Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 212328 AFDALY Area Forecast Discussion National Weather Service Albany NY 628 PM EST Wed Feb 21 2018 .SYNOPSIS... The combination of snowmelt and recent rainfall may lead to some minor flooding over the higher terrain well north and west of the Capital District through tonight. Colder and more seasonable temperatures are expected on Thursday along with some mixed precipitation in the form of snow, sleet and freezing rain. More unsettled weather is expected Friday and during the second half of the weekend. && .NEAR TERM /THROUGH THURSDAY/...
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Flood Watch remains in effect through Thursday morning for Herkimer, Hamilton, and northern Warren Counties... Winter Weather Advisory from 4 AM until 6 PM Thursday for the eastern Catskills, Schoharie Valley and the Helderbergs. Showers are decreasing in coverage but the cold air is spreading through the region with gusty north to northwest winds. Just some minor adjustments to rain chances, sky cover and temperatures through this evening based on current data and trends. A few more details are available in the previous AFD below... A few showers will be across the region this evening with mixed precipitation developing later tonight from southwest to northeast as much colder air will filter back into the region tonight behind the cold frontal passage. Surface high pressure over the Great Lakes will build eastward into the region, allowing the flow to turn out of the north and continue to usher in colder air. Lows will be in the upper teens to mid 30s. On Thursday some isentropic lift and overrunning precipitation is expected. Thermal profiles in the lower levels of the atmosphere will be critical for precipitation type. Expecting a mixture of snow, sleet and some freezing rain. It may be still warm enough for some rain in the mid Hudson Valley and Litchfield county. The freezing rain will be mainly confined to the advisory area and mainly occurring during the morning hours. During the afternoon the primary precipitation type will be snow and some sleet. Highs on Thursday will be slightly above the overnight lows with highs ranging from the upper 20s to upper 30s. Temperatures may fall slightly during the afternoon. Snowfall amounts will range from 1 to 4 inches with up to a tenth of an inch of ice in the advisory area.
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&& .SHORT TERM /THURSDAY NIGHT/... A round of wintry mixed precipitation is possible Friday into Friday evening, mainly for areas above 1000 feet elevation. This would include light accumulations of sleet and freezing rain. Thursday night, high pressure over southern Canada will expand southward somewhat, resulting in the precipitation being shunted south of the forecast area. Cloud cover may clear somewhat for areas along and north of I-90, but will likely increase again toward sunrise Friday ahead of the next system. Some spotty very light snow or sleet is possible over the Catskills and Mid-Hudson Valley after 06Z as a renewed bout of isentropic lift begins. Friday, the high shifts eastward over Nova Scotia while the low level jet magnitudes increase. This will result in a renewed round of moisture transport and isentropic lift, with precipitation becoming likely late morning into the afternoon. We`ll start out the day cold with early morning temps in the teens and 20s, so some mixed precipitation is likely especially at the onset. The high is not in an ideal location to keep cold air locked in place, at least in the north/south valleys below 1000 feet, so currently do not expect much in the way of wintry accumulation there, as temps aloft and at the surface warm enough to support mainly rain as the p-type. Over the higher elevations of the Catskills and Adirondacks, thermal profiles support more in the way of a mixture of sleet and freezing rain for a good portion of the day. This will especially be true over the Adirondacks where a fairly deep snow pack still exists, and it has proven very difficult to scour out the cold air in similar circumstances. Still considerable uncertainty with respect to how much precipitation falls as sleet vs freezing rain, but additional winter weather headlines are a good possibility for the higher terrain above 1000 feet. As the temps aloft increase from west to east, the higher terrain of western New England may hold onto the colder temps longer, so perhaps more sleet or even light snow compared with freezing rain there. Low-level winds veer Friday night spelling a gradual end to the isentropic lift, with weak high pressure expanding in late. A good deal of low-level moisture will still be around, so could see a continuation of light spotty showers or drizzle. Temperatures Friday and Friday night are not expected to budge much, remaining mainly in the upper 20s to upper 30s. Temps across the Adirondacks and western New England above 1500 feet will likely drop back below freezing at night, so could see some lingering icy issues there. Weak high pressure Saturday may result in skies partially clearing and mainly dry conditions. Temps expected to be fairly mild in the upper 30s to near 50, or perhaps a bit warmer depending upon the amount of sunlight received. Clouds will increase in the afternoon ahead of yet another bout of isentropic lift. May even see some rain showers breaking out late in the day as the NAM shows. Only slight to low chance PoPs over southern zones for now. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... The long term period will feature seasonable temperatures with only one main threat for wintry mix. Our period begins Saturday night with a low pressure system from the Midwest amplifying as it travels into southern Canada with high pressure over eastern Quebec slowly retreating eastward. Upper level divergence from a strengthening 300mb jet positioned over the Ohio Valley should aid in the low`s intensification as the system becomes positioned in the jet`s right exit region during the second half of the weekend. There are still discrepancies among the current guidance on how quickly and how strong the low becomes with the GFS the most aggressive, showing it cutting off at 500mb with the Canadian showing a much weaker wave. The ECMWF was still not available for this newest forecast update. Warm air advection associated with the system should bring widespread precipitation into our CWA from southwest to northeast Saturday night into Sunday. Given that the antecedent high should be positioned well to our north in Quebec leading to east-southeast winds over eastern NY/western New England, the air mass ahead of the precipitation should be a bit mild with temperatures in the 40s. While initial precipitation may be rain in many spots outside of the Adirondacks, current guidance suggests cold air damming and evaporative cooling transitioning precipitation to wintry mix by Sunday morning from north to south. The warm front may be stubborn to traverse the area as most guidance shows weak southeast winds persisting in the boundary layer until 18z Sunday. Thus, the wintry mix may continue thru the first half of Sunday. By 18z Sunday, the 850mb jet strengths to 40-50kts which may help warm air mix into the boundary layer as the warm sector moves closer to our CWA. Thus, there is more confidence in the precip type changing to rain after 18z Sunday but still this is a low confidence forecast as cold air is often stubborn to scour out. The GFS and Canadian both show a secondary low developing in southern New England Sunday afternoon which would keep the warmest air of the warm sector to our south and east. Thus, I knocked Sunday`s high temperatures a few degrees to reflect this thinking. The cold front should finally move through Sunday night, ending the precipitation from west to east. High pressure noses into the Northeast from the Ohio Valley in the wake of this system which would lead to breezy conditions Monday with temperatures slightly above normal in the upper 30s to mid 40s. A secondary cold front associated with the 500mb trough axis should then arrive by 00z Tuesday with colder air in the 20s following for Monday night. Despite northwest flow setting up for the mid-week period, temperatures remain seasonable with highs in the mid 30s to low 40s and overnight lows in the 20s. Ridging also sets in mid-week which should keep eastern NY/western New England mainly dry. && .AVIATION /23Z WEDNESDAY THROUGH MONDAY/...
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Very low confidence of any rainfall impacting the TAF sites so will only include a VCSH for KPOU where there may be a few more hours of scattered light rain showers. VFR ceilings and visibilities are expected through tonight until around 11Z-15Z when some intermittent mixed precipitation is expected to begin at all TAF sites. There could be a mix of snow, sleet and rain. After about 15Z, mixed precipitation is expected to become steadier and ceilings and visibilities will lower to the MVFR/IFR levels. KGFL may have VFR bordering on MVFR since much of the precipitation could track mainly south of KGFL. By Thursday afternoon, precipitation type should be snow at KGFL, KALB and KPSF but remain a mix at KPOU. North to northwest winds at 10 to 15 Kt with gusts over 20 Kt this evening will become north at less than 10 Kt by daybreak. North winds will continue through Thursday afternoon at less than 10 Kt. Outlook... Wednesday Night: Moderate Operational Impact. Breezy Chance of SHRA...RA...SN. Thursday: Moderate Operational Impact. Likely RA...SN. Thursday Night: No Operational Impact. NO SIG WX. Friday: High Operational Impact. Likely RA...SN...SLEET. Friday Night: Moderate Operational Impact. Likely RA. Saturday: Moderate Operational Impact. Chance of RA. Saturday Night: Moderate Operational Impact. Chance of RA. Sunday: High Operational Impact. Likely RA.
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&& .HYDROLOGY... A cold front tracking through the region this afternoon and evening will usher in more seasonable temperatures tonight into Thursday, with temperatures falling below freezing over the Adirondacks tonight and ending the runoff from snowmelt. Will maintain Flood Watch over the Adirondacks and western Mohawk Valley as the Mohawk at Little Falls has risen a bit lately, but the overall flood threat in these areas appears to be diminishing. We will also continue to monitor where current ice jams are in place for possible movement through tonight. Flooding has occurred in areas near the Stockade in Schenectady and Scotia due to water backing up near the ice jam on the Mohawk. Parts of this ice jam have broken up, but it is unclear whether this will result in additional flooding or water levels receding. Water levels will continue to be monitored, and additional flood products will be issued if necessary. Snow and wintry mixed precipitation is expected Thursday, with a quarter to half inch of QPF expected mainly along and south of I-90. More rounds of precipitation are expected Friday into the weekend. Current forecasts call for around a quarter to three quarters of an inch during this timeframe, highest south of I-90. This may result in additional river rises. Temperatures are expected to average above normal during this time, but not as warm as we have seen the last two days. 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. && .CLIMATE... High temperature records were broken in many areas on Wednesday. KALB reached 73 degrees at 244 PM EST KGFL reached 66 degrees at 243 PM EST KPOU reached 76 degrees at 415 PM EST which broke the all-time February high temperature. Wed Feb 21st Previous record highs: KALB 65F set in 1981 KGFL 65F set in 1981 KPOU 67F set in 1953 All-time February highs: KALB 74F set Feb. 24, 2017 KGFL 70F set Feb. 25, 2017 KPOU 73F set Feb. 24, 2017 RECORDS FOR KPOU DATE BACK TO 1949... HOWEVER...DATA IS MISSING FROM JANUARY 1993 - JULY 2000. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Winter Weather Advisory from 4 AM to 6 PM EST Thursday for NYZ047-051-058-063. Flood Watch through Thursday morning for NYZ032-033-038-042. MA...None. VT...None. && $$ SYNOPSIS...11/JPV/JVM NEAR TERM...11/NAS SHORT TERM...Thompson LONG TERM...Speciale AVIATION...NAS HYDROLOGY...Thompson/JPV/JVM CLIMATE...

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