Area forecast discussion 
National Weather Service Mount Holly New Jersey 
608 PM EDT Friday may 29 2015 


Synopsis... 
high pressure will reestablish itself off the East Coast tonight 
into Saturday. A cold front is forecast to move across our region on 
Sunday, then stall across the area Monday into Tuesday, as a wave of 
low pressure moves along it. High pressure will build to our north 
early next week, before moving into the area Wednesday into Thursday. 


&& 


Near term /until 6 am Saturday morning/... 
this estf update is mainly to adjust current temperatures. Latest hrrr 
and cospa not showing much convection left and observed surface 
based convective available potential energy have dropped below 1000j on our side of the Bay. 
Convection in Virginia and PA have to take the long Route to get into 
our County Warning Area and no change in mesoscale models dissipating them before 
they come close. Only other change based on increasing consensus 
of low clouds forming over the ocean, we upped sky cover east late 
tonight. 


An area of high pressure remains off the eastern Seaboard, with an 
upper level ridge also extending over the East Coast states and out 
over the Atlantic waters. Light winds through the course of the day 
have gradually shifted from an easterly direction to more of a 
southeast flow, and some return moisture with dewpoints slowly 
creeping upward has been observed over the last few hours. 


Otherwise then through the overnight, the other main element to 
watch will be the possibility for some patchy fog or perhaps a few 
lower clouds to form, mainly from along the coast and into eastern 
portions of our forecast area. While confidence is only moderate at 
best on this occurring at this time, we did keep a mention of patchy 
fog in the forecast for these areas as light southeast to south 
winds will continue through the night and dewpoints rise into the 
60s. Overnight minimum temperatures were a blend of met/mav 
guidance, and we anticipate lows in the 60s across the region. 


&& 


Short term /6 am Saturday morning through 6 PM Saturday/... 
during the daytime Saturday, our forecast area will be on the 
western periphery of lingering offshore high pressure and an upper 
level ridge. In addition, a cold front is expected to be approaching 
slowly from around the eastern Great Lakes, with a Lee-side trough 
possibly developing to the west of our region around the 
Appalachians. These factors, along with some increasing daytime 
instability, will likely be enough for some isolated to perhaps 
scattered showers/thunderstorms to develop from late morning through the 
afternoon. Overall, we focused highest probability of precipitation across our western 
zones. Muggy conditions will be felt across the area, with dewpoints 
into the 60s. Maximum temperatures were a blend of met/mav guidance 
with continuity, and we anticipate highs to reach into the 80s for 
most of the region, except some cooler 70s along the coast and into 
the Poconos. 


&& 


Long term /Saturday night through Friday/... 
the region will be under the influence of a southwest flow aloft as 
a middle-level trough transits the Great Lakes and northeast Continental U.S. Sun 
through Wednesday...while an attendant cold front moving into the region on 
sun becomes quasi-stationary over the middle Atlantic through early next 
week...as the trough gradually amplifies causing the middle-level flow 
to become parallel to it. The flow should become more zonal with 
weak ridging by Wed-Thu...with fair weather expected to return. Temperatures... 
west/the exception of Monday and Tuesday...should be near seasonable normals. 


The main concern during the long term portion of the forecast is 
the potential for convection on sun and heavy rainfall early next 
week. A cold front will approach Sun afternoon...with an anafront-type 
setup...as the bulk of the precipitation is expected to the north and west. 
Ml cape values reach 2-3 kj...while the most favorable bulk shear 
is along and just west of the front. Model soundings indicate an 
environment most favorable for gusty winds with any thunderstorms 
that occur. Heavy rainfall is also possible...given precipitable waters  of 1.5 
inches /1-2 Standard dev above normal/ as well as sluggish storm motion. 


The front stalls over the middle Atlantic region late sun/early Monday 
and this leads to an overrunning regime...as low pressure develops 
along it during the Monday-Tuesday time frame. The main uncertainty here 
is with regard to the placement of the overrunning...as the models 
trend further north...given the tendency toward a more amplified 
trough. The potential exists for 1-2 inches of rainfall...which 
could lead to flooding problems due to dry antecedent conditions 
but there is a high amount of uncertainty at this time. 


&& 


Aviation /22z Friday through Wednesday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


Through this evening...VFR conditions will continue with light 
easterly winds becoming more southeasterly, mostly in the 5 to 8 
knot range. 


Overnight...VFR conditions to start, but guidance is showing the 
possibility of some fog and/or lower clouds developing after 06z, 
especially close to the coast and perhaps farther inland as well. 
While confidence in this occurring is somewhat higher for taf sites 
closer to the coast and for more sheltered locations, we have 
included either MVFR visibilities and/or ceilings for all sites for a few hours 
leading up to daybreak Saturday. Southeast winds will become more 
southerly during the overnight, mainly at 5 knots or less. 


Saturday...some sub-VFR conditions possible early, otherwise mainly 
VFR during the daytime. Some isolated showers/thunderstorms are possible, 
which may locally reduce ceilings/visibilities for a time, but confidence in 
timing/coverage was not high enough to include in the tafs. South- 
southwest winds are expected in the 8 to 10 knot range, gusting at 
times between 15 to 20 knots. 


Outlook... 


Sat night...MVFR possible in low clouds and fog near the coast...especially 
Acy and miv. 


Sun...MVFR likely in rain showers and thunderstorms and rain during the afternoon and evening hours... 
otherwise VFR. 


Sun night through Monday night...MVFR in shra/tsra...low clouds...and fog. 


Tuesday...MVFR in shra/tsra...with gradual improvement to VFR 
possible. 


&& 


Marine... 
sub-advisory conditions will continue for the coastal waters and for 
Delaware Bay through tonight, with generally light southeast winds 
becoming more southerly as the night progresses. Some fog may 
develop over the waters during the overnight and advect to the 
coast, causing locally reduced visibilities. 


Reduced visibilities in fog is possible early Saturday for the 
waters, otherwise sub-Small Craft Advisory conditions are expected through the 
morning. Marginal Small Craft Advisory conditions may be reached Saturday afternoon 
and evening, with wind gusts approaching 25 knots, especially for 
the northern coastal waters. However, confidence was not high enough 
at this time to issue a Small Craft Advisory. We will allow the next 
shift to re-evaluate incoming data. 


Outlook... 


Sat night through Tuesday...Small Craft Advisory conditions possible through the entire 
period...as a cold front stalls over the waters on Sunday and low 
pressure develops along it early next week. At this time...highest 
confidence in seas meeting Small Craft Advisory thresholds. 


&& 


Rip currents... 
new weblink, works best on firefox. Displays the forecast graphic et cetera. 


Www.Weather.Gov/phi/surfrip4 


Upgraded the rip current risk along the central New Jersey coast per 
observed concern and some data indicating potential for moderate. 


Otherwise, low risk continues this afternoon Delaware coast and the 
far northern and far southern New Jersey coasts where onshore winds are 
lighter though a little concerned about a 1 foot 12 second east-southeast 
swell showing up that could elevate the risk slightly there too. 


Chilly to swim most of central and nnj beaches despite above normal 
temperatures on the land with water temperatures there looking to be in the upper 
40s to lower 50s. Further S near lbi...water temperatures maybe 55 to 60, 
snj S of kacy 60-65 and then along the Delaware Atlantic coast upper 50s to 
middle 60s depending on location. 


The outlook for Saturday is low enhanced...with a stronger southerly 
wind gusting to 20 miles per hour during the afternoon. Might be a close call 
for a moderate risk depending on the swell size. For now keeping 
it low risk but not locked into low. 


&& 


Climate... 
may 2015...a top 5 warmest on record for large portions of our area. 


All overnight and forecast information checked through 830 am 
today - Friday may 29. 


Conservative values listed below from our 5 am sft and cooling the 
near midnight Sunday night may 31 low temperature due to northerly flow cold air advection Sunday 
evening. 


Allentown will probably average very close to 65.9 or 6 degrees 
above normal. Por back to 1922. At least 5th warmest on record. 
1991 67.2 
2012 66.1 
1944 66.0 
2004 65.9 




Philadelphia will probably average close to 69.7 degrees or 5.8 
degrees above normal. Second warmest on record. 


1991 70.8 


Number 3 would be 69.2 in 2004. 




Atlantic City may 2015 65.9 or 66.0 or 4.8 to 4.9 above normal 
and probable #2 or #3 por back to 1874 


2004 66.9 
1991 66.0 
2015 




Wilmington Delaware solid por back to 1916 locked into #4 warmest 
1896 70.1 
1991 69.1 
2004 68.2 
2015 around 68.0 


No available monthly historical data for kmpo kged kttn and krdg. 


&& 


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


&& 


$$ 
Synopsis...franck 
near term...gigi/Kline 
short term...Kline 
long term...franck 
aviation...franck/Kline 
marine...franck/Kline 
rip currents... 
climate... 






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