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fxus61 kaly 240503 
afdaly 


Area forecast discussion 
National Weather Service Albany New York 
102 am EDT Thursday Jul 24 2008 


Synopsis... 
a storm in the middle levels of the atmosphere will move through the 
eastern Great Lakes pushing a cold front slowly east...this 
evening through Thursday. Meanwhile a rich flow of tropical 
moisture will feed into the region on southerly winds. As 
disturbances ripple north along the cold front our region will see 
rounds of heavy rain showers...bouts of thunderstorms and the 
potential for severe thunderstorms...particularly from the capital 
district south and east. Thursday night this system will move out 
of our region. Weak high pressure will crest across the region 
Friday and Friday night. A cold front will push through the region 
late Saturday triggering showers and thunderstorms. High pressure 
will build slowly from the Great Lakes into the northeast to start 
the week. 


&& 


Near term /through Thursday/... 
new severe thunderstorms watch issued...band of heaviest rain and 
convection looks to be in central and eastern areas 
overnight...but the western edge of the rain will require at least 
likely in western areas. Will continue to monitor for severe and 
flood potential. 


&& 


Short term /Thursday night/... 
by late Sat afternoon area of rain showers/thunderstorms will set up across east central 
New York with axis just west of Hudson Valley. This will be focused on 
the cold front that will slowly drift east overnight. Focus will shift 
from potential severe to flooding. Rainfall rates of 1-2 
inches/hour are possible. This will enhance the flooding 
threat...therefore Flood Watch remains for the entire County Warning Area. The 
highest threat for flooding will ultimately be where this band 
wavers a bit...before drifting east. The major models have come into 
better agreement than 00 or 06 UTC runs. The GFS slows the 
eastward progress but is faster than the NAM. The NAM is faster 
than pvs run...so there are approaching agreement in timing. NAM 
is still a bit ballistic with quantitative precipitation forecast. 


Current models indicate this maximum axis should happen close to...or 
immediately east of the Hudson River overnight. We currently expected 
widespread rainfall amts of 1-3 inches...with 3-5 inches possible 
within this aforementioned band...and within higher...S/E facing 
portions of the Catskills. 


Thursday heavy rain should gradually shift east during the 
morning...tapering to scattered showers/stems during the 
afternoon in New York but continuing into afternoon in west new eng. Will slow 
departure of rain from pvs forecast. Thursday nt cold front will push through 
region...precipitation should diminish to scattered rain showers. Dry slot and passage of 
500hpa cold pool further west will keep threat of thunderstorms across the 
region. 


Friday 500hpa cut off will lift out of region...but cold pool with 
increase clouds and raise threat of -shra in far northwest...but otherwise a 
dry day as weak surface high builds into the region Friday and Friday nt. 
Saturday warm front moves through fca with warm air advection clouds and -shra possible 
in morning. Cold front will follow with more rain showers/thunderstorms in warm sector 
late Sat afternoon and nt. 


&& 


Long term /Friday through Wednesday/... 
the upper level pattern will feature a persistent trough across the 
Great Lakes/northeast/mid Atlantic...with a Broad Cut-off low over 
much of Quebec. Generally west to northwest flow will be the rule 
for eastern New York and western New England...with occasional 
disturbances moving through in the relatively fast flow aloft. 
Difficult to time individual short waves...but at least early on in 
the period from Saturday night into Sunday morning...a short wave 
trough and associated cold front is forecast to pass through. Will go with 
50-60 probability of precipitation with this system with both GFS/European model (ecmwf) showing at least 
light widespread quantitative precipitation forecast. European model (ecmwf) showing a more substantial wave passing 
by to our south Sunday night into Monday...but looks to be a miss 
for our area. Will mention generic isolated to scattered convection 
through the rest of period...with temperatures close to seasonal averages. 


The upper level low responsible for the midweek drenching will be 
lifting away from the region across eastern Canada on Friday...with 
weak high pressure moving through at the surface. 12z GFS model 
soundings show enough of a cap for most of the day on Friday to 
prevent any convection from occurring...so have kept entire forecast area dry 
throughout the dry. 850 mb temperatures of 13-16 degrees c generally 
equates to highs in the middle 80s across the valleys...with upper 
70s in the higher terrain. 


On Saturday...a low pressure area will move across Ontario into 
Quebec. This system will drag a cold front from the Great Lakes 
which will March eastward towards New England. Convection will fire 
along the both the pre frontal trough and frontal boundary...so have 
already included high chance probability of precipitation for entire County Warning Area...mainly in the afternoon 
and evening hours. Could potentially expect some strong activity...with 
model soundings showing 40 kts of Uni-directional deep layer shear. 
Activity will die off with passing of the frontal boundary during 
Sat night...so have attempted to taper the probability of precipitation accordingly. 


Upper level low will slowly pinwheel across eastern Canada. Heights 
will stay somewhat low Sunday through Tuesday...so have continued 
chance probability of precipitation for those days with diurnal convection possible. GFS also 
hints at a wave developing along the stalled front across the Ohio 
Valley and middle Atlantic...so this could bring some activity to 
southern portions of the County Warning Area for late Monday into Monday night as 
well. With the lower heights and associated cloud cover...temperatures will 
be a few degrees below average for Sunday through Tuesday...with 
generally temperatures right around 80 in the valleys...and lower 70s in 
the higher terrain. 


&& 


Aviation /06z Thursday through Monday/... 
the broad band of rain with embedded thunderstorms continues to 
affect the airports...and will affect gfl...alb and pou through the 
night...and into the daytime period...with only sluggish improvement 
until late. Predominant conditions will be MVFR...with periods of 
IFR visibilities and ceilings...even to as low as LIFR at kgfl early 
this am. Winds will be light and variable until the passage of a 
broad...weak cold front during the day on Thursday. Then winds wash down 
to surface. Left out low level wind shear from kgfl as upper level wind pattern 
appears too weak. But expecting as much as 30 kts surface to 2000 
shear to 40 kts wind maximum at kalb and kpou. This dissipates quickly 
around 12z with the mixing. VFR conditions finally return by late 
afternoon Thursday...until MVFR fog forms at kgfl with abundant fresh 
ground moisture supply and dwindling cloudiness and winds by end of 
taf period. The same may hold true for kalb and kpou...but left it 
at down to 6sm for now. 


Trough in vicinity ahead of Great Lakes cold front provides a downturn 
for Saturday. But Sunday is looking better than before...with high 
pressure making brief return behind the front. Monday...a trough 
means showery conditions will be around...but they should be rather 
isolated in nature with little forcing to provide much more than 
brief daytime squirts. 


Outlook... 
Friday...VFR...no weather. 
Sat...VFR/MVFR...chc shra/tsra. 
Sun...VFR...no sig weather. 
Monday...mostly VFR...chance -shra. 


&& 


Fire weather... 
wet flag conditions will be widespread across the region through 
Thursday...with heavy rainfall associated with several waves of low 
pressure moving along a stationary front. 


&& 


Hydrology... 
model consensus seems to indicate that 3 to 5 inches of rain is 
possible over most of the area. Consensus also indicates that 
heaviest rain will fall from late today through at least Thursday 
morning. Based on flash flood guidance...this amount of rain 
should not cause severe flooding but minor flooding is possible. 
Areas that see higher rainfall totals due to thunderstorms may see 
more significant flooding or flash flooding. A Flood Watch has 
been issued for the entire region...as the exact placement of 
heaviest rainfall...which could exceed 4 inches...is still 
somewhat uncertain. The highest probability is for it to occur 
somewhere near...or immediately east of the Hudson River...but this 
axis could still occur further west. 


Due to the extreme amounts of rainfall forecast by the computer 
models...and the fact that embedded thunderstorms are possible 
during the event...persons with interests along area rivers should 
keep alert for later statements regarding possible flooding. 


&& 


Aly watches/warnings/advisories... 
CT...Flood Watch through Friday morning for ctz001-013. 
New York...Flood Watch through Friday morning for nyz032-033-038>043- 
047>054-058>061-063>066-082>084. 
Massachusetts...Flood Watch through Friday morning for maz001-025. 
Vermont...Flood Watch through Friday morning for vtz013>015. 


&& 


$$ 
Synopsis...NAS 
near term...NAS 
aviation...elh 

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