Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/07/18
Area Forecast Discussion
National Weather Service Boston/Norton MA
1047 PM EST Thu Dec 6 2018
.SYNOPSIS...
Scattered snow showers cross the area tonight ahead of an approaching
cold front. Otherwise, dry and cold weather persist across southern
New England thru this weekend and into next week. High pressure in
control allowing Arctic air to spill across the Northeast as the
main storm track remains S of our region. Perhaps mild conditions
and wet weather return for the following weekend.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
1020 PM Update...
Band of light rain/snow showers has pushed into N CT out of the
Litchfield hills and Berkshires. Temps across that area were
mainly from 32 to 34 degrees at 03Z, so noting a few spots with
either -SHRA or -SHSN, mainly across S CT, but can`t rule out a
brief rain or snow shower as this precip moves across.
As the precip shifts E through the pre dawn hours of Friday,
will not see much in the way of accumulations as T/Td spreads
across central and eastern areas were generally 10 degrees or
greater, though could lower some with the light SW wind flow as
the Arctic front crosses the region between 06Z and 12Z.
Updated to bring conditions current and incorporate into the
remainder of the overnight forecast.
Previous Discussion...
Sweeping Arctic cold front across the E Great Lakes region.
Noting with the thermal discontinuity a brief burst of winds
immediately behind the front collocated with steep lapse rates.
Going with the latest HRRR with wind profiles to account for
this. Gusts upwards of 30 mph possible.
However, moisture and lift with the front are not extensive but
could see scattered rain and snow showers ahead of and along
the front. As winds shift from SW to NW towards daybreak Fri,
column quickly dries back out and ends precip chances. Window
for light wintry precip looks to range from around 00Z western
MA/north central CT, until 09Z-12Z eastern MA/RI.
Behind the front, a reinforcing shot of cold air will work in.
Winds become gusty toward daybreak across the higher terrain of
the interior, and along the coast. Overnight lows expected to
be a couple of degrees below normal, mainly in the 20s. Some
upper teens are possible in the higher terrain of far interior
MA, and some lows in the low-mid 30s expected Cape/Islands and
along the immediate shorelines of MA/RI.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Friday...
Will be a dry but cold day, as cold air advection continues and
surface high pressure builds eastward towards our area. It will
be a blustery day, as W-NW winds increase. Wind gusts should
top out at 25-30 mph, though a few higher terrain locales may
see a few higher gusts.
Sunny/mostly sunny skies forecast, with a few diurnal
stratocumulus clouds. Highs expected to be 5 to 10 degrees below
normal for early December, mainly in the 30s. Anticipate some
upper 20s across the far interior higher terrain, and some highs
around 40 mainly on the Cape and Islands.
Friday Night...
Dry conditions continue, and thanks to cold air advection from
Friday, potential for chilly overnight lows in place. Short wave
energy passing over the area could bring some passing clouds.
However, overall expecting mainly clear skies and diminishing
winds, which will allow for good radiational cooling. Lows in
the teens expected for much of the area. Portions of the far
interior will probably see mins in the single digits, especially
where there is a snow pack in place.
&&
.LONG TERM /SATURDAY THROUGH THURSDAY/...
*/ Highlights...
- Cold, dry conditions into mid-December
- Watch for ocean-effect snows along coastal E MA at times
- Warmer, wetter weather potentially returning around mid-December
*/ Overview...
This pattern is crazy. +ENSO / El Nino Winter resemblance, dominant
H5 N Pacific low contributing to +EPO / +WPO signals. Subsequent H5
ridging into N America, accompanying +H85 temperature anomaly into
Canada. From noted H85 and H2 westerly perturbations from evolving
+ENSO / El Nino, echoing upward through the stratosphere, there is a
resultant cross-polar flow downsheared E of the aforementioned ridge
that evolves across Eastern N America into the N Atlantic. While NE
CONUS slightly colder than average conditions prevail, the H3 sub-
tropical Pacific jet and storm track is pushed S, yielding overall
dry conditions through mid-December, notably with -NAO / -AO trends
that indicate downstream N Atlantic progressive storm pattern while
Arctic air is released S equatorward across the N Hemisphere. Tele-
connections noted above netting a seasonable 2m temperature balance
through December as negative 2m temperature anomalies prevail into
mid-December, with mild Pacific warmth finally edging in around mid-
December continuing potentially through the end of the month as the
aforementioned cross-polar flow shifts E, a dipole of stratospheric
vortices rotating round the N Hemisphere, the MJO sliding from a
phase 2 towards 4 adding to warm westerly perturbations. A potential
return of the storm track N and wetter conditions by mid-December.
*/ Discussion...
A 10-day dry stretch ongoing and forecast which we haven`t seen in
meteorological winter since 2016, prior to that in 2010. Initially
very cold, Arctic air for the weekend associated with high pressure
that`ll keep the storm track well S off the SE CONUS per consensus
of forecast model guidance. However, with deepening storms to our S
comes the isallobaric response. -AO trend, Arctic air unlocked, on
into Thursday morning we could see some of the coldest air of the
season beneath -12 to -18C H85 Arctic airmass. Blustery N winds at
times which will make it feel colder with respect to wind chills,
will be watching for any ocean-effect snows across E MA that`ll
occur given a colder airmass over warmer waters, watching the depth
of moisture parent with any instability. As the associated high
pressure shifts E into the following weekend, we potentially could
see a significant warm-up and return of wetter conditions.
&&
.AVIATION /04Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Friday Night/...High confidence.
03Z update...
Overnight...
Mainly VFR, with CIGS lowering to BKN040-060. May see brief
lowering of CIGS to MVFR with any scattered rain or snow.
Isolated IFR conditions possible across E slopes of the
Berkshires. Conditions should improve from W-E after 08Z, but
may linger across E Mass/RI through 12Z Fri.
Friday into Friday night...
VFR conditions expected. W-NW wind gusting to 20-25 kt, possibly
up to 30 kt across the higher terrain and along the coast. Winds
tapering into the overnight hours.
KBOS Terminal...High confidence in TAF.
KBDL Terminal...High confidence in TAF.
Outlook /Saturday through Tuesday/...
Saturday through Saturday Night: VFR. Breezy.
Sunday: VFR.
Sunday Night through Monday Night: VFR. Breezy.
Tuesday: VFR.
&&
.MARINE...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
Short Term /through Friday Night/...High confidence.
Overnight...
Small Craft Advisory headlines in place. SW winds will increase
this evening, expecting gusts up to 25-30 kt, highest across
the southern waters with seas increasing to 5-7 ft. Scattered
rain and/or snow showers move across with visibility locally
reduced as the precip moves across, but should improve from W-E
after 09Z.
Friday...
Winds shift to NW Fri morning with continued gusts up to 25-30 kt,
with winds diminishing during the afternoon. Seas on the outer
waters 5-7 ft. SCA headlines continue for the coastal waters, except
for Narragansett Bay.
Friday Night...
NW wind gusts around 25 kts early, otherwise winds gradually
diminishing. Seas also gradually subsiding. SCA headlines continue
for the outer coastal waters.
Outlook /Saturday through Tuesday/...
Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.
Saturday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Seas locally approaching 5 ft.
Sunday through Sunday Night: Winds less than 25 kt.
Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Monday Night through Tuesday: Winds less than 25 kt. Seas up to
5 ft.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 4 PM EST Friday for ANZ232>234.
Small Craft Advisory from 3 AM to 4 PM EST Friday for ANZ230.
Small Craft Advisory until 6 PM EST Friday for ANZ231-235-237-
251.
Small Craft Advisory until 7 AM EST Friday for ANZ236.
Small Craft Advisory until 5 AM EST Saturday for ANZ250-254-
255.
Small Craft Advisory until 1 AM EST Saturday for ANZ256.
&&
$$
SYNOPSIS...Sipprell/NMB
NEAR TERM...Sipprell/EVT/NMB
SHORT TERM...NMB
LONG TERM...Sipprell
AVIATION...Sipprell/NMB
MARINE...Sipprell/NMB
Area Forecast Discussion
National Weather Service Tampa Bay Ruskin FL
742 PM EST Thu Dec 6 2018
.UPDATE...
Zonal flow aloft starting to bring upper moisture and cirrus
from Mexico across the Gulf. Locally, moisture and temps
moderating late this afternoon and early evening as seen in
00Z sounding with PWATs up to a half inch. Surface high
pressure over the Deep South keeping easterly low level flow
over the FL Peninsula under inversion at 4k ft. Latest
grids and forecasts on track with cool night around 5 degrees
below seasonal averages.
&&
.AVIATION...
VFR conditions overnight with light winds and SCT cirrus.
&&
.MARINE...
3-4 mb gradient over the E Gulf this evening with slight
evening easterly surge but conditions to remain below
headlines. Latest buoy obs showing winds around 2 ft and
winds 5-10 kts nearshore and 10-15 kts offshore.
&&
.Prev Discussion... /issued 221 PM EST Thu Dec 6 2018/
..Updated to include sea fog potential and severe weather
threat discussions for Saturday Night and Sunday...
SYNOPSIS...
19Z water vapor and H4 RAP analysis show a mid/upper level
zonal flow pattern in place over the northern Gulf/Deep
south states. Stacked WV imagery shows very dry air in the
middle levels of the atmosphere underneath a slight influx
of higher level moisture (noted by some passing cirrus over
the northern parts of the state). This satellite analysis is
confirmed by the 12Z KTBW RAOB, which indicates this drier
layer below roughly 500mb, and a lower dewpoint depression
further up into the troposphere. Even with this influx of
upper moisture, the column itself as a whole is extremely
dry. The measure PW value from the sounding was only 0.23",
which equates to roughly a 5th percentile of values for
early December. In fact, for the date itself, its a new
record low PW, with the previous record low value being
0.35"...although granted...the old record was a rather high
value compared to other nearby dates. Never the less, its
dry.
In the lower levels we find 1030mb high pressure centered
over AL/GA/Carolinas, which will hold in place through
tonight. The flow around this ridge to our north keeps a
general NE/E flow pattern in place. The proximity of the high
center and dry lower levels allowed us to start today with
some rather chilly readings (at least for Florida). Many
spots along and north of the I-4 corridor dropped down into
the 30s, with even a few normally colder locations briefing
seeing upper 20s around sunrise. South of I-4, widespread
40s were seen, with localized cold spots in the upper 30s.
We will now begin a gradual warming trend into the upcoming
weekend, which will prevent any additional threat of
freezing temperatures.
SHORT TERM (Rest of Today through Friday)...
No significant weather concerns are anticipated through the
remainder of the work week. High pressure to our north this
afternoon will hold in place through tonight before
gradually shifting eastward over the Atlantic during
Friday/Friday night. Last night was the coldest night of the
week, and we will now begin a slow but noticeable warm-up
that will continue into the upcoming weekend. The rest of
today will see mostly sunny skies and light easterly winds,
with high temperatures reaching the lower/mid 60s north of
the I-4 corridor and upper 60s to lower 70s further to the
south.
We are still looking for a "chilly" Florida type night, but
not nearly as cold as last night. Most locations can likely
add a good 5-8 degrees to their low temps from last night,
which will keep all area above freezing, even across the
northern Nature Coast. Low temps by sunrise Friday should
reach the upper 30s to middle 40s north of I-4, and
generally fall in the upper 40s to lower 50s further to the
south. Based on the current temp forecast. A few normally
colder locations north of Brooksville could see a brief
period of frost around sunrise Friday, but this would be
limited to high localized and sheltered locations.
A very pleasant day looks to be in store for Friday across
the region under surface high pressure and continued zonal
flow aloft. Embedded within the zonal flow along the
northern Gulf coast look to be a series of very subtle
shortwave impulses. While these disturbances have little
impact on the lower atmosphere, it is likely that they will
support at least passing high level cirrus, if not fully
filtered sunshine over the northern half of the peninsula.
Otherwise, look for mostly sunny skies for the southern half
of the region. High temperatures continue their climb on
Friday, reaching the upper 60s to lower 70s north of I-4,
and generally the middle 70s further to the south.
LONG TERM (Saturday through next Thursday)...
The synoptic pattern across the central and eastern parts of
the CONUS will begin to change rapidly as we head through
the first half of the upcoming weekend. Our next weather
maker will begin to take shape as longwave troughing ejects
quickly eastward over the southern Plains and lower MS
Valley. For us, this means that if you would like to enjoy
some outdoor activities this weekend, the "better" weather
day is almost certainly going to be Saturday, as rain
chances stay near 0%. For those with marine plans, Saturday
will be much better in terms of rain chances, however,
winds will already by ramping up from the southeast and
south, making boating conditions a bit on the rougher side.
As is often the case, the height falls to our west
associated with the approaching trough will help boost
downstream heights over us for the day on Saturday. The
enhanced ridging aloft will enhances the temperature
potential, and the current forecast has all locations in the
region reaching at least the lower 70s, with middle and
upper 70s common south of I-4. Not out of the question that
spots around Fort Myers and away from the immediate coast
will make a run at 80 Saturday afternoon.
Saturday night into Sunday the trough and an associated
surface reflection/low move quickly eastward along the
northern Gulf coast. A cold front will trail south from this
low through the central Gulf and also move quickly eastward
toward our region by Sunday morning. Saturday night looks
rather warm around these parts are steady southerly flow
brings ever increasing tropical air northward across the
peninsula. Much of the overnight (especially Saturday
evening) looks to remain dry, as it will not be until the
late night hours that rain chances begin to increase from
the west ahead of the cold front. The best chances for
rain/storms before sunrise Sunday should exist over the
coastal waters and Nature Coast, and then spread east and
southward fairly quickly Sunday morning/early afternoon. As
with many our winter systems, an all day rain is not
expected, but rather a couple of hours of wet weather
associated with a band of rain/storms along the front. The
upper level support and surface convergence look good enough
with this system to expect a wetting rainfall for most
location, although highest rainfall amount potential will
exist north of I-4 in closer proximity to the best height
falls/QG forcing. The front will be a steady mover and exit
stage right during the later afternoon/evening hours of
Sunday. Showers and storms will exit with the front,
followed by the arrival of our next shot of cooler and drier
air for the early part of next week. This airmass will
arrive on elevated northwesterly winds that will bring rough
conditions to the eastern Gulf of Mexico, and likely an
increased risk of rip currents along our beaches through at
least Monday.
So what about the threat for severe storms Sunday? As is
almost always the case this time of year along the FL west
coast, we will be dealing with a high shear / low CAPE
scenario with this passing front. Although the shear is
mainly unidirectional, it is quite strong no matter what
guidance solution one examines. I tend to lean away from the
70+ low level jet values advertised by the 12Z GFS over the
Nature Coast, as these seem influenced by convective
processes/feedback within the model. However, low level jet
peak values near 50kts in the GFS-FV3 and NAM and resulting
deep layer bulk shear values of 45-55kts are certainly
decent as well, and certainly supportive of organized
convection. These values suggest a damaging wind threat with
some of the storms Sunday...if...if...they are surface
based. This is the big question. The best potential for
adequate surface based instability to bring winds to the
surface lies mainly south of the strongest winds aloft, but
its a close call. We will need to see the impact of the
latest cold snap and offshore winds on the shelf water
temps, especially off the Nature Coast. The cooler these
waters get, the less likely we will see substantial surface
based instability into these zones. Simply stated, there is
a threat for some stronger storms Sunday along this front,
especially from the I-4 corridor northward, and we will have
to monitor instability trends as we get closer to the event
to determine if its a substantial threat, or something that
looks good in NWP and on radar, but does not materialize at
ground level where the impact matter to us.
As it looks now, the period of Monday through next Thursday
look dry, but cool for our part of the state. A little early
to get into detail of whether there will be another threat
for sub-freezing temperatures, as much will depend on the
exact track of the high center into the southeastern states
during the early/middle portion of the week. If a threat for
freezing temps does develop, it would most likely occur
Tuesday and/or Wednesday night. The better potential would
also exist over the Nature Coast counties in closer
proximity to the likely ridge center location and in better
conditions to support boundary layer decoupling/enhanced
radiation cooling.
After midweek, anther gradual warming trend should
commence.
AVIATION (06/16Z through 07/18Z)...
VFR conditions will prevail through the TAF period. NE/E
winds between 6-9kts settle down to 5kts or less overnight
into early Friday morning.
MARINE...
High pressure remains to our north through tonight before
shifting eastward over the Atlantic on Friday. Northeast to
easterly winds continue through Friday before shifting
southeast and then south and increasing on Saturday ahead of
the next approaching cold front. This front will cross the
forecast waters during Sunday with our next chance of rain
and storms. Mariners can expect a period of cautionary to
advisory level winds and seas both preceding and in the wake
of this frontal passage.
High dewpoint air surging northward Saturday night into
Sunday morning may set the stage for a period of sea-fog
potential over the nearshore waters...mainly south of Tarpon
Springs. These sea-fog events can be impacted by very subtle
changes in the forecast, so for now will simply add fog
wording in the forecast. More details will emerge during the
next 24-48 hours if a fog/visibility threat during the
second half of the weekend appears to continue. Any sea-fog
that does develop will end quickly later Sunday
afternoon/eve as the cold front passes by.
FIRE WEATHER...
High pressure hold in control of the region through Friday,
providing a NE/E wind flow across the Florida peninsula.
Temperatures will see a gradual warming trend into the
upcoming weekend, however, a slow increase in low level
moisture will prevent any widespread regions of critically
low relative humidity through Friday. By the weekend, all
areas will see relative humidity well above critical levels.
The next chance of rain/storms will arrive Sunday with a
cold front. Much of the area is likely to see a wetting
rainfall with this frontal passage, followed by drier and
cooler air, under a northwesterly to northerly wind pattern
for the early portion of next week.
Fog Potential...No significant fog or visibility issues are
expected through Friday.
&&
.Preliminary Point Temps/PoPs...
TPA 49 74 58 78 / 0 0 0 0
FMY 53 77 60 80 / 0 0 0 0
GIF 48 75 57 79 / 0 0 0 0
SRQ 53 74 60 77 / 0 0 0 0
BKV 44 74 55 79 / 0 0 0 0
SPG 53 74 60 78 / 0 0 0 0
&&
.TBW WATCHES/WARNINGS/ADVISORIES...
FL...None.
Gulf waters...None.
&&
$$
UPDATE/AVIATION/MARINE...25/Davis
UPPER AIR...19/Hurt
DECISION SUPPORT...69/Close