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Albany, NY WFO Forecast Discussion
000 FXUS61 KALY 081203 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 703 AM EST Fri Dec 8 2023 .SYNOPSIS... A warm front will slowly lift northward today into Saturday, bringing milder temperatures despite considerable cloudiness. A strong cold front will bring a period of heavy rain and gusty winds late Sunday into Sunday night, with rain possibly ending as snow Monday morning as colder air surges into the region. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Cloud layer trapped by an inversion anchored by NW boundary layer flow will persist much of the day over our region. Some clearing in the mid Hudson Valley and NW CT that could remain through at least this morning, with just a few high clouds around. The boundary layer ridge axis is expected to shift east of our region this afternoon, along with a boundary layer wind shift to the west and southwest but winds will be weak. The lower cloud layer should erode slowly from the west and southwest through the day but temperatures should not be able to rise much with the clouds and low sun angle not allowing for much mixing. Highs in the upper 30s to around 40 with mid 30s northern areas. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... The amount of cloud erosion tonight is in question as considerable high clouds are building into our region and the boundary layer southwest winds are expected to be quite weak, while surface winds should be south to south southeast, along with lingering low level moisture. While some breaks in the clouds are likely in some areas, clouds may again be slow to exit in some areas, especially the Hudson River and points east. Some patchy fog is also possible into early Saturday morning. Then, if there are lingering clouds and patchy fog, with the very weak southwest boundary layer winds and weak sun angle, some areas may take quite a bit of time to clear out during the day Saturday. There is a lot of uncertainty and quite a bit of inconsistencies in sources of guidance/ensembles but favoring the cooler side of guidance for highs Saturday. Highs in the mid 40s to near 50 with lower 40s higher terrain. Amplifying upper trough begins its approach Saturday night and strengthening warm advection, as well as boundary winds shifting more south southwest and increasing, will help temperatures warm on Sunday. However, increasing low level jet forcing, moisture advection, upper dynamics proximate to the upper impulse going negative tilt, and isentropic lift, will result in rain spreading over our region through the day. The high amplitude upper trough suggests moisture from the Gulf of Mexico and Atlantic Ocean will result in anomalous moisture and the very strong low level jet forcing will produce a widespread heavy rain with potential localized flooding. In addition to the heavy rain, winds will become gusty, especially in higher terrain, where winds could gust over 40 mph by Sunday afternoon. Some chances for even stronger winds but how much mixing of the strong winds to the surface in the heavier rain is in question. Highs Sunday in the mid to upper 50s with upper 40s to near 50 higher terrain. Upper energy begins to exit and lift north and east Sunday night as the leading edge of a tight boundary layer thermal gradient and wind shift track through our region Sunday night. There are still disagreements in guidance as to the timing of the onset of the passage of the low level cold front, whether it is before midnight or after midnight. Either way, cooling will be occurring by daybreak Monday. Some conditional instability and the strong low level forcing suggests a line of shallow convection or narrow cold frontal rain band, that could even have a rumble of thunder. Some enhanced gusty winds and one last burst of heavy rain is possible. Rain will change to snow in the southern Adirondacks and perhaps parts of the eastern Catskills, with an inch or two in the highest peaks by daybreak Monday. && .LONG TERM /MONDAY THROUGH THURSDAY/... Our main focus for the long term period will be on Monday when a changeover to a period of heavy, wet snow is looking increasingly likely on the backside of our impressive cold front from Sunday night. Confidence is increasing for a secondary sfc low to not only develop along the boundary Sunday night but for it to develop in the equatorward entrance region of a north-to-south oriented 130-50kt jet streak positioned on the leading edge of the parent trough. As the parent trough tracks into the Northeast and trends from a neutral to a slight negative tilt early Monday morning, strong upper level divergence will likely occur, allowing the secondary low to undergo cyclogenesis and deepen. Guidance now indicates it closes off up to 700hPa by 18 UTC Monday as it tracks just to our south/east and pushes into northern New England. This will allow much colder air to quickly advect eastward as gusty sfc winds shift to the northwest. As a result, thermal profiles crash by 12 - 18 UTC Monday and with precipitation still occurring in the deformation zone north/west of our exiting low, precip likely switches to heavy, wet snow Monday morning. This unfortunately coincides with the Monday morning commute so slippery travel conditions are looking increasingly likely, especially for the higher terrain and hill towns in eastern NY and western New England. Wet-bulb zero heights drop down to about 500ft by 12 - 15 UTC so elevations as low as 500ft will likely see some snow accumulations. Even valley areas of the Greater Capital District could see a changeover to wet snow Monday morning as temperatures and dew points drop into the low to mid 30s. With such favorable dynamics in play, forecast soundings also show high omega/lift intersecting the dendritic snow growth zone (DGZ) so the hill towns in the Helderbergs, Taconics, and foothills of the southern Adirondacks/Catskills as well as the higher terrain will likely see a period of moderate to even heavy snowfall rates. Thermal profiles favor lower than climo snow to liquid ratios (SLRs) which will likely yield a wetter/heavier type of snow instead of light/fluffy. The probabilistic WSSI graphics (PWSSI) indicate that these higher terrain and hill towns 1000ft in elevation and higher may experience some snow loading issues given the weight of wet snow. Current PWSSI highlight the southern Adirondacks in its 40 - 60% range for impacts while the northern/eastern Catskills and southern Vermont range 20 - 30%. Helderbergs/Taconics and other hill towns are only in the 10- 20% range. Overall, snow amounts look light to moderate with WPC Winter Storm Outlook showing the greatest probabilities for warning level snow amounts (7" +) limited to the southern/western Adirondacks. This is likely tied to the low SLRs and rather short duration for heavy/wet snow confined mainly to late Sunday night through midday Monday. Some snow loading issues from heavy/wet snow will need to be monitored for these higher terrain areas. To exasperate matters, west-northwest winds will be strong and gusty throughout the day Monday with gusts reaching 30-40mph, potentially higher in the higher terrain areas. Wind advisories may also be needed. The strong winds and weight of heavy wet snow may necessitate winter weather advisories or even isolated winter storm warnings to help us message snow loading impacts for Monday, even if exact snow amounts technically fall below warning criteria. The rest of the week looks fairly quiet and seasonable with potentially an Alberta Clipper dragging an arctic into the Northeast mid-week. Depending on timing and the thermal/moisture gradient, the front may lead to snow showers or even snow squalls but this is still a low confidence forecast. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... As of 12 UTC, MVFR ceilings are in place at ALB, GFL, and PSF with low-end VFR visibility due to some patchy mist. Skies have cleared at POU but mist has resulted in MVFR visibility. These conditions should continue through 15 - 18 UTC but as cirrus clouds continue to spill eastward this morning, low stratus should erode and lead to VFR conditions. There is some uncertainty regarding the exact timing for MVFR ceilings to erode as an incoming warm front will remain to our south which tends to keep low stratus around longer than we expect. For now, we should VFR conditions arriving by 18 - 20 UTC but we would not be surprised if low stratus continue longer, especially at PSF. Assuming low stratus clear late this afternoon into this evening, enough radiational cooling should ensue that low stratus return by 03 - 06 UTC with even some fog possible. IFR ceilings are evening and if they develop, should persist through the end of the TAF period. Light and variable winds expected through 00 UTC/09 before south-southeast winds strengthen towards 5kts tonight. Outlook... Saturday Night: Low Operational Impact. Slight Chance of RA. Sunday: High Operational Impact. Breezy. Definite RA. Sunday Night: High Operational Impact. Windy With Gusts To 31 kts. Definite RA. Monday: Moderate Operational Impact. Windy With Gusts To 31 kts. Likely RA...SN. Monday Night: Moderate Operational Impact. Breezy. Chance of SHSN. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: Low Operational Impact. Breezy. NO SIG WX. && .HYDROLOGY... A strong cold front is expected to move across the region Sunday evening bringing a period of heavy rainfall to the area. Total rainfall from Sunday afternoon into Monday morning will range from 2 to 3 inches across the area. Locally higher amounts cannot be ruled out across the higher terrain of the Catskills. Some rivers could approach bankfull or even minor flood stage. This is supported by latest river ensemble guidance from the HEFS/NAEFS. If this threat materializes will depend on much rain falls, how much snow can melt out of higher elevations, and frozen versus non frozen ground. There could be some nuisance urban and small stream flooding in low lying areas as well. The latest WPC Day 4 Excessive Rainfall Outlook placed the entire hydrologic service area within a marginal risk of excessive rainfall. We will continue to carefully monitor trends. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. MA...None. VT...None. && $$ SYNOPSIS...NAS NEAR TERM...NAS SHORT TERM...NAS LONG TERM...Speciale AVIATION...Speciale HYDROLOGY...