Scientific Forecaster Discussion
fxus61 kphi 241155
Area forecast discussion
National Weather Service Mount Holly New Jersey
655 am EST Wed Jan 24 2018
high pressure will build into the eastern United States through the
end of the week before proceeding offshore on Saturday. A strong
storm system with an accompanying cold front will move through the
region Sunday and Monday. High pressure builds back into the
northeast by the middle of next week.
Near term /until 6 PM this evening/...
today...mostly cloudy this morning with probably some thinning
of the cold air advection cloud cover mid afternoon. A few
flurries/sprinkles near and north of I-78 early today with caa.
Southern Delaware should see more sunshine today than elsewhere.
A gusty northwest wind of 25 to 30 mph this morning- midday
should diminish a bit by mid afternoon. Stayed close (raised 1f)
to the prev fcst Max temps which are decidedly cooler than the
00z/24 GFS MOS. Still the daytime high temp should be within 4f
Short term /6 PM this evening through 6 am Thursday/...
mid and high cloud increases late, especially PA New Jersey. Otherwise
a diminished wind but temps/winds were basically a continuity
forecast from the previous 330 PM Tuesday forecast. Low temps
basically within 2f of normal. I could see these temps running a
few degrees warmer if it becomes overcast for several hours.
Long term /Thursday through Tuesday/...
progressive pattern will continue across the U.S. Through the
period with a surface low moving near or through the area Sunday
and a potent northwest-flow vort Max moving through Monday and
Monday night that will bring our next chance(s) for
Thursday and Friday will feature a trough departing the East
Coast with upstream ridging progressing into the area. A broad
surface high will encompass the region during this period, with
the northern extension of the high originating from central
Canada. This means temperatures will be colder than average,
especially Thursday and Thursday night, before thicknesses
increase with the approaching midlevel ridge on Friday. The GFS
is somewhat more progressive than the CMC/ECMWF, with the
associated statistical guidance considerably warmer on Friday
(10 degrees warmer for phl, E.G.). ensemble simulations and
consensus guidance suggest that the GFS is probably on the fast
side, so I kept temperatures much below mex MOS on Friday,
though not as cool as European model (ecmwf) MOS would suggest. Temperatures
Thursday night are also of somewhat lower confidence, as the
combination of light winds and clear skies will likely allow
temperatures to tank in especially prone Rural/Valley locations.
MOS has been woefully inaccurate in these scenarios much of
this winter, so the lows forecast are below consensus and
potentially still too warm.
Temperatures climb quickly this weekend, with temperatures 10 to
20 degrees above average Saturday and Sunday. The familiar
forecast adjustments were made here, generally increasing
highs/lows at least a degree or two above consensus based on
biases observed for the past year in these patterns. With the
approaching system on Sunday, did not go too out of hand with
temperatures yet, given increased cloud cover and potential
effects of precipitation.
Saturday night and Sunday, a midlevel vort Max will lift east-
northeast through the central U.S. Into the northeast by Sunday
night. There remain considerable differences in the synoptic-
scale details of the associated trough, with the GFS
flatter/faster than the European model (ecmwf) (with the CMC in between). With
tuesday's system, the GFS ended up being too fast and the European model (ecmwf)
was a tad too slow, so a consensus approach on timing is
probably a good idea, though the forecast is weighted much more
strongly to the CMC/European model (ecmwf) timing (which worked out well for the
system affecting the area on tuesday).
The greater uncertainty is with the position/track of the
developing surface low, though there is improved consensus for a
track from the Ohio Valley into the northern mid-Atlantic and
southern New England Sunday and Sunday night. This places the
County Warning Area in the warm sector Sunday, so precipitation will likely be
all liquid during this period. Rain looks especially likely
during the day, with the best consensus between 12z Sunday and
00z Monday, when pops are highest. Quantitative precipitation forecast looks fairly tame, with
the strongest ascent generally north of the area (and then east
as a southern-stream vort Max aids in large-scale lift as the
attendant front moves offshore). However, given the large
discrepancies in spatial details and remaining timing
uncertainty, broadened pops from Saturday night through Sunday
night and cannot rule out higher quantitative precipitation forecast than consensus (which
currently is generally in the 0.10-0.50 inch range for the
Perhaps the most challenging (and interesting) aspect of the
long-range forecast is the upstream behavior of the system, with
ensemble trends strongly favoring a deeper trough. This implies,
for starters, that temperatures may be too warm in the current
operational suite, and there may be sufficient instability
upstream of the front for showers Monday and Monday night,
especially as a kicker vort Max digs into the mid-Atlantic
during this period. The 00z European model (ecmwf) paints a rather interesting
scenario Monday night, with some light snow occurring in parts
of the area as the vort Max swings through. Would like to see
better consensus among the guidance before changing the forecast
too much, but I did extend low pops through Monday night, with
temperatures cold enough for snow in most of the area by the
evening hours. Further refinements to the forecast are likely
here as a lot of model differences need to be worked out.
High pressure builds back in Tuesday and Wednesday, which spells
another cold/dry period for the area.
Aviation /12z Wednesday through Sunday/...
the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg,
kmiv, kacy and surrounding areas.
Today...VFR cigs at or above 4,500 feet thinning this afternoon
to scattered clouds toward sunset. West to northwest winds
10-15 knots with gusts up to 25 knots, perhaps even 28 kt this
Tonight...VFR. Sct-bkn clouds aoa 4000 ft, mostly aoa 15000 ft.
Northwest wind may gust 15 kt.
thursday: VFR with northwest winds 10 to 15 kts with occasional
gusts to 20 kts or so. Somewhat above average confidence.
Thursday night and friday: VFR with light/variable winds. High
Friday night and saturday: VFR with winds between southeast and
southwest 5 to 15 kts (potentially stronger near the coast and
in delmarva). Average confidence.
Saturday night: south to southwest winds 5 to 15 kts
(potentially stronger near the coast) with increasing
cloudiness. Increasing chances of rain, especially west of phl,
with sub-VFR conditions possible. Below average confidence.
Sunday: periods of sub-VFR conditions likely with a good chance
of rain. Winds generally southwest 5 to 15 kts. Average
Small Craft Advisory today only. Water temps cooler than the overriding airmass
and therefore momentum Transfer is limited. Nevertheless, a
pulse of caa later this morning should boost gusts to 25 kt in
the CW for a time. These winds are now developing as this is
written. Its possible, in part dependent on what happens late
this morning, that the Small Craft Advisory may need an extension into tonight,
and even tomorrow but for now...a conservative approach was
applied to the headline due to our uncertainty. We had to lower
our modeled gust speeds over the water, and raise the gusts over
Thursday: marginal advisory conditions possible, especially in
the morning, but confidence is not high.
Thursday night through Friday night: no headlines anticipated.
Saturday and Saturday night: low-end advisory (south to
southwest) winds and seas possible, especially off the New Jersey
Sunday: southwest winds may gust around 20 kts or so, but the
current forecast is for sub-advisory conditions. A good chance
of rain, with visibility restrictions possible.
forecast points...monitoring the Delaware, well within its
banks and expected to remain so. Still the runoff and some ice
forced some decent rises vcnty Tocks Island overnight. At 645 am
the Delaware has at least temporarily stabilized at Tocks Island
near 14 feet...well below the 21 ft fs. No action anticipated,
River ice...we continue to receive reports of solid ice cover
on the Delaware River, but conditions are not as widespread as
last week. We know of solid ice near Trenton from about the
Route 1 bridge south down to about borderntown, or near the Head
of the Tide. We also know of ice further north near and in the
Delaware Water Gap.
With the warm temperatures the last few days combined with yesterday's
rains and rising water levels, melting and fracturing ice will
occur. Restrictions in flow or ice jams are possible as ice
breaks up and begins to move.
Since ice jams can not be predicted with certainty, the best approach
is awareness and to take notice of day to day changes on a river
or stream of concern.
for what its worth: Acy is already 8" above the entire seasonal
normal snowfall... 24.2" vs entire season 16.2.
January average temps...negative departure will warm another
degree or degree and one half for the rest of the month over the
entire area so that monthly norms will be below normal except
possibly Abe and phl.
For phl: based on our forecast these last 7 days of the month,
the month will average normal. That is about 1.2f warmer than an
in-house prediction on the 18th.
So, food for thought. If one were to look at monthly averages
as a determinant of climate, one might look back at phl climate
for January and not see anything unusual (presuming we end up
within 1f of normal). Except we all know better.
The two week period of December 24-Jan 6 was the third coldest
in that period of time for phl, using climate perspectives and
looking back 146 years=equivalent to living in Milwaukee.
Wilmington was 2nd coldest looking back 125 years for that
specific two week period and also equivalent to living in
Atlantic City was 3rd coldest.
For Allentown looking back 96 years, that two week period was
the coldest ever for that time frame and equivalent to living a
normal day-day life in Anchorage.
Marine...Small Craft Advisory until 6 PM EST this evening for anz430-
near term...drag 655
short term...drag 655