Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
1044 PM EDT Wednesday Aug 20 2014
high pressure remains centered to the north and east of the area
through Thursday night. Meanwhile...waves of low pressure aloft
move across the region tonight and again Thursday into Thursday
night. An upper level disturbance will track through the area on
Friday as high pressure builds down from eastern Canada. This high
will gradually build down the eastern Seaboard through the middle
of next week.
Near term /until 6 am Thursday morning/...
showers continue to dry up as they approach western zones. 500 mb
shortwave will move across the region after midnight tonight...and
low level moisture will increase through the night...allowing for
precipitation to reach the ground. Best chances will be across western
zones...but will keep probability of precipitation capped at chance as the activity will
Lows tonight will drop into the upper 60s in/around NYC and in the
low to middle 60s most other locations. Eastern zones will drop into
the middle/upper 50s.
Short term /6 am Thursday morning through Thursday night/...
there will be some showers ongoing during the first half of the
day...as a shortwave swings across the area. Best chances will again
be across western and northern zones...as ridging noses in across
our eastern sections. Included isolated thunder across the approximate
western third of the area...where model fields indicate a little
more in the way of MUCAPE. Additionally...these areas will be less
influenced by the maritime air being advected across the area thanks
to east/southeast onshore flow.
Due to the aforementioned onshore flow and increased cloud
cover...temperatures will be cooler than the previous day...with many areas
staying in the 70s / below normal for this time of year.
As the first wave departs to the east Thursday afternoon and
evening...subsidence aloft and the continued surface ridging poking
in from the north and east will allow most places to be dry later in
the day. Chances will then increase again overnight...as the upper
low to the northwest opens and approaches the area.
Long term /Friday through Wednesday/...
models are in good agreement that the 500 mb pattern across noam at the
start of the long term period will consist of a strong broad ridge
across the southeast Continental U.S. With a deep trough out west with an upper low
cutting off over the Pacific northwest and an Omega block over eastern Canada with
a weak cutoff low moving through New England.
Some uncertainty with the specific details and timing of vorticity maxes
moving around the left side of the upper low once it slides
offshore...but the general trend appears to be decreasing chc's of
showers during Friday as deep layered ridging builds into the northeast
from the north. May need to add slight to low chance probability of precipitation at times through
Sat in subsequent forecast packages to account for these timing
differences. Additionally...the amount of cloud cover for Friday and
Sat is also questionable as a result.
Otherwise...expect dry and seasonable conds through the middle of
next week as the 500 mb flow amplifies in response to the blocking
pattern. Surface high pressure will build down the eastern Seaboard during this
time with an Ely flow expected at least into Monday. This will
contribute to below normal temperatures thought this time...but as
heights rise Tuesday and Wednesday...temperatures will rebound to near normal
Aviation /03z Thursday through Monday/...
weak high pressure remains over the area.
VFR...except tempo IFR at kgon early morning Thursday.
Light and variable winds overnight becoming mostly southeast at 10kt or less
Outlook for 00z Friday through Monday...
Thursday night...VFR. Scattered thunderstorms mainly south and west of the New York metropolitan.
with high pressure still extending across the waters Thursday...and
only starting to lift out Thursday night...winds and seas will
remain below Small Craft Advisory criteria during this time. Easterly flow will be on
the increase late Thursday though.
Wind gusts are expected to remain below Small Craft Advisory levels...although could
come close to 25 knots on the ocean waters late Friday/Friday evening. An
increasing east-NE flow will result in building seas on the ocean with
Small Craft Advisory conds expected between Friday night and Sun night. The gradient
relaxes thereafter with seas diminishing.
a few thunderstorms are possible on Thursday across the lower Hudson
Valley and interior NE New Jersey. Any storms will have the potential to
produce locally heavy rain...but basin averaged totals are forecast
to remain light...as any thunderstorms should be isolated.
No significant rainfall is expected in the extended.