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 152032 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ Issued by National Weather Service BALTIMORE MD/WASHINGTON DC 332 PM EST Wed Nov 15 2017 .SYNOPSIS...
-- Changed Discussion --
High pressure over our area weakens and retreats toward the Canadian Maritimes tonight. A strong cold front moves across our area during Thursday, then high pressure builds in during Friday. A warm front lifts to our north Saturday, followed by a cold front Saturday night. High pressure then builds to our south Monday into Tuesday.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
The most recent surface analysis depicts high pressure centered over the Canadian Maritimes, but with a long extension southwestward along the eastern seaboard. To the west, low pressure is centered in the upper peninsula of Michigan, with a pair of cold fronts extending southward and southwestward. There is also a weak coastal front located near the VA/NC border. Tonight, the cold fronts will slowly combine and make their way eastward as the low pressure moves into southern Canada. At the same time, energy will begin to transfer to a new low pressure developing along the coastal front, which will be moving northward along the coast. FGEN and isentropic lift with this complex system is not strong, but should be enough to allow some showers to make their way eastward into our region, mainly after midnight. Some of these showers will also be home-grown as the developing low on the coastal front moves northward along the coast. Temperatures will remain fairly steady through the night, mostly in the 40s, thanks to increasing clouds and then rain. Rainfall amounts look light, less than 1/4 inch overall, with lesser amounts south and west of PHL.
-- End Changed Discussion --
&& .SHORT TERM /THURSDAY/...
-- Changed Discussion --
As the pair of low pressure systems (one weakening in southern Canada and another strengthening along the coast) moves northeast away from our region, showers will move out as well. However, clouds may linger for some time in the morning as there won`t be a big push to clear things out until the surface front arrives. At this point, best bet for frontal passage is late morning, a little earlier far west and a bit later towards the coast. A few showers may accompany the front over the mountains, but generally expecting a dry passage further south and east. Once the front passes, most places southeast of the ridges should start to see some breaks of sun, along with a pretty gusty winds. Winds will likely be sustained 15-20 with some gusts near 30 mph expected. A few gusts might push 35, especially near the coast and Delaware Bay. Despite the frontal passage, highs should actually be rather mild thanks to a brief surge of milder air immediately ahead of the front combined with downslope flow - most areas should reach the 50s again.
-- End Changed Discussion --
&& .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
-- Changed Discussion --
Summary...Strong cold front moves through Saturday night with milder air ahead of it, followed by colder air and gusty winds. Synoptic Overview...A strong upper-level trough lifts out on Friday. Some weak ridging then arrives, but another upper-level trough quickly arrives Saturday night into Sunday. As more pronounced ridging moves across west-central Canada, a downstream trough is forecast to begin amplifying across the Great Lakes and Northeast Tuesday. The flow aloft overall looks progressive for awhile, however there are signals that next week may feature more amplification with a trough settling into the East. For Thursday night, the winds will diminish some, however given the continuation of cold air advection in the lower levels and the pressure gradient remaining tight this process may be slowed. For Friday and Saturday...The strong upper-level trough moves away during Friday with the flow becoming more zonal. High pressure at the surface builds across our region Friday which will result in less wind through the day. It is noted that the stat guidance especially is warmer for Friday, however the modeled 2 meter temperatures are colder. The latter is rather close to our going forecast, and therefore we opted to make little in the way of changes. Clouds increase Friday night ahead of the next incoming upper-level trough. There is fairly strong warm air advection in advance of this, allowing a warm front to become better defined as it lifts northeastward. This should produce a zone of showers or rain along and to its north, however this appears to be slower in the guidance overall as we go through Saturday. As a result, we slowed down the PoP increase from west to east Saturday. Low pressure is forecast to strengthen as it lifts across the eastern Great Lakes region Saturday morning and then into Canada. The associated cold front sweeps through our area Saturday night. Increasing southerly flow ahead of the cold front Saturday will drive milder air into the region, then be replaced by west to northwest winds behind the frontal passage. We continue to bring in likely to categorical PoPs through Saturday night. Given the timing, held off in adding thunder. For Sunday and Monday...While some showers may linger early Sunday as the cold front shifts offshore, drying is expected. Low pressure tracks near northern New England Sunday, with a tight pressure gradient in place along with cold air advection. Sunday is looking like another breezy/windy day as mixing deepens during the day. The air turns colder and therefore lake effect snow should develop off the eastern Great Lakes. It is possible that a streamer attempts to approach the Poconos later Sunday afternoon and evening. The winds should diminish at least some Sunday night. High pressure starts to build in during Monday, however its center is to our south- southwest. Overall, a cold day is expected Monday. For Tuesday...Renewed upper-level trough development is forecast to take place into the Northeast. This drives low pressure once again near and north of the Great Lakes with a trailing cold front approaching from the west. As the flow backs in response to this system, some warming will be draw northward. The main forcing with this system may end up lifting to our north, therefore continued with a dry forecast at this time.
-- End Changed Discussion --
&& .AVIATION /20Z WEDNESDAY THROUGH MONDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of this afternoon...Generally VFR conditions expected for rest of the afternoon. Mid level clouds continuing to advect north across the region this afternoon in advance of an approaching trough. ACY cigs may flirt with MVFR at times. Light northeast wind gradually becoming southeast rest of this afternoon. Confidence in ceiling forecast height is average, and for winds is above average. Tonight...VFR or high MVFR CIGS to start, then degrading to low MVFR to high IFR CIGS later at night with rain showers. Vis may also drop in showers. Low clouds and mist with reduced cigs/vis may linger thru much of morning before cold front moves through by midday. Gusty W-NW wind after front will persist thru remainder of Thursday, gusts may exceed 30 kts, but cigs and vis improve. Confidence above average on sub MVFR conditions late at night. OUTLOOK... Thursday night...VFR with winds diminishing. Moderate confidence. Friday...VFR overall, then clouds increase and lower some at night. High confidence. Saturday...A period of MVFR/IFR conditions with showers, especially in the afternoon and at night. Some improvement in the conditions should occur late at night as a cold front moves through. Moderate confidence. Sunday...VFR overall. Some flurries or snow showers possible in the afternoon mainly north and west of ABE. Northwesterly winds 15-20 knots with gusts up to 30 knots. Moderate confidence.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
SCA remains for part of waters for rest of afternoon. Winds look to diminish below SCA limits tonight for much of the waters as low pressure approaches. Winds should then increase to high end SCA during the day and gales by Thursday night. Gale Watch has been upgraded to warning. It may need to be adjusted to start earlier during the afternoon Thursday as winds may begin sooner. OUTLOOK... Friday...Gale force gusts within a northwesterly flow may linger Friday morning, however the winds are expected to be diminishing. Saturday and Sunday...Gale force gusts from the southwest are possible Saturday afternoon and evening, then gale force gusts from the west and northwest are possible later Saturday night and Sunday.
-- End Changed Discussion --
&& .CLIMATE... November will probably average below normal throughout our forecast area. It is expected that the last 16 days will average at best normal, more likely...below normal...though how much below normal we`re unsure. I cannot at this time see the departures listed at the end of this section, warming...and suspect they`ll run colder by a degree or 3. The pattern as signaled for many recent days by the NAEFS/GEFS/ECEFS is basically a trough constantly reloading in the northeast USA through the end of the month. So the positive departure excesses from September 14 through November 6 are history. What we`re experiencing now is what fall is supposed to be like...chillier. And its probably going to be a big difference when compared to last November which averaged 1 to 3 degrees above normal. The numbers below represent the departure from average for the first 14 days of the month and those departures will probably go more negative by time the 30th arrives. ACY -0.2 55N -1.2 (ACY Marina) ABE -1.0 ILG -0.9 MPO -3.4 PHL -1.5 RDG -2.7 TTN -1.5 GED +1.0 Basically that says the coldest departures were across the northwest part of our forecast area and the mildest departures from normal, along our southeast edge. && .PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ451>453. Small Craft Advisory from 6 AM to 6 PM EST Thursday for ANZ430- 431-450>453. Gale Warning from 6 PM Thursday to 6 AM EST Friday for ANZ430- 431-450>455. Small Craft Advisory until 6 PM EST Thursday for ANZ454-455.
-- End Changed Discussion --
&& $$ Synopsis...Gorse/RCM Near Term...Drag/Johnson/RCM Short Term...Drag/RCM Long Term...Gorse/RCM Aviation...Drag/Gorse/Johnson/RCM Marine...Drag/Gorse/RCM Climate...PHI

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