As I’m typing on this Wednesday, March 6, the temperature is 12 degrees with a wind chill of minus 6 degrees. The 30-year average high and low for this date are 38 and 23. So far this young month is running 9.2 degrees below average, and that’s including two seasonable days on March 1 and 2. At least I can tell you by the time we reach the ides of March (surely you recall Shakespeare and all his “Beware the ides of March” jazz), we’ll have experienced some above-average temperatures between now and the ides (March 15).
Unfortunately, that burst of warming will be coming courtesy of a deep storm system pulling out of the plains and moving into the Great Lakes.
A 992-millibar low heading over Green Bay will pump up a gusty and warming downslope southerly wind Saturday night, strongest on hilltops and along the Lake Erie shoreline south of the metro area. This will all be out ahead of its trailing cold front. Its strongest winds farther north will come behind the cold front on Sunday. The pressure falls rapidly ahead of the cold front, and jumps quickly upward behind the front. Meteorologists watch these pressure fall/rise couplets with a cold front carefully for the strong wind potential.
Does this setup sound familiar? Didn’t we just go through something like this the Sunday before last? The answer is this event will be vaguely similar but, so far, does not appear to be near the same magnitude. That 992 low is deep, but not nearly so deep as the last storm. The last storm intensified to 971 millibars, which is a significant difference. The pressure gradient around the coming storm will not be as tight as the last, so wind speeds shouldn’t be able to reach the same ferocious velocities. In addition, this storm system will be moving along more rapidly, so the duration of any strong winds it produces should be shorter.
However, this storm will still be deep enough to cause at least limited spotty wind problems. On Saturday night, southerly winds will likely gust to 50 mph along the Lake Erie shoreline:
Once the cold front goes by on Sunday, the barometric pressure jump will quickly ramp up strong southwest winds:
Note I’m not using the term “high winds,” as others and I did in advance of the last storm. In meteorology, “high winds” is a severe weather term with a specific definition: sustained/steady winds of 40 mph for one hour or more, or peak gusts of 58 mph for any duration. At high-wind threshold, more widespread damage becomes likely, which is why people of my ilk don’t like seeing every windy day called a “high wind” day. It dilutes the meaning of the term.
As of now, there is good model agreement winds will stay below the high-wind category, and may reach NWS advisory level for spotty minor damage – which is relatively good news.
The other good news is the air mass behind this storm’s cold front will be more Pacific in origin and not polar. It will turn cooler but not truly cold as was the case behind the deeper storm. For example, here are the NWS headquarters' projected high temperatures for Monday:
Mid- to upper 30s are a far cry from the harsh cold and bitter wind chill we suffered on the Monday following the last storm. Projections have us back into the mid-40s by the following Wednesday.
Now, I’ll return to the dicey topic of St. Patrick’s weekend temperatures and trends. As I wrote Monday, the warming that develops this weekend does not look steady, even in the second half of the month. There are no signs we’ll be returning to the frigid cold we have at this time. However, the NWS ensemble mean upper air pattern for the afternoon of Sunday, March 17 still shows warmer ridging over western North America and colder troughing near the Great Lakes:
Ensemble means 10-plus days in advance represent somewhat smoothed clusters of model output, and can sometimes sharpen in amplitude when we get close to the date in question. That means there is a chance the upper air pattern will be colder than currently represented in the ensemble.
There is good agreement between three ensemble models that a colder trough will be near the Great Lakes at this time. The agreement, if it continues, suggests there is little chance of one of those relatively rare balmy days for the parade.
It is still too early to touch precipitation chances except to say the primary models are not suggesting much more than a cold northwest flow that might bring some Lake Huron flurries, and maybe some bits o’ sun. The latter will be needed, because such a flow would probably keep a cold northwest breeze with us and temperatures in the 30s.
Now that I’m not on TV, I won’t be marching in the parade. With such a forecast, it’s probably better that way. I’m sure Maddie, our giant puppy, will not know what she’s missing.