Weather

542 
fxus61 kaly 071403 
afdaly 


Area forecast discussion 
National Weather Service Albany New York 
1000 am EDT sun Sep 7 2008 


Synopsis... 
Hanna will continue to move northeast today into the 
Canadian Maritimes. High pressure will ridge in from the Midwest 
today through tonight with fair and dry weather. The high will move 
off the New Jersey coast Monday...with a strong cold front bringing 
showers and thunderstorms for Tuesday. 


&& 


Near term /until 6 PM this evening/... 
..a quick update at 845 am... 


Hanna continues to move downstream this morning over eastern New 
England with only a few lingering rain showers persisting over the northern 
Taconics and Berkshires. These showers should die out by 9 am 
with subsidence in the wake of Hanna quickly eroding the low level 
moisture. Brisk west/northwest winds in the wake of Hanna should allow for 
downsloping off the Catskills...and eastern Adirondacks for the Hudson 
River valley. H850 temperatures will be in the +8c to +12c range with 
cold air advection ongoing. Sunshine should be plentiful in the 
PM. Meanwhile...upstream over Michigan and the eastern Great Lakes 
region...a h500 short wave will progress eastward kicking off some 
lake induced showers for west-central New York. Some of these may get close 
to western fringes of the forecast area. We believe based on the 
NAM/GFS/can regional the best chance for isolated rain showers will be over 
the western Adirondacks in the overnight period. 


Updated to remove probability of precipitation and downgrade showers to sprinkles over 
the Taconics/Berkshires/southern Vermont and to add sprinkles over 
the Adirondacks due to upslope effects over the terrain. 


&& 


Short term /6 PM this evening through Tuesday night/... 
Sunday night...the vorticity maximum in the relatively flat h500 flow 
dampens out as it moves towards upstate New York. Isolated rain showers will be 
possible over the western Mohawk Valley/western Adirondacks due to the 
vorticity advection. Meanwhile...surface high pressure will be ridging 
in from Ohio Valley and the Upper Middle Atlantic by 1200 UTC/Mon. 


Monday looks to be a nice late Summer day with surface high pressure 
passing south of New York and New England and moving off the New Jersey coast. 
The middle level flow is zonal...and h850 temperatures will still be around 
+10c near kalb. Most locations will be in the 70s...with a few l80s 
in the valleys and u60s over the eastern Catskills...and southern Adirondacks. 


Monday night...an upper level trough sharpens over the upper MS 
River Valley with a surface wave moving through the northern Great Lakes 
region. The warm front to this system will lift through upstate New York 
early Tuesday morning with some scattered rain showers...especially north and west 
of the greater capital region with the best lift from the thermal 
advection. 


Tuesday could be very interesting as we get into the warm sector 
ahead of a fairly strong cold front. The NAM/GFS both indicate 
dewpoints rising into the 60s with SBCAPE values exceeding 1000 
j/kg over the region. A low level speed maximum in the swirly flow of 
around 50 kts may slice through eastern New York middle day. 0-6km bulk shear 
values are prognosticated to be 45-60 kts. Middle level lapse rates steepen 
close to 7c/km /NAM/GFS/ with the surface cold front and its 
associated short wave energy. We used likely probability of precipitation Tuesday into Tuesday 
night with a chance of thunderstorms and rain showers. Some of the thunderstorms and rain showers could be strong to 
severe depending on the deep shear and instability in place. Storm Prediction Center 
has also latched onto this idea with the entire forecast area in a 
slight risk. We will mention the severe threat in the severe weather potential statement for now. 


Tuesday night...the scattered rain showers and thunderstorms and rain showers should end around midnight 
with strong cold air advection occurring across the forecast area. The 
GFS has h850 temperatures falling close to 0c over portions of the southern 
Adirondacks. A cool Canadian air mass will be building in for the 
middle week. 


&& 


Long term /Wednesday through Saturday/... 
cold air advection in wake of cold front for Wednesday. 850 mb temperatures 
expected to drop to 2-6 celsius during the day. Most of forecast 
area should have highs only in the 60s with middle to upper 50s across 
the higher terrain...Adirondacks and southern Green Mountains. 


Will get chilly Wednesday night with ridge moving over the area. 
Lows in the 40s with 30s across the higher terrain. Have frost in 
the weather grids for late at night as temperatures bottom out. 


Temperatures expected to rebound to seasonable temperatures on 
Thursday as surface high shifts to the east off the New England 
coast and southerly flow develops. 


Low pressure system approaches late in week. The models are not in 
agreement in how they handle the energy associated with this system 
as it moves across country during week...so uncertainty is rather 
high with timing and track. 


Hurricane Ike moving westward across the Gulf of Mexico...refer to 
the products issued by the National Hurricane Center for details. 


&& 


Aviation /12z Sunday through Thursday/... 
Hanna continues to head off to the northeast. MVFR-VFR improving to 
widespread VFR this morning with cloud cover then decreasing. 
Northwest to west winds will become gusty with gusts to 20-25 knots. 
Winds will begin to diminish late this afternoon and will become 
light to calm this evening with MVFR...possibly IFR fog forming late 
at night at kgfl. 


Outlook... 
Monday...VFR...no sig weather. 
Late Monday night...VFR-MVFR...chc shras/tsra. 
Tuesday...VFR-MVFR...tsra/shra likely. 
Tuesday night...VFR...chc rain showers during the evening. 
Wed/Thu...VFR...no sig weather. 


&& 


Fire weather... 
high pressure will build in from the south and west today through 
Monday with mainly dry weather aside from a few showers over the 
western Adirondacks. 


The winds will be brisk from the west or northwest at 10 to 20 
miles per hour. The winds will be light from the west or southwest at 10 miles per hour 
or less Sunday night. The winds will be from the west or southwest on 
Monday at around 10 miles per hour. 


Relative humidity values will fall to 35 to 55 percent this afternoon. They will 
recover to 85 to 100 percent Monday morning...but lower to 35 to 
50 percent during the afternoon. 


&& 


Hydrology... 
have cancelled the Flood Warning for Stevenson dam. Operators 
have closed some gates at the shepaug dam and at the same time 
the pomperaug river has dropped nearly a foot since cresting 
earlier this morning. This has enabled some flood gates to be 
closed at the Stevenson dam...enabling the river to drop below 
flood stage. The Tenmile river crested around 2am and has 
since dropped several inches...resulting in a preliminary 
crest at Gaylordsville. However as flow from upstream arrives 
the Housatonic will rise some more...although the increase will 
be somewhat offset by the diminishing flow of the Tenmile. The 
good news...the Housatonic will remain below flood above Lake 
Lillinonah. Currently the only Flood Warning still in effect 
is for the Still River at Brookfield. That river was cresting 
3 feet above its 12 foot flood stage late this morning...and 
it will remain above flood until around midnight tonight. 


Refer to our public information statements for rainfall reports. The 
highest amounts reported have been 6.48 inches in Rocky River CT and 
6.27 inches in New Milford CT Litchfield County. 


Next chances for rain will come Tuesday as a strong cold front moves 
through. Widespread quantitative precipitation forecast amounts around a half expected with locally 
higher amounts associated with thunderstorms. With the ground wet 
from the rains associated with Hanna...this rain will have some 
effect on the rivers although most of it will soak into the ground. 
A USGS observation well near Pittsfield has indicated a rise of 
about 1.5 inches in the water table there. 


For details on the rivers...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...wasula 
near term...taw/rck 
short term...wasula 
long term...iaa 
aviation...iaa 
fire weather...15 
hydrology...rck 

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