10:30 AM (Wednesday) | ****Major rain event in the eastern US from tomorrow into early Friday with flash flooding concerns****
Paul Dorian
A key factor in the upcoming major rain event for the eastern US will be the influx of tropical moisture from the Gulf of Mexico and southwestern Atlantic. A strong flow of air from south-to-north will develop on Thursday along the east coast ahead of a very slow moving frontal system. Map courtesy NOAA, tropicaltidbits.com
Overview
The active weather pattern that we have been experiencing in the Mid-Atlantic region and Northeast US over the past few weeks will continue well into the month of May aided in part by a continuation of cold air outbreaks from Canada into the central and eastern US. The upper-level jet stream across the country is very active as we wind down the month of April and it has featured numerous strong waves of energy in recent days and another one has dropped southeastward into the Mississippi Valley region from southwestern Canada. This wave of energy aloft and its corresponding surface low pressure system will move very slowly over the next 48 hours due to a blocking pattern in the upper atmosphere over the southern part of Canada. These slow-moving systems and a painfully slow-moving surface frontal boundary zone will combine with an influx of tropical moisture to produce a major rain event from tomorrow into early Friday in the eastern US extending from the Carolinas to New York State. Localized flash flooding is likely to become a serious concern during this upcoming event with 2-4 inches of rain on the table in many areas.
00Z Euro forecast map of total precipitation amounts (in inches) for the upcoming event. Map courtesy Pivotal Weather, ECMWF
Details
A wave of energy at 500 millibars has dropped southeastward today into the Mississippi Valley from Canada and it will now make a move towards the Great Lakes. However, there is a blocking pattern in the upper atmosphere over the southern part of Canada and this will force the upper-level feature to loop back around from the Great Lakes into the Mid-Atlantic region over the next 48 hours. Meanwhile, a north-to-south oriented surface cold frontal system that trails low pressure over the Great Lakes will grind its way towards the eastern seaboard over the next 48 hours in a west-to-east fashion as it becomes aligned with the flow of air in the upper part of the atmosphere.
A vigorous wave of energy will move very slowly over the next 48 hours as it encounters a block in the upper atmosphere over southern Canada. As a result, it will be forced to take a loop from the Great Lakes into the Mid-Atlantic by the time Friday morning rolls around. Maps courtesy NOAA, tropicaltidbits.com
This slow movement will allow the atmosphere to become very moist in the eastern US ahead of the front as an increasingly strong flow of air from south-to-north develops along the eastern seaboard. This flow of air will push tropical moisture up along the east coast on Thursday and Thursday night all the way from the Gulf of Mexico and Caribbean Sea – all setting the stage for excessive rainfall from the Carolinas to New York State. In fact, given the very slow movement of the frontal system and the high precipitable water amounts expected, total rainfall amounts could end up between 2 and 4 inches in much of the eastern US and flash flooding will likely become a serious concern. Indeed, the chance for flash flooding is somewhat high for this upcoming event given the combination of expected heavy rainfall and the already well-saturated grounds from recent rains and the fact that we have had a chilly month of April in the eastern US which has limited evaporation in the top layer of soil.
Cold air outbreaks will continue to move from Canada into the central and eastern US right into the middle of May. Maps courtesy NOAA, tropicaltidbits.com
Looking ahead, the overall active weather pattern is likely to continue in May as cold air outbreaks into the central and eastern US look like they’ll continue right into at least the middle of the month. These cold air outbreaks are combining with increasingly warm and humid air masses across the southern US to not only raise the chances for strong storms and significant rainfall in the Mid-Atlantic region, but they have also contributed to severe weather outbreaks in the southern US with another one possible later today in the southeastern part of the nation.
Meteorologist Paul Dorian
Perspecta, Inc.
perspectaweather.com
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