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Area forecast discussion 
National Weather Service Buffalo New York 
137 PM EDT sun Mar 21 2010 


Synopsis... 
limited moisture between high pressure over Quebec and a cold front 
front that has stalled south of Pennsylvania will impact parts of 
western and north central New York state today. A more widespread 
rain will spread north across the area Monday and Tuesday as an 
low pressure moves east along the stalled front. 


&& 


Near term /through tonight/... 
through 100 PM...skies have cleared out south of the I-90 
Divide...with partly to mostly sunny skies south...and mostly 
cloudy skies north. This has allowed temperatures to rise into 
the upper 50s in southern locations...with some room to rise for 
the next couple hours. Precipitation has largely exited to the 
northeast...with a mixed bag of light precipitation across the 
north country ending. 


Tonight...our region will be playing the waiting game for the next 
system which will eventually bring our region some widespread 
rain. An anomalously deep (-4 Standard deviations for 500 mb hgts) 
upper level low...the same one responsible for the freak Oklahoma 
snowstorm on Saturday...will be churning over the lower 
Mississippi Valley while its surface reflection will be lifting up 
the Ohio Valley. 


As a result...our confluent upper level flow will gradually give 
way to a diffluent flow while low level moisture will be on the 
increase. While the bulk of tonight should be precipitation free...the 
potential for some rain will increase across the western southern tier 
and Finger Lakes region as we progress into the wee hours of Monday 
morning. Temperatures will settle to between 35 and 40 for most 
areas...so there will not be a threat for any mixed precipitation. 


&& 


Short term /Monday through Tuesday night/... 
low pressure centered over Arkansas early this Sunday morning will 
become the main weather maker for our County Warning Area during this time period. 
The low is forecast to move northeast from the Ohio Valley 
Monday...then track east across PA Monday night before reaching the 
New England coast on Tuesday. 


Rain developing ahead of this system will continue to lift slowly to 
the north on Monday and impact the entire County Warning Area by Monday evening. 
Will continue to show a gradual north to south increase in probability of precipitation as 
moisture surges ahead of the low. 


Still looks like the steadiest rain will fall Monday night into 
Tuesday morning when increasing upper level diffluence ahead of the 
deep upper level low will enhance large scale lift across New York 
state. In terms of quantitative precipitation forecast...the latest HPC guidance indicates a general 
0.50 to 0.85 inch of rain across our County Warning Area through Tuesday with the 
highest amounts concentrated over the southern tier. 


Expect the steadiest rain to taper off gradually from west to east 
Tuesday and Tuesday night as the main center of the low shifts east 
into New England. The models still suggest that temperatures aloft 
will get cold enough Tuesday night to support a mix of rain and snow 
across the north country. 


&& 


Long term /Wednesday through Saturday/... 
drier air advecting in behind the departing low will bring mainly 
dry conditions on Wednesday with above average temperatures. 


Wednesday night...the NAM suggests a weak cold front with rather 
limited moisture will push east across New York state. A weak short 
wave accompanying the front may generate enough lift to generate a 
few rain and snow showers east of Lake Ontario for part of Wednesday 
night. 


Thursday, high pressure should bring fair weather with highs in the 
middle to upper 40s. A more significant cold front is forecast to cross 
the area Thursday night with limited moisture. The latest European model (ecmwf) is 
still not quite as cold as the GFS...but any precipitation that accompanies 
the passing cold front will likely change to snow showers before 
daybreak Friday. 


On Friday, the front moves further south into Pennsylvania and 
chilly high pressure over Quebec builds south into the region. Will 
leave in slight chance probability of precipitation from The Finger lakes westward as a cold 
northerly upslope flow south of Lake Ontario may generate an 
isolated rain or snow shower. 


The high will keep dry weather over the area Saturday...but both 
Friday and Saturday will likely see below normal temperatures with 
readings struggling to get out of the 30s east of Lake Ontario. The 
rest of the area should see temperatures in the lower to middle 40s. 


&& 


Aviation /18z Sunday through Friday/... 
for the remainder of this afternoon...have high confidence in VFR 
conditions...except for iag where there is a chance a scattered MVFR ceiling 
may go broken. Otherwise...VFR. 


It appears the GFS model is on the high side with its quantitative precipitation forecast 
tonight...with the majority of other models suggesting it is 
overdone. Therefore...will lean against the GFS MOS...closer to 
NAM MOS for the overnight period. This delays the onset of 
MVFR/IFR conditions as rain and lower ceilings will eventually spread 
in from the SW. Uncertainty increases after 06z as low moisture 
builds beneath a strengthening inversion. 


For Monday...generally expect precipitation to spread from SW to 
NE...though intensity and timing fairly uncertain...with a couple 
hour error in this possible. 


Outlook... 
Monday night...predominantly IFR in rain. 
Tuesday...rain likely...possibly mixed with snow. Predominantly 
MVFR. 
Tuesday night...a chance of rain or snow showers. VFR/MVFR. 
Wednesday through Friday...mainly VFR. 


&& 


Marine... 
no marine flags are expected through the rest of the weekend into 
Monday as relatively weak pressure gradients will be in place across 
the lower lakes. Increasing northeast winds ahead of an approaching 
low will cause more significant waves to develop Monday night and 
Tuesday. 


&& 


Buf watches/warnings/advisories... 
New York...none. 
Marine...none. 


&& 


$$ 


Synopsis...tjp 
near term...apffel/rsh 
short term...tjp 
long term...jjp/tjp 
aviation...apffel 
marine...tjp 

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