Scientific Forecaster Discussion

000 fxus61 kaly 190230 afdaly Area forecast discussion National Weather Service Albany New York 1030 PM EDT Thu Apr 18 2019 Synopsis... milder air will return to the region overnight with plenty of clouds around. Although the day will start mainly dry on Friday, showers will become widespread by late in the day, along with continued warm temperatures. Some heavy rain showers and thunderstorms will be in place Friday night into Saturday, which may allow for some possible flooding across the region. Cloudy and damp, but mild weather, will continue for Sunday into early next week. && Near term /until 6 am Friday morning/... as of 1030 PM EDT...upper level ridge axis is located just east of the region, and a strong meridional trough is located west of the area over the Mississippi Valley. At the surface, low pressure is located over the Great Lakes and a warm front is moving across our western and southern areas at this time. Dewpoints still remain across the 40s for most of our area, but they are starting to creep into the 50s across far western and southern areas. With this pattern in place, plenty of moisture is being transported northward out of the Gulf of Mexico. Infrared satellite imagery shows plenty of clouds in place. Some breaks have developed in the wake of the warm front across southern areas, although the persistent moist southerly flow may allow for some low stratus to redevelop in these areas later tonight, especially across the terrain. Kenx radar still shows a few showers across the Saratoga region and into southern Vermont. These showers will be moving eastward and will be exiting the area shortly. Otherwise, a few additional light spotty showers or some drizzle may occur overnight, mainly for the higher terrain. Hi-res model guidance suggests most areas should be dry overnight, as the warm front continues to lift northward across the entire area. Temperatures look to remain steady or slowly rise through the 50s tonight. Higher terrain locations and the Hudson Valley should continue to see a steady, breezy southerly wind for most of the night. However, sheltered areas may see winds being more light and variable until the warm front fully passes through the area. && Short term /6 am Friday morning through Saturday/... Flood Watch mainly along and north of Interstate 90 beginning Friday evening through Sunday morning. Flood Watch also issued for western New England Saturday and a Flash Flood Watch has been issued for the capital district, Mid-Hudson valley and the Catskills. Upper level low pressure will deepen across the Tennessee Valley on Friday while an upper level jet on the northern edge of the downstream ridge off the East Coast tracks east across southeast Canada. Surface low- pressure will track across southeast Canada on Friday with a trailing cold front sagging south to the Saint Lawrence valley and far northern NY, extending southwest to another, stronger low center over Kentucky. Strengthening frontogenesis near the front over far northern New York and the Saint Lawrence valley will be the focus for heavier rain during the day Friday, in addition, showers will likely develop over central PA into central New York during the afternoon as the surface low pressure to the west and an increasing low-level southerly jet brings considerable moisture transport into that area. Eastern New York and western New England will be east of most of the precipitation on Friday as clouds may break to allow for limited sunshine in southerly flow in the warm sector south of the frontal zone. Friday night the front will sag southward across northern and central New York while surface low pressure tracks northeast along the front toward western PA. A 50 kt low-level jet will intersect the front while much of the PA / New York and New England will be in a favored area for upper-level divergence in the right entrance region of the upper jet moving east toward the Canadian Maritimes. Heavy rain will once again focus along the front from central New York into the Saint Lawrence valley and southward to the Adirondacks. More scattered showers will fall south of the front across the Catskills and Mid-Hudson valley into western New England, however even in those areas localized heavy rain will be possible in convective showers as the atmosphere will become very moist with precipitable water values climbing to around 1.5 inches. High resolution models continue to indicate that the best chance for heavy rain will be across the southern Adirondacks into Vermont, and our Flood Watch will continue in that area where rain and high elevation snow melt will likely result in flooding. Elsewhere we have decided to go with a Flood Watch for western New England and a Flash Flood Watch for the Hudson Valley and Catskills for Friday night into Saturday. Convective showers and more localized heavy rain potential will occur across those areas Friday night as the high resolution models show a variety of possible convective evolutions in our area to the south and east of the main frontal zone. Our current thinking is that convection with potential lines of heavier showers will occur over the Catskills and Hudson Valley. A band of heavier rain associated with an atmospheric river-like feature may develop over western New England Saturday morning. As these features will be somewhat removed from the best larger-scale forcing, their occurrence and evolution are somewhat uncertain, but given the very moist conditions a watch appears to be appropriate. On Saturday, the deepest moisture will shift east of the area by afternoon with the steadiest, heaviest rain shifting east into central and eastern New England. Will continue the Flood Watch for western New England through Saturday afternoon as heavier rains will likely be slow to move out of that area. Further west, much of our area will probably be in a dry slot for awhile with extended dry periods although there could be a few showers re- developing in the afternoon as the upper low over the Ohio Valley slowly advances eastward. The flood potential will remain high along streams and creeks north of the capital district due to continued high elevation snow melt and run-off from Friday night's rainfall. Showers will tend to decrease in coverage again Saturday night with the loss of diurnal heating as the upper low spins east across the central Appalachians toward the central mid- Atlantic. && Long term /Saturday night through Thursday/... an unsettled pattern looks to remain in place for at least the first half of the new work week as we continue to deal with our cut off low. Given the spread in model guidance, this is still a lower confidence forecast. One thing we would like to make a note of is some rivers are forecast to crest early Sunday from the heavy rain Friday night into Saturday. For more on expected river flooding impacts, see our hydrology section. We begin the period on Sunday with a split flow regime in place as our mature cut off low heads into the mid-Atlantic and gradually opens up. With the track of the cut off low trending further south, we have decreased the pop chances to low end chances to account for isolated to scattered showers developing, especially in the afternoon thanks to diurnal heating. The highest probabilities were placed in the Mid-Hudson valley and northwest CT where mid-level lapse rates look to be a bit steeper ranging 5-6c/km given closer proximity to the cut off low and associated upper level cool pool. Did not include slight chance thunder at this time but future forecast may include it for any isolated thunderstorms, if confidence increases. Temperatures should turn cooler compared to previous days with highs remaining in the 60s given cloud coverage and cooler 850mb isotherms associated with the upper level cool pool. Heading into Monday, a surface high slides southeastward through Canada and associated trough should act as a "kicker" and push our cut off low off the East Coast. However, there looks to be an Omega block in the western Atlantic which should slow down the eastward progression of our exiting low. The sub-tropical moisture feed that fed into the northeast from the Friday-Saturday event also looks to be close by positioned just off the East Coast due to the Omega block. Therefore, the model guidance suggests that the exiting cut off low could interact with the moisture feed leading to showers redeveloping. The European model (ecmwf) is the most robust with quantitative precipitation forecast amounts and placement while the GFS and CMC keep quantitative precipitation forecast confined to New England and the Mid-Hudson valley. Given this is still four days away, we went the conservative Route and sided more the GFS/CMC and placed chance probability of precipitation for Monday with highest pops placed in western New England the Mid-Hudson valley. Temperatures should be coolest in areas influenced by showers from our cut off low in the low-mid 60s while dry areas could warm up towards 70. The aforementioned surface high and trough should slide further south and east by Tuesday with a weak cold front moving into the northeast. Guidance still shows this front to be rather weak and washed out but the CMC and European model (ecmwf) show a possible vorticity maximum riding along the boundary which could lead to a more organized area of showers. However, given how weak the boundary looks, we are not sold on this solution and favored the drier GFS output. This is why we only placed low end chance pops for Tuesday to account for a few showers as the cold front pushes through. The northern stream trough should finally push through the northeast by Wednesday, kicking our cut off low out to sea. Canadian high should also slide into northern New England with northwesterly flow ushering in much cooler 850mb isotherms. This should finally lead to more in the way of sunshine as we note a good amount of dry air moving in at 700mb. Temperatures should turn cooler as well with highs in the 50s to low 60s and much lower dew points. Canadian high pressure slides eastward on Thursday as our next system from the Midwest approaches the region. Still much uncertainty on timing of this rain maker but something to watch for the end of next week. Temperatures should remain seasonably cool in the 50s/low 60s. && Aviation /03z Friday through Tuesday/... warm front is in the process of lifting northward across the area. After MVFR/IFR conditions earlier this evening, some breaks have allowed for a brief return to VFR. However, the persistent moist southerly flow could allow for some MVFR cigs to return by later in the overnight hours. Despite the clouds, any showers will be exiting this evening and it should be rain-free for most of the overnight with no additional precip expected. There looks to be a enough of T/dew point spread to prevent any fog from forming at the taf sites, but this may need to be monitored closely. Southerly winds should be around 5-15 kts, with the strongest winds at kalb. 2 kft will be 40-45 kts overnight, some low level wind shear is expected, especially at kpsf/kpou, where surface winds will be fairly light. Towards sunrise, ceilings will probably be MVFR for most sites (ovc cigs will be 1-2 kft). A return to VFR is possible for kalb/kgfl by the late morning hours, otherwise, it looks to remain MVFR with bkn cigs around 2-3 kft through the day. Although 2 kft winds will decrease, surface winds will remain around 10-15 kts through the day from a south to southwest direction. A few showers are possible towards evening (especially at kpou), otherwise, widespread rain looks to hold off until after 00z Saturday. Outlook... Friday night: high operational impact. Breezy definite rain showers...tsra. Saturday: high operational impact. Definite rain showers. Saturday night: moderate operational impact. Chance of rain showers. Sunday: moderate operational impact. Chance of rain showers. Sunday night: moderate operational impact. Chance of rain showers. Monday: moderate operational impact. Chance of rain showers. Monday night: moderate operational impact. Chance of rain showers. Tuesday: low operational impact. Slight chance of rain showers. && Fire weather... we will head into a wetter and more humid pattern late this week into the weekend. Some light showers are likely this morning, and mostly cloudy skies with a few lingering light showers or drizzle into tonight. Southerly winds will be quite strong with some gusts in excess of 30 mph possible, but minimum relative humidity values will remain elevated in the 50 to 60 percent range. Friday will be milder and more humid with relative humidity values only falling into the 70 to 80 percent range. A storm system will tap tropical moisture and bring periods of moderate to heavy rain to the area Friday evening into Saturday. && Hydrology... the only Flood Warning still in effect is the Schroon river at riverbank, where the stage should fall below moderate shortly. Flood Watch continues for the Mohawk Valley, Adirondacks, Lake George and northern Saratoga region into southern Vermont for Friday night into Sunday. In these areas, while there is a little snowmelt occurring per the nohrsc across the higher terrain, previous rainfall and snowmelt have result in near saturated ground and elevated water levels. Latest mmefs suggest many points across these regions will exceed flood stage again and per close coordination, we will issue another Flood Watch. This watch may need to be extended later with future forecasts and coordination. Wpc excessive rainfall outlook remains within the slight risk category across the entire region. 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...Flood Watch from late Friday night through Saturday evening for ctz001-013. New York...Flash Flood Watch from Friday evening through Saturday afternoon for nyz047>054-058>061-063>066. Flood Watch from Friday evening through Sunday morning for nyz032-033-038>043-082>084. Massachusetts...Flood Watch from late Friday night through Saturday evening for maz001-025. Vermont...Flood Watch from Friday evening through Sunday morning for vtz013>015. && $$ Synopsis...frugis near term...frugis short term...mse/bgm

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