Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 100248 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 948 PM EST Mon Jan 9 2017 .SYNOPSIS... A low lifting out of the Midwest will bring a warm front through our region Tuesday night. A secondary warm front is expected Wednesday night. A large high pressure system will then build off the coast of the southeastern U.S. before a cold front sweeps through our region on Friday. High pressure is anticipated to build across southeastern Canada and New England over the coming weekend as low pressure slides across the Ohio River Valley and the Middle Atlantic States. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Skies have mostly cleared out over the forecast area this evening. The cirrus clouds to our west are tending to dissipate as they spill southeastward over the shortwave ridge axis over the upper mid-west. As the ridge axis moves quickly eastward cirrus should increase overnight. In the meantime, the surface ridge axis has shifted slightly offshore but the pressure gradient remains quite weak and winds are very light to calm in some spots. Temperatures over the snow cover in parts of central and southern NJ have already dropped into single digits. Further radiational cooling should be limited as high level clouds increase overnight. Some freezing fog seems possible for the Pine Barrens but not so likely now for the Lehigh Vly and vicinity as the T-Td spread remains rather large. Previous discussion below: The main concern tonight is for some patchy freezing fog to form. Bufkit soundings and local procedures run to determine fog formation showed the potential in parts of the Lehigh Valley southwest toward Reading along with the Pine Barrens. An uncertainty is if the high cloudcover could potentially prevent fog formation. Any freezing fog would create slick spots on roads and bridges tonight if it forms. Mention in the HWO for conditional threat. High pressure will be over the region tonight. However, we will continue to see more high clouds stream northeast into the region. This cloud cover may limit the radiational and cooling due to residual snowcover tonight. We are thinking along the lines that temperatures will be a few degrees cooler that have snow cover than what the MAV/MET/ECMWF suggest. Winds will be fairly light as well.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Wintry mix developing across portions of Eastern PA and Northern NJ early Tuesday afternoon... Winds will increase from the south as low pressure moves well northwest of the region into the Great Lakes bringing a warm front toward the region late Tuesday. Clouds will increase in the morning but the overruning moisture will form a period of snow across Central Pennsylvania and New York that will likely move into the Southern Poconos and Northwest New Jersey by late morning. Up to an inch of snow could fall from this by mid-afternoon as temperatures will be in the 20`s and still cold aloft. Temperatures later in the afternoon will warm aloft where the surface is still below freezing resulting in a change to freezing rain and sleet with the additional precipitation coming in later in the afternoon. Areas south of the Lehigh Valley and Northern new Jersey will warm more rapidly and be located far enough south from the lift. Right now it looks like these areas stay mainly dry with temperatures warming well above freezing in the afternoon. Overall, the MET guidance looks way to warm and did not use it in this forecast on Tuesday with MAV/ECMWF in good agreement. Highs should range from around 30 north and west to near 40 from Philadelphia south and east. Bufkit analysis shows the potential for some higher wind gusts, 15-20 mph from the south in the afternoon hours. We`ll have to watch as well if low level cold hangs on longer than indicated, which is a familiar model bias. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... Tuesday night...Warm front should lift north through the region overnight. As the low level warm tongue moves over the region, expect precip to be rain (for locations above freezing) and freezing rain (for locations above freezing). For temperatures, continued with the non-diurnal temperature trend of increasing temperatures through the overnight hours. However, sided on the colder side of guidance as the boundary layer southerly flow (at least below 850 mb) is limited. Combine that with the fact that the soil temps remain relatively low (thanks to the current cold snap), and would expect the warming trend (at least at the surface) to be slower than normal. Additionally, with recent warm air advection events both the NAM and GFS guidance has been too quick to increase temperatures. The winter weather advisory continues through some of the evening hours to account for a period of freezing rain north and west of the fall line. Once temperatures do increase above freezing, the region should see a prolonged period (at least for January) of above freezing conditions. We will likely stay above freezing through the day on Friday. We should be dry through the day on Wednesday. Another warm front lifting north on Wednesday night (combined with a low lifting into the Great Lakes region) will bring another round of precipitation (all rain) to our region. A cold front on Friday will bring temps back closer to normal to finish out the week. It looks like another front may stall out just south or right over our region Sunday into Monday. This could bring another round of precip, but exactly what type of precip is uncertain due to the uncertainty in the location of the front. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR tonight with winds mostly less than 5 knots. Potential for brief restrictions from patchy freezing fog overnight KMIV or KACY. VFR on Tuesday as well at all sites through 18z. Snow likely to move into KABE and KRDG between 17-20Z, with a potential break late in the afternoon (MVFR/IFR possible after 18z Tuesday at these sites). Wintry mix would be possible again toward sunset. Winds will be from south around 10 knots with slightly higher gusts. Dry at other TAF sites. Outlook... Tuesday night...MVFR likely and IFR possible in rain. Some freezing rain remains possible in the KABE vicinity on Tuesday evening. Low level wind shear is possible due to a strong (60+ knot) low level southwesterly jet overhead. Wednesday...Ceilings and visibility should increase to VFR no later than mid morning and stay VFR through the day. Wednesday night...Conditions falling to MVFR and IFR in rain. Thursday...Conditions improving to VFR. Small chance for MVFR at KABE and KRDG with rain. Thursday night...Low clouds and fog may bring conditions back down to MVFR and IFR. Friday...Morning low clouds and fog with conditions improving to VFR in the afternoon. A chance of showers. Friday night and Saturday...conditions possibly lowering to MVFR with precipitation. Wintry mix possible during the day Saturday at KRDG, KABE, and KTTN.
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&& .MARINE... Waveheights will be fairly low at 1-2 feet with wind gusts around 15 knots from the south Tuesday afternoon. No hazards. Outlook... Tuesday night...Southwest wind gusts of 25 to 30 knots are possible on the coastal waters. There is a small chance for gale force gusts primarily on the coastal waters adjacent to New Jersey. For the Delaware Bay, winds and waves are expected to stay just below SCA criteria at this time. Wednesday and Wednesday night...Once winds and seas drop below SCA criteria by mid day, no more marine headlines are anticipated through this period. Thursday through Saturday...Southwesterly winds may gust above 20 kt at times, but are expected to stay below 25 kt. However, on the ocean waters, seas may increase to 5 to 6 feet through this period. && .CLIMATE... Georgetown`s record low for January 9th is 2 degrees set in 1970 this record was tied this morning. Looking ahead, Thursday should be quite mild and some locations may eventually be forecast within 2 degrees of the following records of 60-63F. ACY 63-1913 ILG 63-1913 ABE 60-1932 RDG 61-1913 No other record information has been posted at this time due to the smaller chance of even coming close to record. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Winter Weather Advisory from 11 AM to 10 PM EST Tuesday for PAZ103-105. Winter Weather Advisory from 11 AM Tuesday to 2 AM EST Wednesday for PAZ054-055-060>062. NJ...Winter Weather Advisory from 11 AM to 10 PM EST Tuesday for NJZ008-009. Winter Weather Advisory from 11 AM Tuesday to 2 AM EST Wednesday for NJZ001-007. DE...None. MD...None. MARINE...Small Craft Advisory from 7 PM Tuesday to 1 PM EST Wednesday for ANZ450>455. && $$ Synopsis...Johnson Near Term...AMC/CMS/Gaines Short Term...CMS/Gaines Long Term...Johnson Aviation...CMS/Gaines/Johnson Marine...CMS/Gaines/Johnson Climate... is the U.S. government's official web portal to all federal, state and local government web resources and services.