Today's Weather Discussion: Another Rain Chance?
Sunday, Nov. 14:
It's going to be a frosty start to the new work/school week in the morning, as numbers will fall off close to the 30 degree mark overnight. Could be a few high-level clouds work in from the west overnight....if a thicker cloud deck moves in, temperatures could remain a few degrees warmer than that. Lower-lying areas that stay totally clear may briefly fall to the upper 20's.
If you read my posts from last week, you'll remember I was going back and forth on what to do with forecast models flip-flopping on whether rain chances would make it this far north for the first half of this week. Well after much deliberation, it looks like both of the models I normally check have agreed that Tuesday would be a good day to have the umbrella on hand.
Surface Map: 6AM Monday
By tomorrow morning, low pressure along the Gulf Coast will be responsible for rain across the Deep South, and moisture should creep far enough to the north to lead to increasing cloud cover over at least the southern half of the region. As this low strengthens, it will begin moving northeast, eventually lifting across middle TN & central KY on Tuesday. This should place us close enough to the low to generate some rain, especially for KY & TN. Rain chances will drop as you move northwest into IL & MO. Rainfall totals should again be pretty light with this system. As I've mentioned before, with our ongoing drought, I'm going to continue to be very conservative with my rainfall forecasts until we finally start seeing signs of a wetter overall pattern. Rainfall estimates with this system range from under 0.25" with the NAM, and around an inch with the GFS......I'm going to lean more toward the NAM and it's 0.25" or so in KY & TN....less in IL & MO.
Moving on....time for a little lesson in weather terminology as we look to Wednesday. Forecast models have been showing a shortwave trough quickly swinging through on Wednesday, along with a surface cold front, that may bring some clouds and a few showers, especially in IL & MO. Some of you may have heard us use the term "shortwave trough" before.....let me fill you in on what that is. Typically, when we talk about a "trough", we're actually referring to a longwave trough.....where looking at the weather map, there is a big "U"-shaped dip in the jet stream that brings colder and sometimes stormy weather. A shortwave is simply a smaller scale area of lower pressure with a pocket of colder air aloft that has cyclonic characteristics. Shortwaves are also known as "mid-level disturbances", and can bring a quick round of unsettled weather. Below is a look at the shortwave we're expecting Wednesday. Notice the downward kink in the white lines...that indicates colder air aloft, and the yellow and red shades indicate something called positive vorticity....which is basically spin in the atmosphere:
GFS 500 mb chart: 6AM Wed.
These features can be tricky for a forecaster, but with little moisture to work with, I'd say little more than some increased cloud cover and a few scattered light showers will be the only affects of this system.
Looking toward late week and next weekend.....after a chilly blast of air Thursday, the overall flow in the atmosphere looks like it will become southwesterly over our part of the country, which will provide a nice warming trend for Friday and into next weekend.
Today's High & Low: 52 / 29
Average High & Low: 58 / 37
Record High & Low: 77 (1964) / 12 (1986)
Precip: November: 0.32" (12.49: below avg for 2010)
Sunrise/Sunset: 6:33 AM / 4:46 PM