Marine Weather and Tide Forecast for Canaan, CT

KEY MESSAGES
1) Two clipper systems will track through the region through the end of this week and into the beginning of next, bringing a mix of rain and snow in addition to low probabilities of significant impacts.

DISCUSSION
Key Message 1...

An anomalous, southern stream, upper-level anticyclone continues to dominate the deep Southwest, extending a large-scale ridge northward that encompasses nearly half the CONUS. Meanwhile, northern stream northwest flow has kept the Great Lakes and northeast under the influence of trough-resembling regime that will continue through much of the remainder of the week.
Ultimately, this will allow multiple clipper systems to track through the region, bringing periods of rain, snow, and a mix thereof into early next week. The first of these clippers is anticipated today through tonight.

A progressive surface low will ride atop the western ridge and eject southeastward out of the Upper Midwest towards the Great Lakes through this morning. Aloft, a once weak associated shortwave embedded within the upper-level northwesterly flow will deepen, triggering a slight intensification of the surface cyclone. By mid- to late-morning, the low will have reached the eastern Great Lakes, extending a horizontal warm/pseudo- stationary front eastward just north of or just along the northern fringe of our Southern Adirondack zones. A stratiform precipitation shield associated with the axis of increasing warm air advection and isentropic lift will then begin to move into the region and expand southeastward through the remaining hours of the morning and preliminary hours of the afternoon.
Initially, sufficient cloud cover should hold temperatures on the cooler side across the Adirondacks such that precipitation begins as snow. Further providing confidence in this element of the forecast is the combination of low level dry air that will enhance the effects of wetbulb cooling where temperatures may just be over freezing at onset, an 850mb FGEN band enhancing vertical ascent thereby providing rapid cooling, and the anticipation of efficient flake production within the dendritic growth zone where strong omega exists. For these reasons, a quick half to inch and a half of snow could accumulate across the highest elevations of the Southern Adirondacks within a couple hours of precipitation onset. In fact, we mentioned moderate snowfall in the forecast for a few hours early this afternoon as the aforementioned strong forcing could lead to some decent rates (0.5-1"/hr per the latest HRRR) for a short period of time. However, persistently increasing warm air advection will quickly force the transition to a rain/snow mix before plain rain becomes the dominant precipitation type.

All areas outside the Southern Adirondacks, aside from isolated high peaks of the Southern Greens, will see plain rain throughout the duration of this event with rates becoming moderate to locally heavy at times. The southeast spread of the stratiform precipitation shield will intersect a southwesterly, 40-50kt 850mb LLJ this afternoon that will promote efficient moisture transport into the still strongly forced environment. Therefore, we also mentioned moderate rainfall for several hours this afternoon, particularly for portions of the Mohawk Valley, Upper-Hudson Valley, Eastern Catskills, and southern Greens where upslope flow will also provide additional forcing for efficient rainfall production. Now, we did mention some moderate rainfall across portions of the Capital Region, Mid-Hudson Valley, and southwest New England as well due to the potential for embedded downpours as the low traverses overhead just before its associated cold front. However, latest HiRes guidance is indicating that there could be some downsloping and shadowing that occurs off the Catskills that could limit the amount of rain that falls in these areas.

Precipitation associated with this first system concludes tonight as it swiftly departs through the region to the east. By early tomorrow morning, dry conditions will be reinforced across the region as drier air filters in beneath a couple of nearby surface highs nudging east and southward. Saturday will therefore be dry ahead of the next clipper that will increase the probability of precipitation once again beginning Saturday night. The forecast for this next system continues to contain its fair share of uncertainty, though confidence is beginning to increase based on latest trends in the guidance.

Similarly to the previous system, another surface low will move into the Great Lakes by Saturday night, tracking originally from the Upper-Midwest. Dissimilarly, this is actually one of several low centers spanning a broad swath of surface low pressure that extends south and west as far as the Texas Panhandle along an elongated cold front. By the time the low adjacent to our area moves into the Great Lakes, upper-level flow will have become quasi- zonal and fairly compact with numerous embedded shortwaves upstream and the further deepened shortwave of the previous system just downstream over Atlantic Canada. This will create a fairly compact baroclinic zone across our area that, at this point, looks to support cooler temperatures and subsequently an initial onset type of snow almost everywhere Saturday night. That said, if the area of low pressure shifts a bit farther north, more of a rain/snow mix or plain rain would be the solution for areas outside of the Adirondacks. A farther south track of the low would mean a more prolonged period of snow across more of the region. The current forecast errs on the side of the latest trends of the low tracking farther south, but that is a bit different than previous days. What's important to note here, though, is that as warm air advection increases with this system and diurnal moderation occurs throughout the day Sunday, snow will ultimately transition to a rain/snow mix and plain rain until snow returns again overnight Sunday. We don't anticipate, at least at this time, any freezing rain or sleet with this system. But the uncertainty pertaining to the position of the low and the resulting duration and spatial spread of snow poses uncertainty in the resulting accumulations. We will continue to monitor over the coming days and provide updates/issue any headlines should they be needed.

Precipitation from this system could linger into Monday night, but by Tuesday, high pressure looks to build in to force the return of regionwide dry conditions. Looking ahead further into next week, additional opportunities for precipitation alternate with dry periods as in typical March fashion. But no significant impacts are anticipated at this time.

AVIATION /06Z FRIDAY THROUGH TUESDAY/
Through 06Z/Sat, mainly VFR conditions are expected through late morning. As a warm front approaches from the west this afternoon, rain is expected to overspread the TAF sites from NW to SE between 18Z-22Z/Fri. Periods of MVFR/IFR (mainly for Vsbys) are expected as the rain tracks through, especially within any pockets of moderate rain. The rain could briefly be mixed with snow at KGFL at the start. The rain should taper off from NW to SE between 23Z Fri-03Z/Sat, however lingering low clouds and mist/drizzle should keep flight conditions MVFR/IFR through at least 06Z/Sat.

Light/variable winds will become south to southeast and increase to 8-15 KT by early afternoon with some gusts of 25-30 KT possible, especially at KALB. South to southeast winds will then gradually decrease to 8-12 KT toward and after sunset, eventually shifting into the west to northwest at 5-10 KT toward and after 06Z/Sat.

Outlook...

Saturday Night: Moderate Operational Impact
Chance of RA
SN.
Sunday: High Operational Impact
Likely RA
SN.
Sunday Night: Moderate Operational Impact
Likely RA
SN.
Monday: Moderate Operational Impact
Chance of RA
SN.
Monday Night: No Operational Impact. NO SIG WX.
Tuesday: No Operational Impact. NO SIG WX.

ALY WATCHES/WARNINGS/ADVISORIES
CT...None.
NY...None.
MA...None.
VT...None.