Weather

202 
fxus61 kaly 060622 
afdaly 


Area forecast discussion 
National Weather Service Albany New York 
120 am EST Tuesday Jan 6 2009 


Synopsis... 
high pressure will build into the region today. It will then move 
to the east and a storm will approach from the southwest tonight. 
This storm will initially track to our west up the Ohio Valley... 
then redevelop to our east off of Long Island by late Wednesday. 
These two storm centers have the potential to bring a significant 
wintry mix from Albany southward...and mostly snow farther north 
and west. 


&& 


Near term /through Tuesday/... 
enjoying a hiatus in the weather at this time (at least most of the 
area). The only exception is some Minor Lake effect taking place 
across our northwest zones. However the temperature Delta response 
from the Lake Ontario through about 5000 feet is marginal and thus 
far...dz values are mainly in the teens (implying mainly flurries). 
This should continue into the night time hours...perhaps getting a 
little more robust as air temperatures lower at bit. For now...let 
the ongoing probability of precipitation from the previous package stand across mainly the 
higher terrain from the Mohawk Valley north for scattered/isolated 
snow showers with little or no accumulation expected. 


Over the majority of the region...looks like a dry night with 
seasonably cold temperatures and a partly cloudy sky. Went with a 
blend of all available machine guidance (except bit colder up north 
with a more extensive snow pack). 


Quiet on Tuesday...at least most of the day. High pressure will 
crest over the region early in the day and begin to slip off the 
east...while another one attempts to build in from the north. While 
never making this far south...this high over eastern Canada looks 
just strong enough to lock in shallow air in place...enough to 
produce problems when the next storm comes marching in. 


&& 


Short term /Tuesday night through Wednesday night/ 
by late Tuesday...or more likely Tuesday night...light snow will 
start moving into our forecast area from the southwest. Initially 
snow flying might run into some dry air and initially evaporate 
before reaching the ground. However...later in the evening snow 
looks to overspread the entire region. Model soundings indicate 
below freezing temperatures initially throughout the column so it 
should be all snow. 


Then...a warm wedge will come streaming in off an increasing low 
level southeasterly jet. The winds off the NAM are not that 
impressively strong...but look strong enough to send a layer of 
above freezing temperatures to as far north as southern Vermont. So 
once again...ptypes come into play...especially from Albany 
southward. 


Looking at both the operational 12z NAM soundings...indicate more 
snow and less mix just north of Albany...with more mix (to freezing 
rain) south of Albany. US usual...Albany itself comes right under 
the old fence...could go either way (more ice...or more snow). 


Taking a look at the sref members...this will be a more mixed event 
coming up even from Albany and somewhat northward...with two 
members showing mostly rain. Meanwhile...the mref members are colder 
with more snow. However...the GFS model 12z soundings are slightly 
warmer than the 12z NAM soundings...warm enough for some mixing even 
north of Albany. The NAM soundings are colder but for the past two 
years (maybe longer) they have had a cold bias. 


For now...hoisted a Winter Storm Watch since the quantitative precipitation forecast is over half an 
inch and we are expecting the precipitation to be almost all 
freezing/frozen precipitation (except for perhaps a couple of hours of rain 
down near kpou). Leaned with a slight warmer solution (at least the 
middle levels) which are supported by the Canadian and European models. 


We have forecasted snow to mix with and change to sleet/freezing 
rain...first south of Albany by overnight Tuesday...and later in the 
day Wednesday around Albany and points a little north. The 
precipitation looks to turn back to snow at the tail end later 
Thursday night. A trailing surface and upper low low moving over 
it...might prolong light snow into even Thursday. So...our thinking 
is this will be a marginal winter storm with snowfall amounts around 
9 inches (mostly all snow))...closer to 6 in albany(mixed with sleet 
and freezing rain) and about 3 in our far southeastern zones...but 
with more ice accretion...approaching half an inch. 


This thinking would likely minimize any possible power outages 
(spotty at worst) except possibly a bit more in the middle Hudson 
Valley/Litchfield Hills. Still..at this time...this storm looks to 
pale in comparison with the December ice storm. 


Went the generally colder mav numbers during this time 
frame. 






&& 


Long term /Thursday through Monday/... 
in the wake of the winter storm...cold air advection will allow for rather cold air 
aloft to pour into the region. Some instability/cyclonic flow/lake 
enhanced snow showers will be possible...so have continued chance probability of precipitation 
of -shsn for much of the day on Thursday. Westerly winds will 
continue to be breezy as well...especially across the Mohawk Valley...with 
some gusts up to 30 miles per hour. 


A weak ridge of high pressure at the surface will be across the 
region for Friday. Despite decent sun...maximum temperatures will only reach 
the middle 20s at best in the valleys...with teens in the higher 
terrain. The winds will begin to weaken somewhat by Friday afternoon due 
to the subsidence as the high moves directly over the area. 


By Friday night...clouds will begin to increase ahead of the next 
storm system to approach the region...which will be a flat clipper 
moving from the Great Lakes towards the northeast. This system is 
still not totally resolved by the models...and the latest European model (ecmwf) 
shows a further north track than the GFS. Even the 12 UTC run of the 
GFS keeps the surface low across the North County...which would not 
be favorable for much precipitation /snowfall/ across our region at all. 
Have only kept chance probability of precipitation for now until the track is better known for 
this system. 


Very cold air will pour into the region following this system for 
Sunday. 850 hpa temperatures drop as low as -20 c to -24 c based on the 
latest GFS for Sunday afternoon...which would allow for below normal 
temperatures. Have gone several degrees below gmos values to account for 
this for Sunday and Monday. Will have to keep an eye for storms next 
week...as a developing +pna...the nao transitioning from negative to 
neutral...and a favorable mjo probably in the 7 or 8 phase could 
allow for an active and cold pattern for the region. 


&& 


Aviation /06z Tuesday through Saturday/... 
winds have slackened at kalb and were light from a generally 
westerly direction across the region. A plume of stratocu extended 
from Lake Ontario across the Adirondacks and at times was resulting 
in a 4000 feet ceiling at kgfl. A few wisps of it were noticed at kalb 
but for the most part skies across the middle part of the forecast 
area were clear. Farther south...high clouds associated with a 
low over the Tennesee valley and its associated warm front 
covered the southern part of the forecast area with bases above 
fl150. A local situation has at times reduced the visibility at 
kgfl to IFR...but otherwise conditions were VFR across the 
forecast area and will remain so well through this afternoon. 


Conditions will start to deteriorate this evening with MVFR 
visiblity due to snow and ceilings lowering to around 3000ft 
at kpou by around midnight. They are likely to deteriorate to 
IFR later tonight as ceilings lower and heavier snowfall 
reduces visiblity...with the snow mixing with and turning to 
sleet/freezing rain south of kalb. 


Outlook... 
Wednesday...IFR vsby/cig. Sn/pl/fzra. 
Wednesday night...slow imprvmt to MVFR precipitation becmg all snow. 
Thursday...MVFR...cig. Chance -shsn. 
Friday...VFR...no sig weather. 
Sat...VFR/MVFR...chc -shsn. 


&& 


Hydrology... 
no hydrology related problems are expected through the week. 


A storm system is expected to bring a wintry mix of precipitation to 
the area Tuesday night and Wednesday. Temperatures are forecast to 
remain cold enough so that melt...and resulting runoff...should be 
insignificant. Models indicate that cold weather will persist into 
next week. Temperatures may be cold enough across the Adirondacks 
and southern Vermont Sunday through Tuesday for some isolated freeze 
up river ice jams to form by Tuesday. Elsewhere....river ice will 
form and thicken. 


Snow water equivalent data from field surveys is expected this week. 
Our initial 08-09 winter Spring flood potential outlook will be 
issued on Friday Jan 9th. 


For details on the rivers...please visit the advanced hydrologic 
prediction service /ahps/ graphs on our website. 


&& 


Aly watches/warnings/advisories... 
CT...Winter Storm Watch from late Tuesday night through Thursday 
morning for ctz001-013. 
New York...Winter Storm Watch from late Tuesday night through Thursday 
morning for nyz032-033-038>043-047>054-058>061-063>066- 
082>084. 
Massachusetts...Winter Storm Watch from late Tuesday night through Thursday 
morning for maz001-025. 
Vermont...Winter Storm Watch from late Tuesday night through Thursday 
morning for vtz013>015. 


&& 


$$ 
Synopsis...rck 
near term...hwjiv 
short term...hwjiv 
long term...frugis 
aviation...rck 
hydrology...dirienzo 

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