Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

Home | 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
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KPHI 221349 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 949 AM EDT Fri Jun 22 2018 .SYNOPSIS... High pressure situated across the region today will gradually move offshore tonight. Meanwhile, a low pressure system organizing over the Mississippi Valley leads to a warm frontal passage on Saturday and a cold frontal passage on Sunday. High pressure over Ontario builds into the region on Monday and slowly moves off the eastern seaboard to a position near Bermuda by Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... We will have a brief reprieve from heat today being solidly in the cool sector. The closed low developing over the Mississippi Valley and progressing towards the Ohio Valley will be making progress closer to our region. However, its associated front will stay a stationary front located south of our region through the day today. There is a chance (likely across Delmarva, decreasing chances as you go further north) for showers across the region through the day, but for the most part the forecasted PoPs are on the lower side of guidance. The reason for this is that in the mid and upper levels, a short wave ridge ahead of the main low will be slowly lifting northeast across our region through the day. As a result, synoptic scale lift will be limited and to get any precipitation we will be relying primarily on orographic lift with the onshore flow. A combination of being in the cool sector as well as onshore flow will help to keep temperatures 5 to 10 degrees below normal, with highs generally in the 70s (and upper 60s in the higher terrain of the southern Poconos). && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... Chances for rain continue to increase both as the short wave ridge lifts further away from our region and as the stationary front begins to transition to a warm front lifting north towards northern Delmarva. Guidance trended slightly slower with the warm front as it is expected to remain south of most of the region even overnight. Instability north of the warm front will be minimal, so thunderstorms are unlikely. Thanks to increasing cloud cover, the diurnal swing in temperatures will be relatively small from today into tonight, with the lows only 5 to 15 degrees below the highs for today. && .LONG TERM /SATURDAY THROUGH THURSDAY/... The main concerns are the severe thunderstorm potential Saturday afternoon and evening including urban and poor drainage flooding, additional showers and thunderstorms Sunday afternoon/eve, and a gradual increase in heat and humidity by the middle of next week. Except for Sunday, the tendency for an onshore component of flow will result in high temperatures several degrees cooler near the immediate coast. Synoptically, a closed low transitioning into an open wave as it ejects northeastward into the eastern Great Lakes promotes a deep layer southwest flow through Sunday, until the longwave trough axis traverses the area on Monday. This will be followed by a broad mid- level ridge through Wednesday, which is expected to be interrupted by a northern stream perturbation on Thursday. Saturday...Low pressure over the Ohio Valley will lift a warm front slowly northward through the region. There is uncertainty regarding how far north the front will make it, and this will determine the severe weather potential, which will be near and south of the front. Favorable parameters include ML CAPE up to 1,500 J/kg and Bulk Shear around 45 kt. Damaging thunderstorm wind gusts are certainly possible, although modest 0-3 km lapse rates and meager D-CAPE suggest limited coverage. Perhaps of more concern is the environment closer to the warm front, where 0-1 km shear over 20 kts and low LCLs could favor a brief spin- up. Hail parameters, including lapse rates in the hail growth zone, are weak so would expect mainly small hail, except for updrafts that are able to rotate closer to the warm front, which would be more favorable for large hail. South of the warm front, a warm and humid day. Model soundings support mixing up to 850 hPa. Raised high temperatures into the mid to upper 80s. Southerly winds will gust 20-25 mph at times. Saturday night...Thunderstorms will diminish around midnight with a drying trend during the overnight hours. Patchy fog is possible in the more sheltered locations northwest of I-95. Sunday...The cold front will move slowly through the area, supporting the development of showers and thunderstorms. Both moisture and instability is limited southeast of the I-95 corridor, so only mentioned a slight chance of thunder. Northwest of I-95, included a chance of thunder, where there is sufficient moisture and instability. Compared to Saturday, the environment is not conducive to severe weather, but gusty winds and heavy rainfall are possible with any thunderstorms that develop. With the flow more offshore, high temperatures will be in the low to mid 80s regionwide. Sunday night through Thursday.... The aformentioned cold front will finally clear the area Sunday night into Monday. As such, chance of showers/storms lingers into Sunday night before a clearing trend for Monday. Highs Monday will generally be in the upper 70s to low 80s with lower humidity. The only exception will be eastern NJ, where mid 80s are possible. Beyond this time, high pressure builds in for Tuesday and Wednesday bringing mainly clear skies with seasonable temperatures. The next system doesn`t arrive until next Thursday bringing a chance of showers and storms. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Rather limited confid with MVFR seeming more predominant again over the Delaware Valley after a period of VFR cigs earlier. Due to the east wind and low level moisture, we`ll probably just have MVFR much of the rest of today. VFR expected KRDG-KABE. Tonight...MVFR and eventually IFR ceilings should develop across the region (including KABE and KRDG) overnight. Showers become increasingly likely as well. However, as with today, I am not expecting too much visibility restrictions as any rain should be light and the continued easterly winds at or near 10kt should limit fog/mist development. Moderate confidence on most aspects of the forecast, but low confidence on the timing of any flight category changes. Outlook... Saturday...Conditions gradually improving to MVFR, with VFR possible by afternoon, especially I-95 corridor terminals. But SHRA and TSRA will lead to brief ceiling/visibility restrictions. Easterly winds gradually backing to the southwest. Southerly winds 10-15 kt gusting around 20 kt southwest of ABE and RDG, with higher gusts possible in TSRA. Medium confidence. Saturday night...TSRA possible until 06Z. Thereafter, MVFR in low clouds and patchy fog, mainly ABE, RDG, MIV, and ACY. Southwest winds less than 10 kt. Low confidence. Sunday...MVFR in low clouds and patchy fog improving to VFR early. Another round of SHRA at all terminals, with TSRA possible at TTN- ABE-RDG, may lead to brief ceiling/visibility restrictions. West- southwest winds around 10 kt. Medium confidence. Sunday night...Spotty MVFR possible due to low clouds and SHRA, especially at ABE and RDG. Otherwise VFR. Winds veering to the northwest around 10 kt. Low confidence. Monday - Tuesday...MVFR in patchy fog possible Monday night into early Tuesday morning. Otherwise VFR. Northwest winds around 10 kt on Monday becoming light and variable Monday night, veering to the northeast on Tuesday. Medium confidence.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
Easterly winds are expected to increase from south to north from this morning through tonight. Seas will subsequently increase as well. Therefore, expect to reach small craft advisory conditions on most of the coastal waters by mid day. For the coastal waters adjacent to the far northern NJ shore, SCA are not expected to be met until very late tonight. On the Delaware Bay, winds and waves are expected to stay below SCA criteria over the northern Bay. However, gusts to 25 kt and enhanced seas will develop across the southern Bay, so the SCA flag was expanded to cover this. Outlook... SCA conditions continue until noon Saturday over the Atlantic Waters of DE and NJ before winds/seas gradually diminish. There will also be the potential for reduced visibilities in showers. For Saturday through Saturday night, warm front lifts north of the waters with east winds shifting to south and eventually SW. Winds should stay below SCA levels but seas may reach around 5 ft by Sunday morning. Late day Saturday into Saturday evening, it`s possible some strong thunderstorms could affect portions of the waters bringing local wind gusts to 34+ knots. Breezy SW winds continue Sunday with seas hovering near or just below SCA levels. Additional late day storms are possible. A cold front crosses the waters Sunday night into early Monday with sub SCA conditions expected behind this feature for late Monday through Tuesday. Rip Currents... A moderate risk is forecast today due to the strengthening onshore wind.
-- End Changed Discussion --
&& .TIDES/COASTAL FLOODING... With a persistent onshore flow through early Saturday, increasingly positive departures from astronomical tides are expected. The high tide of most concern is Friday night, when minor flooding is possible. && .PHI WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until noon EDT Saturday for ANZ451-452. Small Craft Advisory until noon EDT Saturday for ANZ431- 453>455. Small Craft Advisory from 2 AM to noon EDT Saturday for ANZ450.
-- End Changed Discussion --
&& $$ Synopsis...LF Near Term...Johnson Short Term...Johnson Long Term...LF Aviation...Johnson/LF/PO Marine...Johnson/LF/PO Tides/Coastal Flooding...

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