Scientific Forecaster Discussion
Area forecast discussion
National Weather Service New York New York
123 PM EDT sun Apr 26 2015
low pressure over the Canadian Maritimes and another low moving off
the middle Atlantic coast today will consolidate into a broad area of
low pressure over the western Atlantic Monday into Tuesday. A large
area of high pressure will build east across the region by middle
week. Low pressure moving off the southeast coast may impact the
region on Thursday.
Near term /through tonight/...
dry weather so far but diurnal cumulus have expanded and increased in
coverage across the region. Sea breezes have formed along the
coastlines. Temperatures...dewpoints...winds...and cloud coverage
parameters were adjusted to better match the observed trends. Maximum
temperature forecast still looks pretty much on track...overall
upper 50 to near 60. Still cannot rule out a brief light
shower...mostly across the interior for late afternoon into the
Water vapor indicates a large cyclonic circulation over eastern
Canada drifting westward. The models indicate this trend will continue
today. Shortwave energy associated with the system has weakened
significantly in the models. As a result...quantitative precipitation forecast is minimal in the
forecasts. The NAM indicates maybe a few sprinkles or very light
showers spreading southward down the Hudson Valley into the evening before
fizzling over the County Warning Area. Otherwise the data suggests dry. Went with
a dry forecast after 1z with loss of surface based instability. Guidance was
in good agreement with respect to temperatures...so went with a blend. Mixing above 850 mb
per model soundings...and the temperature cap looks to be in vicinity of the
developing cloud deck.
Short term /Monday through Wednesday night/...
scattered showers appear on track for Monday as the upper low center makes its
closest approach and slides down the eastern New England coastline. The
most robust activity eastern zones closer to the upper support. The NAM
only indicates 50-150 j/kg SBCAPE...with the highest values in vicinity of
the Rhode Island border. Rhode Island into eastern Massachusetts gets above 200 j/kg...if this entire system
shifts slightly westward...the isolated thunderstorm threat could extend into the
County Warning Area. For now...thunderstorms not included in the forecast. Temperatures around 0c at
850 mb...but deep mixing to around 800 mb will keep highs only a few
degrees blw climatology. The ribbon of shortwave energy then slides eastward Monday
night and Tuesday. As a result...gradually end precipitation chances Monday night and
kept Tuesday dry. Temperatures approach climatology with heights increasing and
deep mixing continues on northwest flow. Upper ridging then builds in on
Wednesday. A dry forecast Wednesday and Wednesday night. The warming trend continues as
the upper ridge axis builds in. Temperatures should reach into at least the
upper 60s along and west of the Hudson...but the weak pressure field should
result in fairly deep penetration of sea breeze flow.
Long term /Thursday through Saturday/...
the GFS has trended towards the European model (ecmwf) notion of deepening low pressure
somewhere near Hatteras Thursday...then tracking northeastward over the Atlantic Friday
and into the North Atlantic Sat. The model consensus in still that the system
misses US...with perhaps some showers in the warm air advection pattern on Thursday.
Maintained the low probability of precipitation in the forecast through the period...but changes weather
type to rain Friday-Sat as it appears the focus will be on the northern
extent of the precipitation shield as opposed to the development of showery
precipitation at this time. Temperatures a blend of previous and the gmos25.
Aviation /18z Sunday through Friday/...
a weak trough sets up across the area this afternoon. High pressure
then re-establishes itself tonight.
Broken instability this aft/eve. Isolated rain showers activity this
aft/eve...particularly CT terminals.
Weak north/NE flow under thermal trough with winds veering to S for
coastal terminals and backing northwest for western terminals. Seabreeze
along the CT/NYC/Li coast will continue to work north through the
afternoon. Increasing probability for klga to seabreeze late this
afternoon...and moderate probability at kewr.
Winds weaken and become northwest this evening as high pressure
strengthens...with strato-cumulus gradually scattering overnight.
Broken 040-060 strato-cumulus development expected Monday with scattered
shower development in the aft/eve. Brief MVFR possible with rain showers
in the afternoon. Low probability for isolated thunderstorms and rain...mainly kgon. Northwest
winds 10 to 15 knots with gusts to 20 knots Monday afternoon. Winds
generally right of 310 true.
Outlook for 18z Monday through Friday...
late Monday-Monday night...possible MVFR with showers.
Tuesday-Wednesday night...VFR. Isolated rain showers possible Tuesday.
Thursday...VFR. Low probability for -shra.
Friday...low probability for coastal storm.
sub-Small Craft Advisory conditions are forecast through the middle of next week as a
large area of high pressure over the middle section of the country
works slowly east. Marginal gusts are possible Monday night into Tuesday on
the ocean waters as a northerly flow strengthens between a broad area of
low pressure over the western Atlantic and high pressure building in
from the west. Low pressure moving off the southeast coast Thursday may impact
the waters with a strengthening easterly flow and building seas.
significant precipitation is not expected through next week.