Scientific Forecaster Discussion
fxus61 kokx 220123
Area forecast discussion
National Weather Service New York New York
923 PM EDT Sat Oct 21 2017
high pressure remains over the region through Monday.
Strengthening low pressure heads northward into southeast
Canada Monday night into Tuesday with its associated cold front
approaching the region. The cold front will slowly move into the
region Tuesday into Tuesday night. The front will become nearly
stationary Wednesday before gaining more eastward movement
Wednesday night, moving east of the region by early Thursday.
An upper level disturbance follows for Thursday before weak
high pressure settles in late next week.
Near term /until 6 am Sunday morning/...
update for latest temperature/dew point trends, which were
cooler than forecast. Much depends on extent of cloud coverage
for the cirrus moving across. Min temperatures adjusted slightly
based on trends.
One caveat is that with the increase in dewpoints, if clouds
were to decrease more overnight, there could be more in the way
of patchy fog where more radiational cooling is realized. At
this point though, this is a very low probability.
Short term /6 am Sunday morning through Monday/...
high pressure will be situated just offshore with another dry and
mostly sunny day Sunday, with only some cirrus filtering the
sunshine at times. High temperatures will be above normal, but
likely a couple of degrees cooler than yesterday in most cases.
Low level moisture increases Sunday night with a light southeast flow.
Models suggest stratus moving in with better chances of at least a
broken deck occurring west of eastern Li and CT. This leads to a
partly to mostly cloudy Monday. There appears to be enough
isentropic and low level lift for a chance of showers in the
afternoon. Showers would be light as mid levels remain dry. Better
chances are once again west of eastern Li and CT. In spite of the
clouds and onshore flow, highs will still range mostly 70-75.
Long term /Monday night through Saturday/...
deep upper level trough with strong meridional flow will be
approaching the region Monday night as the jet dives into the
southeast. The trough will stretch from Florida through southeast
Canada Tuesday into Wednesday. At the surface, the parent low
pressure area moves from the Great Lakes Monday night into northern
Quebec by early Wednesday. With all the southerly steering flow,
the cold front will have little eastward movement, coming to
almost a halt Wednesday before gaining more eastward movement
Wednesday night. This will be in response to another upstream
diving shortwave that is forecast to move northwest to southeast from the
north central US into the Carolinas. Thereafter, the upper level
trough axis moves across Thursday while the surface cold front
moves farther east into the Atlantic. Ridging and high pressure
return but will be of lesser magnitude late next week.
In terms of weather, rain showers will become more widespread Monday
night into Tuesday, lingering into Tuesday night. Bulk of rain
expected Tuesday afternoon through Tuesday night. The front nearly
coming to a halt Wednesday will keep showers in the forecast
Wednesday before tapering off Wednesday night. The region could even
still see some showers Thursday with the upper level cold pool
associated with the trough axis moving across. Models are
hinting at this with their small quantitative precipitation forecast as the flow becomes more
westerly. Then, mainly dry weather is expected Thursday night
through next Saturday.
Winds could potentially be an issue Tuesday through Tuesday
evening. There is a low level jet ahead of the cold front and
the models have pretty good agreement with the magnitude being
near 50kt Tuesday into Tuesday night. With the deep trough and
high precipitable waters forecast, near 1.75 to 1.8 inches, very
high (above 90th percentile) for this time of year according to
okx sounding climatology, heavy rain will be possible at times,
especially in any thunderstorms. The thunderstorm chances will
be there with strong Omega and low level instability present
within the model guidance. Low level instability is diagnosed
from model cape fields between 100 and 300 j/kg. S-southeast winds of
20-25 mph with gusts 30 to 40 mph are looking more probable
especially along the coast with locally higher winds possible
with any heavier showers or thunderstorms that could potentially
bring down higher winds with downward momentum transport.
Temperatures forecast of lower 70s for highs Tuesday and upper
60s to 70 for highs Wednesday. Highs more in the 60s for the
rest of the days in the long term.
Aviation /01z Sunday through Thursday/...
VFR expected through the taf period as high pressure remains
overhead overnight, then moves east Sunday. High clouds (cirrus)
There is a very low probability of MVFR-IFR fog late tonight at
Winds become light and variable overnight. S/southeast winds 8-12 kt
develop Sunday afternoon.
Outlook for 00z Monday through Thursday...
Sunday night-Monday...MVFR/IFR possible in stratus and fog Sunday
night into Monday morning, then VFR. S/southeast g20 kt Monday afternoon.
Monday night-Tuesday...potential for 6 hr period of S/southeast
g30-40 knots with low level wind shear south-southwest 45-55kt@2kft for coastal terminals. Could
occur during morning push. MVFR/IFR developing in -radz Monday
night, continuing with rain shower and low prob/sparse thunderstorms and rain Tuesday.
Tuesday night-Wednesday...IFR possibly continues in showers
Tue night...improving to MVFR Wed.
Wednesday night-Thursday...VFR, with iso-sct MVFR in showers. West/northwest
tranquil conditions on the waters overnight through Sunday
night as high pressure ridge with a weak pressure gradient
shifts offshore and slowly drifts out to sea. Onshore winds pick
up through the day on Monday, but conditions will remain below
Small Craft Advisory conditions become more probable Monday night on the ocean and
likely Tuesday through Thursday on the ocean. Gales will be
possible Tuesday and Tuesday night, mainly across the ocean with
Small Craft Advisory conditions being likely on non-ocean waters. For Wednesday
through Thursday, the ocean Small Craft Advisory conditions are mainly due to
lingering high seas.
localized minor urban flooding will be possible Tuesday into
Tuesday night but otherwise no other hydrologic problems are
expected with the storm total rain of 1.5 to 2.5 inches mostly
falling Monday night through Wednesday. Locally higher amounts
will be possible.