Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 171054 AFDALY Area Forecast Discussion National Weather Service Albany NY 654 AM EDT Fri Aug 17 2018 .SYNOPSIS... A series of disturbances ahead of a cold front will bring rounds of showers and thunderstorms today into tonight, some of which could result in locally heavy rainfall and gusty winds. The cold front will move through on Saturday along with continued showers over portions of the area, but a drying trend from north to south will take place. Some lingering showers are possible for southern areas Sunday, but to the north it will be dry and not as warm. && .NEAR TERM /THROUGH TONIGHT/... As of 630 am, leading edge of a batch of rainfall on the nose of a strong low- level jet is now roughly from Oswego to Binghamton and moving northeast. This activity is expected to move into the Mohawk Valley and southern Adirondacks over the next hour or so. Farther south, the LLJ is weaker, but showers will become increasingly possible with time this morning. In the wake of this LLJ-forced activity, will likely have a good deal of clouds around, and perhaps some lingering showers into around the noon hour. The question then becomes if enough instability can be realized to generate strong convection in the afternoon and evening hours. Low-level winds remain rather strong with H850 winds of 25-35 kt in the afternoon and evening hours. So despite somewhat marginal deep-layer shear of 25-30 kt, the magnitude of low-level winds suggests rotating storms are possible. HREF mean suggests SBCAPE values of 1500-2500 J/kg are possible in pockets by the mid-afternoon given high boundary layer moisture and despite meager midlevel lapse rates. A forcing mechanism is somewhat unclear, but it appears there may be one or more low- amplitude midlevel disturbances ejecting ahead of the positively tilted trough over the lower Great Lakes. Will have to watch for a prefrontal trough and differential heating boundaries to trigger convection as well. Overall, still a lot of uncertainties with respect to severe weather potential. Main hazards would be damaging winds and perhaps a tornado or two, and cannot rule out large hail should any supercellular structures develop. Though there should be strong enough flow to keep storm motions relatively fast, there is potential for training given the deep southwesterly flow parallel to the slowly approaching cold front, so locally heavy rainfall will be a threat as well. PWAT values are forecast to be in the vicinity of 2 inches once again. Tonight, the positively tilted trough eases its way eastward, so enough dynamical forcing may exist for showers and a few thunderstorms to continue. The surface cold front will approach northern zones overnight as well as it impinges upon the moist airmass. Locally heavy rainfall potential will continue overnight although severe weather threat should diminish with the loss of diurnal heating. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Forcing for ascent from the slowly approaching cold front, augmented by vorticity maxima associated with the shearing positively tilted trough will likely keep some showers around Saturday, especially during the morning and possibly into the afternoon for areas south of the Capital District. There is still some uncertainty with how strong the forcing will be, with the NAM indicating weaker frontal convergence and less shower activity, while the GFS/ECMWF show more widespread activity. A couple of thunderstorms cannot be ruled out, especially over southern zones where some diurnal heating could generate some instability ahead of the front. Temps are somewhat uncertain and will depend on the degree of cloud cover and shower coverage, but it appears they will be near normal. Saturday night into Sunday night, model consensus still supports the cold front finally clearing the area, keeping us under cool easterly to northeasterly flow. However, there has been a trend in some of the GEFS members and especially the 00Z ECMWF to linger the front just south of our area and develop a wave of low pressure upon it, opening the door for continued showers through the weekend. At this point, have introduced chance PoPs for our souther tier of counties. Future forecasts will have to determine whether this northward trend continues. Regardless, cooler than normal temperatures are favored for highs Sunday. && .LONG TERM /MONDAY THROUGH THURSDAY/... For Monday and Monday night, mainly fair weather is expected as surface high pressure ridges in from southeast Canada and an upper level ridge approaches from the Great Lakes and Ohio Valley. Highs on Monday mainly in the 70s, with lows Monday night in the 50s to lower 60s. Tuesday is expected to start out fair as high pressure crests over New England. However, strong low pressure will be moving through the Great Lakes. Some rain showers or thunderstorms may reach western areas around Sunset. Highs Tuesday in the 70s to around 80. Low pressure moving through eastern Canada will drag a cold front through the area Tuesday night. Expect showers and Thunderstorms. Lows Tuesday night mainly in the 60s with some 50s southwest Adirondacks. For Wednesday, a secondary cold front may trigger a few isolated showers and storms in the afternoon and evening. High pressure will ridge in Wednesday night from the Ohio valley bringing fair conditions. Highs Wednesday in the 70s to around 80. Lows Wednesday night in the 50s to around 60. High pressure will continue to bring fair and seasonable weather on Thursday and Thursday night. Highs Thursday in the 70s with lows Thursday night in the 50s to around 60 && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... LIFR in fog at KPSF this morning. Elsewhere VFR. Area of rain showers over central NY will move east this morning bringing rain showers to the TAF sites. Another round of showers and thunderstorms, some of which could be strong to severe are possible between 17Z/FRI to 06Z/SAT. Periods of rain may saturate the atmosphere by Saturday morning and bring low clouds and fog to the TAf sites. Conditions in terms of cigs will likely be VFR/high MVFR in rain showers this morning. Later TAF amendments will have to pinpoint the timing for the thunderstorms. The winds will increase from the south to southeast at 5-10 kts in the late morning. Winds shift to south southwest in the afternoon at 10 to 15kts. Winds KALB due to funneling up the Hudson River Valley could be a little breezier with southerly winds of 10-12 kts with a few gusts approaching 20 kts in the afternoon. Outlook... Saturday: Moderate Operational Impact. Chance of SHRA. Saturday Night: No Operational Impact. NO SIG WX. Sunday: No Operational Impact. NO SIG WX. Sunday Night: No Operational Impact. NO SIG WX. 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. Likely SHRA...TSRA. Wednesday: Moderate Operational Impact. Chance of SHRA...TSRA. && .FIRE WEATHER... A wet period is expected through at least tonight, keeping fire weather concerns to a minimum. Showers will likely linger into at least Saturday morning before a drying trend occurs from south to north. Some showers may linger into Sunday for southern areas, but to the north, a dry northeast flow will set up along with temperatures slightly below normal. && .HYDROLOGY... Another period of wet weather is in store through at least tonight as a series of midlevel disturbances interact with a moist airmass. Showers and thunderstorms will become likely this afternoon. Though there should be strong enough flow to keep storm motions relatively fast, there is potential for training given the deep southwesterly flow parallel to the slowly approaching cold front, so locally heavy rainfall will be a threat as well. PWAT values are forecast to be in the vicinity of 2 inches once again. Urban and poor drainage flooding is possible along with isolated flash flooding. The Mohawk Valley and Catskills along with portions of western New England have seen 150-300% of normal precipitation over the last week, so they may be particularly prone to flooding. Meanwhile, the latest Drought Monitor indicates the southern Adirondacks are experiencing moderate drought conditions. Additional showers and thunderstorms will continue tonight with a continued threat for locally heavy rainfall and possible flooding if additional storms impact areas that saw rainfall during the day. Deep-layer moisture will be on the decrease on Saturday so, while showers and a few thunderstorms may linger, they are not expected to be particularly heavy. Although flooding of small streams and creeks is possible, flooding on main stem rivers is not expected. 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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