Update: Some gusty winds and hail reports now coming in.
MPX: Milaca [Mille Lacs Co, MN] mesonet reports TSTM WND GST of M78 MPH at 05:19 PM CDT — mndot station us-169 mile post 200
MPX: 1 E Sartell [Benton Co, MN] trained spotter reports HAIL of penny size (M0.75 INCH) at 05:28 PM CDT —
Storms are firing in the heat along what we call a “dry line” west of the metro. This is the leading edge of drier air in western Minnesota where dew points are around 40, vs. 50s in eastern MN. The drier air is denser and acts as a cold front, lifting the air ahead.
Image: College of Du Page Weather Lab
Dry lines are common thunderstorms “triggers” in Texas and Oklahoma, but less frequent in Minnesota.
-Latest Twin Cities radar loop
SPC does not expect to issue any severe weather watches with these storms, but the potential for hail and gusty winds is present. Dry air near the surface creates what we call “inverted V” soundings, whcih means rainfall can evaporate and cool as it falls. The cooler denser air sinks and can rush to the ground, creating gusty winds, mcrobursts and even so called “dry microbursts.”
Here’s the “mesoscale discussion” from SPC.
MESOSCALE DISCUSSION 0832
NWS STORM PREDICTION CENTER NORMAN OK
0454 PM CDT FRI MAY 18 2012
AREAS AFFECTED…CNTRL / SRN MN
CONCERNING…SEVERE POTENTIAL…WATCH UNLIKELY
VALID 182154Z – 182300Z
PROBABILITY OF WATCH ISSUANCE…20 PERCENT
SUMMARY…STRONG TSTMS CAPABLE OF LOCALLY ENHANCED WIND GUSTS
APPROACHING SEVERE LEVELS WILL BE POSSIBLE INTO MID-EVENING. A
WATCH IS NOT ANTICIPATED OWING TO THE MARGINAL NATURE OF THE THREAT.
DISCUSSION…A N-S BAND OF TSTMS HAS RECENTLY DEVELOPED FROM NEAR STC SWD TO JUST N OF FRM…APPARENTLY IN ASSOCIATION WITH A WEAK
MIDLEVEL VORTICITY MAXIMUM TRANSLATING NEWD THROUGH THE MID-MO VALLEY. AMBIENT AIR MASS IS CHARACTERIZED BY A HOT AND DEEPLY MIXED BOUNDARY LAYER WHERE T-TD SPREADS ARE APPROACHING 50 F. WHILE
VERTICAL SHEAR WILL REMAIN SUB-OPTIMAL FOR STORM ORGANIZATION AND SUSTENANCE…THE PRESENCE OF STEEP LOW TO MIDLEVEL LAPSE RATES AND DCAPE VALUES AROUND 1500 J/KG MAY PROMOTE STRONG EVAPORATIVE COOLING POTENTIAL WITH RESULTANT SURFACE WIND GUSTS APPROACHING SEVERE LEVELS.
Records Fall Friday:
The Twin Cities broke the record high today with at least 93 degrees. The previous record was 91 set in 1911.
RECORD EVENT REPORT
NATIONAL WEATHER SERVICE CHANHASSEN MN
425 PM CDT FRI MAY 18 2012
…RECORD HIGH TEMPERATURE SET AT MINNEAPOLIS/ST PAUL MN…
A RECORD HIGH TEMPERATURE OF 93 DEGREES WAS SET AT THE TWIN CITIES OF MINNEAPOLIS/ST PAUL MN TODAY.
THIS BREAKS THE OLD RECORD OF 91 SET IN 1911.