![National Oceanic and Atmospheric Administration](/build/images/header/noaa.d87e0251.png)
![National Weather Service](/build/images/header/nws.4e6585d8.png)
![United States Department of Commerce](/build/images/header/doc.b38ba91a.png)
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
164 FXUS61 KCTP 140920 AFDCTP Area Forecast Discussion National Weather Service State College PA 520 AM EDT Sun Jul 14 2024 .SYNOPSIS... Another prolonged and significant heat wave is expected today through Wednesday with max heat index values reaching between 100 and 110 degrees F over parts of south-central PA and the Susquehanna Valley. Isolated late afternoon or early evening thunderstorms are expected to develop from the heat and humidity, however, most places are expected to stay dry through tonight. More organized, and potentially strong to severe thunderstorms are expected each afternoon and evening, Monday through Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Anomalously warm and muggy conditions with mostly clear skies are in store through this morning clearing skies are expected overnight with MinTs running in the lower 70s across the LSQ with some potential for lower 60s across the Laurels and N PA. There remains a likelihood of some radiational/valley fog early today, especially in areas that received rainfall late Sat afternoon/evening with model soundings outlining some low- level moisture overnight. Lows at sunrise will vary from near 60F throughout the perennial cold spots across Northern PA and Somerset County in the southwest. A weak, stationary frontal boundary extending from the Poconos to the Lower Susq Valley early today, separated low 70 dewpoint air from mid and upper 60 dewpoints across the Scent Mtns and Middle Susq Valley. Surface ridge with dry mid-level air across central PA will allow for a very warm to hot day today, with heat index values across the LSQ pushing towards and upwards of 100F and a Heat Advisory (see NPWCTP) has been issued. The biggest uncertainty with regards to heat index values will be PWAT values and SFC dewpoints, the former of which will be lowest this afternoon (0.9 to 1.0 inch) in a narrow band from the Ncent Mtns to the Laurels, while the far SE and NW corners of the CWA will see PWATs AOA 1.4 inches or nearly +1 sigma. If the drier air is able to mix down from the top of the boundary layer (5000-6000 KFT AGL today), heat index values will have some potential to under-perform this afternoon. Highs this afternoon will vary from the mid and upper 80s across the higher terrain of the North and West, to the low and mid 90s over Scent PA and the Lower Susq Valley. PWAT values will increase late today/this evening ahead of weak shortwave which will provide another opportunity for scattered convection. At this time, HREF guidance and its individual members indicates the best moisture and lift for convection will be focused near and just to the east of the stalled out boundary over the Lower Susq Region beginning during the early to mid afternoon, with the second area later this afternoon into early tonight ahead of an approaching/albeit rather flat mid-upper level shortwave where diffluence aloft and deep layer/unidirectional westerly shear will be somewhat better. POPS in the SE will peak around 20 percent this afternoon, and 30-40 percent across the NW Mtns this evening. The Allegheny Front and Central Ridge and Valley Region should see the lowest POPS of 13 percent or less during the daylight hours. A slightly better westerly breeze of 5-10 kts with some gusts into the low-mid teens will boost temps by 2-3 deg F today, but the breeze may help make it feel the same or slightly cooler than Saturday via evaporation of perspiration off the skin. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/... Cloud cover across N/W PA from weakening convection will provide fairly uniform MinTs tonight into Monday morning, ranging from the mid- to- upper 60s to the lower 70s across the LSQ. Confidence in excessive heat risk is higher on Monday, and has lead to the issuance of a Heat Advisory (see NPWCTP) for the south-central Alleghenies and Middle Susquehanna Valley on Monday. The interaction of a modest shortwave trough, coupled with a very warm and humid airmass is currently expected to trigger thunderstorms Monday afternoon into the evening hours with a slightly higher severe threat than over the weekend with shear being be the biggest limiting factor. Collaborated with LWX to maintain the Excessive Heat Watch (through a few more model cycles) for Monday afternoon into Tuesday for the lower Susq given some model uncertainty in SFC dewpoints and precip amounts/impacts from afternoon convection. SPC has placed all of the CWA within a MRGL risk of Severe TSRA Monday as stronger mid and upper diffluence and the approach/presence of a better defined left exit region of the jet will lead to enhanced larger scale lift to help break any weak cap. The Susq Valley and points east, along with sou swrn zones may see the best chance of SHRA/TSRA though on Monday. Precipitation becomes more limited to NW PA overnight Monday and into Tuesday morning. The more important sensible weather overnight into Tuesday will be the lack of reprieve from warm temperatures with MinTs ranging in the upper 60s (N PA) to the mid-to-lower 70s (LSQ) with muggy conditions. && .LONG TERM /TUESDAY THROUGH SATURDAY/... A hot and humid airmass will be across the area on Tuesday. Held onto current high temperatures for Tuesday, given that the thickness is quite high. Some concern for any days up to Wednesday could see showers and storms, given that weak shortwaves track just to our north, around a rather large 500 mb upper level low for mid July. Main chance for storms would be from about route 6 northward. For later Wednesday, a cold front moves across central Pennsylvania. Expect widespread showers and storms across the area, as the cold front drops southeast across the region. Wavy front just to the south and east of the Keystone state on Thursday could still result in a shower or storm, mainly across the southeast. After this, high pressure builds into the area, resulting in less humid weather, with mainly dry conditions. Still some hints that slightly higher dewpoint air could work back into the area by late in the weekend, resulting in a small chance of showers. More information below on the heat for Tuesday. Heat pattern ramps up and peaks early next week as a large Bermuda high pumps increasingly hot and very humid air into CPA. 850mb temps rising to around 22C supports highs peaking between 90-100F with max heat indices 100-110F. High confidence in excessive heat risk lead to the issuance of a heat advisory for the south central Alleghenies and middle Susquehanna Valley on Tue and xheat watch for the lower Susq where max heat index could reach 105-110F. Heat index values will likely push 100F or advy criteria over the Lower Susq Valley Wednesday afternoon. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... CLearing skies, light winds, and muggy conditions overnight have led to the development of patchy fog, especially across the northern valleys and in areas that received rainfall on Saturday. VSBYS and CIGS could briefly dip into the IFR/LIFR range between 10-12Z, mainly at KBFD with a much lower probability at KIPT and KUNV. Elsewhere across Central and Southern PA, conditions will remain VFR this morning. Any fog will quickly burn off after sunrise, leaving predominantly VFR conds today. A few pop-up SHRA/TSRA are possible this afternoon, focused on the NW mtns and the Lower Susq Valley. Therefore, added VCSH later today for BFD, MDT and LNS. Outlook... Mon-Tue...Scattered, mainly aftn, SHRA/TSRA possible. Wed...More widespread SHRA/TSRA, with brief restrictions likely. Thu...Lingering -SHRA diminishing. && .CLIMATE... RECORD TEMPERATURE - A record high temperature of 86 degrees was set today at Bradford, PA. This ties the old record which was set back in 1979. The duration of warm nights is noteworthy -- Harrisburg has not dropped below 70 degrees since July 3rd. Here are the longest stretches with temperatures at or above 70 on record at Harrisburg. # OF DAYS DATES YEAR 17 7/19-8/04 2020 13 8/16-8/28 2021 13 7/13-7/25 2010 12 7/18-7/29 2022 12 7/17-7/28 1999 12 7/20-7/31 1940 11 8/04-8/14 1977 10 8/10-8/19 2016 10 7/14-7/23 2013 10 8/01-8/10 1968 10 7/21-7/30 1898 9 12 times, most recently 7/3-7/11/2020 8 7/04-7/12 2024 ................................................. The minimum temp dipped to 68F yesterday morning (7/12) and therefore ends the streak at 8 consecutive days. Tonight will start another run of lows >=70F which should last until next Thursday night (7/18 or morning of 7/19). && .CTP WATCHES/WARNINGS/ADVISORIES... Heat Advisory from noon Monday to 8 PM EDT Tuesday for PAZ019- 025>028-034-035-045-046-049>053-058. Heat Advisory from noon today to noon EDT Monday for PAZ036- 056-057-059-063>066. Excessive Heat Watch from Monday afternoon through Tuesday evening for PAZ036-056-057-059-063>066. && $$ SYNOPSIS...Lambert/NPB NEAR TERM...Lambert/NPB SHORT TERM...Lambert/NPB LONG TERM...Martin AVIATION...Lambert/Evanego CLIMATE...Evans