Gusty Thunderstorms Have Been Frequent Despite Drought

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PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE CHICAGO IL
855 PM CDT MON AUG 6 2012 /955 PM EDT MON AUG 6 2012/

...GUSTY THUNDERSTORMS HAVE BEEN FREQUENT DESPITE DROUGHT...

WHILE THE SEVERE WEATHER SEASON WAS QUIET AT ITS NORMAL PEAK TIME
OF SPRING AND EARLY SUMMER ACROSS NORTHERN ILLINOIS AND NORTHWEST
INDIANA...IT HAS BECOME MORE ACTIVE SINCE THE TAIL END OF JUNE.
NEARLY 80 PERCENT OF THE PRELIMINARY SEVERE WEATHER REPORTS ACROSS
THE NWS CHICAGO COUNTY WARNING AREA THIS METEOROLOGICAL SUMMER
/JUNE-AUGUST/ HAVE BEEN CONVECTIVE WIND DAMAGE AND/OR OBSERVED
GUSTS. THERE HAVE BEEN APPROXIMATELY 225 PRELIMINARY REPORTS OF
EITHER WIND DAMAGE OR SEVERE CRITERIA WIND GUSTS /58 MPH OR
STRONGER/ RELAYED TO NWS CHICAGO SINCE JUNE 1ST.

SOME OF THE SEVERE WINDS HAVE BEEN EXTREMELY LOCALIZED IN THE FORM
OF MICROBURSTS...WHILE OTHERS HAVE BEEN WIDESPREAD WIND EVENTS
SUCH AS WHAT TRANSPIRED THIS PAST SATURDAY AUGUST 4TH. THUS IT IS
CHALLENGING TO TRY AND QUANTIFY THE NUMBER OF THESE GUSTY
THUNDERSTORMS VERSUS A NORMAL AND HAVE IT BE REPRESENTATIVE
EVERYWHERE. LOOKING AT PEAK CONVECTIVE GUSTS AT TWO INDIVIDUAL
AREA AIRPORTS CAN SHED SOME LIGHT HOWEVER.


CHICAGO...

                           SUMMER 2012*   1996-2011 SUMMER AVERAGE
DAYS WITH GUSTS >=40 MPH        8                   4
DAYS WITH GUSTS >=58 MPH        3                  <1

* = THROUGH AUGUST 6TH

THE THREE SEPARATE OCCASIONS WITH SEVERE WIND GUSTS THIS SUMMER IS
THE MOST OF ANY SUMMER AT CHICAGO OHARE AIRPORT DATING BACK TO AT
LEAST 1996. IT IS INTERESTING TO NOTE THAT THERE WERE SIX DAYS IN
JULY OF THIS YEAR ALONE WITH STORMS PRODUCING 40 MPH OR STRONGER
WINDS. THIS TIES WITH JUNE 2008 WITHIN ANY CALENDAR SUMMER MONTH
SINCE 1996 TO HAVE AS MANY SUCH DAYS AT OHARE.


ROCKFORD...

                           SUMMER 2012*   1996-2011 SUMMER AVERAGE
DAYS WITH GUSTS >=40 MPH        6                   3
DAYS WITH GUSTS >=58 MPH        1                  <1

* = THROUGH AUGUST 6TH

ROCKFORD HAD FOUR DAYS WITH 40 MPH CONVECTIVELY INDUCED GUSTS IN
JULY ALONE...TYING IT WITH JUNE 1998...JULY 2003...AND JUNE 2008
FOR THE MOST IN ANY ONE SUMMER MONTH.


THE MORE FREQUENT GUSTY STORMS CAN BE...AT LEAST IN
PART...ATTRIBUTED TO THE PERSISTENT HOT AND DRY CONDITIONS.
THE ONGOING VAST DROUGHT HAS LIKELY HELPED KEEP THE BOUNDARY
LAYER DRIER THAN NORMAL THROUGH SIGNIFICANTLY LESS
EVAPOTRANSPIRATION FROM WHAT WOULD TYPICALLY BE MOISTURE-LADEN
CROPS...WHICH IS WHY THE DEW POINTS HAVE NOT BEEN FREQUENTLY IN
THE 70S. DRIER NEAR-SURFACE AIR ALLOWS FOR DEEPER MIXING OF THE
LOWER ATMOSPHERE AND OVERALL HIGHER CLOUD BASES. THUNDERSTORMS
THAT ARE ABLE TO DEVELOP OR MOVE INTO SUCH AN ENVIRONMENT CAN HAVE
A HIGHER LIKELIHOOD OF PRODUCING STRONG WINDS AS THEIR DOWNDRAFTS
READILY ACCELERATE TO THE GROUND. IN ADDITION...THE PERSISTENT
UPPER LEVEL RIDGE AND ASSOCIATED STAGNANT HEAT ACROSS THE
MIDSECTION OF THE COUNTRY HAS ALLOWED FOR SCENARIOS IN WHICH THE
UPPER PARTS OF THE ATMOSPHERE ACROSS THE REGION REMAIN WELL-
MIXED...THROUGH WHAT METEOROLOGISTS CALL AN ELEVATED MIXED LAYER.
STORM GROWTH AND ASSOCIATED WIND STRENGTH CAN DEPEND HEAVILY ON
THIS. THE HEAT DOME HAS ALSO ALLOWED FOR THE OCCASIONAL RING-OF-
FIRE WEATHER PATTERN ON ITS PERIPHERY...WITH ORGANIZED STORM
COMPLEXES REGULARLY CAPABLE OF LONG-LASTING WIND EVENTS.

$$

MTF/KACZMAREK


Thunderstorm Wind Events of This Summer

 



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