Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/05/20
Area Forecast Discussion
National Weather Service Caribou ME
937 PM EDT Fri Sep 4 2020
High pressure will build across the region through the weekend
then exit over the Maritimes through Labor Day. There is a
stalled frontal boundary that will remain just north of the
region through the middle of the week.
.NEAR TERM /THROUGH SATURDAY/...
940 PM Update... Adjusted the temps to reflect the current
decrease due to reduced cloud cover. Otherwise, the forecast
was set up nicely by the previous.
Winds will be diminishing this evening as the pres gradient
weakens and the jetstreak aloft pushes to the east. Weak high
pres to the sw will be ridging across the region overnight. 12Z
UA showed some CAA pushing in from Canada this evening allowing
for temps to drop back by early evening. Sounding data from the
NAM, RAP and GFS show a llvl inversion setting up later in the
evening w/clear skies. This inversion will keep the stronger
winds aloft from mixing down to the sfc. A chilly night in
store and given the cooler/drier air in place, temps will drop
back into the mid 40s across the north. Upper 40s north to
lower 50s for central and downeast areas. Some low lying sites
across the NW areas could drop into the upper 30s as the winds
could go calm.
Saturday will feature sunshine in the morning, but some clouds
should develop by mid to late morning as an upper disturbance
moves across the region. There will be a jetstreak of 35-40 kts
around 700 mbs that will aid in generating breezy conditions.
Soundings show an inverted V w/dry air above 700 mbs will allow
for some gusty winds at the sfc w/0-6km shear of 25-30 kts.
Decided to increase the winds a bit to 10-15 mph w/gusts 20-25
mph. There is some llvl warming w/cooler air aloft which would
allow for instability. The sounding data from the NAM and GFS
does show CAPE of 200+ joules w/moderate lapse rates for the
potential for convection or showers. Overall the atmosphere
looks dry above 750 mbs. The 12Z GFS does show some light shower
activity late Saturday across the n and nw. However, the NAM
and GEM are dry and keep showers in Quebec. Interestingly
enough, the NAM does show moisture in the 850-700mb layer
w/decent shear which would be enough to trigger some activity.
but it keeps the region rain-free. The NAM looked to be too
aggressive w/its moisture. Using a blend of the guidance,
decided to stay w/a dry forecast, but did show 20% pops grazing
the WNW border of Maine by the afternoon. It will be tad cooler
w/daytime temps at least 3-5 degs cooler than today.
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
Fair weather can be expected Saturday evening followed by late night
increasing clouds in advance of an approaching weak short wave from
Quebec. The short wave will cross the region early Sunday but not
expecting anything more than a slight chance of a shower,
mainly across the far North and St. John Valley. Otherwise,
partly to mainly sunny skies will be the rule on Sunday with
afternoon highs in the upper 60s to lower 70s North and lower to
mid 70s central and Downeast.
As we head into Sunday Night and Monday a deep layered South to
Southwest flow will develop across the region. High pressure at the
surface will continue to move to the east. Moist Southerly flow
around the high will lead to increasing potential for marine stratus
toward the coast as we go into the overnight Sunday and into Monday.
Otherwise, fair, unseasonably warm, and breezy conditions can
be expected on Monday.
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Unseasonably warm weather is expected much of the mid week period.
A weakening cold front will approach Monday and Monday night.
The strong ridging across the Western Atlantic will not allow
the front to make much progress eastward across the region.
Looks like the next significant frontal passage won`t occur
until Friday. Until then, unseasonably warm weather can be
expected through Thursday.
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
NEAR TERM: VFR for all terminals through Saturday. W winds are
expected to increase to 10-15 mph on Saturday w/some gusts to 25
mph. The highest gusts will be across the northern terminals.
SHORT TERM: Sat Night thru Sun...VFR. SW breeze 5 to 10 kt.
Sun Night thru Wed...VFR. Except MVFR/IFR will be increasingly
possible at night into early morning hours KBHB vcnty.
NEAR TERM: The wind and seas will remain below SCA levels
SHORT TERM: Wind/seas will remain below SCA levels through mid
ME...Beach Hazards Statement from 8 AM EDT Saturday through
Saturday evening for MEZ029-030.
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
850 PM CDT Fri Sep 4 2020
Quick forecast update to retrend hourly temperatures and adjust
overnight PoPs. The HRRR and Texas Tech WRF show limited activity
for the nighttime hours as most of South Central Texas saw rainfall
today working over the atmosphere. There could still be an isolated
shower or thunderstorm, but organized activity and heavy rainfall are
not expected tonight. Have capped PoPs overnight at 20 percent for
most areas and only highlight 30 percent in areas where precipitation
is still ongoing (Williamson and Dimmit Counties), as well as along
our border with the Corpus Office, the Coastal Plains, where
additional light activity is possible by morning.
.PREV DISCUSSION... /ISSUED 626 PM CDT Fri Sep 4 2020/
Convection has moved away from or dissipated in the vicinity of the
area airports. There will be some chance for additional convection
tonight, but chances are too low to include in the TAFs. The last
line of storms moved by AUS and lowered the ceiling. As these storms
move away, the ceiling should rebound to VFR by the start of this
period. All other airports are VFR and all including AUS will be VFR
through the evening and most of the overnight period. MVFR ceilings
will develop in the Austin and San Antonio areas by early morning
Saturday and last until close to noon. There will be a chance for
showers and thunderstorms during the morning. Chances for convection
will increase during the afternoon at all airports. Showers or
thunderstorms will lower conditions to MVFR.
PREV DISCUSSION... /ISSUED 307 PM CDT Fri Sep 4 2020/
SHORT TERM (Tonight through Saturday Night)...
A pesky upper level low caught between strong western CONUS ridging
and another high over the southeast is stuck in a moist environment
with very little steering flow. This has led to widespread
beneficial rainfall for much of south-central TX as showers and
storms sporadically propagate with a general meso-alpha scale
cyclonic motion around the upper low apparent. Precipitable water
values range from about 1.6-2.1" over the area, and with freezing
levels of 13-14 kft, efficient rainfall production is evident with
measured rates of up to 2-3"/hr at times earlier today. As much as
6+" fell near Buda this morning with several additional locations
picking up 2-4" of rain. Although our southwestern Counties have
been mostly dry thus far, they should also get in on some of the
action later on as activity to the north and east slowly propagates
into the region.
In addition to the needed rain, daytime highs will be the coolest in
months across much of the area today. Persistent clouds and showers
may keep Austin from even reaching 80 degrees. Some 90s have been
observed south and west where the clouds have remained away for
The consensus among CAMS is that activity will mostly dwindle
through the evening with a bit of a lull in precipitation overnight.
Uncertainty in the evolution of convection on Saturday is rather
high, especially in terms of which areas will be favored. Most of
the guidance indicates the upper level disturbance will begin to
weaken during the day. Atmospheric moisture content will remain high
thanks to persistent low level flow off the gulf. Redevelopment of
showers and storms seems a decent bet by mid-morning, increasing in
coverage into the afternoon, but likely not reaching the coverage or
intensity of today`s activity. Should be another day of below-normal
highs in the 80s and lower 90s. By late tomorrow night, regional
guidance suggests lingering precipitation should be relegated to
primarily near the Rio Grande.
LONG TERM (Sunday through Friday)...
The upper low/trough axis responsible for the recent active weather
will be in the process of slowly weakening and shifting westward into
northern Mexico on Sunday. We should still see enough lift associated
with this feature to allow for some isolated to scattered showers and
thunderstorms to develop in the afternoon hours. With moisture levels
higher near the coastal plains, this region will be favored for
slightly higher rain chances. We will also see temperatures warm
close to climatological normals for early September, with highs in
the upper 80s to mid 90s. The influence of the upper low/trough axis
continues to wane on Monday and we will only mention a slight chance
of showers and storms across the coastal plains and Highway 77
corridor. Highs will warm slightly compared to Sunday and we should
be close to climatological normals.
On Tuesday, a sharp upper trough will drop southward into the
southern Rockies/Four-corners region. With an increase in southwest
flow aloft expected, any remnants of the upper low/trough over
northern Mexico will be picked up and advected northeastward across
the region. We should see an uptick in rainfall chances, especially
during the afternoon hours. With moisture levels higher to our east,
rain chances will be be favored east of I-35. An increase in cloud
cover should help keep temperatures in the upper 80s to lower 90s for
most of the region. It will also be humid across all areas Tuesday,
but with the expected south to southeasterly breeze and cloud cover,
heat index values are not expected to reach Advisory level.
A significant change still appears on tap for Wednesday as a strong
cold front is set to move in during the daytime hours. The extra lift
provided by the front should also set the stage for scattered shower
and thunderstorm development. Highs on Wednesday are currently
projected to range from the lower 70s in the Hill Country to the mid
80s in the coastal plains. If the cold front winds up being faster
and the rainfall coverage is higher than expected, these temperature
will be too warm. Rain chances will linger into Thursday, but should
be on the decrease as the upper level support largely remains north
of our region. Highs on Thursday will range from the lower 70s in the
Hill Country to the lower 80s across the coastal plains. Most areas
should remain dry as we head into Friday, with temperatures still
below normal under mostly clear skies.
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 83 72 89 73 92 / 60 20 40 20 20
Austin Bergstrom Intl Airport 82 72 89 71 91 / 60 20 40 20 20
New Braunfels Muni Airport 81 73 88 72 91 / 50 20 40 20 20
Burnet Muni Airport 81 70 85 70 89 / 60 30 40 20 10
Del Rio Intl Airport 94 74 91 73 92 / 40 30 30 30 20
Georgetown Muni Airport 81 71 89 71 92 / 60 30 60 20 20
Hondo Muni Airport 91 73 90 71 94 / 60 20 30 20 20
San Marcos Muni Airport 81 72 88 71 91 / 60 20 40 20 20
La Grange - Fayette Regional 85 73 91 74 94 / 70 20 50 10 30
San Antonio Intl Airport 82 74 89 73 92 / 50 20 40 20 20
Stinson Muni Airport 83 73 90 73 92 / 50 20 40 20 20
Area Forecast Discussion
National Weather Service Riverton WY
437 PM MDT Fri Sep 4 2020
.SHORT TERM...(This evening through Sunday night)
Issued at 145 PM MDT Fri Sep 4 2020
A strong upper ridge of high pressure this weekend will keep the
area dry. Record or near record high temperatures are expected
Saturday as 700 mb temperatures warm to between 16 and 18 degrees
Celsius. A weak dry cold front is expected to push south, east of
the Divide late Saturday night into Sunday morning. This will
result in temperatures at least 5 to 10 degrees cooler while
areas over the west will only be a couple degrees cooler.
The hazy/smoky skies look to remain through at least through the
day Saturday as the HRRR show some smoke pushing into the area
from the west.
The main concern will be elevated to critical fire weather
conditions for the beginning of the Labor Day Weekend. For more
details see the fire weather discussion below.
.LONG TERM...(Monday through Friday)
Issued at 200 PM MDT Fri Sep 4 2020
The cold front and strong system from Canada will be on the MT/WY
doorstep Monday morning. Winds will begin switching to the north
along far northern WY and Buffalo area around sunrise, with the
wind shift and colder air moving into central WY east of the
divide by noon. Precipitation with the system is likely to lag
behind the cold front by a few hours and not start in the far
northern Bighorn Basin and Buffalo areas until 10am-noon Monday.
Ahead of the front across southwest and southern WY, westerly flow
will respond to the pressure gradient and increase out of the
west, with the front pushing to drier air from the weekend south
into UT and CO. By 6pm Monday, 700mb temps are expected to drop
below 0C across northern WY, bringing snow to the higher
elevations and foothills. So, rain showers will move southward
through the afternoon as the initial push of the cold front gets
hung up on the divide. From 6pm to 10pm Monday night, models are
indicating the mid-level forcing to catch up with the surface
forcing and push the front strongly southward. North winds will
increase quite a bit and moderate to heavy rain will push from
northern into central WY. The surface front will also push
southward into Sweetwater County and across southwest WY. Models
are showing a very good upslope signature by midnight as well as
strong lift from frontogenesis from central to eastern WY.
Expecting snow levels to drop to the basin floors across northern
WY during the early evening, and across central WY just after
midnight. Temperatures will likely hover right around freezing at
the lower elevations for accumulating snowfall for a few hours
through sunrise. Tuesday morning will see the core of the system
move quickly down the Front Range with residual showers into the
afternoon hours and winds weakening toward the late afternoon.
Strong northwest wind will continue across southern WY through the
day though. Overall, the forecast area should see precipitation
totals ranging from about 0.25" to over 1 inch for the storm. The
Absarokas, Bighorns, and eastern Wind Rivers as well as Casper
Mountain are likely to see 3-6 inches, with the lower elevations
see anywhere from a trace around Greybull to over 2 inches around
With 700mb temps remaining -6C to -10C through the day Tuesday,
Tuesday`s high temps will be record-breaking cold in the 40s east
of the divide. As the storm moves southeastward Tuesday night,
clouds will decrease and clear for temperatures to drop Wednesday
morning. This could be a hard freeze for many areas which have not
yet seen the freezing temperatures from a week ago. The
temperatures will likely get into the low 20s in areas where snow
remains on the ground overnight with the clear skies, such as
around Lander and Casper and Jeffrey City.
Weak high pressure then starts building over the area with NNW
flow on Wednesday, warming the temperatures slightly to the 50s,
though western WY will reach the 60s. Far western WY will rebound
more quickly as that area will not be as influenced by the strong
storm. A weak mid-level system looks to move through the area from
the north late Wednesday into Thursday morning, bringing increased
clouds. Drier high pressure returns Thursday and Friday for more
seasonable conditions, though winds may shift to the north late
Friday due to a system moving into eastern MT.
Overall, a very strong early Fall storm should bring much needed
precipitation to WY late Monday into Tuesday along with very cold
temperatures. High pressure will build after the storm later in
the week to bring back normal September conditions.
.AVIATION...(For the 00Z TAFS through 00Z Sunday)
Issued at 430 PM MDT Fri Sep 4 2020
VFR conditions are expected through the forecast period. Wind speeds
will be light through 18Z Saturday. Breezy conditions are expected
after 18Z Saturday at some terminals. Dry weather will continue.
Issued AT 145 PM MDT Fri Sep 4 2020
A red flag warning is in effect across the entire area for
extremely low relative humidity, record heat, and a Haines Index
of a 6. There will also be breezy westerly winds in many
locations. The far west into the southwestern fire zones will see
red flag conditions again Sunday as windier westerly winds are
expected with continued very low relative humidity.
Areas along and east of the Divide will see a weak cold front pull
south across the fire zones. This will result in cooler
temperatures and slightly higher relative humidity. Also winds in
most places look to be marginal. Thus, have decided to keep a
fire weather watch for much of the area east of the Divide as now
the wind and relative humidity look to be marginal for red flag
conditions. Also the Haines Index in this area drops to a 3 or 4
A major cold front on Monday will bring much colder temperatures,
and higher humidity. Areas east of the Divide should see
significant precipitation with snow likely even in the lower
elevations Monday night into Tuesday morning. Areas west of the
Divide will have less precipitation, with a decent chance of a
wetting rain. Across the southwest, ahead of the cold front Monday,
elevated to possibly critical fire weather conditions could
Red Flag Warning from noon Saturday to 8 PM MDT Sunday for
Red Flag Warning from noon to 8 PM MDT Saturday for WYZ140-275-
Fire Weather Watch from Sunday afternoon through Sunday evening