Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/20/16
Area Forecast Discussion
National Weather Service Taunton MA
958 PM EST Mon Dec 19 2016
.SYNOPSIS...
High pressure ridge will build across the region tonight through
Tuesday, then will slip off the south coast Tuesday night. Light
winds and mainly clear skies will lead to frigid temperatures
tonight, but readings will rebound by mid week. Low pressure
tracks across northern New England Thursday resulting in scattered
rain showers across the region but a few snow showers are possible
across the high terrain of Massachusetts. Dry but cool and
blustery weather follows Thu night into Friday. High pressure
south of New England Christmas Eve results in milder weather
Saturday. A trend toward cooler and unsettled weather is possible
Christmas Day and into early next week but uncertainty remains
high.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
1000 pm update...
Overall trend in the forecast remains on track for this evening.
Wind convergence along the Cape Cod canal will continue ocean
effect snow band over the next couple of hours. Webcams indicate
that major roads still look good, however snow is covering grassy
surfaces. Cannot rule out a quick drop in vsbys due to snow band. Will
continue the SPS for the next few hours.
Temperatures continue to slowly drop has high level cirrus is
beginning to shift eastward. Continued with the coolest guidance
with lows dropping into the single digits away from the coastline.
7 pm update...
1042 mb high over coastal ME this evening continues to stream cold
air on NNE winds over the relatively warm near shore ocean waters.
This has generated a few modest OE snow bands over Cape Cod Bay
into Plymouth county and into the islands. Received a few reports
of up to 0.4 inches in the Sandwich area of the upper Cape. As is
the case with these narrow bands one town could receive up to 2"
while a neighboring town receives very little if any. This will
be the case tonight. Some of the hi res guidance suggest these
bands may rotate northward thru coastal Plymouth county as blyr
winds veer as the 1042 high over coastal ME advects southward.
Eventually overnight as the subsidence inversion lowers it will
squash shallow updraft potential and the bands will fizzle.
However until then expecting bands to produce a dusting to a few
isolated amounts of 1-2" especially from Sandwich to Plymouth.
HRRR appears to be simulating these bands the best out of the hi
res guid suite.
Otherwise cold dry airmass tonight. Jet induced cirrus over the
northeast precluding temps from free falling. Nonetheless a cold
night ahead. Earlier discussion below.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday...
Expect a dry day as high pressure sits across the region. As the
ridge crosses the region, light/variable winds will shift to SW
during the day. This will bring somewhat milder air to the region
as H85 temps slowly rise. Highs will be in the mid-upper 20s
across the higher inland terrain, ranging to the 30s across the
coastal plain.
Will start to see mid and high clouds move in during the
afternoon.
Tuesday night...
The center of the high shifts E as SW winds increase especially
just off the E Mass coast. May see winds pick up to around 15-20
kt across Cape Cod and the islands during the night as low level
jet moves across. Expect low temps to be 10-15 degrees milder than
tonight, mainly in the teens and 20s away from the coast, ranging
to the lower-mid 30s along the S coast. Some clouds lay linger
across the mid and outer Cape as well.
&&
.LONG TERM /WEDNESDAY THROUGH MONDAY/...
Updated 420 pm...
Highlights...
* Dry Wed with moderating temperatures
* Few rain showers possible Thu...perhaps snow showers high terrain
* Dry Fri into Sat and turning milder Saturday
* Unsettled weather may return sometime Christmas and/or Mon
Synoptic Overview...
Northern stream jet dominants the northern CONUS this period with a
parade of low amplitude short waves racing eastward across the
northern states. Streams remain separate/unphased so not expecting
any large or widespread qpf events this period.
Model Preferences...
12z guidance including ensembles are in fairly good agreement thru
Sat and then begin to diverge Christmas into early next week.
Operational EC and its ensembles are stronger with the
southeast/subtropical ridge Sun into early next week. While the GFS
and its ensembles are not as robust yielding a colder airmass
bleeding southward into New England. GEFS for whatever reason has
been lacking dispersion for sometime now with the operational run
and its ensembles very well cluster (i.e. little spread/
uncertainty). EPS at times just the opposite with lots
spread/dispersion. Nonetheless at this time range a blend of all
guid sources including ensembles is probably most skillful. Also
confluent flow and shallow cold air over northern New England into
Quebec is close to climo for this time of year.
Temperatures...
Temps should average at or slightly above normal much of this
period. As for the details...Wed will not be as cold as previous
days with 1040+ mb high currently over the area moving offshore by
then. Further temperature moderation occurs Thu ahead of approaching
cold front. Highs Thu 45-50 likely. Cooler and brisk Thu ngt into
Fri behind the front. Return flow yields milder temps Sat with both
GFS and EC offering +6c to +8c at 925 mb streaming across the
region. Blyr mixing is limited with 1034 mb surface high just
offshore. 12z EPS shows low probs of 50 degs Sat across RI and
eastern MA which seems reasonable. Cooler south coast given near
shore SSTs have cooled off into the low 40s. Then lots of
uncertainty on temps Christmas Day into early next week. EC/EPS
milder than GFS/GEFS given strength of southeast/subtropical ridge
in all 51 EC/EPS members. In fact 12z EPS has 50% probs of 50 deg
temps here Sun and 60% probs on Mon. Given time range and
uncertainty highs Sun and Mon were derived from a model blend.
Precipitation...
As mentioned above lack of amplitude and streams remaining unphased
any qpf events this period should be light and not widespread. Dry
Wed with scattered rain showers possible Thu...perhaps snow showers
across the high terrain. Dry Fri and Sat with low risk of precip Sat
night/Sun into Mon. If GFS/GEFS verify shallow cold air would pose a
low risk of freezing rain northern MA. However if EC/EPS verify
thermal profile likely warm enough to support mainly rain. Given
time range and uncertainty here followed a model blend.
&&
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
03z update...mid to low level clouds have inched a bit farther
west then previously forecast. Have entered MVFR cigs into the
latest TAF update, but conditions should improve back to VFR
overnight.
=================================================================
Short Term /through Tuesday Night/...High confidence.
Tonight...Mainly VFR. MVFR CIGS across Cape Cod and the islands,
with low end VFR CIGS into eastern Plymouth county as ocean effect
clouds move onshore on light N-NE winds. Scattered ocean effect
snow showers moving across Mass and Cape Cod Bays, occasionally
lowering VSBYS to MVFR mainly across the mid and outer Cape.
Conditions should improve to VFR from 05Z to 07Z as winds diminish
and drier air moves in.
Tuesday...VFR. Developing light south winds in the afternoon.
KBOS TAF...VFR. High confidence in TAF.
KBDL TAF...VFR. High confidence in TAF.
Outlook /Wednesday through Saturday/...Moderate to high
confidence.
Updated 420 pm...
Mainly VFR conditions through Fri time frame.
The exception to this is Thursday into Thursday evening, when a
period of MVFR-IFR conditions are possible in rain showers and
perhaps a bit of interior high terrain snow showers.
&&
.MARINE...
Forecaster Confidence Levels.
Low - less than 30 percent.
Moderate - 30 to 60 percent.
High - greater than 60 percent.
10 pm update...Seas have continued to drop over the past few
hours so have let the SCA go for the eastern outer waters. Will
need reevaluate with latest 00z on new headlines for Tuesday/Wed.
======================================================================
Short Term /through Tuesday Night/...High confidence.
Through 00Z...Have continued the small craft mainly for lingering
seas, up to 6 ft on the eastern and southern outer waters. Should
start to subside below 5 ft this evening. N-NE winds up to around
15 kt on the southern open waters will diminish as high pressure
approaches.
Tonight...High pressure moves toward the waters, so winds will
become light N-NW overnight. Seas will subside, so any leftover
small craft advisories should end.
Tuesday and Tuesday night...The high will shift offshore as the
ridge builds south of the waters. Small crafts will likely be
needed on the eastern outer waters as SW winds increase, gusting
up to 25-30 kt Tuesday night. Seas will also build up to 5-6 ft.
Outlook /Wednesday through Saturday/...Moderate to high
confidence.
Updated 420 pm...
Wednesday...modest WNW winds. Dry weather and good vsby.
Thursday and Friday...Low pressure lifting towards the Great
Lakes will generate southerly small craft wind gusts on Thu. This
low will then drag a cold front across the region Thu night/Fri
generating westerly small craft wind gusts of 20 to 30 knots
across most waters. There is a low risk for a period of gale force
wind gusts if a stronger secondary coastal low pressure develops.
Saturday...high pres slides south of New England.
Sunday...winds diminish as high pressure builds in from the
north.
&&
.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.
&&
$$
SYNOPSIS...Nocera/EVT
NEAR TERM...Nocera/Dunten
SHORT TERM...EVT
LONG TERM...Nocera
AVIATION...Nocera/Dunten/EVT
MARINE...Nocera/Dunten/EVT
Area Forecast Discussion
National Weather Service Charleston SC
1026 PM EST Mon Dec 19 2016
.SYNOPSIS...
Low pressure will develop offshore and track away from the area
as high pressure builds into the region Tuesday and Wednesday.
A cold front will push offshore Thursday Night. High pressure
will then expand into the area from the north late week and
shift offshore over the weekend.
&&
.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
Strengthening of the CAD has mostly ceased late this evening,
and isentropic lift is decreasing from south to north across the
CWA. Upglide across southeast South Carolina will continue to
produce drizzle and light showers into the early morning hours.
The HRRR is doing particularly well resolving the primary area
of showers pushing into the waters around Edisto Beach at 3Z,
and the official forecast has been adjusted to reflect the
expectation that this area of light to moderate rainfall will
continue to trek north just off the Charleston Country Coast
through the night. To the south, mainly neutral to weakly
descending isentropic motion across Southeast Georgia will
continue to slowly spread north, bringing increasingly dry
conditions to the area, and POPs have been adjusted downward
with the motion of this feature appropriately.
Temperatures are expected to fluctuate little through sunrise as
there is just enough CAA to maintain the cold airmass, but no
processes to cool it any further. Accordingly, freezing drizzle
remains very unlikely for northern Berkeley County, where dry-
bulb temps are currently in the mid 30s and not expected to
decrease any further.
&&
.SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY/...
Tuesday: Deeper moisture will continue to shift offshore bringing a
lessening chance for rain through the day. However, drizzle is still
likely given the abundant low-level moisture still in place.
Temperatures will struggle to rise much, probably only reaching the
mid to upper 40s north and west and possibly lower 50s near the
Altamaha River.
Tuesday night: Some drizzle could linger, especially in the evening
near the coast. Otherwise it should be dry with temperatures falling
to the mid 30s north and west and lower to mid 40s south and east
toward the coast. There is a very small risk of temperatures dipping
to freezing well inland and causing some patchy black ice.
Wednesday: More sunshine will lead to warmer temperatures into the
mid to upper 50s most locales, possibly lower 60s near the Altamaha
River, although this is still below normal levels.
Wednesday night: Dry and chilly weather expected with excellent
radiational cooling conditions to start the night before some higher
clouds and low-level warm advection help to temper the cooling trend
late. Most inland locales should drop to near 40 with coastal
locales closer to 50, although slightly cooler temperatures are
possible if cloud cover and/or warm advection are less and/or slow
in arriving.
Thursday: Warmer weather expected as low-level warm advection occurs
ahead of an approaching weak cold front. Weak moisture return and
upper forcing should translate to a dry frontal passage but we
maintained at least a slight chance of a shower in the forecast for
now. Temperatures should reach the lower to mid 60s north and west
and mid to upper 60s south and east, a bit above normal. If sky
cover is minimal temperatures could get even warmer.
&&
.LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
The cold front will cross the region Thursday night, and high
pressure will push cooler temps mainly in the 50s into the area
Friday. Then, the air mass will modify this weekend. Slightly above
normal temps in the 60s Saturday should give way to above normal
highs at least in the upper 60s/lower 70s as surface high pressure
shifts into the Atlantic and an upper ridge builds into the
Southeast Christmas day and Monday. As a surface trough develops
near the coast, showers cannot be ruled out across southern counties
Saturday and across the forecast area Christmas day. However,
significant precipitation appears unlikely.
&&
.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
IFR cigs will prevail at KCHS and KSAV through the period, with
periods of LIFR cigs possible in areas of drizzle. There is a
small chance of cigs near to below alternate minimums through
the early morning hours, but confidence is too low to include in
the forecast for now. Areas of fog and drizzle can be expected
at both KCHS into the early morning hours, but significant
impacts on visibility are not expected. Conditions could begin
to improve late Tuesday afternoon, but the notoriously poor
handling of cold air damming by guidance has justified leaving
any improvements out of the forecast for now.
Extended Aviation Outlook: Flight restrictions in low ceilings
through Tuesday night. VFR conditions should develop by midweek.
Brief flight restrictions could develop as a cold front crosses
the area Thursday and Thursday night. VFR conditions are then
likely Friday/Saturday.
&&
.MARINE...
Tonight: Steady north to northeast winds around 20 kt with gusts
to 25 kt or higher will persist across the coastal waters
tonight as the inland wedge persists. Small Craft Advisories
will remain in force for all nearshore and the Georgia offshore
legs. Periods of drizzle will reduce vsbys to less than 2 nm at
times.
Tuesday through Saturday: Advisory conditions expected across the
Charleston County near shore waters into early Tuesday afternoon and
the offshore GA waters into Tuesday night as strong high pressure
builds inland and low pressure develops offshore. Improving
conditions expected Wednesday as high pressure builds over the area
leading to a weaker pressure gradient. On Thursday, winds will shift
to the west-southwest and then north behind a passing cold front
Thursday night. Advisory conditions will be likely, especially late
Thursday night/early Friday into Friday night across the Charleston
County nearshore waters and through Saturday across the offshore GA
waters.
&&
.CHS WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
MARINE...Small Craft Advisory until 10 AM EST Tuesday for AMZ352.
Small Craft Advisory until 1 AM EST Wednesday for AMZ374.
Small Craft Advisory until 1 PM EST Tuesday for AMZ350.
Small Craft Advisory until 5 AM EST Tuesday for AMZ354.
&&
$$
NEAR TERM...CEB
SHORT TERM...RJB
LONG TERM...SPR
AVIATION...CEB
MARINE...CEB/RJB
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
958 PM CST Mon Dec 19 2016
.UPDATE...
A broken to overcast cloud deck between 5,000-8,000 feet has
blanketed much of the region south of a Fredericksburg to Austin
to La Grange line. Therefore, temperatures have been slower to
decrease tonight than previously forecast for these areas while
locations north of this cloud deck have fallen more rapidly.
Clouds should continue to gradually spread north throughout the
evening, leading to slightly warmer temperatures than previously
thought more in line with the ECMWF and NAM. There is still some
potential for temperatures to really bottom out for a harder
freeze over our northernmost counties if skies remain clear given
relatively calm winds, so have maintained some mid to upper 20s in
those areas. Low temperatures elsewhere should generally remain in
the lower to mid 30s, with a light freeze expected north of a Del
Rio to San Antonio to Hallettsville line. Otherwise, have only
made minor changes to the forecast based on observational trends.
&&
.PREV DISCUSSION... /ISSUED 623 PM CST Mon Dec 19 2016/
UPDATE...
00Z Aviation Update Below.
AVIATION...
VFR conditions through the TAF period. A BKN-OVC 5-8k foot cloud
deck will impact areas from DRT-SAT southward this evening and
expand north and lower slightly overnight and Tue. N to NW wind
less than 5 kts overnight at AUS/SAT and variable at DRT. A weak
SE to SW wind will develop Tue afternoon.
PREV DISCUSSION... /ISSUED 232 PM CST Mon Dec 19 2016/
SHORT TERM (Tonight through Tuesday Night)...
Main highlight through the next 36 hours will be the hard freeze
again tonight through Tuesday morning for the northern 2/3rds of
the area. A freeze warning will not be issued as it is policy that
once a hard freeze has occurred in the beginning of the cold
season, freeze warnings are not issued unless highly unusual and
frigid cold (<10-15F) was expected.
Cloud cover has held off for the most part this afternoon and
this has at least allowed for a "warm-up" into the low to upper
40s across most of the region. The Hill Country however, still
remains in the upper 30s. Tricky forecast tonight will revolve
around temperatures and cloud cover potential. Latest visible
satellite imagery reveals an overcast 7000ft stratus cloud deck
advancing north into the Rio Grande Plains to the Texas Coast this
afternoon. NAM BUFR soundings are more aggressive in bringing
this elevated cloud deck into into a good portion of the region
overnight vs. GFS BUFR soundings. The HRRR has not initialized
this cloud cover well. Isentropic upglide appears to be weakly
present in concurrence with lowering condensation pressure
deficits that hints at more cloud cover being possible through out
the overnight period. Given that dewpoints are in the single
digits and winds have fallen to 5-10 mph, cooling will happen
rapidly after sunset prior to the clouds arrival. The question
will be how much cloud cover occurs overnight to keep temperatures
elevated. Superblend guidance was too warm last night and appears
so again tonight given the much colder LAMP and do a degree, the
MET and MAVMOS guidance as well. Have lowered temps from the
superblend towards this consensus despite the cloud likelihood as
the quick temperature drops should occur prior to and during the
cloud transient status overnight.
By Tuesday, surface high pressure will begin to shift east and
then southerly winds will occur with clouds decreasing. This will
be the start of a warming phase through Wednesday.
LONG TERM (Wednesday through Monday)...
A brief warm-up period will occur into Wednesday before a dry
cold front moves through Thursday morning. This front will not be
as cold as the previous front. Another warm-up trend is expected
over the weekend with rain chances returning and south winds ahead
of another potential front late weekend or early next week.
General zonal flow will occur through mid-week with gradual low-
level airmass modification occurring. Temperatures should rebound
into the 60s Wednesday with the deeper southerly and southwesterly
flow in the SFC-700mb layer. However, a cold front will push
through Thursday morning as a strong surface high pressure and
Great Lakes trough aid in higher equatorward airmass momentum from
the north. This front is not expected to bring precipitation to
the area as PWATs only look to recover to 0.7-1". Temperatures
will fall back to below normal late week.
The effects of this front will be short lived as by Friday, return
moisture and flow will commence along the Texas coast with decent
airmass advection occurring by Saturday morning. Soundings and
isentropic surfaces appear saturated in the low-levels and this
could spell drizzle, low clouds, and fog possibilities. Streamer
type showers could occur through the day Saturday as WAA occurs
underneath a capping inversion. This trend will continue into
Sunday with highs reaching back into the low 70s and light
scattered showers being possible east of the US 281 corridor to
the Texas coast.
Models diverge early next week as to if a stronger frontal passage
will occur through the area. GFS has backed off with South-
Central Texas now remaining on the warm side whereas the ECMWF
brings the front through with a much deeper trough over the
western CONUS Christmas Day. Have blended the long-term for now
before a more clear trend can be established.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 43 31 52 36 64 / 0 0 0 0 0
Austin Bergstrom Intl Airport 44 30 51 36 64 / 0 0 0 0 0
New Braunfels Muni Airport 46 31 51 35 64 / 0 0 0 0 0
Burnet Muni Airport 41 29 51 34 64 / 0 0 0 0 0
Del Rio Intl Airport 45 33 55 37 62 / 0 0 0 0 0
Georgetown Muni Airport 42 27 51 35 64 / 0 0 0 0 0
Hondo Muni Airport 49 35 54 35 64 / 0 0 0 0 0
San Marcos Muni Airport 44 31 51 35 64 / 0 0 0 0 0
La Grange - Fayette Regional 44 30 51 36 65 / 0 0 0 0 0
San Antonio Intl Airport 47 35 53 36 63 / 0 0 0 0 0
Stinson Muni Airport 47 35 53 37 63 / 0 0 0 0 0
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Mesoscale/Aviation...Runyen
Synoptic/Grids...LH
Public Service/Data Collection...33
Area Forecast Discussion
National Weather Service Melbourne FL
901 PM EST Mon Dec 19 2016
.DISCUSSION...
Current-Tue...Frontal boundary across north-central FL to continue
to drop southward overnight into central FL, then into the southern
peninsula on Tue where it will become quasi-stationary. Scattered
shower and isolated lightning storm activity on a downward trend
over the I-4 corridor this evening. Frontal boundary, deep moisture,
and sea breeze/mesoscale boundary interactions will keep activity
ongoing into the night. However, instability and forcing remain
relatively weak. The HRRR suggests greatest pcpn chances overnight
will remain nearest the southward sagging front where LLVL
convergence remains strongest.
The juicy airmass and relative weak cool air advection behind the
front will keep overnight lows still mild. Expect lows in the middle
60s over the interior and Volusia coast, except lower 60s possible
north of I-4. Upper 60s to around 70 degrees likely along the
immediate Space/Treasure coasts.
Light winds and moisture in the low-levels will aid for fog/low
stratus cloud development overnight into Tue morning. The grunge
once it develops/builds in will be hard to erase on Tue with MOS
guidance suggesting fog lingering into at least mid morning and low
cloud ceilings around most if not the whole day for a good chunk of
ECFL.
The N/NNE flow will combine with the thick cloud cover on Tue to
keep aftn max temps in the L/M70s acrs the I-4 Corridor...lower
overall cloud cover S of I-4 will allow temps to manage into the
M/U70s, and near 80F along the Treasure Coast.
Aside from low lvl forcing in the vcnty of the frontal boundary
itself, little in the lcl WX pattern to support anything more than
30PoPs along the Space/Treasure coasts, 15 to 20pct interior...in
the form of low-topped, low QPF shras on Tue. The next forecast
shift may be able to trim this back, at least northward/interior.
&&
.AVIATION...Weak frontal boundary to slide southward into central FL
later this evening/overnight. Decreasing intensity in evening
showers, though greatest chances will remain INVOF the boundary
where LLVL convergence is best. Patchy fog to areas of fog
development with low ceilings (combined grunge) to set in later this
evening/overnight. In fact, visibility/ceilings will be slow to
improve past mid Tue morning as frontal boundary settles into south
FL and becomes quasi-stationary.
&&
.MARINE...Overnight...Weak frontal boundary to slide southward
across the coastal waters late this evening and overnight. Light
onshore winds generally south of the Cape with winds becoming NNW-
NNE behind the front northward. Wind speeds generally AOB 10 kts,
but may approach 15 kts across the Volusia County waters late in the
night. Sea fog...locally dense...continues near shore and north from
the Cape this evening with these conditions expected into the
daylight hours Tue morning. Cautionary statements to continue for
the Volusia coast out 60nm as 2-3 ft seas near shore and 3-4 ft
offshore gradually build overnight to 4-6 ft away from the coast.
South of Cape Canaveral, seas 2-3 ft near shore and 3-4 ft offshore.
Tue...previous...Marginal to poor conditions as the front stalls
over S FL with a brisk N/NE breeze dvlpg in its wake. Shallow
inverted sfc trof will help generate a moderate to fresh N/NE breeze
from Sebastian Inlet northward with seas building to 4-6FT...up to
7FT off the Volusia Co coast. South of Sebastian Inlet, light to
gentle E/NE breeze bcmg a gentle to moderate N/NE breeze with seas 2-
4FT...up to 5FT in the Gulf Stream.
&&
.MLB WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...None.
&&
$$
Sedlock/Kelly