Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 260752 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 352 AM EDT TUE JUL 26 2016 .SYNOPSIS...
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A cold front will stall near or just to the south of the area today. This front will gradually lift north by the end of the week with areas of low pressure developing along this boundary causing periods of showers and thunderstorms, mainly toward the end of the work week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The last of the precipitation was moving off the Delaware coast at 3:30 AM. An impulse traveling in the mid level flow was passing overhead early this morning and it was accompanied by a surface trough. Both features should pass off the coast with decreasing dew point temperatures in their wake. We are expecting patchy fog and low clouds early this morning, especially where heavy precipitation fell. Both should be quick to dissipate this morning as the atmosphere begins to mix and dew point readings lower. The sky is forecast to be mostly sunny for today with only some cirrus overhead along with scattered cumulus developing. Maximum temperatures are expected to be in the middle 90s for today, except in our far northern counties and along the immediate coast. Afternoon dew point readings should be in the 60s in our northern and central counties and in the lower 70s in the south. Heat index values will likely fall just short of 100 in the urban corridor from Trenton to Philadelphia to Wilmington. As a result, we will not issue a Heat Advisory or Excessive Heat Warning. The same is true for some of our Delmarva counties which may just nudge their excessive heat criterion of a 105 heat index. All other areas in our region should also remain below their criteria. The atmosphere will likely remain capped over much of our forecast area for this afternoon so we are not anticipating any showers and thunderstorms with one exception. There should be marginal instability across Talbot County and Caroline County in Maryland and Sussex County in Delaware along with a slightly weaker cap there. We will mention a slight chance of precipitation for those counties. The wind should favor the west and northwest around 10 mph for today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
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Weak high pressure is forecast to nose into our region from the west for tonight. As a result, we are expecting a mainly clear sky. The only exception will be our far southern counties where there may be some lingering scattered shower and thunderstorm activity. Temperatures are expected to fall into the 60s in our northern counties and into the 70s elsewhere with a light and variable wind.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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The stalled frontal boundary across the delmarva will be the main focus of attention over the next few days. Available medium range guidance all keep the high pw air just south of the boundary with values in excess of 2". Heat indices Wednesday look to top out in the lower to middle 90s climbing to the middle to upper 90s from the Philadelphia metro area southward to the delmarva Thursday. Precipitation chances remain confined to southern portions of the forecast area Wednesday with increasing chances Thursday into Friday for the remainder of the area. Temperatures Wednesday on track to be a couple of degrees cooler than today, but with building heights Thursday temps rebound into the mid 90s in the metropolitan areas with upper 80s/lower 90s near the water. Forecast for the Thursday through Saturday period remains complicated. Medium range deterministic guidance is highly divergent as to the evolution of the shortwave trough spinning up a surface wave on the retreating warm front. The ECMWF remains on the slower end of the solution while the GFS is faster and generates a lot more QPF. The Canadian is in between. At this point, forecast will lean heavily on ensemble means are probably the most sensible approach until more agreement develops across the medium range guidance. In the sensible weather this would suggest keeping pops fairly constrained during the day Thursday with the best chances for storms late Thursday night through Friday. Precipitation chances will continue through the weekend before dryer air moves into the mid-Atlantic early next week. Temperatures this weekend and early next week expected to be closer to climatological normals.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Areas of low clouds and fog are expected through about 1100Z to 1200Z. Otherwise VFR conditions are anticipated through the TAF periods under a mainly clear sky. We are not forecasting any precipitation at or around our TAF sites. A light and variable wind early this morning should settle into the west and northwest around 10 knots for today. The wind is forecast to become light and variable for tonight. Outlook... Wednesday through Saturday...Mainly VFR conditions expected. Scattered showers and thunderstorms Thursday and Friday, with MVFR/IFR conditions possible with any shower and thunderstorm activity.
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&& .MARINE...
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The wind direction should favor the northwest and west this morning before backing toward the southwest and south for this afternoon and evening. The wind may turn around toward the north late tonight. Speeds should remain 15 knots or less. Wave heights on our ocean waters are expected to favor the 2 to 3 foot range. Waves on Delaware Bay should be 2 feet or less. Outlook... Wednesday through Saturday...Sub-advisory conditions are expected to continue on the area waters through most of the work week. Expect higher winds and waves in and near scattered showers and thunderstorms that will be more likely at the end of the week. Rip Currents... There is a low risk for the development of dangerous rip currents for today. We are anticipating an offshore wind this morning around 10 mph becoming south to southwest for this afternoon. There will likely be a southerly 2 foot swell with a period of about 5 or 6 seconds. The probably risk for the development of dangerous rip currents on Wednesday is also low. Conditions will be similar to those of today except the wind should be mainly onshore during both the morning and afternoon hours.
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&& .CLIMATE... The last time the temperature reached or exceeded 98F at PHL was three years ago on July 18, 2013. The last 100-degree day at PHL occurred four years ago on July 18, 2012. Record high temperatures for Today through Thursday are below. Site 26th 27th 28th ---- ---- ---- ---- PHL... 101-1892 101-1940 100-1941 ABE... 98-1940 98-1955 97-1949 ACY... 96-2011 99-2005 98-1999 ILG... 99-1894 100-1894 101-1894 TTN... 99-1892 100-1894 101-1894 GED... 97-2012 98-2005 99-1949 RDG... 99-1940 98-1955 99-1941 MPO... 89-1949 91-1955 93-1949 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Manning Near Term...Iovino Short Term...Iovino Long Term...Manning Aviation...Iovino/Manning Marine...Iovino/Manning Climate...Staff

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