MU's Current Conditions: (at 11:38) Temp: 77 F | Dew Point: 72 | Wind: SSE - 4 mph
SPECIAL WEATHER DISCUSSION (Updated twice weekly, but more often when storms threaten.)

* No More Heat Waves Through Month's End *

10:00am Tuesday, June 20:
The average number of 90-degree days in June is five for the Lancaster area. So far this month we've had three days in the 90s, all coming with last week's heat wave (June 11 - 13). Looking ahead, we have a chance to get near 90 this Thursday and/or Friday (our official forecast is 86 - 90 for both days), but after than it's hard to see another 90-degree day through month's end...and perhaps until after the 4th of July. If I'm right about this, then we won't experience another heat wave (defined as 3 or more consecutive days with highs of 90 or above) in the next two weeks!

Short-term, we've got delightful conditions today, with moderate humidity and a pleasant breeze, in the wake of yesterday's thunderstorms and the passage of a front overnight. This air mass will gradually modify over the next three days as southwesterly flow brings us increasing moisture and warmth. Some clouds will develop both Wednesday and Thursday, but little more than an afternoon sprinkle or isolated shower is likely...if anything at all. There's a better chance for scattered showers (perhaps isolated thunderstorms) during the period from Thursday evening through Friday night as tropical moisture flows into the region from the Gulf coast region (where a weak tropical cyclone may form in the next 24 hours). Dew points will rise into the low 70s on Friday, so it will be quite muggy.

The weekend forecast is a bit uncertain at this time (10am Tuesday), as the potential tropical system along the Gulf coast will play a role. Right now, however, this system should be rather weak and strong jet stream flow across the north should help it accelerate remnant moisture through the Mid-Atlantic this weekend...with drier air filtering into PA from the northwest. The more likely threat of tropical downpours this weekend is to our south (across the Virginias and Delmarva), although a shift farther north would bring us some showers, too.

Next week's weather pattern will be dominated by a broad jet stream trough across the Great Lakes and Northeast. This pattern will bring us another cold front sometime Sunday night or Monday (with a few showers) followed by a comfortable Canadian high pressure taking control for much of the week. Partly to mostly sunny days and mainly clear nights with highs between mid 70s and mid 80s would be tough to beat! While a return of seasonably warm conditions is likely by the end of next week, I just don't see another sustained spell of 90-degree weather before month's end. --Horst

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