Area Forecast Discussion

WHAT HAS CHANGED

* tweaks to sky cover

KEY MESSAGES

1) Noticeably cooler/pleasant and rain-free start to the week 2) Warm/humid conditions return mid to late week with best odds for rain Thursday

DISCUSSION

KEY MESSAGE 1: Noticeably cooler/pleasant and rain-free start to the week

Sky has cleared out. But, thin high clouds are moving into the west, and will gradually overspread most of Central PA overnight. That shouldn't matter to the river valley fog which should be starting to show up by midnight.

Prev...

Refreshing airmass behind cold front today with dewpoints in the 40s and 50s. Fair weather cu across much of the region with max coverage near the Great Lakes. Max temps will be 10 to 15 degrees lower/cooler vs. Sunday ranging from the mid 60s in the northern tier mtns to the mid 70s in the southern valleys along the MD line.

Strong radiational cooling pattern tonight into early Tuesday morning with very low pwats beneath area of high pressure migrating over CPA. Min temps into the upper 30s are definitely in play in the usual northern tier cold spots with 40-50F lows anticipated elsewhere (4-8F below climo). This setup favors valley fog formation with localized visibility restrictions below 1 mile.

Wide 25-35 degree diurnal range fcst Tuesday with another pleasant afternoon with max temps in the upper 60s to mid 70s.

KEY MESSAGE 2: Warm/humid conditions return mid to late week with best odds for rain Thursday

Return SSW flow on the back side of the high pressure system will pump the dewpoints and moisture/humidity back up from mid to late week. Best rain/QPF signal at this time is on Thursday 9/17 as a weak front sinks southward from the eastern Great Lakes. If the front can push south of the MD line, most of Friday could be dry. Precip odds then steadily increase over the weekend ahead of next frontal system progression from the Great Lakes. Large scale upper level ridging should support a mid to late week warming trend with the largest hi/lo departure from climo Wed-Thu.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Looking at mainly clear skies through 06Z Wed. Some mid and high clouds later today and tonight, mainly across the northwest at sites like BFD.

With very high 500 mb heights in place, main support for any showers will be mainly north of the PA, NY border prior to early afternoon on Wed. Support for showers and isolated storms. More in the way of widespread showers will be possible on Thursday,

Outlook...

Wed...AM fog possible, otherwise mainly VFR.

Thu-Sat...Increasing SHRA/TSRA chances, mainly on Thu, restrictions possible.

CTP WATCHES / WARNINGS / ADVISORIES

None.