Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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069 FXUS61 KPHI 202133 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 533 PM EDT Thu Jul 20 2017 .SYNOPSIS... A cold front will approach the area tonight and cross through by Friday morning. Weak high pressure will then prevail through Saturday. Another front and associated low pressure will be across the area Saturday night through Monday. High pressure will then move in next Tuesday and remain into the middle of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... ... Severe Thunderstorm Watch till 10 pm... The spotty showers that have been developing over the lower Susquehanna River Valley and parts of Maryland, Delaware and southern New Jersey this afternoon have not been getting much traction. A capping inversion aloft has been limiting the vertical development of the cells. Our main concern is the convective complex that was moving into the Poconos. It is expected to impact our northern counties this evening and recent trends in the data have it making a common southward turn toward the Philadelphia metro and central New Jersey as well. This complex of storms has a history of wind damage as it moves southeast. Lapse rates are steep along with mixed layer CAPE of 1,000 J/KG CAPE or higher, shear is more modest but sufficient for complex to maintain through the evening hours. Updated pops considerably based on this information from Philadelphia and points north with the expectation of a period of thunderstorms with damaging winds and heavy rain moving northwest to southeast across these portions of the region. Hail can not be ruled out as well. Late this evening, we will loose peak heating and the decrease of instability which will lead to decreasing trends of any convection. The sky over our region should become clear to partly cloudy. A surface trough trailing the convective complex is expected to pass through our forecast area late tonight. The wind is anticipated to become light and variable overnight. Low temperatures should be mostly in the 70s. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Maximum temperatures on Friday will be similar to those of today. However, the humidity is forecast to be slightly lower. We will leave the Excessive Heat Warning in place for the urban corridor. However, other areas should fall a bit short of their criteria for a Heat Advisory. The sky is expected to be mostly sunny on Friday. We will not mention any precipitation due to the lack of any significant triggering mechanism along with the continued existence of a capping inversion aloft. The wind should favor the west and southwest on Friday around 5 to 10 MPH. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... The heat wave will continue on into the weekend, but it will gradually weaken with temperatures more in line with normal after Monday. A few recent model runs are showing than high temperatures around 90 degrees readings are possible Monday, something which has changed since yesterday, but for now we will continue with upper 80s across the Philadelphia metro area and for Delmarva too. Dew point temperatures will be lower over the area Saturday, but then climb back to steamy values Sunday and early Monday. A front will cross the area Monday and drier and cooler air will arrive behind that for the middle of next week. Shower and tstm chances will be rather low Friday night and into Saturday morning, but then increase from w to e through the afternoon as the the front and humid air return to the area. High chance to low likely pops will be over the area Sunday into Monday as the system passes the region. Lower pops will be over the area Tuesday and Wednesday with high pressure settling over the region. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions are expected through much of the TAF period with one notable exception. A complex of thunderstorms is forecast to pass across parts of eastern Pennsylvania and northern and central New Jersey this evening. The storms now look to have a higher potential to impact KPNE and KPHL but look to stay north of KILG, KMIV and KACY, they are expected to impact the areas around KRDG, KABE KTTN, KPNE and KPHL between about 2200Z and 0200Z. The thunderstorms may bring localized wind gusts of 30 to 35 knots from the northwest. Additonal adm coming shortly to account for this as of 5:30 pm. Also, patchy visibility restrictions are possible during the late night and early morning hours especially in areas where rain falls this evening. We are not anticipating any showers or thunderstorms on Friday. A light southwest wind this evening is expected to become light and variable tonight. A light northwest wind is anticipated for Friday morning, then it should become west and southwest as the day progresses. OUTLOOK... Fri night thru Saturday morning...VFR expected. Saturday afternoon thru Monday...Mostly VFR. Sct showers and tstms with lower conditions possible. Tue...Mostly VFR. && .MARINE... High pressure over the Atlantic will continue to influence the coastal waters of Delaware and New Jersey for tonight. A weak frontal boundary from the northwest is forecast to arrive early on Friday. The wind should favor the south and southwest at less than 15 knots tonight, becoming west to southwest on Friday. Wave heights on our ocean waters will remain around 2 to 4 feet and waves on Delaware Bay should be 1 to 2 feet. Thunderstorms on the coastal waters from ACY northward may result in gusty winds for a few hours this evening. OUTLOOK... Sub-SCA conditions overall. The main hazard will be sct tstms mainly between Saturday afternoon and Monday. Locally higher winds and seas with tstms. Bring your NOAA weather radio along to get alerts. RIP CURRENTS... The underlying 10 to 14 second southeasterly swell is forecast to persist into Friday. As a result, we will continue the moderate risk for the development of dangerous rip currents through that time. && .EQUIPMENT... The KDOV dew point readings are unrepresentative of the area and should not be used when diagnosing humidity/heat indices and meteorological analysis of meteorological items which use dewpoint in a calculation. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Heat Advisory until 7 PM EDT this evening for PAZ060>062-101- 103-105. Excessive Heat Warning until 8 PM EDT Friday for PAZ070-071- 102-104-106. NJ...Heat Advisory until 7 PM EDT this evening for NJZ009-010-012- 013-016-020>023-027. Excessive Heat Warning until 8 PM EDT Friday for NJZ015- 017>019. DE...Heat Advisory until 7 PM EDT this evening for DEZ002-003. Excessive Heat Warning until 8 PM EDT Friday for DEZ001. MD...Heat Advisory until 7 PM EDT this evening for MDZ008-012-015- 019-020. MARINE...None. && $$ Synopsis...O`Hara Near Term...Gaines/Iovino Short Term...Iovino Long Term...O`Hara Aviation...Gaines/Iovino/O`Hara Marine...Iovino/O`Hara Equipment...

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