Area forecast discussion National Weather Service Mount Holly New Jersey 941 PM EST Sat Nov 22 2014 Synopsis... strong high pressure is edging offshore. Low pressure developing over the Central Plains will rapidly intensify as it moves into the Great Lakes Sunday night...drawing a strong warm front north through our area. The low will be near James Bay Monday evening as it sends a cold front eastward across the eastern Seaboard states. High pressure follows later Tuesday. Low pressure develops off the Carolina's Wednesday and moves east of New England on Thanksgiving. Canadian high pressure heads southeast into the Ohio Valley Friday. && Near term /until 6 am Sunday morning/... high pressure will continue to shift off the middle Atlantic coast through tonight. As the flow backs some more in combination with a surface high sliding to our southeast, a large area of warm air advection will occur through tonight. This is more noted to our west and northwest closer to the core of a low-level jet. This will maintain some isentropic lift as the warming chips away at the remaining cooler airmass at the surface. This process is leading to an area of cloudiness that continues to spread east across much of the County Warning Area. The warm air advection and associated lift with the aforementioned short wave has been generating an area of light precipitation from central New York/Pennsylvania on northeastward. Some of this will move across our region through this evening in the form of sprinkles, however with the main low- level jet passing to our north along with the better lift there, any precipitation should be rather light and spotty. The forecast soundings continue to show a rather dry layer in the lowest levels and this combined with weak forcing results very light precipitation. There is little model support to bring in measurable precipitation, and the wpc quantitative precipitation forecast is pretty much dry. Temperatures through the evening in the coldest spots look just warm enough to prevent any frozen precipitation. Did raise low temperatures some with the latest 9:30 PM update. Cloud cover has kept temperatures up across most of the region. Down in the southern Delaware-Maryland-Virginia temperatures are running several degrees cooler outside the cloud shield. && Short term /6 am Sunday morning through 6 PM Sunday/... an upper-level trough is forecast to be amplifying during Sunday across the plains. This will allow some ridging to develop downstream, resulting in the surface high to become anchored offshore. This will provide a southerly flow and with warm air advection continuing and even strengthening some during the day, a warmer day is anticipated. The location of a low-level jet in combination of some short wave energy and isentropic lift should keep any morning light precipitation focused to our north. Meanwhile, a warm front will continue to organize to our south as low pressure consolidates in the vicinity of the Tennessee Valley by late in the day. While there will be some clouds around, some thinning should occur for a time before an increase develops again toward evening. It appears that any organized lift remains away from our area, therefore we will carry a dry forecast during the daylight hours. As for high temperatures, a GFS/NAM MOS blend was generally used. && Long term /Sunday night through Saturday/... **record warmth Monday followed by a potential winter storm/event for portions of our area wednesday** Another high amplitude trough near 100w longitude to start Sunday night lifts northeastward into Quebec by Tuesday with a new trough evolving over the eastern USA Wednesday but full of uncertainty regarding the short wave interactions - amplitude and translation speeds. So while a middle Atlantic coastal winter event is forecast, it is not yet a lock due to the previously mentioned uncertainty. A general cyclonic flow at middle levels continues over the northeast USA Thursday into the weekend with uncertainty regarding the embedded short waves. Temperatures: calendar day averages have been below normal since the 13th (9 consecutive days). Models agree on temperatures about 15 to 20 degrees above normal Monday...maybe 5 degrees above normal Tuesday... below normal Wednesday-Friday and 5 to 10 degrees below normal Saturday. Forecast basis: unless otherwise noted the long term period of this forecast is generally based on a 50 50 blend of the 12z/22 NAM/GFS MOS for the period Sunday night-Monday night. Then the 12z/22 GFS MOS is applied Tuesday and Tuesday night. Thereafter (wednesday onward) the 1522z/22 wpc gridded guidance which at times is blended 50 50 with the 12z/22 GFS mexmos. All this is eventually checked against the 12z/22 European model (ecmwf) to see if we're in the ballpark with European model (ecmwf) cyclically persistent 18z 2 meter temperatures. Precipitation probability guidance is checked against the 09z/22 sref 3hrly probability of precipitation for .01 through 00z Wednesday and thereafter the 12z/22 gefs 6hr probability of precipitation for 0.05. The dailies... Sunday night...warm air advection with periods of showery rains...mainly after midnight and possibly heavy for a time. An isolated severe thunderstorm is not impossible in del/New Jersey with swi -1, tt 48, ki 32 and 60-70kt wind at 850 mb on the European model (ecmwf) in the 3am-6 am (08z-11z) time frame. 12z NAM has similar elevated instability at 09z Monday. 12z GFS least robust of the three 12z models mentioned. Grids have the chance thunderstorm in snj and the Delaware-Maryland-Virginia early Monday morning. Monday...becoming partly sunny...windy and warm (after early morning showers race NE at 50 kts (near 60 mph). Record warmth expected and southwest wind gusts of 35-40 miles per hour. Blended transport wind supports 40 miles per hour gusts in the afternoon...possibly 45. Monday night...partly cloudy with maybe a low topped sprinkle or shower accompanying the cold front prior to midnight. Tuesday...partly to mostly sunny (mostly cirrus)...breezy and still with temperatures about 5 degrees above normal. Wednesday...a coastal storm is likely. The operational European model (ecmwf) is pretty stable these past two cycles and has been consistently furthest west with this opportunity for precipitation the past several days. The 12z GFS has moved west with the track. No lock on the track since short wave interactions show variability in the ensembles. Still...it looks as if the boundary layer temperature is going to govern where its mostly snow. Daytime temperatures 5 to 10 degrees below normal. Advise all with travel plans Wednesday afternoon and night in our forecast area to closely monitor future forecasts. This could become a snow storm for portions of our forecast area with plowable snow and near freezing temperatures....especially the Interstate 95 corridor. That would mean a significant impact due to Holiday travel and one of the busiest air travel days of the year. If this forecast remains similar Sunday...briefing packages would begin Sunday afternoon around 330 PM. Thursday into Friday morning...considerable cloudiness with a chance of snow showers or flurries as the prime trough shifts across the area. Friday-Saturday...wpc guidance with colder than normal temperatures as a low level west-northwest flow appears to prevail with Canadian high pressure heading east-southeastward through the Ohio Valley to the Middle Atlantic States. && Aviation /03z Sunday through Thursday/... the following discussion is for kphl, kpne, kttn, kabe, krdg, kilg, kmiv, kacy and surrounding areas. Tonight...VFR, with areas of ceilings at or above 5,000 feet. Southwesterly winds diminishing to 5 knots or less. Sunday...VFR, with ceilings at times above 5,000 feet. Southwest winds 5-10 knots, becoming southeast late. Sunday night... VFR through the evening with increasing clouds and gradually lowering ceilings. Light rain possible after 03z from phl south. Outlook... 04z Monday through 12z Monday...very poor flying conds with MVFR expected and IFR possible if not probable in periods of showery rains. Rain could be heavy at times with a possible thunderstorm after 06z/24 Sunday night. East to southeast wind could gust in the 25 to 30 knots range toward 09z Monday. Low level wind shear potential at kacy near 09z Monday. High confidence. Monday and Monday night...improving to VFR scattered-broken at or above 3500 feet (after any lingering showers rapidly depart northeastward by 14z). SW wind gust 30-38 knots. Cold front passage/shift Monday evening with a possible brief shower or sprinkle...especially east PA. MDT confidence. Wednesday...much uncertainty depending on the track of a coastal low. Could be VFR if low is far enough east or MVFR/IFR in rain/snow and wind if low is far enough west. As it stands with todays model and NCEP collaborated guidance...plan on precipitation changing to some snow and a period of IFR conditions. Confidence low to moderate. Thursday...VFR ceilings with a possible brief period of MVFR conds in scattered snow showers or flurries. && Marine... a southwesterly flow will occur through Sunday as strong high pressure shifts offshore and into the western Atlantic. As this occurs, the pressure gradient is forecast to tighten some through much of tonight. A low-level jet is forecast to track mainly to our north, however the 925 mb winds increase to near 30 knots tonight. The forecast soundings indicate some mixing occurs, although surface gusts may be marginal. The southwesterly flow should also build the seas, however the strongest winds and highest seas may setup to our northeast. Since there is still potential, we will maintain the Small Craft Advisory through 11z Sunday for all but the Delaware Bay. The conditions should generally be below advisory criteria Sunday. Outlook... Sunday night through Monday...gale watch has been issued with strongest inflow southeast winds of potential 35-40 knots gusts near dawn Monday. Winds shift SW in the warm sector and may gust 35 knots along the coast where near record warmth prevails. Blended 12z/22 NAM/GFS transport wind supports gale gusts 06z Monday- 02z Tuesday. For now the gale watch ends at 22z Monday. Monday night into Tuesday....a cold frontal passage and Small Craft Advisory conds as seas and wind eventually subside late Tuesday. Wednesday-Thursday...plan on Small Craft Advisory conditions redeveloping as a coastal low develops. Small potential for a gale late Wednesday. && Climate... for our eight climate sites, here are the record high temperatures for November 24th and the most recent year of occurrence. Record highs 11/24: Acy: 72 set in 1999 phl: 71 set in 1979 ilg: 73 set in 1979 abe: 69 set in 1931 ttn: 71 set in 1979 ged: 75 set in 1992 rdg: 69 set in 1979 mpo: 64 set in 1931 && Phi watches/warnings/advisories... PA...none. New Jersey...none. Delaware...none. Maryland...none. Marine...gale watch from late Sunday night through Monday afternoon for anz430-431-450>455. Small Craft Advisory until 6 am EST Sunday for anz450>455. && $$ Synopsis...drag near term...Gaines/gorse short term...gorse long term...drag aviation...drag/Gaines/gorse marine...drag/gorse climate...
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