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000 
FXUS61 KBOX 231534
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1034 AM EST Tue Jan 23 2018

.SYNOPSIS...
Freezing rain across portions of northern MA will change to
plain rain by early afternoon. Otherwise...heavy rain is the
main story this afternoon along with strong winds across 
portions of eastern MA and RI. Blustery, dry and colder weather 
follows Wednesday through Friday, then a warming trend next 
weekend. A cold front may bring showers next Sunday or Monday.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

*/ Highlights...

* Freezing Rain changes to plain rain across northern MA by 1 pm
* Heavy rain/isolated thunderstorm risk this afternoon
* Brief poor drainage street flooding possible
* Period of strong wind gusts along and southeast of BOS-PVD corridor

Freezing Rain...

Moderate to heavy freezing rain being reported across portions
of central and northeast MA. While surface warm front is still
quite a distance to the south of this region...latent heat
release was slowing bringing temperatures into the 30 to 32
degree range but still some upper 20s in extreme northeast MA.
Some locations may pickup an additional 0.15 inches of ice
accretion...but latent heat should do its trick and change the 
area to all rain by 1 pm. Greatest icing risk will be in far 
northeast MA near the NH border...where a few locations could 
see total ice accretion of one quarter inch.

Dense Fog...

Areas of dense fog persisted away from areas of heavier
precipitation. Dense fog has reformed on the south coast with
mild/moist air over running the relatively cold ocean.
Also...areas of dense fog still impacting some of the region so
opted to extend advisory until 1 pm and then re-evaluate.

Heavy Rainfall...

Closed low over the OH valley with emerging warm conveyor belt (WCB) 
advancing up the eastern seaboard. Strong jet dynamics associated 
with this feature as 925 and 850 mb wind anomalies increase to +3 SD 
this afternoon across this area. Subtropical moisture associated 
with this WCB increases to +3 SD as well. The combination of strong 
forcing for ascent, subtropical moisture and steepening mid level 
lapse rates supports periods of heavy rain along with the risk of a 
thunderstorm or two. The progressive nature of the system will 
limit heavy rainfall duration to about 6 hrs and also cap 
rainfall totals to about 0.75 to 1.25 inches. 

Strong Wind Threat...

Impressive low level jet up to 85 kts at 925 mb develops this 
afternoon along the south coast. This results in very strong low 
level WAA and a stout inversion developing, limiting the risk of 
strong winds aloft from reaching the surface. However with dew pts 
rising into the mid 50s along with steepening mid level lapse rates 
models generating a few hundred joules of MUcape. In addition, most 
of the Hi Res guidance generating impressive model simulated 
reflectivity this afternoon with a broken line of low top convection 
with embedded stronger elements. This low top convection may result 
in an isolated T-storm with strong gusty winds aloft reaching the 
surface. Will continue with the wind advisory for the coastal plain 
of RI and southeast MA as warm sector likely overspreads this area 
yielding the greatest risk for strong winds aloft mixing to the 
surface. 

Temperatures...

Very strong WAA yields +12C temps at 925 mb across RI and southeast 
MA this afternoon. Despite showers highs will likely approach 60 
across RI and southeast MA. Record high for PVD today is 64/1906, 
thus there is a very low probability of approaching this 
record. However...portions of northern MA and parts of the CT 
River Valley may not be able to mix out completely so its 
possible some of these locations only see high temps reach into 
the 40s. Coolest high temps expected in far northern MA.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM WEDNESDAY/...
425 AM update...

Tonight...

Frontal passage occurs this evening with strong post frontal drying, 
so expect decreasing clouds and a drying trend from west to east 
early. Temps may initially jump upward across the interior where 
shallow cold air was unable to scour out during the day, as post 
frontal winds mix down warm air aloft initially before CAA develops. 
However core of cold air is delayed until Wed night/Thu. Thus only 
seasonably cold tonight.

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...
*/ Highlights...

 - Slightly unseasonable, breezy through the remainder of the week 
 - Mild conditions along with wet weather return early next week

*/ Overview...

Fairly benign pattern for the remainder of January. Progressive flow 
across the CONUS with colder, Arctic air locked up around the Hudson 
Bay / Davis Straight region. H3 jet streak with wave break out over 
the N-Central Pacific, H5 ridge into the Bering Straight, downstream 
H5 trof into the Gulf of AK into the W CONUS, but overall flat, an 
unimpeded flow downstream, not greatly amplified, so long as traffic 
does not bottle up across the N Atlantic. Milder pattern lies ahead 
of any synoptic disturbances, wet weather as well, followed by cold 
that is not as deep, slightly unseasonable, lacking a deeper Arctic 
connection. However, watching early February closely. Aforementioned 
H3 wave break progressing E, potential H5 ridge into the W CONUS, a 
nod to ensemble signals of a +PNA pattern emerging. Winter isn't 
over just yet. 

*/ Discussion...

Through Friday...

Quiet and cold. Cyclonic flow persisting aloft, additional mid-level 
energy rotating through, cold air advection enhanced and maintained, 
boundary layer mixing up around H9 through which NW flow prevails, 
looking at slightly below seasonable conditions (typically mid 30s 
for highs, around 20 for lows) and breezy conditions. Talking wind 
chills as low as the single digits, possibly below zero for the N/W 
high terrain. Scattered cloud decks, flurries over the Berkshires, 
NW wind gusts as high as 30 to 35 mph, otherwise quiet. Some thought 
as to refreezing ice jams, but cold not as deep, so perhaps river 
flows elevated by Tuesday rains are uninhibited as ice jams would 
not be expected to refreeze so quickly.

Weekend into early next week...

Expunging cold air prior to the onset of the next Pacific-origin 
disturbance. Question progressive nature and subsequent morphology 
with the potential downstream traffic. Certain Arctic air remains 
locked up around the Hudson Bay region, the approaching system warm-
core, exhibiting inside-runner behavior along regions of better baro-
clinicity N and W, looking at another period of mild conditions and 
wet weather over much of the NE CONUS followed by return colder air 
however not exceptionally deep. However, acknowledge the spread in 
ensemble member solutions, nothing is certain. Preference to slower 
EC/UKmet solutions, parent with GEFS beginning to signal anomalous S-
influx trends. Cold ground prevailing, certain of fog / visibility 
issues, potential for flooding with the possibility of moderate to 
heavy rain, more so with swollen and/or ice jammed river basins. 
Some uncertainty how quickly cold air is scoured out prior to and 
with potential onset of wet weather.

&&

.AVIATION /15Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...

Today...Moderate to high confidence. Mainly IFR to LIFR
conditions in periods of heavy rain and areas of fog which was 
locally dense. Vsbys should improve some this afternoon with the
heavy rain and perhaps an isolated t-storm or two. Still 
dealing with FZRA across parts of northern MA...which should 
change to plain rain by 1 pm. Strong LLWS present over the 
shallow inversion. While the interior will struggle to mix 
out...should see a period of southerly 35 to 40 knot wind gusts 
along the coastal plain during the mid to late afternoon.

Tonight...

Big improvement with any leftover IFR/LIFR eastern MA around 00z
quickly improving to VFR by 03z or so. Elsewhere VFR with
developing gusty SW winds. Any leftover showers over Cape Cod
and Nantucket at 00z quickly moves offshore. Thus dry runways
overnight. 

KBOS Terminal...high confidence in TAF on overall trends but
lower confidence on exact details. Heavy showers with possibly
embedded Thunder 17z-22 and LLWS.

KBDL Terminal...high confidence in TAF on overall trends but
lower confidence on exact details. Heavy showers with possibly
embedded Thunder 15z-18z

Outlook /Wednesday through Saturday/...

Tuesday: Mainly IFR, with local MVFR possible. Strong winds
with gusts to 40 kt. SHRA, areas FG, FZRA likely, isolated
TSRA.

Tuesday Night: Mainly VFR, with local IFR possible. Windy with
gusts to 35 kt. Areas FG, slight chance SHRA.

Wednesday: VFR. Windy with areas gusts to 30 kt. 

Wednesday Night: VFR. Breezy. 

Thursday through Thursday Night: VFR. Windy with local gusts to
30 kt. 

Friday: VFR. Breezy. 

Friday Night through Saturday: Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...

Today...

Southerly Gales develop with strongest winds along the waters of RI 
and southeast MA this afternoon. Showers and fog limit vsby. 

Tonight...

Front sweeps across the region early this evening with winds 
shifting from S to west. Thus southerly gales diminish with the wind 
shift along with vsby improving. 

Outlook /Wednesday through Saturday/...

Tuesday: Moderate risk for gale force winds with areas of gusts
up to 45 kt. Rough seas up to 13 ft. Rain showers, areas fog,
isolated thunderstorms. Visibility 1 nm or less.

Tuesday Night: Low risk for gale force winds with gusts up to
35 kt. Rough seas up to 12 ft. Chance of rain showers, areas
fog. Local visibility 1 nm or less.

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of rough seas. 

Wednesday Night: Winds less than 25 kt. Local rough seas. 

Thursday: Moderate risk for Small Craft Advisory winds with
local gusts up to 30 kt. Areas of seas approaching 5 ft. 

Thursday Night: Moderate risk for Small Craft Advisory winds
with local gusts up to 30 kt. Local rough seas. 

Friday: Winds less than 25 kt. Seas locally approaching 5 ft. 

Friday Night: Winds less than 25 kt. 

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Areas of seas approaching 5 ft.

&&

.HYDROLOGY...
The heavy rain will mainly just result in typical brief nuisance poor 
drainage street flooding. However...a Flood Watch has been issued for 
the Millers River near Athol where an ice jam remains frozen in place 
and has the potential to cause additional flooding.  A Flood Warning 
also remains in effect for the CT River at Middle Haddam...where this 
heavy rain may result in increased flooding problems as a result of 
the ice jam.

For details on specific area rivers, including observed and 
forecast river stages, please visit the Advanced Hydrologic 
Prediction Service (AHPS) graphs on our website.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Dense Fog Advisory until 1 PM EST this afternoon for 
     CTZ002>004.
MA...Dense Fog Advisory until 1 PM EST this afternoon for 
     MAZ002>024-026.
     Wind Advisory until 7 PM EST this evening for MAZ013-015>024.
     Winter Weather Advisory until 1 PM EST this afternoon for 
     MAZ002>008-012-014-026.
     Flood Watch until 6 PM EST this evening for MAZ003-004.
RI...Dense Fog Advisory until 1 PM EST this afternoon for 
     RIZ001>008.
     Wind Advisory until 7 PM EST this evening for RIZ002>008.
MARINE...Gale Warning until 8 PM EST this evening for ANZ232>235-237-
     250-254>256.
     Gale Warning until 6 PM EST this evening for ANZ230-231-236-
     251.

&&

$$
SYNOPSIS...Frank/Nocera/Sipprell
NEAR TERM...Frank/Nocera

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