Area Forecast Discussion
Issued by NWS Albany, NY

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000 FXUS61 KALY 271724 AFDALY Area Forecast Discussion National Weather Service Albany NY 124 PM EDT Tue Jun 27 2017 .SYNOPSIS... A strong upper level low and a cold front will bring scattered showers and thunderstorms to eastern New York and western New England today. The cool air mass will be over the region tonight, as high pressure will build in from the Mid Atlantic Region for Wednesday with the best chance of a shower or isolated thunderstorm north of the Capital Region and Mohawk Valley. A warm front will approach from the Ohio Valley and lower Great Lakes Region bringing more showers and a chance of thunderstorms Thursday into Thursday night. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Marginal Risk for Severe Thunderstorms continues through this afternoon for much of eastern NY/adjacent western New England... As of 1240 PM EDT, potent upper level shortwave across western NYS continues to translate east/northeast. Increasing upper level forcing, combined with cooling mid level temperatures/steepening low and mid level lapse rates will lead to numerous showers/isolated thunderstorms through the remainder of the afternoon for locations near and especially north of I-90, with more scattered coverage to the south, where forcing will be slightly weaker. Taller convective elements will be capable of small hail/gusty winds, with locally heavy downpours likely otherwise. It is quite possible that although hail size may remain generally sub- severe, there could be quite a bit of it accumulating in some stronger and/or slower moving cells. Also, given such strong forcing and cooling aloft, despite limited sunshine, we can not rule out isolated larger hail/damaging wind gusts. The stronger wind gusts would be more likely in any thunderstorms that tend to merge/form clusters and/or small bowing line segments, which in combination with strong wet bulb cooling, could produce strong winds. There is a Marginal Risk for severe thunderstorms today across eastern NY and western New England.... Upper impulse in western NY heading east and convection with small hail occurring out there already. Band of showers heading into the southern Adirondacks and Schoharie Valley now, will exit through midday. The dry area between the band of rain and the convection seen in satellite imagery should fill in as daytime heating occurs. So, coverage of showers and isolated thunderstorms will increase, with chances for small hail and gusty winds. Area soundings at 12Z show wet bulb zero levels are quite low with the cold air aloft and convective initiation temperatures are around 70 in eastern NY but only in the lower 60s in western NY, the atmosphere that will be tracking into our region through the afternoon. The previous AFD has a few more details and is below... H500 heights are 2 to 3 standard deviations below normal based on the latest GEFS with the anomalous upper trough. Short-wave energy associated with the upper trough and a cold front/sfc trough will focus scattered to numerous showers and thunderstorms this afternoon. Some sunshine this morning into the early afternoon will allow for enough heating to occur for some strong to potentially severe thunderstorms to impact the region. Low and mid-level height falls will occur ahead of the upper level trough. The cold pool and the differential cyclonic vorticity advection with the upper low will allow for showers and thunderstorms to develop. The big change from yesterday is that the model guidance from the NAM and the GFS is showing more Surface-based instability. SBCAPES are in the 500-1500 J/kg range with sfc dewpts in the 50s to around 60F. The HI-RES NCAR Ensembles have mean SBCAPES in the 750-1000 J/kg range over the forecast area in the afternoon. The 0-6 km bulk shear values increase to 40-50 kts with the greatest shear from the Capital Region/southern VT/eastern Catskills south and east. Wet-bulb zero heights are forecasted low in the 6-8 kft AGL range with steep mid-level lapse rates in the 6.5-7.25 C/km range. Organized convection with perhaps some mini-supercells are possible, though multi- cells will likely be the dominate mode. Large Hail and some damaging will be the main threats with the taller updrafts associated with some of the thunderstorms. The unidirectional southwesterly flow in the low to mid levels of the troposphere may allow for some lines to form with bowing segments or some the hail cores descending from the thunderstorms could produce some damaging winds, though hail looks to be the primary threat. Enhanced wording was kept in the grids for small hail and gusty winds. The convection should quickly fire up between noon-2 pm across eastern NY based on the latest CAMs /3-km HRRR and 3-km NAM/. PWATS will be in the 0.7-1.0" range which are normal to slightly below normal for this time of year, but some quick bursts of rain will be possible with the hail and wind threats. High temps will be around 10 degrees below normal with upper 60s to lower 70s in most of the valley areas, except the mid- Hudson Valley where some mid and upper 70s are possible...and upper 50s to mid 60s will be common over the hills and mountains.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH THURSDAY NIGHT/... Tonight...The showers and thunderstorm should taper and diminish quickly in the late afternoon and early evening. A few lake enhanced showers may persist until midnight for the western Adirondacks and some slight to low chance pops were kept in the forecast. The short-wave embedded in the upper trough pivots and lifts northeast into southern Quebec. H850 temps fall to +5C to +7C over the region. Some clearing in the wake of the cold front/sfc trough coupled with wet ground and light winds will promote some patchy fog formation. Lows will be in the upper 40s to lower 50s across the region. Wednesday...The mid and upper level trough progresses downstream of the forecast area. The residual cold pool coupled with a weak short-wave in the west to northwest flow aloft will trigger some isolated to scattered showers and possibly isolated thunderstorms north of the Mohawk Valley and the Capital Region into the Lake George Region, southern Adirondacks, and southern VT. SBCAPEs look low this day at less than 500 J/kg. High pressure will be ridging in from the south near the Mid Atlantic Region with partly sunny and dry conditions for most of the forecast area. Temps will rebound a tad closer to normal with many mid to upper 70 readings in the valleys, and mid 60s to lower 70s over the higher elevations. A few 80F readings will be possible in the mid-Hudson Valley. Wednesday Night...Fair conditions persist most of the night with mid and high clouds increasing from the south and west ahead of a warm front over the Ohio Valley and Great Lakes Region especially after midnight. Some radiational cooling early on before the clouds increase will allow for lows to be mainly in the 50s with a few upper 40s over the mtns. Thu-Thu night...The mid and upper level flow becomes zonal. Warm advection occurs in the low to mid levels. A low pressure system will be approaching the Great Lakes Region with a warm front extending S/SE across the eastern Great Lakes Region into PA. Strong isentropic lift increases in the late morning into the afternoon with a strengthening south to southwest low-level jet of 35-40+ kts. A period of rain or showers may overspread the region by the late morning into the afternoon. This is variable in the guidance. It is difficult to determine if an MCS will impact the region late THU into THU night. MUCAPES do increase close to 500-1000 J/kg by the late afternoon into the early evening with Showalter values of 0 to -3C from the latest GFS. The evening period looks unsettled with possibly nocturnal convection with increasing PWATS to 1.25-1.75" and potentially bands of showers and thunderstorms moving across the forecast area in the THU night. Much of eastern NY is in a Marginal Risk (outside of Dutchess Co) in Day 3. Right now, locations that may break into the warm sector look to be south of the I-90 corridor. Temps may get into the upper 70s to lower 80s from the the Capital Region/Mohawk Valley/Berkshires and points south, and mid 60s to mid 70s northward. In the more humid air mass lows will be in the mid to upper 60s excepts upper 50s to lower 60s over the Adirondacks, southern Greens and Lake George Region. && .LONG TERM /FRIDAY THROUGH MONDAY/... The period starts out on Friday with a diffuse surface boundary over the region, with increasingly warm and humid conditions. Southwest zonal flow aloft will allow for a few possible disturbances to move through, which could fairly easily trigger diurnally driven showers and thunderstorms given the warm and humid air mass in place. Early look at instability indicates the potential for 1000-2000 J/Kg of SBCAPE with moderate shear so will have to watch for some potentially stronger storms. Convection could linger well into the evening, but should weaken overnight. It will be muggy with lows in the 60s. Saturday still looking like a day with a better chance for more widespread and organized convection. A surface cyclone is forecast to track eastward into central/southern Quebec, while a series of surface boundaries moves across our area starting with a pre-frontal trough Saturday afternoon. The trough will be the focus for numerous showers and thunderstorms developing, some of which could be strong to severe. Too early for specifics, but potentially moderate to large magnitude of instability may develop given sufficient sunshine early in the day. Any storms will be capable of producing locally heavy rainfall as PWATs surge to between +1 to +2 STDEV above normal, which is significant for early July. High temperatures will depend on amount of sunshine, but overall mid to upper 80s seems reasonable for most valley locations, with high dewpoints in the 65 to 70 degree range making it feel more humid. Showers and thunderstorms will remain likely Saturday night, as the system`s cold front starts to push through. Still getting good model consensus on this, with timing in decent agreement as well. The cold front may not clear the area by Sunday, so additional showers and storms will be possible, but mainly scattered in coverage and not as intense as Saturday`s potential thunderstorms. It will remain warm, but with a slight drop in humidity behind the cold front. We could finally see a more tranquil weather day next Monday, but with zonal flow and weak troughiness in place, widely scattered diurnal showers and thunderstorms cannot be ruled out. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/...
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Scattered showers and thunderstorms across the region with the upper energy that is tracking through. Carrying VCSH through about 20Z-21Z when a more organized area of showers and thunderstorms out to the west is timed to be in the vicinity of KALB and KGFL, with VCTS between 21Z-23Z. Adding VCTS to KPOU and KPSF about an hour later. Indicating tempo for borderline MVFR/IFR conditions in any thunderstorms. After 23Z, back to VCSH with VFR conditions and the VCSH ends around 01Z-02Z. The sky should have more scattered clouds with variable broken but above 3000 feet. By around 08Z-09Z some fog is possible at KPSF, KGFL and KPOU. Any possible fog ends 11Z-12Z and VFR conditions prevail at all TAF sites through Wednesday morning. South to southwest winds at 10 Kt or less this afternoon will diminish to light tonight. Winds become west to northwest at less than 10 Kt Wednesday morning. Outlook... Wednesday Night: No Operational Impact. NO SIG WX. Thursday: High Operational Impact. Likely SHRA...TSRA. Thursday Night: High Operational Impact. Likely SHRA...TSRA. Friday: Moderate Operational Impact. Chance of SHRA...TSRA. Friday Night: Moderate Operational Impact. Chance of SHRA...TSRA. Saturday: High Operational Impact. Likely SHRA...TSRA. Saturday Night: High Operational Impact. Likely SHRA...TSRA. Sunday: Moderate Operational Impact. Chance of SHRA...TSRA.
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&& .FIRE WEATHER... A strong upper level low and a cold front will bring scattered showers and thunderstorms to eastern New York and western New England today. High pressure will build in from the Mid Atlantic Region for Wednesday with the best chance of a shower or isolated thunderstorm north of the Capital Region and Mohawk Valley. A warm front will approach from the Ohio Valley and lower Great Lakes Region bringing more showers and a chance of thunderstorms Thursday into Thursday night. The RH values will lower to 45 to 70 percent this afternoon and then recover close to 100 percent tonight. Expect minimum RH values of 35 to 55 percent on Wednesday. The winds will from the southwest to northwest at 5 to 15 mph today. The winds will be from the southwest to west at 10 mph or less tonight, and then increase from the west to northwest at 10 to 15 mph with some gusts to 25 mph on Wednesday. Winds will be stronger, and variable in direction in and near any thunderstorms. && .HYDROLOGY... No widespread hydrological problems are anticipated over the next several days. Scattered to numerous showers and thunderstorms are expected today, mainly during the afternoon and evening hours, as a cold front and upper low impact the region. Basin average rainfall amounts will generally be a tenth to a third of an inch in some locations. A brief period of mainly dry weather is expected most of Wednesday into Wednesday night with ridging briefly building in from the south. An active pattern sets up Thursday into the weekend with showers and thunderstorms possible with increasing humidity levels. Rainfall amounts will vary based on where any convection occurs. The most widespread potential rainfall is expected Thursday and Saturday. Rainfall amounts THU-THU night may range from a quarter of an inch to an inch with some locally higher amounts in thunderstorms. The higher totals right now may be across the northern basins of the HSA. 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...Wasula NEAR TERM...KL/NAS/Wasula SHORT TERM...Wasula LONG TERM...JPV AVIATION...NAS FIRE WEATHER...KL/Wasula HYDROLOGY...KL/Wasula

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