Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251122 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 722 AM EDT Sun Sep 25 2016 .SYNOPSIS... Cool and dry weather continues into Monday. Low pressure may bring showers to southern New England some time late Monday night into Wednesday morning. Otherwise, seasonable and mostly dry weather is expected much of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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730 AM update... Overall trend in the forecast remains on track for today. Clear skies overhead as temps radiate out this morning. Frost Adv appears to be in a good location so will keep it going. Will have to issue a new one for tonight but will wait until temps warm above 38F this morning. Otherwise radiational fog has developed over valley locations, this will dissipate over the next hour or two. Previous Discussion... Otherwise, it`s going to be a beautiful SKC start to the day, refreshing and sunny. With this cooler than normal start, H85 and H92 temps dropping to the lower 10th percentile of climatology, not expecting a warm day, as temps will likely hold in the low-mid 60s at most locations. Could see a few sites overachieve thanks to it only being early in the fall period, and continued dry conditions. Otherwise, a light 10-20 mph NW breeze will add to the fall-feel especially through the afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Tonight... With H92 temps dipping as low as +5C, clear skies and a very weak pres gradient, expect better inversion development overnight tonight than even last night. Guidance that has handled temps will early this morning (MET especially) are as much as 2-4F cooler early Mon morning. Agree with previous forecaster that more widespread frost is likely across the region, with several locations in NW MA and even portions of CT and the interior coastal plain dropping to the mid-upper 30s. A few sites may approach freezing, in the normally coldest valleys. Therefore, expect another round of frost headlines to be coming through the day today, but with current ongoing headline, will allow day-shift to issue. For now, will have an SPS highlighting the risk to allow as much lead-time as possible. Mon... Core of high pres moves E allowing for slight return flow. This suggests both weak warm advection and increase in column moisture. So instead of the steady SKC conditions, expect more clouds building over the region through the day. Even though column is moistening ahead of an occluding low pres, expect any actual precip to hold off until the fronts arrive by the overnight hours. POPs will reflect this. Temperatures a bit closer to seasonable normals. H85 temps increase from near 0C Sun to an average around +5C on Mon. With full mixing, looking at highs more the upper 60s and low 70s. The good news, is the humidity should remain low most of the day, in spite of the increase in moisture, mixing should keep sfc dwpts mainly in the 30s. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... HIGHLIGHTS... * Seasonable temperatures expected much of the long term * Frontal system will bring showers to the area Tuesday * Quite a bit of uncertainty in the pattern for mid to late week Overview/confidence... High confidence in widespread rain fall late Monday into Tuesday as frontal system pass through. Thereafter models show low predictability and thus high uncertainty in regards to the cut-off low over the eastern half of the CONUS. GFS continues to be the more progressive solution opening up the low by late Friday into Saturday while the EC keeps the cut-off low around through the upcoming weekend. The UKMET seems to be more inline with the EC whereas the GEFS are inbetween the solutions. For now, continued with model blend until guidance becomes more inline. Monday night into Tuesday...Moderate Confidence. Upper level ridge will move overhead Monday night as WAA spills into the region. Overnight temps will begin to fall during the evening hours before remaining steady or even rising by the early morning hours. A few showers are possible after midnight, within the higher theta-e plume, but the bulk of the rain will move through on Tuesday. Ahead of the FROPA, temperatures will warm into low 70s across the area. Dewpoints will be on the rise as well making it feel a bit more humid. Appears the best timing for precip will be Tuesday morning which could make way to a rough morning commute. GEFS continue to show 70-80 percent probs of over a half of an inch of rain, so confidence is increasing in widespread rainfall. Went ahead and bumped pops to categorical as all guidance is signally for rain across the area. A good pressure gradient develops behind the passing frontal system which could result in gusty winds near 25 mph. A few higher gusts are possible within the heavier rain showers as 40 kt LLJ develops over the region. Cannot rule out a rumble of thunder across the immediate south coast as there is some elevated instability. But because potential is still uncertain kept it out of the forecast for now. Wednesday and Beyond...Low Confidence. Again low confidence with this forecast as models seem to always struggle with cut-off lows. Depending on the guidance, passing frontal system on Tuesday could stall the front close enough to southern New England that passing waves rotating around cut-off could keep showers in the vicinity through the remainder of the week. Biggest question is the high pressure to the north of the region. If it will build in enough to keep the front and precip far enough south to keep the region dry. The EC thinks it will for Wed into Thursday while the GFS is more progressive keeping the high too far north bringing precip in as early as Wed. Because of the large spread in guidance will keep a slight chc of pop through the week until details and timing can be distinguished. Seasonable temperatures can be expected for this period. && .AVIATION /11Z SUNDAY THROUGH THURSDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...High confidence. VFR. A few diurnal cu. Otherwise SKC. Some 15-20 kt NW winds during the daylight hours today, diminishing after sunset. VFR again for tomorrow. Sea breeze potential on the coastlines. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Monday Night through Thursday/... Monday night thru Tuesday...Moderate confidence. VFR through the period with localized MVFR in rain on Tuesday. Gusty southerly winds near 30 kts across East coastal terminals. Wednesday into Thursday...Low confidence. Most likely VFR for much of this time, but model uncertainty could mean periods of MVFR in lower clouds and scattered showers.
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&& .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...High confidence. Through 15Z (11Am local)... A resurgence of winds will allow some gusts to reach 25-30 kt out of the NW, particularly on the ocean waters before they begin to subside. Seas build during this period as well, 5-6 ft thanks to a combination of this wind and a southerly swell from Karl. After 15Z into tonight... Winds remain NW but generally below 20 kt. They shift slowly to the S tonight, but stay light. Seas will begin to decline, but take until overnight for the ocean waters to fully dissipate below 5 ft. Therefore some small craft advisories will linger into the overnight hours. Tomorrow... Mainly quiet boating weather as high pres slips over, then east of the waters. Outlook /Monday Night through Thursday/... Tuesday...High confidence. Strong cold frontal system will approach the waters on Tuesday increasing both seas and winds. Ahead of the front southerly winds will increase close to gales with seas building near 7-8 feet as a response. Vsbys will drop within any heavy rain showers as the front passes. Low risk for a rumble of thunder across the southern waters. Wednesday and Thursday...spread in the guidance has resulted in a low confidence forecast. Could see small craft conditions on the outer waters for a time as front stalls across the waters. Passing waves could increase both seas and winds each day. Again low confidence forecast. && .CLIMATE... Record low temperatures... September 25th / 26th (last set in...) Boston ....... 38 (1950) / 34 (1879) Hartford ..... 30 (1963) / 33 (1978) Providence ... 36 (1963) / 37 (1967) Worcester .... 31 (1944) / 28 (1925) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Frost Advisory until 8 AM EDT this morning for MAZ002>004-008. RI...None. MARINE...Small Craft Advisory until 11 AM EDT this morning for ANZ231>234-251. Small Craft Advisory until 2 PM EDT this afternoon for ANZ235- 237. Small Craft Advisory until 3 AM EDT Monday for ANZ250-254-255. Small Craft Advisory until 5 PM EDT this afternoon for ANZ256. && $$ SYNOPSIS...Doody/Dunten NEAR TERM...Doody/Dunten SHORT TERM...Doody LONG TERM...Dunten AVIATION...Doody/Dunten MARINE...Doody/Dunten CLIMATE...staff

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