Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 292029 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 429 PM EDT Sat Apr 29 2017 .SYNOPSIS... A weak cold front will cross the area tonight before dissipating south of the region Sunday. A ridge of high pressure will be across the area Sunday before low pressure and its associated fronts move towards the Middle Atlantic later Monday and Monday night. High pressure will build in for the middle of next week. Another low will affect our area towards the end of next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Near record to record warmth occurring in some places this afternoon. An upper-level ridge, centered just off the coast of the Carolinas, is forecast to build slightly to the north over our area tonight. This is in response to a potent closed low across the Central and Southern Plains. Meanwhile, a surface cold front (located just to our northwest at mid-afternoon) will settle south-southeastward across our area tonight with high pressure building across portions of eastern Canada. A notable airmass change will occur through tonight behind the cold front and courtesy of the aforementioned high pressure system. For the rest of this afternoon and going through this evening, a very warm to hot airmass is in place ahead of the cold front. The dew points have mixed out some for several spots this afternoon, which has eased up the humid feel a bit. An analysis shows instability has been gradually increasing northward as the convective debris cloudiness has thinned quite a bit allowing for more heating of the boundary layer. There is not much in the way of forcing though, with one notable short wave tracking across western and central Pennsylvania northeastward. The associated convection with this continues to weaken, although some showers may clip the southern Poconos. There is some isolated renewed development to its south/southwest however. The best chance, and even this looks to be on the lower side, appears to be across portions of Delmarva and southern New Jersey where some high-res model guidance wants to move some convection across early this evening. It appears that Philadelphia is on the northern edge of this potential convection. This is less certain as there does not appear to be much forcing for convective organization plus the mid level ridge is building some. We will continue to place the highest (chance) PoPs across these areas for awhile this evening then gradually lower and shift them southward with the cold front. Given the amount of instability across the southern zones along with some drying aloft could result in a few storms that are able to develop produce locally gusty winds this evening. Otherwise, a wind shift to the north and northeast will occur through the night as the cold front works southward. This will drive some drier air southward as a result and the forecast soundings are not really robust with low clouds/fog developing as a result. There should at least be some stratocumulus development especially as the northeast low-level flow gets going. Low temperatures are mostly a MOS/continuity blend. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/... The weather will be rather different Sunday compared to today (Saturday) in the wake of a cold front. This front is expected to clear our entire area before stalling in a west to east orientation. An upper-level ridge axis should be moving across our area, allowing surface high pressure to build to our north and east. This will allow for a northeast low-level flow which should become east and then southeast with time. This will allow for a much cooler airmass to be over our area, enhanced by the flow off the colder ocean waters. While there may be areas of stratocumulus, the cloud bases may lower especially in the afternoon as the flow turns more east and southeast resulting in some increase in the moisture. Overall though, there should be a fair amount of cloudiness across the region during the day. As of now other than some slight chance PoPs early across parts of Delaware and Maryland, opted to go with a dry forecast as there is no real clear forcing with the southward/stalling front. Any remaining instability in the southern areas should be more elevated given the onshore low-level flow. High temperatures were a MOS/continuity blend, then some tweaks were made mostly along the coast. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... A weak ridge of high pressure will be across the area during the start of the long range. It will remain in place through Monday before moving to the east. Dry weather is expected Sunday night, then clouds will increase Monday along with the chances for a few showers across the N/W areas Monday afternoon. Temperatures will be above normal with highs Monday in the low 80s over srn NJ and Delmarva while highs will be in the mid/upper 70s across the N/W areas. A low pressure system across the upper Great Lakes Monday morning will move NE across southern Canada through Wednesday. A strong cold front will move across the Middle Atlantic Mon night and into early Tue. There appears to be a decent chc for showers and tstms with this front, so only small changes to the already high pops were made today. We have categorical pops N/W and high Likely S/E. It could be a 1/4 to 1/2 inch rain producer, higher in tstms. On Tuesday, the front will be east of the area, but the lingering upper low aloft will lead us to keep the chc for some showers into the early afternoon. High temps Tue will still be a little above normal S/E but by Wed, readings will be close to normal for early May. A short period for far weather Wed/Wed night with an area of high pressure across the area. Another low will approach Thu and will again bring decent chc for showers and sct tstms (Delmarva) for the end of next week. We have some likely pops for many areas Thu/Thu night and chc pops for Fri/Sat. Temperatures will be near or below normal towards the end of the week. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of this afternoon...VFR with clouds at or above 5000 feet. There is a chance for a few showers and thunderstorms to develop after 21z mostly southwest of PHL. The coverage and timing of showers/thunderstorms is low. A VCTS is carried for PHL, ILG, MIV and ACY toward early evening. Winds varying between west-southwest and west-northwest around 10 knots with local gusts to around 20 knots at times. Tonight...A few showers or thunderstorms possible mainly in the evening especially near and southwest through east of PHL with locally reduced ceilings/visibilities, otherwise any ceilings should remain VFR. Northwest winds mostly 10 knots or less, becoming north and then northeast. Sunday...VFR ceilings may lower to MVFR through the day, however confidence is on the lower side. Northeast winds around 10 knots, becoming east and southeast in the afternoon. OUTLOOK... Sun night thru Mon Afternoon...Mostly VFR expected. Mon night thru Tue...Restrictions with showers especially Mon night. Tue night thru Wed night...Mostly VFR. Patchy morning fog psbl. Thu...Restrictions possible with showers. && .MARINE... The conditions are expected to remain below Small Craft Advisory criteria through Sunday. A few thunderstorms this evening may produce locally gusty winds, however coverage and timing is uncertain. A cold front will cross the area this evening, resulting in a wind shift to the northwest and north then to the northeast through the night. There could be a northeast to east wind surge Sunday especially across the northern coastal waters zones, however held gusts below 25 knots. The duration of this does not look long enough and therefore kept seas 4 feet or less. OUTLOOK... Sun night thru Mon morning...Sub-SCA conditions with Fair weather. Mon afternoon thru Tue night...SCA expected. Showers with sct tstms. Tue night...SCA on the ocean and sub-SCA across Del Bay. Fair. Wed thru Thu...Sub-SCA. Fair thru Wed night then sct showers Thu. && .CLIMATE... We have already issued a RER product for a new record high temperature at Georgetown, DE...91 at 241PM. Atlantic City was 1 shy as of 330 PM (91) and think that might be it. Atlantic city doesn`t normally reach 90 until June 11 although the statistical database may be skewed to cooler temperatures closer to the coast. The earliest 90 degree day at Atlantic City occurred April 7, 2010. **Record or number 2 warmest April on record expected** Presuming our forecast temps these last 36 hrs of April are accurate, we are assured of a top 2 warmest April on record in much of our forecast area. Sunday is probably the critical day for determining record or not. Below: April projected within the top April average temps, the normal for April and the period of record (POR). This includes todays (29th) high and low temperatures through 4 PM. Sundays max temps may occur at 1 am and the min temps Sunday evening. PHL normal 54.0 POR 1874 59.5 2017 Projected warmest ever: still could slip .2 degrees. 59.4 1994 58.5 1921 58.4 2010 57.9 1941 ABE normal 49.9 POR 1922 56.8 projecting record and almost cant miss a record. 56.4 1941 54.7 1994 ACY normal 51.7 POR 1874 57.6 projecting record and almost cant miss. 56.3 2010 56.1 2011 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...O`Hara Near Term...Gorse Short Term...Gorse Long Term...O`Hara Aviation...Gorse/O`Hara Marine...Gorse/O`Hara Climate...428 PM

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