Scientific Forecaster Discussion
fxus61 kphi 250119
Area forecast discussion
National Weather Service Mount Holly New Jersey
819 PM EST Fri Nov 24 2017
an area of high pressure is just to our south tonight. A cold front
will cross the mid Atlantic states late Saturday, with a small
reinforcing cold frontal passage Monday afternoon. High pressure
builds across our region Monday night, then offshore Tuesday.
Another cold frontal passage is expected Tuesday night. High
pressure is expected to briefly build across the area Wednesday
night. Yet another cold front should arrive Thursday night or
Near term /until 6 am Saturday morning/...
forecast running on track, so no significant changes will be
made and will adjust hourly grids based on latest surface obs.
Otherwise, high pressure will continue to move away from the
region tonight and give way to an approaching cold front coming
into our region from the west by Saturday morning. South winds 5
to 10 miles per hour will go light and variable for most areas by midnight
or so tonight. Favorable conditions for substantial radiational
cooling on tap. Areas near The Pine Barrens and valley areas in
northern New Jersey will likely have another night in the 20's
with more urban locations and Delmarva in the 30's. Lows are a
couple degrees cooler than a met/mav blend for this reason.
Skies should remain clear given the high pressure as we will
still have some influence in our region.
Short term /6 am Saturday morning through 6 PM Saturday/...
enough lift and moisture should be present for mid and high
level clouds to move into the region late in the day. However,
dry air is present several thousand feet up on modeled
soundings. As a result, this forecast is rather skeptical for
any scattered rain showers to form in the afternoon with the GFS
likely overdone on quantitative precipitation forecast. Continued with slight shower chances in
the afternoon to account for this possibility though.
Temperatures will warm into the 50's with areas in eastern PA
seeing clouds coming in sooner to keep temperatures from warming
much above 50. New Jersey and Delaware will have more sunshine
and a better opportunity to take advantage of mid-level warmth
to make a run at 60 for highs, likely going a bit above met/mav
Long term /Saturday night through Friday/...
**basically rainfree through Thursday afternoon**
500 mb: a short wave trough crossing the the northeast Saturday
night intensifies and is reinforced over the Maritimes Sunday into
Monday night, temporarily keeping a substantial warmup over the
central USA at Bay. Ridging Tuesday begins a warmup in the
afternoon but that too may be cutoff as another short wave spins
eastward along the US Canadian border on Wednesday, with
ridging-warming resuming for Thursday.
Temperatures: the month of November as a whole was averaging
below normal through today. This mornings mins were 5 to 11
degrees below normal. Todays calendar day averages ranged from
+2f at kmpo to several degrees below normal elsewhere except 6
below normal at kged. Departures so far as of 11/23 are the
Model operational guidance Sat-Fri suggests that the average
temperature in this 7 day period ending December 1 will be at
least 4 degrees above normal. The warmest calendar day positive
departure of nearly 10 degrees should occur on Wednesday.
Ensembles from both models favor warm but I could see cool air
leaking southward, especially Tuesday. Also nights are likely
to see radiational cooling below guidance since its been dry
recently with no measurable rain forecast until Thursday night
or Friday. So Monday night and again Wednesday night could end
up below statistical guidance.
Forecast basis: as a start, and unless otherwise noted, Sat
night-Sun night a 50 50 blend of the 12z/24 GFS/NAM was used,
then the 12z/24 mex MOS for Monday, with the 15z/24 wpc 12 hr
gridded elements of pop, Max-min temps, as well as their 6 hour
TD/wind/sky for the long term period Monday night-Friday.
Saturday night...any evening sprinkle NW portion ends early and a
gusty northwest wind develops toward dawn Sunday. Clearing late,
except mostly cloudy Poconos where there is a slight chance of
flurries late. Confidence: well above average.
Sunday...partly to mostly sunny, breezy and Max temps about
8-10 degrees cooler than Saturday. Northwest wind gusty 25 to
35 mph, especially New Jersey and EPA. Confidence: well above average.
Monday...partly sunny and several degrees milder ahead of the next
cold front. Still a gusty west to northwest wind to around 20 mph.
Confidence: well above average.
Tuesday...low confidence on temps: the GFS since the 12z
Thursday/23rd cycle has been much warmer both on mins/maxs as
compared to the below normal model fcst of ggem and until
recently the European model (ecmwf). Todays ec warmed up. Otherwise sunny.
Wednesday...waa...partly to mostly sunny. Confidence: average
Thursday...partly to mostly sunny. Confidence: below average.
Friday...showers possible with the next cold front during the
morning but timing uncertainty. Confidence: below average
Aviation /01z Saturday through Wednesday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg,
kilg, kmiv, kacy and surrounding areas.
Tonight: VFR. S to SW winds 5-10 kt, becoming lgt/vrb. High
Saturday: VFR. Increasing mid and high level clouds in the
afternoon. Southwesterly winds becoming westerly late in the
afternoon and generally around or just under 10 knots. A few
wind gusts of 15 knots possible as well during the afternoon.
Saturday night...generally VFR ceilings early then VFR sct clouds
late. Isolated showers possible during the evening. Wind
becoming west to northwest and gusting 20-25 knots later on.
Moderate to high confidence on VFR conditions. Low confidence on
showers and any brief sub - VFR conditions. High confidence on
Sunday...VFR. Northwest wind gusty 25-33 kt, diminishing after
sunset. Confidence: well above average.
Monday...VFR. West to northwest gusty 20-25 kt. Confidence:
well above average.
Tuesday...VFR. Southwest wind. Confidence: well above average.
Wednesday...VFR. West wind. Confidence: well above average.
seas will remain rather steady around three feet into Saturday,
but will start to build Saturday afternoon. Seas will stay under
five feet. Southerly or southwesterly wind gusts around 10
knots will increase to 15-20 knots Saturday afternoon. High
confidence on sub-Small Craft Advisory conditions.
Saturday night-Sunday...Small Craft Advisory (sca) conditions
forecast and the advisory has been issued for northwest wind
gusts 25 to possibly as high as 35 kt, mainly Sunday morning.
Confidence: well above average.
Sunday night-Monday...Small Craft Advisory possible, mainly the Atlantic waters.
Monday night...winds eventually diminishing below the Small Craft Advisory 25
knot criterion. Confidence: above average.
Tuesday...conditions may return to Small Craft Advisory levels
late. Confidence: below average.
Wednesday...no marine headline anticipated. Confidence: average.
its dry now and will be windier and possibly drier this Sunday
afternoon. Right now, no action with our partners. Our relative humidity
forecast will need to drop another 5 to 8 percent for partner
discussion of a possible Sunday afternoon Special Weather Statement. There should be
no problem experiencing frequent gusts above 20 miles per hour Sunday
November average temperature departures at several long term
climate locations project as follows with the reality through
today and our 330 PM forecast through the 30th.
Normal forecast dep
Abe 42.7 42.6 -0.1
Acy international Airport 46.8 46.7 -0.1
Phl 47.6 47.0 -0.6
Ridge 44.1 42.9 -1.2
These departures from normal are one half to 1 degree warmer
than the departures so far, so that kmpo and krdg are likely
1-2f below normal, all others within +.5 to -0.7 (near normal)
except Ged may end up 1f above normal.
The greatest uncertainty is for the 28th-30th that show
potential for even warmer days that currently forecast.
When put in perspective... this looks to be a seasonable
Tomorrow we may know more on whether rain will occur prior to
midnight Thursday night and then look at rainfall rankings for 6
of our long term climate sites.
Marine...Small Craft Advisory from 2 am to noon EST Sunday for anz430-