Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 290527 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1227 AM EST Tue Nov 29 2016 .SYNOPSIS...
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Strong low pressure is forecast to move across the Great Lakes during the mid week period. The low will pull a couple of warm fronts through our region Tuesday and Wednesday before a strong cold front arrives from the west Wednesday night. A secondary low is expected to develop over southern New England Wednesday night before moving across Nova Scotia Thursday. High pressure follows for Friday into the weekend, then low pressure or a cold front may affect our weather Sunday night and Monday.
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&& .NEAR TERM /THROUGH TODAY/...
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Through early this morning, the cloud cover continues to gradually lower as moisture increases from the south ahead of a warm front. This along with a light south-southeast surface wind should help keep temperatures steady or even rise some. Some tweaks were made to the temperature and dew point grids prior to 12z today. A potent upper-level trough will remain well to our west today, however a strong short wave trough rotating northward up across the eastern Great Lakes early this morning will help drive rain into our area. Today will be part one of much needed rainfall. As the aforementioned system lifts into the Great Lakes, a robust low-level jet from a southerly direction on the order of 50-65 knots overspreads the area this morning. This will then shift east and offshore during the afternoon. This feature will drive increasing warm air and moisture advections across our area. The moisture advection is evident in the low-level theta-e fields as well as PW values increasing to 1.5 inches by later this morning. This will result in a corridor of enhanced lift across much of the area, therefore periods of rain will occur from southwest to northeast, some of which can be briefly heavy. Given the soaring PW values, rainfall amounts should average in the 1-2 inch range however some locally higher amounts are possible especially if some convective elements occur. While some elevated instability may develop, the profiles via forecast soundings are rather saturated therefore we opted to not add in thunder at this time. We continued with a rapid increase in the PoPs this morning, and the steadier rain may be centered from the I-95 corridor on north and westward. As a surface warm front lifts northward during the course of day, pushed by the robust low-level jet, boundary layer warming will allow for turbulent mixing and therefore breezy conditions are expected to develop for much of the area especially closer to the coast. The gusty winds will then diminish toward evening. High temperatures are mostly a blend of continuity and MOS. The hourly temperature and dew point grids were adjusted with the latest obs, then the LAMP/LAV guidance was blended in.
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&& .SHORT TERM /TONIGHT/...
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A deep mid level low is forecast to be located over Minnesota and vicinity on Tuesday night. The initial shot of rain should be working its way off the coast on Tuesday evening. Some clearing may follow. We are anticipating areas of fog on Tuesday night due to the clearing and light wind along with abundant lingering low level moisture. A second warm front approaching from the south and southwest will aid in the process, as well.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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A deep mid level feature is expected to pass across the Great Lakes on Wednesday and Wednesday night before reaching southern Quebec and Atlantic Canada late in the week. A mid level ridge should begin building over the eastern states during the weekend. The model guidance begins to diverge significantly for the early part of next week. Warm advection aloft along with a connection to the Gulf of Mexico will result in the development of additional rain in our region on Wednesday. As a cold front begins to approach from the west late in the day, additional lift should result in increasing rainfall rates. A moderate to heavy rainfall is anticipated into Wednesday evening along with a chance of thunder. Additional rainfall totals of 0.75 to 1.25 inches are possible across parts of eastern Pennsylvania and northern New Jersey with lesser amounts on the coastal plain. Locally higher amounts are possible in the upslope regions. The cold front is expected to pass though our region around midnight on Wednesday night. Temperatures will be about 15 degrees above normal from Tuesday night into Wednesday evening ahead of the boundary. Dry air and a return to near normal temperatures should follow for the late week period into the weekend. A west northwest flow may bring some cold advection stratocumulus at times, especially to our northwestern counties. We have mentioned a chance of precipitation for Sunday night and Monday. However, the spread in the guidance makes this a low confidence forecast. The GFS is suggesting a cold frontal passage while the ECMWF is indicating that a strong area of low pressure will influence our weather at that time.
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&& .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Through Tuesday...Clouds lower through this morning. Periods of rain spreading across the area from southwest to northeast mainly between 09-11Z at RDG and ABE, the I-95 terminals between 11-13Z, and MIV/ACY between 12-15Z. The ceilings quickly lower to MVFR after the rain begins, then periods of IFR for much of the day. The visibilities will lower to MVFR/IFR during heavier rain. Low-level wind shear is included for a time this morning as a southerly low-level jet (at 2,000 feet) increases to 45-55 knots. This occurs initially when surface winds are southeasterly at 10 knots or less. The surface winds will increase after a warm front passes through from south to north later in the morning and the low- level jet shifts east, therefore low-level wind shear concerns decrease. Southerly surface winds will increase to 12-18 knots with gusts to around 25 knots across much of the area from later this morning through mid/late afternoon. Tuesday night...Any lingering rain ends early with MVFR/IFR ceilings continuing, however areas of fog should develop as clouds may thin some in combination with light winds and lots of leftover moisture. Confidence regarding low ceilings is lower than average as they may clear out for a time especially in the RDG to ABE corridor. OUTLOOK... Wednesday...IFR conditions with low ceilings and fog should improve to MVFR and possibly VFR during the day. However, rain is expected to build into the region and it will become moderate to heavy at times with the potential for IFR conditions returning. Wednesday night...MVFR and IFR conditions in moderate to heavy rain during the evening with a chance of thunder. A strong cold front should arrive around midnight followed by clearing and improvement to VFR. Low level wind shear is possible in the evening due the the expectation of a 45 to 50 knot low level southwesterly jet at that time. Thursday through Saturday...mainly VFR.
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&& .MARINE... Sly winds and seas will gradually increase tonight but remain below SCA levels. SCA in effect for the waters Tuesday. A 50 kt low-level jet will move overhead Tuesday. Sly winds are forecast to strengthen to 20-30 kt during the afternoon. Poor lapse rates owing to warm air atop the cooler waters do not favor stronger winds mixing down to the surface. Held off on upgrading to a GLW in this setup but there is still a possibility of a isolated gale-force gusts late in the day. Seas will build to 5-8 ft by the afternoon. OUTLOOK... Tuesday night and Wednesday...A Small Craft Advisory is in effect for our ocean waters for wave heights of 5 to 7 feet. Also, wind gusts of 25 to 30 knots are possible on Tuesday evening and again on Wednesday afternoon. Wednesday night...Wind gusts of 25 to 30 knots are possible initially from the southwest then from the west following the passage of a cold front after midnight. There could be a brief surge of gale force gusts on either side of the frontal passage. Thursday through Saturday...West to northwest wind gusts of 25 to 30 knots are possible through the period. && .HYDROLOGY...
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QPF guidance was in decent agreement regarding the placement of the axis of heaviest rainfall from this midweek event setting up somewhere in the CWA (generally eastern Pennsylvania and northern New Jersey) although there are some differences in QPF amounts. Storm total rainfall will most likely average 1-2 inches but isolated higher amounts of 3+ inches are certainly possible if the heaviest rain from both waves falls over the same area. Conversely, some areas on the coastal plain may receive less than an inch of rain. We are not expecting main stem flooding or even smaller basin flooding since these rainfall amounts will be spread out over a 48 hour period and the antecedent conditions are dry. Poor drainage flooding is always a possibility if the localized 3+ inch rainfall amounts materialize but impacts from this type of flooding are generally minor. Some poor drainage flooding though could be locally enhanced where fallen leaves clog storm drains.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 6 AM this morning to 6 PM EST Wednesday for ANZ450>455. Small Craft Advisory from 6 AM this morning to 6 PM EST this evening for ANZ430-431.
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&& $$ Synopsis...Iovino Near Term...Gorse Short Term...Iovino/Klein Long Term...Iovino Aviation...Gorse/Iovino Marine...Iovino/Klein Hydrology...

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