Area Forecast Discussion
Issued by NWS State College, PA
Issued by NWS State College, PA
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005 FXUS61 KCTP 201608 AFDCTP Area Forecast Discussion National Weather Service State College PA 1208 PM EDT Thu Jun 20 2024 .SYNOPSIS... The center of a subtropical upper level high over Pennsylvania will sink southward over the next few days. A weak cold front will approach and stall out over the region Friday and Saturday. A more significant cold front is likely to push through Sunday night or early Monday bringing brief relief from the humid weather. && .NEAR TERM /THROUGH TONIGHT/... A weak mid and upper level shortwave centered over Lake Ontario with a southward training trough/narrow vort lobe into NW PA will bring the focus for any convection over our NE counties during the next several hours. As weak deep layer subsidence in the wake of the aforementioned shortwave wanes across NW PA late this afternoon/evening and the Lake Erie breeze makes its greatest inland penetration the convective depth should increase within an area of HREF MU CAPE close to 2000 J/KG near and just to the west of KBFD. Will make some minor modifications to the timing/placement of POPS across the north and continue to maintain nil POPS south and east of the I-80/I-99 corridors. Otherwise, very little change to other elements of the forecast within this rather hot and dry airmass with light sfc wind. Previous Disc... Sfc dewpoints are expected to rebound to the m-u60s, and some spots (NY border) get around 70F for Td today. Maxes are pretty much unchanged, and have pretty much copied the MaxTs from yesterday into today. While this will result in heat index values not quite getting to 100 in most/all places today, the Heat Advisory still looks warranted for everyone using the logic of the past few days. The majority of the storms will be across wrn NY state where the heights are lowering. There will be more organization to the storms today vs the past couple of days. While shear is higher today, it is still fairly unimpressive. The large CAPEs and weakening cap over the nrn tier lead to a bit more concern for damaging gusts and marginal (1") hail - mainly along and N of Route 6, but some stronger storms could drop down as far S as I-80. Little/no precip is expected in the srn half of the area, but if anyone could see a stray shower/storm, it would pop off the highest ridges of the Laurels. Have kept the PoPs nil there for now. The threat for heavy rainfall is still here. Despite slightly lower PWATs today, the storms still won`t be moving too fast. Also, the nrn tier does have the lowest FFG numbers for the CWA as they have been the recipients of the most rainfall lately. The threat is not widespread enough to post a flash flood watch at this point. As the storms diminish tonight, fog is expected to form and could get dense overnight. Mins hold in the 65-70F range. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... The ring-of-fire will be along the nrn tier again Friday with a weakness in the sfc pressure over the nrn and central counties. The heights continue to lower and this lowers the stability for the aftn and evening even further for Fri vs Thurs. This will allow for convection to be scattered about a wider area on Fri. Some threat of severe wind/hail still exists. SPC has a MRGL risk over most of the CWA. This seems warranted. But, the similarities to Thurs may mean that the risk may be a little higher than advertised at this point, and we could see us get bumped up to a SLGT risk with later updates. Temps will start out 3-5F higher on Fri AM vs Thurs and help the SErn 2/3rds of the CWA get into the m90s or better. The higher Td on Fri will give us just enough of a boost to have more places get at or above 100 heat index. The storms should diminish from W-E Fri night. Since more places should receive rainfall Fri and early Fri night and some clearing is expected behind the storms, we should get a more- widespread fog to form. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Medium range guidance indicates PA will remain under a low amplitude upper level ridge through the upcoming weekend with a strong surface high parked near Bermuda, resulting in a continuation of the heat and humidity. Ring of fire convection looks likely Friday and Saturday, especially along the northern tier of the state, closest a stalled front near the PA/NY border. Model 0-6km shear remains weak Friday, but a slight increase in mid level flow could result in a better chance of organized severe wx over Northern PA Saturday PM. Current 2m and 850mb temps plumes indicate some of the hottest weather of this heat wave will occur between Friday and Sunday, so may need to extend the heat advisory, which currently only lasts through Saturday. Mean EPS 850 temps peak near 22C across Southern PA late in the weekend, supportive of max temps near 100F across the Lower Susq Valley. Most locations should see a round of showers/tsra Sunday PM into Monday AM associated with the passage of the shortwave trough and attendant cold front. Behind this feature, expect a return to fair and more seasonable conditions early next week. A surge of warmer weather currently looks likely midweek ahead of an upstream cold front, which could also be accompanied by our next round of showers/tsra. && .AVIATION /16Z THURSDAY THROUGH MONDAY/... VFR conditions are expected areawide for most of the day. All guidance shows thunderstorms developing near the New York border during the late afternoon/early evening, but there are differences in the models with respect to how far south the storms reach. At this point, BFD appears to be the most likely airfield to be impacted. Brief visibility reductions will be possible in any thunderstorms, along with the potential for strong winds. Model soundings support fog development overnight across the north and the HREF shows greater than 50% probabilities of visibilities dropping below 1/2 mile after 06Z at BFD. Outlook... Fri-Sun...Predominantly VFR, with continued heat and isold aftn/eve SHRA/TSRA. Density altitude concerns possible. Mon...Predominantly VFR, with brief reductions possible in scattered SHRA/TSRA as a cold front crosses the area. && .CLIMATE... A period of warmer than average temperatures is expected across much of central Pennsylvania through the end of the week, with record high temperatures at multiple cities being challenged every day through Saturday. Two records were either set or tied for sites on Tuesday: * A record high temperature of 92 degrees was set at Altoona on Tuesday Jun 18, which tied the old record of 92 degrees set back in 1994. * A record high temperature of 90 degrees was set at Bradford on Tuesday Jun 18. This broke the e old record of 87 degrees set back in 1993. One record was set on Wednesday: * A record high temperature of 88 degrees was set at Bradford on Wednesday Jun 19, breaking the old record of 87 degrees set in 1987. The record high temperatures for some sites across central PA that could be challenged are outlined below: ............ Jun 20 .... Jun 21 .... Jun 22 .. Harrisburg 98/1931 98/1923 nn/YYYY Williamsport 101/1923 97/1933 nn/YYYY State College 94/1953 94/1988 nn/YYYY Highest Max Temperatures for Central Pennsylvania Observing sites for June (date of occurrence is in parentheses: State College 96 in 1952 (26th) and 1933 (29th) Harrisburg 100 in 1966 (27th), 1952 (26th), and 1934 (29th) Williamsport 104 in 1925 (5th) Altoona 97 in 1971 (28th) and 1953 (21st) Bradford 93 in 2022 (22nd) Longest run of consecutive days with max temp >=90 in June: State College 6 (24-29th 1966) Harrisburg 10* (19-28th 1943) Williamsport 9 (18-26th 1923) Altoona 8 (13-20th 1994) Bradford 0 (has not occurred since POR started at site in 1957) *Harrisburg had a run of 11 days with temperatures greater than 90 degrees that started on 26th and ended on July 6th in 1901. && .CTP WATCHES/WARNINGS/ADVISORIES... Heat Advisory until 8 PM EDT Saturday for PAZ004>006-010>012- 017>019-024>028-033>037-041-042-045-046-049>053-056>059- 063>066. && $$ SYNOPSIS...Lambert/Dangelo NEAR TERM...Lambert/Dangelo SHORT TERM...Dangelo LONG TERM...Fitzgerald AVIATION...Lambert/Bauco CLIMATE...Evans/Colbert