Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201520 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1020 AM EST Mon Feb 20 2017 .SYNOPSIS... A brief return to seasonably cool weather occurs today through Tuesday with high pressure in control. Strong low pressure developing across the Central Plains slowly lifting towards the Great Lakes will result in an extended period of unseasonably mild temperatures Wednesday through Saturday. A cold front will cross the region Saturday, likely bringing some rain, followed by more seasonable temperatures by Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10 AM update... *** A return to seasonably cool weather today *** Closed mid level low over New Brunswick and Nova Scotia this morning will support CAA into southern New England today. Core of cold air associated with this system circulates into our region this afternoon behind short wave trough currently moving thru NH. SPC mesoanalysis shows 850 temps drop to about -10C with the passage of this feature. Thus 850 temps go from about -5C/-6C this morning downward to about -10C this afternoon. This CAA will offset diurnal heating with surface temps not rising much from their current values at 10 am. In addition behind this short wave and associated increased CAA NNW winds will reinvigorate with gusts increasing to 20 to 30 mph this afternoon. This will provide a bit of a wind chill. This short wave energy advecting across eastern MA will result in some patchy clouds this afternoon and will be enhanced over Cape Cod by OES with 850 temps of -6C lowering to -10C over SST of about +3C/+4C. Thus mostly cloudy over the Cape with more sunshine westward. Previous discussion... Mid level trough axis amplifies east of southern New England as additional shortwave energy crosses the region. This will result in dry northwest flow today, but decent cold air advection will allow 850T drop to between -8C and -10C by afternoon. Column is fairly dry so plenty of sunshine. This combined with a rather mild start should allow highs in the upper 30s across the higher mainly the lower to middle 40s elsewhere. Bufkit soundings show 20 to 25 mph wind gusts developing later this morning and afternoon as mixing increases.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Tonight... Large high pressure builds across southern New England tonight. The result will be mainly clear skies, except for some ocean- effect clouds across the Cape/Nantucket as winds become northerly. Otherwise, light winds/mainly clear skies elsewhere should allow for overnight lows in the teens across the outlying locations with lower to middle 20s in the urban heat islands of downtown Boston/Providence. Tuesday... High pressure overhead Tuesday morning will slowly shift offshore by late in the afternoon. Plenty of sun expected during the morning...but some mid/high level cloudiness should move across the region from west to east during the afternoon. Mid level temperatures will be warming as height fields rise, but a chilly start and relatively weak mixing will keep high temps mainly in the lower to middle 40s. Weak pressure gradient should allow sea breezes to develop along the eastern MA coast and may keep highs in the upper 30s for those locations. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Light rain/pockets of freezing rain Tue night into Wed * Thursday looks to be our warmest day * More likely for widespread rain Friday night into Saturday Overview and model preferences...20/00z guidance was is good agreement with overall trends through Thursday. Even beyond Thursday there is some agreement on a similar pattern, just a lot of uncertainty with the details. The main uncertainty derives from a potent shortwave moving east from the West Coast about mid week. How this shortwave amplifies a downstream trough toward the end of this week, will determine the timing of a more widespread precipitation event. Preferred a consensus approach for this period to smooth over the less predictable mesoscale details. Above average confidence in the forecast through Thursday. Low confidence in the details beyond Thursday. Details... Tuesday night into Wednesday... High pressure off the East Coast holds on strong. With the core of this high pressure well to our south, expecting a persistent south wind to develop. The resulting rising heights should lead to a predominantly rain event as a cold front tries to push south through our region. The issue will be surface temperatures. There is still a risk of patchy freezing rain Tuesday night, mainly across the normally colder spots in north central and western MA. Not expecting much in the way of ice, but enough that overnight, early AM commutes could be slippery on untreated roadways. Still expecting improvement to drier and warmer weather Wednesday, as a a front moves back north as a warm front. With a strong high pressure offshore, the current timing of the forecast for this period may be too fast. Something to be monitored over the next day. Thursday and Friday... Modest clipper-like low pressure should move through the Great Lakes Thursday. This appears to be the favored storm track for the next series of storms. Increasing south to southwest flow should make Thursday the warmest day we`ve had in a while. Just a slight chance of a shower as this low passes by. Some slight cooling for Friday, especially with increasing clouds ahead of a warm front. Timing of overrunning precipitation still looks to hold until Friday night. Next weekend...As previously mentioned, have low confidence in the details in this portion of the forecast, mainly due to timing issues. Have greater confidence in another low pressure moving through the Great Lakes Saturday. Precipitable water values anticipated to be greater than 1 inch, which should mean the risk for moderate to heavy rainfall at times. Within the warm sector of the Great Lakes low pressure, the combination of a strong low level jet at 925 mb, and modest instability, could lead to isolated thunderstorms if everything lines up. Conditions improve Sunday, with a return to much more seasonable temperatures in the wake of this stronger system. && .AVIATION /15Z MONDAY THROUGH FRIDAY/...
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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 Tuesday/... 10 AM update... SKC much of the region today with SCT040 across eastern MA with marginal MVFR cigs BKN030-035 across Cape Cod. Also NNW winds 15-20 KT at late morning will increase to 20-25 kt this afternoon. Previous forecast captures this well so no major changes from 12z TAFs. Earlier discussion below. ============================================================== Today...High confidence. Mainly VFR, but some brief marginal MVFR CIGS are possible, with the highest risk across Cape Cod. Northwest winds will gust to 20 knots later this morning and afternoon, with up to 25 knots across portions of the Cape/Nantucket. Tonight and Tuesday...High confidence. VFR except some marginal MVFR CIGS possible into Tuesday morning across portions of Cape Cod. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Tuesday Night through Friday/... Tuesday night into Wednesday...Moderate confidence. Overnight low-moderate risk for some MVFR/IFR CIGS along with occasional MVFR vsbys in light rainfall. Low risk for some light freezing rain, mainly Worcester Hills and western MA. Improvement to VFR gradually after sunrise Wednesday. Winds shift to the W-SW. Thursday and Friday...High confidence. Mainly VFR. Low risk for some mixed MVFR CIGS by late day Friday, but these may hold off until Friday night.
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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 Tuesday/... Today...High confidence. Northwest wind gusts of 20 to 30 knots in the cold air advection pattern. The strongest of those winds gusts will occur across our eastern waters. Small craft headlines posted for all waters except Boston Harbor and Narragansett Bay. Tonight...High confidence. Lingering marginal small craft wind gusts/seas across our eastern waters this evening should diminish after midnight as high pressure builds in from the west. Tuesday...High confidence. High pressure overhead will result in light winds and flat seas. Outlook /Tuesday Night through Friday/... Winds and seas expected to remain below Small Craft Advisory thresholds through this period. Winds mainly south to southwest through Thursday. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ231- 232. Small Craft Advisory until 1 PM EST this afternoon for ANZ233>235-237-251. Small Craft Advisory until 4 AM EST Tuesday for ANZ250-254-255. Small Craft Advisory until 3 PM EST this afternoon for ANZ256. && $$ SYNOPSIS...Belk/Frank NEAR TERM...Belk/Frank/Nocera SHORT TERM...Frank LONG TERM...Belk AVIATION...Belk/Frank/Nocera MARINE...Belk/Frank is the U.S. government's official web portal to all federal, state and local government web resources and services.