000 
fxus61 kphi 261255 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
855 am EDT Mon Jun 26 2017 


Synopsis... 
a large area of surface high pressure builds into the eastern United 
States early in the new week before moving offshore on Wednesday. A 
series of upper troughs will swing through the East Coast during 
this time as well. A series of low pressure systems will pass north 
of the region late this week and into the new weekend, and each low 
will drag a weak boundary through the region during this time. A 
more developed area of low pressure is possible Sunday. 


&& 


Near term /until 6 PM this evening/... 
900 am update: forecast is in good shape, and no changes were 
made for the morning update. 


Previous discussion below... 


A strong short wave dropping southeastward from the Midwest and 
upper Great Lakes early this morning will amplify an upper- 
level trough eastward through the day. This will result in 
gradual height falls across our area by late in the day. At the 
surface, a weak cold front across the area early should tend to 
dissipate through the day or become a surface trough. 


The model guidance shows several short waves within the flow 
out ahead of the aforementioned amplifying trough. This along 
with cooling aloft should generate enough lift and instability 
to develop showers and thunder (probably low-topped) to our 
northwest and west. Much of the guidance keeps this activity 
just to our west/northwest by late in the day, however terrain 
influence may help pop a few isolated showers in the 
northwestern zones after 18z/2 PM. The forecast soundings 
overall show a fair amount of dry air, however there is some 
instability that develops this afternoon. The forecast amount of 
instability within these soundings looks to be minimal and 
given that convection will probably be low-topped, we only 
carried a shower mention and kept pops across the northwest 
zones no higher than slight chance. We also slowed down the 
arrival of the mentionable pops. The forecast soundings show the 
convective temperatures being reached more likely across the 
interior, therefore placed the higher sky cover mainly near and 
west of I-95. 


Based on the incoming height falls through the day, the 
thickness values will also lower some and therefore high 
temperatures are expected to be a bit cooler than yesterday. The 
flow should be light enough to allow the surface winds to turn 
more southerly along the coast. The high temperatures are mostly 
a blend of MOS and continuity. 


&& 


Short term /6 PM this evening through 6 am Tuesday/... 
an upper-level trough will continue to sharpen across the 
eastern Great Lakes and Ohio Valley through the night. This will 
drive weak low pressure just north of the Great Lakes, with 
either a weak cold front or surface trough extending southward 
from it. There is plenty of short wave energy within this 
trough, however much of this looks to hang back over the Great 
Lakes and Ohio Valley. The main short wave is forecast to move 
across the eastern Great Lakes late tonight, and this is where 
much of the shower activity should be focused. For our area, 
some guidance is a bit more robust with a lead short wave and 
want to produce a few showers/thunder overnight near the 
Delaware valley. This cannot be ruled out as there may still be 
a surface trough in place or weak incoming cold front, however 
confidence is not all that high and therefore kept it dry for 
now. 


Otherwise, there should be more cloudiness around for awhile 
tonight especially the mid level variety as some instability may 
linger with cooling aloft. The lowering of the dew points 
during the day today should recover some tonight as winds go 
light, however despite more cloud cover for a time the 
temperatures are expected to be cooler given the overall air 
mass will be cooling with the incoming upper-level trough. Low 
temperatures were mainly a blend of continuity and MOS. 


&& 


Long term /Tuesday through Sunday/... 
the long term period will start off relatively cool and dry, as 
high pressure and an upper trough build in from the west. When 
both the high and the trough move offshore during the mid-week 
period, return flow will usher a hot and humid airmass back into 
the region for the end of the week and into next weekend. 


By Tuesday, the center of the surface high positions itself 
over the southeast U.S. And the base of the upper trough digs 
into the Ohio Valley and Appalachians. A few strong shortwaves 
will dive into the base of the trough, and this trough will 
traverse the East Coast in the afternoon and evening. There is 
not much moisture associated with this systems, as a drying west 
winds result in surface dewpoints in the upper 40s to around 
50.Although isolated to scattered showers and thunderstorms are 
possible, do not think they will be long lived or widespread. 
Highest pops will be to the north and south, where the strongest 
shortwaves will be. Highs remain several degrees below normal, 
generally in the mid to upper 70s, though the Poconos will be 
about 10 degrees cooler. 


Any lingering showers will taper off in the evening as the 
trough moves offshore. By Wednesday morning, the center of the 
high establishes itself over the mid-Atlantic. Dry and pleasant 
conditions on tap with low humidity values as highs will 
approach 80 for most of the region, and dewpoints will be in the 
low 50s. 


Surface high pressure begins to move offshore Wednesday night. 
This results in a pattern shift for the end of the week and 
weekend, as heat and humidity gradually build. 


With surface high pressure entrenched off the southeast U.S. 
Coast, and an upper ridge gradually builds east through the end 
of the week, return flow sets up and pushes temps through the 
80s on Thursday, and gradually into the lower 90s Friday and 
Saturday. In addition, surface dewpoints rise back up, first 
into the low 60s Thursday, and then approaching 70 and low 70s 
over the weekend. 


Meanwhile, several strong shortwaves will dive into the 
northern states, and several areas of low pressure will develop 
to the west and will pass north of the region. As they track 
north of the region, they will drag a weak frontal boundary 
through the northeast and mid-Atlantic. Will carry slight 
chance-chance pops from Thursday through Saturday. 


Upper ridge moves offshore late Saturday, and then an upper 
trough begins to dig towards the East Coast. Sunday could 
feature a bit more precip across the region as low pressure 
develops south of the region and lifts to the north. Will carry 
high chance pops for Sunday. 


&& 


Aviation /13z Monday through Friday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, 
kilg, kmiv, kacy and surrounding areas. 


Today...VFR. An isolated shower is possible after 18z north and 
west of krdg and kabe. Light and variable winds becoming 
northwest to west 5-10 knots, however turning from the south at 
kacy in the afternoon with some sea breeze influence. 


Tonight...VFR ceilings at times, mainly at or above 7000 feet. 
While a shower around is possible, coverage and occurrence is 
rather low. Southwest winds (locally south) less than 10 knots, 
becoming light and variable at most terminals. 


Outlook... 


Tuesday: mainly VFR. Isolated to scattered rain showers/thunderstorms and rain possible 
with brief MVFR or lower conditions. West-SW winds 10-15 knots with 
gusts to 20 knots in the afternoon. 


Tuesday night...VFR. Any lingering rain showers/thunderstorms and rain taper off in the 
evening. Light west-northwest winds. 


Wednesday...VFR. West winds 5-10 knots. Gusts 15-18 knots possible in 
the afternoon. 


Wednesday night...VFR. S winds 5-10 knots. 


Thursday...VFR. Isolated rain showers/thunderstorms and rain possible at kabe/krdg. S 
winds 5- 10 knots north and west of I-95, and 10-15 knots with 20-25 
knots gusts at terminals south and east of I-95. 


Thursday night and Friday...mainly VFR, but scattered rain showers/thunderstorms and rain 
possible, mainly north and west of I-95. SW winds 10-15 knots with 
gusts up to 20 knots. 


&& 


Marine... 
the conditions are expected to remain below Small Craft 
Advisory criteria through tonight. A northwesterly wind will 
turn southwest to south this afternoon and tonight (possibly 
south-southeast in Delaware Bay for a time as a sea/Bay breeze 
occurs). While some gustiness will occur at times, gusts are 
expected to be less than 25 knots. 


Outlook... 


Tuesday...sub-sca conditions. Scattered showers and 
thunderstorms. Possible. 


Tuesday night...any showers and thunderstorms taper off in the 
evening. Sub-Small Craft Advisory conditions. 


Wednesday...sub-sca conditions. 


Thursday through friday: Small Craft Advisory winds/seas possible as stronger 
southwesterly winds become established. A slight chance of 
storms on Friday. 


Rip currents... 
the forecast conditions through this evening should result in a 
low risk for the development of dangerous rip currents. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...none. 


&& 


$$ 
Synopsis...mps 



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