textproduct: Burlington

WHAT HAS CHANGED

As of 742 PM EDT Monday...

Issued a quick update to increase PoPs across mainly northern areas through the evening. Persistent radar returns can be seen streaming along and just south of the international border. This activity is associated with a cold front and will continue to slowly push southward over the next several hours. While much of this precipitation is not yet reaching the ground, have seen a few reports of light rain and drizzle. So have gone ahead and adjusted PoPs to 30-50% in northern areas, though rainfall amounts will remain very light.

KEY MESSAGES

As of 306 PM EDT Monday...

1. Round 1 of rain with wintry mix near the international border Tuesday into Wednesday.

2. Round 2 of Rain with wintry mix near the international border Thursday into Friday.

3. River rises expected with local lowland field flooding possible Tuesday into Wednesday.

4. Active and warm weather conditions will likely continue into the weekend.

DISCUSSION

As of 306 PM EDT Monday...

KEY MESSAGE 1: A low pressure system tracks west to east Tuesday into Wednesday, with a track near the international border. As the low moves into the region, cold high pressure will be trying to build down from Canada. The precipitation will begin as rain showers as a warm front type features pushes into the region late tonight into tomorrow due to the already warm antecedent airmass. However, as the high builds down and winds switch to northerly, surface temperatures will drop to around freezing across the northern Champlain Valley, St. Lawrence Valley, and far northern Adirondacks. The rain showers should eventually change to freezing rain showers there. A dry slot should occur during much of the day tomorrow, but a second round of rain looks to move through late tomorrow into Wednesday morning. By this point, temperatures will likely be cold enough for freezing rain to begin in the aforementioned areas. Currently, up to 0.2 tenths of ice is expected, but this is a very uncertain forecast. Model guidance is widely split and a high sun angle may prevent enough cooling during the day for icing to occur. A reasonable high end solution would probably be 0.2 to 0.4 inches like forecast by the HRRR or NAM, while a reasonable low end solution is nothing as forecast by much of the global guidance and couple of the other CAMs. Overall, QPF totals are expected to be between 0.5 to 1.5 inches with higher totals farther south. Some elevated instability could cause a few rumbles of thunder and local convective enhancement of the rainfall, though the majority of that should remain to the south.

KEY MESSAGE 2: Another storm system makes a run at the region for late Thursday into Friday, though the trend in storm track to the north continues. Canadian high pressure will be established on Thursday and it will provide a cold antecedent airmass for this low pressure to run into. With the current expected storm track, the precipitation looks to start as a wintry mix and transition to all rain. Combined GEFS/EPS/CAN ensemble probabilities of 1 inch or more of snow generally range between 30-70 percent, 3 are between 5-20 percent and 6 are less than 10 percent. The highest probabilities are farther northeast. Probabilities of 0.1 inch or more of freezing rain are between 20-40 percent for the favored locations east of the Greens and in southern Essex County NY. The caveat here is that with the warming trend and looking at the new deterministic guidance, these probabilities will likely continue to come down a bit, especially with the snow.

KEY MESSAGE 3: Despite a gradual southward shift in the heaviest precipitation, sharp river rises are still expected Tuesday into Wednesday and lowland field type flooding remains possible. Overall, the expected 0.5 to 1.5 inch totals over 36 hours would not cause much of a threat by themselves, but some elevated instability and associated rainfall enhancement will likely lead to locally higher totals. The heaviest rainfall axis looks to set up over central and southern areas, where local amounts up to around two inches are possible. However, there will be some notable factors limiting the flood threat. The first is that the rain looks to come through in two mostly separate rounds, with almost twelve hours in between, giving time for rivers to take up the water. The second is that there will be relatively cool surface temperatures and dew points, especially where the snowpack remains at the higher elevations. Dew points only look to reach the upper 30s and low 40s, with maximum temperatures not much higher. A gradually cooling trend should allow snowmelt to decline further going into Tuesday night. With that being said, several rivers look to approach Action Stage and minor flooding cannot be ruled out in a reasonable worst case scenario. The river forecast to minor for the East Branch of the Ausable River in Ausable Forks is on the high side, with ensemble guidance averaging below that and shadowing effects likely limiting precipitation as well.

KEY MESSAGE 4: An early season Bermuda High will peak in intensity Thursday night with only a gradual decay expected. A pair of weather systems across the western US will send impulses northeastward before finally tracking across the Northeast over the weekend when the deep layer ridging starts to decay off the Atlantic. Thursday night into Friday will feature mixed precipitation and rain trending scattered during the day. High temperatures will climb into the 50s to 60s again. The track of low pressure Friday afternoon is somewhat uncertain, but medium range guidance may be overestimating how far north a 1005-1010mb surface low can get against a 1037-1040mb high over Quebec Province. The area of low pressure will bend towards a more eastward, or east-southeast, track, perhaps overhead. The farther south it goes, the earlier we see precipitation return. Most of the available moisture will be in the vicinity of the surface low and less outside. Some marginal instability of 100-250 J/kg will be possible , but without better forcing and the presence of dry air, coverage may be scattered. The low track will also influence the degree of destabilization possible. Briefly drier conditions will ensue after the low shifts east Friday night into Saturday. Somewhat cooler air will try to shuffle back south, but with little success against the stronger system incoming.

The next system will pack a little more punch. Stronger southwesterly 850mb flow and more warm, moist air will be present as the area of stronger high pressure in Quebec Province moves out. This second surface low will likely track north of Montreal, and medium range guidance suggests a well-defined front. We'll see how much of it may get broken up to terrain shadowing against the faster 850mb flow, but for now, rain showers appear very likely, though the exact time window will be tacked down later.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Through 00Z Wednesday...VFR conditions currently prevail at all terminals this evening, but expect things to deteriorate overnight, particularly after 06z, as precipitation spreads across the region. Ceilings will lower through MVFR 06z-12z, then continue to drop to below 1000 ft and into IFR range by mid day Tuesday. Steady rain and mist will lower visibility to 4-6SM through 15z, then precipitation looks to become more showery. KMSS will likely transition over to freezing rain around 12z and remain at or below freezing through much of the remainder of the TAF period. Gusty S/SW winds will lighten and trend more toward the W/NW overnight as a cold front moves southward. They will remain NW/N through much of the day on Tuesday, mainly AOB 10 kt. Some LLWS will be possible late in the period as a low level jet moves in, but have mainly left this out of the TAFs for now as it will mainly be after 21z.

Outlook...

Tuesday Night: Mainly IFR, with areas MVFR possible. Definite RA, Definite FZRA. Wednesday: Mainly MVFR, with local IFR possible. Chance RA, Chance FZRA. Wednesday Night: Mainly VFR, with areas MVFR possible. Chance RA, Slight chance FZRA, Slight chance SN. Thursday: Mainly MVFR, with local VFR possible. Likely RA, Chance SN, Chance FZRA. Thursday Night: MVFR and IFR. Definite RA, Definite FZRA, Definite SN. Friday: Mainly MVFR, with local IFR possible. Likely RA, Slight chance TSRA. Friday Night: Mainly MVFR, with local IFR possible. Chance RA. Saturday: Mainly VFR, with areas MVFR possible. Chance RA.

EQUIPMENT

The Colchester Reef meteorological station is out of service. This site is not serviced by the NWS. An estimated return to service is May 1st. Please contact us if you observe winds significantly deviating from the recreational forecast.

BTV WATCHES/WARNINGS/ADVISORIES

VT...Winter Weather Advisory from 5 AM Tuesday to 9 AM EDT Wednesday for VTZ001. NY...Winter Weather Advisory from 5 AM Tuesday to 9 AM EDT Wednesday for NYZ026>028-030-031.