NWS Boston/Norton, MA wrote its last area forecast discussion before the first event at Jan 24, 4:00 AM EST, 1 hour earlier.
Area forecast discussion, Jan 24, 4:00 AM EST, 1 hour before
Area Forecast Discussion
National Weather Service Boston/Norton MA
400 AM EST Thu Jan 24 2019
.SYNOPSIS...
Low pressure over the Great Lakes will swing a cold front through
Southern New England late afternoon and evening. Showers ahead of
the front will move across the region through the day, bringing
heavy rain and strong winds. Heavy rain will cause potential
flooding, strong winds may cause damage. Behind the front, colder
more seasonable weather moves back in Friday. Colder weather
arrives early in the weekend.
&&
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
One trough, embedded in the general flow, will sweep into New
England by this evening. The shortwave trough is supported by a 170-
kt upper jet. The right entrance region of the jet, supportive of
generating lift, will move across our area today and off to the east
by evening. Strong pressure falls over the West Virginia/Central
Appalachians area, and a secondary low appears to be forming there.
This will tighten the gradient at low levels, drawing a strong low
level jet over Southern New England.
Heavy rain... As noted the past few days, high precipitable water
values are forecast to move over our area today. Values are forecast
around 1.25 inches. This value is well above normal, and about as
high as the PW gets this time of year. Expect periods of heavy rain
today, with the most favorable time coming as the jet entrance
region approaches and maximizes lift. Expect rainfall of 1-2 inches,
potential for locally higher amounts. Warm advection will bring mild
temperatures, reaching the 50s most places. Places with snow on the
ground will see a sizable snowmelt, which will add to the
amount of water running off. This suggests potential for
extensive urban/small stream flooding, possibly some river
flooding. A Flash Flood Watch continues through the day.
Strong Winds... Already a strong low level jet over the region with
speeds of 65 kt. The deepening secondary low will increase those
speeds, with guidance suggesting 100 kt at 850 mb and 85 kt at 925
mb this afternoon. These speeds are at or above max observed
climatological values of wind speed at those level, and suggests
strong surface speeds. The area of maximum gusts looks to be along
the RI and SE Mass coasts, diminishing to the north and west. We
are maintaining a high wind warning in RI and SE Mass and a wind
advisory from Nrn RI through NE Mass. Expect some downed trees,
scattered power failures, and other damage.
Instability is so-so, but K Index values do reach 30+ and Total
values 45-48. The kinematic structure of the storm may allow an
organized line to form. Could be isolated thunderstorms accompanying
the cold front.
Cold front moves through late in the day, around 20-23Z. Heavy rain
and strong winds should diminish by that time.
&&
.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
A sharper upper trough digs over the Great Lakes tonight and sweeps
across New England Friday. This draws drier air across our area
behind the cold front but ahead of the upper trough. Expect clearing
skies tonight. Lower heights and temperatures aloft also suggest
cooling temperatures, although no lower than seasonable levels.
Temps and heights aloft continue to fall Friday, as the trough
sweeps through along with its supported second cold front. Temps
reach below-normal levels but not excessively so. Cold advection
mixing to near 850 mb and temps there around -12C suggest max sfc
temps Friday in the 30s.
&&
.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
*/ Highlights ...
- Cold, dry conditions Saturday
- Watching potential outcomes Sunday along an Arctic front
- Another onset wintry weather, follow-up soaker Tue-Wed
- Potential late week Arctic blast
Overview and model preferences...
Little change through the mid-term periods as the entire E half
of the CONUS is defined by very deep longwave trof, with a link
to the polar vortex. The key remains the mean trof axis, which,
as previous forecaster noted in the 5-day mean height
anomalies, lies generally between the Mississippi and Ohio River
valleys. While this also introduces generally negative low-mid
lvl temp anomalies, as the first two lobes of the polar vortex
rotate through (late weekend and early next week), they begin to
pivot poleward, with the sfc low pres moving inland of New
England. This action does have consequences, however, as each
lobe begins to shift the mean trof axis E, such that yet another
arctic intrusion will need to be monitored late week. Continue
to note enough agreement between both operational and ensemble
guidance that a consensus blend can be used as a baseline.
Details...
Fri night into Sat...
Arctic cold frontal passage late Fri will lead to strong cold
advection continuing into Sat morning. H85 temp anomalies nearly
-10C. This suggests mins in the single digits to low 20s,
coldest in NW valleys in spite of some evening clouds/SHSN
associated with the cold FROPA. Sat highs mainly in the 20s to
low 30s.
Sun into Mon...
Modest warm advection and resulting isentropic lift, combined
with a PWAT plume between 0.5-0.75 suggest at least a low risk
for precipitation across New England as double-barreled low pres
slides through NY, ON and QC. This double barreled low does
have some coastal connection, as an inverted trof, which could
provide a localized focus for heavier precip. However best
dynamic forcing and convergence lie to the west and only catch
up once the best frontogenesis is across Northern New England.
Something to watch, because if this occurs earlier, but for now,
chance POPs and showery vs. stratiform is preferred. Thermal
profiles through the column generally cold enough for p-type
remaining SN except where diurnal warming leads to highs in the
mid 30s to low 40s, particularly on Sun.
Tue into Wed...
Second lobe of the polar vortex rotates through, yielding low
pres development well to the SW. Strong warm advection leads the
sfc low pres, allowing low and mid lvl temps to warm, similarly
to the current storm system although with high pres orientation
to maintain cold air longer per latest guidance. With
development to the south, PWAT plume is higher than that
associated with the Sun/Mon low pres, potentially close to or
around 1.00 inches. If this warm advection occurs as progged,
thermal profiles support a white to wet scenario, with a risk
for continued flooding if rivers remain elevated. Will need to
watch this track/timing as some may remain cold enough for
SN/ice longer depending on the synoptic setup, particularly of
high pres to the N.
Late week...
This wave/arctic cutoff continues to shift the trof axis E,
suggesting a better link to modified arctic air, suggesting a
late week cool down. Any waves moving through this trof will
have to be monitored, but confidence in any one is very low at
this time.
&&
.AVIATION /09Z 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/...Moderate to high confidence.
Today...
Widespread IFR cigs/vsbys in rain with some heavy rain. Isolated
thunderstorm possible. Strong south-southwest winds at 2000-3000
feet, reaching 85 kt and creating Low Level Wind Shear. Greatest
impact will be from midday through 4 PM. Winds shift from the
west 4 PM to 7 PM as a cold front sweeps west to east across our
area.
Tonight...
West wind gusting 20-30 kt. Rain ending in the evening.
Cigs/vsbys improving to VFR by midnight.
Friday...
VFR. Winds gusting to 25 kt.
KBOS Terminal...
Conditions lowering during morning push, at lowest midday and
early afternoon, then improving during afternoon push.
Rain overspreads the airport this morning. MVFR cigs lower to
IFR by mid morning. IFR cigs/vsbys in locally heavy rain this
afternoon. Winds increase from south with gusts to 45 kt, then
shift out of west toward 23Z and diminish. Conditions then
improve. South winds to 75 kt at 2000 ft AGL, which will create
low level wind shear.
KBDL Terminal...
Conditions lower to IFR during morning push, with worst of
conditions late morning/early afternoon. Can't rule out a
rumble of thunder, and isolated south wind gusts up to 50 kts
possible. LLWS impact picks up through afternoon. Cold front
moves through around 20Z at which point winds shift from the
west and conditions improve.
Outlook /Friday Night through Monday/...
Friday Night through Saturday Night: Mainly VFR.
Sunday: Mainly VFR, with areas IFR possible. Breezy. Slight
chance SHRA, slight chance SHSN.
Sunday Night: Mainly VFR, with local IFR possible. Breezy.
Slight chance SHSN.
Monday: VFR. Breezy.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Friday/...Moderate confidence.
Today...
Strong south gales expected through most of the day. Brief storm
force winds possible, but mainly as gusts and mainly during
heavier bursts of rain. Seas build to 14 feet on the eastern
outer waters, with 17-19 feet in the southern outer waters.
South winds may try to drive these seas on the southern waters
toward shore.
Areas of fog may become locally dense as anomalously high
dewpoints move over the cold ocean.
Tonight...
Winds shift out of the west during the evening, around 6-8 PM.
Winds should diminish by that time, with gusts up to 30 kt.
Rough seas with 14-17 feet in the evening, diminishing during
the night.
Friday...
West winds with gusts up to 25 kt. Seas 5 to 10 feet but slowly
diminishing.
Outlook /Friday Night through Monday/...
Friday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas.
Saturday through Sunday: Winds less than 25 kt. Seas up to 5
ft. Slight chance of rain showers, slight chance of snow
showers.
Sunday Night and Monday: Low risk for Small Craft Advisory
winds with gusts up to 25 kt. Seas up to 5 ft.
&&
.TIDES/COASTAL FLOODING...
Strong S-SW winds drive seas against the South Coast, especially
RI and adjacent Mass. Sea height forecasts south of RI jumped
about 5 feet with this model run. The numbers drop off farther
east off the Islands. We will be adding a coastal flood advisory
from the Buzzards Bay area through the RI coast.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flash Flood Watch through late tonight for CTZ002>004.
MA...High Wind Warning from 9 AM this morning to 7 PM EST this
evening for MAZ018>024.
Coastal Flood Advisory from 7 AM this morning to 2 PM EST this
afternoon for MAZ020>022.
Flash Flood Watch through late tonight for MAZ002>022-026.
Wind Advisory from 9 AM this morning to 5 PM EST this
afternoon for MAZ005>007-013>017.
RI...High Wind Warning from 9 AM this morning to 7 PM EST this
evening for RIZ005>008.
Coastal Flood Advisory from 7 AM this morning to 2 PM EST this
afternoon for RIZ006>008.
Flash Flood Watch through late tonight for RIZ001>007.
Wind Advisory from 9 AM this morning to 5 PM EST this
afternoon for RIZ001>004.
MARINE...Gale Warning until 9 PM EST this evening for ANZ231>235-237-
251.
Gale Warning from 7 AM this morning to 7 PM EST this evening
for ANZ230.
Gale Warning from 7 AM this morning to 8 PM EST this evening
for ANZ236.
Gale Warning until 11 PM EST this evening for ANZ250-254>256.
&&
SYNOPSIS...WTB/Doody
NEAR TERM...WTB
SHORT TERM...WTB
LONG TERM...Doody
AVIATION...WTB/Doody
MARINE...WTB/Doody
TIDES/COASTAL FLOODING...WTB