By Skip Rigney

Rainy weather that set in on Thursday night will taper off Saturday morning, but not before dumping one to three inches inches of rain across south Mississippi. The slow moving system prompted the National Weather Service to issue a Flash Flood Watch on Friday and caution that a few locations could receive up to four inches before the precipitation comes to an end.

One cause of the soggy weather was a low pressure circulation several miles above the earth’s surface. On Friday the upper low was over Oklahoma and Texas and was forecast to move slowly into Arkansas and Missouri on Saturday. The upper low was accompanied at the surface by a rather complicated tangle of multiple low pressure centers and fronts, including a tropical low in the western Gulf.

These disturbances and their associated rising air motions tapped into a plume of tropical moisture streaming north out of the Gulf on Thursday night and continued to do so Friday and Friday night. Forecasters anticipated that the Flash Flood Watch for most of south Mississippi and southeast Louisiana would be lifted by Saturday morning or midday, which is when they expect the rain to have moved to our east.

On Sunday the low pressure system will have moved far to our north over the Great Lakes.

The frontal boundaries will have consolidated into a weak cool front and moved to our east over the Florida Panhandle. That will put us in a northerly flow of dry, but not particularly cool air on Sunday.

Overall, Sunday looks like a pleasant day with mostly sunny skies. Temperatures will start in the 50s and climb into the 70s by midday Sunday.

However, while we’re enjoying a mild Sunday afternoon, a mass of very cold air will be spilling southward out of Canada into the Rocky Mountain states.

Tourists at the Old Faithful Geyser in Yellowstone National Park in Wyoming will need to bundle up, because temperatures there aren’t expected to get much above 20 degrees Sunday.

Like most cold fronts, this one is headed southward and eastward, in other words, toward us. However, the two most reliable computer forecast models are in major disagreement about when the cold front will arrive in our area. They also disagree about whether the core of the cold air plunges all the way to the Gulf Coast or is shunted eastward before it gets here.

The trick-or-treaters may need to bundle up on Thursday evening as temperatures plummet into the 40s. Or, according to other models, the cold front may not have arrived yet, and temperatures could be in the 70s. And, depending on which model you choose to believe, chances of the youngsters encountering a shower on their candy gathering rounds cover a wide range, from about 10 to 50 percent.

The models will probably come into much better agreement by Monday. Fortunately, even if they don’t, most of us don’t have to figure out which model to bet on. The meteorologists at the National Weather Service in Slidell will do the hard work for us. They post their updated forecasts twice each day, around 4 a.m. and 4 p.m. at www.weather.gov.