Radar — KBOX
Surface Analysis — Eastern U.S. (North)
Satellite
Nearest monitored road: School Street (Secondary)
Expanded the flood watch to include worcester, windham, and providence counties. Increased rainfall totals with a widespread two to four inches expected for most areas, and up to five to seven inches possible for the berkshires and worcester hills.
- prolonged period of heavy rain slowly overspreads the region from west to east overnight through wednesday evening. Expecting areas of street and poor drainage flooding with the greatest risk across the interior where a flood watch remains in effect through 8PM wednesday night.
- improving conditions with nuisance showers friday followed by a drier weekend, becoming unsettled late weekend into early next week.
Key message 1...prolonged period of heavy rain slowly overspreads the region from west to east overnight through wednesday evening. Expecting areas of street and poor drainage flooding with the greatest risk across the interior where a flood watch remains in effect through 8PM wednesday night.
Bottom line up front: expected rainfall totals have increased, and in some areas, significantly so since the last update. We now expect a widespread swath of 2 to 4 inches of rain with areas locally seeing as much as 5 to 7 inches. The most likely locations to exceed 5 inches will be across the berkshires and worcester hills with orographic enhancement. In these areas, there may be some local river/stream rises, otherwise, the main concern is for urban/poor drainage flooding. Thus, we opted to expand the flood watch to include worcester, windham, and providence counties given recent trends to increase QPF in those areas. To reiterate, if you live in the hillier terrain of the berkshires or worcester hills, or in an urban/poor drainage area, this event will bring a significant risk for potentially life-threatening flash flooding. Be sure to have a way of receiving warnings especially at night when some of the heaviest rain likely falls across western massachusetts.
Anomalously deep mid level low that will be the main driver of our upcoming heavy rain event continues to amplify over western ny this afternoon. Eventually, there will be a response to this impulse at the surface in the form of rapidly developing surface low. The combination of favorable upper-level dynamics, and strong near- surface flow advecting copious amounts of moisture over our cwa set the stage for a prolonged, and in some localized instances, life- threatening heavy rain event. Details on the exact placement of heavy rain remain somewhat uncertain as even now, there are differences in the evolution of the occlusion and surface low between guidance. Global guidance has trended closer to the coast with the surface low and thus puts the bulk of the heaviest QPF to the north of the region. The cams continue to show a further offshore solution with a secondary swath of high QPF along a W-E oriented axis of frontogenesis across E central massachusetts wednesday evening into thursday. These changes reflect locally stronger forcing across these areas as the surface low occludes later wednesday into thursday. Guidance shows strong surface convergence and east to west oriented axis of enhanced frontogenesis developing as surface low pressure turns the flow more easterly in these areas. Combine that with high pwats and orographic enhancement over the hillier terrain of worcester county and eastern connecticut and there is the potential for flash flooding. Further to the west, SE and E flow will serve to enhance upslope flow and rainfall totals in the berkshires as well. In this area, training storms (continually moving over the same location) likely leads to widespread flooding as the surface low slowly moves E. Timing for the heaviest rain would begin as early as this evening for interior sne, while eastern ma is likely to stay dry until late tonight night/wednesday morning. Areas of heavy rain will move E over those areas later wednesday morning, with heavy rain increasing in coverage through much of the afternoon as surface low pressure approaches from the S. There will be plenty of instability for tall convective cells as mucape increases to around 500 j/kg. Model soundings show deep warm clouds with >90% saturation extending through much of the column allowing the atmosphere to use ~90% of the 1.5-2.0" pwats for torrential rainfall. Unfortunately for outdoor plans this appears to be a long duration event. Showers and drizzle stick around through at least friday. The good news is that the heavy rain of wednesday and early thursday will wane as the low becomes vertically stacked under an upper level low.
Key message 2...improving conditions with nuisance showers friday followed by a drier weekend, becoming unsettled late weekend into early next week.
Nuisance rain showers will continue on friday with the vertically stacked system remaining over southern new england. Despite a saturated atmosphere with pwats well above climatology, less favorable jet dynamics will result in widely scattered light rain showers rather than the tropical downpours experienced over the previous two days. In a bit of better news, confidence continues to increase that the mid-level ridge across the northwestern atlantic ocean will de-amplify enough to allow this system to progress eastward, with subtle mid-level ridging building in for the upcoming weekend. This should lead to a drier weekend, albeit not as sunny as the previous weekend. Nevertheless, flow will return to the south- southwest, advecting warmer temperatures back into the region, which will be a welcome relief after a few raw late july days. Highs friday will generally be in the upper 70S to around 80f. This weekend trends a couple of degrees warmer, with seasonable temperatures in the lower 80S. Late in the weekend into monday and tuesday, the pattern becomes unsettled once again as our next chance for rain arrives. Given the 5 to 6 day forecast horizon, additional changes are likely.
Forecaster confidence levels...
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
00Z taf update:
Tonight...moderate confidence.
VFR to MVFR to start this evening with instances of sct'd heavy downpours across western terminals. Though, do not feel these will reach eastern terminals as it lifts NNE. S to SSE winds overnight. Ceilings lowering during the second half of the night to MVFR/IFR. Areas of fog possible ahead of the rain for the islands predawn wednesday.
Wednesday and wednesday night...moderate confidence.
IFR/MVFR in continued periods of heavy rain. SSE to E winds 10-15 KTS with gusts to 25 KTS possible. Potential for llws for eastern terminals overnights.
Kbos terminal...moderate confidence.
Kbdl terminal...moderate confidence.
Outlook /wednesday night through sunday/...
Thursday: mainly VFR, with local IFR possible. Breezy. Shra likely, isolated tsra.
Thursday night: mainly VFR, with local IFR possible. Chance shra, isolated tsra.
Friday: VFR. Slight chance shra, isolated tsra.
Friday night through saturday night: VFR.
Sunday: mainly VFR, with local IFR possible. Slight chance shra, slight chance tsra.
Forecaster confidence levels...
Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.
Through thursday...high confidence.
An anomalous midsummer low pressure system will bring a prolonged period of unsettled weather to the southern new england coastal waters beginning this evening and continuing through thursday. Periods of heavy rain, reduced visibilities, and embedded thunderstorms are expected through much of the period. A small craft advisory remains in effect for all waters through wednesday, and for the outer coastal waters through thursday. South to southeast winds increase tonight, with gusts of 25 to 30 KT expected on wednesday. Seas build to 4 to 6 ft, highest across the outer waters. Wind direction becomes more variable on thursday as the surface low tracks across the southern new england coastal waters. East to northeast winds ahead of the low will shift to north to northwest in its wake, although the eastern waters may remain northeasterly longer before the system gradually departs thursday night.
Outlook /wednesday night through sunday/...
Thursday through thursday night: winds less than 25 KT. Seas up to 5 ft. Chance of rain showers, isolated thunderstorms.
Friday: winds less than 25 KT. Seas up to 5 ft.
Friday night: winds less than 25 KT. Areas of seas approaching 5 ft.
Saturday: winds less than 25 KT. Seas locally approaching 5 ft.
Saturday night through sunday: winds less than 25 KT.