textproduct: State College

WHAT HAS CHANGED

* Minor changes to the previous fcst.

KEY MESSAGES

1) More storms expected for central PA Sunday afternoon and evening. Some likely severe.

2) Rare, SPC Day 6 outlook for SVR TSRA potential across much of PA on Thu 6/18

DISCUSSION

KEY MESSAGE 1: 1) More storms expected for central PA Sunday afternoon and evening. Some likely severe.

AFter a fair and dry day and night, the air will get muggier on Sunday, especially in the Lower Susq. Dewpoints 65-70F are expected by mid-afternoon. Upper trough crossing the Great Lakes will drive strong forcing across during the peak heating and early evening. SPC outlook for Sunday paints a risk of tornadoes across the SE, where hodographs are slightly curved and helicity exceeds 200. CAPE at LNS is not all that fat, but nears 1100J/kg in the mid-aftn with deep layer (0-6km) shear of 40KT. LCLs are low there, too. But, the rest of the CWA will probably realized less CAPE due to lower dewpoints. UNV CAPE almost non- existent, but shear just slightly higher. BFD has a significant cap overhead until mid-aftn, but the lift from the nearing front and falling heights work. Thus, there could be two areas of convection develop simultaneously (W and SE), then the western convection should slide east and impact some of the central zones. However, the instability does look limited in the central zones. SPC SLGT risk of svr tstms covers most of the CWA and the WPC ERO MRGL risk are also touches the wrn mtns. Some convection should hang on after sunset until a cold front pushes through (00Z NW - 04Z SE), but it should be out of the CWA around 11 PM. The main action will be out ahead of the front during peak heating.

KEY MESSAGE 2: Rare, SPC Day 6 outlook for SVR TSRA potential across much of PA on Thu 6/18

The nose of a very strong, 40+ KT swrly 850 mb jet 50+ KT at 700 mb (both being 3+ sigma on the standardized anomaly scale), the the right entrance region of a 100 KT 250 mb jet and PWATS around 1.5 inches (with the potential of a EML surging in from the west ahead of a strong sfc cold front) will bring the ideal synoptic setup for a severe weather outbreak here in the CWA. As always, even with the moisture, instability and shear present, such strong forcing could produces plenty of clouds and early day convection to stabilize the atmos and decrease the potential for significant afternoon severe weather. We'll be monitoring this potential closely as we head into the start of the new week.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Very high (> 80%) confidence in VFR conditions continuing through 18Z Sunday with current observations outlining clear skies across the entire Commonwealth as of 06Z Sunday. increasingmid-to-high level deck is current being observed on recent ECONUS Nighttime Microphysics satellite, with observations across central Ohio outlining ceilings over 10,000ft AGL. This will likely continue to move eastward and impact many, if not all, of central Pennsylvania's terminals prior to 18Z.

Recent HREF does outline an initial shot of moisture potentially bringing some shower/storm activity between 15Z-21Z across SE PA (MDT/LNS); however, lower confidence on this occurring with more recent hi-res model guidance pushing this activity south of the PA-MD border at this time. There will remain a slight (~30-40%) chance of this activity at the airfields that is not accounted for in this TAF package; however, and should continue to be monitored as we get into the late morning hours. Model guidance does agree on more widespread shower/storm coverage along a cold frontal passage, and have went slightly more aggressive for TSRA mentions on this cycle with narrowing of PROB30 windows to two- three hour windows based on more recent HRRR/HREF model guidance and the more recent GLAMP guidance. TSRA will likely bring a drop in visibility, but not expecting widespread lower ceilings that warrant longer-term mentions in the TAF package. Confidence remains high in TSRA; however, timing differences warrant keeping PROB30s this cycle to see a couple more runs to CAMs in order to gain more robust confidence in the timing and to avoid having three hours of TSRA mentions when we're looking at faster moving TSRA that will likely impact airfields for around one hour, or even less in most cases. PROB30s extended all the way to MDT/LNS this cycle, given concern for TSRA across E PA. After the cold frontal passage, guidance indicated a mixed bag in ceilings; however, have not went as aggressive on lower ceilings given some low-level dry air that looks to work into the area after the frontal passage; however, clearing behind this feature could lead to development of low-level (IFR/LIFR) restrictions.

Outlook...

Mon...Mostly VFR with isolated -SHRA possible.

Tue...Mostly VFR with isolated -SHRA/-TSRA possible.

Wed...Higher chances for -SHRA/-TSRA, restrictions more likely.

Thu...Restrictions possible in -SHRA/-TSRA.

CTP WATCHES/WARNINGS/ADVISORIES

None.