Showers Possible Today, Beautiful Week Ahead – Saturday 10 a.m.
September 8, 2012 Leave a comment
Big changes are in store for Central Alabama over the next 24 hours. Much drier air and cooler temperatures are on the way, but before they get here, we`ve got one more system to deal with.
A longwave trough is parked over the eastern third of Canada this morning and before it retreats further off to the north two more shortwave troughs will affect us as they round the southern periphery of the larger trough. The first is the one responsible for the approaching cold front this morning. Prefrontal activity has been ongoing ahead of the cold front for the last 6-10 hours, creating a line of showers and thunderstorms which has been weakening since midnight. This precipitation is on our door step and the question in the short term will be, how much more activity will we see today as the front moves through the area. Currently stretching from ArkLaTex northeastward into the Great Lakes, the front is expected to close in on Central Alabama through the morning hours. Models are pretty consistent with a couple of things: First, having the front approaching the I-20 corridor around the noon hour today and second, the idea of post frontal showers. It is likely that because the parent low is so far off to the north and there really isn`t a whole lot of synoptic support for organized convection, it will take the afternoon heating of the day to help create the necessary instability for thunderstorms. Because of this, the main area of focus for thunderstorms this afternoon will be along and south of Interstate 20. The good news is there isn`t a whole lot of synoptic support. This means there won`t be much in the way of shear to sustain updraft growth. 0-6km bulk shear of 20-25 kts ahead of the front is about all this system looks to muster across our area and this should curb any concerns about severe weather. Post frontal showers will be possible through the afternoon, but will be of little consequence.
The second of the two shortwave troughs will round the base of the longwave trough tonight and this will be the instigator in keeping the front moving through the state. Rain should end from northwest to southeast after sunset this evening and dry air will replace the rain fairly quickly.
The next question will be how cool will it get tonight. Looking upstream, post frontal dew points in the upper 40s and low 50s are fairly prevalent in the mid-Mississippi Valley. Dew points in the low to middle 50s would lead to unseasonably cool temperatures for Sunday morning.
The rest of the forecast has us dominated by high pressure aloft and at the surface. This means dry conditions all week and below normal temperatures can be expected Sunday through Tuesday, with a slight warming trend throughout the workweek.