166 FXUS61 KBOX 110935 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 535 AM EDT Thu Oct 11 2018 .SYNOPSIS... Rain will push across the region today ahead of a cold front. The precipitation will fall heavily at times this afternoon through tonight, with the potential for flash flooding to occur. Isolated thunderstorms are also possible. The remnants of Michael will pass SE of Nantucket Friday morning, bringing a continued threat for possible flooding across the immediate south coast along with gusty winds. High pressure builds in from the Midwest over the weekend with drier air and much cooler temperatures. A couple of disturbances move through early next week and may bring a few showers. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Backdoor cold front has down to W of KASH to E of KBED to KBOS as weak low pres developed over the last several hours E of Cape Ann as denoted on the 08Z MSAS surface analysis. Winds at KBOS shifted to E-NE at 08Z and temp fell from 70 degs at 07Z to 64 at 08Z. Patchy fog has also developed across NE Mass into SE NH with T/Td spreads of 1-3 degs. S of the front, while the T/Td spreads remain low, fog not as prevalent through most of the early morning hours. The exception is across Cape Cod and the islands, where visibility has lowered to 1SM or less, lowest on Nantucket at 08Z. However, the visibility there had improved earlier and suspect it will linger at about 1SM or less. So, have ended the Dense Fog Advisory there. Leading edge of rainfall has reached into the mid and upper Hudson Valley into the Berkshires as seen on latest NE regional 88D radar imagery, with -RA reported from KPSF-KAQW-KRUT. This appears to be well timed by short range model guidance. Should see the precip shift steadily E through the day. Should start to see the heavier rain push into N central and western areas around midday, along with increasing instability. TQ values for elevated convection increase to the upper teens and K indices increase to the mid-upper 30s during the day, along with LIs lower to near or below zero. Have added isolated thunderstorms to the forecast from midday through the afternoon. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Highlights... * Backdoor front should shift back N this morning as cold front approaches * Increasing moisture will bring heavier rainfall to the region from midday through Friday morning * Flash Flood Watch remains in effect through late tonight * Marine headlines have been issued for Friday Discussion... H5 ridge axis pushes E of the region by mid morning, allowing increasing moisture plume to work across the region. Showers already have reached into the Berkshires as low pressure moves into eastern Ontario to Hudson Bay during the day. Precip extends across eastern/central NY state SW into central PA and into the interior mid Atlc states early this morning. TS Michael's moisture also slowly moving across the Carolinas. Will see the backdoor front shift back N this morning as strong low pressure shifts N of the Great Lakes. Flooding... The Flash Flood Watch remains in effect for the entire region as increasing deep moisture plume shifts E. Noting PWAT swath, forecasted to increase to 4-5 SD above normal, or up to 2.2 to 2.3 inches by midday across the region. Mid level trough and strong difluence aloft will allow strong lift to push E, so will see the precip shield, with areas of heavy rainfall arrive this afternoon and evening across central and western areas, shifting E tonight. Then, the moisture from the remnants of Michael will approach after midnight tonight into Friday morning as the remnant low passes near or S of the 40N/70W benchmark. Another swath of heavy rainfall is expected, though the heaviest precip will be confined to S coastal areas. However, could see some copious amounts from near KEWB eastward to Cape Cod and the islands. Went along with previous forecast thinking of using the highest QPF guidance with the deep tropical moisture streaming across the region. Have forecasted amounts ranging from 0.8 to 1.25 inches near and N of the Mass Pike, ranging up to around 1.5 inches into NE CT/RI/interior SE Mass. Could see up to 2-4 inches along the immediate S coast and possibly higher amounts across the lower Cape, Nantucket and Martha's Vineyard. Winds... Should see SW wind gusts up to around 25-30 kt this afternoon and evening ahead of approaching cold front. Some higher gusts are possible with the strong lift and instability, along with drag from any heavier precip which may allow winds up to around 40-45 kt to mix down. Will see another period of strong wind gusts Friday morning and midday as the remnants of Michael passes S of the region. May see another round of gusts up to 25-45 kt mainly along the S coast, Cape Cod and the islands. Marine... Have issued Gale Warnings and Small Craft Advisories for most of the waters for Friday as the remnants of Michael pass. Gusts up to 40 kt are likely, highest near and S of the islands. This will pass quickly, so will see a rather short duration of the gale force winds, but Small Crafts will linger into Friday evening. There may be SW wind gusts up to 25-30 kt across the southern waters this afternoon and evening ahead of the approaching cold front as well. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Big Picture... Broad upper trough over the Northeastern USA while upper ridge sits over the Gulf States and a second ridge builds over the Pacific Northwest. Several shortwave troughs move through the Northeast broad trough with increasing uncertainty on their timing after the weekend. Mass fields agree on one shortwave moving through on Saturday, then a second either Monday or Tuesday and a third possible on Wednesday or later. Contour heights are below normal Saturday, then trend to normal or a little above early next week. Clouds may keep temps a few degrees cooler than the trend would indicate for next week. Therefore we expect a cooling trend to below normal temps over the weekend, then near normal during next week. Mass fields are in good agreement Saturday, and thermal fields are in agreement through early Monday. So confidence is high through the weekend, moderate early next week, and low midweek. Concerns... Friday night through Sunday... Diminishing NW wind Friday night as the remnants of Michael move off well south of Nova Scotia. Could be some gusts near 20 knots early, but should trend lighter overnight. Shortwave trough passes overhead Saturday with cold pool minus 22C to minus 24C. This should support clouds and may generate enough instability to allow scattered showers. Cross sections show a briefly deep moisture layer, but dynamic lift is rather weak. Midwest high pressure and upper ridge move through during Saturday night. Dew points upstream are in the 20s, but even moderation over the next three days would suggest 30s for our area. Fair skies, light wind, and expected dew points would allow min temps in the 30s most places. This will be favorable for areas of frost in the interior as well as the low spots of Eastern MA and RI. High pressure maintains fair weather Sunday, with a light west- southwest surface flow as the high slips offshore. Moisture fields suggest increasing mid and high clouds during the day. Mixing to 925 mb and temps equiv to -2C at 850 mb suggest max temps in the 50s. Monday through Wednesday... GFS and ECMWF show a cold fropa on Monday, although the GFS shows signs of showers while the ECMWF shows a dry passage. Both models then stall the front to our south and then bring a wave along the front Tuesday. Cold pool aloft may generate some instability to help clouds/showers form inland Wednesday. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...Moderate confidence. Through 12Z...Areas of VLIFR CIGS/VSBYS across Cape Cod and the islands. Elsewhere, mix of VFR-MVFR CIGS/VFR VSBYS. MVFR-IFR CIGS as far N as KOWD-KORH-KBAF and into the northern portion of the CT Valley. Otherwise, may see local MVFR CIGS across the remainder of the region (NE and N central MA). Will continue to monitor for a period of fog moving SW into NE Mass after 06Z behind a backdoor cold front. Today and Tonight...Expect mainly MVFR CIGS/VSBYS except lingering IFR-LIFR across the Cape and islands through mid-late morning. Expect -RA/RA to move in from W-E this morning through midday. Local +RA and isolated TSRA. SW winds gusting up to around 30 kt along the S coast terminals. RA/TSRA activity will be heaviest and prolonged over SE New England this afternoon and tonight. Conditions improve to VFR from W-E after midnight across central and W areas, with lower conditions lingering across RI/E Mass. Friday...MVFR-IFR conditions linger along S coastal areas as the remnants of Michael pass around midday, with MVFR to local IFR conditions. NW winds gusting up to 25-35 kt possible along the immediate coast, and especially across outer Cape and Nantucket. The precip and any convection shift offshore early Friday. KBOS Terminal...Moderate confidence in TAF. IFR CIGS/MVFR-IFR VSBYS through most of the morning push with light E-NE winds. Winds should shift to S-SW around midday or early afternoon. CIGS remain MVFR-IFR through the day with mainly VFR VSBYS during the afternoon. KBDL Terminal...Moderate confidence in TAF. General MVFR-IFR CIGS/MVFR VSBYS in developing -RA/RA and patchy fog. Low risk of TSRA this afternoon/tonight. Outlook /Friday Night through Monday/...High Confidence over the weekend, Moderate confidence Sunday night and Monday. Friday Night: VFR. Breezy. Saturday: Mainly VFR, with areas MVFR possible in any showers. Breezy. Chance SHRA. Saturday Night: VFR. Sunday: VFR. Breezy afternoon. Sunday Night: Mainly VFR, with areas MVFR possible. Windy with local gusts to 30 kt. Slight chance SHRA. Monday: Mainly MVFR, with areas VFR possible. Windy with local gusts to 30 kt. Chance SHRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Gale Warnings and Small Craft Advisories issued for Friday with the passage of the remnants of Michael. Rain and isolated thunderstorms move across the waters from mid morning through tonight, with locally heavy rainfall likely. SW winds may gust up to 20-30 kt this afternoon/evening ahead of approaching cold front. Reduced visibility in areas of fog mainly across the waters around and E/S of Cape Cod and the islands. The cold front will push across the waters tonight, but will slow its progression as the remnants of Michael pass Friday morning to midday. NW winds will gust up to 30-40 kt near and S and E of Cape Cod and the islands. Will also see lingering rain and a few thunderstorms until Michael passes, then should push east. Expect seas to build to around 5 ft this afternoon and evening on the southern outer waters, then up to 6 to 11 feet during Friday, highest on the outer waters. Outlook /Friday Night through Monday/...High Confidence through Sunday, Moderate confidence sunday night and Monday. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Sunday: Winds less than 25 kt. Sunday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Monday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of seas approaching 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Flash Flood Watch from 11 AM EDT this morning through late tonight for CTZ002>004. MA...Flash Flood Watch from 2 PM EDT this afternoon through Friday morning for MAZ017>021. Flash Flood Watch from 11 AM EDT this morning through late tonight for MAZ002>016-026. Flash Flood Watch from this afternoon through Friday afternoon for MAZ022>024. RI...Flash Flood Watch from 2 PM EDT this afternoon through Friday morning for RIZ001>008. MARINE...Gale Warning from 11 AM to 4 PM EDT Friday for ANZ232. Gale Warning from 10 AM to 2 PM EDT Friday for ANZ233>235-237. Small Craft Advisory from 10 AM to 6 PM EDT Friday for ANZ231- 250. Small Craft Advisory from 10 AM to 3 PM EDT Friday for ANZ236. Small Craft Advisory from 11 AM to 6 PM EDT Friday for ANZ251. Gale Warning from 11 AM to 5 PM EDT Friday for ANZ254. Gale Warning from 9 AM to 5 PM EDT Friday for ANZ255-256. && $$ SYNOPSIS...WTB/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...WTB AVIATION...WTB/EVT MARINE...WTB/EVT