Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KPHI 161538 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1138 AM EDT Fri Mar 16 2018 .SYNOPSIS... Low pressure remains over the Canadian Maritimes through Saturday, then weakens as it moves eastward. Meanwhile, a cold front moves through the region early this morning followed by high pressure slowly building toward our area by late day. A weak area of low pressure will quickly slide to our south Saturday, then high pressure arrives for Sunday. Low pressure in the Central Plains later Sunday and Monday tracks eastward, and should result in another coastal storm impacting the area for Tuesday into Wednesday before moving to off the New England coast Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
Snow showers tapering off. The heaviest snow shower is across southeast NJ. Only trace amounts of snow expected. Isolated snow showers and flurries may persist over the Poconos through this afternoon. A reinforcing shot of colder air will spread into the region as the afternoon progresses. Forecast high temperatures range from the upper 20s in the Poconos to mid 40s along and S/E of I-95. The readings are about 15 degrees below normal for the middle of March for the higher elevations of NE PA/NW NJ and more representative of climo for January. Elsewhere, highs will be about 10 degrees below and more representative of mid February. High pressure over the Upper Midwest will nose southeastward toward the central Appalachians, helping to strengthen the pressure gradient across our region today with the low stalled over eastern Canada. The result will be a breezy W-NW wind around 20 mph, gusting 30-35 mph this afternoon.
-- End Changed Discussion --
&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... High pressure builds to our S/W tonight with the surface ridge axis extending SEwd from the Upper Midwest to the central Mid- Atlantic region. The pressure gradient will relax a bit as the ridge axis shifts ever- so-slightly closer to our region but it will still be breezy in the evening. The gradient may weaken enough across far SE PA, E MD and S DE to allow for winds to become light late tonight. Accordingly, a sharper drop in temps may occur before daybreak across these southern zones under increasingly favorable radiational cooling conditions. Low temperatures range from the mid teens in the Poconos to the mid 20s along and S/E of I-95, which are roughly 5-10 degrees below climo. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Saturday through Sunday night... Persistent pattern remains in place with an upper level trough situated over eastern Canada putting the area in a broad, cyclonic flow. To start the period Saturday, the tail end of a cold front will move south and brush across the area but this will be a dry front with no major impacts on sensible weather other than helping provide breezy conditions (though not as windy as Friday). However what will have to be watched is a wave moving out of the midwest and skirting by just south of the area. The GFS continues to be most robust with this feature indicating upwards of a quarter inch of QPF over the southern Delmarva on the northern edge of this system while the NAM keeps precip just south of the area. GEM Regional is in between these two extremes. Current forecast for POPs/QPF doesn`t change much from previous one and basically follows this middle ground solution bringing some precip into the Delmarva with even some slight chances for rain brushing far south NJ near Cape May. As such, expect some rain to break out across the Delmarva Saturday afternoon with temps initially in the low to mid 40s. What will have to watched though is that the air will be quite dry at the surface and depending on how much precip falls, there may be enough wet bulb cooling to change precip over to wet snow before it moves out by early evening. Confidence not high regarding this and even if it occurs, there probably wouldn`t be much if any snow accumulation. Elsewhere for Saturday, SE PA and central and northern NJ will see a dry day with sunshine filtered at times by mid and high clouds from the aformentioned system to the south. Highs will be generally in the 40s except 30s across the southern Poconos. For Saturday night, system quickly moves out in the early evening with an otherwise clear and chilly night on tap as high pressure noses back into the Ohio Valley resulting in a NW flow. This high will bring sunshine with continuing seasonally cool weather for Sunday with highs once again mainly in the 40s except 30s across the southern Poconos. Another clear and cold night will follow for Sunday night. Monday through Thursday... The main story during this period will be the east coast storm threat for the Tuesday through Wednesday period. In the meantime, the period starts off dry for Monday under the influence of high pressure with sunshine giving way to increasing high clouds by late day. Highs will be mainly in the 40s except 30s over the southern Poconos. Beyond this time, attention turns to the next east coast storm.... Forecast models continue to show a strong signal for an east coast storm during the Tuesday - Wednesday period of next week. In fact the latest trends are for the storm to be a little slower to arrive but to potentially be very slow moving with an extended period of precip and winds for the middle of next week over the mid Atlantic. The other potential hazard that will need to be monitored is coastal flood threat, especially given this slower trend which could bring a prolonged period of strong NE winds. General trend has also been for the low to be farther south and east favoring a colder, potentially snowier solution. Both the GFS and latest ECMWF track low pressure east into Tennessee by next Tuesday and then indicate secondary development will occur near the North Carolina coast by late day. Precip should move into the area during the day either as rain, snow or a mix of rain/snow. At this early juncture, rain looks to be favored along and S/E of the I-95 corridor with snow or a mix possible farther north/west, but again, it`s early so we are not yet confident in these forecast details. Winds will also strengthen out of the northeast through the day. Heading into the Tuesday night into Wednesday period, the secondary low looks to take over as it deepens and slows down near or just off the coast as the system begins to close off aloft. This slower movement could keep precip in place over the area right through much of Wednesday. A big forecast challenge at this time will continue to be precip type. The lift and precip with the system along with winds becoming more northerly as the low moves off the coast could result in a change to mainly snow later Tuesday night or Wednesday. But again, it`s early to have much confidence in these forecast details. Also, wet snow falling during the daytime at this time of year with marginal temperatures may have a hard time accumulating. Despite these uncertainties, in the big picture confidence continues to grow that there will be a coastal storm impacting the area around the middle of next week but it`s going to take at least a couple more days until we can be more confident in details such as precip types and amounts. The storm should finally move north and east of the area by next Thursday with precip over the area diminishing but cool temperatures lingering in its wake with a NW flow. So no warm up for the next week as pattern we`ve been stuck in remains in place. && .AVIATION /16Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Most of the terminals should be clear from -SHSN. The heaviest snow shower will pass between KWWD and KACY through 1615Z or so. Otherwise, VFR. Variable mid-level deck today with CIGs varying between 4500-7000 ft AGL. W-NW winds 15-20 kt with gusts up to 30 kt through the afternoon. Tonight...VFR with clearing skies. W-NW winds will gradually decrease throughout the night with gusts diminishing at a faster rate after sunset. Outlook... Saturday through Sunday...Mainly VFR. A little light rain could brush KMIV and KACY late Saturday but this should not bring any restrictions. Monday...Clouds increase especially late day and at night, with possible MVFR/IFR conditions developing overnight if precipitation arrives. Tuesday...Widespread MVFR/IFR conditions with rain/snow possible. Low confidence with the details.
-- End Changed Discussion --
&& .MARINE... Strong Small Craft Advisory conditions on the waters today, and there may be a period from around 4pm-8pm for a few gale force gusts on the ocean waters. Confidence in widespread gales is low, so opted to keep the SCA going. The SCA, which also includes the DE Bay, will continue into tonight. Outlook... Saturday and Sunday...The conditions should be mostly below Small Craft Advisory criteria, however a northerly wind surge with gusts 20-25 knots may occur Saturday night. Winds may also be near SCA levels during the first part of Saturday. Monday...The conditions are anticipated to be below Small Craft Advisory criteria, although winds should start to increase from an easterly direction later Monday night. Tuesday...Winds increase as a coastal storm approaches and should at least be at strong SCA levels by late day. The magnitude of the winds and seas will depend on the track and strength of a coastal storm. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ450>455. Small Craft Advisory until 4 AM EDT Saturday for ANZ430-431. && $$ Synopsis...Fitzsimmons Near Term...MPS Short Term...Klein Long Term...Fitzsimmons Aviation...Fitzsimmons/Klein/MPS Marine...Fitzsimmons/Klein/MPS is the U.S. government's official web portal to all federal, state and local government web resources and services.