Area Forecast Discussion

WHAT HAS CHANGED

Lowered temperatures through the rest of the overnight period with calm winds and some breaks in the cloud cover. Confidence remains fairly high in severe weather potential this afternoon into the evening, with the primary threat being damaging winds. Also, some uncertainty surrounding how warm temperatures next week will get, with some signals that temperatures could end up well below the current forecast.

KEY MESSAGES

1) There is a slight risk for severe thunderstorms this afternoon and evening for most of the region outside of the southern Adirondacks, which have a marginal risk. The main threat will be damaging winds, but isolated large hail and locally heavy rain will also be possible.

2) After a brief cooldown Sunday and Monday, temperatures trend back to above normal for the middle and end of next week.

DISCUSSION

KEY MESSAGE 1... As of 2:45 AM EDT...1004 mb sfc low is currently tracking from Ontario into southern Quebec in association with a fairly potent positively tilted upper trough. Out ahead of these features, calm winds and some breaks in the cloud cover have allowed temperatures to drop below the previous forecast, with many high terrain areas in the mid 50s to around 60, while valley areas remain in the 60s per latest NYS Mesonet and ASOS obs. Many places have likely already hit their overnight lows, as increasing mid and high clouds will allow temps to hold steady or even rise slightly over the next few hours. Current radar imagery shows an area of showers tracking into and north of our southern ADKs in association with mid-level warm advection. These showers should remain confined to our far northern areas into this morning. An isolated rumble of thunder will be possible, with current SPC mesoanalysis showing some pockets of elevated instability.

This morning, showers continue across our southern ADKs, possibly scraping the far upper Hudson Valley and/or southern VT as the aforementioned sfc low tracks eastwards. A weak pre-frontal trough will track through the region this morning, but isn't expected to lead to much convection given instability won't have much time to build. However, the sfc low strengthens as it tracks through southern Quebec this afternoon, dragging an attendant cold front across the region. This will be the main forcing mechanism to ignite more widespread showers and thunderstorms, some of which could be strong to severe. These showers and storms will track through the region from northwest to southeast this afternoon and evening before ending early tonight. Highs climb into the 70s for the high terrain to upper 80s near the I-84 corridor. For southern areas, it will be hot, but heat indices are expected to fall a few to several degrees short of advisory criteria.

SPC has maintained their slight risk for severe weather across most of the region today, which makes sense given the atmospheric setup. The cold front will be running into a moderately unstable airmass with 1000-1500 J/kg of SBCAPE overlapping with 30-40 kt of deep-layer shear this afternoon, with much of this shear in the lowest 3 km thanks to a strengthening southwesterly LLJ. Deep layer shear vectors look to have just enough of a perpendicular component to the approaching boundary that some discrete cells will be possible this afternoon as CI occurs, especially since low-level forcing doesn't look overly impressive ahead of the cold front with winds veering to the SW behind this morning's pre-frontal trough. However, but rather impressive height falls aloft and divergence associated with the exit region of a cyclonically curved upper jet streak will lead to strong forcing aloft. Given this, combined with straight hodographs that will lead to splitting cells, and rather deep cold pools due to a well mixed BL, storms should grow upscale into clusters or line segments fairly quickly. The main threat will be damaging winds (DCAPE values up to ~1000 J/kg), especially as cold pools congeal and upscale growth occurs. However, straight hodographs and decently strong EL winds will also support a secondary threat for large hail with any initial discrete cells. Will mention that SPC has removed the 2% tornado threat from our area, which makes sense given a lack of veering winds in the low-levels and relatively high LCLs expected today.

While we are fairly confident in the severe weather potential, as our analysis is supported by CAMs and machine learning guidance, a potential limiting factor is if there is more cloud cover around today that limits daytime heating and thus limits instability. Some mid-level dry air this afternoon could also potentially inhibit CI. These outcomes could lead to a more isolated severe threat, but seem like less-likely scenarios at this point.

The other, secondary threat to mention is the possibility for locally heavy rain. PWATs climb to around 1.5" this afternoon, and mean mid to upper-level flow will have enough of a component parallel to the approaching boundary that some backbuilding or training of convection can't be ruled out. While storm motions look moderately fast, any backbuilding convection may move slower with Corfidi upshear vectors ~10 kt. WPC has not included our area in an ERO, which makes sense and agrees with our thinking given how dry it has been recently. That said, while we aren't overly concerned about hydro issues, localized ponding of water would be possible if storms happen to train/backbuild over any of our urban areas.

KEY MESSAGE 2... The cold front tracks off to our east tonight. The severe threat comes to an end, but some lingering showers will be possible tonight and tomorrow, especially across northern and high terrain areas. This will be due to the upper trough remaining over our region and a fairly strong embedded shortwave rotating through tomorrow morning. Sunday does not look like a washout, however, with shower activity expected to decrease by late afternoon and evening as the upper trough slides to the east. Cooler and drier air also moves into the region tomorrow behind tonight's cold frontal passage, with highs in the 70s for the high terrain to low 80s for most of the rest of the region. To start the week, upper ridging amplifies over the Great Lakes, but with our region downstream of the ridge sfc high pressure building into the region will continue to result in cool advection with northerly flow. Dry conditions prevail through at least Tuesday with large-scale subsidence and the sfc high building overhead. Given persistent NBM warm bias, we lowered temps Monday and Tuesday by a few to several degrees. While temps begin to warm Tuesday as the upper ridge slides eastwards, heat indices should remain several degrees below advisory criteria.

For the middle and end of the week, confidence decreases as the upper ridge slides overhead, but may be suppressed by a broad upper trough tracking overtop the ridge. This could result in some scattered showers and more cloud cover each day. Temperatures remain above normal, but will likely not end up as high as the deterministic forecast shows. WPC did knock down NBM temps a couple degrees Thu/Fri, but we still feel this forecast is too warm (or, think of it as showing a worst-case scenario) with highs more likely to be in the mid and upper 80s, closer to MEX/ECM guidance. Dew points will be increasing though, so it will feel more muggy for the second half of the week. Will continue to monitor for potential heat impacts, but given current thinking we may get through much of next week without needing heat advisories.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Through 18z Sunday...A low pressure system and upper-level shortwave will continue to impact eastern New York and western New England through late this evening, bringing potentially widespread showers and thunderstorms this afternoon through this evening. While all terminal obs are currently indicating VFR conditions, MVFR to IFR conditions can be anticipated with any thunderstorms that cross through the terminals due to lowered ceilings and reductions to visibility driven by heavy rainfall. Winds will also likely be very gusty within any thunderstorms that develop and cross through terminal boundary, particularly if any become severe. The period of greatest probability for thunderstorms lies between 21z-02z. Once shower and thunderstorm activity ends this evening, a fairly quick return to VFR conditions is expected at all terminals with the exception of PSF where an MVFR ceiling could linger through tomorrow morning.

Winds are beginning to pick up out of the south to southwest with latest obs reporting sustained speeds around 5-10kt and a gust at ALB of 19kt. With the system's pre-frontal trough/wind shift boundary beginning to depart the region, winds will gradually begin to shift more consistently to the southwest. Once the cold front moves through tonight, winds will shift more to the west to northwest by tomorrow morning. Immediately behind the boundary, winds will remain quite breezy with sustained speeds around 6-10kt and gusts up to 20kt at ALB and PSF. But by tomorrow morning, all terminals will be gusting out of the northwest at speeds ranging from 18-28kt. It is important to note, too, that there will be a period of LLWS everywhere, except POU, tonight between 00-08z while a low-level jet passes.

Outlook...

Sunday Night: No Operational Impact. NO SIG WX. Monday: No Operational Impact. NO SIG WX. 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. Chance of SHRA...TSRA. Wednesday Night: Moderate Operational Impact. Chance of SHRA. Thursday: Moderate Operational Impact. Chance of SHRA...TSRA.

ALY WATCHES / WARNINGS / ADVISORIES

CT...None. NY...None. MA...None. VT...None.