Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 261101 AFDALY Area Forecast Discussion National Weather Service Albany NY 701 AM EDT Wed Apr 26 2017 .SYNOPSIS... A low pressure system over the Delmarva will slowly creep northeastward along the coast today, bringing cloudy skies and some light showers or drizzle. Gradual clearing is expected Thursday as the system pulls away, along with warmer temperatures. A weakening cold front will bring a chance of showers and a few thunderstorms Thursday night into early Friday, with dry and warm weather expected Friday afternoon. && .NEAR TERM /THROUGH TONIGHT/... As of 630 am, little uptick in shower/drizzle coverage this morning, mainly from the Catskills/Hudson Valley eastward. Hires models continue this activity into mid-morning before diminishing. Slight update to PoPs to delay their diminishing slightly. Nearly stacked upper low now spinning off the Delmarva coast with the best moisture plume evident on water vapor imagery targeting southeastern New England. Steady rainfall really failed to materialize overnight due to weak/disorganized ascent. Drier midlevel air evident on GOES-16 low-level water vapor creeping into northern New Jersey and will continue to translate into the ALY CWA today. Still have PoPs in place for much of the day for the potential for spotty light showers and drizzle, as forecast soundings indicate copious low-level moisture trapped beneath a strong inversion. Forecast challenge today will be with high temperatures. With low clouds noted upstream and all guidance pointing to a cloudy day, have sided a couple degrees cooler than the MET MOS, which itself is several degrees cooler than the MAV MOS. NAM 2m temps may actually be a better bet, which are cooler than the MET MOS. One cannot be too sure however, since the airmass above the inversion is warm (H85 temps around 10C, and late April sunshine is strong. Highest temps may end up being over the western Mohawk Valley where they stand the best chance for some clearing today. Weak flow tonight as the low shifts south of 40N/70W. Expect mainly cloudy skies and perhaps a couple patches of drizzle and light fog. Mild with lows in the upper 40s to mid-50s. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Thursday, brief shortwave ridging builds in as the coastal low continues to drift away, and a shortwave trough ejects northeastward across the Upper Midwest. The surface low will move nearly due north across Lake Michigan and into northern Ontario, remaining well west of our area. So while we will technically be in the warm sector, we won`t see strong southerly surface winds, and they will actually have a bit of an easterly component. Model soundings continue to show moisture trapped beneath the inversion, but with more of a clearing trend likely by the afternoon. Have again sided with the cooler MET MOS, but even that guidance is around 10F warmer than climo in the Hudson Valley. Once again, the warmest temps should be found over the western Mohawk Valley where they stand to see the most sun/mixing. Thursday night, weakening front from the Canadian low pressure system will approach the region. Convergence along the front and height falls appear weak but nonzero, and lift may be augmented by approaching poleward jet exit region. A bit of elevated instability will be in place with modest midlevel lapse rates. So, chance of showers and isolated t-storms into early Friday. A clearing trend is expected Friday afternoon as drier air works into the region. A very mild day with highs in the upper 60s to upper 70s. Mild Friday night beneath upper ridging and light southerly flow. && .LONG TERM /SATURDAY THROUGH TUESDAY/... The extended forecast period will remain a bit unsettled with a frontal boundary impacting the region for most of the weekend into early next week. The weekend opens with a stalled frontal boundary over upstate NY and into New England. The medium range guidance varies some with the exact position and alignment of the stationary front. In the southwest flow aloft the 00Z GFS/Canadian GGEM do have a weak impulse moving along the front for isolated to scattered showers and isolated afternoon thunderstorms. The 00Z ECMWF is the outlier with zonal flow aloft, and high pressure building in quicker from south of James Bay compared to the other guidance. A warm day is expected with H850 temps +10C to +16C from northwest to southeast over the region to start the day, and low-level cold advection in the afternoon with the front sagging south. Highs will generally be in the upper 50s to upper 60s north and west of the Capital Region and Upper Hudson River Valley...with 70s from those locations south and east, and even a few 80F readings near the mid-Hudson Valley. Any isolated to scattered showers should end quickly Sat night with the cold front drifting south of the region with a Canadian Sfc High building in for a short time with lows in the 40s to lower 50s, except for some mid and upper 30s over the Adirondack Park, and southern Greens. Sunday may actually start off nice and dry with the sfc anticyclone to the north, and also an H500 ridge trying to ridge from off the Mid Atlantic Coast. Clouds will be on the increase from the west/southwest during the afternoon with a chance of showers west of the Hudson River Valley, and slight chance to the east, as low pressure moves into the central MS River Valley, and its attendant warm front (the old cold front) moves northward from the OH Valley and PA. There is also a slight chc of thunderstorms due to weak elevated instability. Better chances of showers Sunday night with the warm front setting up just south and west of the forecast area over PA and west-central. Good isentropic lift and moisture convergence with the boundary may continue the showers into Monday morning. Highs on Sunday will generally be in the mid and upper 60s in the valley areas, and upper 50s to mid 60s over the hills and mountains. Lows Sunday night due to wet bulbing will be in the 40s to lower 50s. Monday into Tuesday...Some uncertainty with the forecast on Monday, as a strong sfc cyclone moves into the Upper Midwest and western Great Lakes Region. The warm front placement is variable in the deterministic and ensemble guidance. A blend of the guidance favored high chc/low likely pops for most of the region with a chance of afternoon thunderstorms if we get into a warm sector ahead of the cold front. Modest amounts of instability are forecasted by the latest 00Z GFS. Sfc dewpts do get into the 50s. The best convergence with the cold front looks to be late Monday afternoon into the nighttime period, so we continued high chc and likely pops for showers and a slight/low chc of thunderstorms. Highs Monday were lowered some due to the rain cooled air and clouds possibly lingering with 60s to lower 70s, as lows will only fall back into the mid 40s to mid 50s. The cold front drifts south of the region Tuesday, but a short-wave pivoting around the H500 upper low south of James Bay way focus some isolated to scattered showers, as temps trend back to seasonal normals with highs in the 50s to lower 60s over the higher terrain, and mid and upper 60s in the valleys. && .AVIATION /11Z WEDNESDAY THROUGH SUNDAY/...
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Coastal low pressure system near the Delmarva region will slowly move north/northeast along the East Coast to east of Long Island by late this afternoon/early this evening. Periods of intermittent light rain/showers/drizzle will be possible this morning into early this afternoon. The cutoff low will shift east of the region tonight. Widespread low MVFR and spotty IFR conditions continue for KALB/KPSF/KPOU. Further north, low VFR cigs persists near KGFL, but with the abundant low-level moisture in place, we expect cigs to lower to MVFR levels between 12Z-14Z there, and continue most of the afternoon. KALB/KPSF/KPOU will continue to have some light rain showers this morning with cigs either low MVFR or IFR. The showers should taper by the late morning, as some VCSH groups were continued into the afternoon at KPOU/KPSF. Cigs will be slow to rise much with bases generally at 1-2.5 kft AGL during the late morning into the afternoon. MVFR cigs are expected into the early evening at all the TAF sites generally in the 1.0-2.5kft AGL range. The model soundings still show a lot of moisture trapped under an inversion, as the cigs may remain in the 1.0-2.0 kft AGL range most of the overnight period /after 04Z/, with some IFR stratus forming near KPSF after 06Z. Some patchy drizzle may persist there. The winds will be north to east at 8 kts or less this morning. They will continue to be from the north to northeast at 4 to 6kts during the afternoon before becoming light to calm overnight. Outlook... Thursday Night: Moderate Operational Impact. Chance of SHRA...TSRA. Friday: Low Operational Impact. Slight Chance of SHRA...TSRA. Friday Night: Low Operational Impact. Slight Chance of SHRA. Saturday: Moderate Operational Impact. Chance of SHRA...TSRA. Saturday Night: No Operational Impact. NO SIG WX. Sunday: Low Operational Impact. Slight Chance of SHRA...TSRA. Sunday Night: Moderate Operational Impact. Chance of SHRA. Monday: Moderate Operational Impact. Chance of SHRA...TSRA.
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&& .FIRE WEATHER... Moist easterly flow will be in place through early Thursday as a low pressure system drifts up the coast. Today will feature plenty of clouds and a few showers or areas of drizzle with RH values only falling into the 60 to 85 percent range. Winds will be light out of the east to northeast. Milder temperatures are expected Thursday with possibly some clearing skies in the afternoon, and RH values falling to the 50 to 65 percent range. Winds will be from the southeast, increasing to 5 to 15 mph in the afternoon. A weakening cold front will bring the chance for showers Thursday night into early Friday. Friday will turn very warm and drier in the wake of the front, with highs in the upper 60s to upper 70s and RH values falling into the 40 to 50 percent range. Winds will be southwest at 5 to 10 mph. && .HYDROLOGY... A few showers or areas of drizzle are expected today, with minimal QPF. A weakening cold front will bring the chance for showers and isolated thunderstorms Thursday night into early Friday. Basin-average rainfall amounts are expected to be light. Additional chances for light showers will occur over the 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. && .ALY WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. MA...None. VT...None. && $$ SYNOPSIS...Thompson NEAR TERM...Thompson SHORT TERM...Thompson LONG TERM...Wasula AVIATION...Wasula FIRE WEATHER...Thompson HYDROLOGY...Thompson

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