171 
fxus61 kphi 210746 
afdphi 


Area forecast discussion 
National Weather Service Mount Holly New Jersey 
346 am EDT sun Mar 21 2010 


Synopsis... 
high pressure will remain over the region for one more day and dry 
weather and very warm temperatures are in store again. The high 
will move to the east tonight. An area of low pressure developing 
over the lower Mississippi Valley will approach the region tonight 
and move across the area on Monday, bringing rain. The low will 
move away on Tuesday. High pressure will then build back in for 
Wednesday and Thursday. A cold front and surface low will bring 
another chance of rain to the area by Friday. 


&& 


Near term /through 6 PM this evening/... 
another generally nice day is in store for the region, as high 
pressure maintains its grip for one more day. There will be more 
in the way of clouds and as a result temperatures will be a bit cooler, 
but still way above normal for this time of year. MOS guidance looks 
reasonable and was generally followed. High temperatures will be in the 60s 
in many areas, with some locations touching or exceeding 70 degrees. 


&& 


Short term /6 PM this evening through Tuesday/... 
tonight looks to be mainly quiet weather wise, in advance of the next 
storm which will be taking shape across the lower MS valley. This low 
will reach the Ohio Valley this evening and then move toward the middle-Atlantic 
on Monday. Attm, it looks as if most, if not all, of the rain will 
hold off until after daybreak on Monday. The precipitation should begin 
during the morning hours on Monday and and become steadier and 
heavier during the evening and overnight hours as a decent shortwave is 
prognosticated to move through. There is some decent Omega, and a warm front 
nearby, but the low level jet is only around 40 or so kts. Of course, with 
the upper low approaching overnight, there will be abundant cold, 
unstable air aloft. So, will keep the mention of thunder in the 
fcst, mainly over southern areas, which puts US in very good agreement 
with the Storm Prediction Center outlook. 


At this time, it looks like the heaviest rain and highest quantitative precipitation forecast 
would be in northern portions of the region. Latest quantitative precipitation forecast generally has 
between 1/4 and 1/2 inch across much of the Delaware-Maryland-Virginia and southern New Jersey. 1/2 
to 1 inch across the I-95 corridor and 1 to 1.5 inches across northern New Jersey 
and northestern PA. The models have trended a bit downward this run, but it 
may not matter, especially across northern New Jersey where rivers and streams 
are still running high from last week's storm. Since the heaviest 
rain looks to occur Monday night, will hold off on any watches. 
However, if the current numbers still hold across northern areas, a 
Flood Watch would become necessary for a portion of the region. 


The models are now less robust for Tuesday, with virtually all of 
the guidance now ending the precipitation and improving things after the 
morning hours. The only exception is the ECMWF, which continues to 
keep things ongoing into later Tuesday or Tuesday night. If the 
European model (ecmwf) were correct, probability of precipitation would have to be raised on 
Tuesday/Tuesday night. Tuesday still looks relatively cloudy 
though, but of course with the Spring sun, if there are some 
breaks, that will have a positive effect on temperatures. For now will go 
with the MOS guidance. 




&& 


Long term /Tuesday night through Saturday/... 
there could be some showers behind the low on Tuesday night, but 
then high pressure builds in for Wednesday and Thu, bring dry and warm 
(albeit not as warm as it has been) weather. By Thursday night into 
Friday, a low moves across southeastern Canada and a cold front extending southward 
from it will approach the region. This front, coupled with a low 
across the lower MS valley will bring another chance of rain Friday. 
Current guidance, with the exception of the ECMWF, indicates the 
best chances may be over southern areas. The ec brings the slug of precipitation 
further north. However, we have several days to see how the models trend 
with this sys, but will leave chance probability of precipitation for now. High pressure then 
builds in for Sat. 




&& 


Aviation /06z Sunday through Thursday/... 
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, 
kmiv, kacy and surrounding areas. 


VFR conditions still in place and will remain so throughout the 
remainder of the weekend, except that some light fog or haze could 
form around miv this morning. The visibility restriction will only be a 
temporary issue and should mix out by late morning. 


Late in the evening on Sunday we start to see increasing clouds with 
lowering decks...mainly broken becoming overcast although still VFR 
ceilings. There may be a brief period in the morning on Monday with some 
minor visibility restrictions across all the taf sites as a low pressure 
system nears the region from the west. Visibility restrictions should lift 
by late morning, but with the low pressure and its associated cold 
front swinging through the skies will thicken and lower 
substantially to MVFR conditions. Rain with possibly embedded 
thunderstorms will be persistent throughout the day. 


Outlook... 
ceilings will remain down Monday through most of the day on Tuesday 
before the strong cold front makes its way completely through the 
area. The showers will likely continue through Tuesday before the 
low pressure makes its way far enough to the east of the region. 
High pressure will then build in from the west for the middle and 
latter parts of the week, bringing a return to fair weather and VFR 
flying conditions. 


&& 


Marine... 
quiet conditions will continue through the remainder of the weekend 
before the high pressure, that provided the tranquil weather, pulls 
further to the east. A low pressure system with an associated cold 
front nears later on Monday providing our waters with another round 
of rain with the possibility of embedded thunderstorms. With the low 
approaching and the pressure gradient tightening the winds and waves 
will be on the increase from south to north. Still being a few 
periods away from the onset of Small Craft Advisory criteria, the flags have only 
been raised on the southern waters and the entire Bay, although they 
will more than likely be extended further north at a later time. 


There may be a lull in the action, with the winds that is, on 
Tuesday with the low pressure directly overhead. Once the low passes 
to the east, winds will again pick up out of the west northwest with 
gusts possibly exceeding Small Craft Advisory conditions still as the pressure 
gradient tightens again with high pressure building in behind the 
departing low. Seas should start to relax from south to north later 
in the week when the high completely settles over our waters. 


&& 


Hydrology... 
many thanks to the has forecaster at marfc for running a contingency 
what if scenario for US. We ran a basinwide average of 1.75 inches 
of rain in 18 hours in hopes of leaning toward a worse case scenario 
for this upcoming event. With that rainfall most gaged streams will 
come close to flood stage. The assunpink, Neshaminy, Passaic would 
reach minor flooding and the Millstone at Blackwells Mills would 
reach moderate flooding. Headwater guidance for northern New Jersey 
starts showing problems with flooding once 12 hour rainfall exceeds an 
inch while the rest of our County Warning Area its generally more than an inch and a 
half. Right now no problems are expected on the Delaware. 


We will continue to monitor model trends and will continue to word 
possible flooding in the severe weather potential statement. The latest models have trended 
slightly downward with their qpfs, but it may not be enough. The 
most problematic area still looks to be northern New Jersey. 


&& 


Phi watches/warnings/advisories... 
PA...none. 
New Jersey...none. 
Delaware...none. 
Maryland...none. 
Marine...Small Craft Advisory from 8 am Monday to 8 PM EDT Tuesday for 
anz430-431-452>455. 


&& 


$$ 
Synopsis...nierenberg 
near term...nierenberg 
short term...nierenberg 
long term...nierenberg 
aviation...Heavener 
marine...Heavener 
hydrology...gigi/nierenberg 

National Weather Service Glossary of Abbreviations

Non-Expanded Version (with abbreviations)