252 FXUS61 KPHI 021324 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 924 AM EDT Wed May 2 2018 .SYNOPSIS... High pressure remains entrenched offshore of the southeast coast through Friday. A cold front will approach the area from the north Thursday but not make it into the area. As an area of low pressure moves through the Great Lakes on Friday and across northern New England Friday night, it will pull a cold front across the east coast overnight Friday into Saturday morning. This front will likely stall near the area Saturday night into Sunday, before another cold front pushes across the east coast Sunday night into Monday. High pressure is then expected to return for Tuesday into Wednesday of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Forecast on track, so no significant changes will be made to the database. Will adjust hourly grids based on latest surface obs. Surface high pressure was located off the Southeast U.S. coast (just to the west of Bermuda). Above the surface, this ridge extends farther westward with height. Broad anticyclonic flow around the high (S-SWly at the surface and Wly aloft) will continue the supply of anomalously warm air over much of the eastern CONUS today. Warm-air advection and adiabatic compression from building subsidence beneath the ridge will yield even warmer temperatures today compared to what we saw yesterday. Max temperatures were computed by mixing 850 mb temps from a model blend dry adiabatically down to the surface and then were blended with gridded MAV/MET. A third step involved blending hi-res models for coastal areas. This multi-step approach hopefully removes the cool bias from just using the stat guidance and highlights the sharp temperature gradient near the coast. The end result is forecast highs generally in the mid 80s (70s at the NJ/DE beaches and the Poconos). A few spots may reach the upper 80s, especially along the urban I-95 corridor and in interior Delmarva. Sunny skies are expected for most of the day although there will likely be an increase in high clouds late this afternoon across western zones. W-SW winds will increase to around 15 mph this afternoon with gusts of 20-25 mph with the breeziest conditions occurring from about 4-7 PM. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... W-SW flow around the offshore high will continue into tonight. Overall, a mild night can be expected although that only tells part of the story as temperatures will likely vary considerably from location to location. In the sheltered/rural valleys where surface winds will decouple from the boundary layer, low temperatures will drop into the upper 50s. Meanwhile, more urbanized locales and areas where a light breeze persists through the night, temperatures will likely remain in the mid 60s. High clouds will increase from W to E tonight as cirrus from upstream convection spills into the area. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Hot conditions are expected for the end of the work week, with the potential for some unsettled weather for the end of the week and into this weekend. High pressure remains entrenched offshore of the southeast coast for Thursday and Friday, which will keep a very warm return flow across the area. This return flow will allow for temperatures to warm significantly across the area, potentially reaching records on Thursday and Friday for some areas. On Thursday into Thursday night, a cold front will approach the area from the north, but will remain north of the area. However, a surface trough will likely develop across the area, and as a couple of weak short wave/vorticity impulses slide across the area during the day and into the overnight. This could help lead to a chance of scattered/isolated showers/thunderstorms, especially for northeast Pennsylvania and northern New Jersey. For Friday and Friday night, low pressure will be moving across the Great Lakes region and into northern New England. This will pull a cold front across the area later in the day and into the overnight. As several short wave/vorticity impulses move across the area, there will again be a chance of scattered/isolated showers/thunderstorms, especially for eastern Pennsylvania and northern New Jersey during the afternoon, before moving eastward during the evening, before diminishing overnight. The front is expected to stall out across the east coast Saturday into Sunday, before another cold front pushes across the east coast Sunday night into Monday. There will be a chance of showers through the weekend into Monday. Saturday's showers may be more focused near the cold front across southern New Jersey and Delaware and Maryland, while the showers Sunday into Monday would most likely be associated with the second frontal passage. High pressure is then expected to return to the east coast Tuesday into Wednesday of next week which will provide fair conditions across the area. After the very warm conditions Thursday and Friday, cooler temperatures will return for the weekend behind the cold front and continue into early next week, especially Monday behind the second cold front. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR. Light W-SW winds this morning (under 10 kt) will increase to 10-15 kt this afternoon. Gusts will peak in the 20-25 kt range in the 19-00Z period. Tonight...VFR. Wind gusts should drop off quickly around sunset while W-SW winds diminish at a more gradual rate tonight (around 10 kt just after sunset to 5 kt or less overnight). Similar to what happened last night, LLWS conditions will likely develop tonight as surface winds become light and a Wly nocturnal jet strengthens to 40-45 kt in the lowest 1-2 kft AGL. OUTLOOK... Thursday-Friday...Generally VFR. There is a chance of showers or isolated thunderstorms, especially for northeast Pennsylvania and northern New Jersey which could temporarily lead to lower conditions. Southwest wind gusts 20-25 knots during the daytime hours.. Friday night...Generally VFR. There is a chance of showers or thunderstorms, which may temporarily lower conditions. Winds may continue to gust 20-25 knots into the evening hours. Saturday-Saturday night...Generally VFR. There is a chance of showers, especially for southern New Jersey and Delaware and Maryland, which may temporarily lower conditions. Sunday...Generally VFR. There is a chance of showers for all locations which may temporarily lower conditions. && .MARINE... Generally sub-SCA conditions. However, there is a potential for stronger gusts near 25 kt to affect nearshore waters late this afternoon due to deeper mixing on land. Farther away from the coast, enhanced S-SW flow associated with the development of an Ambrose jet could reach 20+ kt late this afternoon and this evening in our northern coastal waters. OUTLOOK... Thursday-Friday night...Near shore waters may gust 25 knots at times, especially during the afternoon Thursday and Friday. Farther offshore may have a more difficult time mixing down the strong gusts with an inversion over the waters. Seas may also build to 5-6 feet. Saturday-Sunday...Conditions expected to fall below Small Craft Advisory levels by Saturday morning and remain below advisory levels through Sunday. Cold water concerns for water activities: With high temperatures for inland locales approaching 90 in some areas Wednesday through Friday, there is a propensity for some to flock to the beach. For those considering boating or swimming in the ocean, there will be a risk for hypothermia with water temperatures only in the 50s. Those planning to be on the water should dress for the water temperature, not the air temperature, especially given the much warmer conditions farther inland. && .FIRE WEATHER... A Red Flag Warning was issued for all of our eastern PA and NJ zones for today (10 AM - 9 PM). Dry conditions will continue today with 10- hr fuel moisture at or below 6 percent area wide and minimum RHs expected to be between 20-25 percent along and east of I-95 and 25- 30 percent farther west. Winds will increase to around 10 mph late this morning, then to around 15 mph with gusts of 20-25 mph this afternoon and early evening (the breeziest conditions are expected from about 4-7 PM). A Special Weather Statement was issued for an enhanced fire spread risk today in DE and NE MD as red flag criteria in these states of 20 mph sustained winds will not be met. All statements/headlines were coordinated yesterday with state fire partners yesterday morning. There is still the chance for near Red Flag conditions Thursday and Friday across portions of central/southern New Jersey and southeast Pennsylvania. Right now the forecast is for min RH values around 30-35 percent. Winds will easily gust in the 20-30 mph range, so if the RH values lower, we may need to consider fire weather headlines in the future for these area. && .CLIMATE... Following an extended period of colder than normal conditions this past winter and so far this spring, the five-day stretch of well above normal temperatures that started on Tuesday and continues through Saturday, May 5th may seem like a heatwave. Outside of the cooler coastal locales and the higher elevations in NE PA and NW NJ, the mean high temperature over these five days are forecast to be in the lower to mid 80s (with two days near 90 degrees on Thursday and Friday), which is representative of normal highs for mid June. Additionally, this will likely be the warmest 5-day stretch the area has experienced since late September (September 24-28). For Philadelphia: The high temperature is forecast to be at least 5 degrees above normal for 5 consecutive days (May 1-5) and at least 10 degrees above normal for 3 consecutive days (May 2-4). The last time Philadelphia recorded this many days in a row with high temperatures of 5+ degrees above normal was January 19-23, 2018 and January 20-23, 2018 for 10+ degrees above normal. However, the anticipated magnitude of the heat is by no means unprecedented for early May where highs around 90 degrees have been observed before: Several climate sites will likely be with 1-4 degrees of their respective daily high temperature records today. The greater risk for record-tying or record-break high temperatures will generally be tomorrow (May 3) and Friday (May 4). Below are the daily high temperature records for May 2-4 at our first-order climate sites: Site May 2 May 3 May 4 Allentown 90 (2001) 91 (2001) 92 (2001) Atlantic City 88 (2010) 89 (2001, 1913) 91 (1965) Georgetown 87 (1986) 90 (1965) 89 (2001, 1965) Mount Pocono 83 (1913) 85 (1913) 84 (1944) Philadelphia 89 (2010) 90 (2001, 1913) 91 (2001) Reading 89 (1899) 90 (2001) 90 (1913, 2001) Trenton 88 (2010) 90 (1913) 89 (2001) Wilmington 90 (1894) 90 (1913) 88 (1965) && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Red Flag Warning until 9 PM EDT this evening for PAZ054-055- 060>062-070-071-101>106. NJ...Red Flag Warning until 9 PM EDT this evening for NJZ001- 007>010-012>027. DE...None. MD...None. MARINE...None. && $$ Synopsis...Robertson Near Term...Klein/MPS Short Term...Klein Long Term...Robertson Aviation...Klein/Robertson/MPS Marine...Klein/Robertson/MPS Fire Weather... Climate...