NWS Technical Forecast Discussion


Observed at
Lowell, Massachusetts
03-21-2019 02:00 PM

Temperature

50.8°F

Hour Change

1.6°F

Humidity

43%

Hour Change

-4%

Dewpoint

29.1°F

Hour Change

-0.7°F

Wind

4 mph from 158° (SSE)

Wind Gust

9 mph

Barometer

30.093 inHg

3 Hour Trend

-0.094 inHg

Today's Rain

0.00 in

Rain Rate

0.00 in/hr

Rain Last Hour

0.00 in

Monthly Rain

1.50 in

Yearly Rain

6.90 in

Wind Chill

50.8°F

Heat Index

50.8°F

Est. Cumulus Base

5105 feet

Today Highs / Lows

High Temperature

Low Temperature

50.8°F at 01:59 PM

31.6°F at 06:36 AM

High Humidity

Low Humidity

88% at 06:53 AM

41% at 11:56 AM

High Dewpoint

Low Dewpoint

32.2°F at 11:12 AM

26.0°F at 12:02 AM

High Barometer

Low Barometer

30.287 inHg at 12:00 AM

30.093 inHg at 01:59 PM

High Wind Gust

19 mph from 84° at 11:47 AM

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

30.1°F at 08:12 AM

High Heat Index

50.8°F at 01:59 PM

Yesterday's Statistics

High Temperature

Low Temperature

53.3°F at 03:45 PM

22.2°F at 07:08 AM

High Humidity

Low Humidity

84% at 07:17 AM

29% at 03:31 PM

High Dewpoint

Low Dewpoint

31.5°F at 07:02 PM

16.6°F at 12:00 AM

High Barometer

Low Barometer

30.422 inHg at 07:56 AM

30.233 inHg at 06:01 PM

High Wind Gust

16 mph from 148° at 02:14 PM

Rain

0.00 in

High Rain Rate

0.00 in/hr at 12:00 AM

Low Wind Chill

22.2°F at 07:08 AM

High Heat Index

53.3°F at 03:45 PM

000
FXUS61 KBOX 211401
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1001 AM EDT Thu Mar 21 2019

.SYNOPSIS...

High pressure south of Nova Scotia provides mainly dry and
seasonable conditions today. A coastal storm impacts the region
tonight into early Friday morning with periods of rain, heavy at
times, and gusty winds. Steady rain tapers off to
showers/drizzle Friday.  Snow showers linger Friday night, with
windy conditions expected late Friday night into Saturday.
Milder Sunday and Monday, a return to colder than normal
conditions is expected Tuesday in mid next week.

&&

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

10 am update...

An abundance of mid level cloudiness has overspread much of the
region as of mid-late morning, but there was still some sunshine
across far eastern MA. However, expect clouds to advance across
this region as well in the next few hours.

As previous forecast mentioned...bulk of deeper forcing/moisture
remains to our west today. There is enough warm advection for a
few showers from time to time across western MA/northern CT, but
most of the rain holds off until tonight even in this region.
Dry weather should pretty much prevail across eastern MA/RI
through the afternoon. High temperatures should top out well
into the 40s to near 50 in most locations. The coolest temps
will be found along the east slopes of the Berks as well as the
immediate coast with onshore flow off the cold ocean.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
4 AM update ...

Tonight ...

Negative tilt closed low over the Mid Atlc states and corresponding
coastal low tracks northeast up the coastline into RI/eastern MA by
12z Fri. This system captures plume of subtropical moisture
currently off the NC coast with PWATs AOA 1.0 inches (+1 standard
deviation (SD) from climo) streaming into southern New England
overnight. Strong onshore wind anomalies of +2 SD AT 925 mb and 850
mb will be acting on this moisture plume to yield a period of heavy
rainfall roughly from 04z to 10z. If this timing holds heavy rain
likely exits northeast before the morning commute commences. System
is progressive so window of heavy rainfall is limited to 3 to 6
hours and this will cap rainfall totals to 0.35 to 0.75 inches.
Isolated amounts of 1+ inches are possible given elevated
instability yielding potential convection. However any 1+ inch
amounts should be very isolated with confined to northeast MA.

PTYPE...model soundings suggest there could be enough evaporative
cooling for some snow and/or sleet mixed in with the rain early this
evening across northern CT into western-central MA. However this
will be short lived so bulk of event will be all rain.

Friday ...

Vertically stacked/occluded low moves slowly northward from LI at
12z then up the I-95 corridor of RI into eastern MA, while still
intensifying from about 990 mb low to 983 mb along the Maine coast
by 8 pm. During this time mid level dry slot moves across the region
in the morning resulting in a transition to drizzle and lower top
showers as the morning progresses. A second round of showers in the
afternoon as comma-head rotates thru the region. Maybe a period of
dense fog in the morning especially across RI and eastern MA as low
tracks overhead. Improving during the afternoon as the low exits
into Maine and winds shift to the NW with colder drier air
overspreading the region. So a period of mild weather across RI and
eastern MA where warm sector invades yielding early highs of 45-50.
However only in the upper 30s to lower 40s across the interior.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Highlights...

* Snow showers and wind Friday night into Saturday.
* Milder Sunday into early Monday.
* Rain/snow shower mix on Monday
* Cold air returns late Monday into mid next week.

Overview and model preferences...
Two lobes of the arctic vortex to monitor as amplified mid lvl
ridge across the Continental Divide gradually dissipates in
favor of a more zonal pattern across the CONUS. Meanwhile,
downstream remains generally zonal, reflective of the positive
NAO/AO setup. In any case, a period of generally colder than
normal conditions are expected into the middle portions of next
week, except where rising heights on Sun between these two
arctic lobes. The first, linked to occluding low pres in the Bay
of Fundy will have strong wrap-around component Fri night
featuring a change to SN and strong winds. The second, a
stronger lobe, settles across N Quebec and Labrador, with
longwave trof settling across the NE. Will need to watch this
as vort-maxes rotate around the trof, but given the zonal flow
offshore, suppression and fast movement of any baroclinic waves
is favored at this time. However, given the typical uncertainty
handling these waves, will need to watch the mid week period.
Otherwise, a general consensus blend of guidance will be used to
baseline this update.

Details...

Fri night into Sat...
As low pres occludes toward the Bay of Fundy, noting strong
comma head lift wrapping into S New England. With it, modest
theta-e within the cold conveyor suggests that decent precip may
linger into the overnight hours. CAA and BL suppression
suggests that this precip falls as SN. Enhancement by mid lvl
lapse rates above H7 near 7.0C/km. Therefore, a few bursts of
heavy SN cannot be ruled out. This is especially true in the
Berkshires as well as central MA/CT hills where an upslope
component can be realized. Spotty amounts may exceed an inch or
two where all of these factors coincide.

Otherwise, high pres upstream is building toward +1030mb with
strong pres rises. CAA will allow lower lvl mixing to exceed H85
where LLJ is about 40-50kt. Therefore, will flirt with wind
advisory criteria, which will last into the day on Sat. Aside
from the inherent wind impacts, early Sat wind chills are likely
to fall into the single digits and remain in the teens and 20s
throughout the day.

Sun...
Brief reprieve as mid lvl height rise in advance of the
secondary, stronger arctic lobe. This should briefly allow temps
to reach near or above seasonal normals thanks to the high,
late March sun angle. Mainly dry as high pres slides to the S.

Mon into Tue...
Reinforcing arctic wave, the lower lvl feature coincident with
arctic lobe settling just to the S, moves through likely late
Mon based on current mean between ensembles and operational
guidance. Weak frontal wave connected to subtropical moisture
may allow for some SHRA/SHSN. Although ana-frontal lift looks
favored based on the frontal wave development. The main impact,
will be the introduction of another cold period, with H85 temp
anomalies nearing 3 std deviations below normal, or 20C lower
than usual. For what its worth, the progged H85 temps are
near record low values per the SPC sounding climatology. Expect
a period of below normal temps, where its possible highs will
struggle to break out of the 30s.

Mid/late week...
As mentioned above, with cutoff settling near Labrador,
longwave trof dipping toward the mid-Atlantic, and progressive
flow offshore. Expect stalled frontal boundary to remain S, such
that any coastal wave developing along it remains suppressed to
the S. However, given this is toward the end of the long term
period, confidence in solutions remains somewhat low. Although
widely variable spatially, ensemble members from both the ECENS
and GEFS favor this, so this update will reflect this thinking.

&&

.AVIATION /14Z 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/...High confidence.

Late this morning through the afternoon...

Mainly VFR despite a mid level cloud deck and a few showers from
time to time across western MA/northern CT. We can not rule out
some brief MVFR conditions in the interior...but VFR should
dominate.

Tonight ...

LLWS likely across RI and eastern MA peaking 06z-09z as strong
low level SE jet 50-60 kt moves across the region. VFR at 00z
quickly lowers to MVFR and then IFR after 06z as rain
overspreads the region 03z-06z. Rain heavy at times along with isolated
-TSRA possible.

Friday ...

At 12z heavy rain over northeast MA exits northward with lighter
showers/drizzle remainder of the day. IFR/LIFR in the morning
lifts to MVFR during the afternoon. Winds becoming NW and
increasing up to 40 kt by late afternoon/early evening.

KBOS Terminal...High confidence in TAF. Dry weather thru the
daylight hours then rain overspreading terminal 03z-06z Friday.
LLWS 06z-09z Fri with WS020/14050KT

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night: Mainly MVFR, with local IFR possible. Strong
winds with areas of gusts up to 40 kt. Scattered SHRA,
scattered SHSN.

Saturday: Mainly VFR, with local MVFR possible. Strong winds
with local gusts up to 40 kt.

Saturday Night: VFR. Windy with gusts up to 30 kt.

Sunday into Monday: Mainly VFR.

&&

.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.

Today ...

Ridge of high pressure from south of Nova Scotia into southern New
England will provide light to modest SE winds, dry weather and good
vsby.

Tonight ...

Strengthening low pressure moves from the MD coast to LI. East winds
increase to 20 to 30 kt along with periods of heavy rain and fog
yielding poor vsby.

Friday ...

Strengthening low pres moves from LI at 12z into RI and eastern MA
during the afternoon, then into coastal ME by evening. Showers,
drizzle and areas of dense fog lower vsby but improves from south to
north as winds shift to the west and increase up to 40 kt.

Outlook /Friday Night through Monday/...

Friday Night into Saturday: Gale force winds with gusts up to
40 kt. Rough seas up to 14 ft.

Saturday Night: Low risk for gale force winds with gusts up to
35 kt. Areas of rough seas.

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas.

Sunday Night into Monday: Winds less than 25 kt. Areas of seas
approaching 5 ft. Chance of rain.

&&

.TIDES/COASTAL FLOODING...
Strongest winds and surge still appear to arrive during low tide,
around 09z Friday. However with low pressure overhead at high tide
(18z Fri) and pressure rises not arriving until after high tide,
there could be enough leftover surge and wave action for minor
coastal flooding. Greatest risk is across northeast MA coastline
including Cape Ann. Astro tide in Boston 17z Fri is 11.7 ft. Surge
values could range from 0.5 to 1.0 ft with ensemble storm surge from
Stevens Institute the highest. Nonetheless worse case appears to be
minor coastal flooding.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Gale Watch from Friday evening through Saturday evening for
     ANZ231>235-237-250-251-254>256.
     Small Craft Advisory from 9 PM this evening to 6 PM EDT Friday
     for ANZ232>234.
     Gale Watch from late Friday night through Saturday evening for
     ANZ230-236.
     Small Craft Advisory from midnight tonight to 6 PM EDT Friday
     for ANZ231-251.
     Small Craft Advisory from 6 PM this evening to 6 PM EDT Friday
     for ANZ235-237.
     Small Craft Advisory from 8 PM this evening to 6 PM EDT Friday
     for ANZ250.
     Small Craft Advisory until 6 PM EDT Friday for ANZ254>256.

&&

$$
SYNOPSIS...Nocera/Doody
NEAR TERM...Frank
SHORT TERM...Nocera
LONG TERM...Doody
AVIATION...Frank/Nocera/Doody
MARINE...Nocera/Doody
TIDES/COASTAL FLOODING...Staff

NWS BOX Office Area Forecast Discussion