KALY issues Area Forecast Discussion (AFD) valid 2019-12-02T05:23:00Z 178 FXUS61 KALY 020523 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 1223 AM EST Mon Dec 2 2019 .SYNOPSIS... A storm system will bring periods of snow to the region through Monday night, with some sleet and freezing rain mixing in for southeastern areas tonight. Heavy snowfall amounts are expected for most of the forecast area by the time snow tapers off around daybreak Tuesday. Improving conditions are forecast for Tuesday with continued cold temperatures. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... As of 1220 AM EST, persistent intense snow band continues to affect areas close to and immediately north of I-90 in NY and MA, with snowfall rates of 1-2"/hour. Spotter reports indicate total amounts of 12-15 inches within the immediate Capital Region and higher elevations of southern VT, with locally higher amounts noted. Outside this band, precipitation remains much more spotty/intermittent, with a mix of sleet/freezing rain across the SE Catskills, mid Hudson Valley and NW CT/southern Berkshire County, and mainly light snow to the north across the southern Adirondacks, except for some transient moderate bursts of snow. The band of heavy snow appears to remain coincident within an area of dual upper level jet structure, as well as at the northwest edge of the low level jet impinging on the region from the east/southeast. As the upper level jet dynamics shift eastward, we expect this band to gradually weaken and shift east over the next few hours, with precipitation becoming more spotty across the region. Areas to the south and east of the Capital Region should continue to have a sleet/freezing rain/drizzle mix, with periods of snow to the north and west. Some mixing with sleet could eventually reach the I-90 corridor once precipitation intensity decreases. Temps will likely hold steady or slowly rise through sunrise, in the mid/upper 20s to lower 30s. Gusty east/northeast winds will persist across higher elevations of western New England and the Taconics, where some gusts of up to 35 mph will remain possible. Previous discussion follows... As of 949 PM EST...Large upper level low is slowly moving across the eastern Ohio Valley. At the surface, 3 hr pressure falls of up to 5 mb have been ongoing offshore southern New England in response to a developing surface low. The 00z KALY sounding is showing a low level southwesterly jet of around 35 kts. This warm advection has been allowing for a steady shield of precipitation across the region. Instead of translating through the area, the developing storm's warm conveyor belt has been backfilling the precip across the area, resulting in a persistent and steady area of precipitation. The southeastern Catskills, Mid Hudson Valley, southern Taconics, southern Berkshires and NW CT have been seeing a wintry mix of sleet and freezing rain mixing in at times as temps around 700-850 hpa are just nudging above freezing. However, the remainder of the area has been seeing just snow, with the entire thermal profile below 0C. Snowfall rates within the Capital Region have been 1 to 2 inches per hour since the late afternoon/early evening, with the heaviest amounts falling just west and north Albany. Some heavy batches have also been occurring across the Taconics and into southern VT, with some some rates of up to 3 inches per hour certainly possible as well. The NYS Mesonet & KALB observer has been instrumental in assessing the snowfall rates. Special Weather Statements and social media updates have been issued to address these high rates and dangerous travel across the region. 3km HRRR/NAM suggest steady precip will continue through at least midnight. Mixing with sleet/freezing rain looks to have gotten its farthest northerly extent and it should be slowly shrinking back south and east through the overnight hours. After midnight, precip may start to become lighter and more intermittent, with the steadiest precip located across the higher terrain. While we expected several additional inches through midnight, amounts after midnight will be on the lighter side (mainly just a few inches at most). Some drying aloft will also move in for late tonight. It will be borderline for ice nuclei to be present at all times, so some spotty freezing rain/freezing drizzle could occur in some areas (especially across western New England). Temps look to be fairly steady in the 20s late this evening but will start to creep up late tonight. All areas will remain below freezing, but temps may reach the upper 20s to low 30s towards sunrise, with the warmest temps in southern valley areas. && .SHORT TERM /6 AM THIS MORNING THROUGH TUESDAY NIGHT/... For Monday-Monday night, as the mid/upper level low slowly tracks east to northeast south of NYC/LI, mid level frontogenesis and deformation should bring bands of enhanced precipitation across the region, especially in the afternoon and evening. There remains some uncertainty on where these bands pivot, which is where greatest additional snowfall amounts will ultimately occur. It appears that after a brief lull in the morning (mainly east of the Hudson River), precipitation intensity will increase in the afternoon, and with cooling aloft, P-type should be mainly snow. Periods of moderate to heavy snow will become possible in the afternoon and evening hours, initially across the Mohawk Valley/eastern Catskills by late morning, then spreading into the Capital Region/Saratoga region during the afternoon hours, and eventually southern VT/western MA into the mid Hudson Valley and NW CT by sunset. If bands consolidate during this time, snowfall rates in some areas could reach or exceed 1-2 inches/hour. Bands of moderate to locally heavy snow should gradually shift south and east during Monday evening as the main mid level low shifts east. During this time, the mid Hudson Valley/NW CT and western MA may have the heaviest snowfall. Snow should eventually decrease in intensity from NW to SE through the night. Highs on Monday in the 20s to around 32. lows Monday night in the mid teens in the hills to mid 20s in the mid Hudson Valley. One of the main attributes to this storm system will be that total amounts will be spread out over a 36+ hour period (ending around daybreak Tuesday), with the potential for a lull in snowfall sometime late tonight into Monday morning. The snow will be intermittent and come in bursts at times where intensity increases, especially Monday afternoon/night. Tuesday will start mostly cloudy with a chance of a few snow showers/flurries early, with breaks in the clouds developing later in the day as high pressure starts to ridge in from the Ohio valley. Highs on Tuesday from the mid 20s hills to mid 30s valleys. Tuesday night looks to start mainly clear, but clouds will increase after midnight as a cold front approaches from the northwest. Lows Tuesday night mainly in the teens to low 20s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Wednesday into Thursday, a shortwave trough will dig across the Northeastern US. Moisture looks to be limited with this trough, but some snow showers are likely mainly west of the Hudson over the higher terrain. Some lake effect will contribute to the snowfall over the western Adirondacks as 850 mb temps over the lake drop to around -12C by 12Z Thursday. Expect mostly cloudy skies over the valleys and areas along the Hudson eastward, but little to no precipitation. Midlevel height rises later on Thursday may lead to some clearing in the valleys, with lake effect snow over the Adirondacks diminishing late as well. The period of subsidence associated with height rises looks to be limited to later Thursday into Thursday night, with another quick- moving shortwave on its heels for Friday. This looks to be a stronger cold front with the potential for snow showers extending into the valleys. While temperatures Wednesday through Friday look to be several degrees below normal, even colder temperatures are possible for next Saturday if model trends hold. && .AVIATION /05Z MONDAY THROUGH FRIDAY/... A winter storm continues to unfold across the region this evening. Moderate to briefly heavy snowfall is expected to continue at KALB through around 05Z, with the best chance for +SN through 02Z. IFR vsby expected to continue at KPSF/KGFL in snow, with potentially LIFR at KPSF through around 03Z. At KPOU, a wintry mix of snow, sleet, and freezing rain is expected to continue much of the night. It may lighten in intensity at times with MVFR vsby. Snow may transition to a wintry mix at KPSF/KALB/KGFL beginning in the 03-06Z time frame as precipitation intensity diminishes somewhat. Visibilities will improve at times after 06Z, but IFR conditions are expected to prevail. The snow will fill back in during the day on Monday. The snow is expected to be mainly light, but could briefly be heavier where banding sets up. IFR conditions are expected to prevail, with LIFR possible at times. Winds will be from the east to north at around 10 kt through much of the TAF period, gusting to 20 kt at times. Low-level wind shear conditions are likely at KPOU/KPSF early in the TAF period. Outlook... Monday Night: No Operational Impact. NO SIG WX. Tuesday: Low Operational Impact. NO SIG WX. Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: No Operational Impact. NO SIG WX. Wednesday Night: No Operational Impact. NO SIG WX. Thursday: Moderate Operational Impact. Chance of SHSN. Thursday Night: Low Operational Impact. Slight Chance of SHSN. Friday: No Operational Impact. NO SIG WX. && .HYDROLOGY... A winter storm will bring widespread moderate to heavy snowfall across eastern New York and western New England. Some mixed precipitation is possible at times, but no immediate hydrologic response is expected. Otherwise, some light snow is possible at times this week, with temperatures remaining below normal. This will allow the snow pack to be maintained and for ice to build and thicken on waterways. For details on specific area rivers and lakes, including latest observed and forecast river stages and lake elevations, please visit the Advanced Hydrologic Prediction Service /AHPS/ graphs on our website. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Warning until 7 AM EST Tuesday for CTZ001-013. NY...Winter Storm Warning until 7 AM EST Tuesday for NYZ038>043- 047>054-058>061-063>066-082>084. Winter Weather Advisory until 7 AM EST Tuesday for NYZ032-033. MA...Winter Storm Warning until 7 AM EST Tuesday for MAZ001-025. VT...Winter Storm Warning until 7 AM EST Tuesday for VTZ013>015. && $$ SYNOPSIS...SND/Frugis/KL NEAR TERM...Frugis/KL SHORT TERM...SND/KL LONG TERM...Thompson AVIATION...JLV HYDROLOGY...Thompson