Severe weather outbreak likely Saturday

Batten down the weather hatches.

A severe weather outbreak is likely Saturday afternoon and evening across Minnesota. A strong low pressure system over southern Canada sweeps a powerful cold front into a humid unstable air mass over Minnesota Saturday. Expect a squall line of severe thunderstorms to develop ahead of the advancing front.

Severe weather watches and warnings are almost a certainty Saturday afternoon and evening. In fact, NOAA's Storm Prediction Center has raised the severe threat level to "enhanced" which is the 3rd highest risk out of 5 categories.

Here's a closer look ta how to interpret NOAA's severe risk categories.

Storms Saturday will likely produce damaging winds and hail. A few tornadoes or gustnadoes may also form as the storms advance across Minnesota Saturday. Here's more from NOAA's Storm Prediction Center's convective outlook for Saturday.

...SUMMARY...

SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED LATE SATURDAY AFTERNOON AND EVENING ACROSS THE UPPER MIDWEST AND LOWER MISSOURI VALLEY. DAMAGING WINDS...LARGE HAIL...AND A FEW TORNADOES WILL BE POSSIBLE.

...UPPER MIDWEST AND LOWER MO VALLEY...

HAVE UPGRADED/EXPANDED SEVERE PROBABILITIES WITH INCREASED CONFIDENCE IN WIDESPREAD TSTM DEVELOPMENT AND A CONCENTRATED CORRIDOR OF GREATER SEVERE POTENTIAL ANTICIPATED FROM MN TO SERN NEB.

VIGOROUS SHORTWAVE TROUGH CURRENTLY OVER SRN BRITISH COLUMBIA SHOULD DIG ESE INTO THE UPPER MS VALLEY BY 12Z/SUN. THIS WILL SUPPORT DOWNSTREAM CYCLOGENESIS WITH A RELATIVELY DEEP SURFACE LOW TRACKING FROM THE CNTRL DAKOTAS TO NWRN ONTARIO DURING THE PERIOD. A PLUME OF SEASONABLY RICH LOW-LEVEL MOISTURE CHARACTERIZED BY MEAN MIXING RATIOS OF 13-18 G/KG WILL BE ADVECTED N ON PERSISTENT SLYS FROM THE SRN PLAINS/WRN GULF ON D1. THIS SHOULD FOSTER MIDDLE 60S TO LOWER 70S SURFACE DEW POINTS BY SAT AFTERNOON AHEAD OF A COLD FRONT ADVANCING ESE ACROSS THE REGION.

AN EXPANDING EML PLUME SHOULD PROVIDE SUFFICIENT CAPPING TO PRECLUDE OPEN WARM SECTOR DEVELOPMENT IN THE UPPER MIDWEST. LATE AFTERNOON TSTMS WILL LIKELY INITIATE AS A CONCENTRATED AREA OF HEIGHT FALLS/LARGE SCALE FORCING FOR ASCENT OVERSPREADS THE N/S-ORIENTED PORTION OF THE COLD FRONT NEAR THE DAKOTAS/MN BORDER. THIS ACTIVITY SHOULD BE ON THE ERN FRINGE OF A STRONG MID-LEVEL SWLY JET PROGGED TO LIE FROM NRN NEB INTO SWRN MN AT 23/00Z. GIVEN THE DEGREE OF FORCING ASCENT...CONVECTION SHOULD QUICKLY GROW UPSCALE INTO A SQUALL LINE WHICH MAY ACCELERATE ENE IN THE EARLY/MID-EVENING AS MID-LEVEL WINDS STRENGTHEN. INITIAL MIX OF SEVERE HAIL/WIND SHOULD BECOME A PREDOMINANT DAMAGING WIND RISK IN MN WITH A FEW EMBEDDED SUPERCELL/MESOVORTEX STRUCTURES CAPABLE OF TORNADOES.

The Twin Cities NWS chimes in with the unusual nature of the storm for August and the associated severe risk in their forecast discussion.

A SECOND ANOMALOUSLY DEEP LOW PRESSURE STORM SYSTEM WITHIN A WEEK WILL PASS ACROSS THE REGION THIS WEEKEND. GEFS M-CLIMATE RETURN INTERVAL ONCE AGAIN SHOWS THE SURFACE AND UPPER LEVEL LOW PRESSURE WITH THIS SYSTEM IS OUTSIDE THE CLIMATE WINDOW FOR THIS TIME OF YEAR. MODEL GUIDANCE REMAINS IN REALLY GOOD AGREEMENT WITH A SURFACE LOW DEEPENING TO 994 MB ON SATURDAY AS IT MOVES NORTHEAST ACROSS THE DAKOTAS TO NORTHWEST MINNESOTA BY SATURDAY EVENING. A STRONG COLD FRONT WILL ENTER WESTERN MN LATE IN THE AFTERNOON AND SWEEP EASTWARD ACROSS OUR ENTIRE FA BY SUNDAY MORNING.

VARIOUS CAMS SHOW SOME PRETTY STOUT CONVECTION DEVELOPING ACROSS WEST CENTRAL THROUGH NORTHWEST MN AROUND MID AFTERNOON WITH THE LINE FILLING IN SOUTHWARD AS THE ACTIVITY MOVES EASTWARD IN THE LATE AFTERNOON. THE INITIAL CONVECTIVE DEVELOPMENT IS NEAR THE BEST DIFFERENTIAL DIVERGENCE ASSOCIATED WITH A COUPLED UPPER LEVEL JET. CWASP VALUES REMAIN VERY HIGH ALONG AND AHEAD OF THE FRONT. CONDITIONAL TORNADO VALUES ARE ALSO QUITE HIGH ACROSS CENTRAL MN SATURDAY AFTERNOON. THIS IS COLLOCATED WITH THE BEST SURFACE PRESSURE FALLS.

A CHECK OF THE CIPS ANALOGS CONTINUES TO POINT TO AN ACTIVE DAY WITH ALL FORMS OF SEVERE WEATHER POSSIBLE. IT/S INTERESTING TO NOTE THAT THE ANALOGS NOW HAVE SEP 16TH 2006...WHICH WAS THE ROGERS TORNADO. THIS DAY ALSO HAD STRONG LOW LEVEL SOUTHERLY WINDS ALONG WITH A MID LEVEL WIND MAX PUSHING INTO WESTERN MN. CERTAINLY AN ACTIVE WEATHER PATTERN IS POSSIBLE DURING THE AFTERNOON AND EVENING. ANOTHER CONCERN ON SATURDAY IS THE POSSIBILITY THAT A WIND ADVISORY MAY BE NEEDED FOR SOUTHERN MN IN THE MORNING. INDICATIONS FOR 30 MPH SUSTAINED WINDS CONTINUE ON VARIOUS MODEL SOLUTIONS.

Bottom line: Expect severe weather watches and warning to be posted Saturday afternoon and evening across Minnesota including the Twin Cities metro. Severe thunderstorms with damaging winds and large hail are likely, and a few tornadoes are possible.

Forecast: Taste of September

Sunday's cold front sweeps in another unseasonably cool and dry air mass. Look for a quiet and sunny forecast into early next week.

Smoky skies Friday

You may have noticed the pale white tinted sky across Minnesota Friday. That's the smoke plume I talked about Thursday gliding east over Minnesota. Check it out, you can clearly see the thick smoke plumes aloft over the Dakotas and Minnesota on NASA's MODIS Terra shot Friday.

Here's NOAA's smoke mapper.

Hurricane Danny may struggle

How does El Nino affect Atlantic hurricanes? The textbook case may be Hurricane Danny, who is expected to encounter stronger wind shear and drier air in the next 48 hours. Danny should weaken below hurricane threshold as it approaches the Caribbean islands.