Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
552 FXUS61 KCTP 170910 AFDCTP Area Forecast Discussion National Weather Service State College PA 510 AM EDT Tue Sep 17 2024 .SYNOPSIS... An area of low pressure centered near Charlotte, NC this morning will drift slowly north into Virginia during the middle of the week, before tracking east and off the coast by Thursday. An upper level ridge over the Great Lakes is likely to build into Pennsylvania by next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A well-aligned ESE flow in the 925-850 mb layer has pushed the leading, NW edge of a lower stratocu deck to around a KAOO to KUNV and KSEG line as of 08Z, while variable amounts of mainly high clouds were noted across the Laurel Highlands and Northern Mtns of PA. Based on the 00Z HREF, there should be about another 30 NM of NW drift to these lower clouds before vertical mixing entrains dry air from aloft and helps to erode the cloud deck back toward the SE beginning about 14-15Z today. A fair amount of mid and high clouds will blanket the region for the midday and afternoon hours today, thanks to the deep, serly flow on the Northeast side of the PTC-8 remnants. POPS through the early afternoon hours today will be near zero in all areas, though a few, non-measurable sprinkles are possible in the south. The persistent/deep SE to ESE flow will continue to transport moisture off the Western Atlantic and Some limited valley fog will be possible through 13Z today in north central PA. Temps to start the day will be about 5 deg warmer than yesterday morning across the bulk of the CWA, whereas 24 hr temp change in the northern tier is expected to be closer to 0. && .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY/... Operational and EFS models runs continue to keep it drier than earlier expectations for Tues night-Wed period as the weakening sfc and upper low across North Carolina and VA drifts very slowly NE and off the Delmarva coast by the end of this period. Dry air holds tough in place in low and mid levels across much of the Commonwealth. Drought begets drought. Per collaboration with WFOs PHI and BGM, POPS were trimmed 10-15 percent across Scent PA and portions of the Lower Susq region for Wed/Wed evening. The bulk of latest guidance continues to indicate that the associated easterly low level jet and plume of Atlantic moisture associated with this system will weaken quickly as the disturbance moves north. However, it will come close enough to support a slight chance of showers over the southern tier counties late Today. Any rainfall that reaches Southern PA Tuesday should be very light (0.10 of an inch or less). Thickening cloud cover and an upsloping east-southeasterly flow should hold temperatures down today across the Laurel Highlands, where readings likely won`t climb get out of the 60s. Elsewhere, model RH profiles support filtered sunshine through a veil of altocu and cirrus, with the brightest skies near the NY border. Max temps across the remainder of the Susq Valley, Central and Northern Mtns will be in the mid 70s to low 80s which is 5-10 deg F above normal for Mid September. The best chance of showers or a few short periods of steadier light rain across Central PA appears to come late tonight and Wednesday, as the remnant low makes its closest pass to PA before shifting off of the East Coast late in the week. The bulk of recent guidance keeps the easterly low level jet and associated highest pwats just south of the Mason Dixon Line. The combination of increased moisture and large scale forcing ahead of the upper low currently targets areas just south of PA for locally heavy rain. Most likely rainfall by late Wed based on ensemble output ranges from <0.1 inch over Northern PA to around 0.5 inches over the southern tier. Recent dryness suggests the threat of flooding is low, even if a northward shift in the models brings the heavier rain into Southern PA. A 20-30 pct chance for rain continues into Thu, as various small low pressure centers attempt to take shape off the Mid Atl coast. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... 1030 PM Monday update holds minor changes for the late week and weekend. Only small/20 PoPs for the most part, and mainly for the SE. Prev... An upper level low over the region will keep clouds and showers around through most of the extended period. The best timing for showers remains unclear as this will be dependent upon the timing of multiple surface lows that will track near Central PA. Uncertainty begins to increase towards the weekend as there is quite a bit of spread in the guidance with respect to a building ridge to our west and how quick it pushes eastward. Ensembles suggest that the upper low will be slower to be replaced by ridging than had been shown over the past few days which will keep the chance for a few showers around through the weekend. Temperatures will generally be on a slight downward trend through the period with highs in the upper 60s and low 70s by Sunday and Monday. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... Lower ceilings across southern PA are being observed with MDT/LNS already down towards high-end MVFR restrictions as of 06Z Tuesday. Expect restrictions to continue at MDT/LNS through ~14Z with high (70-80%) confidence before lower-level clouds begin mixing out. Model guidance shows modest agreement with regards to lower clouds making their way into AOO/JST near 08Z with lower-level clouds continuing to bring MVFR restrictions through 18Z Tuesday. GLAMP guidance has been persistent with regards to IFR thresholds being met at JST, and given higher probabilities of IFR conditions in the 10-12Z timeframe have continued to outline these conditions with moderate (~60%) confidence in this timeframe. Uncertainty remains with northward progression of the lower-level cloud deck brining MVFR conditions to UNV/IPT so have outlined SCT lower-level clouds with a brief period of MVFR conditions at UNV near sunrise. In the 18Z Tuesday timeframe through the end of the TAF period, VFR conditions are expected with moderate-to-high confidence (50-70%). Some lower-level clouds could begin pushing their way into the southern airfields (JST/AOO/MDT/LNS); however, the best chances for restrictions come after 06Z Wednesday so have opted to keep mentions of scattered low-level clouds at this time. Outlook... Wed...SHRA w/ Isolated PM TSRA, highest chances across SE PA. Thu-Fri...Lingering showers possible, mainly across the east and south. Sat...Mainly dry conditions. && .CLIMATE... The first day of Autumn 2024 (Fall Equinox) begins at 8:44 am EDT on September 22nd. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/Dangelo NEAR TERM...Lambert/Dangelo SHORT TERM...Lambert/Dangelo LONG TERM...Lambert/Dangelo/Bauco AVIATION...NPB CLIMATE...NPB