The weather maps are getting a little ahead of themselves.
An unusually strong fall-like low pressure system winds up and spins toward Minnesota Tuesday. The inbound low deepens significantly as it moves in, drawing significant moisture from the south, and unseasonable cool air from the north. The result? Increasing waves of showers, wind and falling temperatures. Here's a look at the low pressure track, an Omaha-to-Lake-Superior pathway.
This system has all the earmarks of a fall season low pressure storm. If this was November, winter storm warnings would be flying for a big chunk of Minnesota Tuesday.
Here's some interesting perspective on the unusual seasonal nature of this storm from the Twin Cities NWS forecast discussion. Feed your inner Weather Geek.
AN UNSEASONABLY DEEP LOW PRESSURE SYSTEM WILL PASS NORTHEAST ACROSS THE REGION FROM TUESDAY INTO WEDNESDAY. NAEFS AND GEFS CLIMATOLOGY INDICATE THIS FEATURE IS OUTSIDE THE CLIMATE WINDOW FOR THE RESPECTIVE DATA PERIODS (1979 AND 1985). HENCE...WE ARE DEALING WITH SOMETHING QUITE UNUSUAL FOR THIS TIME OF YEAR. THE UPPER LEVEL DRIVER FOR THIS SYSTEM WAS OVER MT THIS AFTERNOON ACCOMPANIED BY A DEVELOPING PV BOOT. AS THIS SYSTEM STRENGTHENS TO OUR SOUTHWEST ON TUESDAY...SHOWERS WILL BECOME MORE NUMEROUS ACROSS THE FA ALONG WITH SCATTERED THUNDERSTORMS.
Temperatures will not climb out of the 60s for a big chunk of Minnesota Tuesday and Wednesday. The average high for Oct. 1 in the Twin Cities is 64 degrees. Let's cut to the forecast chase scene. Here's a closer look at rainfall timing and the arrival of unseasonably chilly temperatures through Wednesday.
This system has all the earmarks of being an "efficient" rainfall producer. It's the right mix of tropical moisture to the south, and cold air feeding into the system from the north, to wring out impressive rainfall totals. The models are gung-ho on another 1- to 2-inch soaking for the metro.
Here's a wider look at the system rainfall, with a swath of soaking rains across the Upper Midwest. Some 2- to 3-inch totals may include the Iron Range and North Shore.
Keep the umbrella handy and hang on tight in the gusty October-like gales.
Severe risk in southeast Minnesota
On the warmer side of the system there should be enough warmth, and plenty of energy and directional wind shear. A few severe storms are likely to clip southeast Minnesota just south and east of the metro. We'll have to keep an eye on the potential for some damaging winds, and even an isolated tornadic storm. Here's the risk zone Tuesday.
Summer returns Thursday
This one-off storm does not signify the end of summer as we know it. It also doesn't tell us anything about the prospects for an early fall. My hunch is fall will be nice this year. If the Super El Niño continues to develop, winter may be relatively balmy as well.
Southerly breezes and sunshine return Thursday, and temperatures (and humidity) respond back to summer levels as we close the week.
Tropical trouble ahead? Cape Verde season arrives
The brewing El Niño has probably contributed to a quiet hurricane season so far. But this week a developing wave (96L) coming off the west coast of Africa has a chance to develop into the first tropical cyclone of the so-called Cape Verde season.
Weather Underground Hurricane expert Dr. Jeff Masters has more.
Cape Verde season gears up
If 96L becomes a tropical storm, it will be Danny, the fourth named storm of this year’s Atlantic season. Based on data from 1966 through 2009, the fourth named storm typically occurs around August 23, so a tropical storm this week would be more or less on schedule. It would also be the first named storm to form in the Cape Verde region, where some of the most powerful Atlantic hurricanes originate. An informal definition of the peak Cape Verde season is from August 20 to September 20, although tropical storm formation becomes increasingly common throughout August across the deep tropics of the Atlantic. Already, a string of increasingly potent waves has been shuttling from Africa into the eastern Atlantic. However, all of these waves have collapsed as they approach the western Atlantic and the hostile conditions fostered by El Niño, including very high wind shear over the Caribbean and relatively stable air over much of the North Atlantic. Tropical cyclone activity often tapers off prematurely in the Atlantic during El Niño years, so it may become even more difficult to get Cape Verde storms toward September and October. We’ll see if this week’s wave happens to encounter El Niño at a weak point.