Area Forecast Discussion

WHAT HAS CHANGED

Frost advisories issued for parts of the area for tonight. Most of the freeze watch upgraded to a freeze warning.

KEY MESSAGES

1) Rain showers through the rest of today.

2) A colder air mass settles in, with near freezing temperatures inland tonight and sub-freezing temperatures for much of the area outside NYC and some immediate suburbs to the west/east Monday night.

3) Milder weather returns mid to late week, with a potential cooldown for next weekend.

DISCUSSION

KEY MESSAGE 1

Jet-induced post-frontal showers over most of the area except ern CT/Long Island as of 2 PM will swing east this afternoon. A few wet flakes may mix in across the highest elevations well NW of NYC. Later on, as a strong mid level shortwave trough swings across early this evening, some isolated showers may occur from NYC north/west as there will still be enough moisture and elevated instability present, though not quite enough for thunder. QPF after 18Z remains relatively light, on the order of 1-2 tenths of an inch at most.

KEY MESSAGE 2

Frost advisories issued for coastal CT and outlying NY/NJ suburbs for late tonight into early Mon AM as temps there fall to the mid 30s after midnight. Some sub-freezing temps likely in the interior valleys, but did not issue freeze warnings there as the growing season there starts on Monday.

A secondary front moving through on Mon will bring a chance of showers. Some wet snowflakes may mix in well NW of NYC in the morning. Temps will be on the cool side, with highs only from the upper 40s to mid 50s.

The coldest temperatures early next week appear likely Monday night, with clearing skies and light winds helping to efficiently cool the BL. Sided with colder of NBM and GFS/NAM MOS guidance, with lows from the mid 20s to lower 30s over most of the area except for far eastern Long Island, NYC and some areas just outside. Upgraded the freeze watch to a warning for most of those areas, but kept the watch going for Nassau County as temps there may remain just above freezing. Record daily low temps are even in reach for a few stations: see the Climate section below for details.

Temperatures remain below normal on Tuesday with highs mostly 50-55. High pressure overhead will shift offshore Tuesday night, setting up a weak return flow and a milder night compared to Monday night with lows from the upper 30s to mid 40s.

.KEY MESSAGE 3... Following the departure of an upper trough across the area, heights will build aloft mid week as ridging builds east from the mid section of the country. This will allow for a warmup from Wednesday into Thursday. The forecast then becomes a bit more challenging at the end of the week as jet energy dropping down the east side of the upper ridge across eastern Canada carves out an upper low near the Canadian Maritimes. This then sets up a block of the incoming ridge, weakening it, and potentially allowing a back door cold front to drop SW across New England and into the area on Friday, the latter of which could serve as a focusing mechanism for showers heading into the weekend. It is too early to be specific with any details, but a cooler weekend with a low chance for rain will be advertised at this time. NBM spread in the box and whisker plots is clearly showing an increasing spread heading toward Friday and next weekend. This is likely do to the timing and location of the backdoor cold front.

At this time, using the NBM deterministic forecast, highs Thursday get into the 60s along the coast, and 65-70 from NYC and points north and west. This is looks to be the warmest day of the week. Lows will be in the 40s to around 50. Temperatures will then begin to gradually cool down Friday into the weekend. Highs could struggle to get out of the 50s next weekend.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Another cold front follows late tonight into early Monday, followed by high pressure building from the west.

Mainly MVFR with showers to start, but conditions will improve from west to east. Showers end 20z-22z with flight categories gradually prevailing VFR. VFR prevails this evening into tonight.

There is a chance for showers and MVFR, possibly mixed with wet snow well NW of NYC terminals Monday morning. Have included a PROB30 for this potential.

NW winds around 15 kt with gusts around 25 kt this afternoon. Winds and gusts should start weakening after 19z, ending around 00z. WNW-NW winds fall below 10 kt tonight, then back to the SW early Monday morning.

NY Metro (KEWR/KLGA/KJFK/KTEB) TAF Uncertainty

Timing of improving flight categories may be off by 1-2 hours.

Peak gusts around 30 kt possible through 20z and end time of wind gusts this evening may be off by 1-2 hours.

Start time of gusts Monday may be off by 1-3 hours.

OUTLOOK FOR 18Z MONDAY THROUGH FRIDAY

Monday: VFR. NW wind gusts 20 kt.

Tuesday: VFR.

Wednesday: Mainly VFR. Slight chance of showers in the morning.

Thursday-Friday: VFR.

Detailed information, including hourly TAF wind component forecasts, can be found at: https:/www.weather.gov/zny/n90

MARINE

SCA in effect for all waters as NW winds gust to 25-30 kt after a cold frontal passage, with ocean seas 5-7 ft. Gusts could briefly peak at 35 kt on the ern ocean waters early this evening. SCA extended into early evening for these gusts for the far ern Sound and Peconic/Gardiners Bays, also for the near shore ocean waters from Fire Island Inlet to Moriches Inlet.

Quiet on all waters thereafter through Fri night.

CLIMATE

Daily record low temperatures for Tue Apr 21:

KEWR: 31/1981 KBDR: 29/1956 KNYC: 26/1875 KLGA: 33/1956 KJFK: 34/1956 KISP: 30/1965

OKX WATCHES / WARNINGS / ADVISORIES

CT...Freeze Warning from midnight Monday night to 9 AM EDT Tuesday for CTZ005>012. Frost Advisory from midnight tonight to 8 AM EDT Monday for CTZ009>012. NY...Freeze Warning from midnight Monday night to 9 AM EDT Tuesday for NYZ067>071-078>081. Frost Advisory from midnight tonight to 8 AM EDT Monday for NYZ069>071-078>081. Freeze Watch from late Monday night through Tuesday morning for NYZ177-179. NJ...Freeze Warning from midnight Monday night to 9 AM EDT Tuesday for NJZ002-004-103>108. Frost Advisory from midnight tonight to 8 AM EDT Monday for NJZ002-004-103-104. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ331- 335-345-355. Small Craft Advisory until 9 PM EDT this evening for ANZ332- 338-340-353. Small Craft Advisory until 11 PM EDT this evening for ANZ350.