Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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945 FXUS61 KPHI 261430 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1030 AM EDT TUE JUL 26 2016 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A cold front was still to our north and west over upstate New York and back toward the Ohio River Valley this morning. The pre-frontal trough that was the focus for yesterday afternoon`s round of severe storms was positioned just to our south across southeast VA. The cold front is expected to weaken as the boundary catches up with the pre-frontal trough this afternoon. As this happens, the primary surface trough may actually reform slightly farther northwest. West-northwest winds behind the trough axis has advected drier air into the northern two-thirds of the region. Although dewpoints are still high (upper 60s/lower 70s) in eastern PA and central/northwestern NJ, dewpoints will lower 5-10F from what they began at this morning as the drier air mixes down during peak heating late this morning and afternoon. Heat indices this afternoon will be close to dry-bulb temperatures (generally mid 90s) across this part of the forecast area The drier air will have a difficult time reaching our south zones with the surface trough lifting back northward today into extreme southern NJ, central and southern Delaware, and eastern Maryland. The combination of high temperatures in the mid 90s and dewpoints in the low to mid 70s will yield heat indices between 103-107F across mid Delmarva. A Heat Advisory was issued for Kent and Sussex Counties in DE and Queen Annes, Carolina and Talbot Counties in MD. The same area covered in the Heat Advisory will also be at risk for an afternoon thunderstorm. Locally heavy rainfall cannot be ruled out with the airmass remaining moist (PWATs still around 2 inches), slow storm motion (under 15 kt) and the potential for multiple storms to develop along the quasi-stationary surface trough. The low coverage of storms (mainly isolated) and sandy Delmarva soils will limit the overall flash flooding risk. One or two storms may also contain locally strong winds given they are forming in an environment conducive for wet microburst. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/... 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. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... 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. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. 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. && .MARINE... 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. && .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...Heat Advisory until 7 PM EDT this evening for DEZ002-003. MD...Heat Advisory until 7 PM EDT this evening for MDZ015-019-020. MARINE...None. && $$ Synopsis...Manning Near Term...Klein Short Term...Iovino Long Term...Manning Aviation...Iovino/Klein/Manning Marine...Iovino/Manning Climate...Staff

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