577 
fxus61 kaly 220014 
afdaly 


Area forecast discussion 
National Weather Service Albany New York 
705 PM EST Sat Nov 21 2009 


Synopsis... 
a large ridge of high pressure will cover the northeast...sliding 
off into Canadian Maritimes late Monday. Clouds over the region 
will diminish with generally clear skies Sunday into Monday. Our 
weather will turn unsettled much of the upcoming week. First a low 
pressure area will move northeast from the Carolina coast Monday 
night and Tuesday. Then midweek a series of much stronger storms 
will move though the Midwest and Great Lakes. 


&& 


Near term /through tonight/... 
skies have cleared from the Hudson Valley eastward except for a 
small patch of clouds just west of the northern Taconics along 
and just west of the New York/VT/MA state line. Will be making some 
minor changes in the grids but for the most part the forecast 
is in good shape. Temperatures were mostly in the low to middle 
40s. Latest satellite images show little change in the area 
of clouds that cover upstate New York west of the Hudson 
Valley along with adjacent parts of PA...lakes Ontario and 
Erie...and southern Ontario. 


***Previous near term...issued at 245 PM today...*** 
surface high in the Great Lakes and Ohio Valley continues to gradually 
build into the region. West to northwest flow across the lakes and 
an inversion at the boundary layer has resulted in widespread cloud 
cover. However...areas in Lee of the eastern Catskills...Berkshires 
and southern Green Mountains have seen relatively little cloud cover 
due to downslope. 


Recent satellite trends are consistent with trends seen in 
guidance...with clearing and drying beginning to work south from 
near the Canadian border. This clearing and drying will build south 
through the evening and night...but there is some question about 
how far west the clearing will get...due to proximity to Lake 
Ontario. For areas around and east of the Hudson Valley...clearing 
should spread across the region by the early morning hours. Areas 
of the western Mohawk Valley to Schoharie valley and parts of the 
Catskills may be a bit slower to clear. Still...by sunrise... 
suggesting all areas will clear. With at least a couple/few hours 
of clearing before sunrise...temperatures should fall to near 
guidance levels...even though temperatures will not fall much until 
clearing occurs. 


Upstream surface dew points not too dry...so low temperatures should 
not be much below guidance in areas that see the longest period of 
clearing...and maybe a bit above guidance where clearing is most 
delayed. Most temperature bust potential tonight looks to be in the 
western Mohawk Valley...Schoharie valley and parts of the 
Catskills...where timing of clearing in question. 


&& 


Short term /Sunday through Monday/... 
rather impressive ridge over region for this period at surface and aloft. 
The 500hpa short wave axis (fm west Maryland to cape cod) will be exiting 
the region at start of the period and taking with it most of the 
forcing that resulted in the clouds that were trapped under the 
inversion. WRF also shows drying and dry air advection just prior 
to this period. So Sunday should be a sunny day with above normal 
temperatures and any residual clouds will go quickly. 


For the most part we have model consistency (ecmwf/Gem/GFS/nam) 
for system placement and timing through Monday. The exception is 
the NAM now pushes threat of rain into southeast fca late Monday...about 
3-6 hours faster than rest of the crowd. But the consensus 
remains for a partly sunny and dry day in most of the area with 
just chance probability of precipitation along the southern peripheral counties. So there 
should be little change in the forecast. 


The other discontinuity is the mav and met temperatures are about 5-10 
degrees apart Sunday...the met being the cold one. This in spite 
of both models indicating similar sensible weather (sunny..light 
winds..under high), and having about the same 925 hpa forecasted 
temperatures (3-5c)as well. This difference in the met/mav is reflected 
in their model soundings and particularly around maximum temperature time @ 
18utc. While the new NAM physics have generally been better since 
the upgrade something seems squirrelly in the met temperatures Sunday. 


Today so far wheres there no sun temperatures are still middle 40s to around 
50...and well into the 50s where the sun is shining. Could just 
blend the two...but given the comparison to today..fcst will go 
with the mav temperatures 


&& 


Long term /Monday night through Saturday/... 
Monday into Monday night the lingering 500hpa trough from the Middle 
Atlantic States phases with a trough lifting NE from Gulf Coast states. Still 
considerable variation in the phasing and the surface response...but 
GFS/European model (ecmwf) and NAM produce a coastal low Monday nt that lifts NE. 
The model tracks are still quite varied. The GFS/European model (ecmwf) keep fca on 
periphery of system with threat of only lt rn in southeast fca...the NAM 
a bit more aggressive with quantitative precipitation forecast and further West. Bottom line will 
introduce chance probability of precipitation Monday nt into Tuesday mainly in southeast half of fca. 


Once this first system passes there's as much agreement as you 
usually get in the efp for the rest of the period. There are few 
significant differences bwtn HPC...the European model (ecmwf) that just came in and 
the GFS. Will populate with HPC grids for efp. 


It appears this extended period will be a game changer. After 
tuesdays weak coastal departs a series of short waves phase into a 
deep and large 500hpa cut off over the Mississippi Valley as 
another cutoff organizes over south central Canada. These systems 
interact with each other during the extended period creating a 
dumbelling action around each other over the Great Lakes..Midwest and 
upper Great Plains for much of the week till they phase into a massive 
cutoff lover the eastern Seaboard to end the week. The main storm 
tracks will pass to our west at first...with the final one a 
coastal by the weekend. The result will be an unsettled period as 
we head into the Thanksgiving travel and Holiday period. There 
will be several frontal passages and their bouts of precipitation. 
Temperatures will remain near or above normal till the end of the week when 
it will turn noticeably colder. 


&& 


Aviation /20z Saturday through Thursday/... 
high pressure will build east across the region Saturday through 
Sunday. 


Much of the forecast area west of the Hudson Valley was covered 
by a deck of low stratus that was 2500-3500 feet above sea level...which had 
resulted in MVFR ceilings at kalb for a while this afternoon. 
However these clouds have cleared out of most of the Hudson 
Valley and at 7pm...00z...skies were clear at kalb...kgfl...and 
kpou. There was a small area of low clouds east of Albany which 
has resulted in a MVFR ceiling at kpsf...and areas of IFR ceilings may 
be expectd across the Taconic ridge east of the Hudson Valley 
and also over higher elevs of the Catskills and Adirondacks 
west of the Hudson Valley. 


The clearing skies...along with diminishing winds...has brought 
about another complication...that being the possibility of 
radiation fog. Temperatures are expected to drop the next few 
hours with radiational cooling and are likely to get close to the 
dewpoint right shortly before midnight. We have forecast MVFR 
visibility at kgfl starting at 04z...with IFR in fog possible by 
05z...and IFR ceiling and visby likely after 08z. A light north wind off 
the Mohawk River will probably result in MVFR fog starting around 
07z. At this point ... a light northwesterly flow...we are 
expecting kpou to remain VFR with 6 miles in light fog. 


Winds at kalb will turn north around 3 kts later this evening 
and will be calm at kgfl and kpou. 


For Sunday...fog and low clouds will burn off and mix out 1 to 
2 hours after sunrise. After that...a beautiful VFR day with 
mostly clear skies...and light north/northeasterly winds. 


Outlook... 
Sun night...VFR...no sig weather. 
Mon-Tue...VFR-MVFR...chc of rain. 
Wednesday...VFR...chc of showers. 


&& 


Hydrology... 
with dry conditions expected to last at least into Monday rivers 
will continue recede through Monday. The next threat of rain will 
be late Monday into Tuesday. Consensus of models is for 0.10 to 
0.70 inches mainly in the southeast. But alot of uncertainty 
remains with the storm track and amounts could vary. This event 
should have modest impact on rivers and streams. Further out an 
unsettled period of weather Thursday into the weekend could result 
in significant precipitation amounts. 


For details on specific area rivers and lakes...including 
observed and forecast river stages and lake elevations...please 
visit the advanced hydrologic prediction service /ahps/ graphs on 
our website. 


&& 


Aly watches/warnings/advisories... 
CT...none. 
New York...none. 
Massachusetts...none. 
Vermont...none. 


&& 


$$ 
Synopsis...Snyder 
near term...NAS 
short term...Snyder 
long term...Snyder 
aviation...rck 
hydrology...Snyder 

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