Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 290206 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 906 PM EST Mon Nov 28 2016 .SYNOPSIS... High pressure will continue to lose its influence over our weather tonight. Strong low pressure is forecast to pass across the Great Lakes during the mid week period. The low should pull a couple of warm fronts through our region on Tuesday and Wednesday before a strong cold front arrives from the west on Wednesday night. A secondary low is expected to develop over southern New England on Wednesday night before moving across Nova Scotia on Thursday. High pressure is anticipated to follow for Friday into the weekend. Low pressure or a cold front may affect our weather on Sunday night and Monday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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As of mid-evening, a light southeast surface flow continues over the forecast area, although a few locations have calm conditions which have allowed temperatures to fall to near the forecast mins. A high-level overcast now covers most of the area and these clouds should thicken and lower with time tonight and prevent too much additonal cooling. Meanwhile the nearest rain is back over central Ohio, but the latest model guidance has rain spreading west to east across eastern PA, NJ and northern Delmarva between about 500 and 900 am. Temperatures are expected to be well above freezing everywhere by the time rain begins. Previous discussion below: Surface observations across the forecast area this afternoon indicate a light southerly return flow has developed in response to high pressure moving off the Mid-Atlantic coast. The high will shift farther offshore tonight as a storm system over the central CONUS expands its reach farther downstream. While the low pressure center will remain nearly stationary tonight over the Northern Plains, a warm front will become better defined farther east across the Mid- Atlantic region. This warm front is expected to lift northward and into the area early Tuesday morning. Expect tranquil weather through this evening with a shortwave ridge aloft taking place along the eastern seaboard. High clouds ahead of the approaching storm system will continue to overspread the region from southwest to northeast this evening. Clouds should be thin enough, especially across northeastern PA and northern NJ, to not have much of an impact on radiational cooling this evening. Therefore, temperatures will likely fall sharply after sunset, especially in the sheltered valleys (where winds in the boundary layer are most likely to decouple). Min temperature across most of the area may occur earlier in the night than usual (within a few hours of midnight) as clouds thicken, strengthening winds help mix the nocturnal boundary-layer, and WAA increases. NWP models are in reasonably good agreement regarding the arrival time of the precipitation late tonight. Expect the rain to reach our western zones in PA by around 3 AM. Rain may hold off until around daybreak east of the Delaware Valley.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... The aforementioned warm front will lift northward through the region on Tuesday. A 50-60 kt southerly low-level jet on the eastern flank of the storm system will draw warm, moisture air from the Gulf of Mexico northward and up the eastern seaboard. This will produce a good overrunning setup across the warm front boundary. Rain will continue to expand eastward across the area during the morning. The rain looks to be widespread for much of the day, resulting in a washout tomorrow. Models continue to differ slightly on where the best lift and axis of heaviest rain falls tomorrow, with one camp of guidance targeting our far western zones (RDG-MPO- FWN) while the eastern solutions depict the I-95 corridor. The small difference seems to be tied to where the warm front gets hung up. Rainfall amounts within this heavier band look to be 1-2 inches on Tuesday. High temperatures in the warm sector south of the warm front may reach the mid 60s while temperatures north of the boundary will only be in the 50s. Southerly winds in the warm sector are expected to become breezy. Wind speeds near 20 mph with gust to 30 mph are forecast for the afternoon in the coastal plain of NJ and Delmarva. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... A deep mid level low is forecast to be located over Minnesota and vicinity on Tuesday night. The 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. 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. 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. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR through 06Z. High clouds will continue to expand northeastward across the region with CIGs gradually lowering to mid-levels. Sly winds around 5kt this evening may back slightly out of the SE tonight. Rain moves in to RDG-ABE between 08-10Z, the I-95 terminals between 10-12Z and ACY between 12-14Z. CIGs will quickly lower to MVFR after the rain begins. Expect periods of MVFR and IFR conditions in rain for much of the day. LLWS was added to the TAFs for Tuesday morning, when forecast profiles show southerly winds associated with a low-level jet increase to 50 kt while SE winds at the surface are 10 kt or less. Surface winds will increase after a warm front passes thru from south to north later in the morning and LLWS concerns will lower. Southerly winds at the surface will increase to 15-20 kt with gusts 25-30 kt across most of the area during the afternoon. OUTLOOK... Tuesday night...Low ceilings and fog are expected to develop along with IFR conditions. 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... 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. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 6 AM Tuesday to 6 PM EST Wednesday for ANZ450>455. Small Craft Advisory from 6 AM to 6 PM EST Tuesday for ANZ430- 431. && $$ Synopsis...Iovino Near Term...AMC/Klein Short Term...Klein Long Term...Iovino Aviation...Iovino/Klein Marine...Iovino/Klein Hydrology...

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