FXUS61 KPHI 260813 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 413 AM EDT Sun May 26 2019 .SYNOPSIS... A warm front will continue to move away from the area this morning. A cold front attached to low pressure across Canada will move through the region later today. High pressure will settle across the area Monday then another disturbance will be across the area Tuesday. An unsettled pattern is expected for the middle and end of the upcoming week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The area will reside in the warm sector for most of the daylight hours before a cold front approaches late this afternoon. West of I- 95 a stratus deck is evident on satellite imagery/observations and expect this to expand eastward through the early morning period. This stratus should burn off sometime this morning given a drier westerly flow and strong late May sun. Once the stratus burns off we should be off to the races as far as temperatures go, with just about everywhere getting to at least 80 and many locations (particularly Delmarva and the I-95 corridor) making a run at 90. Dewpoints should generally be in the low to mid 60s although there is some uncertainty based on the mixing potential (initially we will be fairly dry aloft). The big story today will be the chance of convection this afternoon into this evening , with strong-severe storms possible. We should be capped for the morning and early afternoon so not expecting any storms before about 18Z. As the capping erodes (from NW to SE) we could see isolated-scattered storms develop over primarily the northern half of the forecast area in association with the prefrontal trough. The environment at that time is not particularly favorable for severe convection with SBCAPE generally around or under 1000 J/kg, however given 40 kts of shear some locally strong storms will be possible (given decent low-lvl dewpoint depressions downburst winds will be the main threat with this early activity). The more favorable timing for any severe storms looks to be late this afternoon into this evening as the cold front/shortwave approach (this is detailed in the Short Term section). && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... The best period for severe storms looks to be the 21-03Z time frame ahead of/along the cold front and convectively enhanced shortwave. Guidance has storms developing upstream and then growing upscale as they approach the area late this afternoon into the early evening. The best convective parameter space (largely a function of low-lvl moisture) will reside over the southern half of the area (more or less Philadelphia southward), where MLCAPE of around 1500 J/kg will combine with 40 kts or so of westerly shear to create the potential for an organized cluster of storms with damaging winds being the biggest threat (but hail is also possible). Low-lvl shear will be particularly unimpressive (low-lvl flow in general will be quite weak) so the tornado threat is negligible. Of note, some models (particularly the NAM-nest) continue to advertise MLCAPE well in excess of 2000 J/kg over much of the western part of the forecast area, which if realized would result in a more widespread severe threat. Currently think this is unlikely to occur as its pre-convective dewpoints seem too high given westerly flow and mixing of drier air from aloft... consequently think the HRRR instability will be closer to reality. The front will move through this evening with drying behind it. This is not a particularly impressive front from a thermal or kinematic perspective so drying will be gradual and precipitation will likely continue into the overnight. Storms will wane from north to south with the severe threat diminishing after 03Z as the surface-based instability diminishes. Given abundant cloud cover and high dewpoints overnight mins will be warm (mid to upper 60s outside of the far north where upper 50s/lower 60s will be possible) && .LONG TERM /MONDAY THROUGH SATURDAY/... A rather changeable pattern across the area this upcoming week with alternating days of (mostly) dry weather and some weak systems which will bring some sct showers and tstms. Right now, Mon/Wed/Fri are probably going to be the days with the lowest pops. Although there could be some morning showers across Delmarva early Mon. On Wed, a couple showers psbl far N/W. Tue will see low pressure and a front affecting the area, so showers and some tstms are expected with the greatest pops (likely) across the nrn areas. The models become somewhat varied by Thu/Fri, but the possibility for some showers will be retained with the GFS and EC showing some rains arriving late Thu. Some much above normal temperatures will arrive during the middle of the week with upper 80s and low 90s in many areas. Up until then, above normal readings (4 to 6 degrees above) will be over the area Mon/Tue. The much above normal will probably break late next week, with readings back near normal for Fri/Sat. && .AVIATION /08Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today... Low-MVFR stratus should scatter out around 11-13Z, with VFR conditions generally prevailing through the day. Scattered showers and thunderstorms will be possible this afternoon particularly after 18z with lowered flight categories possible. Winds will generally be from the west around 10 kts with occasional gusts to 15-20kts. Tonight... Showers/thunderstorms possible in the evening, however VFR conditions under mid-lvl cloudiness expected to prevail. Winds shifting more northerly overnight. Outlook... Mon/Tue...VFR much of the time. A few showers early Monday and Tue. Wed/Thu...VFR Wed. Sct showers later Thu with lower conditions psbl. && .MARINE... Sub-SCA conditions are expected Sunday into Sunday night with seas generally around 3 feet and gusts up to around 15 kts. Thunderstorms with gusty/erratic winds will be possible late this afternoon into this evening. Outlook... Generally sub-SCA thru the period. There is the possibility for some SCA gusts later Thu, but confid in this is low attm. Sct showers and tstms Mon morning, Tue and Thu. Rip Currents... The risk for the formation of dangerous rip currents is low through this evening. The low risk may continue into Monday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...O'Hara Near Term...Carr Short Term...Carr Long Term...O'Hara Aviation...Carr/O'Hara Marine...Carr/O'Hara