Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 202048 AFDALY Area Forecast Discussion National Weather Service Albany NY 348 PM EST Mon Nov 20 2017 .SYNOPSIS...
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Light snow and lake effect snow showers will dissipate this evening as a warm front lifts northward tonight. In its wake, looking at fair and milder weather for Tuesday as temperatures warm to above normal ahead of an approaching cold front. This cold front will bring the chance for additional precipitation overnight Tuesday into Wednesday morning.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 330 PM EST...Main challenge in the near term is the combination of lake effect snow and approaching warm front. Lake effect snow continues downwind of Lake Ontario this afternoon. Trends from both radar and GOES16 data suggest the upstream moisture feed is becoming disrupted a bit along with warm advection occurring upstream. However, the complicated aspect to this forecast is the approaching warm front where some seeder- feeder processes is underway along with increasing isentropic lift 280-290K surface. Upstream radar and observations indicate an area of light snow was evolving and tracking northeast and per the HRRR/HRRRX, seems a period of light snow or flurries can be expected this evening across the central and northern portions of the forecast area. Visibilities upstream remain quite high so little accumulation is expected with the warm frontal passage. The lake bands at that time should have lifted northward and weakened so we will hold onto the advisory for now with an additional few inches of snow expected. Skies should begin to clear from southwest to northeast overnight as strong dry advection with increase low jet magnitudes unfold across the county warning forecast area. Overnight lows will generally remain into the 20s to around 30F for some valley locations.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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Digging upstream short wave approaches the western Great Lakes through the day Tuesday. This in turn will allow for downstream ridging to commence along with the southwest flow regime. A good deal of November sunshine is in the forecast as just how high temperatures will get and just how much of those wind magnitudes mix down to the surface. A downsloping component should aid with milder temperatures for valley locations as we will shade closer to the warmer side of the guidance envelope. Along with the warmer temperatures, BUFKIT momentum transfer for those higher wind magnitudes suggest we tap into the 20-30KT range during the day. So a relatively mild and breezy day appears to be unfolding for Tuesday for entire region. The aforementioned upstream trough amplifies further with strengthening baroclinicity and frontogenesis is the result Tuesday night. In addition, strengthening upper level jet and diffluence across the southeast CONUS brings about a developing surface wave tracking along or just east of the coastline. While NCEP Model Suite and international guidance differ with this track of this coastal wave, consensus was a bit east to limit its direct impact to the region. But the cold front will impact most of the region overnight with the chance of precipitation increasing from northwest to southeast. As per thermal profiles, seems initially a mainly wet start to the onset of precipitation, then as colder air quickly advects in from the west, a transition to rain/snow to just snow is expected mainly west of the Hudson toward sunrise Wednesday. This front is quite progressive and its timing would exit our eastern zones by mid-morning Wednesday. Then brisk westerly winds within cold advection will be the main story through the remainder of the daylight hours. There might be some minor lake response but profiles suggest subsidence layer is rather quick to lower at this time so minimal to no lake effect impacts expected. Clearing skies and light winds expected toward sunset Wednesday which should last into the nighttime period as yet another ridge axis at all levels tracks across the region. Should be rather chilly with mainly lower half of the 20s expected.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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This will be a period of relatively dry conditions with just one system of any real consequence. Thanksgiving evening meals will begin with partly cloudy and seasonably cool conditions, and temperatures dipping below freezing everywhere well before midnight. A cold front will barely make it into our region, and could produce a period of light snow showers or flurries in the Adirondacks. Low pressure racing eastward across southern Canada will bring most of our region a quick hit of showers on Saturday. Timing will decide if it will be more snow or rain, overall, but since it looks like more of a daytime event, from the Capital Region on south, we can expect any snowy start to quickly mix over to rain. Even most areas in the Adirondacks and Greens will likely see more liquid, and no accumulating snow. The cold front with this system, expected to come through in double- barrel form, will bring us colder than normal air, with high temperatures by Friday ranging from only the lower and mid 20s in the Adirondacks...to the upper 30s in the Mid-Hudson Valley. A trof of low pressure stays well north of New York State and weakens early next week as high pressure begins to build in from the deep south. High temperatures will peak on Saturday, with the readings in the mid 30s to upper 40s range. Lows peak at just below freezing Friday night, with similar values Saturday night, but lows will range from only around 10 degrees to the mid 20s Sunday night.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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VFR conditions generally expected to prevail at the KALB/KPOU/KGFL/KPSF TAF sites through the 24 hour period ending 18Z Tuesday. The only exception would be if any fragments of lake effect snow bands make it to KALB/KGFL terminals. Will mention VCSH in TAFs for these sites, with the expected time window from around 21Z-00Z this evening. Some hi-res guidance indicating the possibility for a narrow band of snow showers, but confidence is low due to complex set up with warm advection developing but lake effect moisture/instability remaining. At worst, about a 1-2 hour period of MVFR conditions with snow showers would occur, but best approximation is for VFR conditions mentioning VCSH at this time. Skies will clear tonight as the flow becomes S-SW and any lake effect snow showers lift well north of the region. VFR conditions will prevail through early Tuesday afternoon with mainly clear skies. Winds through the rest of the day will be W-SW around 10-12 kt with some occasional gusts near 20 kt. Winds tonight will become S-SW around 3-6 kt, increasing to 10-15 kt by early Tuesday afternoon. Outlook... Tuesday Night: Moderate Operational Impact. Chance of SHRA. Wednesday: Low Operational Impact. Breezy Slight Chance of SHRA. Wednesday Night: No Operational Impact. NO SIG WX. Thanksgiving Day: No Operational Impact. NO SIG WX. Thursday Night: No Operational Impact. NO SIG WX. Friday: No Operational Impact. NO SIG WX. Friday Night: No Operational Impact. NO SIG WX. Saturday: Moderate Operational Impact. Chance of SHRA...SHSN.
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&& .FIRE WEATHER...
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Light snow and lake effect snow showers will dissipate this evening as a warm front lifts northward tonight. In its wake, looking at fair and milder weather for Tuesday as temperatures warm to above normal ahead of an approaching cold front. This cold front will bring the chance for additional precipitation overnight Tuesday into Wednesday morning.
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&& .HYDROLOGY...
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No hydrologic problems are expected this week. Lake effect snows will shift northward to the western and southern Adirondacks and weaken this evening. Otherwise isolated to scattered showers are expected across the remainder of the region with drier conditions overnight. Fair and milder weather for Tuesday with some rain and snow showers expected late Tuesday night and Wednesday morning as a cold front crosses the region and an area of low pressure passes well south and east of Long Island. QPF amounts are expected to be light with less than a quarter of an inch. Fair weather returns for Thanksgiving with unsettled weather expected this weekend. 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.
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&& .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Winter Weather Advisory until 9 PM EST this evening for NYZ032- 033. MA...None. VT...None. && $$ SYNOPSIS...BGM NEAR TERM...BGM SHORT TERM...BGM LONG TERM...ELH AVIATION...JPV FIRE WEATHER...BGM HYDROLOGY...IAA/BGM

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