Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 210927 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 527 AM EDT TUE JUN 21 2016 .SYNOPSIS...
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A cold front in northern Pennsylvania will cross the Mid Atlantic states later today through tonight. Weak high pressure will cross the region on Wednesday. A low pressure system will cross the southern Great Lakes Wednesday night, passing over northern New Jersey on Thursday and moving to our east Thursday night. High pressure will return for Friday and persist through the weekend. A cold front will approach from the west on Monday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Through 8 am...Attention is focused on the esewd moving lines of convection in eastern PA (decaying) and along the NJ and DE coasts. Should be mainly brief heavy rain, lightning and a gust to around 30 kt and all out of area or dissipated by 9 am. May still need an SPS for an early morning TSTM or mws`s for the coasts. We had VIl to 55 in Monroe County around 0748z and 40 kt evident aloft but just sps`d. No wind reports so far. Also 33 kt at the Port of Wilmington DE around 0715z, Brandywine around 0842z and 39kt at Cape May at 0915z. All this convection at a relative convective down time (early morning) suggests the potency of what should be coming for a portion of our forecast area late today. The hourly updated HRRR continues showing short lines/clusters of 45-55 kt gusts associated 1-1.5 inch 30 minute tstms tracking esewd thru se PA, and s NJ into DE mid-late afternoon. Today...Complex situation. The cold front will be easing across e central and northeast PA as well as northern NJ during midday with westerly winds gusting to 15 or 20 mph during the afternoon and a drying out there with less or little chance of rain there after 8 am today. Have a small chance in up there during mid afternoon but confidence on rainfall near and north of I-78 is well below average. Further south of I-78...convection refires during the afternoon. Exactly where is still tbd but am expecting hot and humid conditions from se PA through southern NJ southward... roughly MQS-WRI-BLM southward where winds become southwest during the afternoon and gust 20-28 mph...strongest gradient gusts Delaware. That permits pooling of 2000J ML CAPE. The considerable instability and high 0-6km bulk shear environment together with the cold front initiation of convection should allow for lines of strong to severe thunderstorms Delmarva into far southern NJ, possibly into PHL and central NJ as well. PWAT 1.8 on the Delmarva this afternoon dries to less than 1 inch near I80. Gust 50-55 kt and hail expected in a few storms. Brief poor drainage flooding rains but fast movement of the cells should reduce potential for any flash flooding, or if any, its very very small area. No FFA. Convective timing for PHL: maybe 7AM on PA remnants then 3-5PM this afternoon. Enhanced wording continues in the forecast, basically PHL south and east. If no short fuse convective SPS`s are issued, we will at 6am issue a 12 hr sps featuring the Delmarva and s NJ for potentially SVR storms late Today. Heat wave probably becomes official at KPHL KTTN, KPNE, KVAY, today where 90-93F expected. Even KSMQ, KABE and KRDG may nudge 90 this afternoon. Convective debris or newly developing convection between 16z and 18z might nix some of these 90F forecasts but have applied a basic pattern to the fcst. a band of sct early morning showers and tstms...drying out late morning. refiring early-mid afternoon. Heat index expected to rise to between 92-96F today...highest vicinity KACY/KMIV and central-southern Del/e MD. This forecast did not have the benefit of the 00z/21 NSSL WRF and SPC WRF which we could not see prior to our fcst issuance.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
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A broad brush tonight. dewpoints rise a bit and there may be a secondary band of convection that develops in E PA and NJ during the early night, separate from the probably going out to sea SVR over the Delmarva. Eventually the dry air aloft dominates near and after midnight. It will cool down significantly near and north of I-78 tonight where pwat dries to .8". Sfc temps probably down into the 50s (FWN and MPO 53). It will be more difficult to cool below normal from PHL south and east where residual warmth and rh will be difficult to erode behind the cold front. Patchy dense fog possible late at night, especially nw NJ and e PA countryside. Wind becoming northwest everywhere. This part of the forecast was a 50 50 blend of the 00z/21 gfs/nam mos with adjustments as needed.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/... Wednesday...Weak high pressure will slide across the Mid-Atlantic, keeping us dry for the day. Thursday...Low pressure will cross the lower Great Lakes region pushing east through the day. The low will cross our area Thursday afternoon/evening and then move off to the northeast late Thursday. Thursday could be quite an active day across the region. The center of the low looks to move across Pennsylvania and into northern NJ, and with considerable moisture available we could see some decent rainfall across our area. Meanwhile, the southern portions of the forecast areas will remain firmly placed in the warm sector, allowing for destabilization to occur through the day. The possibility for strong to possibly severe thunderstorms will continue across the area, especially the Delmarva and extreme southern NJ. With the recent spate of dry weather across our region, we could certainly use some good rainfall. However, PWATs are running high, 1.50-2.00 inches and this could very well lead to heavy rain falling across the forecast area. We will need to monitor the threat for any flood/flash flood concerns. At this time, expect poor drainage and low lying areas may experience localized flooding. Friday through Sunday...Surface high pressure will build across the region, drying us out through the weekend. With an east southeast flow at the surface, especially along the coast, we will be slightly cooler through the weekend than we have been the past few days. Highs will reach into the 80s on Friday and Saturday but the airmass will modify through the weekend and by Sunday, we will see temperatures creeping back into the upper 80s to lower 90s. Monday...Low pressure will cross eastern Canada early in the week. The attendant cold front will approach our area from the west on Monday. The models show that the front will move through our area sometime later Monday or Tuesday but some timing and strength issues remain. && .AVIATION /09Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through 1230z Today...VFR sct-bkn cu fields aoa 6000 ft and sct showers and isolated tstms will exit the taf sites fm nw to se this morning, probably by 1230z. After 1230z Today...VFR sct-bkn aoa 5000 ft. Showers/tstms vicinity the TAF sites from KPNE/KPHL/KILG southeastward to KACY and KMIV sometime between 18z and 24z/21. Pls see TAFS for our best effort on timing and keep checking through the day. Thinking strongest storms with brief IFR conditions in heavy rain, possible hail and potential westerly wind gusts 40-50kt vicinity KMIV and KACY. This latter expectation is subject to change. Otherwise, gradient west wind to 15-18kt KRDG/KABE and possibly KTTN by midday. Vicinity KPHL the gradient wind is predominantly southwest with a possible period of gusts to 20 kt early this afternoon. Meanwhile vicinity KACY and KMIV gradient southwest wind gusts to around 23 kt are expected this afternoon. This evening...Mainly VFR cigs. A chance of showers and thunderstorms from around KPHL southeastward which could briefly lower conditions to MVFR or IFR. Late Tonight...VFR becoming Clear with a northwest wind. patchy mvfr fog possible at the non urban taf sites. OUTLOOK... Wednesday through Wednesday evening...mainly VFR. Late Wednesday night through Thursday evening...Conditions varying between VFR and MVFR with a chance of showers. Also, there is a chance of thunderstorms that may reduce conditions into the IFR category. Late Thursday night and early Friday morning...Mainly VFR with patchy fog possibly reducing the ceiling and visibility into the MVFR or IFR range. Late Friday morning through Saturday...Mainly VFR.
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&& .MARINE...
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SCA likely to be issued around 6AM for the DE and far southern NJ waters where the NAM continues highlighting 25 kt gradient sw wind gusts this afternoon. Also expect probable sct 35-50 kt westerly wind gusts associated with thunderstorms this afternoon/ evening. Winds and seas probably below sca criteria late tonight behind the cold front. RIP CURRENTS...There is a moderate risk for the formation of dangerous rip currents today along the southern and central New Jersey shore. For the Delaware Beaches, the south southwesterly flow is more off shore, so have chosen to go with a low risk for now. Across the Monmouth County shore, a cold front is expected to arrive relatively early in the day, bringing a shift to northwesterly flow, limiting the risk there. OUTLOOK... Wednesday through Thursday...No marine headlines are anticipated. Thursday night and Friday...Wave heights on our ocean waters may build near 5 feet in a southeast to northeast flow. Friday night and Saturday...No marine headlines are anticipated.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Meola Near Term...Drag 528 Short Term...Drag 528 Long Term...Meola Aviation...Drag/Iovino/Meola 528 Marine...Drag/Iovino/Meola 528

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