000 FXUS61 KALY 230007 AFDALY AREA FORECAST DISCUSSION National Weather Service Albany NY 707 PM EST Sat Feb 22 2020 .SYNOPSIS... Fair and mild weather is expected Sunday and Monday. A low pressure system will bring periods of precipitation Tuesday through Thursday with mild temperatures continuing. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... As of 6:45PM...Adjusted temperatures and dew points to better match current conditions. Where the winds are still a bit breezy in valley areas, temperatures remain mild in the mid to upper 30s. However, once the winds become calm, surface observations show areas quickly cooling as clear skies allow for radiational cooling. High terrain areas have already decoupled and temperatures have fallen into the 20s. Dew points are lower than what we was shown so we adjusted the current forecast to show values in the teens to near 20. The RAP handled dew points the best so used that to better reflect NYS mesonet and ASOS stations. Otherwise, forecast remains on track. Previous forecast...The forecast area remains within a modest surface pressure gradient between low pressure over northern Quebec and high pressure over the Deep South/Ohio Valley. Very dry airmass in place with PWAT on the 12Z KALY sounding of 0.09". Skies are mainly clear aside from over the southern Adirondacks where overcast skies remain as some lake moisture is trapped beneath an inversion. Another difficult low temperature forecast for tonight, as a modest pressure gradient will remain over the area, but with deep snowpack over areas outside of the Capital District/Mid- Hudson Valley/southern Litchfield, potential for good radiational cooling in sheltered areas under clear skies. It does not look as cold in those sheltered, snow-packed areas as last night as the airmass has moderated. Stuck close to the blended guidance as it was overall not too much different than MOS guidance, and it is nearly impossible to capture all of the local variations in low temperatures in these situations. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY/... Sunday into Monday, a low pressure system moving from the Canadian Prairies into Quebec will draw up a progressively milder airmass into the Northeast, with 925 mb temperatures reaching 0 to 5C by Monday. A weak shortwave will pass through the region on Sunday, which could result in some scattered midlevel clouds, but otherwise plenty of sunshine is expected. Forecast soundings show good mixing for this time of year, with highs likely around 10F above normal. Monday, highs are expected to be even a few degrees warmer than Sunday, with 50s expected in the Hudson Valley from the Capital District on south. Clouds will increase late in the day into the overnight hours ahead of a low pressure system moving into the Ohio Valley. Monday night into Tuesday, moisture and lift associated with the approaching Ohio Valley low will slow their northeastward progress as the low weakens and drifts northward. Still, some light precipitation will be possible, particularly later on Tuesday as isentropic lift increases modestly. Early indication on p-type is mainly rain for the valleys given the antecedent mild airmass, with some snow or rain/snow mix for higher elevations. Increased lows Monday night from blended guidance given increasing cloud cover and mild airmass such that below freezing temperatures are confined to the high terrain north of I-90. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... An active weather pattern ensues for the final days of February with multiple chances for precipitation. Initially, precipitation looks to fall as a cold rain for most except for a brief period of snow at the onset for the higher terrain. However, by Thursday, a much colder air mass surges into the Northeast leading to wrap around/upslope snow showers that may transition to a potentially notable lake effect snow shower event for Friday/Saturday. Read on for details. We start off the long term on Tuesday night with a deepening cut-off low in the Midwest with southwesterly flow downstream strengthening and leading to warm air advection and isentropic lift over the Northeast. While current guidance does not show an anchoring high to our north, we do notice a large area of high pressure over central and eastern Canada with some weak cold air damming signatures present as overrunning precipitation ensues Tuesday night. This suggests that higher elevations and areas north of I-90 could be cold enough to initially support a period of snow, especially as wet- bulbing processes allow for diabatic cooling, while valley areas should likely experience a cold rain or brief rain/snow mix before becoming rain. Temperatures Tuesday night should gradually warm overnight. The best mid-level moisture escapes to our north during the day on Wednesday as the impressive closed/mature low remains in place over the Midwest with the ECWMF and CMC-NH showing its warm sector and mid-level dry slot pushing into the Northeast. As a result, precipitation (mainly in the form of rain) should become lighter and more disorganized but due to continued warm air advection, we still show chance or likely POPs. Temperatures Wednesday will be milder than normal thanks to warm sector influence so except highs in the upper 30s to mid 40s. Our closed low intensifies further heading into Wednesday night as the overall trough becomes negatively tilted and guidance continues to show its potent cold front sweeping into the Northeast Wednesday evening with a secondary low developing either off the NJ coast or over New England. Should this occur, eastern NY/western New England would be on the northwest quadrant of the developing low which could lead to a period of moderate precipitation moving into our area. Given the run-to-run consistency regarding this intensification, we decided to continue showing likely POPs after 00z Thursday. A much colder air mass quickly wraps into the region behind the system's potent cold front and as the winds in the boundary layer quickly shift westerly and cool, enough mild air may remain the mid- levels that the western Adirondacks and southern Greens mix with some sleet before becoming snow Wednesday night. Other areas should see a transition from rain to snow overnight. Uncertainty remains regarding how much precipitation falls once the temperature profiles become cold enough to support snow. This is something we will have to iron out as the event gets closer but current guidance suggests a quick end to the steady precipitation; however, the mature/upper level closed low looks to move into Ontario for Thursday with cold air advection continuing throughout the day leading to wrap around and upslope snow showers. Valley areas may be mild enough to support rain/snow mix as highs look to rise into the mid-upper 30s. By Thursday night, a secondary reinforcing shot of cold air moves into the Northeast and with the Lake Ontario waters still mild, the critical delta-T should be well surpassed as 850mb isotherms are currently analyzed to fall to -16C to -18C. This should allow lake effect snow showers to ensue and with the favorable westerly flow continuing into Friday, lake effect snow could continue into the daytime. Depending on the exact wind regime and instability profiles, this could lead to a notable lake effect event. Temperatures turn much cooler Friday and Saturday with highs only reaching into the 20s with overnight lows falling into the teens and single digits. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... VFR conditions will prevail through 00 UTC Monday. Westerly winds near 5-8kts will finally weaken this evening and we tried to time out when winds would decrease in the current update. Winds at PSF may remain near 5KTS overnight. By 14-16 UTC tomorrow, winds should increase again to 5-7kts but should be oriented out of the south-southwest and continue as such through the day. Outlook... Sunday Night: No Operational Impact. NO SIG WX. Monday: No Operational Impact. NO SIG WX. Monday Night: Low Operational Impact. NO SIG WX. Tuesday: Moderate Operational Impact. Chance of SHRA. Tuesday Night: Moderate Operational Impact. Definite RA...SN. Wednesday: Moderate Operational Impact. Definite RA. Wednesday Night: High Operational Impact. Definite RA...SN. Thursday: Moderate Operational Impact. Likely SHRA. && .HYDROLOGY... Dry weather will continue through Monday with mild temperatures expected. Light precipitation is possible Monday night into Tuesday with more appreciable precipitation Wednesday into Thursday. Mild temperatures will continue with perhaps a cool down by the end of the week. 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...Speciale AVIATION...Speciale HYDROLOGY...Thompson