Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/28/20
AREA FORECAST DISCUSSION
National Weather Service Albany NY
949 PM EDT Thu Aug 27 2020
.SYNOPSIS...
A frontal boundary will move south of the region and
become stationary near the New York and Pennsylvania border tonight,
as the showers and thunderstorms will end early this evening. Friday
will begin mainly dry, but as the frontal boundary begins to move
northward the threat for showers and some thunderstorms will
increase again late in the afternoon into the overnight period. A
widespread soaking rainfall with some periods of heavy rainfall is
expected for Saturday, but fair and dry weather will return Sunday
into early next week with high pressure building in.
&&
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
Outside of a potential isolated shower in the southern
Adirondacks into the early morning hours, mainly dry the rest
of the night with some patchy fog developing in some areas. The
cooler air has sunk south of our region and the very tight low
level temperature and dew point gradient is south of our region.
southern areas will be a little warmer than northern areas
since the northern part of the temperature and dew point
gradient is over those areas and is relatively stationary. Just
some minor adjustments to rain chances, temperatures and sky
cover through tonight. Previous AFD has a few more details and
is below...
Several wind damage reports have come in so far, but no
confirmation on any tornadoes. We did get one severe hail report
of 1.25" in Stanfordville, Dutchess Co. A few NYS mesonet
sites have received 1-2" of rain in the past 24 hrs such as
Tannersville 2.00", Red Hook 1.72", and Dover Plains 1.02" as of
6 pm.
That weak disturbance or sfc wave moves along the boundary into
early this evening, so we continued some showers and a slight
chance of thunderstorms. The front will drift south of the
forecast area overnight and become stationary. This should be a
progressive impulse in the northwest flow aloft. Some lake
enhanced or upslope showers may persist along the western
Adirondacks. The sct showers and isolated thunderstorms will end
early and some patchy fog may form if the skies clear some. The
latest 3-km HRRR has pretty much all the showery activity over
around midnight. Lows will generally be in the 50s to lower/mid
60s, as temps should not move much from present readings
especially over the northern half of the forecast area.
&&
.SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY NIGHT/...
Tomorrow...Weak high pressure builds in briefly in the northwest
flow. Some patchy fog and stratus will gradually burn off in the
late morning. The frontal boundary that became stationary over
the NY-PA into northern NJ border will begin to gradually lift
north/northeast in the afternoon. Some isolated to scattered
showers and thunderstorms may begin to develop for locations
south and west of the Capital Region in the late afternoon in
the 21Z-00Z time frame with the low-level theta-e advection and
warm advection increasing again. The mid and upper level flow
becomes more zonal late in the day. Sfc dewpts will be in the
mid 50s to mid 60s, as it will be a bit humid especially from
the Capital Region south and east. Highs will generally be in
the mid 70s to lower 80s in the valley areas, except the mid
Hudson Valley where some mid 80s are possible. Expect upper 60s
to mid 70s over the higher terrain.
Fri night...A series of short-waves in the zonal flow will
impact the region. The initial weak wave will lift the warm
front northward. PWATS begin to increase +1 to +2 STDEVs above
normal. MUCAPES are about 250-750 J/kg for portions of the
forecast area with Showalter indices 0 to -2 C. Some showers
with isolated to scattered thunderstorms are possible with the
the elevated instability. The coverage of showers and some
thunderstorms will increase especially after midnight. It will
be humid with lows in the mid and upper 50s over north of the
Mohawk Valley and Capital District and lower 60s from these
areas to around 70F in the mid Hudson Valley/NW CT.
Saturday...As the initial northern stream wave lifts north and
east of the region the showers and thunderstorms will increase
in coverage with PWATS in the 1.50-2.0+ inch range. Some
low to moderate amounts of instability will be present. Also
the right entrance region of a jet streak may tap into some of
the leftover moisture from former Tropical Cyclone Laura. The
cold front from the system approaches late in the day. SPC
continues to have southeast portions of the CWA in the Day 3
Marginal Risk /southeast Catskills, Mid Hudson Valley, southern
Berkshires and the Mid Hudson Valley/. Some strong thunderstorms
may be possible, but the amount of instability continues to be
in question which may limit and strong to severe threat (mainly
due to clouds and periodic showers). It looks like a widespread
soaking rainfall of 1-2 inches or so is possible, but we will
have to monitor for any training heavy showers or thunderstorms
for isolated flash flooding. We are not confident for a Flash
Flood Watch, as we will have to see how much rain falls from the
present convection. Overall, WPC continues a Marginal Risk in
their Day 3 Excessive Rainfall graphics. We will also keep
mention of the heavy rainfall in the HWO. Highs Saturday will
generally be in the upper 60s to upper 70s with a few lower 80s
in the mid Hudson Valley. It will be humid with dewpts in the
60s to lower 70s.
Saturday night...The cold front moves through the forecast area
with a drier and less humid air mass moving into the region.
The upper trough axis moves through shortly before of just
after midnight. We ended the threat for showers and isolated
thunderstorms prior to 06Z/SUN, and just kept some slight to low
chance PoPs in north/northwest of the Capital Region. Lows fall
back into the 50s to around 60F with a few upper 40s over the
southern Adirondacks.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
We start off the extended with the forecast area beginning to dry
out as the storm system from Saturday (discussed in the short term)
pushes out effectively placing the are on the backside of an
associated upper trough. Cooler and less humid air will advect into
the region on Sunday as a result of being on the backside of this
cyclonic flow. There is a slight chance for some diurnal orographic
enhanced clouds and showers developing during the late
morning/afternoon hours. Higher elevations are at highest risk for
any shower activity. Otherwise, expect a comfortable day under
mostly to partly sunny skies.
On Monday, a surface high pressure system will further build into
the region from the northwest. This will effectively result in
another tranquil day weather wise with comfortable temperature and
humidity levels.
Things get a bit interesting beginning on Tuesday. Global forecast
models and their ensembles are advertising a strong, fall-like
surface cold front associated with a deep upper trough extending
from central Canada southward into the north-central U.S. With
ridging to our southeast, the jet stream pattern will be configured
in a way that will allow for broad southwest flow aloft over our FA.
This will allow for the energy and moisture to stream poleward
towards our area. As that happens, the aforementioned upper
trough/surface cold front as it continues to translate eastward will
marry with energy and moisture from the southern stream. The
combination of these features will effectively increase shower and
thunderstorm chances Tuesday and Wednesday.
A secondary cold front associated with upper troughing over central
Canada into the central U.S. will swing down from Canada into the
Great Lakes region on Thursday potentially phasing with
energy/moisture from the south ultimately bringing our forecast area
another chance for showers and thunderstorms.
Temperatures will start off cooler than normal on Sunday with 850 mb
temps ~2 standard deviations below normal transitioning to warmer
than normal temperatures Tuesday through Thursday, courtesy of the
upper level setup (southwest flow aloft) discussed above.
&&
.AVIATION /02Z FRIDAY THROUGH TUESDAY/...
Greatest coverage of showers and isolated thunderstorms around
KPOU but some scattered showers around KGFL, KALB and KPSF
ending by 02Z-04Z. The rain and low level moisture will support
some MVFR to IFR ceilings but visibilities will be VFR, except
in showers through this evening. After about 02Z-04Z, MVFR
ceilings will prevail at KGFL and KPOU but IFR ceilings at KALB
and KPSF. Some MVFR visibilities in fog are possible as well at
all TAF sites developing 06Z-09Z, with fog dissipating by 12Z.
After 12Z clouds break up and VFR conditions prevail at all TAF
sites Friday morning and afternoon as weak high pressure builds
in.
Light and variable winds less than 6 Kt this evening will
become nearly calm. Winds become variable to west and northwest
at around 6 Kt Friday morning and afternoon.
Outlook...
Friday Night: High Operational Impact. Definite SHRA...TSRA.
Saturday: High Operational Impact. Definite SHRA...TSRA.
Saturday Night: Moderate Operational Impact. Chance of SHRA...TSRA.
Sunday: No Operational Impact. NO SIG WX.
Sunday Night: No Operational Impact. NO SIG WX.
Monday: No Operational Impact. NO SIG WX.
Monday Night: No Operational Impact. NO SIG WX.
Tuesday: Moderate Operational Impact. Chance of SHRA...TSRA.
&&
.FIRE WEATHER...
A frontal boundary will move south of the region and
become stationary near the New York and Pennsylvania border tonight,
as the showers and thunderstorms will end early this evening. Friday
will begin mainly dry, but as the frontal boundary begins to move
northward the threat for showers and some thunderstorms will
increase again late in the afternoon into the overnight period. A
widespread soaking rainfall with some periods of heavy rainfall is
expected for Saturday, but fair and dry weather will return Sunday
into early next week with high pressure building in.
The RH values will be high Friday morning at around 100 percent
with some patchy fog. The minimum RH values during the afternoon
will be in the 50 to 65 percent range. Expect the RH values to
increase close to 100 percent again Friday night into Saturday
morning with the showers and thunderstorms moving in.
The winds will be light and variable in direction tonight into
Friday night at 10 mph or less, except some stronger gusts are
possible with any thunderstorms.
&&
.HYDROLOGY...
No widespread problems are expected on the main stem river the
next several days.
Showers and thunderstorms may contain locally heavy downpours
into early this evening for the southeast Catskills, mid Hudson
Valley and NW CT. An isolated flash flood is possible. Flooding
of urban, poor drainage and low lying areas will also be
possible.
After a mainly dry day on Friday, more showers and thunderstorms
are expected Friday night into Saturday. High PWAT values will
allow for more heavy downpours and some isolated flash
flooding/urban flooding cannot be ruled out once again. Overall,
a widespread 1 to 2 inch soaking rainfall is possible. The
latest MMEFS guidance does not have any river points reach flood
stage.
Dry weather is then expected for Sunday into Monday which will
allow for river and stream flows to recede.
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.
&&
.ALY WATCHES/WARNINGS/ADVISORIES...
CT...None.
NY...None.
MA...None.
VT...None.
&&
$$
SYNOPSIS...Wasula
NEAR TERM...NAS/Wasula
SHORT TERM...Wasula
LONG TERM...Evbuoma
AVIATION...NAS
FIRE WEATHER...Wasula
HYDROLOGY...Frugis/Wasula
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
823 PM EDT Thu Aug 27 2020
.UPDATE...
Overall, convection has been very minimal across Se Mi this evening.
The better deep layer moisture convergence along the nose of the
strongest inflow has been focused across central Wisconsin. Recent
satellite data and model thickness fields suggest this Wisconsin
convection will be quasi stationary through the first half of the
night. Persistent west-southwest flow into srn Lower Mi overnight
will however drive some enhanced low level moisture into the area.
This will also help stall the cold front now sinking south across
metro Detroit, likely aiding in low level convergence. This and
decent elevated instability suggests there will be some eastward
development of upstream convection into Se Mi during the overnight.
Any convectively induced mid level short wave perturbation over
Wisconsin this evening will also advance into srn Lower Mi later
tonight, allowing some increase in ascent. So while a forecast update
will be issued to lower convective chances late this evening, high
chance to likely pops remain warranted overnight.
With 0-3KM MU Cape forecast to approach 2000 J/kg from the southwest
overnight, some stronger storms/isolated severe still seems
reasonable. Regional radar imagery has shown convection to favor some
training as the inflow intersects the low level theta e gradient.
Given this and with precip water approaching 2 inches overnight,
locally high rain totals remain possible.
&&
.PREV DISCUSSION...
Issued at 647 PM EDT Thu Aug 27 2020
AVIATION...
Subtle subsidence in the wake of earlier convection and some mixing
out of sfc moisture has resulted in an environment over Se Mi which
is temporarily hostile to convective development. Low level SW flow
across nrn Indiana and cntl/ern Wisconsin is allowing for upscale
convective growth attm. While the focus for more organized convective
development overnight will remain over Wisconsin, low level moisture
and higher instability is expected advect back into Se Mi from the
west, focusing along a stalled out front. So there is the expectation
for some showers and thunderstorms to expand into Se Mi from the
west during the overnight. The remnant front will develop into a warm
front by Fri morning as increased sw flow to the west drives warmer
and more moist air into Se Mi. The latest RAP and LAMP guidance
suggests this will result in some low stratus development over the
area Fri morning; MVFR with some IFR certainly possible.
For DTW...Regional radar indicates some convective initiation to the
northeast of metro this evening off a cold front. The better chances
for deep convection off this looks to remain across srn Ontario.
Chances for thunderstorms will increase markedly during the
overnight. Timing of the better TSRA potential at metro carries a
good deal of uncertainty. There does however seem to be at least a
moderate to high potential for TSRA to be impacting much of the
airspace late tonight through daybreak Friday.
DTW THRESHOLD PROBABILITIES...
* Moderate in thunderstorms overnight through Friday evening.
PREV DISCUSSION...
Issued at 327 PM EDT Thu Aug 27 2020
DISCUSSION...
A hot and humid day, as temperatures in the Detroit Metro area
climbed into the lower 90s. Fortunately, dew pts are mixing down
into the mid to upper 60 with MLcapes still hovering around 1500
J/kg (per SPC mesoscale analysis at 19z) across far eastern areas.
Additional shower/thunderstorm activity has developed along and
south of the border with the secondary moisture axis, but effective
bulk shear quickly diminishes south of I-69, so the prospects for
severe storms remains low/isolated to close out the day.
A good deal of upper level energy over the northern Rockies will
result in a significant pattern shift for the weekend, as the
digging upper level trough encompasses the Great Lakes and East
coast on Saturday, absorbing the remnants of Laura as well. It
appears the true tropical moisture will slide south of the Michigan
border, but still an opportunity for heavy rainfall Friday
evening/night with the large scale northern stream forcing and above
normal moisture/PW values already in place over Midwest.
The lead upper level energy/height falls will be sliding into the
upper Mississippi River Valley Friday morning, and this should be
sufficient to activate the warm front/left over instability gradient
over the Western Great Lakes extending east into Lower Michigan.
Granted, there is not much of a low level jet developing overnight,
but skinny MUcapes in the 1000-2000 J/kg range and subtle mid level
cooling should be sufficient with deep moisture in place (PW Values
around 1.75 inches rising up to 2 inches on Friday with 700 MB dew
pts near 5 C) to develop activity late tonight/Friday morning,
although the exact location remains problematic, but will favor
areas along and north of M-59.
Warm front attempts to lift north during the day on Friday, and
possible brief lull in activity Friday afternoon (although
confidence is low) before main surface wave and cold front arrives
Friday evening/night. With strong dynamics/wind fields (45-50 knots
at 850 MB), severe storms will be a significant concern, as majority
of models show a good deal of surface based instability, even with
the night timing setting. 0-1 KM bulk shear on the order of 20-30
knots will also support rotation, as the actual surface low or
triple point looks to be tracking close to Saginaw Bay.
Breezy post frontal northwest winds on Saturday will usher in cooler
and drier air for the Weekend, as 850 MB temps slip into the upper
single numbers. Decent agreement amongst Canadian/GFS/Euro with
sprawling high pressure persisting into Monday before next shortwave
trough is progged to move through Monday night or Tuesday. With the
main height fall center tracking through Ontario (well north of the
area), showers/thunderstorms with the fropa are far from a given.
MARINE...
Active stretch of weather heading into the weekend as a series of
fronts pass over the region. A cold front over southern Lake Huron
will continue slowly southward eventually stalling over Lake Erie
later tonight. The front will transition to a warm front on Friday
as a low pressure system begins working across the central Great
Lakes. There is a chance of thunderstorms with the warm front as it
lifts northward Friday afternoon and evening and additional chances
overnight as a cold front then sweeps across the area. Outside of
thunderstorm activity, mild air and a light gradient will keep winds
generally under 20 knots with minor wave activity. This changes on
Saturday behind the cold front as northwest flow ushers in a colder
and more unstable airmass.
HYDROLOGY...
Rounds of showers and thunderstorms are expected tonight through
Friday night, with plenty of dry periods in between. The airmass in
place will be moist/near tropical, thus any thunderstorm will
produce very heavy rainfall. Most locations will likely receive
between 1 to 2 inches of rain by Saturday morning, with any training
of thunderstorms leading to locally higher amounts (several inches)
which could lead to flooding. One round of numerous showers and
thunderstorms will likely occur late tonight into Friday morning,
with another widespread round of activity late Friday into Friday
night. At the very least, flood prone low-lying and urban areas can
expected to see minor flooding. Dry weather is expected to settle in
for the weekend.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
UPDATE.......SC
AVIATION.....SC
DISCUSSION...SF
MARINE.......DRK
HYDROLOGY....SF
You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.
Area Forecast Discussion
National Weather Service Grand Rapids MI
958 PM EDT Thu Aug 27 2020
LATEST UPDATE...
Update
.SYNOPSIS...
Issued at 325 PM EDT Thu Aug 27 2020
- Thunderstorms expected through Friday night
- Cooler beginning Saturday
&&
.UPDATE...
Issued at 958 PM EDT Thu Aug 27 2020
Tstms are expected to become more numerous toward/after midnight
in the vicinity of the I-96 corridor, then become widespread
after 3-4 am. This is where best moisture pooling and moisture
flux convergence at 850mb is shown in the latest RAP updates.
Even though the low level jet is only around 20kts, H8 dew points
are in excess of 15C and PWATs are over two inches - about as good
as it gets. Feel the main threat overnight is heavy rain and
localized flooding, with severe weather a lower threat.
Considerable flash flooding has been occurring upstream in south
central WI this evening, indicative of just how moist the
atmosphere is. Fortunately we have been very dry here in srn Lwr
MI and soils are quite dry, but if the type of rain rates that
have been occurring upstream in WI set up in our area later
tonight, there could still be some issues by daybreak.
&&
.DISCUSSION...(This evening through next Thursday)
Issued at 325 PM EDT Thu Aug 27 2020
-- Thunderstorms expected through Friday night --
We`re in the middle of an active period. A stationary boundary
extends from central Wisconsin east across central Lower this
afternoon and will remain there until a cold front sweeps east
across the state Friday evening.
Latest radar shows a decaying line of showers and storms extending
from Wisconsin across he northern CWA. Shear is generally around 45kts
north of M-46 but substantially less than that south of there. Thus,
if we`re going to see any severe storms this afternoon, it would be
over the northern cwa. Water vapor imagery shows a short wave moving
across the Straits and so we`re about to be in a AVA area which
should act to keep a lid on storms.
The bigger show is likely tonight out west in the Plains. A strong
LLJ develops and intersects the frontal boundary and a 75kt mid
level jet sweeps in from the west. We could see a forward
propagating MCS develop and move east into Wisconsin late tonight.
However, the LLJ decreases when it reaches eastern Wisconsin. How
much momentum the MCS has will determine what, if anything makes it
into Lower Michigan. Certainly, we could see some storms Friday
morning but the higher likelihood is later in the day ahead of the
cold front. Strong moisture pooling ahead of the front...PWATs
around 2.4 inches...coupled with max heating should fire storms over
Wisconsin again which would then move east late afternoon/early
evening. The LLJ rapidly increases ahead of the front to around
60kts and so chances for severe storms will increase as the
afternoon progresses. Given the high precipitable water values,
heavy rain is a real threat and localized flooding is a possibility.
Once the front moves through after 06z, the rain will end.
-- Cooler beginning Saturday --
H8 temps will fall from 20c ahead of the front late Friday to around
10c behind the front Saturday afternoon. This will set the stage for
a prolonged period cooler weather with highs in the 70s. Lows in the
50s will begin Saturday night and continue through next week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 807 PM EDT Thu Aug 27 2020
Hard to nail down the specifics in the TAFs when it comes to
convection, but in general have played it as follows: Tstms
becoming scattered to numerous after 03Z from MKG to GRR to LAN,
then fairly widespread/persistent for this same area from roughly
08Z to 14Z. MVFR is likely once the storms become more
widespread, with IFR to LIFR vsbys also possible when heavier
downpours are occurring.
Some uncertainty if the I-94 TAF sites (AZO/BTL/JXN) will see
much tstm activity or if most of it will be just to the north
(along and north the I-96 corridor), so did not go with any
periods of prevailing thunder for these sites in this update.
This area should still, however, get at least a period of lower
MVFR to IFR cigs early Friday.
Friday morning showers and storms expected to diminish by Noon
but additional storms expected to return by later in the day,
probably after 20-21Z.
&&
.MARINE...
Issued at 325 PM EDT Thu Aug 27 2020
Thunderstorms could be locally strong to severe and pose a threat to
boaters tonight through Friday night.
Wind and waves will increase Saturday behind a cold front. A Small
Craft Advisory will likely be needed then.
&&
.HYDROLOGY...
Issued at 321 PM EDT Wed Aug 26 2020
Another 1-1.5 inches of rain fell earlier today along parts of the
US-10 corridor, which is the same area that received the heavy rain
yesterday as well. The soils in these areas will be able to handle
less rainfall over the next day or so, making flooding more of a
possibility. Unfortunately, it looks like somewhere between this
area and the I-96 corridor will be in line for another round of
heavy rain (1-2 inches possible) late tonight into tomorrow morning,
which will lead to the possibility of localized flooding.
By Friday evening, the highest risk for heavy rain may shift a bit
further south (south of a line from Grand Rapids to Lansing) which
would be helpful as soils in this area are much drier as they
haven`t had recent heavy rains. Nevertheless, a quick 2-3 inches of
rain - especially near the cities and urban areas - would result in
localized flooding and ponding of water on roads and in low spots
and other poor drainage areas.
When all is said and done, by Saturday morning, most parts of West
Michigan will likely have seen at least an inch or two of rain since
the start of this period of active weather earlier in the week. No
river flooding is expected at this time, as water levels are
currently very low and there is lots of space in the rivers to
handle any runoff.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&
$$
UPDATE...Meade
SYNOPSIS...04
DISCUSSION...04
AVIATION...Meade
HYDROLOGY...AMD
MARINE...04
Area Forecast Discussion
National Weather Service Houston/Galveston TX
625 PM CDT Thu Aug 27 2020
.AVIATION...
Some SHRA activity generally W of SGR will dissipate early this evening.
Could see some more SHRA development overnight as a weakness moves across
the area. With daytime heating, might see better SHRA/TSRA coverage
in the afternoon with the best concentration possibly setting up in/around
the coastal counties in association with the sea breeze front. Things
should quiet down in the evening. Mostly VFR except in/around the possible
SHRA/TSRA. Light and somewhat variable winds tonight becoming SSW then
S at around 10 knots as the day progresses tomorrow. 42
&&
.PREV DISCUSSION... /ISSUED 325 PM CDT Thu Aug 27 2020/
SHORT TERM [Tonight Through Friday]...
Am still expecting scattered showers and thunderstorms to develop
later this afternoon into the evening as a weak trough of low
pressure lingers in the wake of Laura coupled with strong heating.
There should be a gap in precipitation for the rest of the evening
but showers will again be possible late tonight into the early
morning hours of Friday due the weakness aloft and some speed and
directional convergence along the coast. The 17z HRRR is
increasingly bullish with what looks like a feeder band into Laura
developing near or just off the upper Texas coast. Overnight lows
will be on the warm side with low temperatures only falling into the
mid and upper 70`s.
On Friday, 850 mb temperatures are very warm and bringing these
values down dry adiabatically produces high temperatures in the
upper 90`s to around 100 degrees. There won`t be a tremendous amount
of mixing so dew points will remain moderate to high. Heat index
values will range between 105-110 degrees and a Heat Advisory may be
needed over parts of the area tomorrow. Held back on issuing the
Advisory because the strong heating coupled with PW values between
2.00 and 2.20 inches will yield some aftn storms. Convective temps
are in the middle 90`s and only weak capping is noted, so aftn
storms might be just enough to cool things off. Any late afternoon
convection will wane with the loss of heating early Friday
evening.
43
LONG TERM [Friday Night Through Thursday]...
With the departure of Laura, which should weaken to Depression
status by Friday night as it takes a more northeastward
trajectory, we should begin to experience a gradual return to a
more typical summertime weather pattern heading into the weekend.
As surface high pressure re-establishes dominance over the eastern Gulf
of Mexico and an upper ridge begins to build into the central
CONUS, look for a return to onshore winds by Friday evening. Low-
level moisture transport should remain steady through the weekend
with global models in general agreement showing surface PW values
near or above 2.0 in. With daytime highs on course to stay in the
mid to upper 90s across most of the area and forecast soundings
indicating convective temperatures in the vicinity of these
values, conditions should be favorable for the development of
scattered to isolated showers and thunderstorms through the
weekend and into the beginning of next week. Have generally
maintained PoPs from the previous forecast package during this
time with values reaching the 30%s and 40%s during the afternoon
hours. Daily activity should dissipate upon the loss of daytime
heating.
The prevailing ridge axis should exit eastward by Tuesday as an
upper trough axis digs into the central plains. 12Z GFS/ECMWF
runs still showing significant differences in the timing of this
feature, with the latter solution being the slower of the two. 12Z
ECMWF continues to bring a surface cold front to the doorstep of
the CWA by Wednesday afternoon, but keeps the boundary to our
north. Currently have included only slight chance PoPs in the NW
counties as a result.
Heat will continue to be a concern in the coming week. Look for
max heat index values to climb into the upper 100s and potentially
exceed advisory criteria through the weekend and into the middle
of next week. We`ll likely need to consider the issuance of Heat
Advisories in the coming forecast packages. It will remain
important to practice heat safety if you`re heading outdoors in
the coming days.
Cady
MARINE...
Marine conditions will continue to improve today and tonight. Winds
and seas are now below Small Craft Advisory criteria and thus the
SCA has been discontinued for Galveston Bay and Caution Flags will
replace the Gulf waters` SCA. Along the coasts, the Coastal Flood
Advisory for the Matagorda island will be allowed to expire at 3 PM
CDT today. The Coastal Flood Warning for the Galveston Islands and
Bolivar Peninsula will expire at 3 PM CDT and based on the current
conditions along these areas, will be followed by a Coastal Flood
Advisory which will be in effect through at least midnight CDT
tonight.
For this weekend, winds of 15 KTS or less and seas of 2-4 FT are
expected across the Gulf waters. A surge of tropical moisture will
move into the region Sunday night and will lead to an increase of
shower and thunderstorm activity. By early next into midweek, winds
will strengthen to 15-20 KTS and may require Caution Flags for the
bays and Gulf waters. In response to the stronger winds, seas will
rise to around 4-6 FT. Winds and seas will relax as we approach the
end of the work week.
Elsewhere in the tropics, there are two tropical waves...one located
in the far eastern tropical Atlantic near the Cabo Verde Islands and
another over the central tropical Atlantic. Formation chance for
both tropical waves are low (30% or less) at this time, but may
increase in the next several days. Mariners should continue to
monitor the progress of these two features. 24
&&
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 78 100 77 99 76 / 20 20 20 10 0
Houston (IAH) 81 97 79 97 80 / 20 40 30 30 20
Galveston (GLS) 84 93 84 93 83 / 40 40 30 40 30
&&
.HGX WATCHES/WARNINGS/ADVISORIES...
TX...Coastal Flood Advisory until midnight CDT tonight for the
following zones: Galveston Island and Bolivar Peninsula.
GM...NONE.
&&
$$
Area Forecast Discussion
National Weather Service Lincoln IL
847 PM CDT Thu Aug 27 2020
.SYNOPSIS...
Issued at 315 PM CDT Thu Aug 27 2020
Heat and humidity will continue through tomorrow, before a cold
front pushes south through Illinois Friday night. Isolated showers
and thunderstorms will be possible into this evening, then storm
chances return Friday afternoon and overnight. A few storms could
become severe Friday night ahead of the cold front.
&&
.UPDATE...
Issued at 847 PM CDT Thu Aug 27 2020
While the center of tropical depression Laura is expected to pass
through the southern tip of Illinois Friday, bands of showers and
thunderstorms circulating around the system could push into
southeast IL after midnight, mainly south of I-70, but possibly up
to around I-72 by sunrise. Direct impacts due to heavy rainfall or
severe weather are not expected through tonight. Moisture
associated with the system, however, could become a factor later
in the day. The warm, moist air mass overnight should limit lows
to the low to mid 70s tonight. Current forecast grids are on track
overnight, however have trimmed out evening PoPs and sent updates.
&&
.SHORT TERM...(This evening through Friday)
ISSUED AT 315 PM CDT Thu Aug 27 2020
High clouds advancing well ahead of the remnants of Laura are
covering the southern half of Illinois, with an east-west line of
storms just beginning to form west of Evansville. That line is
drifting northward and appears poised to advance into our
southeast counties later this afternoon. CAMs are pointing toward
an expansion of the convection also starting to bubble up along a
convergence line from west of Springfield to Champaign. That line
of storms is expected to quickly drift off to the northeast and
dissipate by 8-9 pm this evening. Have therefore continued the
downward trend in PoPs across our counties early this evening.
Another wave of showers/storms are expected to progress northward
into our southern counties just before sunrise on Friday, with our
areas south of I-72 under the threat of storms all day on Friday.
Slight chances of storms will be present north of I-72, as the
airmass remains hot, unstable, and with high moisture content. One
more day of high heat is on tap for Friday, with highs in the low
90s north and mid to upper 80s south. Heat indices should remain
below advisory criteria of 105F, but it will be uncomfortably hot
in any areas that see sunshine on Friday.
.LONG TERM...(Friday night through Thursday)
ISSUED AT 315 PM CDT Thu Aug 27 2020
A cold front will progress south through our CWA Friday night, as
the remnant low pressure center from Laura pass across the tip of
southern Illinois. A wave of showers/storms will likely be
ongoing in our southeast counties Friday evening before the front
reaches our NW counties toward 10 pm. SPC has continued with the
Slight Risk north of I-72 and Marginal Risk south of there for the
cold frontal passage. While 0-6km wind shear levels at 40-45kt are
sufficient for rotating updrafts, marginal MUCAPE instability of
1000-1500 J/kg may be a limiting factor with that severe event.
There may actually be some decent severe potential with a line of
storms the HRRR is showing for late afternoon from McLean to
Vermilion counties. That will bear watching.
For the FROPA portion of the event, the NAMnest is showing a
broken line of supercells reaching Knox county around 10 pm, then
progressing south toward I-72 as it dissipates. The HRRR develops
a line over our NW counties late evening, then drifts that south
through 2 am. Plenty of variation with even other models showing
similar timing but limited convection ahead of the front. Will
monitor for updates to timing and storm severity potential.
A noticeable change in air mass is on tap behind that Friday
night cold front. Highs will remain mainly in the lower 80s with
even some upper 70s for highs on Tuesday. Periodic rain and storm
chances will be present from late Sunday night through Thursday,
as zonal to northwest flow provide a steady feed of shortwaves
next week. Rainfall amounts for the week could accumulate up to 2"
in portions of our area, that have been primarily dry for several
weeks.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 624 PM CDT Thu Aug 27 2020
After early evening diurnal cloud cover dissipates this evening,
lowering cloud heights expected through central IL terminals,
especially I-55 southeastward, and at least low chances for
showers and thunderstorms developing from 12Z onward.
Nevertheless, predominantly VFR conditions should continue
through the period, with chances for thunderstorms too low for
mention except at KCMI after 16Z where VCTS mentioned in current
TAF. Winds SE-SSW up to 12 kts through the period.
&&
.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...37
SYNOPSIS...Shimon
SHORT TERM...Shimon
LONG TERM...Shimon
AVIATION...37
Area Forecast Discussion
National Weather Service Marquette MI
746 PM EDT Thu Aug 27 2020
.SHORT TERM...(This evening through Friday)
Issued at 412 PM EDT THU AUG 27 2020
WV imagery and RAP analysis indicated a mainly zonal pattern across
southern Canada and the northern CONUS. Upstream shortwaves were
located over southern Alberta and the northern Rockies. At the
surface, a ridge extended from northwest Ontario into the western
Great Lakes while a trough was developing over the western Plains.
Fair weather cu prevailed over most of Upper Michigan with some
thicker sratocu over the east.
Tonight, favorable radiational cooling with mostly clear skies
before clouds thicken over the west and south late, and light winds
will allow temps to drop into the lower 50s inland. With afternoon
dewpoints around 60, patchy/areas of fog is likely to develop.
Friday, as the upstream shrtwvs approach and a sfc trough/low
strengthens along with WAA and moisture advection, showers will
spread across Upper Michigan from the southwest. Strong 300k-305k
isentropic lift with upstream 850 winds to 30-40 knots and 850 mb
dewpoints to around 14C (PWAT to 1.75 inches), may support some
moderate to locally heavy rain. With MUCAPE values only into the 500-
1000 J/Kg range over the south half, mainly sct/isold embedded
elevated tsra are expected. The models show significant
variability in the strength/position of the developing sfc low
over the U.P. or northern WI and location of the larger QPF. For
now, expect the heaviest rain is expected over the south, closest
to the 850-700 mb front and instability.
.LONG TERM...(Friday night through Thursday)
Issued at 325 PM EDT THU AUG 27 2020
By the start of this forecast period, a good portion of the precip
should already be winding down, albeit still ongoing, especially
in the south-central and east. As the night progresses and this
convection moves east of the area, the well-advertised Canadian
trough axis trekking across Ontario and its associated cold front
may very well continue to trigger additional showers, with thunder
not completely out of the question. Once the axis passes though, a
socked-in type situation looks to set itself up with LL stratus
and/or drizzle lingering across portions of the northern half of
the U.P. as moisture wraps around the backside of the departing
low, with an assist from Lake Superior under NW flow. By the time
Sunday rolls around, expect a pleasant, benign weather day as
ridging/high pressure briefly takes over.
The deterministic models really can`t make up their minds on
what`s going to eventually evolve as a deep trough traverses along
the U.S./Canadian border early next week. Between the three long-
term deterministic models as well as from model run to model run
of each respective model, it`s either going to trigger rapid
cyclogenesis in the northern Plains (although now the 12Z GFS
depicts this cyclogenesis occurring as it crosses western Lake
Superior) that tracks across the U.P. northeastward into Ontario,
or a weak disturbance that simply becomes absorbed into the
overarching system as it passes across the Upper Great Lakes.
Regardless of whichever solution comes to fruition, it`s safe to
say that precip is anticipated as another cold front marches
through. The finder details will need to be refined over the
coming days as models finally (hopefully) come into better
agreement with reality.
Temperatures through the long-term forecast period will remain
near or below normal for this time of year, with a cooldown seen
at the start behind the aforementioned fropa. Highs in the 60s and
70s will dominate into next week with a slight warming trend early
next week ahead of the latter fropa. For Saturday night into
early Sunday, those with sensitive plants and vegetation in
interior locations may want to consider that lows may dip to as
cool as near 40 degrees.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 745 PM EDT THU AUG 27 2020
VFR conditions will continue tonight into tomorrow morning. Fog
chances look to be less than what they were earlier today, so they
were left out of the TAFs. Cigs and vis will lower as rain moves in
from the west Friday morning and afternoon; KIWD should see MVFR
conditions start in the late morning, with LIFR conditions setting
in by early afternoon. KSAW should see MVFR conditions by late
afternoon, with LIFR conditions moving-in by early evening. While
not mentioned, there is a small chance for thunderstorms near KIWD
and KSAW, with the greatest chance near KIWD. KCMX should not have
to worry about thunderstorms, and conditions look to only drop to
MVFR then IFR by late afternoon.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 412 PM EDT THU AUG 27 2020
High pressure then will briefly take over tonight into Friday as
winds diminish blo 15 knots. Winds will increase to around 20
knots over the west as one low pressure wave moves through to the
south. Another low pressure system follows over Lake Superior on
Saturday morning as NW winds increase behind cold-air advection.
Expecting gusts to around 30 knots, with some gale-force gusts to
35 knots expected. Winds relax again on Sunday below 20 knots
before a cold front approaches Lake Superior Monday night as winds
increase from the south to around 25 knots ahead of it.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
Beach Hazards Statement until 9 PM EDT this evening for MIZ006.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...JLB
LONG TERM...lg
AVIATION...TAP
MARINE...JLB
Area Forecast Discussion
National Weather Service Nashville TN
736 PM CDT Thu Aug 27 2020
.UPDATE...
FOR EVENING DISCUSSION.
&&
.DISCUSSION...
Results from the OHX 00Z sounding show that our instability and
moisture have increased significantly, and also our shear values.
The lifted index this evening sits at -7 and the CAPE is a robust
2,711 J/kg. Precipitable water is up to 2.01 inches, and even the
0-3 km SRH has crept up to 105. Scattered convection is ongoing
across Middle Tennessee, although there are no warnings currently
in effect. The HRRR does show some convection persisting
throughout the night before the activity starts to increase in
earnest tomorrow with the approach of Laura`s remnants. At this
time, the center of Tropical Storm Laura is situated just south of
Little Rock with a central pressure of 992 mb. The low is
expected to turn northeastward overnight and continue toward the
ENE during the day tomorrow, and this is when we`ll start to see
our greatest impacts here in Middle Tennessee. As for now, the
hourly grids are holding up reasonably well, so no major forecast
changes are planned at this time. We`ll keep isolated POP`s in
for the overnight period to handle any convection that does
develop.
&&
.AVIATION...
00Z TAF DISCUSSION.
CKV/BNA/MQY/CSV...VFR conditions expected thru 28/18Z. MVFR to
IFR vsbys 28/18Z-28/24Z as what is expected to be then Tropical
Depression Laura moves across NW portions of mid state region.
Will mention VCSH thru at least 28/06Z all terminals as
uncertainty continues on actual movement of shwrs across terminal
locations, but can certainly not rule out in vcnty. Expect more
pronounced chance of shwrs/tstms from 28/11Z-28/24Z. Will mention
VCTS here also due to continuing uncertainty to actual movement
across terminals, but can not rule out in vicinity. Consensus
model solution depicting moderate shwrs, heavy shwrs CKV,
impacting terminals 28/18Z-28/24Z, but direct impacts from tstms
remain uncertain, thus VCTS remarks continue. Initial light
E/SE winds will become predominately S sustained 10-15 kts after
28/11Z with gusts 25-30 kts possible.
&&
.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION......08
AVIATION........JB Wright
Area Forecast Discussion
National Weather Service Reno NV
316 PM PDT Thu Aug 27 2020
.SYNOPSIS...
Isolated thunderstorms are expected in eastern California Friday
and Saturday, and possibly into portions of western and west-central
Nevada on Friday. Slightly above average afternoon temperatures are
expected through the weekend with cool starts to each day. Winds
will remain generally light through the weekend.
&&
.DISCUSSION...
The main changes to the forecast were to add isolated thunderstorms
to portions of Pershing and Churchill counties Friday afternoon
and evening and to introduce 5-10% chances for showers to that
same area late tonight and Friday morning.
Currently, cumulus with very isolated thunderstorms have developed
north of Susanville and Gerlach as deformation around a northern
CA upper low combines with weak surface convergence to promote
building convection. Any activity should dissipate by dark.
However, late tonight into early Friday there are simulated signs
of elevated convection out in the west-central NV basin and range
as the upper low`s deformation axis drops farther south and possibly
combines with a lower level boundary. This is most prominent in the
NAM; however, the HRRR has also started showing signs of possible
convection by around 3-4 AM Friday although most of the HREF members
do not. With only a few models showing nocturnal convection, confidence
is quite low so chances were left at between 5-10%. It may wind
up just being some high-based altocumulus with a few castellanus
mixed in.
Friday afternoon and evening, the deformation axis hangs around with
isolated showers or thunderstorms expected in eastern CA and portions
of the Sierra. There is also an increased chance for a few showers
and/or thunderstorms out in western and west-central Nevada. The HRRR
has been especially bullish on convection in Pershing and Churchill
counties, with a few possible cells working back into the Reno-Sparks
and Virginia City areas. As with the nocturnal convection, the HREF
(except for the HRRR) is much less promising away from the Sierra
so confidence remains low. Still, isolated showers/storms were
introduced to west-central Nevada as that is the area of heaviest
simulated HRRR coverage Friday afternoon/evening...with a 10%
chance brought west to the Reno-Sparks area (at least some building
cumulus expected).
Saturday, the deformation looks to weaken considerably as the upper
low drops to the south towards the central CA coast. This is expected
to lessen the threat for showers/storms except for the Sierra south
of Hwy 50 and possibly in the favored convective formation area near
and northeast of Truckee (in CA).
Sunday and Monday, a ridge of high pressure looks to slowly build
over northeast CA and western NV from the northeast Pacific. It is
expected to increase in strength next Tuesday through Thursday.
This is expected to bring an end to the threat for showers and
thunderstorms next week, with temperatures around average through
Monday rising to above average by Wednesday and Thursday. For
Tuesday, there remains some uncertainty with the range of highs
between the upper 80s and mid 90s for lower valleys. With both
ends of the range possible, current highs for Tuesday are taking a
middle of the road approach. -Snyder
&&
.AVIATION...
The showers and thunderstorms yesterday evening brought a welcome
relief from the wildfire smoke, but we can see out the window to the
north smoke starting to drift back into the region. Satellite imagery
confirms this is primarily impacting areas north of a Lake Davis-
Pyramid Lake-KLOL line. Weak westerly flow this afternoon could bring
a bit more smoke into these regions, with lighter north northwest
flow bringing it south into the Greater Reno-Sparks-Carson City
areas overnight as evidenced in the HRRRx near surface smoke model.
Most locations will likely stay VFR at the surface, but anticipate
localized MVFR with definite slantwise degradation and potential
terrain obscuration, especially in the immediate vicinity of any
wildfires.
Otherwise, generally light winds today and Friday with VFR conditions.
Isolated thunderstorms are possible in far northeast California into
northern Nevada near the Oregon border. Gusty and erratic outflows
along with brief heavy rainfall are the greatest concerns. On Friday,
additional storms are possible along the Sierra north into northeast
CA, with a low chance also extending out into west-central NV along
a deformation axis of a weak upper low. With little storm motion,
storms will likely follow the terrain with less than a 10% chance
of direct impacts at any of the terminal sites. -Dawn
&&
.FIRE WEATHER...
Isolated thunderstorms are possible again this afternoon mainly from
north of Susanville into far northern Nevada near the Oregon border.
While storms are not anticipated directly over ongoing fires (less
than a 10% chance), outflows and enhanced plume growth could certainly
impact wildfires.
We are likely to see additional storms on Friday along the Sierra
into northeast California, which could impact ongoing wildfires.
With light to slightly easterly flow, storms are likely to hug the
terrain and be on the wetter side, but erratic outflow winds remain
a concern. Otherwise, lingering deformation could allow a few storms
to form through the central Nevada Basin and Range as well.
Winds aren`t looking as strong for Sunday into Monday, which is good
news. Northerly wind gusts of 20-25 mph are possible, corresponding
with a fairly dry airmass (min RH values 8-12%), so locally critical
conditions are possible. At this point there is a 1 in 5 chance we
could see stronger winds with gusts up to 30 mph. -Dawn
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno