334 
fxus61 kphi 220851 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
351 am EST sun Nov 22 2009 


Synopsis... 
high pressure over the eastern Great Lakes region will strengthen 
and move to the Canadian Maritimes by Monday morning and then 
recede east. Fairly weak low pressure developing near the Gulf 
Coast will move off the southeast coast by Monday morning and then 
lift northeast. The low will pass by to our east on Tuesday. A 
cold front from the west is expected to arrive on Thursday. 


&& 


Near term /until 6 PM this evening/... 
we are going to follow the optimistic guidance with regard to sky 
cover today and keep the stratocumulus clouds out of our area. 
Eventually, some high clouds will begin to invade from the south 
as the southern stream system begins to approach. Since we do seem 
to have a middle level Rex block over US, we don't push the increase 
in clouds too much. 


The winds today will begin to increase some out of the northeast 
/especially as one moves toward the coast/, more in response to surface 
high pressure strengthening to the north than cyclongenesis off 
the southeast coast. The European model (ecmwf) continues to show a rather cool 
h925 for late this afternoon in response to the flow and the 
strengthening high, so our maximum temperature forecast is a blend of 
continuity and the cooler met guidance. 


&& 


Short term /6 PM this evening through Tuesday night/... 
the middle level Rex block is prognosticated by all models to begin to 
weaken and lift away tonight. Still, it is this feature that makes 
US continue to keep our second period forecast mainly dry with 
only some slight chance probability of precipitation south. The surface flow starts to 
veer just a little and strengthen a bit more, perhaps enough to bring 
in some lower level moisture and low clouds. Certainly, middle and 
high level clouds will be on the increase as the middle level weak 
ridge axis upstream of The Block weakens further. Guidance and 
continuity were all pretty close on mins and were followed. 


On Monday and Monday night, we start to see and then do see 
ingredients for rain come together over at least the eastern part 
of the forecast area. It should be noted that the NAM pushes 
everything a bit further to the west than the European model (ecmwf) does despite 
their good agreement on the surface and 500 mb forecasts. They both 
have q-vector convergence and frontogenesis with decent isentropic 
lift and Theta-E advection, but the European model (ecmwf) wants all this more 
focused near the coast and over the open water than the NAM. Since 
the mav probability of precipitation were lower than the met pops, we have come down in 
between the two to reflect the possibility that the NAM is too far 
west with the action. In parting deference to the lifting and 
weakening Rex block, we start the day with only slight chance 
probability of precipitation near and northwest of the I-95 corridor and then increase 
them in the afternoon. Further southeast, we start with chance probability of precipitation 
and then increase them. Am not seeing any signs of instability 
with this system over our area, so have not hit the quantitative precipitation forecast values very 
hard. 


Our maximum temperatures on Monday are a blend of continuity and the 
mean of the disparate stat guidance, perhaps leaning a bit on the 
mild side where precipitation is less likely or will start last 
and on the cooler side further southeast. Our min temperatures for Monday 
night try to shrink the diurnal oscillation. For now, we have 
disregarded the possibility that warmer air riding over the 
surface will make it down. 


There should be a decent northeast wind thanks to the gradient 
between the receding high and the advancing low, but not the same 
in strength or persistence as the one we experienced just after 
Veteran's Day. 


Models soundings show trapped moisture and the hint of a trailing 
wave for Tuesday, and so we continue with the chance of 
precipitation. We try to carve out some sort of break on Tuesday 
night. We should see the winds begin to decrease on Tuesday and 
continue to do so on Tuesday night. Temperatures were a blend of 
guidance and continuity. 


&& 


Long term /Wednesday through Saturday/... 
all models agree that a significant change in the pattern occurs 
during the end of the week. We start off with a broad SW flow on 
the eastern portion of a Midwest trough on Tuesday 
night...eventually the Midwest trough moves east, but deepens as 
it heads east. The upper trough then becomes closed off as it 
moves through the region. 


This means that we have quite a bit of clouds and possible 
showers late Tuesday night and Wednesday due to moisture spreading 
over the region within the SW flow aloft. Wednesday night through 
Thanksgiving and into Thursday night, we could see rain as a 
frontal system associated with the upper trough moves through from 
the west. Then on Friday, cooler drier air arrives, but we still 
could have rain showers with the cyclonic flow aloft. Friday night 
and Saturday, it gets cold enough that some snow showers are 
possible north, but the rest of the area should be dry with 
downslope northwest flow. Also on Saturday, it should be breezy/windy 
with the northwest flow. 


HPC forecasts have the situation well in hand and in general their 
guidance has been followed. 


&& 


Aviation /08z Sunday through Thursday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


Surface high pressure over the eastern Great Lakes and southeastern 
Canada will move northeastward more fully into southeastern Canada 
this morning. The upper trough from New England to the Ohio Valley 
above the surface high was moving east-southeastward...and the 
better flow to the southeast of the trough was where the high clouds 
had been generated yesterday. These moved off early Saturday night. 
This set-up was leaving our region in a cloud-free area this 
morning...and this should mostly continue today. Only krdg had a 
tempo group in its taf for light fog for the hours near sunrise 
in view of Saturday morning/S brief foray down to 2 miles...and also 
in view of MOS guidance around 12z. 


As the low level flow veers from north to northeast today...the 
onshore flow will bring in moisture tonight. MOS guidance is in 
agreement on bringing in low clouds overnight...with the NAM MOS 
being more pessimistic than the GFS. For now, ceilings will be 
lowered to marginal VFR in the area of midnight, with just a mention 
of scattered 8 hundred and low marginal VFR overcast for the late 
night period and toward Monday morning. Southern taf sites may stand 
a small chance of rain overnight...but with such a small chance, and 
visibilities likely not being affected, this will be left out of the 
kmiv, kacy, and kilg tafs for now. 


Outlook... 
Monday should be the time period when ceilings are marginal VFR to 
even IFR in developing rain, as low pressure lifts slowly off the 
middle Atlantic coast. The low will linger in our area into or possibly 
through Tuesday...with unsettled conditions loitering Wednesday as 
well. 


&& 


Marine... 
surface high pressure over the eastern Great Lakes and southeastern 
Canada will move northeastward more fully into southeastern Canada 
this morning. As low pressure develops off the U.S. East Coast and 
lifts northward today...a better gradient between the low to the 
south and the high to the north will form over our area during this 
afternoon and be in place tonight and Monday, and perhaps into 
Tuesday as well. If the NAM pressure pattern turns out to a better 
solution than the GFS, which shows the low closer to the coast along 
with a stronger gradient, then winds and gusts may be a bit stronger 
than Small Craft Advisory territory. The 00z European model (ecmwf) seems to be more 
in line with the 00z GFS, and not as pronounced as the NAM which 
apparently has overcooked the trough aloft. For now, the Small Craft 
Advisory that will be coming into effect south this afternoon and 
north this evening, and which currently extends through Monday, will 
be stretched through Monday night. Advisory level seas, and maybe 
winds, could be in effect for a good part of this week as there are 
several lows which look to impact our area. Presently, conditions 
are not forecast to reach advisory levels over Delaware Bay. 
However, the forecast will be brought to near advisory territory 
there, and future forecasters may need to fold at least lower 
Delaware Bay into the advisory if conditions are a bit stronger than 
forecast. 




&& 


Tides/coastal flooding... 
a persistent northeast flow over the next several days will cause 
above normal water levels. As low pressure lifts northward along the 
middle Atlantic coast, a fresh onshore flow starting tonight and 
persisting at least into Tuesday will bear watching. Aviation storm 
surge guidance is not creating dramatic effects, but it may be 
underdone as it only brings anomalies of a half foot above normal. 
Tide levels may be more like 1.0 to 1.5 feet above normal, and, with 
recent severe beach erosion, this may cause some problems in a few 
areas. If confidence builds in this scenario, some type of coastal 
product may need to be issued on today's day shift. For now, 
the situation will continue to be monitored. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...Small Craft Advisory from 1 PM this afternoon to 6 am EST 
Tuesday for anz452>455. 
Small Craft Advisory from 6 PM this evening to 6 am EST 
Tuesday for anz450-451. 


&& 


$$ 
Synopsis...delisi 
near term...delisi 
short term...delisi 
long term...stauber 
aviation... 
marine... 
tides/coastal flooding...