Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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228 FXUS61 KBOX 021701 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 101 PM EDT Tue Jul 2 2024 .SYNOPSIS... High pressure over New York moves southeastward into the southern off waters through Wednesday. Expect full sun, seasonably warm temperatures and low levels of humidity today and Wednesday. Cloud cover increases Wednesday evening ahead of a weak cold front that moves through Southern New England on the Independence Day holiday, bringing a risk for showers and thunderstorms. Pop-up showers possible on Friday, but a more unsettled weather pattern develops for the weekend. Temperatures are generally seasonable to slightly above normal, but with elevated humidity levels from Independence Day into the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 850 AM Update... * Sunny with highs mainly in the 80s today & low humidity A ridge of high pressure will remain in control of our weather today. The result will be sunshine and a beautiful day for early July standards. 850T around +13C should allow many locations to see afternoon highs in the middle 80s. It will be a few degrees cooler along the immediate coast as sea breezes kick in with a weak pressure gradient...but high should still reach the upper 70s to near 80. More importantly...dewpoints in the upper 40s and 50s will make for a very comfortable afternoon especially for this time of year. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... High pressure expected to open tonight over eastern NY to shift SE thru tonight into the southern offshore waters and generally maintain that position through Wed. Thus continued tranquil weather is expected both tonight and Wednesday, although will see periods of high clouds spill into Southern New England. The question mark for tonight is on potential for patchy radiation fog at least in the river valleys. We do get into a modest southerly flow late tonight and that should bring dewpoints up somewhat (into the mid/upper 50s). Models for tonight seem pretty mixed on the potential and also is not really hinted at in the MOS progs either, but it seems like one of those nights where you could get at least river valley fog to develop with good radiational cooling expected. MOS used for lows in given radiational cooling, with lows in the 50s for most, though the urban areas and hills could see readings near 60. Modest southerly gradient expected for Wed, but think weak flow aloft should again favor seabreezes on both coasts. More of a mix of sun and high clouds for Wed, along with dewpoints rising to near 60 so humidity levels should be tolerable. Highs in the 80s, with late- day highs on the eastern MA coast once seabreeze-driven winds shift to the SW. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights: * A couple showers are possible, along with increased humidity on Independence Day. * Warm, humid, and showers about for Friday and this coming weekend, but timing remains uncertain. Thursday and Friday: Axis of the mid-level ridge is oriented from southwest to northeast but is shifting offshore and deamplifying, allowing for a zonal pattern. There is good agreement for Thursday a surface low pressure system moves from west to east across Quebec and weak cold front moving across New England. Overall weak forcing, thus do not expect a washout, despite PWATs between 1.5 and 2.0 inches. Ensembles, like DESI show less than a 10% probability for 0.25" of new rainfall for Thursday afternoon, with a realistic/likelihood for a few hundredths of an inch of new rainfall are between 40% and 50%. Timing remains uncertain given no large scale forcing, but expect we will have a better idea once the high-res models are able to capture the meso scale features. As of 02/00z, NAM 3KM only goes out to 12z Thursday or 8am on July 4th. Heading into Friday, there are subtle height rises along with weak shortwave energy traversing through the zonal mid-level regime. As PWATs remain well above normal, 1.5" to 1.8", and even higher values along the southern coast nearing 2.25". Again, fairly low probabilities for new rainfall, around 25% probability of 0.1". Important to note, that localized heavier downpours still cannot be ruled out a this point in time given how moisture rich the atmosphere is. And as you might imagine, with anomolously high PWATs, dew points are elevated and will be the type of humidity you can feel. Both Thursday and Friday air temperatures in the middle and upper 80s with dew points in the upper 60s and low 70s. Overnight lows are in the middle to upper 60s, with low 70s possible in urban centers. Saturday and Sunday: Unsettled pattern into the weekend ahead, while model guidance is in a good amount of agreement on the mid-level pattern, there is a good deal of uncertainty in the surface features. Right now, it appears a warm front lifts across the region some time Saturday and cold front passage on Sunday. The air mass is still quite warm and muggy this coming weekend, but could change, especially for Sunday depending on the timing of the front. For now, highs are generally middle to upper 80s with the potential for oppressive humidity, as dew points are in the low 70s. Monday: Mid-level high over Bermuda with a trough over the eastern third of the CONUS. There is spread in the surface features amongst 02/00z guidance and have very low confidence in this part of the forecast. && .AVIATION /18Z TUESDAY THROUGH SATURDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 18z TAF Update... Tonight through Wednesday night...High Confidence. VFR conditions persist through Wed night. Localized sea breezes come to an end early this evening...otherwise calm/light S winds tonight. SSW winds increase to between 5 and 15 knots Wed morning. Sea breezes will likely develop again along portions of the immediate coast...but they should kick by late afternoon. S-SW winds generally 10 knots or less Wed night. KBOS TAF...High confidence in TAF. Sea breezes kick out by 01z-02z this evening. Another round of sea breezes develop Wed am but they should shift out by late Wed afternoon as the winds shift to the S. KBDL TAF...High confidence in TAF. Outlook /Thursday through Saturday/... Independence Day: VFR. Breezy. Slight chance SHRA. Thursday Night through Friday Night: VFR. Slight chance SHRA. Saturday: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Generally pleasant marine weather conditions as broad high pressure gradually builds into the waters by Wed. Northerly winds this morning around 10-15 kt to steadily decrease this afternoon (becoming ESE near the immediate eastern MA coast), then begin to shift to light SW late in the overnight hrs. Light SSW winds for Wed, with local ESE winds near the immediate shorelines for Wed. Seas 3 ft or less all waters. Outlook /Wednesday Night through Saturday/... Wednesday Night: Winds less than 25 kt. Independence Day through Saturday: Winds less than 25 kt. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Loconto/Dooley NEAR TERM...Frank SHORT TERM...Loconto LONG TERM...Dooley AVIATION...Frank/Dooley MARINE...Loconto/Dooley