Area forecast discussion
National Weather Service New York New York
351 am EDT Tuesday may 21 2013
Synopsis...
a frontal boundary remains just north of the area today through Wednesday.
A cold front will pass through the area Thursday evening into
Thursday night. High pressure will return for the weekend and early
next week.
&&
Near term /until 6 PM this evening/...
will need to monitor fog/stratus early this morning. Lack of observation
has made it more difficult early this morning to ascertain extent
of fog this morning...but will maintain dense fog advisory for now.
Otherwise...frontal boundary remains to the north as ridge builds
aloft. The front will move little as it remains parallel to upper flow.
A general south to southwest flow prevails...and expect
temperatures away from the south facing shores to soar today. 800 mb
hpa temperatures 12-16c...and forecast soundings indicate temperatures to 30c or
greater during maximum heating. MOS temperatures generally accepted with 80s
many locations...except 70s eastern Long Island and southeastern CT.
Marginal instability is expected to build by afternoon...assuming
dew points remain in the middle 60s. However...these dew points
likely mix out slightly as lapse rates steepen. Thermal trough
could be the focus for some convection...but the bulk of the
showers and thunderstorms should ride along the front. As such...interior
sections should see highest chances for precipitation this
afternoon...but mesoscale model forecast reflectivity moving southeast toward
coastal locales by evening...although likely weakening as they hit the
marine layer.
&&
Short term /6 PM this evening through 6 PM Wednesday/...
any lingering convection this evening should diminish in coverage
as the night progresses. Although frontal boundary nearby could
trigger an isolated shower or thunderstorm overnight. Main issue tonight
will be the development of fog once again as southerly winds
prevail and the airmass remains quite moist.
Lows will be quite warm...60s per MOS.
For Wednesday...ridge slowly shifts east as upstream trough
finally makes eastward progress. However...another warm day is on
tap. Morning fog and stratus will give way to at least partial
sunshine. Once again...convection should be scattered at best with
weak to marginal instability in place.
&&
Long term /Wednesday night through Monday/...
a cold front is expected to drop southeast from near the Canadian
border Wednesday night into Thursday morning. The cold front is
expected to move across the area Thursday evening triggering scattered
showers and thunderstorms. This front will then move offshore by
Friday morning with a wave of low pressure moving northeast along
it...keeping showers across the area through Friday afternoon.
Expect highs on Thursday to be in the middle to upper 70s with lows
Thursday night in upper 50s to around 60.
Friday night through Monday...an area of high pressure will
drop southeast from central Canada into the central US and build
eastward through Memorial Day. Highs Saturday through Memorial Day
are expected to be in the upper 60s to around 70 with lows in the
middle 40s to lower 50s.
&&
Aviation /08z Tuesday through Saturday/...
warm...moist air over the region is resulting in the formation of
fog. Conds ranging from VFR to LIFR across the area...but visibilities
have been trending down and expect this to continue through
sunrise. SW flow typically does not produce widespread LIFR/vlifr
fog...but the best chance would be at kbdr/kisp/kgon with the flow
off the water. Khpn is also expected to drop to these levels as
well. The rest of the terminals should eventually reach at least
IFR...but timing and duration is uncertain. Amendments may be
needed through into the daylight hours. Patchy LIFR stratus may
also develop...however it's a bit difficult to see on infrared Sat due
to thin high clouds. Conds gradually improve to VFR by midday.
Meanwhile...a cold front will slowly sag down from the north with
a surface trough developing in the Lee of the Appalachians. Convection
may fire on either of these boundaries...but there's some question
how far S and west thunderstorms will make it before the fizzle due to the
loss of daytime heating. Only have tempo at kswf late this
afternoon/early evening for this.
Fog/stratus likely tonight...however timing is uncertain.
Outlook for 06z Wednesday through Saturday...
Tuesday night...becoming IFR with fog and stratus.
Wed-Fri...scattered showers/tstms. At night...IFR possible
with stratus/fog.
Sat...VFR.
&&
Marine...
dense fog across the waters this morning should improve some by
afternoon. South winds prevail through the day today...but sub Small Craft Advisory
conditions are anticipated.
Continued south to southwest flow is forecast for tonight and
Wednesday as a frontal boundary remains to the north. Deep low
level inversion and minimal temperature/dew point spread will warrant
inclusion of fog over the waters tonight and possibly into
Wednesday.
Seas will remain below 5 feet over the ocean waters...1 feet or less
elsewhere today and likely tonight.
Latest wave watch iii guidance for the ocean waters suggest 5 to
6 feet seas by Wednesday due to persistent south flow and possible
southerly swell. However...wave watch has been overforecasting
seas by a foot or two...so confidence in this happening is not
high at this time.
Seas expected to be above Small Craft Advisory levels Wednesday night...with 25 knots
wind gusts possible on the ocean waters by Wednesday evening. A cold
front will move across the area waters Thursday evening into
Thursday night...with high pressure building in at the surface on
late on Friday. Winds could be below Small Craft Advisory levels by Friday
morning...with seas remaining above Small Craft Advisory criteria through Saturday
morning.
&&
Hydrology...
isolated to scattered showers or thunderstorms late in the day today...mainly
inland. Impacts will be minimal.
Scattered showers/thunderstorms Wednesday-Thursday will be capable of producing locally heavy
rainfall...with the best chances north/west of NYC. Total basin
average quantitative precipitation forecast for Wednesday-Thursday could be 1/4 to 1/2 inch...with locally higher
amts in thunderstorms.
For details on specific area rivers and lakes...including observed
and forecast river stages and lake elevations...please visit the
advanced hydrologic prediction service /ahps/ graphs on our website.
&&
Okx watches/warnings/advisories...
CT...dense fog advisory until 10 am EDT this morning for ctz009>012.
New York...dense fog advisory until 10 am EDT this morning for nyz071-
078>081-177-179.
New Jersey...none.
Marine...dense fog advisory until noon EDT today for anz330-335-338-340-
345-350-353-355.
&&
$$
