660 FXUS61 KALY 060221 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 1021 PM EDT Sun Sep 5 2021 .SYNOPSIS... Mostly cloudy skies continue this afternoon. Scattered showers and an isolated rumble of thunder will be possible as a cold front approaches our area from the west. There will be a chance for a few showers and an isolated thunderstorm again on Labor Day, especially across the southern Adirondacks. More sun is expected tomorrow afternoon behind another cold frontal passage. Pleasant weather is expected Tuesday, but there will once again be a chance for showers and thunderstorms Wednesday with a few lingering showers possible for the end of the week. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... .UPDATE as of 1015 PM EDT, showers associated with the cold front are currently tracking through the Capital District and into the Mid-Hudson valley. Some low stratus has also settled in ahead of the front. With that said, the near term forecast remains on track outside of freshening up the hourly temps. .PREVIOUS DISCUSSION. As of 700 PM EDT, latest radar imagery shows showers associated with the cold front currently tracking through the southern Adirondacks and western Mohawk Valley. The wind shift to the west-northwest is evident in surface observations just east of Lake Ontario. The last visible image of the day shows clear skies behind the front. These clear skies should gradually work into the region overnight. .PREVIOUS DISCUSSION. The first few rounds of showers this morning and early this afternoon have mainly passed through to our east at this time. This afternoon, the main player for our weather over the next several hours will be a cold front approaching from the west. This cold front is associated with a surface low located near James Bay in Canada that developed in response to a strong closed upper low. As we head through the afternoon, this upper low will slowly drift eastwards and the cold front will approach our region from the west. Per the WPC surface analysis and current obs, the cold front looks to be located across western NY at this time where a surface pressure trough can be seen in the MSLP field. SA broken line of showers has developed ahead of this cold front and is beginning to track into Herkimer county as of 3:30 PM EDT. Some NYS Mesonet stations have picked up a quick 0.1-0.25" with this line of showers, so a brief period of moderate to heavy rain will be possible as this line moves through the region over the next few hours. Will continue to mention slight chance for thunder through this evening as there are a few breaks in the cloud cover ahead of this line of showers which could lead to some weak destabilization. However, have not seen much in the way of lightning activity up to this point, and instability generally looks very limited due to weak lapse rates and lack of daytime heating, so not expecting widespread thunder and not expecting severe weather despite 0-6 km bulk shear values near 50 kts. Will maintain chances for showers this evening and early tonight as the cold front passes through our region, but guidance suggests we should see a break in the shower activity behind the cold front. In fact, some partial clearing will be possible behind the cold frontal passage tonight as a weak surface pressure ridge builds into the region with dry air aloft also expected to work its way in after midnight. Clearing trend is also supported by current satellite imagery, which shows clearing upstream over and to the west of the Great Lakes. Any breaks that develop in the cloud cover may allow for some fog development towards Monday morning. With very little mixing today and low dew point depressions, we won't need efficient radiational cooling in order to see some fog. Overnight lows will also depend on the degree of clearing, but are currently expected to drop into the 50s for most areas. && .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/... Monday clouds will be on the increase again during the morning, with a chance for showers as well. A shortwave trough will rotate around the base of the closed upper low currently located over northern Ontario. As the aforementioned shortwave rotates around the base of the upper low through upstate NY/southern Canada, the trough will become negatively tilted. Meanwhile, another cold front is expected to track southeastward towards our region from the Great Lakes. The combination of the low- level front, height falls, strong cyclonic vorticity advection, and jet dynamics (the southern Adirondacks will be located in the left exit region of a 125 kt 300 mb jet streak) will all provide strong forcing for ascent. However, moisture looks to be more limited than on Sunday. The best forcing will be to the north of our region, which is where the best chance for showers and thunderstorms will be, but still expecting a line or broken line of showers with a few embedded thunderstorms to track across portions of the southern Adirondacks from west to east late tomorrow morning into early afternoon. Therefore, have included some likely PoPs during this timeframe for the southern Adirondacks and Saratoga/Lake George region. With strong height falls ahead of the approaching upper disturbance, lapse rates (mid and low- level) look to steepen compared to those in place today. Despite limited instability once again, cannot rule out an isolated storm with a stronger wind gust or some small sub-severe hail across portions of the southern Adirondacks late tomorrow morning or early in the afternoon. SPC only has our region in a general thunder risk at this point, which lines ups with our current thinking. There could be a few lingering showers, especially for eastern areas through the mid afternoon. However, a much cooler airmass will be advected into the region as the low-level winds become northwesterly behind the cold frontal passage. Cold advection as well as high pressure building in from the southwest, height falls aloft, and anticyclonic vorticity advection should all lead to subsidence behind the cold front that will effectively put an end to the chance for showers by mid-late afternoon. High temperatures may only reach the low/mid 60s in the southern Adirondacks, but could reach the mid-upper 70s for valley locations in our southeastern zones that will spend more time ahead of the cold front tomorrow. It will also become breezy behind the cold frontal passage, with wind gusts of 20-25 mph possible. Tomorrow night, large-scale subsidence continues across the region with upper-level heights continuing to rise and high pressure continuing to build in from the southwest. The pressure gradient should being to weaken overnight, which will allow winds to become light to calm by morning. Depending on how quickly we decouple, some fog formation will be possible by Tuesday night. Nighttime lows may also be a few degrees cooler if winds decrease earlier than currently forecast, as all other indications are that it should be a favorable night for radiational cooling. Tuesday looks to be a very pleasant late-summer/early fall day. After a cool start Tuesday morning, temperatures will recover to the mid 60s (high terrain) to mid 70s (valleys) for daytime highs. Upper-level ridging will lead to mainly clear and dry weather. Tuesday evening and Tuesday night...winds become southwesterly as high pressure slides offshore to our southeast. This will help advect a warmer and more humid airmass into our region, with a warm frontal passage expected sometime Tuesday night. Therefore, expecting warmer nighttime lows (mainly in the 50s to around 60) with more clouds around. Still some uncertainty as to how quickly precipitation will move in ahead of our next frontal passage, so will just mention slight chance to low chance PoPs for our northwestern zones towards Wednesday morning at this time. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... The H500 large-scale upper level pattern during the long-term forecast period over North America will undergo a transition going from an amplified, dipole pattern consisting of a warm western U.S. vs. a cooler eastern U.S. to start the period to a more zonal/semi- zonal pattern by the end of the week into the weekend. Additionally, the weather pattern is expected to remain progressive in nature during this long-term forecast period. Locally across eastern New York and western New England, the weather pattern will feature wet weather to start off the period that includes synoptically-driven showers and thunderstorms Wednesday into Thursday, followed by some lake effect, perhaps diurnally- enhanced rain showers on Thursday and possibly again on Friday before tranquil weather conditions take over Friday through the weekend. A normal to cooler than normal bias in temperatures can be expected during this period courtesy of an anomalously strong upper level trough that will be in place over the region. We start off the period on Wednesday with a pretty potent 990-995 mb storm system which will be centered over eastern Ontario (just south of the Hudson Bay) by 12z Wednesday. Kinematics will not be in short supply as this storm system will be associated with 90-110+ kt winds at 250 mb on its's leeward side. Given the size and spatial scope of this storm system, some pretty gusty winds (i.e. 25-40 kt H850 winds) will cover a large real estate extending over 2,000 miles from the Dakotas to the U.S. eastern seaboard. Locally over eastern New York and western New England, we will be placed on the eastern edge of this storm system's wind field. That said, Wednesday could be quite breezy at times with south-southwesterly winds at 10-15 kts gusting up to 25 kts at the surface. Outside, of the size and wind field associated with this storm system, will be the prospects for showers and thunderstorms during the day on Wednesday. Isentropic lifting, increased moisture advection, and warm air advection (WAA) will be taking place Wednesday morning into Wednesday afternoon as the ALY forecast area sits within the warm sector of the storm system. During this timeframe, we'll see temperatures climb into the mid 70s to near 80F and dewpoint values rise into the mid to upper 60s. Modest instability values (i.e. SBCAPE values ranging between 500-1500+ J/kg) and strong forcing (i.e. 0-6 km bulk shear values over 40 kts) will be sufficient enough for thunderstorm development, some of which could be strong. Some salient details such as timing and extent of influence still needs to be figured out, but at this point, it appears that the best timetable for showers and storms will be during the afternoon and evening hours on Wednesday as a cold front associated with this storm system approaches from the west/southwest. Showers and thunderstorms should come to an end Wednesday night into Thursday due to the loss of sunlight and daytime heating. Amid the cold fropa, cold air advection (CAA) will result in a cooler and drier airmass regime to take place. Broad cyclonic flow aloft, favorable thermodynamics between Lake Ontario and the airmass just overhead, a westerly fetch extending through the length of Lake Ontario, and several mid-upper perturbations overhead, will result in the potential for lake-effect showers or diurnally driven showers downwind of Lake Ontario Thursday and possibly again on Friday as the aforementioned upper trough slowly pulls away. Saturday through Sunday, dry and tranquil weather conditions will return areawide as a large and strong 1020 mb surface high pressure system builds into the region. High temperatures on Wednesday is forecast to climb into the mid 70s to near 80F (upper 60s to lower 70s higher elevations). Overnight low temperatures are forecast to be in the lower 60s along the Hudson Valley (mid to upper 50s higher elevations). On Thursday, behind the cold front, high temperatures is forecast to only climb into the mid 70s (mid 60s to lower 70s higher elevations). Overnight lows Thursday night into Friday is expected to be in the 50s most places (upper 40s higher elevations). Friday through Sunday, highs will reach the lower 70s (upper 50s to mid 60s higher elevations). Overnight lows Friday night through Sunday night, will be in the 50s most places (upper 40s higher terrain). && .AVIATION /02Z MONDAY THROUGH FRIDAY/... Showers associated with the cold front are currently tracking through the southern Adirondacks and western Mohawk Valley this evening. As these showers track eastward, they may briefly impact KGFL/KALB through about 03Z. Mid and high level moisture should exit in concert with a frontal passage around 04- 06Z. This presents the opportunity for fog and/or low clouds to develop thereafter. Lowered flight conditions with this TAF cycle for the second half of the night, with IFR/LIFR expected in cigs and/or vsby. Flight conditions expected to improve back to VFR roughly 12-14Z Mon, but another disturbance may bring scattered showers Monday afternoon (after 18Z). Skies should generally clear towards the end of the TAF forecast period. Winds will become light and variable overnight before turning west to southwest at 5 to 10 kt Monday mid-morning. Outlook... Monday Night: No Operational Impact. NO SIG WX. Tuesday: No Operational Impact. NO SIG WX. Tuesday Night: No Operational Impact. NO SIG WX. Wednesday: Moderate Operational Impact. Breezy. Chance of SHRA...TSRA. Wednesday Night: High Operational Impact. Likely SHRA...TSRA. Thursday: Low Operational Impact. Slight Chance of SHRA. Thursday Night: No Operational Impact. NO SIG WX. Friday: Low Operational Impact. Slight Chance of SHRA. && .FIRE WEATHER... RH values will remain above 80 percent this afternoon with a mostly cloudy sky and some passing rain showers. Rainfall will generally be 0.1-0.25" or less, except across the southern Adirondacks where up to a half inch is possible. Showers come to an end tonight, with RH values recovering to 100%. Additional showers will be possible Monday, especially across the southern Adirondacks. RH values Monday afternoon will drop to 50-60% behind a cold frontal passage. Winds this afternoon will remain southerly at around 10 kts with gusts of 15-20 kts possible. Winds become light tonight at less than 5 kts, but will increase to around 10 kts again tomorrow with gusts of 15-20 kts possible once again. Winds tomorrow will become west/northwesterly behind the cold frontal passage && .HYDROLOGY... Thanks to several days of dry weather following the heavy rainfall from the remains of TC Ida, all rivers and streams have receded back within their banks. While some rivers are still elevated (such as the Housatonic), levels will continue to fall over the next few days. Some spotty showers and thunderstorms are expected this evening into tonight, with additional showers possible Monday. Basin average amounts look fairly light, with rainfall amounts generally between 0.1-0.25" or less, except across the southern Adirondacks where up to a half inch is possible. As a result, this rainfall won't be enough for a significant response and area rivers and streams will continue to slowly fall. After a dry day on Tuesday, more showers and thunderstorms are possible for Wednesday. 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...Main NEAR TERM...Main/JLV SHORT TERM...Main LONG TERM...Evbuoma AVIATION...Thompson/JLV FIRE WEATHER...Frugis/Main HYDROLOGY...Frugis/Main