Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
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
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KPHI 231929 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 329 PM EDT Thu Mar 23 2017 .SYNOPSIS...
-- Changed Discussion --
High pressure across the middle Atlantic will move offshore by Friday, while a warm front moves through the Ohio Valley. This frontal boundary will become nearly stationary near our region through Tuesday, as several waves of low pressure move along it. A cold frontal passage is expected Wednesday, followed by Canadian high pressure building into our area on Thursday.
-- End Changed Discussion --
&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
-- Changed Discussion --
It looks very likely now that any precip will hold off until after sunrise tomorrow morning. All the same, we will be monitoring temperature trends very carefully overnight as that could have implications for precipitation type once it does begin Friday morning. Until the clouds move in, we will have efficient radiational cooling conditions with light winds and dry boundary layer conditions. For now, I have gone mostly on the colder side of guidance for temperatures, with lows ranging from the upper teens to lower 30s.
-- End Changed Discussion --
&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/...
-- Changed Discussion --
As mentioned earlier, a big factor in how precipitation will begin will be how quickly clouds move in tonight and how much radiational cooling we have before then. Further complicating precip type is that the air will likely remain quite dry at least through the morning hours until moisture advection begins. Thus, could see some wetbulb effects further lowering the temperature with and just before the start of precipitation. All that to say, we have the highest confidence that the southern Poconos will see a wintry mix of precipitation. For Carbon and Monroe Counties, will issue a winter weather advisory through the morning hours. Much less confident (but still possible) for the next row of counties including NW NJ, Lehigh Valley, and Berks Co. Delmarva and far southern NJ are unlikely to get any precip at all. By early afternoon, expect all locations to be above freezing and all precipitation to be rain.
-- End Changed Discussion --
&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
-- Changed Discussion --
An unsettled period of weather is in store this weekend thru the middle of next week. At the mid-levels across the conus, a generally zonal northern stream flow will be in place, while several shortwave disturbances traverse the southern stream. Meanwhile at the surface, Canadian and sub-tropical high pressure systems will maintain a frontal boundary in the vicinity of our region until a more substantial frontal passage on Wednesday. The primary uncertainty will be the location of the aforementioned boundary, along with the timing of several areas of low pressure that ride along it, and accompanying areas of precipitation. Of most concern is the potential of mixed precipitation Sunday night. On Saturday, the NAM and EC are most extensive with the overrunning precipitation associated with the stationary boundary to our north. The GFS looks more reasonable with the placement of the precip in relation to the frontal boundary, confining PoPs to the northern half of our CWA, and our forecast reflects this. As the frontal boundary moves southward in response to Canadian high pressure building to the north, scattered showers are possible across our entire area Saturday night into Sunday. As low pressure moves through the Ohio Valley into the Great Lakes from Sunday night into Monday, more substantial overrunning precip is likely during this time frame. As mentioned previously, there is some potential for mixed precipitation Sunday night into Monday morning. A review of plan view 2-meter and 850 hPa temperatures, 1000 to 500 hPa and 1000 to 850 hPa thicknesses, model p-type, ens plume diagrams, model soundings, and CIPS Analogs points to freezing rain as the primary concern. There is a high amount of uncertainty, especially at this range in the forecast, which translates into low confidence. The probability for freezing rain is low at this time, therefore it was not mentioned in the HWO (per our directives), but this will need to reassessed with future forecast packages. Also, please note that ice map on our website is for Friday, March 23. Expect showers to continue Monday night into Wednesday, and another round of more substantial precip likely centered on Tuesday night into Wednesday, associated with a cold frontal passage. There is uncertainty with the timing of this front, particularly given the time range, but a gradual return to fair weather should occur on Wednesday and continue into Thursday. Temperature-wise, at or above normal through the period.
-- End Changed Discussion --
&& .AVIATION /20Z THURSDAY THROUGH TUESDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions will continue through at least 12Z. After 12Z, there is an increasing risk for precipitation (expected to be all rain at the TAF sites, but freezing precipitation will be possible N and W of KABE and KRDG). With any rain, brief MVFR conditions will be possible. The rain should move out by mid afternoon bringing a return to VFR conditions. Light and variable winds may continue through much of the overnight hours before settling in out of the south by 12Z Friday. OUTLOOK... Saturday and Sunday...A period of MVFR is possible in low clouds, especially northwest of an ACY-MIV line. Otherwise, VFR. Southwest winds 10 to 15 knots on Saturday will shift to the east Saturday night into Sunday, increasing to 10-20 knots. Sunday night thru Tuesday...Periods of MVFR possible in low clouds and fog. South-southwest winds Sunday night into Monday may shift to the east-southeast Monday night and Tuesday, generally at or below 20 knots.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Winds and seas should stay below SCA criteria tonight into tomorrow morning. By mid day tomorrow, winds will increase. Gusts above 25 kt will be possible especially for the New Jersey Coastal waters through the afternoon hours. OUTLOOK... If confidence increases for elevated winds and seas to linger into Saturday night, the Small Craft Advisory (SCA) may need to be extended further into this time frame. As a front moves south across the waters on Sunday, winds and seas may increase to SCA levels during the day, mainly across the northern NJ waters. Looking ahead to Monday and Tuesday, wave heights may build in excess of five feet during this period. Therefore, a SCA may be needed.
-- End Changed Discussion --
&& .PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...Winter Weather Advisory from 8 AM to 1 PM EDT Friday for PAZ054-055. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 10 AM to 8 PM EDT Friday for ANZ450>453.
-- End Changed Discussion --
&& $$ Synopsis...Franck Near Term...Johnson Short Term...Johnson Long Term...Franck Aviation...Franck/Johnson Marine...Franck/Johnson

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.