Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/17/20

Area Forecast Discussion
National Weather Service Binghamton NY
936 PM EST Wed Dec 16 2020 .SYNOPSIS... A strong nor`easter will produce heavy, rapidly accumulating snow tonight across central NY and northeast PA. The snow ends Thursday morning with cool and quiet conditions Friday into Saturday. && .NEAR TERM /THROUGH THURSDAY/... 10 pm update: Latest mesoscale models have continued to nudge the heaviest snow band a little further northward for the overnight hours. This has resulted in amounts going up a few inches in the Southern Tier and slightly lower across southern portions of NE PA. The current snow band across the Northern Tier of PA should lift into the Southern Tier of NY as well then stay in place through the overnight. Top totals are still expected to be around two feet. 7 pm update: With the early evening update, we added Yates county to the winter storm warning based on reports over 2 inches as of the update time and the latest mesoscale models which are inching north with the higher snowfall totals. The prospects of an intense band are increasing for later this evening into the overnight. Incorporated the latest NAM guidance which keeps the best FGEN forcing just north of Scranton from Wyoming county eastward to central Wayne county. Snowfall rates suggested by the FGEN along with model QPF and snow ratios suggest snowfall rates of 3 inches or so setting up over these locations. The latest 22Z HRRR has this band located farther to the north into the Southern Tier of NY so it is an evolving setup for later tonight. Snowfall totals over two feet are likely to occur where this intense snow band is located. We now show that stripe in the latest snowfall map. Another issue, is the potential for sleet mixture around the Scranton area looks higher. A look at the KDIX CC line shows the warm nose quickly advancing northward into the Lehigh Valley as of 7pm. Although precipitation rates are high this update leans more in the direction of the HRRR which which warms a layer up between 800 and 900 mb just above freezing for a few hours. 255 pm update... Significant nor`easter remains the focus of attention for the near term with heavy snowfall expected tonight across much of the forecast area. Snowfall rates will be fairly impressive at times tonight as well with the potential for thundersnow into parts of ne PA. The ridge tops of the Poconos and the Catskills may see some stronger gusts tonight too, which will create blowing and drifting snow. Rapidly deepening surface low off the the Carolina coast will lift to the north tonight and become positioned off the NJ coast by Thursday morning. As this occurs a positively tilted 500 mb short wave will rotate across the Ohio Valley and mid Atlantic region and combine with a coupled jet streak to provide robust broad large scale lift. A fairly rich supply of moisture from the Atlantic will get entrained into the surface low from the east and be able to interact with a strengthening band of mid level frontogenesis which is expected to set up over ern PA into southern NY/nrn NJ late this evening and overnight. The combination of this strong layer lifting mechanism and a weak amount of elevated instability may provide enough ingredients for a few strikes of thunder over the Poconos and into the southern Catskills. There is also a concern for gusty east/ne winds as the system wraps up off the Jersey coast. Winds will pick up early this evening and remain around 5 to 15 mph with gusts 20 mph through the overnight. Some of the higher peaks of central NY and ne PA may see gusts up to 30 mph. Areas that see stronger gusts may be impacted by blowing and drifting snow. Visibilities may be reduced to near zero at times. Much of the region will likely see broad snowfall rates of 1/2 to 1 inch per hour. However, the deformation zone on the back side of the system will be capable of producing snowfall rates of 2 to 3 inches per hour at times with some isolated locations of ne PA getting into a convective mode and potentially seeing short bursts as high as 4 inches per hour. The period of heaviest snow will be from around 6 pm to around 3 am. Total snow amounts will be roughly 18 to 24 inches in ne PA portions of Southern Tier in NY and into the southern Catskills (cannot rule out a few higher amounts, especially in the higher terrain)...12 to 18 inches along the southern tier of NY and into the nrn Catskills...and around 4 to 8 inches from the nrn Finger Lakes into the srn Tug Hill. The snow is expected to taper off west to east as the system pulls out late tonight. Visibilities will improve rapidly around sunrise with most of the lingering light snow after 7 am dissipating just before noon. Conditions should remain dry through the rest of the afternoon. Temperatures will remain below average with lows tonight dipping into the teens and lower 20s. Highs on Thursday will be only reaching into the mid 20s to lower 30s. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... 330 AM Update... CAA over Lake Ontario keeps cloud cover over the Finger Lakes region into NE PA while eastern regions of central NY start to clear as high pressure builds in Thursday night. With fresh snow and dry air aloft, areas that clear in the eastern regions of central NY and the Twin Tiers can see temperatures quickly fall into the single digits while areas that stay cloudy keeps overnight lows in the low 20s. Friday, high pressure moves overhead with much of the remaining clouds clearing. Friday night once again has a challenging overnight low forecast with a disturbance moving in from the west bring in clouds, mainly for the Finger lakes and the western counties in the Twin Tiers region. Lows are currently forecasted to be in the teens for these regions as the clouds move in and reduce radiational cooling but changes in timing will result in large changes both up or down. Everywhere else will see lows down into the single digits. SW flow ahead of a shortwave moving in from the Great Lakes on Saturday brings in warmer air with highs back up around freezing. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... 330 AM Update... Chances for snow showers arrive Saturday night, mainly north of the PA border, as the trough swings from the Lower Midwest into northern NY. A change over to a rain/snow mix is expected into Sunday as temperatures climb back up into the mid and even upper 30s. We briefly dry out into Monday with some weak ridging. However, later Monday night, a trough developing over southern Canada will begin to dig into our region, which will bring in our next chances for snow showers into Tuesday. Again, this will be mainly north of the PA border, before high pressure beginning to build in for the middle of next week brings an end to precip chances. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... Snow, heavy at times, will continue to affect the terminals through the overnight hours. IFR conditions will persist through mid-morning Thursday. The heaviest snow will fall from KAVP to KBGM, where we will see prolonged visibility restrictions of 1/4SM to 1/2SM. Ceilings will fluctuate between 500 and 1500 feet. In addition, KAVP will experience LLWS conditions as a low level jet moves over the terminal. KITH and KELM will also experience visibility restrictions of 1/2SM or less through late tonight. The snow will intensify at KSYR and KRME between 00z and 03z, but isn`t expected to be as heavy as the snow to the south. A mix of MVFR and IFR restrictions are expected by late Thursday morning as a few snow showers continue to affect the region. VFR conditions will develop from west to east between 18z Thursday and 00z Friday. Outlook... Thursday night through Saturday night...VFR. Sunday...Chance of rain/snow showers and associated restrictions. Monday...Generally VFR conditions with a few rain/snow showers possible north. && .BGM WATCHES/WARNINGS/ADVISORIES... PA...Winter Storm Warning until 10 AM EST Thursday for PAZ038>040- 043-044-047-048-072. NY...Winter Storm Warning until 10 AM EST Thursday for NYZ044>046- 055>057-062. Winter Weather Advisory until 10 AM EST Thursday for NYZ009- 018-036-037. Winter Storm Warning until 7 AM EST Thursday for NYZ015- 022>025. Winter Weather Advisory until 7 AM EST Thursday for NYZ016-017. && $$ SYNOPSIS...BJT NEAR TERM...BJT/MWG SHORT TERM...AJG LONG TERM...HLC AVIATION...DJP
Area Forecast Discussion
National Weather Service Denver/Boulder CO
825 PM MST Wed Dec 16 2020 .UPDATE... Issued at 815 PM MST Wed Dec 16 2020 Minor updates to the forecast tonight. Blending of observed temps into forecast on autopilot, and see no reason to adjust overnight lows. Band of high clouds moving across the western slopes may clip the western edge of our forecast area for a few hours. 01z HRRR run has a good handle on these and blended in a little of that model for the rest of the night. Otherwise terrain induced overcast skies in the mountains and foothills. Berthoud pass observation has 1/2 mile visbility in snow but with gust to 36 kts more likely blowing snow on that ridgetop. CDOT webcams difficult to decipher, but roads appear to be OK and snow not visible in the headlights. && .SHORT TERM...(This evening through Thursday) Issued at 210 PM MST Wed Dec 16 2020 The forecast is on track without significant changes today. Light snowfall on west facing slopes west of the Continental Divide continues to diminish, with stations and webcams reporting gradually greater visibilities and higher cloud bases. Snowfall should end late this evening as expected. We reduced QPF on the mountain ridges around the Indian Peaks as models are likely overestimating the remaining snowfall potential this evening as they have been doing all day. Overnight lows will be a bit higher tonight in areas not dominated by cold air pooling. Expect a near seasonal normal overnight low in the upper teens or lower 20s in the Denver metro area and Front Range foothills, with single digits to low teens in the South Platte River Valley and much of Lincoln County, and high teens elsewhere on the plains. The mountains will see single digit overnight lows again. The upper ridge will continue to advance over the Rockies tonight and Colorado should be under the ridge axis by morning. Southerly surface flow during the day will provide some warm advection to offset the remaining snow cover, but the mountain valleys and South Platte Valley will remain under stubborn inversions throughout the day, resulting in chilly temps. Expect highs in the 40s on the plains and 30s in the mountains. The next trough will be advancing to the Rockies through the day. Ahead of it, flow aloft over northeast Colorado will increase and turn southwesterly, and upper level QG subsidence will be replaced by weak ascent. Light snow may develop again on the west slopes to the west of the Continental divide, but little to no QPF is expected through midnight Thursday. .LONG TERM...(Thursday night through Wednesday) Issued at 300 PM MST Wed Dec 16 2020 The trough for Thursday night and Friday continues to fade a little in the models. The best lift will rush across the mountains early Friday morning and the plains by midday. There may be a shallow layer of north winds, but on a larger scale, there will be northwest winds not far off the ground that should keep a dry layer for the expected light showers to fall into. There should be a period of light snow for all the mountain areas, with a few heavier showers possible. On the plains, it`s virga or light showers for a few hours as the area of lift goes by. Previous snow amounts look good, mostly 2-4" in the mountains and an inch or less at lower elevations. There`s another weak shortwave in strengthening northwest flow Saturday. This should keep some moisture over the mountains and some wave cloudiness. Behind this we`ll quickly get into warm advection with a stable layer above the mountains. There should be some wave amplification though the flow is not very strong yet on Saturday. By Sunday the flow is stronger, and it looks like we`ll have a period behind the Saturday trough with northerly flow at jet level which could reflect the wave energy and provide more of a high wind threat for the Front Range on Sunday. By Monday the flow is decreasing a bit. Model blend is similar to the previous forecast, with temperatures rising into the 50s for Sunday through Tuesday. There will still be some wind in the mountains, but not much of a high wind threat. There`s still pretty good agreement on a strong cold front for Wednesday, but the lift and moisture now look like they`ll mainly be north and northeast of Colorado. We could still get a quick shot of light showers again, but the main impact will be the cold front. The brunt of the cold air will likely also be east of us, but dropping back into the 30s for a day still looks likely. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 459 PM MST Wed Dec 16 2020 VFR through the period. Wind have calmed down at KAPA and shifted to NW at KBJC. Wind forecast to remain from the NW at KBJC closer to the foothills and mountain wind effects. At KAPA and KDEN normal drainage regimes to bring generally southerly wind. Weak upper level wave to enter the area Thursday, with lowering and thickening clouds but remaining well above VFR limits. Toward mid day Thursday a weak wind shift will move in on the plains, affecting KDEN and KAPA with northeast flow for part of the day. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hanson SHORT TERM...Direnzo LONG TERM...Gimmestad AVIATION...Hanson
Area Forecast Discussion
National Weather Service Burlington VT
1034 PM EST Wed Dec 16 2020 .SYNOPSIS... Snow will overspread the North Country tonight through Thursday morning. Snowfall accumulations will vary sharply across the North Country with 6 to 12 inches expected across Rutland and Windsor Counties, while a dusting to an inch or two is expected further north over northern New York into northern Vermont. A difficult morning commute is likely for many on Thursday, before the snow tapers off to flurries by mid afternoon. Chilly temperatures prevail the next couple of days, before a warming trend develops by the weekend. && .NEAR TERM /THROUGH THURSDAY NIGHT/... As of 946 PM EST Wednesday...Winter Storm Warning continues for Rutland/Windsor for 6 to 10 inches of snowfall with localized higher amounts possible south of Route 4, while winter wx advisory continues for Addison and Orange counties for 2 to 6 inches of snow. Overall forecast in good shape and no big changes needed at this time. Only tweak was to up the timing just a bit as snow has moved into Rutland County based on observations and webcams. Rest of forecast remains unchanged. Previous Discussion... No significant changes were made to this forecast package, just minor adjustments to sharpen expected north-south snowfall gradient, as guidance has come into better agreement. Water vapor shows sharp mid/upper lvl trof acrs the Ohio Valley, while IR sat indicates rapidly cooling cloud tops acrs central PA, angling toward southern/central New England, as confluent flow prevails acrs North Atlantic. I have to admit, the water vapor/satl imagery with this developing system is pretty impressive this aftn, especially the advection of moisture and the expanding coverage of cooling cloud tops over central PA. Meanwhile, potent 5h vort is helping to enhance 1010mb sfc low pres near Cape Hatteras per latest analysis, while widespread precip continues to expand in areal coverage over most of the eastern Conus. Noticing visibilities with moderate to locally heavy snowfall in the 1/4 to 1/2sm range over central Pa, with light snow already at KBGM. Our fcst challenge remains unchanged, with how quickly mid/upper lvl circulation de- amplifies in the fast confluent flow aloft and exact placement/evolution of mesoscale band of moderate to heavy snowfall acrs southern/central VT. Consensus among meso-scale modeling supports 7h/5h circulation moving from eastern PA into southern New England, while strong band of 7h fgen forcing lifts pivots from the Catskills into southern VT. The GEM/NAM and RAP show this band reaching southern Rutland/Windsor Counties, while GFS/ECMWF is along the MA/VT state line. Latest trends support the heaviest snowfall potential associated with this band of enhanced fgen forcing mainly along and south of Route 4 acrs Windsor/Rutland Counties. HREF highlights >60% of 1 to 1.5 inch per hour snowfall rates acrs this area, with sharp northern side weakening. These band structures and associated movement north, along with enhanced snowfall rates are extremely difficult to predict, and become a nowcasting event as they develop on the radar. It should be noted snowfall amounts typically drop off sharply on either side of these bands, as dynamics are weaker, uvvs in the favorable snow growth is less favorable, resulting in lower snow ratios. Utilizing a general consensus indicates the fgen band lifts into extreme southern Rutland/Windsor Counties, before shifting to the east. The SREF plume snowfall for VSF ranges from 2 inches to 26 inches, indicating the large spread acrs our southern areas. For our messaging we will continue with a general 6 to 10 inches with localized 12 inches or more possible south of Route 4, while amounts quickly drop off acrs central and northern VT. If the band stays south of our cwa, amounts will be much less. Snow ratios of 12 to 15 to 1 are likely within the mesoscale band with 10 to 13 to 1 outside the band over most of central/northern Vt and eastern Dacks. Snow develops btwn 02-04z acrs southern VT and spreads northward into much of the dacks and northern/central VT btwn 04z-08z. The heaviest snowfall rates occur btwn 09z-15z on Thurs, creating a hazardous morning commute, especially southern/central cwa, with vis below 1/2sm and snowfall rates of 1 to 1.5 inch per hour. Mid/upper lvl trof axis lingers along with good 850 to 500mb moisture through 18z Monday, before dissipating. Expecting snow to linger acrs central/southern VT thru 18z, before tapering off to scattered flurries by 21z. Temps with thickening clouds tonight and snow developing hold in the 5F to 15F range, while warm into the mid teens to lower 20s on Thurs. A chilly night with fresh snow pack is anticipated for central/southern section on Thurs Night/Fri AM with lows 0F to +15F. && .SHORT TERM /FRIDAY THROUGH SATURDAY/... As of 1032 PM EST Wednesday...Surface high pressure will settle across the North Country Friday night giving way to clear skies and overnight lows in the single digits. A relatively warmer day can be expected on Saturday with highs in the upper 20s to low 30s as high pressure moves offshore and the flow aloft becomes southwesterly. Clouds will increase on Saturday as well associated with an upper level low passing to the north during this time. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... As of 1032 PM EST Wednesday...A series of upper-level shortwave troughs will pass overhead early next week bringing a chance of precipitation to the North Country. A decaying frontal boundary will accompany said shortwave passages, though will likely become washed- out as it traverses the forecast area. The best chance for precipitation will be across northern New York Sunday afternoon and into the overnight hours, mainly in the form of snow showers. However, there could be a mix of rain/snow within the Saint Lawrence Valley with the advection of relatively warmer air. By Monday morning, showers will become more lake effect driven and confined to areas downwind of Lake Ontario. Still, precipitation will be light with little to no snow accumulation expected. High temperatures Sunday and Monday will be in the mid to upper 30s with overnight lows in the 20s. Additional chances for precipitation exist Tuesday as another shortwave trough passes to the north. Again, precipitation will mainly be in the form of snow, though a mix of rain/snow is possible within broader valleys. Little accumulation is expected during this time. Temperatures will trend cooler thereafter with highs in the 20s for mid- week. && .AVIATION /04Z THURSDAY THROUGH MONDAY/... Through 00Z Friday...VFR conditions are expected through 06z then as snow moves up into the region ceilings and visibilities will lower into the 1 to 3 mile range, but 1/4 mile at KRUT where snow will be heavy. Ceilings will lower into the 800 to 1500 foot range. Conditions will slowly improve into the MVFR and VFR categories after 18z. One item of note...KMSS will be on the edge of the snow and are expected to only see some snow showers and conditions will be MVFR/VFR for the entire period. Winds will generally be from the north at speeds of 10 knots or less. Outlook... Thursday Night: VFR. NO SIG WX. Friday: VFR. NO SIG WX. Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. Saturday Night: VFR. Slight chance SHSN. Sunday: Mainly VFR, with areas MVFR possible. Slight chance SHSN. Sunday Night: Mainly MVFR, with areas IFR possible. Slight chance SHSN. Monday: Mainly MVFR, with local IFR possible. NO SIG WX. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Winter Storm Warning until 4 PM EST Thursday for VTZ011-012- 019. Winter Weather Advisory until 4 PM EST Thursday for VTZ009-010- 018. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Evenson/Taber SHORT TERM...Hammond LONG TERM...Hammond AVIATION...Evenson
National Weather Service Eureka CA
259 PM PST Wed Dec 16 2020 .SYNOPSIS...A frontal system will bring widespread moderate to briefly heavy rain to the area through tonight. Gusty evening winds along the coast and overnight high elevation snow can also be expected tonight. The precipitation will taper to lingering showers on Thursday. && .DISCUSSION...After some areas of fog this morning, warm frontal rains have been spreading across the area through the day. A cold front will bring heavier rains later this afternoon and overnight. Overall precipitation amounts look similar to last weekend`s system (1-3 inches across most of the area with less than an inch across Lake and S Mendocino counties), but there could be some rainfall amounts over 3 inches across some SW facing mountainous terrain of Del Norte and extreme northern Humboldt counties. The bulk of the rain will fall tonight, with some lingering showers into Thursday morning. There is a slight chance of thunderstorms tonight, mainly over the coastal waters. The most problematic part of the forecast is high elevation snow amounts, particularly at Scott Mountain Pass tonight. The highest QPF values area expected before 06Z, with snow levels beginning to drop just after that time. Current observational data suggests wet bulb temperatures several degrees above freezing across the Trinity Horn (NE Trinity county), and models suggest snow levels are likely just above pass level. Additionally, snow levels are forecast to rise a bit more late this afternoon and perhaps early this evening before falling overnight. This leaves a period between about 9 PM and 3 AM when there will be some accumulating snow around Scott Mountain Pass. At this time, it appears snow totals may top out at around 2 inches at road level with more snow at higher elevations. There may be a delay in the snow sticking to the ground as well, as surface temperatures will be slightly above freezing and the roadways will be wet. HRRR probabilistic guidance shows a 60% probability of 2"> snow near the pass, with 30% of 4"> snow. At this point, there is not enough certainty in over 2" of snow sticking to the roadway to warrant a Snow Advisory, but the oncoming will continue to monitor conditions through the evening for a possible short fuse advisory. After another break in the weather of Friday, another storm system will bring mostly light rain generally N of Cape Mendocino. The GFS and ECMWF models are in better agreement than yesterday, with rains starting a bit later on Saturday and persisting into Monday. /SEC && .AVIATION...Flight categories vary across the CWA as frontal boundaries pass through. KCEC is expected to remain in IFR until the evening. Rain, lower visibility, wind gusts and wind shear are in effect at the coastal terminals. KACV has been in VFR for most of the day but is expected to diminish in the early evening and improve overnight as winds ease and ceilings lift. Showers will continue intermittently through the TAF period for the entire CWA with a possible reprieve by late tomorrow morning. KUKI looks to have less severity of wind shear but IFR with reduced visibility and rain. Southerly winds are to switch to a NW bearing by tomorrow morning. /EYS && .MARINE...Have continued the hazardous seas warning for the northern outer waters this evening. Any one wave group may not quite be meeting our criteria, but the combination of a west-northwest swell currently around 11 to 14 feet at 15 seconds and some steep southerly seas associated with strong winds ahead of a cold front is resulting in some confused and rather hazardous sea conditions out there. As that cold front passes by, winds will ease substantially and shift to the southwest and west, then northwest overnight. The swell will gradually decay, but will remain elevated into the 10 to 12 ft range into Friday. Another reinforcing swell projected around 10 to 12 ft at 15 seconds will arrive late Friday into Saturday, probably resulting in continued Small Craft Advisories for all our coastal waters into the weekend. Otherwise, moderate northwesterly winds on Thursday in the wake of our front will diminish into Friday, then shift back toward southerly for the weekend as another front tries to approach from the north. These southerly winds may be locally stronger and gusty toward or north of the Oregon border, but do not look particularly strong in our waters. Thus, the swell will likely be the main contributor to the overall sea state from Friday through the weekend, as opposed to more locally-generated steeper southerly seas. /AD && .BEACH HAZARDS...Elected to allow the high surf advisories to expire at noon today. Looking at buoy data, there were probably still some breaking waves around 17 to 20 feet at that hour, highest along the Mendocino coast, but those have continued to come down steadily this afternoon, well below advisory criteria. Expect there will still be some 13 to 17 ft breakers into this evening along west-northwest- facing beaches, and some pretty nasty conditions with the cold front working through and southerly winds gusting to 30 mph locally near exposed beaches and coastal headlands. /AD && .EKA WATCHES/WARNINGS/ADVISORIES... CA...None. NORTHWEST CALIFORNIA COASTAL WATERS... Small Craft Advisory until 9 AM Friday for PZZ450-455-475. Hazardous Seas Warning until 8 PM this evening for PZZ470. $$ Visit us at Follow us on Facebook and Twitter at: For forecast zone information see the forecast zone map online:
Area Forecast Discussion
National Weather Service New York NY
750 PM EST Wed Dec 16 2020 .SYNOPSIS... High pressure to the north will slowly retreat as low pressure moves northward up the Mid Atlantic coast. This low will intensify as it approaches the region, turning east and passing south of Long Island tonight into Thursday. High pressure will then build in from the west through the first half of the weekend before moving offshore late in the day Saturday. A series of weak disturbances will move across the area Sunday and Monday, followed by a stronger cold frontal passage Monday night into Tuesday. High pressure will briefly return for the middle of next week. && .NEAR TERM /THROUGH THURSDAY/... Strong thermal forcing overrunning a 1037mb polar high centered over eastern Canada, bleeding southward into southern New England, has resulted in 2-3 inches of snow across portions of the NYC metro, NE NJ, and Long Island, with snowfall rates of 1-2 inches an hour. This activity will overspread CT and the Lower Hudson Valley the next couple of hours as cold, dry air (dew points in the single digits to lower teens) saturates. Thus far, the NAMNest, the warmer of the solutions aloft, was handling the thermo profile best when compared to the 00Z OKX sounding. It was around 0c at 825mb, while the GFS and HRRR were several degrees cooler. Strong lift though will keep this area generally isothermal and below freezing the next few hours. The key here will be the position of the coastal front and how far north and west the warm nose (around 750 mb) gets overnight. There is even some evidence that the boundary layer will warm sufficiently after midnight (due to east winds) for some rain across eastern sections of Long Island and perhaps coastal SE CT. The front end dump of snow may make this a moot point with warning level snows likely achieved before this changeover even happens later tonight. Greatest pressure falls of 7mb in the last 3 hours just east of the Delmarva with a 1004 mb low east Wallops Island, VA. The low will continue to track northward and hug the coast, as a negatively tilted shortwave trough works NE across the central Appalachians. The low will eventually turn east running into the blocking high over eastern Canada, passing south of Long Island overnight into Thursday morning. The primary question remains how far north the low will come before making its eastward turn, which in turn dictates how much, if any, warm air is able to work into the area at the surface and aloft. From a big picture perspective, the models have been very consistent with the position of the low over the past 24 hours, with only minor changes from run to run. However, given how close the low is forecast to come to the region, even minor changes in the location of the low will have a significant impact on snowfall totals, especially along the coast. In addition, high resolution models are indicating the potential for a dry slot to develop across Long Island and perhaps as far north as southern Connecticut. Model soundings also indicate some loss of saturation in the dendritic growth zone during this same period, all of which could at the very least limit the intensity of precipitation, and possibly allow precipitation to change to drizzle for a period. With that said, global model soundings remain below freezing throughout the event, keeping precipitation all snow. Winds will become more northerly as the low pulls east towards daybreak, which will allow colder air to filter back into the region, changing precipitation back to snow everywhere. Snow will eventually wrap up from west to east from late morning into the early afternoon. Snowfall accumulations will range from 12-18 inches across the Lower Hudson Valley, interior northeast New Jersey, and interior southwestern Connecticut, where precipitation will remain all snow. Snow totals will range from 10-15 inches across much of the New York City metro area and western Long Island, although totals could be a few inches lower across coastal portions of Brooklyn, Queens, and Nassau County. Across the rest of Long Island and far southeastern Connecticut, snowfall totals will range from 4-12 inches, lowest across the Twin Forks and immediate south facing coastlines. In addition to the snow, winds will increase this evening as the deepening low approaches. Winds could gust to 35-45 mph across much of the area overnight, with gusts to 45-55 mph possible across far eastern Long Island. While these winds would result in blizzard to near-blizzard conditions at times, they also correspond with the greatest potential for mixing. With that in mind, made no changes to headlines, with a Winter Storm Warning remaining in effect for the entire area. While breezy conditions will continue into the morning as precipitation changes back to snow, with decreasing snowfall intensity visibilities should remain above 1/4 mile. && .SHORT TERM /THURSDAY NIGHT/... Winds will gradually diminish Thursday night as the low continues to move east away from the area. With a fresh snowpack, lows will range from the lower teens across typically cooler interior locations to the low 20s along the coast. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Not a whole lot of change in the global models from what we saw 24 hours ago. A progressive, yet amplified upper flow will feature ridging building in from the west Friday into Saturday with a broad upper trough reestablishing itself across the NE quarter of the CONUS Sunday into early next week. At the surface, high pressure settles over the area late Friday night into Saturday morning before moving offshore late in the day. Late Saturday night into Monday, a disjointed upper trough will send a series of weak shortwaves into the area with a low chance for light precipitation to the NW of NYC late Saturday night into the first half of Sunday. It looks cold enough for for light snow shower activity with little or no accumulation expected. A cold front will then move across the area Tuesday morning with some cooler air gradually filtering in through Wednesday morning. The cold frontal passage looks to be dry, but a rain or snow shower across the hills well north and west of NYC is not out of the question. Temperatures will gradually moderate through the period, with readings 5 to 10 degrees below normal at the start, to slightly above normal by early next week. Following a cold frontal passage Tuesday morning, temperatures will return to near normal Tuesday night and Wednesday. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... ***HIGH IMPACT WINTER STORM IN PROGRESS*** Low pressure moving NNE along the Mid Atlantic Coast tonight will turn E off the New Jersey coast early Thursday morning, and then pass S of Long Island through the day on Thursday. Bands of moderate to heavy snow with LIFR conds are spreading into the area attm. Some sleet should mix in along the coast for a couple of hours after 05Z-06Z (KEWR/KJFK/KLGA/KISP and briefly at KTEB), then precip should change back to light snow after 08Z-09Z. ENE winds will ramp up quickly this evening to 30-35G40-45kt, highest at KBDR with its Long Island Sound exposure. Wind shear is also expected tonight, generally starting after 02Z and ending after 05Z in the NYC metros, and 07Z-08Z farther east. This will occur at 2000 ft with a ENE direction and speed of 50 to 55 kt. Storm total snowfall of 10-16 inches is expected, with the higher amts at the terminals NW of NYC. Snow should gradually taper off from W-E through the day on Thu. VFR conds with gradually diminishing N winds forecast through the day, with a chance that MVFR cigs could last through the day. ...NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty... AMD possible to fine-tune flight cat and precip types. .OUTLOOK FOR 00Z FRIDAY THROUGH MONDAY... .Thursday night through Saturday...VFR. .Sunday...Possibly MVFR at times with snow showers. .Monday...VFR. Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ && .MARINE... Winds will continue to increase on all waters this evening as a strengthening area of low pressure approaches and moves across the waters. A Storm Warning is effect on the ocean waters with gusts 50-55 kt expected overnight. Elsewhere, Gale Warnings remain in effect, with winds expected to gust to around 40 kt. In addition, seas will continue to build, with 12-16 ft seas expected on the ocean by Thursday morning and 3-7 ft on the Long Island Sound. Winds will gradually diminish during the day on Thursday, falling below SCA criteria on all waters by Thursday night, although ocean seas will continue to remain elevated. Northerly winds will continue to diminish Friday with high pressure building across the waters into Saturday. The high builds offshore late Saturday with a weak return flow into early next week. Sub SCA conditions are then forecast into early next week. && .HYDROLOGY... A winter storm will bring liquid equivalent precipitation totals of 1-1.5 inches through the day on Thursday, with the majority falling through Thursday morning. Any melting should be slow as high temperatures remain below 40 until the weekend. && .TIDES/COASTAL FLOODING... Surge is expected to build to 2 1/2 to 3 1/2 ft in most spots across Lower NY/NJ harbor, W LIS, and south shore bays of W LI on NE winds ramping up to solid gale/marginal storm force this evening. Widespread moderate coastal impacts are expected along the south shore bays of Nassau County. Along W LI Sound, combo of 3-5 ft surf and elevated water levels will bring minor to moderate coastal impacts for shoreline roads and properties, particularly coastal Westchester and NW LI. Storm surge will likely peak out at 4-5 ft in spots tonight during time of low tide, but then is likely to settle back to 2 1/2 to 3 1/2 ft during the times of high tide Thu morning/afternoon as winds shift to the north. These water levels, during a higher astronomical tide Thu AM/early aft, will bring potential for more widespread minor to moderate coastal impacts with Thursday morning/early aft high tide. Highest probability of widespread moderate coastal flood impacts (2 to locally 3 ft inundation) is along vulnerable south shore bays of LI and Queens with limited tidal drainage, with widespread minor to locally moderate impacts (1 to locally 2ft inundation) elsewhere. Have stayed close to deterministic surge guidance and NYHOPS weighted mean, with expectation of wind shifting to a less conducive N flow for surge. Will have to monitor guidance trends. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Warning until 1 PM EST Thursday for CTZ005>012. Coastal Flood Advisory from 9 AM to 2 PM EST Thursday for CTZ009. Coastal Flood Advisory from 11 PM this evening to 2 AM EST Thursday for CTZ009-010. NY...Winter Storm Warning until 1 PM EST Thursday for NYZ067>075- 078>081-176>179. Coastal Flood Advisory until 3 AM EST Thursday for NYZ079>081. Coastal Flood Advisory from 9 AM to 2 PM EST Thursday for NYZ071-078-079-081-177. Coastal Flood Advisory until 1 AM EST Thursday for NYZ072-074- 075-178. Coastal Flood Advisory from 8 AM to 11 AM EST Thursday for NYZ072-074-075. Coastal Flood Advisory from 11 PM this evening to 2 AM EST Thursday for NYZ073-176. Coastal Flood Warning until 1 AM EST Thursday for NYZ179. Coastal Flood Warning from 8 AM to 2 PM EST Thursday for NYZ080-178-179. Coastal Flood Warning from 11 PM this evening to 2 AM EST Thursday for NYZ071-078-177. NJ...Winter Storm Warning until 1 PM EST Thursday for NJZ002-004- 006-103>108. Coastal Flood Advisory until 1 AM EST Thursday for NJZ006-106- 108. Coastal Flood Advisory from 8 AM to 11 AM EST Thursday for NJZ006-106-108. MARINE...Gale Warning until 1 PM EST Thursday for ANZ330-335-338-340- 345. Storm Warning until 7 AM EST Thursday for ANZ350-353-355. && $$ SYNOPSIS...FEB/DW NEAR TERM...FEB/DW SHORT TERM...FEB LONG TERM...DW AVIATION...BG MARINE...FEB/DW HYDROLOGY...FEB/DW TIDES/COASTAL FLOODING...NV
Area Forecast Discussion
National Weather Service Blacksburg VA
924 PM EST Wed Dec 16 2020 .SYNOPSIS... Low pressure off the North Carolina coast will head north and northeast off the mid- Atlantic by Thursday with wintry weather ending tonight. Residual snow showers will be leftover along our western slopes through Thursday night before surface high pressure settles in Friday. High pressure stays in place into Saturday before a weak system arrives late Saturday into Saturday evening. && .NEAR TERM /THROUGH THURSDAY/... As of 920 PM EST Wednesday Winter storm ending, headlines will be cancelled. Last of the precip is exiting the piedmont. Will see some lingering snow showers/snizzle/freezing drizzle potential late tonight across the western slopes but not enough to warrant extending an advisory/warning. Given the main impact from the storm is over, will be cancelling the warnings/advisories early. However, will issue an SPS for slick roads for the overnight. Previous discussion from early this evening... Dry slot moving across the piedmont/foothills mid afternoon, with deformation arriving in the mountains. HRRR and Nested NAM and RAP have decent handle on where precip is, but still differences in ptype. 18z RNK sounding showed a pronounced warm nose to 4.2C above 850mb. This had led to mostly a freezing rain/sleet event for the area today. Forecast model soundings suggest cooling of the warm nose heading into the evening and with some enhanced lift with the deformation zone, should be some snow mixing into the mountains through this evening which could lay down a 1 to 3 inch amount. We let the advisory expire east as most temps are running above freezing and by the time the precip exits the piedmont this evening, temperatures will be back toward freezing. Still a threat of re-freeze so may issue special wx statement to account for this. Previous discussion from early this afternoon... Wintry mix impacting most of the area overnight into Thursday morning. This system has been largely composed of a sleet and freezing rain mix in our area. Some of the higher elevation locations had up to an inch or inch and a half in the Greenbrier Valley early this morning, but on the whole, sleet and freezing rain have been the order of the day due to a warm nose around 850-750mb. Comparing the 16/12Z sounding at RNK to the 16/18Z sounding currently in progress, that warm layer has grown in magnitude (less than a degree Celsius this morning, to ~4 degrees this afternoon). This indicates that the main precip type in the NRV and likely much of the CWA will remain sleet/freezing rain this afternoon. This evening colder air will wrap around behind the system with some enhanced northwest flow from an upper trough. As this erodes the warm layer, things will slowly transition to snow, mostly along mountain ridges from Greenbrier down to Tazewell, and perhaps in the NC High Country. Upslope effects in these areas will serve to enhance snowfall. There is a lesser chance of accumulating snow reaching all the way east to the Blue Ridge, so outside of the mountainous areas there may only be an inch or two. Lingering upslope will last until around midnight and perhaps a little longer in Western Greenbrier. There is a possibility of a refreeze on the roads Thursday morning, as some of the ice and snow from today melts and then cold morning temperatures freeze it back up. The threat is greatest on untreated roads and overpasses/bridges. Other than that, Thursday looks to be a quiet weather day with highs in the 30s and low 40s as high pressure approaches from the southeast CONUS. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... As of 115 PM EST Wednesday... Quieter weather returns with a slight chance of some light precipitation by Sunday. Upper-level trough will be centered over the eastern United States Friday night, with weak northwest flow keeping the chance for snow showers for the western mountains. Any accumulations Friday night should remain light. Snow showers will taper off Friday afternoon. Tranquil weather is expected for Saturday as surface high pressure builds overhead. High pressure shifts east as weak system approaches our area from the west. It is possible there may be enough antecedent cold air remaining that there could be a light mix of rain/snow for the western portions of the CWA. It is very unlikely this will be widespread and currently expecting little to no snow accumulations. Daytime temperatures will moderate each day through Saturday, but overnight lows both Friday and Saturday will be cold. This could allow for spots to refreeze overnight from any melting that occurs during the day. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 145 PM EST Wednesday... Long term forecast highlights for Sunday some rain and snow, followed by mostly warming weather. A cold front will travel through our region Sunday with a chance for rain and snow showers mainly in the west. Forecasted model soundings support a mix of snow and rain showers Sunday morning, before turning over to mostly just rain by the afternoon besides some of the higher areas like western Greenbrier. Questions remain on the development of low pressure center across the Gulf to Southeast. In any case, this feature remains to our south. For Monday, more zonal flow in the mid levels persist as a new, weaker upper level trough per ECMWF and GEFS dips southward Monday night into Tuesday. A few snow flurries may be possible along the western slopes. Temperatures will moderate Tuesday into Wednesday, as a strong upper level trough develops over the western/central U.S., setting us under a large area of high pressure. A cold front approaches Wednesday night into Thursday with a chance of rain and snow showers. Medium confidence in the long term forecast. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... As of 620 PM EST Wednesday... Very poor flying conditions this evening into overnight expected, especially along/west of the Blue Ridge, but even this evening at LYH/DAN. The wintry wx will impact ROA/BCB/BLF/LWB moreso than LYH/DAN. Cigs should improve to MVFR east of the Blue Ridge between 05z- 10z, then scatter out Thu morning after sunup. Across the mountains, low clouds are expected to linger til mid morning, but should see it lifting to MVFR at ROA/BCB/LWB in the 11-17z time frame, with VFR at ROA by late morning. BLF should keep IFR til midday, then MVFR though confidence is low on the speed of this happening. As for vsbys looking at IFR at times with wintry wx this evening, then MVFR/IFR with fog til Thu morning for some terminals. Flying conditions are poor with low ceilings and a mix of mainly sleet and freezing rain across all local airports. Ceilings will fall to low-end MVFR/IFR and visibilities down to 3SM or less in the widespread precipitation by 14Z. Vsbys should become VFR by late morning Thursday. Extended Aviation Discussion... Lingering sub-VFR is possible into early Friday morning at BLF/LWB, while rest of the area goes VFR. Expect VFR Friday into the weekend, though a weak system may bring sub-VFR cigs to the mountains Sat evening into Sunday. Most will keep VFR through Monday. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...Winter Storm Warning until midnight EST tonight for VAZ010>020- 022>024-032>035. Winter Weather Advisory until midnight EST tonight for VAZ007- 009. NC...Winter Storm Warning until midnight EST tonight for NCZ001-002- 018. WV...Winter Storm Warning until midnight EST tonight for WVZ042>044- 507-508. && $$ SYNOPSIS...NF/WP NEAR TERM...VFJ/WP SHORT TERM...BMG LONG TERM...KK AVIATION...NF/VFJ/WP
Area Forecast Discussion
National Weather Service Tulsa OK
810 PM CST Wed Dec 16 2020 .DISCUSSION... The main change to the forecast this evening was to adjust the fog forecast for the overnight into Thursday morning. Time height plots of moisture indicate that the hydrolapse (rate of change of humidity with height) is unfavorable for fog development across much of eastern Oklahoma. However, conditions across the Ozark Plateau (far northwest Arkansas and nearby areas of northeast Oklahoma) appear much more favorable for fog development. One caveat is the low clouds currently over the area. The 00Z HRRR suggests that the west to east clearing trend observed on satellite will continue thru the night, with areas mentioned earlier clearing out after 09Z. So there appears to be a window for the potential of fog development before the giant energy ball starts heating things up Thursday morning. With temps below freezing, if fog forms and is dense enough, slick spots could develop on bridges and overpasses in freezing fog. Confidence isn`t overly high, mainly because there`s really no guidance that shows fog and there is still some uncertainty with the clearing of the low clouds. If the low clouds don`t clear, the fog potential would be much lower. Due to the lower confidence, will not issue any headlines at this time. Will mention potential in graphics and the Hazardous Weather Outlook. Lacy && .PREV DISCUSSION... /Issued 522 PM CST Wed Dec 16 2020/ AVIATION... CONCERNING TAF SITES KTUL/KRVS/KBVO/KMLC/KXNA/KFYV/KFSM/KROG. Conditions will improve to VFR at the Oklahoma sites early this evening, and at the Arkansas sites later tonight. VFR conditions will then prevail for the rest of the forecast period. PREV DISCUSSION... /Issued 228 PM CST Wed Dec 16 2020/ DISCUSSION... It`s another cold afternoon across the region today with highs generally in the mid 30s across the forecast area under persistent cloudiness. Clouds will begin to clear from west to east later this afternoon and evening. Temperatures will drop into the mid to low 20s for most areas tonight under surface high pressure. Some areas where there is still substantial snow pack and where skies clear could see temps drop into the upper teens. Some patchy fog/freezing fog will also be possible mainly north of I-40 tomorrow morning where skies clear this evening. Tomorrow... a mid-level ridge will build into the area which will allow temperatures to rebound into the upper 40s - mid 50s under sunny skies. Bumped temperatures up a bit mainly south of I-40 where there is no snow cover. Highs could remain a little cooler in areas that received the greatest snowfall that will require substantial melting tomorrow. By Friday, a mid level trough begins to dig into the Desert Southwest which will bring southwesterly flow aloft. This will aid in surface cyclogenesis across the High Plains with a cold front stretching from the Northern Plains into the Texas Panhandle by Friday morning. With a surface high settling across the Southeast U.S., a tight surface pressure gradient will form by Friday afternoon which will lead to strong south winds on Friday with gusts in excess of 30 mph common across northern Oklahoma as we mix into a strong 40-50kt low level jet at 925mb. Cold front will pass through the area from northwest to southeast on Friday night. With weak moisture return across much of the area by Friday, expecting most areas north of I-40 to be dry with best chances for some light showers across Southeast Oklahoma where better moisture will be in place. Saturday and beyond... Saturday will be a bit cooler in the wake of the frontal passage with highs back down to near climatological normal for this time of year. After Saturday, a warming trend will begin as mid and upper level ridging builds into the area and southwesterly downslope winds return to the area. Monday and Tuesday will see highs well above normal with many places jumping back into the 60s. The next strong cold front is currently forecast to move through the area on Wednesday, but appears mostly dry at this time. This will drop temperatures back down near normal for Christmas Eve and into Christmas Day. Bowlan && .PRELIMINARY POINT TEMPS/POPS... TUL 24 49 35 56 / 0 0 0 0 FSM 27 51 30 57 / 0 0 0 0 MLC 26 54 35 56 / 0 0 0 0 BVO 22 48 31 54 / 0 0 0 0 FYV 23 49 28 55 / 0 0 0 0 BYV 24 47 30 54 / 0 0 0 0 MKO 24 46 32 55 / 0 0 0 0 MIO 24 47 31 55 / 0 0 0 0 F10 24 50 34 55 / 0 0 0 0 HHW 27 55 32 57 / 0 0 0 0 && .TSA WATCHES/WARNINGS/ADVISORIES... OK...None. AR...None. && $$ SHORT TERM...30