591 
fxus61 kokx 061939 
afdokx 


Area forecast discussion 
National Weather Service Upton New York 
339 PM EDT Monday Oct 6 2008 


Synopsis... 
a large area of cool Canadian high pressure will build over the 
region on Tuesday and then slide south of the area on Wednesday 
resulting in clear/sunny skies. Milder temperatures along with 
clouds and possibly light precipitation is expected to return 
Thursday into Friday as a southwesterly flow set up. The unsettled 
weather may continue into the weekend. 


&& 


Near term /until 6 am Tuesday morning/... 
upper level short wave clearly seen on water vapor imagery continues 
to rapidly swing southeast across the region pressing the cirrus 
deck off well to the southeast. Thicknesses are actually 540 or less 
dm over the eastern areas late this afternoon - but rise 
significantly overnight. 


Clouds/light precipitation from the instability and cold advection this 
afternoon will quickly dissipate with the loss of heating and the 
increasing stability. North-northwest flow prevails in the low levels through 
morning and only the protected locals will decouple from the 
boundary layer. 


Low temperatures in the 40s (50 lga) for most locations except well inland 
where 30s prevail. (Upper 30s in The Pine Barrens of Li - but wind 
prevents being even colder there) 


Frost advisory is up - but thinking is that this will be mainly 
patchy frost in the protected valleys. Will reword the advisory 
to reflect this idea. 


&& 


Short term /6 am Tuesday morning through Thursday/... 
high pressure slides southeast across the region on Tuesday. Light 
winds for Wednesday am with clear skies indicates more of a 
widespread frost and will include interior Suffolk County as 
well. Temperatures by Wednesday morning drop into the 20s in the 
northwest per mav MOS (which is cooler than other mos), which 
seems good based on the clear skies and calm winds. Thus am 
issuing a freeze watch and wording the colder areas as widespread 
frost. This should be the killing frost - normal time for first 
frost is Oct 10 for our northern areas. 


Return flow warms temperatures for Wednesday night as clouds advect in. 


Light precipitation possible by late Thursday. 


&& 


Long term /Thursday night through Monday/... 
still large differences in the medium range model guidance for later 
this week...especially with regard to Pacific jet energy moving ito 
southern Canada...which in turn translates to low forecast 
confidence. The 00z European model (ecmwf) was more aggressive with this jet 
energy...undercutting eastern Canadian ridging beginning Thursday and 
producing drying northwest flow aloft for Friday and beyond as strong high 
pressure develops/builds down from the Great Lakes. Meanwhile...a 
southern stream cutoff low gets trapped underneath a building long 
wave ridge along 80w...which is suspect as European model (ecmwf) southerly bias with 
southern stream cutoff lows may be coming into play. 


The 12z GFS is weaker with the jet moving across Canada and appears 
to be trending toward the ecwmf...but does not allow the southern 
stream low to become cut off from the westerlies...bringing it up 
into the area with a good shot of rain Friday into Friday night. 


Both models have also dug their heels in with respect to 
trends...and the Canadian has flip-flopped from a GFS-like solution 
in the 00z run to European model (ecmwf)-like in the 12z...further reflecting the 
uncertainty. As a result will have to carry low chance pop through 
much of the long term...with very low confidence in forecast 
details. 


&& 


Aviation /20z Monday through Saturday/... 
VFR through the taf period. Will have a brief period of broken 
050-100 developing from north to S from 19-20z then dissipating 
around sunset. Will be sky clear after that. 


For winds...observations not showing gustiness originally 
advertised for this afternoon...except at higher elevations...so 
have removed from tafs. Still cannot rule out one to two hors of 
gusts of 15 to 20 knots...but not enough confidence to reflect in 
tafs. Winds will become northwest at all terminals within the next 2-3 
hours at around 10 knots (from northwest to se)...then become northerly at 
around 5 knots (light and variable northern lower Hudson Valley 
terminals and kteb) overnight...then pick back up out of the northwest 
at around 10 knots by middle morning. 


Outlook for 18z Tuesday through Saturday... 
VFR through Thursday. A slow moving storm system will possibly 
bring sub-VFR conditions from Thursday night into 
Saturday...depending on its exact track. A low confidence forecast 
in the extended for the weekend. 


&& 


Marine... 
high pressure slides across the region on Tuesday changing the 
flow to southerly on Wednesday. Tranquil winds and seas expected 
through Thursday. 


For the long term...forecast reflects quiet conditions from Thursday 
night and beyond...but confidence is low beginning Friday night. If 12z 
GFS solution of weak low pressure moving up the coast comes to 
pass...Small Craft Advisory conditions in the form of hazardous seas could occur Friday 
night into Sat night. 


&& 


Hydrology... 
no major hydrology concerns through the forecast period at this time. Some 
light precipitation is expected late Thursday into Friday. 


&& 


Okx watches/warnings/advisories... 
CT...frost advisory from 2 am to 8 am EDT Tuesday for ctz005>008. 
New York...frost advisory from 2 am to 8 am EDT Tuesday for nyz067-068. 
Freeze watch from late Tuesday night through Wednesday morning 
for nyz067-068. 
New Jersey...frost advisory from 2 am to 8 am EDT Tuesday for njz002. 
Freeze watch from late Tuesday night through Wednesday morning 
for njz002. 
Marine...none. 


&& 


$$ 
Synopsis...jst 
near term...jst 
short term...jst 
long term...bg 
aviation...pfm 
marine...bg/jst 
hydrology...jst