Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 190823 AFDALY Area Forecast Discussion National Weather Service Albany NY 423 AM EDT Sun Aug 19 2018 .SYNOPSIS... Today will be mainly dry with seasonable temperatures for much of the area, although areas from the southern Berkshires to the Catskills and on south will see a bit more cloud cover, cooler temperatures, and perhaps a few showers. Calm and seasonable weather is expected tonight into Tuesday morning. Showers and thunderstorms associated with a strong low pressure system are expected late Tuesday into early Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 400 am, stratus has remained widespread across most of the forecast area, except for far northern zones where fog is prevalent. Have removed fog from the forecast elsewhere and adjusted temperatures upward to match current obs. Loosely organized area of surface low pressure will be located offshore of New Jersey today while high pressure becomes centered over the Gaspe Peninsula of Quebec. One of the main challenges today will be how quickly drier air can advect in on the low/midlevel northeasterly winds to erode the existing cloud deck. Have generally kept cloud cover around a bit longer than blended guidance. Areas from the Berkshires to the Catskills and points south may remain mostly cloudy for the majority of the day as some moisture at higher levels in the atmosphere may add to the cloud cover. With weak midlevel vorticity maxima moving through along with weak low-level frontogenesis and the poleward exit region of a 60 kt upper jet, could see enough forcing for ascent for a few showers in these locales. Have gone toward the cool end of the guidance envelope for highs here with generally upper 60s to mid-70s. Further north toward the Capital District, Upper Hudson Valley and Mohawk Valley, a bit more sunshine is expected to send temps into the upper 70s to near 80. This is a somewhat low confidence forecast however, and will hinge upon the progression of the cloud cover. Tonight, the low-level anticyclone is expected to expand into the area, resulting in a continued diminishing trend in the cloud cover. Low temps expected to be near to slightly cooler than normal, with 50s common and some 40s across portions of the Adirondacks. Typically prone spots may see patchy fog. && .SHORT TERM /MONDAY THROUGH TUESDAY/... Expect a tranquil day Monday as we remain under the influence of the surface high and under weak midlevel flow. Partly to mostly sunny skies expected with near seasonable temps. Monday night into Tuesday, a strong midlevel trough over the Upper Midwest will deamplify a bit as it tracks eastward toward Lake Erie. Low-level winds will turn southeasterly ahead of this feature. These winds along with gradually increasing high clouds will likely allow for Monday night to be a bit milder than Sunday night, but depending on the speed of the system, we could still see good radiational cooling conditions for at least the first part of the night. Dynamical lift will increase Tuesday afternoon and evening ahead of the shortwave, and a very strong southerly low-level jet (40 kt at 850 mb) translates into the region, increasing moisture transport. Winds of this magnitude are approaching 4 standard deviations above normal. The overall strength of the surface low, modeled by the deterministic and ensemble guidance around 998 mb at 00Z Wed over southeast Ontario, is 3 to 4 standard deviations below normal. So we are certainly looking at an unseasonably strong and dynamic system for this time of year. Model consensus favors most of the precip associated with this system occurring after the short term period, but some showers and possibly a thunderstorm will be possible late in the day mainly west of the Hudson Valley. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... Anomalous low pressure for late August moves up the Saint Lawrence River Valley Tuesday night into Wednesday. Tuesday night, strong southwesterly 850mb jet should push northeastward into our region leading to widespread precipitation. GEFS shows 850 wind anomaly and 850 moisture flux of 4-5 SD above normal across the northern half of forecast area. PWATs are forecast in the 1.5 to 2 inch range across the area. Negative showalter index indicates elevated instability so a few rumbles of thunder and some locally heavy rainfall possible. Lows Tuesday night in the 60s. On Wednesday, a secondary cold front will cross the area. Ahead of the front, a line of showers and thunderstorms may develop in the warm sector. At this time, it looks like the main threat area for thunderstorms would be south and east of Albany, but timing the front 3 days out is always tough. Highs Wednesday will range from the upper 60s southern Adirondacks to low 80s mid-Hudson Valley. By Wednesday afternoon and night, it looks to turn breezy as the impressive surface low (which its 990-995mb MSLP 3-4 standard deviations below normal for this time of year according to the GEFS) moves through northern New England/southern Canada leading to a decent pressure rise/fall couplet and isallobaric wind field. Wind gusts of 20-30mph are forecast Wednesday afternoon/evening in the Adirondacks, Mohawk Valley, Capital District, Southern Vermont and northern Berkshire County. Cold advection will lead to gradually falling temperatures Wednesday afternoon as well and we should see a drastic drop in humidity heading into Wednesday night. Overnight lows should be comfortable falling into the 50s, with 40s southern Adirondacks. Pleasant conditions remain in place Thursday and Friday as large scale high pressure and weak ridging moves in from the Midwest. Temperatures should be closer to normal for late August only reaching into the upper 70s to around 80 both days. Humidity level remains low as well thanks to the northerly flow. Lows Friday and Saturday in the 50s. The weak ridge axis should move into eastern New England heading into Saturday which should lead to a southerly flow aloft. This in turn should allow temperatures to warm up a few degrees Saturday reaching into the low 80s in the valleys with 70s in the hill towns. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... Easterly flow of moist air around low pressure currently south of Long Island, coupled with an upper level low pressure system, is causing and area of low clouds and spotty light rain. -RA reported at KALB and KPSF along with MVFR cigs. VFR cigs at KGFL and KPOU. Low clouds expected to only slowly erode after sunrise on Sunday. Cigs should rise to VFR level all TAF sites by 19/12Z. Some dense (IFR) radiational fog is possible at KGFL if clouds erode a little faster overnight tonight. Winds will be north to northeast overnight at 5 to 10 kts. Winds Sunday will turn from northeast to southeast at 5 to 10 kts. Outlook... Monday: No Operational Impact. NO SIG WX. Monday Night: No Operational Impact. NO SIG WX. Tuesday: Moderate Operational Impact. Chance of SHRA...TSRA. Tuesday Night: High Operational Impact. Definite SHRA...TSRA. Wednesday: High Operational Impact. Likely SHRA...TSRA. Wednesday Night: No Operational Impact. NO SIG WX. Thursday: No Operational Impact. NO SIG WX. Thursday Night: No Operational Impact. NO SIG WX. Friday: No Operational Impact. NO SIG WX. && .FIRE WEATHER... High pressure located to the northeast will keep precipitation out of the forecast for the most part through Tuesday morning. A few sprinkles are possible early this morning, and a few showers are possible throughout the day today from the Berkshires to the Catskills and points south. Temperatures here will be a bit cooler than normal today, but seasonable elsewhere today and everywhere on Monday. RH values will mainly fall into the 45 to 55 percent range today and Monday with a light easterly to northeasterly wind. Showers and thunderstorms will be likely late Tuesday into early Wednesday ahead of a strong low pressure system. && .HYDROLOGY... A mainly dry period is expected through Tuesday morning, although a few light showers are possible today from the Berkshires to the Catskills and points south. This will allow river levels to recede. Showers and thunderstorms will be likely late Tuesday into early Wednesday ahead of a strong low pressure system. 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...SND AVIATION...SND FIRE WEATHER...Thompson HYDROLOGY...Thompson

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