Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Mount Holly New Jersey
1129 am EDT Thursday Jul 24 2014
a cold frontal boundary will continue moving offshore
today. High pressure will build across the Ohio Valley tonight and
on Friday. The high pressure system will move east of the region on
Saturday and be followed by the passage of a warm front from the
south by Saturday night and be located to our north on Sunday.
Another cold frontal boundary then will sweep from west to east
across the region on Monday. A high pressure system will build in
behind the cold front for the middle half of next week.
Near term /until 6 PM this evening/...
the cold front has moved south of our County Warning Area.
Next estf update we will shave back mention of probability of precipitation further. The
hrrr and cospa trend has been for less and less. This is likely
due to the cirrus shield slowing our temperature ascent to the convective
temperature as most of our temperature errors have been on the high side. Some
of the showers in Nova have been underdone by the mesoscale models,
so will keep a buffer low chance into central Delaware-Maryland-Virginia and parts of
southeastern New Jersey. Based on the slower temperature ascent and where they are
currently occurring, we now have the mention of thunder only in
our far southern County Warning Area and adjacent coastal waters. Fairly uniform maximum
temperatures away from the higher terrain expected this afternoon.
Short term /6 PM this evening through 6 am Friday/...
high pressure will build eastward and into the area tonight. Any precipitation will
end early and the sky will clear. Overall, a quiet night is in
Long term /Friday through Wednesday/...
Friday and Friday night: high pressure glides east from the Ohio
Valley into our region. Variable winds, plenty of sunshine and not
that hot since this airmass will be coming from Canada! Little
spread in the models on most if not all weather elements. Trickiest
part of this period is how much radiational cooling can occur in
rural areas before the flow turns more southerly by Saturday.
Opted to go a touch cooler than mex/mav/met in a few spots with
lows Friday night.
Saturday and Saturday night: a warm front approaches the region from
the south and with a departing high pressure the flow turns
southerly. Modeled momentum Transfer suggests some gusts close to 20
miles per hour are possible in the afternoon, went higher than a Standard
125% for wind gusts. Middle-level and surface temperatures look to
respond in kind after the warm frontal passage, 925 mb temperatures near 20-22c
should yield surface temperatures just under 90 for phl and in the
80's elsewhere across the region. Humidity is on the rise but this
will be like more typical July heat with heat index values well
under advisory levels. The warm front may provide enough lift for
some scattered showers and thunderstorms focused across the
northern part of the region. The 21z sref and the last two European model (ecmwf)
runs have these pined down well. Increasing cin coupled with 700
mb temperatures near 10c could allow for the formation of a weak cap
across the southern part of the region, being further away lower
chance probability of precipitation were warranted when compared to locations further
Sunday and Sunday night: continued west-southwest flow in the warm
sector. The last few GFS runs have been more aggressive with
convection by the afternoon and evening hours. A common theme this
Summer. Think the GFS is to aggressive with this. However, storm
chances should increase as the main low pressure system and cold
front approach the region. Good agreement among the GFS ensembles,
European model (ecmwf) ensemble mean and the operational models that the highest
chance will be Sunday night. Maintained low end likely probability of precipitation across the
north and high end chance across the south. For quantitative precipitation forecast stayed close to
the sref and European model (ecmwf) similar to Saturday. Though did raise it slightly
to account for the more aggressive GFS. Temperatures may be rain
cooled Sunday but did not go in that direction at this time. Fair shot at 90
for phl with slightly warmer modeled middle-level temperatures than
Monday and Monday night: the cold front moves through likely Monday
afternoon. However this should be to little to late in terms of
another round of showers and storms. The main cape axis is likely to
offshore at this time and little is left for a trigger besides the
actual frontal boundary. However maintained low chance probability of precipitation since the
front will still be in the region. Cleared conditions out Monday
night with a return to westerly flow. Another gusty day as once
modeled momentum Transfer shows potential for some gusts near 20
miles per hour.
Tuesday and wednesday: another Canadian airmass comes down into the
region as the same general pattern from the wintertime continues
with few breaks. Cool northwesterly flow will be in place as most
locations struggle to 80 for a high. Even with this abnormally cool
airmass there is good agreement among the mex, wpc and modeled two
meter temperatures. Trended slightly cooler than wpc given the
latest 00z European model (ecmwf) which is on the coolest end of the model guidance.
Lapse rates may steepen up Tuesday afternoon for the formation of
some cumulus and spotty showers/thunder on the backside of the trough
across the north with the aid of elevation. Otherwise both days
look mostly sunny.
Aviation /16z Thursday through Monday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Generally VFR conds are expected today. There could be some rain showers or
isolated tsra, mainly S later this morning through Erly evening which could
briefly decrease cigs/vsbys. However, odds are low enough to not
mention in the individual taf sites. Wind is expected to be northwest or
north around 10 kts today decreasing to less than 10 kts tonight.
Friday and Friday night: VFR
Saturday through monday: brief MVFR and IFR restrictions in
scattered thunderstorms. Highest chance for restrictions is on
Sunday afternoon and evening for rdg, Abe, ttn, and points north.
with high pressure building into the region, no marine headlines are
anticipated through the near and short term periods.
Friday through Saturday night: seas and winds expected to stay under
Small Craft Advisory criteria. A few wind gusts around 20 knots possible Saturday
Sunday and monday: seas increase to four feet on Sunday and perhaps
five feet by Monday morning before falling below five feet Monday
night. A few wind gusts around 20 knots possible Sunday and Monday