626 
fxus61 kphi 231456 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
956 am EST Monday Nov 23 2009 


Synopsis... 
high pressure over eastern Nova Scotia this morning will recede 
east. Fairly weak low pressure off the southeast coast will lift 
northeast and pass well to the east of Delaware and New Jersey 
tonight. Very weak high pressure will reside over the area late 
Tuesday and Wednesday, then a cold front from the west will arrive 
on Thursday. Low pressure is forecast to develop off the southeast 
coast on Thursday and it should move up into New England on 
Friday. High pressure is expected to build slowly into our region 
from the west during the weekend. 


&& 


Near term /until 6 PM this evening/... 
based on latest satellite and radar trends...we have continued the 
trend of slowing the advance of rain into our County Warning Area. Subsidence behind 
the closed low near NYC has helped break down the SC in the 
northern part of our cwa, some middle and high level clouds should 
move into that area ahead of the next short wave this afternoon. 
Maximum temperatures left as is for now, will make another re-assessment around 
11 am. 




Rain was advancing slowly toward the Virginia Northern Neck early 
this morning, and that was about in line with i295 to i300 lift 
off the NAM and European model (ecmwf). Unfortunately, after that the models 
refuse to come together. Placement of best dynamics, isentropic 
lift and lower level frontogenesis are in flux by end of this 
period, and so we have gone with a forecast that combines 
indications off the 00z European model (ecmwf) /which shows more run-to-run 
continuity/, continuity with the previous forecast and 
nowcasting. This has made US slow the progress of rain into the 
central and northern parts of the forecast area and back off on 
the probability of precipitation some in the northwest. Still not seeing instability 
prognosticated for our area, so not seeing a reason to raise quantitative precipitation forecast values 
much. 


On temperatures, we start from a fairly warm place, and 
indications from h925 temperature forecasts are that colder air does 
not look to get pulled down from the north today. We therefore 
have sided with warmer guidance. 


The gradient between the fairly weak surface low advancing from 
the south and the fairly strong high retreating to the northeast 
will make for a decent flow today. 


&& 


Short term /6 PM this evening through Wednesday/... 
the best combination of synoptic and mesoscale ingredients comes 
together tonight as the main short wave approaches with an 
attendant upper level jet. We shift the axis of main precipitation 
a little east of the 00z European model (ecmwf). The European model (ecmwf) has been oscillating 
its focus a bit from offshore to onshore the past few runs, and it 
has taken more of an onshore flavor this run. We still don't see 
any signs of instability. 


We continue the temperature forecast that minimizes the diurnal 
oscillation from the near term, and we weaken the winds gradually 
as we expect the low to pass well off the coast and slowly take 
the gradient between it and the northeastern high away from US. 


Energy from the middle level impulse passes Tuesday morning. We 
therefore continue ramping down the probability of precipitation on Tuesday. We do not 
dry out much, as the surface high that builds in looks very weak, 
and by Wednesday we may begin to feel some affect from the next 
advancing system. 


We maintain continuity on temperatures Tuesday and Tuesday night, 
and then in response to both mav and met guidance we raise 
temperatures a bit on Wednesday. 


&& 


Long term /Wednesday night through Sunday/... 
a pattern change will continue to get underway as we start this 
period. The computer models are in good agreement that a trough 
will amplify across the northern plains and Great Lakes region as 
strong energy dives southeastward. The short wave energy, coupled 
with the jet stream positioning, will tend to lead to a closed low 
from the Great Lakes region down to the Ohio Valley. While this 
synoptic evolution is agreed upon fairly well by the computer 
guidance, details especially from late Thursday into Saturday 
becomes more difficult along with lower confidence as to the 
location and track of a closed midlevel center /as it moves east 
and northeastward through the central Appalachians and northeast/. 
Given the uncertainty, we initialized the database with HPC 
guidance /comprised of the European model (ecmwf) for Wednesday night through 
Thursday night, then the European model (ecmwf)/GFS ensemble means for Friday 
through Sunday/. We did make some adjustments though after 
additional collaboration with our surrounding offices. 


Based on the above, an initial cold front will be arriving 
Wednesday night as the upper-level trough amplifies to our west. 
As the system closes off and slides eastward, energy rotating 
around this will tend to keep the chance of at least some showers on 
Thursday. There is some hints in some of the model guidance that 
an inverted trough may extend across portions of our area late 
Thursday into Friday as a new surface low forms to our east. If 
this is present, then precipitation could be enhanced some 
especially as the midlevel low approaches. For Friday, the surface 
low is forecast to be pulling up into the vicinity of southern New 
England and our area will be under a colder cyclonic flow. Given 
the colder air arriving aloft, we cannot rule out showers 
/convective?/ With even some snow possible especially across the 
northern areas. For now, we just kept the mention of snow across 
the far northern zones. If enough moisture and instability is 
around as the closed low moves by, would not rule out some small 
hail/graupel with some showers. A brisk northwest flow is forecast 
to setup as we go through Friday and Saturday. This could keep 
some rain/snow showers going Saturday especially across the far 
northern zones as some Lake Erie/Ontario moisture could get pulled 
southeastward in the form of streamers. High pressure then builds 
to our south Sunday with the northwesterly flow gradually on the 
decrease. 


&& 


Aviation /15z Monday through Friday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


High pressure over the Canadian maritime provinces of Canada 
continues to cause an east to northeast flow over the area early 
today. Moisture is increasing across the area resulting in lowering 
ceilings today. Light rains and further lowering ceilings will arrive 
this afternoon across the taf sites. The timing of the lowering 
conditions is not certain...so expect amds through the day. Winds 
will be mainly NE around 10 to 15 kts today. 


Outlook... 
as the storm system tracks away from our area tonight, the nerly 
flow looks to continue. This will keep the low-level moisture in 
place, therefore low ceilings and/or visibilities along with some 
rain and drizzle will continue. We may have to deal with a prolonged 
period of lower ceilings Tuesday and Wednesday as moisture gets 
trapped. A frontal boundary is forecast to approach late Wednesday, 
then a storm system is forecast to develop to our east later in the 
week. This may bring some wind and rain to the area. 


&& 


Marine... 
strong high pressure is well to the north and a weak low will be 
moving offshore of the East Coast today and Tuesday. These features 
will keep a decent NE flow over the waters through Tuesday. Small Craft Advisory 
flags are already in place for the coastal waters and lower del 
Bay...and will be extended into upper del Bay too. The Small Craft Advisory flag 
continue into Tuesday for the coastal waters. Seas out at the buoys 
are 6 to 8 feet early this morning. Conditions should diminish Tuesday night 
and sub-Small Craft Advisory conditions will be around Wednesday into Thursday. Another low will 
approach Friday likely creating more hazardous winds and seas on the 
waters. 


&& 


Tides/coastal flooding... 
tidal departures are beginning to increase now that the NE flow has 
developed. During the previous high tide...the greater departures 
were located across the southern coastal waters and lower Delaware Bay. 
The next high tide will be the higher of the two high tides...and 
since the NE wind is expected to continue today...The Levels will 
probably come close to minor tidal flooding levels. A coastal Flood 
Advisory will be issued for the next high tide. I will not issue it 
for Monmouth County (and northward) since greater departures are 
needed there...and the wind direction may not favor higher 
departures there. We will continue to monitor through today. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...coastal Flood Advisory until 3 PM EST this afternoon for 
njz020>027. 
Delaware...coastal Flood Advisory until 3 PM EST this afternoon for 
dez002>004. 
Maryland...none. 
Marine...Small Craft Advisory until 2 am EST Wednesday for anz450>455. 
Small Craft Advisory until 11 PM EST this evening for anz430- 
431. 


&& 


$$ 
Synopsis...delisi 
near term...delisi/gigi 
short term...delisi 
long term...gorse 
aviation...O'Hara 
marine...O'Hara 
tides/coastal flooding...O'Hara 

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