Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 261804 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 204 PM EDT Sun Mar 26 2017 .SYNOPSIS... Canadian high pressure is our primary weather influence today. Low pressure from the Mississippi Valley into the Great Lakes on Monday will draw a warm front northward through most of our region. The low will move into southern New England Tuesday night pulling the frontal system off the coast. Canadian high pressure will edge into our area Wednesday and Thursday. Thereafter, low pressure in the Ohio Valley on Friday should exit seaward from the mid Altantic coast next Saturday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 930 am update: No changes to the forecast this morning. Onshore flow to the north of a backdoor cold front is inundating the region this morning with low clouds and occasional drizzle. Mount Pocono remains below freezing, so a light glaze may occur on trees, but no societal impacts have been observed or reported to this point. Conditions will change little through the day, with temperatures unable to rise in the low clouds and maritime origins of the low-level flow. Expect little to no measurable precipitation through the daytime hours as the midlevels should remain relatively dry. Previous discussion... High pressure across Quebec/Maine will move offshore today while weak low pressure slowly moves to near Chicago by evening. A steady onshore flow will continue across our area thru the day. This will promote an abundance of low clouds and fog along with some light rain and drizzle at times. Pops will be greatest across the northern areas where we have hi chc pops and the pops taper off s/e to slgt chc across srn DE. Unlike Saturday, temperatures will be below normal, with highs only in the 40s in most areas, and a few low 50s over Delmarva. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... The overall pattern will not change much tonight with high pressure north/east and weak low pressure moving closer across the Great Lakes. The onshore flow will continue and the chances for more measurable rains will increase tonight. The best chances will again be across the southern Poconos, Lehigh valley and north NJ where we will have categorical pops. The pops decrease back to likely over the Del Valley and cntrl NJ and the chc pops over south NJ and srn DE. Patchy fog and drizzle will occur between the bouts of rain. Overall qpf will not be that great, a few hundredths across the south and up to 1/4 inch up north. && .LONG TERM /MONDAY THROUGH SATURDAY/... 500 MB: A southern stream weakening short short wave crosses our area Monday followed by a strengthening northern stream short wave Tuesday, that closes off, east of New England Wednesday. The next southern stream short wave probably passes to our south at the end of the week. Westerly flow should follow for the weekend before a trough tries to form in the Mississippi Valley early next week. Temperatures: Calendar day averages Tuesday 10 to 15 degrees above normal, near 5 above normal Wednesday, nearly normal Thursday through Saturday. Forecast basis: 50 50 blended 00z/26 GFS/NAM MOS Monday-Tuesday, then 00z/26 MEXMOS Tuesday night and thereafter WPC guidance Wednesday-Saturday. The dailies... Monday...Despite winds turning south or southeast, the question becomes how much warming can occur with a lack of mixing and considerable cloud cover. Showers possible with the short wave passage and waa, especially early in the day. Dense fog may form along the warm front and along the water where the dewpoints exceed the SSTs in the 40s. Tuesday...Dense fog potential early in the day. Now that we`ve had almost a day of southerly flow, it may be easier to warm to the guidance values. There should be a batch of showers and isolated TSTMs associated with a developing negative tilt northern stream short wave that will shove all the moisture out to sea at night with a wind shift to westerly. (EC and to an extent the GGEM are 6-12 hrs slower but have sided with the previous fcst for continuity as well as the 00z/26 GEFS which emphasizes low pressure tracking ewd from northern PA to near POU by 23z/27. Wednesday...Partly sunny and nice. Northwest wind gusty 20 to 30 mph. Thursday...Fair. Northwest gusty 15 mph. Friday...Mostly cloudy with a chance of precipitation, mostly rain if it occurs. Lots of uncertainty on track of the event with a wide ranging set of model solutions , inclusive of a little wet snow potential near and n of I80. LOW confidence and have followed WPC guidance. GEFS confluence of the nrn and srn stream is across northern PA. Saturday...clearing after any pcpn ends in the morning. Below average confidence on pcpn occurrence. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. For the 18Z TAFs...General MVFR conditions will continue through early this evening, likely deteriorating to IFR or possibly LIFR during the overnight hours. Moderate confidence that light rain will move in between 03Z and 06Z at KRDG/KABE and by 09Z at KTTN/KPNE/KPHL/KILG. There may be slow improvement to MVFR after sunrise, but scattered showers may continue through the morning hours. Less confidence of precip at KACY/KMIV. Winds generally east 10-15 kts through early evening with a trend toward S or SSW late tonight through the morning hours tomorrow. OUTLOOK... Monday thru Monday night...Periods of MVFR/IFR in low clouds and fog, with showers especially to start the day. VFR cigs may still develop Monday afternoon from around I-95 and points southeast. South to southwest wind. Confidence: average Tuesday...IFR/LIFR st/fog possible in the morning but would probably become VFR CIGS in the afternoon, with a period of MVFR/IFR conds possible in shower. During the afternoon-evening, there is 800J MLCAPE modeled, some instability and a neg tilt short wave so a tstm is possible. Confidence: average Wednesday...VFR. Northwest gusty 25 kt. Confidence: average Thursday...VFR. Northwest gusty 15 kt. Confidence: average
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&& .MARINE... We will keep the SCA flags as they are on the waters and just raise the next segment with the 330 am issuance, instead of waiting until 6 a.m. The onshore flow will continue today and a gradual building of seas will continue. Scattered showers and patchy fog expected. OUTLOOK... Monday thru Wednesday...Seas may remain elevated Monday into Tuesday, and the SCA may need to extended into this period. Quite a bit of uncertainty with regards to winds and seas on Wednesday, which may be near SCA thresholds. Confidence: average Thursday...Sub-SCA. Confidence: above average && .TIDES/COASTAL FLOODING... Onshore flow is expected through Monday morning, with easterly wind gusts up to 25 MPH at times today. Astronomical tides are also increasing, coincident with the New Moon this Monday, March 27. The ESTOFS remains most aggressive of the guidance suite, with near minor flooding for the sunrise Monday high tide along the DE and NJ oceanfront, and it has has outperformed the other guidance recently. Both the SIT multi model review and GFS ETSS are more conservative. ESTOFS trends for positive departures (surge) appear to be lessening. The wind will also be trending more parallel (southerly) to the shore by sunrise Monday, so any minor tidal inundation flood risk remains a low confidence forecast with no action at this time. && .CLIMATE... March as a whole for PHL, is still on track to average one half to 1 degree below normal, despite the warmth of ydy through Wednesday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 8 AM EDT Monday for ANZ450>453. && $$ Synopsis...Drag Near Term...CMS/O`Hara Short Term...O`Hara Long Term...Drag Aviation...CMS/Drag/O`Hara Marine...Drag/O`Hara Tides/Coastal Flooding...Drag Climate...Drag is the U.S. government's official web portal to all federal, state and local government web resources and services.