Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
305 FXUS61 KBOX 191904 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 304 PM EDT Sun May 19 2024 .SYNOPSIS... The coastal storm that has brought low clouds, drizzle and cool northeast winds to RI and eastern MA, finally begins to exit out to sea tonight. This gives way to a significant pattern shift to drier and warmer weather beginning Monday. Very warm temperatures are expected on Tuesday and Wednesday, with temperatures reaching into the 80s, with an outside chance a few locations see 90 degrees on Wednesday. Humidity levels will be on the low side accompanying that midweek warmth, hence, a somewhat dry heat. A cold front arrives on Thursday with the potential for showers and thunderstorms. A drier and more seasonable air mass then filters in for late in the week into at least the early part of Memorial Day Weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 3 PM Update: Low level moist onshore jet continues to deliver overcast conditions and some spotty drizzle across RI and eastern MA, including Cape Cod and the Islands. Meanwhile, breaks in the overcast are occurring across CT into MA, eastward into the Worcester Hills. Temps are responding to the strong May sunshine, with temps warming through the 60s there and a few low 70s, including 71 at BDL currently. Meanwhile, short wave energy traversing southward from the ME coast will continue to delay height rises from advancing eastward today. This also results in a nearly stationary low level ENE jet into eastern MA and RI, with the low level jet slowly shifting southward overnight, along with ridge of high pressure advecting south into SNE. Thus, drier trends overnight. However, low level moisture will likely remained trapped beneath the subsidence inversion from the surface ridge building southward. Hence, low clouds will remain stubborn across RI and eastern MA tonight and likely drifting back into CT and western/central MA, along with patchy fog possible. This low level moisture will yield seasonably cool temps overnight, with lows in the upper 40s and lower 50s. Although, it will feel cooler with northeast winds 15-25 mph, highest over southeast MA and RI, slowly slackening tonight as the surface ridge builds southward. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... 3 PM update... * Big improvement, more sunshine & warmer temperatures * Low 80s possible CT River Valley, including Hartford/Springfield Monday... Once short wave energy exits the eastern MA coast tonight, this allows height rises to advect Monday across the region from west to east and more importantly, low level jet easing and moving offshore. This ridging and associated subsidence will allow strong May sunshine to erode low level moisture/clouds and possible patchy fog Monday morning and give way to at least partial afternoon sunshine to the entire region. 12z models have trended warmer and this seems reasonable given the height rises and morning clouds giving way to at least partial late May sunshine. 850 mb temps increase to about +12C and 925 mb temps warm to +18C to +20C western MA, to +13C across southeast MA. This will support highs in the low 80s across western MA/CT, with much of the region seeing highs in the 70s and as far southeast into the I-95 corridor of MA/RI. With surface ridge over the area, afternoon seabreezes will develop and cap highs in the 60s for the coastline, possibly only into the upper 50s for the outer Cape and Nantucket. Monday night... Deep layer ridge over SNE will provide dry weather. Light winds and dew pts slightly above normal (low 50s), may yield patchy fog. This will also result in mild overnight temps, with lows 50-55. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Highlights: * Very warm temperatures Tuesday and Wednesday away from the southeast coast, with readings into the 80s. Warmest day is Wednesday, and a few locations in the Connecticut and Merrimack Valleys could see their first 90-degree temperature in 2024 on Wednesday! Humidity levels will be tolerable - a "dry heat". * Cold front moves through sometime on Thursday. Timing of the front is still uncertain but the timing will influence how warm temperatures get and also the potential for thunderstorms, which could be strong. * Drier with more seasonable temperatures for late in the week into the early Memorial Day Weekend. Details: 00z ensembles continue to advertise a significant warm spell for at least Tuesday and Wednesday for most of Southern New England. Full sun and southwest downsloping breezes, combined with 850 mb temps around +13 to +15C should be fairly common on Tuesday with 850 mb temps rising about a degree or so on Wednesday. It is likely that the Providence to Plymouth corridor on southward to Cape Cod and the Islands would be the cooler locations given southwest flow off the water, with values in the 70s to lower 80s and upper 60s-around 70 for Cape Cod. Very warm temperatures are expected further north and west from there, with persistent SW flow keeping the eastern MA sea breeze from developing. Of the two days, Wednesday projects as the warmest. Highs on Tuesday away from the southern coast should reach into the lower to mid 80s, with readings near 80 for the North Shore into Greater Boston. Probabilistic maximum temperature data from the NBM for Wednesday indicates 50-70% probs for highs reaching the 90- degree mark in the CT and Merrimack Valleys! Mid to upper 80s being common to the Providence-Plymouth corridor. Kept highs for southeast coastal New England on Wednesday into the 70s to low 80s. Thus it is looking likely that we`ll see summerlike temperatures making their first appearance in 2024 on Tuesday and Wednesday for a large part of Southern New England, with many likely not yet acclimatized to this warmth as yet. It`s also more of the "toasty" heat versus the oppressive/muggy kind: very warm ambient air temps but with tolerable humidity levels, as dewpoints are expected in the mid to upper 50s. A cold front then approaches sometime on Thursday, with increasing cloud cover. The biggest question mark is on the timing of the front, which will influence both how warm we get pre-frontal passage and the potential potency of showers and t-storms along and ahead of the front. Not out of the question that Thursday could still be quite warm if we see a slower timing similar to the ECMWF. Kept temps a little cooler than NBM but even with clouds we should see highs reach the lower to mid 80s again for most except southeast New England. Thursday could also feature scattered strong to perhaps severe t-storms too if the timing of the front coincides with peak daytime heating; GFS shows a convective environment with about 1000 J/kg of CAPE with about 40-45 kt of wind shear in the 0-6 km layer for Thursday. Machine-learning progs from Colorado State weren`t available with the 00z guidance but the prior run hinted at the potential for storms becoming severe in interior sections of New England. Kept PoP around 30-50 percent, but those will need to be adjusted pending the timing of the front. But Thursday should be the next best chance for rains. A more seasonable airmass then returns on NW flow for Friday and Saturday, with drier weather also returning. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update: Through 00z... Improving cigs to MVFR continue to spread from west to east across CT and MA into the Worcester Hills, RI and even into parts of southeast MA. Some uncertainty how much farther eastward this progresses before sunset. Radar still picking up some spotty drizzle across southeast MA into RI. This should slowly shift south through 00z. NE winds 10-15 kt with gusts up to 25 kt across Cape Cod and the islands. After 00z... Decreasing trends with IFR (possibly LIFR) cigs and MVFR vsbys in fog drifting and developing westward from the coastline into the interior overnight. Any areas of drizzle during the evening should come to an end after midnight. NE winds 10-15 kt with gusts up to 20 kt in the evening across southeast MA, will slacken overnight. Monday... IFR/LIFR cigs with mainly MVFR vsbys in fog early, will slowly improve to VFR all terminals, but obviously delayed until the afternoon or late in the day across Cape Cod and the Islands. Light NE winds become east and then southeast late in the day. Monday night... VFR but MVFR vsbys developing in patchy fog. KBOS TAF...High confidence in TAF trends but lower on exact timing. MVFR cigs and VFR vsbys this evening, then lowering to IFR/LIFR cigs with MVFR vsby overnight into Monday morning. Then eventually improving to VFR by Monday afternoon. NE winds tonight, becoming east Monday and then southeast late in the day. KBDL TAF...High confidence in TAF trends but lower on exact timing. VFR continues into early evening, then some uncertainty how low cigs and vsbys overnight into Monday morning, as low clouds and patchy fog develop overnight. High confidence in improving conditions Monday to VFR by midday or so. Outlook /Tuesday through Friday/... Tuesday through Tuesday Night: VFR. Wednesday through Wednesday Night: VFR. Breezy. Thursday: VFR. Breezy. Chance SHRA, chance TSRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 3 PM update... Tonight...high confidence. Offshore low continues to generate marginal SCA with NE winds up to 25 kt (in gusts, not sustained) and seas up to 6 ft across the eastern MA waters, slowly subside tonight. Vsby may be reduced to 1- 3 miles at times in drizzle and fog. Monday... High confidence Lows clouds/drizzle and patchy early morning fog with vsbys 1-3 miles, slowly burns off with improving conditions mid to late afternoon. High pressure over SNE results in light NE winds become east and then southeast late in the day. Monday night...high confidence. Ridge of high pressure crest over the waters, yielding light SE winds becoming SW. Patchy fog may limit vsby at times. Outlook /Tuesday through Friday/... Tuesday through Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers, isolated thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ250. Small Craft Advisory until 2 PM EDT Monday for ANZ254. && $$ SYNOPSIS...Nocera/Dooley NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...Loconto AVIATION...Loconto/Nocera MARINE...Loconto/Nocera