606 
fxus61 kphi 180747 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
347 am EDT Thursday Mar 18 2010 


Synopsis... 
an area of high pressure centered well to our southwest today will 
settle eastward during the next few days. The eastern extent of 
this system however will continue to dominant our weather as a low 
pressure system slides well to our south today into Friday. As the 
high pressure system moves off the coast Saturday, a low pressure 
system will continue to organize in the middle Mississippi Valley. 
This storm will gradually track eastward and move across our area 
late Sunday and Monday. High pressure then gradually builds into our 
region Tuesday through Wednesday. 


&& 


Near term /until 6 PM this evening/... 
a 06z surface analysis placed low pressure off the South Carolina 
coast and high pressure centered over the Southern Plains. A frontal 
boundary was draped from the Canadian Maritimes westward across 
southern Canada. An upper air analysis placed troughing over Canada 
with a separate more closed low over the southeastern U.S. A 
midlevel ridge was from the southwestern U.S. Northeastward toward 
the Midwest. A 300 mb jet was located from the Pacific northwest, 
eastward across southern Canada. Another 300 mb jet was cyclonically 
curved from the Southern Plains to the Gulf of Mexico then off the 
southeastern U.S. Coast. Temperatures early this morning vary quite 
a bit across the County Warning Area. Just a little bit of wind at some locales is 
holding the temperature up by several degrees compared to other 
areas. 


Our region remains between stronger upper-level flow over southern 
Canada and across the Gulf Coast region. A well defined midlevel low 
over the southeastern U.S. Today will gradually move eastward. This 
will toss some high clouds across our far southern zones at times, 
however an east-west band of subsidence will keep this cloud shield 
from moving much farther to the north. Meanwhile, the stronger flow 
across southern Canada will generate high cloudiness and some of 
this may move across the northern part of the County Warning Area today. Overall, a 
good deal of sunshine is expected once again across the region. The 
low to middle level flow is once again on the light side today as high 
pressure in the Southern Plains is stretch into the middle Atlantic. 
This light flow in the boundary layer combined with warm afternoon 
temperatures, will promote a sea breeze to develop. We tried to 
depict this again in the wind grids. A tough call on the dew points 
today as they have come up some during the night in many places. 
There is plenty of dry air to mix down to the surface, although the 
boundary layer flow is on the light side. As we get plenty of 
boundary layer heating today, dew points should lower below MOS 
guidance at most locales especially away from the coastal areas. 
This will result in rather low relative humidity values, but the 
winds will be light enough to lessen a fire weather threat. 


As for temperatures, we generally utilized an evenly weighted blend 
of the GFS/NAM MOS although did raise the highs up a little bit from 
there for some locales given we should be a bit warmer than 
yesterday. 


&& 


Short term /6 PM this evening through Saturday/... 
as the system across the southeastern U.S. Departs tonight and 
Friday, some additional ridging is forecast to build into our area. 
This should tend to keep energy sliding across southern Canada to 
our north. There are some hints that a weak frontal boundary tries 
to settle southward late tonight and Friday. If this boundary is 
discernible, it may not get to far south as midlevel ridging is 
forecast to build some. As a result, we will maintain the stretch of 
rather mild temperatures. The systems tracking well to our north and 
one well to our south however will toss some high clouds our way 
tonight and Friday. 


A vigorous system will be organizing across the central/Southern 
Plains Friday night and Saturday. As this system amplifies and moves 
eastward, the warm air advection on its east side will strengthen and also build 
the ridge some along the East Coast. The model guidance mostly 
shifts the midlevel ridge axis to our east during the day Saturday, 
therefore we may be able to get some high cloudiness arriving during 
the course of the day. 


As for temperatures, we leaned toward the higher MOS guidance for 
highs and even went a little above in some locales. Despite the 
wealth of rain this past weekend and early this week, the top layer 
of the ground will continue to dry out decently, therefore with 
nearly full sunshine, temperatures should have no problem getting 
well into the 60s for most places with even some lower 70s 
especially in the urban areas. The flow is still rather light on 
Friday, therefore another sea breeze may occur and we shaved the 
highs down some along the coast. The low-level flow looks to 
increase some during Saturday which may keep a true sea breeze at 
Bay, although the surface winds overall should back to a southerly 
direction. 


&& 


Long term /Saturday night through Wednesday/... 
a surface low and associated cold front is forecast to track 
northeastward and now track very near our area late Sunday and 
Monday. There has been a tendency in the model guidance to show more 
of a spread with the timing of this entire system, especially as it 
originally looked like just a strong frontal passage. It appears that 
the model guidance was trending faster with the frontal passage 
timing, although the 00z European model (ecmwf) is much slower with this system. It 
closes off the midlevel circulation more with the surface low 
slower, stronger and farther to the south. The European model (ecmwf) may be strong 
with the surface low. The 00z GFS is more toward the European model (ecmwf) solution 
with a slower eastward motion of the surface low and cold front, 
although not as slow as the European model (ecmwf). The surface low is also farther to 
the south. The stronger midlevel center and slower eastward 
progression appears to be tied to the northern and southern streams 
remaining more separate. This allows more of a cutoff low, which has 
been the theme this entire winter. This system does look rather 
strong with warmth and increasing moisture ahead of it and turning 
colder behind it. 


Some of the model forecast soundings indicate some elevated 
instability developing ahead of this system, although the cape 
profiles are rather skinny with low values due to a saturated 
profile. Given the increasing low to middle level wind field, coupled 
with ample lift with the upper trough and surface front, we may have 
some convection accompany this system. We will continue with the 
likely probability of precipitation for showers and a chance of thunder, although delayed these 
ramping up by several hours. There is a decent amount of moisture 
advection forecast ahead of the front with dew points rising into 
the lower 50s. For now, we increased the dew points Sunday into 
Monday a good 15 degrees from continuity. This would introduce the 
potential for heavy rain, which the chance looks to have increased with 
the midlevel center stronger and the surface low farther south. We 
will have to watch this for a potential flood threat. The slower 
look of this system had US increased the probability of precipitation through at least 
midday Monday then increase to chance probability of precipitation Monday afternoon. The 
strengthening low to middle level flow along with stronger low-level 
warm air advection will allow for milder temperatures Sunday night therefore these 
were increased from continuity. 


Once the front sweeps east of our cwa, cooler and breezy/windy 
conditions settle in Monday night and Tuesday as cyclonic flow 
arrives and the upper-level trough moves through. Monday may end up 
having a non-diurnal temperature trend especially across the 
northwestern part of the County Warning Area as cold air advection kicks in. A surface high 
pressure system then gradually settles in for Tuesday and Wednesday 
with less wind. Temperatures are expected to start on the warm side 
with some areas possibly peaking into the lower 70s Sunday, then 
trending colder during Monday and Monday with some moderation 
Tuesday and Wednesday. That is all for now. Thanks to the 
surrounding offices for the collaboration early this morning. Have a 
good one! 


&& 


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


VFR conditions with mainly clear skies are expected through the taf 
period. Light west winds should be the rule, although winds are 
forecast to go onshore at Acy and ilg during the afternoon as a 
sea/Bay breeze develops. 


Outlook... 
VFR into the weekend. The next system with the possibility of lower 
clouds and showers may arrive as early as Sunday night, although our 
models have been slowing its progress down. 


&& 


Marine... 
light winds will continue across the waters through at least the 
first part of the weekend. Winds will eventually begin to increase 
as the next frontal system approaches, although the timing of this 
is uncertain due to a model trend of slowing the system down. 
Whether or not winds eventually reach gale force /either ahead of 
the system or - perhaps more likely- in its wake/ also is uncertain. 


Regarding seas, they have dropped below 6 feet in swells at the south 
end of our Atlantic waters /44009/, while at the north end they were 
down to about 4 feet /44065/. The advisory will be dropped from Cape 
May south early this morning. 


We then should be advisory-free until at least Sunday night. 


&& 


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


&& 


$$ 
Synopsis...gorse 
near term...gorse 
short term...gorse 
long term...gorse 
aviation...delisi 
marine...delisi 

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