Area Forecast Discussion


803 
FXUS61 KBOX 250901
AFDBOX
Area Forecast Discussion
National Weather Service Taunton MA
401 AM EST Sun Feb 25 2018
.SYNOPSIS...
A fast moving low pressure system will bring rain today to the 
coastal plain and a mixture of sleet, snow and freezing rain
changing to rain across interior Massachusetts. High pressure 
will bring mainly dry and mild temperatures Monday through 
Wednesday. There is the potential for a strong coastal storm 
late next week that if it impacts our region may bring 
significant rain and/or snow...strong winds on the coast along 
with potential coastal flooding. This storm is far from a 
certainty at this point...but given the ingredients in place 
does bear watching.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
*** Mixed wintry precip today across interior, especially
 northern MA ***
Leading edge of precip shield is approaching SNE from the west
and will overspread the region through 7 am. PWATs 2-3SD above 
normal combined with good low level isentropic ascent will bring
a moderate QPF event with widespread precip today. Progressive 
system so much of the precip will be exiting the region by late 
afternoon or early evening. 
A mixed bag of wintry precip is expected given warm nose aloft 
and presence of low level cold air. In fact models are 
indicating temps in the 950-925 mb layer cooling to 0 to -2C 
near the south coast this morning and down to -5C near the NH 
border. With warming in the 850-700 mb layer advancing northward
this will set up a good sleet signal this morning, especially 
across northern MA. In addition, with sfc warm front remaining
south of New Eng and sfc wave tracking along the boundary, low
level northerly winds will help to lock in cold air at the
surface, especially higher terrain which will increase threat of
icing after warming aloft changes precip to rain. 
North of the Mass Pike...
Cold air is initially deep enough for some snow especially 
toward NH border and NE MA for at least a few hours after precip
onset before changing to freezing rain and rain. Snow in NE MA 
may last until late morning as warmer air aloft coming up from 
the SW. An inch or 2 of snow accum is possible, mainly along and
north of route 2 into Essex county with low risk for 3 inches 
in portions of northern Essex county. Some minor sleet accum is
also possible down to the Mass Pike region. Regarding freezing 
rain, it appears greatest threat for appreciable icing will be 
over higher elevations in the Berkshires and Worcester hills 
where temps may hold at or below freezing much of the day. We 
relied heavily on 3km NAM and WRF-ARW which shows the cold air 
over higher terrain. Potential for localized 0.10-0.20" ice 
accretion over the Worcester hills and especially the Berkshires
with less than 0.10" elsewhere. 
South of the Mass Pike...
Precip will be mostly rain but will likely mix with sleet for a
few hours this morning across northern CT, northern RI and along
the I-95 corridor to BOS. Freezing rain is less of a threat 
south of the pike, but may still see a few hours of freezing 
rain over higher terrain in northern CT and central MA.
Advisories largely unchanged but we dropped it for coastal 
Essex county and SE Middlesex county where temps expected to
remain above freezing with just a mix of rain and sleet.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
Precip will exit eastern New Eng by early evening, otherwise a
dry night expected. Stratus and patchy fog in the evening may
clear overnight, but any clearing may lead to more fog 
developing. Patchy black ice will also be a concern overnight 
with moisture near the ground and lows dropping to upper 20s to 
lower 30s away from the coast.
&&
.LONG TERM /MONDAY THROUGH SATURDAY/...
*/ Highlights...
 - Quiet, dry, near-seasonable early week period 
 - Possible stormy pattern late week, beginning of March 
*/ Overview...
Blocky N Atlantic pattern associated with an anomalous -NAO of 4 to 
5 standard deviations (SD) below average, associated +3 SD H5 high 
retrograding W into SE Canada, parent 1040+ surface high, pressing 
the thermal wind axis S thru which N/S stream impulses merge having 
dug through a prevailing W CONUS H5 trof before ejecting, stretching 
E. Energy piling up, slowed, pressed S by high pressure building N, 
favorable storm development emerges off the E CONUS coast. Airmass 
juxtaposition key as to outcomes towards the end of the week after a 
quiet start. Only confidence is persistent NE winds of significant 
duration during high astro-tides, coastal flooding concerns. Lower 
confidence otherwise, consensus forecast guidance heavily weighted 
with ensemble means continues. Hit targets of opportunity below. 
*/ Discussion...
Thursday into the weekend...
Battle of airmasses between an ejecting low out of the Central CONUS 
up against building high pressure into Canada. Slowed pattern, each 
building their own weight, juxtaposition between the two ultimately 
determining outcomes. Strong -NAO, -4 to -5 SD, would expect a cool, 
dry setup for NE CONUS, storm track lying further S per block. Mid-
Atlantic getting crushed. Interrogating Washington DC top 10 snows 
versus the NAO time series after 1948, 5 out of 7 storms, 3 prior to 
1948, were associated with a -NAO around -3. Recall February 2010? 
Washington DC "snowmageddon" of 17.8"? Monthly NAO averaged near -2. 
Cherry picking data? Perhaps. CIPS analogs? Interrogating where NAO 
indices <= -1, noting trend of sliding low S of New England, further 
so with a stronger -NAO. 
Ensemble members clustering off the Delmarva Peninsula while model 
deterministic solutions are hugging further N close to Long Island. 
Believe S trend is emerging per 25.0z EC. Echoing prior forecaster, 
strong -NAO, subsequent block, storms forced E, slowed, evolving 
into coastal storms, but storms could get suppressed S. It is all 
about timing. Simply wait and see with later forecasts. But per 
climatology, prefer ensemble clustering / 25.0z EC which are further 
S compared to all other guidance.
Thursday into Friday lingering into Saturday, will continue with 
chance PoPs. Warm-core system, absent Arctic air, precip-type issues 
mainly as rain / snow first glance. Confident of persistent NE winds 
during high astro-tides, coastal flooding concerns.
&&
.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent. 
Moderate - 30 to 60 percent.   
High - greater than 60 percent.
Short Term /through Tonight/...
Through 12z...Conditions lowering to MVFR in western/central  
New Eng 08-12z as precip overspreads the region. VFR likely
holding until 12z E/NE MA before deteriorating. Ptype mostly 
snow and sleet at the onset north of the Pike, and rain mixed 
with sleet to the south. 
Today...Moderate confidence. Widespread IFR developing. North 
of the pike, mostly sleet with some snow NE MA changing to rain 
but pockets of freezing rain persisting over the Berkshires and 
Worcester hills. South of the Pike, rain mixed with sleet in the
morning, with pockets of freezing rain in the morning over 
higher terrain in northern CT and central MA. Precip exits by 
late afternoon/ or early evening. East wind gusts to 25-30 kt 
developing along the coast. 
Tonight...Moderate confidence. IFR conditions with patchy fog in
the evening, improving to VFR after midnight. Dry conditions. 
KBOS Terminal...Moderate confidence in TAF. Lowering to IFR 
today then improving tonight. Rain mixed with sleet in the 
morning.
KBDL Terminal...Moderate confidence in TAF. Lowering to IFR 
today then improving tonight. Rain mixed sleet in the morning. 
Low risk of a few hours of freezing rain in the morning. 
Outlook /Monday through Thursday/...Moderate to high 
confidence.
Monday through Monday Night: VFR. Breezy. 
Tuesday through Wednesday Night: VFR. 
Thursday: Mainly VFR, with local MVFR possible. Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent. 
Moderate - 30 to 60 percent. 
High - greater than 60 percent.
Short Term /through Tonight/...Moderate confidence.
Today...A period of marginal easterly gales likely across much 
of the open waters today as low level jet moves over the waters.
Cold air above the boundary layer will promote decent mixing 
this morning but inversion will strengthen during the
afternoon. Rain and fog will reduce vsbys. 
Tonight...Winds diminishing and becoming NW during the night.
Speeds dropping below SCA but hazardous seas will continue over
outer eastern waters. 
Outlook /Monday through Thursday/...Moderate to high
confidence.
Monday: Winds less than 25 kt. Seas up to 5 ft. 
Monday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. 
Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. 
Tuesday Night: Winds less than 25 kt. 
Wednesday: Winds less than 25 kt. Seas locally approaching
5 ft. 
Wednesday Night: Winds less than 25 kt. 
Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
&&
.TIDES/COASTAL FLOODING...
Thursday through Saturday...
The potential for coastal flooding and beach erosion exists on
several high tide cycles late next week. This will depend upon
the development of a potential strong/long duration coastal
storm. While it is too early to give more specific
information...high astronomical tides and the potential for a
strong coastal storm will need to be watched especially along
the eastern MA coast.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Winter Weather Advisory until 1 PM EST this afternoon for 
     CTZ002>004.
MA...Winter Weather Advisory until 1 PM EST this afternoon for 
     MAZ005-006-009>012.
     Winter Weather Advisory until 4 PM EST this afternoon for 
     MAZ002>004-008-026.
RI...None.
MARINE...Gale Warning from 9 AM this morning to 3 PM EST this afternoon 
     for ANZ231>234.
     Small Craft Advisory until 6 PM EST this evening for ANZ230.
     Small Craft Advisory until 3 PM EST this afternoon for ANZ236.
     Gale Warning until 1 PM EST this afternoon for ANZ235-237.
     Gale Warning from 10 AM this morning to 6 PM EST this evening 
     for ANZ250-254.
     Small Craft Advisory until 5 AM EST Monday for ANZ251.
     Gale Warning until 3 PM EST this afternoon for ANZ255-256.
&&
$$
SYNOPSIS...KJC/Sipprell
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...Sipprell
AVIATION...KJC/Sipprell
MARINE...KJC/Sipprell
TIDES/COASTAL FLOODING...