Area forecast discussion
National Weather Service New York New York
1147 am EDT sun may 19 2013
Synopsis...
a stationary front will remain to the S through tonight...then
lift to the north Monday into Monday night. A cold front will drop
through on Tuesday...then remain nearby before lifting back north
as a warm front on Thursday. A cold frontal passage will occur
late in the week or early next weekend.
&&
Near term /through tonight/...
weak warm air advection causing light rain to progress across the area this
morning. Updated probability of precipitation today and tonight based on latest radar
trends...with the rain shifting more into eastern sections this
afternoon. Do not see much in the way of forcing tonight so pop
only low chance...with areas of fog/drizzle as low levels remain
very moist.
There is some weak instability aloft late tonight and early Monday
morning...so mentioned isolated thunderstorms.
Highs will only reach the lower 60s today...5-10 degree below average.
Lows tonight will be near to slightly above average...in the middle and
upper 50s.
&&
Short term /Monday through Tuesday/...
the region will be warm sectored on Monday as a cold front
approaches from the north. Expect at least partial clearing to
occur...which will determine amount of daytime heating/instability.
As front aligns with the flow aloft which is relatively weak
/10-20 knots/ and as precipitable water increases to 1.5 inches there is possibility
of training of slow moving heavy showers/thunderstorms with
attendant urban flooding issues. Confidence low at this time.
Any convection should wane Monday evening as the front drops through.
Uncertain just how far S the boundary gets...kept chance pop for
afternoon showers/thunderstorms on Tuesday...mainly north and west of NYC.
Temperatures will be around 5 degrees above average...with a noticeably more
humid air mass in place as well.
&&
Long term /Tuesday night through Saturday/...
predictability issues during this time period have to do with the
interaction of eastern Canadian troughing and central US troughing
this week. The interaction of these two energies will determine the
magnitude of East Coast ridging for the midweek. Models signaling a
return to East Coast troughing for the weekend as East Coast ridging
builds offshore into the western Atlantic.
Showers and thunderstorms could continue Tuesday night...with
indications of a wave of low pressure tracking east along the
sagging frontal boundary. Moisture pooling and steering flow
parallel to the surface boundary would present a flash flood
threat if this pattern materialized.
Then for the middle-late week period the interaction of the earlier
mentioned upper features will be critical to the location of the
frontal boundary. Latest guidance has strongly converged on the
backdoor cold front pushing south through the region Tuesday
night...and then back north as a warm front on Thursday. If the
front does pass south...onshore flow and clouds would likely drop
maximum temperatures to seasonable or slightly below seasonable levels for
Wednesday...several degrees cooler then forecast.
Regardless of where the warm front ends up...if this boundary
remains close to the region...shortwaves at the southern edge of the
westerlies may allow for convective complexes to form and track west
to east along this boundary through the middle-late week period. Any
mesoscale convective system would bring the threat for heavy rain and severe weather.
By the end of the week...models are signaling varying degrees of
phasing of the Midwest upper trough and eastern Canadian upper
trough. This will have a cold front passing through the region
sometime Friday into Sat...with shower and thunderstorm activity
finally exiting in it wake. Degree of phasing of upper energies will
determine timing and activity along the front.
&&
Aviation /15z Sunday through Thursday/...
high pressure passes to the east today as a frontal boundary
remains to the south.
Ceilings around the NYC metropolitan terminals have fallen to MVFR and IFR
thinking at this time...little improvement is expected today. So
adjusted tafs accordingly. Terminals east of NYC...remain VFR.
Would expect conditions to fall to MVFR as the day progresses. Do
expect on and off light rain this morning for most terminals. Kgon
may not see rain until this afternoon.
Please see individual terminal forecasts for specifics and best
deterministic forecasts...but MVFR ceilings likely prevail through
much of the afternoon with a lower probability of ceilings under
1 kft.
Expect IFR or lower ceilings/visibilities to continue this evening and
remain through tonight.
Winds generally southeast...with higher sustained winds during the
daytime hours. Winds turn to the south or southwest tonight and
will be light.
Outlook for 12z Monday through Thursday...
Monday...improvement to VFR by middle to late morning. Scattered
showers...and isolated thunderstorms with brief MVFR conds possible
in the afternoon.
Monday night...MVFR or lower conditions likely with low clouds and
fog.
Tuesday-Thursday...chance of MVFR of lower conditions in showers
and thunderstorms.
&&
Marine...
high pressure passes east of the waters today. As it does
so...southerly winds will increase to 15 to 20 knots...mainly across
the ocean waters. Ocean seas still only 2-3 feet...but could touch 5
feet by late day...so pushed start time of ocean Small Craft Advisory forward to 4
PM.
By tonight...low pressure passes to the north of the waters. Winds
turn toward the southwest through Monday. A frontal boundary
approaches from the north by Tuesday...and winds lighten and could
shift around to the northeast or east depending on how far south
the front moves.
Eventually this front is expected to move back to the north
resulting in a wind shift to the south once again by middle week.
Wave watch has been running high...but latest guidance has captured the
trends and slowly builds seas today. May undercut ocean sea forecasts
slightly early in the week...but seas remain rather rough through
Monday on the ocean waters due to persistent southerly fetch and
swells.
Will follow wind direction and speed climatology for sea/wave forecasts
across Li sound and the surrounding harbors and bays.
&&
Hydrology...
up to 2 tenths of an inch quantitative precipitation forecast expected through tonight.
Periods of showers/thunderstorms Monday through Friday...are capable of
producing locally heavy rainfall...with an attendant low flash
flood threat.
&&
Okx watches/warnings/advisories...
CT...none.
New York...none.
New Jersey...none.
Marine...Small Craft Advisory from 4 PM this afternoon to 9 am EDT
Monday for anz355.
Small Craft Advisory from 4 PM this afternoon to 6 PM EDT
Monday for anz350-353.
&&
$$
