Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 200933 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 533 AM EDT MON JUN 20 2016 .SYNOPSIS... High pressure will continue to influence our weather today. A surface trough approaching from the northwest will arrive late tonight, followed by a cold frontal passage Tuesday night. High pressure briefly regains control Wednesday. Low pressure is anticipated to move quickly from the Ohio River Valley on Thursday to the waters off the Middle Atlantic coast on Thursday night. High pressure will follow eastward to the Middle Atlantic Coast later Friday through the coming weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Happy first day of summer! Summer will officially begin at 634 pm today and the weather will definitely reflect more summer-like conditions. High pressure remains in control of the weather across our region once again today. The airmass remains dry and with mostly sunny skies through much of the day, we will see temperatures rise well into the 80s to lower 90s across the region. Areas along the coast will remain cooler with highs only reaching into the low to mid 80s. Without much moisture around, the humidity levels will remain low and as a result the heat index values will be at or below the actual temperatures today. The high starts to sink to the south through this afternoon as a weak cold front pushes down from the northwest. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... Low pressure will cross well to the north of our area. The low has a weak cold front that will drop down into our area tonight. Clouds will start to fill in from north to south as the front approaches. As the front moves through, there is just enough moisture available for some showers to move through late tonight into Tuesday morning. In addition, marginal instability may allow for some thunderstorms to accompany the front. The front, as previously noted, is weak in nature and as it reaches our area, it is expected to weaken further and we do not anticipate that the showers or thunderstorms will be all that strong. It seems the cooler air remains to the northwest of our area until the front fully cross through the region, so temperatures overnight will remain warm, in the 60s to near 70. && .LONG TERM /TUESDAY THROUGH SUNDAY/... **Dry pattern across our area this month looks to continue through at least Wednesday** 500MB: A short wave trough moving southeast through the Great Lakes Tuesday and into the northeast USA is followed by another next Thursday. Considerable ridging develops next weekend. Temperatures: the month as a whole through the 20th has averaged within 2 degrees of normal. Calendar day averages will still be about 5 degrees above normal Tuesday, then cool to near or a bit below normal Wednesday-Friday before probably warming a bit above normal next weekend. Forecast basis: Unless otherwise noted, a 50 50 blend of the 00z/20 GFS/NAM MOS guidance Tuesday-Wednesday, thereafter the 00z/20 GFS MEX MOS for Wednesday night-Thursday and WPC Guidance Thursday night- Sunday. The dailies... Increased diurnals are occuring because of dry surface soils, resulting in cooler nights and warmer days than might be expected with greater soil moisture. The dry topsoils are related to the more than 50 percent deficit of normal rainfall this month and also the considerable wind related drying episodes of June 8th and 12th. Probable 3 day modest heat wave looks to occur with day3 (Tuesday) a bit uncertain but probable for portions of the I-95 corridor. Tuesday...Partly to mostly sunny, very warm to hot and more humid. A remnant surface trough associated with the predawn convection is anticipated to settle across the southern part of our region on Tuesday. Showers and thunderstorms are expected to re-fire along the boundary during the afternoon in advance of a mid level short wave and surface cold front approaching from the northwest. Therefore, severe thunderstorm potential Delmarva, especially vicinity and south of KESN-KGED where modeled MLCAPE is between 1500-2000J, along with TT in the mid 50s, plenty of instability and 0-6KM bulk shear over 40 kt. PWAT 1.75 inches over the Delmarva but fast moving storms prevent anything more than brief poor drainage street flooding. Max temps 90-93F east of I-95 to the coasts (westerly wind component) and probably to PHL as well. Westerly winds gust 15-20 mph in e PA and N 1/2 NJ during the afternoon while more humid southwest winds gust 15-20 mph Delmarva and s NJ during the afternoon (I95 sewd), prior to lines of strong thunderstorm development there. Confidence: Above average. Tuesday night...Whatever convection develops in our region on Tuesday afternoon should work its way off the coast on Tuesday night along with the mid level short wave trough and the surface cold front. Dewpoints lower late at night. May be a little patchy fog which is not now in the forecast. Confidence: above average. Wednesday...Mostly Sunny and seasonable. West winds gust 20-25 mph during the afternoon. PWAT down to .8 inches. Nice day! Confidence: well above average. Thursday...Warm air advection showers and thunderstorms ahead of and near low pressure approaching from the west. SVR storms possible near the warm front along with 1-3 inches of rain, presumably Delmarva where the most extensive showers and thunderstorms should occur. Thinking the GFS and ECMWF are too far north. Modeled MLCAPE from the 00z/20 GFS is 1000-1500J along and somewhere to the south of I78 (warm front). Plenty of 0-6KM bulk shear (over 40 kt), instability and TT probably near 50- 52. PWAT back up to 1.75" Delmarva. Variable winds...probably easterly most of the area but may briefly shift south or southwest southern part of the forecast area south of the temporarily northward oscillating warm front. High temperatures Thursday are highly uncertain and dependent on most persistent showers and thickest cloud cover. Blended the 00z/20 MEX temps with our previous fcst from Sunday afternoon and then shaved a few degrees near PHL where I think showers will be more persistent as compared to near I80 in NNJ. We also note the GGEM is relatively dry Thursday. So confidence on details is average or below with least confidence in max temps. Thursday night...Convection ends from to east. patchy fog may develop in the leftover moist airmass but that is not in the fcst at this time. Friday...Improving weather with clearing. Seasonably cool. Northeast wind. Confidence. Above average. This coming weekend...Daytime temps should begin warming above normal and probably rainfree. Looks like a nice weekend. Confidence: above average && .AVIATION /10Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR conditions expected. Light and variable winds this morning will become south southwest by this afternoon, around 10 knots or less across the terminals. A seabreeze is expected to develop once again today in the light flow. However, there is some uncertainty as to whether it will be as efficient as Sunday`s seabreeze and move well inland. For now, the seabreeze is reflected in KACY`s TAF only. Tonight...A cold front will start to move into the region late tonight. Some showers, possibly a thunderstorm, are expected to accompany the front as it moves through from west to east. Increasing cloud cover through the evening/overnight. Southwest winds will become more westerly overnight but are expected to remain 10 knot or less. OUTLOOK... Confidence in the outlooked days below is well above average with only the timing and extent of thunderstorms Tuesday and Thursday a bit less certain. Tuesday...Mainly VFR. A chance of showers and thunderstorms which could briefly lower conditions to MVFR or IFR during the afternoon or evening, mainly vicinity KMIV-KILG-KACY (primarily just south and east of KPHL). Severe thunderstorm potential (strong westerly wind gusts near 50kt and large hail) is relatively high for southern DE Tuesday afternoon. Gradient (not thunderstorm influenced) west winds gust 15-20 kt during the afternoon over E PA and N 1/2 NJ, but somewhere near or just southeast of KPHL, afternoon winds will be southwest gusting to 15-20 kt, especially KMIV. Late Tuesday night through Wednesday night...mainly VFR. Westerly winds Wednesday will gust to 20-25 kt. Thursday...Vfr cigs lower to mvfr or ifr conditions in probable showers with tstms possible, especially KPHL area southward. Some severe tstm potential appears to exist for the Delmarva. Friday...Mainly VFR. northeast wind. && .MARINE...
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Fairly quiet conditions are expected to continue across the area waters. Seas of 2 to 3 feet across the ocean front, 1 to 2 feet on the Delaware Bay. Winds will generally be out of the south around 10 knots, with some gusts near 20 knots this afternoon. No headlines are anticipated through tonight. RIP CURRENTS: A predominantly 2 foot east-southeast swell of around 8 seconds will continue today. With offshore winds this morning, the rip current risk for today will be low. As the winds turn to the southeast in the developing seabreeze, the risk for the development of dangerous rip currents may increase and approach moderate. OUTLOOK... Monday night through Thursday...No marine headlines are anticipated. Thursday night and Friday...Wave heights on our ocean waters may build near 5 feet in a southeast to northeast flow and an SCA may be needed at that time. Fog might also be a problem. RIP CURRENTS: At this time we have less concern about the formation of dangerous rip currents Tuesday, in part because the wind will have less of an onshore component. It will be a low enhanced risk day. Low risk does not mean NO risk. A hot day with water temperatures above normal makes it easier to swim. For safety, please do not swim along jetties and piers where rip currents tend to recur. Preferably, swim within eyesight of our lifeguards.
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&& .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Drag Near Term...Meola Short Term...Meola Long Term...Drag Aviation...Drag/Meola Marine...Drag/Meola 532a

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