Updraft: July 28, 2011 Archive

Twin Cities dew point record confirmed; "Outflow" on doppler

Posted at 5:47 PM on July 28, 2011 by Paul Huttner (3 Comments)
Filed under: Record

It's official.

We sweated through the wettest air mass ever recorded in Twin Cities history on July 19th.

The details from the Minnesota Climate Working Group.

Record Dew Point Temperature in the Twin Cities: July 19, 2011

"The National Weather Service Forecast Office (NWS) in Chanhassen and the DNR State Climatology Office have conferred on last week's extraordinary dew point temperatures in the Twin Cities. It was agreed that the 82 degree F dew point temperature value reported at 3:00 PM and again at 4:00 PM on Tuesday July 19, 2011 at the Twin Cities International Airport will be considered by these offices as the highest dew point temperature ever recorded in the Twin Cities. The old record in the Twin Cities was 81 degrees at 11:00 am on July 30, 1999.

It is known that July 19 dew point temperatures exceeded 82 degrees F at moments between the routine hourly observations. However, in the interest of historical consistency and practicality in establishing future records, only hourly dew point temperature measurements were utilized to determine the new record.

Heat index values on July 19 were extraordinarily high. The 4:00 PM observation may have tied or set an all-time heat index record for the Twin Cities. The air temperature reported at that hour was 95 degrees F and was paired with the 82 degree F dew point temperature. In the next few weeks, the heat index formula used by the NWS hourly "Weather Roundup" product will be used with the historical hourly air temperature/dew point temperature data set to create a heat index climatology. Another announcement will be sent when this is completed."

"Outflow Boundary" visible on Twin Cities doppler:

An interesting feature showed up on Twin Cities radar today.

Arcing yellow line is an "outflow boundary" in the south metro Thursday PM.

Here's the explanation to an astute MPR listener, John who asked about the feature on radar.

"Hi John!

Great observation! What you're seeing is an "outflow boundary" from the storms in southeast Minnesota.

Basically the storms send out a gust front (even on the back side of some systems) and it's propagating westward toward the metro.

The "higher reflectivity" is likely a line of towering cumulus along the boundary.

It's running out of steam as it fights light northwest surface winds, as you can see it's now nearly stationary.

Outflow boundaries have to be watched for T-Storm development, as the convergence they create can spawn updrafts and generate new storms. Can't rule out an isolated T-Storm firing along this boundary tonight in the southeast metro!"

Flash flood warnings near Rochester:

BULLETIN - EAS ACTIVATION REQUESTED
FLASH FLOOD WARNING
NATIONAL WEATHER SERVICE LA CROSSE WI
343 PM CDT THU JUL 28 2011

THE NATIONAL WEATHER SERVICE IN LA CROSSE HAS ISSUED A

* FLASH FLOOD WARNING FOR...
NORTHERN MOWER COUNTY IN SOUTHEAST MINNESOTA...
SOUTHERN DODGE COUNTY IN SOUTHEAST MINNESOTA...
SOUTHWESTERN OLMSTED COUNTY IN SOUTHEAST MINNESOTA...

* UNTIL 730 PM CDT

* AT 337 PM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED
SLOW MOVING THUNDERSTORMS WITH VERY HEAVY RAINFALL ACROSS THE
WARNED AREA. DOPPLER RADAR ESTIMATES ONE TO TWO INCHES OF RAIN HAS
ALREADY FALLEN AND AN ADDITIONAL ONE TO TWO INCHES IS POSSIBLE
BEFORE THE STORMS DIMINISH OVER THE NEXT FEW HOURS.

* RUNOFF FROM THIS EXCESSIVE RAINFALL WILL CAUSE FLASH FLOODING TO
OCCUR. SOME LOCATIONS THAT WILL EXPERIENCE FLOODING INCLUDE...
THE CITY OF AUSTIN...BROWNSDALE...GRAND MEADOW...HAYFIELD AND
STEWARTVILLE. SOME STREAMS THAT COULD EXPERIENCE FLOODING INCLUDE
DOBBINS CREEK...NORTH BRANCH OF THE ROOT RIVER AND THE EAST AND
WEST FORKS OF THE CEDAR RIVER.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

EXCESSIVE RUNOFF FROM HEAVY RAINFALL WILL CAUSE FLOODING OF SMALL
CREEKS AND STREAMS...COUNTRY ROADS...AS WELL AS FARMLAND ALONG THE
BANKS OF CREEKS AND STREAMS.

A FLASH FLOOD WARNING MEANS THAT FLOODING IS IMMINENT OR OCCURRING.
IF YOU ARE IN THE WARNING AREA MOVE TO HIGHER GROUND IMMEDIATELY.
RESIDENTS LIVING ALONG STREAMS AND CREEKS SHOULD TAKE IMMEDIATE
PRECAUTIONS TO PROTECT LIFE AND PROPERTY. DO NOT ATTEMPT TO CROSS
SWIFTLY FLOWING WATERS OR WATERS OF UNKNOWN DEPTH BY FOOT OR BY
AUTOMOBILE.

PH

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