Area Forecast Discussion
Issued by NWS Mt. Holly, NJ
Issued by NWS Mt. Holly, NJ
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668 FXUS61 KPHI 141925 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 325 PM EDT Sun Jul 14 2024 .SYNOPSIS... Bermuda high pressure remains offshore through the middle of the week. A thermal trough looks to develop east of the Appalachians Monday and Tuesday. Excessive heat and humidity are expected through Wednesday along with daily thunderstorm chances. A cold front will cross the region Wednesday night into Thursday, stalling out and lingering near or just south of the area through the end of the week. && .NEAR TERM /THROUGH MONDAY/... Surface high pressure builds over the Northeast today before sliding south of the region tonight. Zonal flow aloft sets up, and an increasingly hot and humid airmass spreads into the region. A shortwave trough passing through the region has resulted in scattered shower and storm development. Given how hot and humid it will be, SB CAPE values will be upwards of 1500 to 2000 J/kg. 0-6 km Bulk Shear will be limited. Despite this, the higher instability and Dcape values meant that there will be a potential for pulse type storms with downburst winds. Because this is diurnally driven, should see storms diminish in coverage by sunset. A warm and muggy night on tap for tonight with lows in the 70s. Patchy fog may develop once again, especially along the coasts. Another short wave trough will approach the region tomorrow. Exact timing is uncertain, but at this point, it appears as if the prime period will be late afternoon into the evening. As with Sunday, prime concerns with any storms will be downburst winds and heavy rain. There may be a small inversion around 800 mb (based on some model soundings), which could slightly limit the instability, but models were depicting a similar case today, and given the amount of heating, don`t think it will make a significant impact in limiting convective potential. None the less, with a lack of a focus for surface convergence, do not expect widespread storms. Rather, it should be scattered (similar to the coverage we`re seeing today. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... Excessive heat and humidity continuing, likely peaking on Tuesday, along with daily chances for thunderstorms. High pressure anchored in the western Atlantic and low pressure across the Great Lakes will focus heat and humidity northward across the East Coast. A more zonal flow aloft is forecast, although with a trough and jet feature approaching gradually through the period. Meanwhile, a convective complex (MCS) upstream across the Midwest to the eastern Great Lakes may toss some clouds into at least portions of our area. The trajectory for this looks to mostly follow areas to our west and northwest, with even a convectively induced surface low tracking near the eastern Great Lakes to northern New York. There is some potential this activity turns more southeastward into growing instability, or additional development takes place on the southward tail of the associated shortwave. The convection should generally be favored during the afternoon and evening time frame, mainly near and northwest of I-95 where diurnal instability is greater Monday evening and Tuesday afternoon and evening. There is considerable uncertainty however on the convective evolution and also the severe weather risk with this setup, especially given the more zonal flow aloft. Overall, any severe weather risk (and greater coverage of thunderstorms) will be determined by upstream convection and therefore the predictability in our area remains low at this time. Low temperatures Monday night will be mainly in the low to mid 70s, warmest near urban centers and across Delmarva. The excessively hot and humid stretch continues through Tuesday and Tuesday night. For Tuesday, temperatures increase even more along with lower chances for convection during the daytime period. Tuesday is still expected to be the hottest and most oppressive of this stretch, with highs largely in the upper 90s. Dew points remaining in the lower 70s will support peak heat indices of 105-110 degrees across much of the area. Lows Tuesday night will likely be the warmest of this hot stretch, with lows in the mid to upper 70s in many areas, and near 80 degrees in the urban centers. Given the latest forecast for Monday and Tuesday`s temperatures and heat indices, we`ve upgraded portions of the Heat Advisory and Excessive Heat Watch to an Excessive Heat Warning (Heat Advisory for lower Delaware and northwest New Jersey). Additionally, a Heat Advisory was issued for Carbon and Monroe Counties in PA, coastal Monmouth and inland Cape May Counties in NJ (these zones did not previously have a watch in effect). && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Summary...Excessive heat Wednesday begins to diminish as a cold front and associated showers and thunderstorms move toward the region late Wednesday, then temperatures should be closer to average Thursday through Saturday with lowered humidity. Synoptic Overview...An upper-level trough is forecast to pivot into and across the Northeast and Mid-Atlantic regions Thursday into Friday. The western Atlantic ridge may try to expand eastward again into the Mid-Atlantic Saturday, however an upper- level trough is forecast to remain from eastern Canada down across the Great Lakes and into the Mid-Mississippi Valley. This may be enough to keep the main part of the ridge at bay along with the associated hotter temperatures. At the surface, a cold front arrives Wednesday night and gradually shifts offshore during Thursday. High pressure should then extend eastward into our area Friday into Saturday. For Wednesday and Thursday...As an upper-level trough arrives, a cold front will approach during the day Wednesday before crossing our region Wednesday night and Thursday. A pre-frontal trough may also develop on the leeward side of the mountains. This combined with increasing forcing for ascent and greater effective shear should result in showers and thunderstorms developing and becoming more widespread with time, especially by late afternoon and evening. The convective organization may be more tied to the pre-frontal trough as it shifts eastward later Wednesday, and given ample instability and enough shear some thunderstorms could be strong to severe Wednesday afternoon and evening. The details however remain a bit unclear. The highest PoPs are included Wednesday afternoon and evening, however the PoPs remain at least in the chance range Thursday for most of the region as the front may be slow to clear our area. High temperatures are forecast to be well into the 90s yet again, with resulting heat indices near 100-107 or so across much of the area (especially along and south of I-78. Thus, the Excessive Heat Watch remains in effect for Wednesday. The arrival of convection and also the cold front will knock down the excessive heat, and therefore Thursday is expected to be noticeably cooler and drier than Wednesday. For Friday and Saturday...The main part of the upper-level trough should be lifting up across the Canadian Maritimes later Friday, however this trough (weaker form) may extend southwestward across the Great Lakes and into the Mid- Mississippi Valley. Pending that the front clears our entire area by Friday and drier air advects in, precipitation chances then drop off during this time frame. Surface high pressure centered near the Midwest should then extend eastward with time and into our area. This should promote a more light northerly flow, although may result in a sea breeze both days, and therefore temperatures much closer to average and also lowered humidity. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR. Scattered afternoon SHRA/TSRA with potential for gusty and variable winds in the vicinity of any storms. Winds prevailing out of the SW. However, afternoon sea breezes will turn winds S first at KMIV/KACY, then at the I-95 corridor terminals late in the afternoon. Tonight...VFR initially. MVFR or lower VSBYs in fog possible after 06Z. Highest potential for VSBY restrictions in fog will be at KMIV/KACY. LGT/VRB winds. Moderate confidence. Monday...Primarily VFR. Showers and storms will be possible after 18Z, which could result in brief restrictions if they move over a TAF site. Winds starting light and variable, but should favor southwesterly direction for most of the day. Moderate confidence. Outlook... Monday night through Tuesday night...Generally prevailing VFR. A 20-30% chance of showers or thunderstorms, mainly northwest of I-95. Wednesday and Thursday...Showers and thunderstorms likely, especially Wednesday afternoon and evening. && .MARINE... Winds and seas should stay below Small Craft Advisory criteria through Monday. However, locally higher winds are possible in the vicinity of any storms, especially Monday afternoon and evening. Patchy fog may continue through tonight, especially for waters very close to the coast. Outlook... Monday night through Tuesday night...The conditions should be below Small Craft Advisory criteria. Some fog possible at times. Wednesday and Thursday...A Small Craft Advisory may be needed, especially Wednesday. Showers and thunderstorms develop Wednesday afternoon with some continuing into Thursday. Areas of fog possible. Rip Currents... For Monday and Tuesday, south to southwest flow will average 10 to 15 mph with wave heights only 1 to 3 feet and a 5 to 7 second period. Therefore, there is a LOW risk for the development of dangerous and life threatening rip currents for both the New Jersey Shore and the Delaware Beaches. Some areas of fog at times will cause reduced visibility along the shoreline. For specific beach forecasts, visit weather.gov/beach/phi && .CLIMATE... Near record breaking temperatures are forecast from Monday through Wednesday. Records for our climate sites are listed below: Record High Temperatures July 15 Site Record/Year Allentown (ABE) 98/1995 AC Airport (ACY) 100/1995 AC Marina (55N) 99/1995 Georgetown (GED) 96/1993 Mount Pocono (MPO) 92/1954 Philadelphia (PHL) 103/1995 Reading (RDG) 96/1995 Trenton (TTN) 101/1995 Wilmington (ILG) 99/1995 & 1997 Record Warmest Low Temperatures July 15 Site Record/Year Allentown (ABE) 79/1995 AC Airport (ACY) 78/1995 AC Marina (55N) 80/1995 Georgetown (GED) 75/2012 & 2016 Mount Pocono (MPO) 69/2013 Philadelphia (PHL) 81/1995 Reading (RDG) 79/1995 Trenton (TTN) 78/1995 Wilmington (ILG) 78/1995 Record High Temperatures July 16 Site Record/Year Allentown (ABE) 101/1988 AC Airport (ACY) 100/1983 AC Marina (55N) 100/1983 Georgetown (GED) 97/1953 & 1992 Mount Pocono (MPO) 93/1988 Philadelphia (PHL) 102/1988 Reading (RDG) 100/1900 Trenton (TTN) 102/1988 Wilmington (ILG) 100/1983 Record Warmest Temperatures July 16 Site Record/Year Allentown (ABE) 76/1983 AC Airport (ACY) 77/1983 AC Marina (55N) 80/2013 Georgetown (GED) 80/1955 Mount Pocono (MPO) 70/1955 Philadelphia (PHL) 80/2013 Reading (RDG) 78/1955 Trenton (TTN) 78/1983 Wilmington (ILG) 77/2013 Record High Temperatures July 17 Site Record/Year Allentown (ABE) 99/1999 AC Airport (ACY) 99/2012 AC Marina (55N) 95/1937 Georgetown (GED) 100/2019 Mount Pocono (MPO) 91/1999 Philadelphia (PHL) 102/1988 Reading (RDG) 102/1988 Trenton (TTN) 100/1988 Wilmington (ILG) 100/1988 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Excessive Heat Warning until 6 AM EDT Wednesday for PAZ060>062- 070-071-101>106. Excessive Heat Watch from Wednesday morning through Wednesday evening for PAZ060>062-070-071-101>106. Heat Advisory from 10 AM Monday to 8 PM EDT Tuesday for PAZ054- 055. NJ...Excessive Heat Warning until 6 AM EDT Wednesday for NJZ009-010- 012-013-015-017>020-027. Excessive Heat Watch from Wednesday morning through Wednesday evening for NJZ001-007>010-012-013-015>022-027. Heat Advisory from 10 AM Monday to 6 AM EDT Wednesday for NJZ001-007-008-014-023. Heat Advisory until 6 AM EDT Wednesday for NJZ016-021-022. DE...Excessive Heat Warning until 6 AM EDT Wednesday for DEZ001. Excessive Heat Watch from Wednesday morning through Wednesday evening for DEZ001>004. Heat Advisory from 10 AM Monday to 6 AM EDT Wednesday for DEZ002>004. MD...Excessive Heat Watch from Wednesday morning through Wednesday evening for MDZ012-015-019-020. Excessive Heat Warning from 10 AM Monday to 6 AM EDT Wednesday for MDZ012-015-019-020. MARINE...None. && $$ SYNOPSIS...Staarmann NEAR TERM...Johnson SHORT TERM...Gorse/Staarmann LONG TERM...Gorse/Staarmann AVIATION...Johnson/Staarmann MARINE...Hoeflich/Johnson/Staarmann CLIMATE...Staarmann