586 FXUS61 KPHI 301443 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 943 AM EST Wed Jan 30 2019 .SYNOPSIS... An Arctic front will move across the region later today. Arctic high pressure then builds south and east, and will be centered over New Jersey Thursday night before moving offshore on Friday. A weak clipper system passes through the region Friday afternoon. High pressure reestablishes itself over the region for the start of the weekend before moving out to sea on Sunday. Low pressure passing north of the region drags a cold front into the Northeast early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The main impact for this period will revolve around the expected snow showers/squalls. The only change I made this morning to the forecast was to bump PoPs up to likely across the northern 2/3rds. The timing was good to go. Both CTP and LWX to our west are already issuing Snow Squall Warnings. We have already issued an SPS to highlight potential impacts and will continue to issue SPSs or SQWs as needed today. Less than an inch of snow is expected with these snow showers/squalls. The more significant threat will be the potential for near whiteout conditions as the brief bursts of snow and winds greater than 35 mph work together. Previous discussion... 630 Update: Update was decreasing temperatures and dewpoints in northwestern portions of the fcst.area where calm winds and snow cover has resulted in more cooling than was expected. Also tweaked PoPs slightly to reflect hi-res guidance being slightly slower with pushing the precipitation band through the area this afternoon. Previous discussion below: The main weather story today will be the arrival of an arctic front this afternoon and the potential for snow squalls and gusty winds. The secondary Sfc low which spawned over the area Tuesday evening will continue to progress northward into Maine & the Canadian Maritimes during the day today. Behind this feature and ahead of the Arctic high pressure to our west, pressures will fall locally this morning and winds will back to the south/southwest. Temperatures will be cool but no overly so across the region as the Arctic front will not arrive until this afternoon. Areas in eastern PA/Northern NJ that received appreciable snow on Tuesday may be slower to warm (not to mention the front will pass through these areas first limiting the time they have to warm). Expecting a fairly active early-mid afternoon period as the artic front pushes through the area. Guidance is currently depicting a favorable setup for snow-squalls as the boundary is strongly frontogenetic around 700-850mb, with low stability exemplified by >0 SBCAPE values (a rarity this time of year) and -EPV overtop the zone of 850 FGEN. Although snow accumulations will be fairly meager (generally .5 inches or less) with this boundary due to its quick moving nature and lack of moisture, there will be the potential for a period of low visibilities and strong winds. Wind gusts over 50 mph are possible with this feature as BUFR soundings show a very impressive mixed layer for January standards, with potential mixing to around 700mb. Currently most of the hi-res guidance has the boundary entering the CWA around 17-18Z, pushing through the I-95 corridor about an hour later, and then exiting offshore after about 21Z. Behind the boundary it will get progressively colder this afternoon/evening as the airmass more or less bottoms out (850 temps cooling to around or less than -25C by this evening). Not only will it be cold but strong pressure rises combined with strong winds aloft and modest (relative to earlier in the day) mixing will make for gusty winds through the afternoon and into the evening. Given the favorable synoptic setup behind the front, combined with the favorable convective setup associated with the boundary decided to hoist a wind advisory for the entire area through the day, with the understanding that the potential for the highest gusts will be with the convective line. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM THURSDAY/... Tonight into Thursday morning the main story will be the cold, as the coldest airmass of the season briefly settles over the area. Overnight lows Thursday morning will be in the single- digits over most of the area, with negative values possible in interior PA and NW NJ. These low temperatures combined with WNW winds around 10 kts. will result in min wind chills between -10 and -15 for most of the area (with values as low as -25 over the Poconos) Thursday morning. Consequently have issued a wind chill advisory for Wednesday night/Thursday morning for the entire fcst. area apart from southern Delmarva where values look to remain just above criteria. Have issued a wind chill warning for Carbon/Monroe counties where wind chill values look to dip below -25 particularly in the Poconos. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Arctic high pressure builds into the Ohio Valley on Thursday. Frigid airmass remains in place, with 850 mb temps ranging from -20C to -24C, and 1000-500 mb thickness values will range from 500 to 505 dam. West winds will range from 10-15 mph with gusts up to 20 mph. This results in surface temps topping off in the single digits in the southern Poconos, and otherwise in the teens for the rest of southeast PA, NJ, and the northern half of Delmarva, and in the lower 20s in southern Delmarva. Wind chills in the morning will be as low as -25 to -30 in the southern Poconos, and otherwise from around -10 to -15. By late afternoon, wind chills will struggle to get out of the single digits, and will struggle to rise above zero degrees north and west of the Fall Line. The Wind Chill Warning and Wind Chill Advisory will remain in place for most of the region through Thursday morning. The high will become centered over the VA/NC coast Friday night. Mainly clear and cold conditions continue, with lows Thursday night generally in the single digits, except for 0 to 5 below in the southern Poconos and northern NJ, and around 10 above in southern Delmarva. Wind chills will be as low as 15 below in the southern Poconos. High pressure moves offshore on Friday, and light return flow sets up behind the departing high. Temperatures start to warm up a bit, but will still be below normal. Highs top off in the teens in the southern Poconos, and otherwise in the low to mid 20s. A weak clipper system will pass through the region in the afternoon, resulting in less than an inch of snow for generally the southern half of the region. High pressure builds in behind the departing clipper system, and a warmer airmass spreads into the region. Temperatures return to normal on Saturday with highs in the 30s, then going into the second half of the weekend highs climb into the 40s. For the start of the new week, highs climb to well above normal levels, generally in the 50s and may approach 60 in some spots on Tuesday. A series of impulses will bring some light precip to the area Sunday, then going into the new week, several waves of low pressure will develop out ahead of a cold front. This will keep at least chance PoPs in the forecast Monday and Monday night, and then with the approach of the cold front on Tuesday, more widespread precip will be possible. && .AVIATION /15Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Expecting VFR conditions with gradually increasing southerly/southwesterly winds through the morning at all TAF sites. A brief period of IFR CIGS/Vsbys and high winds in snow squalls is possible this afternoon at all terminals. The most likely period for these squalls will be around 17-22Z with a natural West to East progression through the terminals in that period. Behind this feature skies will clear out and gusty West/Northwest winds will settle in at all TAF sites. Tonight...Cold with VFR conditions and W/NW winds at all sites. OUTLOOK... Thursday...VFR. West winds 10-15 kt with gusts up to 20 kt. High confidence. Thursday night...VFR. Light winds. High confidence. Friday...MVFR/IFR conditions possible in -SN, especially south of KPHL. West winds, becoming NW. Friday night...VFR. Light N winds. Saturday through Sunday...VFR. Light westerly winds Saturday turn light southwesterly Saturday night and Sunday. Slight chance for MVFR conditions Sunday afternoon. && .MARINE... Southerly winds and seas will begin to increase through the morning with SCA-Gale conditions likely. A period of snow squalls will be possible later this afternoon with gusty winds possible. Gale-force Westerly winds will become established this afternoon and persist into this evening. The likelihood of freezing spray will increase later this afternoon and into Wednesday night behind an arctic front. Outlook... Thursday-Thursday night...SCA expected Thursday, gradually falling below SCA criteria Thursday night. Freezing spray possible. Seas 3 to 5 ft diminishing to 2 to 4 ft Thursday night. Friday through Sunday...Generally sub-SCA conditions expected for the period. && .CLIMATE... Record Temperatures for 1/31: Coldest Maximum Coldest Minimum Site ABE 16/1936 -9/1948 ACY 22/1966 0/1948 PHL 21/1935 3/1948 ILG 19/1935 3/1948 RDG 19/1936 -6/1905 TTN 19/1936 -1/1920 MPO 8/1920 -15/1908 GED 23/1948 1/1948 && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Wind Advisory until 10 PM EST this evening for PAZ054-055- 060>062-070-071-101>106. Wind Chill Advisory from 7 PM this evening to 10 AM EST Thursday for PAZ060>062-070-071-101>106. Wind Chill Warning from 4 PM this afternoon to 4 PM EST Thursday for PAZ054-055. NJ...Wind Advisory until 10 PM EST this evening for NJZ001-007>010- 012>027. Wind Chill Advisory from 7 PM this evening to 10 AM EST Thursday for NJZ001-007>010-012>027. DE...Wind Advisory until 10 PM EST this evening for DEZ001>004. Wind Chill Advisory from 7 PM this evening to 10 AM EST Thursday for DEZ001. MD...Wind Advisory until 10 PM EST this evening for MDZ008-012-015- 019-020. Wind Chill Advisory from 7 PM this evening to 10 AM EST Thursday for MDZ008. MARINE...Gale Warning until midnight EST tonight for ANZ430-431-450>455. && $$ Synopsis... Near Term...Carr/Fitzsimmons/Kruzdlo Short Term...Carr/Fitzsimmons Long Term...MPS Aviation...Carr/Fitzsimmons/MPS Marine...Carr/Fitzsimmons/MPS Climate...