Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/04/20
AREA FORECAST DISCUSSION
National Weather Service Albany NY
958 PM EST Thu Dec 3 2020
Clouds will be on the increase tonight through tomorrow, as the
combination of an approaching upper level disturbance
progressing southward across the Great Lakes and an upper level
low pressure system approaching from the Southern Plains. These
two systems may act in tandem to develop a coastal storm which
may impact portions of the region later Friday into the first
half of the weekend with some significant snow. The second half
of the weekend looks more tranquil but cooler.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
As of 955 PM EST...High pressure continues to move east of the
Mid Atlantic Coast tonight. Mid and high clouds will continue to
increase based on the GOES-16 IR imagery from the
west/northwest with a northern stream disturbance and from the
southwest from a southern stream one. Temps fell off quickly
over the southern Adirondacks, Helderbergs, portions of the
Mohawk Valley and northwest of the Capital Region, the southern
and central Taconics, as well as the sheltered valleys across
western New England into the mid 20s to lower 30s, but the winds
increasing slightly from the south/southwest and the clouds
should decrease the rate of fall and allow temps to steady or
slowly rise. Some locations in the mid Hudson Valley and the
Capital Region continue to be in the lower to mid 40s. The 00Z
KALY sounding is dry with a PWAT at 0.18" and the sfc dewpts
continues to be in the teens to mid 20s. We backed off the PoPs
some across the southern Dacks based on the latest 3-km HRRR and
NAMnest. Some snow showers may clip locations north of Old
Forge between 4-6 am. Otherwise, expect mainly virga.
Expect a weak lake response as the northern stream upper trough
approaches with some light snow showers expected to develop
with a coating to less than a half an inch. Lows will range from
the mid 20s to mid 30s, but again temps may steady or slightly
rise overnight in the warm advection with southwest flow aloft.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Winter Storm Watch for southern Vermont and Berkshires for
Saturday into Saturday night...
NCEP Model Suite and international guidance offer a variety of
solutions with some ensemble trends suggesting a little westward
track with the eventual coastal storm. The aforementioned
ingredients aloft are forecast to try phasing to commence late
Friday into Friday night. Ahead of this system, diffluence
aloft and moist cold advection will keep the clouds and threat
for additional lake enhanced snows into portions of the Dacks
through the daylight hours. Eventually, a baroclinic zone sets
up around the I84 corridor where additional precipitation should
develop throughout the day. Here, boundary layer temperatures
may remain mild enough for mostly rain to occur as highs will
generally be into the 40s with mid-upr 30s for the Dacks.
Friday night into Saturday, this is the time period of potential
impact with developing coastal storm as upper waves attempt to
phase. While we will not go into detail with all of the model
diagnosis, the NAM was discounted due to potentially not
sampling the upper wave in Canada to well due to grid domains as
opposed to the global models. Here, we used a blended approach
of the GFS/ECMWF and GEFS which suggest a little left of
guidance which points toward a bit higher QPF. The other
challenge will be temperature profiles as initially a rain/snow
mixture. Then dynamics and wet bulb process should commence
with a transition to all snow during the afternoon and evening
hours as coastal storm deepens. Combination of deformation and
upslope winds into the Catskills may result in several inches of
snow accumulations. As confidence is moderate at this time, and
close coordination with neighboring offices, we will issue a
winter storm watch for Berks and southern VT. Additional
adjustments are to be expected to the forecast so we advice
everyone to stay tuned for further updates.
This storm will quickly track into the Gulf of Maine Saturday
night with a diminishing trend of snowfall through the evening
hours, mainly for areas east of the Hudson River Valley. Then
the wind field and surface wind gust magnitudes will increase
and some potential for blowing of the snow is possible where it
accumulates. Snow density will likely be higher so where snow
does accumulate on trees, could see some weight and downed limbs
along with the increasing winds. Overnight lows Friday night
into the 30s and 20s Saturday night.
.LONG TERM /SUNDAY THROUGH THURSDAY/...
In the wake of potential Saturday storm system, lingering
cold/cyclonic flow aloft should promote areas of clouds, and at
least some scattered snow showers/flurries across the region
Sunday. There could be some embedded heavier Lake
Effect/enhanced bands as well, especially Sunday morning .
Otherwise, blustery conditions with west/northwest winds
possibly gusting up to 30-40 mph. Highs mainly in the 30s for
valleys, and 20s across higher terrain areas.
Weak low/mid level ridging builds into the region Sunday night-
Monday, with below normal temperatures expected. An upper level
disturbance and cold pool aloft may approach from the Great Lakes
region late Monday into Tuesday. Although overall moisture looks
limited, with steep low/mid level lapse rates, will include at least
slight chance/low chance PoPs for isolated/scattered snow
showers/flurries, with higher terrain areas most favored. Continued
below normal temperatures, with highs Monday-Tuesday mainly in the
30s for valley areas, and 20s across higher terrain. Overnight lows
mainly in the teens/lower 20s, with some potential for even colder
min temps in any areas where a snowpack exists and winds decouple.
Another clipper-like system may approach from the Great Lakes for
Wednesday-Thursday, with some light snow or snow showers possible,
especially areas north of I-90. Otherwise, a mix of clouds and sun
with a slight moderation in temps possible, with mid 30s to lower
40s in valley areas (warmest south of I-90), and overnight lows
mainly in the 20s, with some teens possible across the southern
Adirondacks Wednesday morning.
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
High pressure will move off the Mid Atlantic Coast tonight. A
pair of upper level disturbances will bring increasing clouds
overnight into Friday. Some showers or light rain will be
possible tomorrow afternoon into the evening especially south
and east of KALB.
VFR conditions are expected prior to 18Z/FRI with mid and high
clouds thickening and lowering tonight. Cigs will be in the 6-10
kft AGL range after 12Z/FRI some isolated to scattered very
light showers that may reach KPSF south to KPOU between 16Z-
20Z/FRI with cigs lowering to low VFR levels at 3.5-4.0 kft AGL.
After 20Z/KPOU may have MVFR cigs/vsbys with a steadier light
rainfall. KPSF we kept low VFR, but the light rain may persist
Further north, we included PROB30 groups at KALB/KGFL after
19Z/20Z, as the coverage of showers looked less certain. Cigs
will be VFR or very high MVFR at KGFL.
The winds will be light from the south to southwest at 4-7 kts
tonight. They will increase from the south to southwest at 8-13
kts in the late morning into the afternoon with a few gusts
around 20 kts at KALB.
Low level wind shear is possible tonight between 03Z-06Z/FRI,
as surface winds decrease from the south/southwest to 5 kts or
less, while winds around 2 kft AGL increase from the southwest
to 30-40 kts. We continued LLWS groups at KGFL, KPSF and KPOU
until about 13Z-15Z/FRI.
Friday Night: Moderate Operational Impact. Chance of RA.
Saturday: Moderate Operational Impact. Breezy. Chance of RA...SN.
Saturday Night: Moderate Operational Impact. Windy With Gusts To 30 kts. Chance of SN.
Sunday: Moderate Operational Impact. Breezy. Chance of SHSN.
Sunday Night: No Operational Impact. NO SIG WX.
Monday: Low Operational Impact. Isolated SHSN.
Monday Night to Tuesday: No Operational Impact. NO SIG WX.
Still some uncertainty to where the highest QPF will occur
along with precipitation types as a moisture rich coastal storm
is possible this weekend. Main impact concerns are mainly to the
southeast of Albany where initially precipitation falls as rain
then transitions to snow later Saturday into Saturday night.
Since many areas across the region received a soaking rain event
on Monday that resulted in 1 - 3 inches of rain, soils are
saturated and river levels running high. Therefore, should the
system`s precipitation shield track overhead, we will have to
monitor the potential for flooding, especially in the eastern
Catskills which received the highest rainfall amounts earlier
this week. Depending on the storm track, there could also be a
sharp QPF cut-off over our area.
For details on specific area rivers and lakes, including
observed and forecast river stages and lake elevations, please
visit the Advanced Hydrologic Prediction Service /AHPS/ graphs
on our website.
MA...Winter Storm Watch from Saturday morning through Sunday
morning for MAZ001-025.
VT...Winter Storm Watch from Saturday morning through Sunday
morning for VTZ013>015.
Area Forecast Discussion
National Weather Service La Crosse WI
518 PM CST Thu Dec 3 2020
.SHORT TERM...(This evening through Friday)
Issued at 159 PM CST Thu Dec 3 2020
With fairly quiet weather continuing through Friday, the main
concern in the short term is cloud trends. A very subtle shortwave
is currently moving into the area early this afternoon. This has
only been producing some mid to high clouds, though, so not much
impact beyond some increasing clouds for late afternoon.
Temperatures have risen into the upper 30s to 40 for most areas,
with an increase of a few more degrees possible.
Tonight, a shortwave will push south across Lake Superior into
northern Michigan. With the bulk of the forcing east of the area and
a dry atmospheric column, the only real impact will be a cold front
being dragged through from north to south during the morning hours
on Friday. Lows are expected to be in the 20s.
Friday will likely be a few degrees cooler than today given cold air
advection much of the day, with highs mainly in the 30s. Cloud cover
will be a big question, as model guidance differs considerably on
how extensive low-level moisture will be behind the cold front, with
the RAP suggesting low clouds sink southward in the morning and make
for a much cloudier day than the going forecast. Meanwhile, the
NAMNest/ARW/NMM would confine clouds to a much narrower area along
the front or even keep them entirely in far north-central WI. The
RAP forecast sounding shows very dry air just above a narrow layer
of moisture, and current obs upstream near the MN/Ontario border
where some of this moisture should currently be located per the RAP
do not show much in the way of low cloud, so will take a sunnier
approach for the time being.
.LONG TERM...(Friday night through Thursday)
Issued at 159 PM CST Thu Dec 3 2020
The stretch of quiet, early December weather looks to continue
well into next week. The only break in this looks to occur Sunday
as a strong short wave trough drops out of Canada and rolls across
the Upper Midwest. This wave looks to be pretty strong but due to
its orientation in the upper air flow pattern, does not look to
produce much more than some weak to possibly moderate pv advection
in the 500-300 mb layer. A weak area of low pressure at the
surface looks to remain east of the area as it moves south over or
near Lake Superior. Some weak frontogenesis looks to be displaced
well to the west of area ahead of where the best low level cold
air push/baroclinic zone will be. As a result, the overall amount
of lift from this system currently looks to be rather weak. Some
of the 03.12Z models are starting to suggest the potential for
some very light snow with this wave while the overall consensus is
still for a dry forecast. Given the strength of the wave,
concerned that the models might not be producing enough
precipitation and as a start, will introduce some flurries late
Saturday night through Sunday for about the eastern half of the
By the middle of next week, the flow does look to be transitioning
to more of a southwest flow pattern. Initially, this should allow
some warmer air to be pushed into the area with highs for the
middle of next week expected to reach well into the 30s and 40s.
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 518 PM CST Thu Dec 3 2020
VFR conditions expected through the TAF period with scattered mid
to high level clouds overnight. Winds will be out of the
west/southwest at just under 10 kts before becoming more
northwesterly/northerly as a cold front pushes through on Friday
morning. Guidance still hints at a thin layer of moisture pushing
in as the front moves through, which may bring in some clouds in
the 1000 to 2000 ft agl layer. However, not much in the way of
cloud cover currently upstream, despite guidance suggesting there
should be. In addition, latest guidance has trended farther east
with the deepest moisture, so any MVFR ceilings should remain over
the eastern part of Wisconsin. That said, still think at least
some lower clouds could linger through the day, so kept SCT
mention from previous forecast.
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
524 PM CST Thu Dec 3 2020
Northerly winds continue to bring dry air to the region. All
terminals will be VFR through this TAF period. Winds will be remain
from the north becoming lighter overnight and picking back up to 5 to
10 kts Friday morning.
.PREV DISCUSSION... /ISSUED 249 PM CST Thu Dec 3 2020/
SHORT TERM (Tonight through Friday Night)...
A quiet and seasonally cool Thursday is ongoing. RAP analysis at 500
mb indicates a low centered near NW OK while the trough extends back
into southeastern AZ. There were some cirrus that developed late
this morning over our northern zones in the right entrance region of
the 500mb jet that has a maxima just to the south of the low, over N
TX. This cloud cover has mostly diminished, but may fill back in
some as we head into tonight. In addition, northwest flow at the
surface has increased to 10-20 mph with gusts to 25 and occasionally
near 30 mph. This will help keep temperatures below average today,
with highs in the 50s. One or two spots south may be able to break
Overnight, the upper level pattern shows the back edge of the trough
breaking and cutting off over northern Mexico. Locally, surface
winds will weaken and another cool night is in store with lows again
expected to dip below freezing (and perhaps as low as the mid 20s in
a couple spots) over the Hill Country and some other low-lying areas
mainly north of I-10/US-90. Lows south should be in the mid-upper
On Friday, high clouds are forecast to gradually diminish. Winds
will remain more tame compared to today, and so high temperatures
should be a couple degrees warmer, in the 57-64 degree range
primarily. The aforementioned closed low over northern Mexico will
then push towards south-central TX at the end of the period,
increasing our cloud cover west on Friday night and potentially
bringing a light shower or two near the Rio Grande early Saturday
morning. However, model soundings show a dry layer below 7000 feet
and a relatively shallow (2-3000 ft) layer of saturation, so any
precipitation reaching the ground seems unlikely.
LONG TERM (Saturday through Thursday)...
Weak high pressure at the surface will remain in place on Saturday,
leading to light northerly winds for most of the region. Meanwhile, an
upper level low over northern Mexico will begin to shift eastward
into Texas. We should see plenty of mid level cloud cover associated
with this low and expect partly to mostly cloudy skies along with
highs in the lower 50s to near 60 degrees. Depending on the amount
of Pacific moisture this system is able to tap, we could see a brief
shower or sprinkle of rain across Val Verde and Edwards counties.
However, with the low-levels generally remaining dry, we will only
mention a 20-30 percent chance of rain for Saturday.
Late Saturday into early Sunday, the upper low moves across south
central Texas into north Texas. As the upper low departs, we will see
clearing skies from west to east on Sunday. As the upper low moves
east, a weak cold front will follow and move into the region on
Sunday. Despite the passage of the cold front, we will see warmer
temperatures on Sunday as we should see plenty of sunshine. Highs
will be in the upper 50s to mid 60s. Mid-level northerly flow across
the southern U.S. plains will favor a continuation of northerly winds
at the surface as we head into next week. We have eased back
slightly on the forecast highs for Monday and Tuesday, but again
with plenty of sunshine and dry air, we should manage to warm into
the 60s across most of the region.
Surface high pressure begins to slide east of the region toward the
middle of the upcoming week. With southerly winds in the low-levels
set to return on Wednesday and Thursday, temperatures will warm to
above normal levels for early December. Highs will be in the mid 60s
to lower 70s along with lows in the lower 40s to lower 50s. As of
right now, we will keep the forecast toward the middle of next week.
We do expect an upper level trough to be situated to our west, but
with model disagreement on how far south the trough axis will extend,
we prefer to keep the forecast dry at this time.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 35 61 37 61 40 / 0 0 0 - -
Austin Bergstrom Intl Airport 34 61 33 61 39 / 0 0 0 - 10
New Braunfels Muni Airport 34 62 35 62 39 / 0 0 0 10 10
Burnet Muni Airport 30 59 33 59 37 / 0 0 0 - -
Del Rio Intl Airport 35 63 40 60 38 / 0 0 20 10 -
Georgetown Muni Airport 31 60 33 61 39 / 0 0 0 - -
Hondo Muni Airport 31 63 35 61 36 / 0 0 10 10 10
San Marcos Muni Airport 32 61 33 60 38 / 0 0 0 10 10
La Grange - Fayette Regional 34 59 33 61 39 / 0 0 0 - 10
San Antonio Intl Airport 36 62 38 60 40 / 0 0 - 10 10
Stinson Muni Airport 37 62 39 60 39 / 0 0 - 10 10