Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 200519 AFDALY Area Forecast Discussion National Weather Service Albany NY 1219 AM EST Mon Feb 20 2017 .SYNOPSIS... An upper level disturbance moves through tonight with high pressure building back into the region behind it. Another weak mid-level disturbance approaching from the west will bring chances for light mixed wintry precipitation Tuesday evening through Tuesday night. Temperatures will generally be above average this week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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As of 1215 AM EST, Stationary front has settled south and oriented across the southern half of the forecast area. The tail of a band of clouds north of Lake Huron is eroding already. Based on trajectories in satellite imagery and cloud cover forecasts in guidance, cloud cover forecasts in guidance may be overdone for tonight into Monday morning in terms of southernmost extent. Guidance has been struggling to resolve the surface through boundary layer in the past week, with misrepresented cloud cover and winds through the low levels. So, with the thought that there will be a period of partly to mostly cloudy sky and some steady light winds through most of not all night in many areas, not straying far from guidance but siding with warmer guidance. Lows in the 30s with some 20s northern areas and maybe around 30 southern areas where less cloud cover potential. Boundary layer winds will be quite strong and shifting more to the north to northwest. Winds usually mix down more efficiently in cold advection. So, the odds are that most areas should see steady light winds tonight but still not sure if decreasing snow pack will create enough of an inversion to prevent winds from mixing down in some areas toward daybreak. Any areas that go calm will see colder temperatures.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH WEDNESDAY/... As said earlier, guidance has had considerable issues resolving the surface through boundary layer for some time now and with the tail of the cloud cover north of Lake Huron eroding already, would like to believe the suggestion from guidance that most areas will see lots of sun Monday. So, even with boundary layer temperatures cooling considerably, mixing potential would support highs at least a couple of degrees warmer than the warmest guidance, as long as we mix to around 850 hPa. Even if we mix to 925 hPa the highs should be at about the warmer guidance. So, highs Monday in the 40s, but near 50 southern areas and mid to upper 30s northern areas. The low level ridging shifts overhead Monday night and with a clear sky and nearly calm winds, temperatures will have a chance to fall into the teens to around 20. A quick moving upper impulse approaches our region Tuesday and some mid and high clouds should move into our region through the afternoon. There may be some spotty light rain in western areas by late Tuesday afternoon. Warmer boundary layer temperatures, west boundary layer winds and some sun filtered only by mid and high clouds in the afternoon should help temperatures to warm to the mid to upper 40s many areas but lower 40s northern areas. A shot of warm advection and isentropic lift will support patches of light rain and mixed precipitation Tuesday night. The mixed precipitation should be confined to the usual colder spots of northern areas, southern VT and the Berkshires. Since there are just chances, just mentioning the mix in the Hazardous Weather Outlook. The system exits later Tuesday night and with a warmer airmass and boundary layer temperatures in our region, Wednesday is expected to be sunny with a more significant warm up. West boundary layer flow should also help with mixing. Since guidance has again been struggling with temperature forecasts showing a cold bias, highs Wednesday solidly in the 50s, but some mid 40s northern areas and pushing 60 in southern areas. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Highly changeable conditions are expected through the long term, with the main storm track remaining north and west of the region. However, toward the end of the week into next weekend, as a stronger storm tracks from Colorado into the western Great Lakes, there is some suggestion that high pressure across eastern Canada builds southward. Depending on how strong and far south any potential sfc high builds, there could be a bout of wintry precipitation across at least northern portions of the region sometime between Friday and Saturday, with rain or showers elsewhere. A weak system should track north of the region on Thursday, with a cold front trailing from this system settling southward late Thursday or Thursday night. Some spotty rain showers or sprinkles may accompany the front. Before the front passes, a deep west/southwest flow should allow for very mild/warm temperatures regionwide, with highs reaching the 40s and 50s for most areas, with some 60s quite possible across portions of the mid Hudson Valley, if not even further north in the Hudson Valley. Gradual cooling spreads south and east Thursday night into Friday behind the front, with the main uncertainty being how far south this colder air seeps, again related to the strength of the high across eastern Canada. Although most global models currently suggest a fairly weak high, with the brunt of the low level cold air remaining north of the region, we have seen several instances this cold season where models are initially too weak/far north with such highs. So, have gone a bit colder than blended model guidance for Fri-Sat temperatures, with highs mainly in the 30s and 40s, and nighttime lows in the 30s. As the low approaches the Great Lakes, strengthening isentropic lift should allow precipitation to increase across the region sometime Friday and continue into Saturday, although there are timing differences among the global models, with some holding off any precip until Saturday. For now, have indicated chance pops Fri-Sat, with mainly rain, except for pockets of freezing rain across portions of the southern Adirondacks, Mohawk Valley and southern VT. Again, trends will have to be watched through the week, as the potential for more widespread and persistent mixed precipitation exists. The system`s cold/occluded front should move east of the region by Sunday, with windy and seasonably cool conditions in its wake, in addition to possible upslope and/or Lake Effect snow showers across northern areas. High temperatures should mainly be in the 30s and 40s. && .AVIATION /05Z MONDAY THROUGH FRIDAY/... Patches of cloud cover in the 4-6 kft AGL layer will move across the terminals from time to time overnight along and behind a cold frontal passage. Mainly clear skies are expected Monday as high pressure builds into the region. Northwest winds tonight at 10 kt or less. Winds will veer to a more northerly direction on Monday, gusting to 15-20kt at times before diminishing to 10 kt or less in the evening. Outlook... Monday Night: No Operational Impact. NO SIG WX. Tuesday: Low Operational Impact. Slight Chance of RA. Tuesday Night: Moderate Operational Impact. Chance of RA. Wednesday: No Operational Impact. NO SIG WX. Wednesday Night: No Operational Impact. NO SIG WX. Thursday: Moderate Operational Impact. Chance of SHRA. Thursday Night: No Operational Impact. NO SIG WX. Friday: Moderate Operational Impact. Chance of RA. && .HYDROLOGY... No widespread hydro problems are expected into the middle of next week with limited chances of widespread precipitation. Milder temperatures are expected into early next week. Although these warmer temperatures will promote some snow melt during the day, it won`t be accompanied by any significant rainfall and strong southerly winds, and overnight temperatures will fall below freezing. This will allow for a controlled and gradual diurnal melt of the snowpack in place. Only small and minor rises can be expected on rivers and streams through the early to middle portion of next week. With another approaching storm system, a light mix of precipitation to rain showers is expected Tuesday night into Wednesday. This looks fairly light and is not expected to have a major impact on the hydro service area 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. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. MA...None. VT...None. && $$ SYNOPSIS...NAS NEAR TERM...KL/11/NAS SHORT TERM...NAS LONG TERM...KL AVIATION...Thompson HYDROLOGY...NAS

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