Scientific Forecaster Discussion

NWS Discussion
			
				

Area forecast discussion 
National Weather Service Mount Holly New Jersey 
346 PM EDT Tuesday Jun 18 2013 


Synopsis... 
a cold front will move off the coast tonight as weak low pressure 
moves along it. High pressure from the Great Lakes region will then 
build into the northeast and middle-Atlantic tomorrow. The center of 
this high will shift offshore on Thursday. A reinforcing shot of 
Canadian high pressure moves toward the region on Friday...then off 
the coast on Saturday. A return flow around this high will bring an 
increase in heat and humidity and a threat of scattered showers and 
thunderstorms this weekend and into early next week. 
&& 






Near term /until 6 am Wednesday morning/... 
very tropical-ish airmass in place this evening and tonight as a 
weak frontal boundary sags across the Middle-Atlantic States. There is 
ample elevated instability around the region to maintain the 
current shower/thunderstorm activity east across our region. With 
the weakened flow aloft any more storms that initiate will move very 
slowly and inundate the areas they pass over. We had several flash 
flood warnings issued this afternoon and saw hourly rainfall rates 
exceed 1.5+ inches from eastern Pennsylvania into southern New 
Jersey. 


Everything will be sliding offshore over the next couple of hours 
though the cold front to our north may touch off even more widely 
scattered showers. Could not remove all chances through the evening 
hours as some of the hi-res models show these showers traversing the 
region. Not expecting the torrential downpours and convection to be 
an issue as heating to our north and west has been weakened with the 
extensive middle and higher level clouds. The cumulus field well to our 
northwest is really flat looking as dewpoints behind the front are 
in the middle to upper-50s. The front could however pose an issue in 
terms of fog/stratus formation late tonight. Depending on how fast 
it slides through and we get the drier dewpoints might allow a 
widespread fog to form under a building inversion (near the front) 
and with the added moisture from todays rain. Do not think it will 
dense enough to have to worry about headlines, but it could become 
thick in some spots. 


Overnight lows were a straight blend of the met/mav. 
&& 


Short term /6 am Wednesday morning through 6 PM Wednesday/... 
the cold front will continue to push further south and east and the 
drying northerly flow behind the front increases. Middle-level and 
surface ridging start to re-enter the region from the 
west-northwest which helps to keep our region dry for the most 
part. Continue with some slight chance probability of precipitation across the extreme 
southern Delaware-Maryland-Virginia where some low-level convergence along the front 
may still exist and where dewpoints will continue to pool in the 
upper-60s. Temperatures will be a couple degrees cooler tomorrow 
behind the front and a basic blend of the met/mav was used for highs. 
&& 


Long term /Wednesday night through Tuesday/... 
surface high pressure is expected to build over the region Wednesday 
night...with the center of the high moving off the coast on 
Thursday. A reinforcing shot of Canadian high pressure moves toward 
the region on Friday...then off the coast on Saturday. This high 
should then influence weather over the area into next week as a 
southwest flow on its western side brings in warm and humid air. 
A chance of showers or thunderstorms are possible just about 
everyday from Sunday into early next week...but most of the time 
should be rain free. This looks more like a typical Summer time 
pattern in the middle portions of the atmosphere as a ridge tries to 
build east from the High Plains. Temperatures will start off in the 
normal range....then climb above normal late in the weekend and 
early next week. 
&& 


Aviation /20z Tuesday through Sunday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


This evening...very complex forecast with mostly VFR expected. 
Numerous showers and thunderstorms will continue to plague our 
terminals over the next couple of hours as a wave of low pressure 
moves through. The heavier showers and thunderstorms will cause 
local IFR conditions winds will predominantly be out of the 
east-southeast and remain light for this afternoon. Multiple outflow 
boundaries and heavier showers will cause temporary gusts with 
variable directions. 


Tonight...weak cold front to the northwest will slowly drag itself 
towards the region tonight and tries to push through. Winds should 
back towards the southwest and then north behind the front. If the 
front slows even further or stalls just to the north we could have 
issues with stratus and fog through the morning hours....IFR/MVFR 
possible. 


Wednesday...VFR with scattered ceilings. Will maintain a northerly wind 
behind the front around 10kts. 


Outlook... 


Wednesday night through Sunday...VFR except in morning fog/haze or 
mainly afternoon and evening showers/thunderstorms. 


&& 


Marine... 
sub-advisory conditions look to persist across our waters tonight 
and tomorrow. A weak cold front will move through late tonight into 
Wednesday morning as high pressure sinks towards the south. Winds 
will start off easterly and then turn northerly behind the front 
tomorrow. The pressure gradient may become tight for a period 
tomorrow afternoon and could produce some marginal small craft gusts 
but did not have the confidence or longevity of the event to put up 
a flag. Seas will climb upwards of 4 feet through tomorrow as 
conditions become more tranquil later in the day. 


Outlook... no headlines are expected through Sunday. 


&& 


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


&& 


$$ 
Synopsis...miketta 
near term...Heavener 
short term...Heavener 
long term...miketta 
aviation...Heavener 
marine...Heavener