By driving an autumnal Great Lakes low within an overall warm air mass and you’ve got the recipe for some wild weather. As most of us know, warm and cold do not mix but add TROPICAL moisture into the mix and you’ve got trouble. The perfect ingredients came together for not 1, 2 but 3 MAJOR and historic flooding events.

Monday it was Detroit where 4.57″ fell, making for the 2nd wettest day on record, Tuesday it was DC-Baltimore where locally 10″ fell and last but by no means least and most extreme of all was Islip, NY. Over 5″ within 1 hr, 11″ within 2. 3 major metropolitan areas hit by record rain and flash flooding 3 days in a row.

SEE last two US posts for the flooding event and totals from Detroit and DC.

 

TOP IMAGE CREDIT: WeatherGoneWILD

The reason for such extreme rains?

Strong upper energy spinning around a fall-like Great Lakes upper low with strong surface low containing unusually cold air just above the surface while warm, tropical air and moisture was sucked in from the south, southeast. The warm, moisture rich air was one thing but the storm system and associated front forced the atmosphere to increase it’s precipitable water content.

The reason for such extreme rain over a multi-hour period was thanks to the ‘training’ effect. Heavy, tropical rain bands which aligned directly over Detroit, DC-Baltimore as Islip.

In today’s post I want to look at yesterday morning’s unbelievable rains.

Here was the scene from Holbrook, NY at the height of yesterday morning’s epic rains.

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…RECORD DAILY MAXIMUM RAINFALL SET AT ISLIP NY…

A RECORD RAINFALL OF 13.51 INCHES WAS SET AT ISLIP NY TODAY AUGUST 13.
THIS BREAKS THE OLD RECORD OF 0.91 SET IN 2013.

…RECORD NEW YORK STATE 24 HOUR PRECIPITATION BROKEN AT ISLIP
MACARTHUR AIRPORT TODAY…

A PRELIMINARY NEW YORK STATE 24 HOUR PRECIPITATION RECORD WAS BROKEN
AT ISLIP LONG ISLAND TODAY. TOTAL 24 HOUR PRECIPITATION AT ISLIP AS
OF 9:30 AM WAS 13.57 INCHES. THIS BREAKS THE PREVIOUS RECORD OF 11.6
INCHES AT TANNERSVILLE NY ON AUGUST 27-28 2011 DURING
HURRICANE/TROPICAL STORM IRENE.

THE 24 HOUR PERIOD FOR THIS RAINFALL EVENT WILL END AT 11PM ON
AUGUST 13. THIS REPORT WILL BE UPDATED AFTER MIDNIGHT FOR ANY
ADDITIONAL RAINFALL THAT MAY FALL.

THIS RECORD WILL REMAIN PRELIMINARY UNTIL THE NATIONAL WEATHER
SERVICE AND THE NATIONAL CLIMATIC DATA CENTER CONFIRMS THESE
REPORTS.

…RECORD MONTHLY MAXIMUM RAINFALL FOR THE MONTH OF AUGUST BROKEN AT
ISLIP MACARTHUR AIRPORT TODAY…

A RECORD MAXIMUM MONTHLY RAINFALL FOR THE MONTH OF AUGUST OF 14.03
INCHES WAS SET AT ISLIP NY TODAY. THIS BREAKS THE PREVIOUS RECORD OF
13.78 INCHES SET BACK IN AUGUST OF 1990.

THESE REPORTS ARE PRELIMINARY AND WILL BE UPDATED LATER IF AND WHEN
MORE RAIN FALLS AT ISLIP.

System is finally offshore leaving behind chilly air mass which sends lows to freezing across Wisconsin, low 50s all the way to Alabama.

Current 500mb (GFS)

Current surface (GFS)

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