MU's Current Conditions: (at 05:16) Temp: 67 F | Dew Point: 66 | Wind: SSE - 14 mph
SPECIAL WEATHER DISCUSSION (Updated twice weekly, but more often when storms threaten.)

* Somewhat Cooler Pattern Developing *

10:00am Monday, October 23:
After five straight days of gorgeous "sunny and 70s" afternoon conditions, clouds are returning to the region...and somewhat cooler air will follow for the second half of the week. The jet stream is in the process of amplifying both to our up- and down-stream, so the west-to-east propagation of systems will slow down...and the changing conditions will be gradual.

Short-term, today's morning fog and low clouds will be slow to thin, but afternoon temps should rise to around 70 as skies brighten a bit later on. Meanwhile, a strong upper-level system is lifting from the Ohio Valley into the eastern Lakes with a cold front limping eastward. This front--and the moisture-rich air mass proceeding it--will slowly cross the Commonwealth tonight into early Tuesday. Scattered showers and perhaps even a few isolated gusty thunderstorms will cross Lancaster mainly between 12am - 10am Tuesday. Some localized heavy downpours and wind gusts to 50mph are possible late tonight into early Tuesday. But skies will clear Tuesday afternoon with highs reaching the low 70s for a final day.

A trailing upper-level system and cold front will cross the region Wednesday into Wednesday night ushering in a brief blast of seasonably cool--but not cold--air for the second half of the week. A stray shower is possible Wednesday afternoon or night, but most of the late-week period will be dry...with afternoon highs in the low 60s and overnights in the 40s. The weekend will bring slightly milder conditions (highs in the mid/upper 60s) with partly sunny skies giving way to increasing clouds and a few showers on Sunday...and perhaps a period of rain Sunday afternoon or night, if a low pressure or tropical wave (from the Caribbean) tracks up along the East coast.

Next week looks to bring additional jet stream amplification with some hints of sustained troughiness from the Plains and Upper Midwest to the west slope of the Appalachians for the first week or so of November. The coldest air of the season so far will dump into the Midwest and Mid-Atlantic early next week (even a few snow showers in the highest terrain of WV & PA) with Halloween highs only in the mid 50s in Lancaster. Some moderation back to near-normal is likely for the second half of next week, although I do not see a major warm up or another spell of Indian Summer. As a general overview of the first week of November...I expect the coldest air (relative to normal) to set up over the Northern Plains and Upper Midwest while milder air prevails over the Western States, the Southeast, and perhaps up along the East Coast...with near-average temps near the Appalachians (and much of central and western PA). This *may* be a preview of this winter's temperature trends (in the mean) across the I'll present in my Winter Outlook....coming November 1st! --Horst

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