textproduct: Boston / Norton

WHAT HAS CHANGED

Increased confidence in patchy freezing drizzle/fog that may result in icy conditions on untreated surfaces tonight into Friday morning.

KEY MESSAGES

- Areas of freezing fog tonight into Friday morning. Light rain overnight Friday. - A low-pressure system brings a soaking rainfall Saturday, with rain possibly lingering into Sunday.

- A cold front brings cool and blustery conditions back to the region late Sunday into Monday.

DISCUSSION

KEY MESSAGE 1...Patches of freezing fog tonight into Friday morning. Light rain overnight Friday.

Surface high pressure moves offshore overnight. Light return flow allows dew point temperatures to rise into the upper 20s/ lower 30s. BUFKIT soundings show ideal conditions for fog with an inversion near the surface along with a saturated layer up to about 1 kft. Given the surface temperatures are below freezing, patchy freezing fog is likely late tonight into Friday morning. Thankfully, the freezing fog threat will quickly diminish after 12z Friday as surface temperatures warm above freezing. Strengthening southwest winds aloft result in strong WAA with 850mb temperatures rising between +4C to +6C Friday afternoon. As a result, it should be a warmer day with highs climbing into the mid and upper 40s for most of the region. NBM even shows areas of southern Massachusetts and Rhode Island touching 50F. Surface warm front moves through southern New England Friday night into early Saturday morning. Guidance still shows a broken band of showers with QPF between 0.10 and 0.25 inches, certainly not a washout. Highest totals will be further to the north across northern New England, with the parent low pressure system. No p-type issues expected with this event as temperatures Friday night remain in the low-40s at the coast and upper 30s across interior locations.

KEY MESSAGE 2...A low-pressure system brings a soaking rainfall Saturday, with rain possibly lingering into Sunday.

Shortwave energy arrives well ahead of the parent shortwave back over the Northern Great Plains on Saturday. This allows several weak surface lows to spin up along the nearshore baroclinic zone and bring rain to the region on Saturday. With a warm airmass in place and extra moisture flowing in from the mid-Atlantic, PWATS surge to around 0.9 to 1.1 inches. Best forcing and moisture will be near the south coast as the wave of low pressure passes just offshore. There is still quite a bit of spread in QPF totals, as ensembles show wide ranges in the 25th-75th percentiles. Regardless, QPF will be highest near the south coast, where the 25th-75th percentile range is between .35 and 1.15 inches, while further north, the range is .15 to 0.55 inches.

Saturday morning should remain dry, with rain moving in from south to north in the late morning to early afternoon. Given that rain will begin during the daytime hours, freezing rain concerns will be limited, likely occurring only in pockets of the northern high terrain where cold air may be tough to scour out.

Rain ends from west to east late Saturday evening into the overnight. Another wave of low pressure rides up the stalled frontal boundary offshore, possibly bringing another round of rain to the south coast on Sunday. High temperatures over the weekend remain mild, with mid to upper 40s on Saturday, then upper 30s to low 40s on Sunday.

KEY MESSAGE 3...A cold front brings cool and blustery conditions back to the region late Sunday into Monday.

A cold front moves through the region Sunday evening, helping clear out the remaining rain. The cold front will squeeze out the remaining moisture from the weekend, leading to isolated snow showers and possibly weak snow squalls Sunday evening. Temperatures will crash Sunday night, bottoming out in the low to mid 20s. Any remaining standing water from this weekends rain will freeze by Monday morning, possibly leading to some slippery conditions for the Monday AM commute. High temperatures on Monday will recover into the low to mid 30s, but gusty west winds at 20-25mph will bring the wind chill index into the low 20s.

Looking ahead into next week, cool and dry conditions persist through Wednesday or Thursday, with the pattern possibly turning more active again late in the week into next weekend.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

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 start, low-level moisture leads to lower visibility after 03z-04z, between 2SM to 5SM. With freezing temperatures expected any moisture can refreeze on untreated surfaces. Areas in southeast Massachusetts and Rhode Island have a low chance, less than 30% of visibility to lower below 1/2 mile, there freezing fog or freezing drizzle is possible, opt'd to include a PROB30 for KPVD. Light south wind less than 5 knots.

Friday... Moderate Confidence (timing of lowering ceilings).

VFR, trending to MVFR by mid afternoon as a warm front approaches. Showery rain possible around and after 00z.

Friday Night...Moderate Confidence on timing of precipitation.

MVFR, potential for isolated IFR. Areas of -SHRA move in from W-E between 22z-00z winding down between 03-06z Friday night.

KBOS Terminal... Moderate Confidence.

MVFR to IFR visibility developing tonight, potential for dense fog and IFR ceilings 08z to 13z.

KBDL Terminal... High Confidence.

MVFR to IFR visibility developing tonight, potential for dense fog and IFR ceilings 09z to 14z.

Outlook /Saturday through Tuesday/...

Saturday: Mainly VFR, with local MVFR possible. Chance RA, chance FZRA.

Saturday Night: Mainly IFR, with areas MVFR possible. RA, chance FZRA.

Sunday: Mainly VFR, with areas IFR possible. Breezy. Chance RA, chance FZRA.

Sunday Night: VFR. Windy with local gusts up to 30 kt. Chance RA, slight chance SN.

Monday: VFR. Windy with local gusts up to 30 kt.

Monday Night through Tuesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent.

Today through Saturday... High Confidence.

A lull over the waters tonight, wind increases from the south on Friday as a warm front lifts over the region. Gusting between 20 to 25 knots and seas increasing 4 to 6 feet by Friday night. Small craft conditions for most of the waters except the bays and harbors 00z to 12z Saturday. Seas calm later Saturday morning before another system approaches from the S late Sat into Sat night.

Outlook /Saturday through Tuesday/...

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain.

Saturday Night: Winds less than 25 kt. Local rough seas. Rain.

Sunday: Winds less than 25 kt. Areas of rough seas. Rain likely.

Sunday Night: Strong winds with gusts up to 40 kt. Areas of rough seas. Chance of rain, slight chance of snow.

Monday: Strong winds with gusts up to 35 kt. Areas of rough seas.

Monday Night through Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 7 PM Friday to 3 AM EST Saturday for ANZ235-237. Small Craft Advisory from 7 PM Friday to 7 AM EST Saturday for ANZ250-254>256.