699 FXUS61 KPHI 141616 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1216 PM EDT Wed Oct 14 2020 .SYNOPSIS... The center of high pressure slides to our south today, however it crests across our area later today into tonight before shifting offshore into Thursday. Low pressure tracks across Ontario and Quebec Canada Thursday and Friday, pulling a strong cold front across our region during Friday as low pressure develops along it. The low and cold front shifts to our northeast Friday night into Saturday. High pressure then builds in later Saturday before shifting offshore Sunday into early next week. && .NEAR TERM /THROUGH TONIGHT/... Surface high pressure continues to center over North Carolina this afternoon. A beautiful autumn day with sunny skies and high temperatures around 70 degrees. Tonight, surface high pressure will slowly migrate offshore with winds backing from the south/southwest. Some guidance is hinting at some high clouds possible, but this appears transient at best as the upper level jet streak will only be temporarily located across the northern zones before once again lifting. Expect low temperatures in the upper 40s to lower 50s. && .SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/... Thursday, surface high pressure will be located off the eastern coast of the United States with a potent mid-level wave over southern Ontario. This wave is forecast to pull northeast into Quebec with a surface cold front trailing southwest across the Ohio Valley. Ahead of this front, strong low level WAA will commence with 850 mb temperatures rising from around 7/8 degrees C on Wednesday to near 14/15 degrees C on Thursday. Forecast soundings are again showing mostly clear skies, which will support high temperatures in the mid to upper 70s. Thursday night into Friday, a surface cold front will slowly approach the region from the west. Low temperatures Friday morning will only fall into the mid 50s as cloud cover rapidly increases. && .LONG TERM /FRIDAY THROUGH TUESDAY/... Summary...Much colder by later Friday and continuing Saturday (some rain Friday and Friday night); Warming up some early next week. Synoptic Overview...A sharpening upper-level trough is forecast to swing across the East Friday into Saturday, with an associated strong cold front moving through during Friday. Low pressure along the front lifts to our northeast to start Saturday, then the flow aloft turns more westerly and weakens. Surface high pressure builds back into our area later Saturday before shifting offshore Sunday into Monday. The next cold front may approach later Tuesday as the next upper-level trough shifts eastward. For Friday and Saturday...An upper-level trough across the Great Lakes, Midwest and northern Plains is forecast to shift eastward, sharpening across the Northeast Friday night. Strengthening southerly flow ahead of a strong cold front will transport deeper moisture into our area, with an axis of precipitable water between 1.0-1.5 inches. While some timing differences still exist among the guidance, the front itself looks to move through during Friday with much of the rain occurring along and behind it (ana-front type setup). The upper-level trough is forecast to take on a negative tilt as it arrives in the East later Friday. Strong short wave energy rounding the base of the trough along with a robust wind field will drive surface low pressure development along the front as it is crossing our area during Friday. The surface low development and increasing large scale ascent from the incoming sharpening trough should allow rapid development of rain during the course of Friday. Good jet dynamics in concert with a ribbon of frontogenetic forcing near and behind the front and west of the surface low should enhance the rainfall for a time (moderate to heavy intensity) especially later Friday. The instability looks to be rather weak especially given much if not all of our area should be behind the front during the strongest forcing. However as the trough takes on a negative tilt, enhanced forcing for a time could result in a low-topped narrow convective band embedded in the overall rain shield. There will be strong shear in place, however the ana-front characteristic should tend to favor less of a convective potential. Given this, continued to keep no mention of thunder in the forecast at this time. The negatively tilted upper-level trough and surface low pressure are forecast to be lifting to our northeast Saturday. The main band of rain should have cleared the area early Saturday morning with perhaps some leftover showers to start the day, then quick drying should take place from southwest to northeast as the flow turns less cyclonic and surface high pressure starts to build in. It will be noticeably colder especially later Friday through Saturday, with many areas staying at or below 60 degrees on Saturday and there will be a gusty northwesterly breeze adding to the chill. The winds should rapidly diminish Saturday night as the pressure gradient weakens with incoming high pressure. This should set the stage for good radiational cooling conditions, and therefore some frost development is possible early Sunday morning across portions of the region. For Sunday through Tuesday...High pressure builds across our region and then eventually offshore Sunday and Sunday night, remaining offshore on Monday. As this occurs, a strong upper-level trough is forecast to be moving across the upper Midwest and Great Lakes then into adjacent Canada. This should result in a warm front lifting to our northwest with increasing south to southwesterly flow becoming established across our region. This time frame looks to be mostly on the dry side but a warming trend is forecast in the wake of departing surface high pressure. A cold front may approach the area Tuesday ahead of the next incoming upper-level trough, however the timing is less certain. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR. W winds less than 10 kt. High confidence. Tonight... VFR conditions with only some high clouds towards KABE and KRDG. High Confidence. Thursday... VFR conditions with winds increasing in speed from the south. Gusts of 20 to 25 mph will be possible Thursday afternoon. High confidence. Thursday night... A surface cold front will approach from the west with VFR clouds thickening and light rain slowly moving in behind the front. Overall, most of the Thursday night period appears to be dry at this point with VFR conditions. Moderate confidence. Outlook... Friday...VFR ceilings lower to MVFR then to IFR during the day as rain develops and becomes moderate to heavy at times through much of the night. Southerly winds 5-10 knots, becoming northwesterly as a cold front moves through. Low confidence regarding the timing details of the sub-VFR conditions and also the wind shift. Saturday and Sunday...VFR. Northwest winds 10-15 knots with gusts 20- 25 knots Saturday then quickly diminishing late in the day and at night; Southerly winds less than 10 knots Sunday. Moderate confidence. && .MARINE... Today...Northwest winds slowly back from the west at 10 to 15 knots. Seas 2 to 4 feet. Tonight... Winds continuing to back from the south around 10 knots. Seas 2 to 4 feet. Thursday... South winds 15 to 20 knots, gusting 25 to 30 knots. Seas building to around 5 feet. Outlook... Friday and Saturday...Small Craft Advisory probable Friday night and Saturday as winds turn northwesterly and gusty. Winds should then quickly diminish Saturday night. Sunday...The conditions are anticipated to be below Small Craft Advisory criteria. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Gorse Near Term...Haines/MPS Short Term...Haines Long Term...Gorse Aviation...Gorse/Haines Marine...Gorse/Haines