second half of April. This 2-meter temperature anomaly forecast map from the 00Z Euro features colder-than-normal conditions for the eastern two-thirds of the nation in the 3rd week of the month. Map courtesy Weather Bell Analytics at “weatherbell.com”, ECMWF

Overview

A very active weather pattern will continue across much of the nation during the next week or two in part due to a continuation of cold air outbreaks into the central and eastern US.  These on-going cold air outbreaks from Canada will combine with increasingly warm and humid conditions across the southern US to make it quite unstable on many days going forward in many parts of the nation and it’ll increase chances for widespread severe weather outbreaks.

Currently, a strong storm is swirling over southern California with heavy rainfall and by mid-day Thursday, a strong cold front will advance across the Great Lakes and to the eastern seaboard.  Winds will increase markedly in the Mid-Atlantic/NE US from later tomorrow into Friday with damaging gusts possible.  A major storm system is then likely to form this weekend over the central US and it should take a northeast turn towards the Great Lakes region while a secondary system forms near the east coast. The result of this Sunday/Monday storm system could be some heavy rainfall in the eastern US, accumulating snow across the Upper Midwest, and perhaps a widespread severe weather outbreak in the southern US extending from Texas/Louisiana to the Carolinas.

One of the strong indicators that a colder-than-normal pattern is setting up in the central and eastern US has been the teleconnection index known as the North Atlantic Oscillation (NAO). When this index is in “negative” territory for an extended period of time this time of year as shown in the latest forecast, it oftens indicates favorable conditions for colder-than-normal air masses to drop from Canada into the central and eastern US. Another teleconnection index known as the Madden-Julian Oscillation (MJO) also supports the idea of a colder-than-normal pattern setting up for the central and eastern US (see video discussion). Plot courtesy NOAA

Details

Overnight thunderstorms in the Mid-Atlantic region reached strong-to-severe levels in many areas as they dropped southeastward along a frontal boundary zone.  While it’ll be warmer and quieter today in the DC-to-Philly-to-NYC corridor, there can be some isolated-to-scattered PM showers and thunderstorms as some instability remains.  On Thursday, a strong cold front will drop southeastward into the I-95 corridor during the mid-day or early afternoon hours and it will be accompanied by showers and perhaps a strong thunderstorm or two.  Perhaps the bigger story with this strong cold front will be the winds which will markedly increase later tomorrow and continue at high levels on Thursday night and Friday – perhaps even to damaging levels at 50+ mph.  A colder-than-normal air mass will flood the Mid-Atlantic region and NE US on Thursday night and Friday and it’ll stay below-normal going into the weekend as well.

00Z Euro forecast map for early Monday afternoon, April 13th, with a strong storm in the eastern US and another cold air outbreak showing up across the Northern Plains and Upper Midwest. Map courtesy WSI, Inc., ECMWF

By later in the weekend, the storm that is currently pounding southern California will regain strength over the middle of the country.  This storm is likely to then push to the northeast towards the Great Lakes region while a secondary low pressure forms near the east coast and it could bring a soaking rainfall to the eastern seaboard in the Sunday night/Monday time frame.  Furthermore, there is the threat for severe weather later this weekend associated with this potential storm; especially, across the southern states from Texas/Louisiana to the Carolinas.  The combination of very warm and humid air in the warm sector of the storm will combine with very strong winds in lower and middle levels of the atmosphere to increase chances for a severe weather outbreak in the southern US.

The 7-day total precipitation amounts by NOAA between today and next Wednesday suggests an active weather pattern will continue across the nation. Much of the rainfall seen on this forecast map across southern California will fall over the next 24 hours or so while the eastern third of the nation may seen a bulk of its precipitation fall from later this weekend into early next week.

Another cold air outbreak is destined to reach the eastern US around Tuesday of next week after dropping southeastward from central Canada to the Great Lakes.  Once this cold air mass arrives, the colder-than-normal weather pattern may actually become rather sustained across the central and eastern US through the remainder of the month April.  This doesn’t mean that each and every day will be colder-than-normal in these areas, but it does mean that we are likely to see below-normal averages for the second half of the month of April in much of the central and eastern US…and a continuation of an active overall weather pattern.

The 12Z GEM forecast map of total snowfall over the next ten days is pretty impressive considering it is for early-to-mid April. Courtesy tropicaltidbits.com, Canadian Meteorological Center

Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com

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Video discussion: