Area Forecast Discussion

WHAT HAS CHANGED

The greatest risk for potential severe threat trending towards the Mohawk Valley, Greater Capital Region, southern VT southward based on latest CAMS in the mid/late pm into the early evening. Damaging winds remain the main threat.

Winds were increased late this pm into tomorrow based on the upstream observations, and the cold advection tonight into tomorrow with the cold front with better mixing.

Lowered max temps from the NBM warmer values Mon/Tue 2-4 degrees based on the warm bias and better alignment with other guidance. Uncertainty continues how warm the forecast area gets in the middle to end of next week based on the medium range guidance.

KEY MESSAGES

1) There continues to be a Slight risk (Level 2 of 5) for severe thunderstorms this afternoon and early evening for most of the region outside of the southern Adirondacks, which have a Marginal Risk (Level 1 of 5). The main threat will be damaging winds, but isolated large hail and locally heavy rain will also be possible.

2) Cooler and drier weather returns late Sun into Mon with temps trending back above normal by the mid week.

DISCUSSION

KEY MESSAGE 1... As of 235 PM EDT...A low pressure system /~1000 hPa/ continues to move across extreme southeast Ontario into south Quebec early this afternoon, as a pre-frontal sfc trough produced some showers and clouds mainly along and north of the Capital Region earlier today. The clouds and showers have limited the instability so far over the southern Adirondacks, Lake George northern Saratoga Region into parts of southern-central VT. The best SBCAPE based on the latest SPC RAP meso-analysis is from the Mohawk Valley, Capital Region, extreme southern VT south and west in the 500-1000+ J/kg range. The CAMs have been trending southward slightly and a littler later with convection developing in the pre-frontal sfc trough zone between the cold front and sfc trough. Low and mid-level heights begin to fall and the better mid and upper level jet forcing will be over western-central NY. Winds have picked up with gusts 35-50 mph seen over western NY ahead of the cold front.

The positively-tilted mid and upper trough approaches late this afternoon into tonight with its attendant cold with the latest HREFs showings mean SBCAPE's rising into the 750-1250 J/kg range especially from the Mohawk Valley, Capital Region, and southern VT southward. The 0-6 km bulk shear increases to 30-40 KT. Some discrete cells may form between 19Z-21Z (3-5 pm) and evolve into a line or broken line with the greatest impact from south the southern Dacks or along the Tri Cities south and east. The 3-km NAM/WRF-ARF are little more widespread than the 3-km HRRR with convective coverage. The 3-km HRRR shows less instability based on the morning/early pm showers compared to the 3-km NAM/WRF. The sfc temps are a bit higher on the 3-km NAM/WRF-ARW. Model soundings show inverted-V signatures, steep low-level lapse rates, and DCAPEs in the 750-1000 J/kg range. The low-level jet increases in the 0-3 km layer from the southwest or southwest/west helping advect into more low-level moisture but will also be perpendicular to the flow aloft for any cells to form into a line. Along the line...bowing cells and cold pools may yield wind damage 20Z to 00Z/Sun along and south of I-90. Mid level lapse rates are only 5.5-6C/km with pockets 6-6.5C/km, so large hail looks lesser of a threat compared to damaging winds. SPC continues to have wind damage probs up to 30% from Schoharie County, the Capital District, and the Berkshires south and west. Damaging winds could bring down trees, power lines and large tree limbs. Enhanced wording continues in the forecast grids and we will monitor for any potential convective watch.

PWATS rise to the 1.2-1.5" range and some brief locally heavy downpours are possible with the showers and thunderstorms. We are not expecting flash flooding at this time, but the threat is non-zero in case any convection trains/back builds. FFG values are high, its been dry and we not highlighted in the WPC ERO. Localized ponding of water on roads is possible if storms happen to train or backbuild on/over any urban areas.

KEY MESSAGE 2... The cold front moves across the region tonight. The showers and thunderstorms will end prior to midnight. Some upslope showers may linger over the western Adirondacks and southern Greens. Some patchy fog may form south of the Capital Region and near the Lake George Region. Otherwise, cold advection will be occurring with breezy west winds. Lows fall back into the 50s to lower 60s. Isolated to scattered showers especially from the I-90 corridor northward will occur in the late morning through the mid afternoon with the upper level trough moving overheard. In the cyclonic flow with an embedded short-wave, mid level lapse rates will steepen. Instability is low in the 200-500 J/kg range based on the HREFs, as a few isolated thunderstorms are possible from the Hudson River Valley eastward, but as the afternoon progress the showers will decrease in coverage in the mid to late pm. Temps will be cooler than today with 60s to lower 70s over the higher terrain and mid 70s to spotty lower 80s (mid Hudson Valley) in the valleys. Northwest winds will be 10-20 mph with some gusts 20-30 mph with better mixing/momentum transfer and we went above the NBM guidance.

High pressure builds in Sun night into Mon with drier weather and cooler temps briefly. Lows fall into the mid 40s to mid 50s Sun night with decreasing winds. The sfc ridge brings mostly sunny skies for Mon with near to slightly above normal temps. Highs will be in the upper 70s to lower 80s in the valleys and upper 60s to mid 70s in the valleys. Temps radiate Mon night into Tue morning with the high pressure over the NY and upper Mid Atlantic corridor with lows in the upper 40s to mid 50s. Low-level warm advection and heights rise on Tue with the sfc high to the south and west allow temps to continue to rise above normal. The air mass remains dry and due to the NBM warm bias we lowered 2-4 degrees for highs and coordinated with WFOs. Highs will be in the mid and upper 80s for the valleys and upper 70s to mid 80s over the hills and mtns with heat indices below advisory thresholds. Temps and heat indices rise from the mid week onward into Fri. Some uncertainty exists how hot we get based on the latest NBM/WPC forecast for late next week. A warm front and a short-wave brings a chance for showers and thunderstorms for Wed. Sfc dewpoints rise for the late week and with temps in the mid 80s to lower/mid 90s in the forecast some locations may need heat headlines late in the week into next weekend,as it gets more humid. Again, quite a bit of uncertainty continues to exist.

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: Low Operational Impact. Slight Chance of SHRA. Wednesday: Moderate Operational Impact. Chance of SHRA...TSRA. Wednesday Night: Moderate Operational Impact. Chance of SHRA...TSRA. Thursday: Moderate Operational Impact. Chance of SHRA...TSRA.

ALY WATCHES / WARNINGS / ADVISORIES

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