* Warmer Weekend to Preceed Arrival of Fall *

10:00am Thursday, September 18:
A weak area of Canadian high pressure building across the Northeastern US will sustain the pleasant Fall-like weather a couple more days before a brief return of warmer conditions this weekend. As this high pressure exits the coast Friday afternoon, a period of easterly flow will affect the region Friday night into early Saturday. The result will be some low clouds late Friday into Saturday, however, developing south and southwesterly flow Saturday will ultimate lead to warmer and a bit more muggy conditions Saturday afternoon into Sunday. While high temps will hold in the low 70s today and Friday, the weekend will warm a few degrees above normal with highs in the upper 70s to low 80s.

The next front will move through Sunday evening with a just a couple of showers possible late Sunday afternoon into the overnight. There's a chance that Sunday night's front may entrain some of the remnant moisture from ODILE (the tropical cyclone that moved in over Baja and into the southwestern US early this week); if so, the showers could produce a little more in the way of some needed rain Sunday night....but don't bet on it.

The first half of next week will be dominated by deepening northwest flow as a trough pivots over the Great Lakes and Northeast. A large area of high pressure will then usher in another cool, comfortable air mass Monday night through Wednesday. Daytime highs will hold in the upper 60s to low 70s Monday and Tuesday, and overnight lows will drop into the low 40s...and perhaps even the upper 30s. Patchy frost is likely in parts of central and northern PA, but the first widespread frost in our area is unlikely for at least a few more weeks.

Beyond that, I see another moderating trend late next week into the final weekend of September as high temps return to around 80 degrees. And looking ahead to October, I see more of the same...as a mild pattern may take hold in the East for part of the month.

11:30am Monday, September 15:
Persistent west and northwesterly flow will bring us a comfortable week with temps running a few degrees below normal. Highs will be mainly in the low to mid 70s and overnight lows in the mid 40s to low 50s. Only a passing front late tonight looks to bring a brief round of showers (between midnight and daybreak Tuesday); otherwise we have a mainly dry week ahead.

While relatively benign, nearly zonal flow prevails over the lower 48 to start the week, there are a couple of things of interest to track over the next week or so. First is Hurricane ODILE now moving in off the Pacific into southern Baja. This system will weaken while tracking slowly northward towards Arizona--remnant moisture from this storm unfortunately may bring another round of heavy rain to parts of Arizona on/around Thursday. Beyond that, the moisture will be entrained by a mid-latitude trough crossing the Rockies on Friday...and this moisture may help fuel showers farther east, perhaps in the Midwest on Saturday and Ohio Valley or Great Lakes Sunday (and possibly here in PA next Monday?). Ahead of this trough, southwesterly flow will result in a warming trend across the Commonwealth with highs reaching the upper 70s to near 80 on Sunday.

Next week may begin with a few showers on Sunday night or Monday, before another large Canadian high pressure system settles in with cool, dry conditions into the midweek. Some long-range guidance points to a large jet stream ridge developing in western North America next week--if so, a deep trough may develop over the Eastern states late next week bringing much below normal conditions and possibly the first snow flakes of the season at the highest terrain of the region (places above 4,000 feet such as Blue Knob, PA and Snowshoe, WV).

P.S. Here's a link to the latest episode of MU's Weather Watch, a fully student-produced bi-weekly show.

Issued: 9-18-14 (Horst)