Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 200320 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 1020 PM EST Sat Jan 19 2019 .SYNOPSIS... Snow will increase in intensity and become heavy tonight in advance of a warm front to a storm system moving out of the Tennessee Valley and then redeveloping and reaching the Jersey Coast Sunday morning. Some mixed precipitation of sleet and freezing rain is possible from the Capital Region and points east and south, as the low pressure system moves towards Long Island. The snow and mixed precipitation will diminish Sunday afternoon, as the cyclone moves into the Gulf of Maine. Dangerously cold wind chills are expected Sunday night into Monday with frigid temperatures and blustery winds. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Winter Storm Warning for Eastern NY and western New England until 4 pm Sunday... Updated at 10 pm... Snow is increasing in intensity late this evening as a strong system approaches from the southwest. We still expect the heaviest precipitation to fall from about midnight to 8 am as an axis of very strong low-level frontogenesis and warm advection translates across the area on the northeast flank of the system tracking from the Ohio Valley across Pennsylvania. Precipitation type is still snow as far south as northern NJ and central Pa late this evening, however we expect the snow / sleet and freezing rain boundaries to beginning moving north after midnight. Details on the exact location of those boundaries as they reach their farthest northward location around 12z Sunday continue to be the main source of uncertainty with this forecast. The models have not handled the low-level temperatures very well this evening and this will likely effect the track of the surface low as it tracks across the northern mid-Atlantic late tonight. Temperatures have been colder than forecast especially in the upper Hudson Valley and southern Adirondacks where readings have dropped down into the single digits to near zero. The latest 00z NAM forecast is a bit farther south with the track of the surface low and is just a bit colder with its thermal profiles than the previous couple of runs, however it would still support a change from snow to sleet as far north as the northern part of the Capital District around daybreak Sunday. We suspect that when all is said and done sleet will mix with the snow just about up to Saratoga Springs Sunday morning which will cut back on snow amounts from that area south. South of Albany there will be a stripe of freezing rain with the potential for significant icing up to half an inch from the Catskills through the mid- Hudson Valley. Obviously with a forecast this complex there are uncertainties but the current forecast seems to handle things about as well as could be expected at this point. Updated at 7 pm... a large area of mostly light snow has overspread the area well ahead of a significant wave moving northeast up the Ohio Valley. Snowfall in our area thus far has been mostly light with accumulations through 7 pm of 2 inches or less. Upstream observations and high resolution models all indicate that snowfall rates will increase significantly toward midnight as the wave approaches and strong upward vertical motion develops in association with a band of strong low-to-mid level frontogenensis on the northeast side of low pressure tracking from the Ohio Valley toward Pennsylvania. Low-level temperature gradients with this system are already quite impressive this evening as temperatures have fallen below zero over northern NY, and into the single digits and lower teens in the upper Hudson Valley and Capital District, while remaining in the 20s to near 30 in the mid-Hudson Valley. Temperatures are also warmer east and west of the Hudson Valley indicating that the cold air is being funneled down the valley. Only changes with this update were to delay the heavy snow until around midnight for most areas and also to adjust temperatures to the current trends. Previous discussion is below. The latest trends in data and guidance indicate the precipitation transition zone is expected to build a bit farther north and west than previous data and guidance suggested. There is quite a good consensus in sources of guidance and radar and satellite trends are also consistent with sources of near term guidance. Snow is in the process of spreading across the region and the heavier/steadier snow is in the OH Valley and central Appalachians building northeast. Warm air aloft will change snow to sleet from about the Capital District through central/northern Taconics to parts of southern VT and points east and south. North surface winds will keep surface temperatures quite cold across the region and the depth of the coldest air will determine where there will be mostly sleet and where there will be a period of freezing rain. The best chance for the shallowest cold air is in areas just east of the Catskills, through mid Hudson Valley, NW CT and southern Berkshires, where some accumulating freezing rain is likely. The sleet and freezing rain will begin before sunrise in all areas that see the mix and end through the late morning and midday Sunday. Somewhere in the freezing rain zone could see a third of an inch of ice or greater. The boundary layer warming being drawn north may be more of a function of stronger boundary layer frontogenesis drawing warm air northward but stronger anchoring of the cold airmass to the north as well. There is a very impressive surface temperature gradient across NY and New England right now seen in the NY Mesonet and other data sources with below zero to the north and solidly in the 30s in the south. Based on CSTAR research, strong frontogenesis should set up from the western/central Mohawk Valley through southern Adirondacks, Lake George Saratoga Region to parts of southern VT supporting a lateral quasi stationary mesoscale band with enhanced snowfall rates of greater than 2 inches per hour. That is where yardsticks will likely be needed to measure the storm total snows. Mixed precipitation will reduce snow amounts in the Capital Region and points east and south but still enough snow will fall for a significant impact across the region. Temperatures tonight will likely fall only a couple or few degrees from current temperatures. Steadier snow will help temperatures to fall in addition to in addition to northerly surface winds and ageostrophic low level winds anchoring cold air from the north. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/... Winter Storm Warning for eastern NY and western New England until 4 pm Sunday Precipitation tapers off rapidly through Sunday morning and ends as snow showers Sunday afternoon as the cold air spreads from northwest to southeast and winds pick up from the north and northwest. The core of the northern stream upper low drops through our region Sunday night through Monday with snow showers and flurries mainly in the western Mohawk Valley, Schoharie Valley and eastern Catskills but some flurries are possible everywhere into Sunday night. Extreme cold and gusty winds spread across the region Sunday night and cold air is anchored over the region through Monday night. Wind chills Sunday night and Monday drop to well below zero and some wind chill headlines may be needed once the storm begins to depart and once we can zero in on the specific areas that will reach criteria. Lows Sunday night below zero in many areas with single numbers in southern areas. Highs Monday in the single numbers but below zero in northern areas. Intervals of clouds and some flurries are possible through Monday until the upper low exits. The strong low level ridging approaches Monday night, the sky will clear and winds trend to light by sunrise Tuesday. Lows early Tuesday morning will be below zero again in most places. Warm advection begins Tuesday with highs in the 20s but teens in northern areas. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The long term forecast period will begin with high pressure departing to our east and an upper level trough approaching from the west. This will result in increasing clouds from west to east throughout the day on Wednesday. There will also be increasing chances for precipitation throughout the day with a low pressure system approaching from the Great Lakes region. The Capital Region and locations to the south will see a chance for mixed precipitation while locations to the North of I-90 will see a better chance for all snow. The front draping to the south looks to stall out somewhere along the East Coast late Wednesday into Thursday. Guidance suggests the potential for cyclogenesis along this boundary with low pressure translating from SW to NE along the boundary. This will bring chances for snow and mixed precipitation Thursday and Friday, primarily over western New England. The exact details will have to be worked out as we head through the week seeing as there is quite a bit of uncertainty within the guidance. Lingering upper level cyclonic flow will be in place on Saturday so there will be a chance for some snow showers across the region. Temperatures will generally be near normal with highs in the 20s/30s and lows in the teens/20s. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... A complex winter storm will affect the area tonight through Sunday morning. Light snow has overspread the TAF sites early this evening. The snow will become heavier toward midnight with vsbys lowering from near to just above 1 mile at many locations until midnight, down below a mile after midnight. The snow will then change to sleet from south to north after midnight, with sleet then freezing rain at POU after 07z, and sleet as far north as ALB and PSF by 10-12z. Meanwhile, GFL should remain all snow through Sunday morning. The precipitation could end as a little snow late Sunday morning or early in the afternoon at ALB/PSF/POU, then clouds will break toward evening. Winds will be from the north- northeast at 5 to 10 kts through tonight, shifting to northwest at 10 to 15 kts with gusts to 25 kts Sunday afternoon. Outlook... Sunday Night: Moderate Operational Impact. Windy With Gusts To 33.0 NO SIG WX. Martin Luther King Jr Day: Moderate Operational Impact. Windy With Gusts To 30.0 NO SIG WX. Monday Night: Moderate Operational Impact. Windy With Gusts To 30.0 NO SIG WX. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: Moderate Operational Impact. Chance of SN. Wednesday: High Operational Impact. Likely RA...SN...SLEET. Wednesday Night: High Operational Impact. Likely SN...SLEET. Thursday: Moderate Operational Impact. Likely SN. && .HYDROLOGY... A potent winter storm will impact the region today into Sunday afternoon. The precipitation type is expected to be mainly snow, with a wintry mix possible across the southern Berkshires, southeast Catskills, mid Hudson Valley, southern Taconics, and northwest Connecticut. Total liquid equivalent precipitation will generally be in the 1 to 1.5 inch range with some slightly higher amounts over the southern most basins. This precipitation will not have an immediate impact on area rivers and streams as it will be frozen/freezing precipitation. With the strong southeast flow, the tidal gauge at Poughkeepsie may hit the caution stage late Sunday morning into the early afternoon. Very cold and mainly dry weather is expected Monday into Tuesday. Another storm with snow or a wintry mix changing to rain is expected late Tuesday night through Wednesday, although precip amounts and precip types are still uncertain at this time. For details on specific area rivers and lakes, including observed and forecast river stages and lake elevations, please visit the Advanced Hydrologic Prediction Service /AHPS/ graphs on our website. && .EQUIPMENT... Intermittent radar outage is being worked on. Thank you for your patience. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Warning until 4 PM EST Sunday for CTZ001-013. NY...Winter Storm Warning until 4 PM EST Sunday for NYZ032-033- 038>043-047>054-058>061-063>066-082>084. MA...Winter Storm Warning until 4 PM EST Sunday for MAZ001-025. VT...Winter Storm Warning until 4 PM EST Sunday for VTZ013>015. && $$ SYNOPSIS...NAS NEAR TERM...MSE/NAS SHORT TERM...NAS LONG TERM...Cebulko AVIATION...MSE/BGM HYDROLOGY...NAS EQUIPMENT...

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