Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/22/21
Area Forecast Discussion...UPDATED
National Weather Service Brownsville TX
701 PM CDT Thu Oct 21 2021
.DISCUSSION...Updated for latest aviation discussion below.
&&
.AVIATION...The afternoon sea breeze has cleared the RGV and is
producing only some isold conv over Zapata County. So expect the
short term to remain rain free for the time being. The surface
winds will decrease later tonight which will combine with the
elevated surface dewpoints to allow for some increased potential
for fog formation across mainly the northern Ranchlands later
tonight into Fri morning. Some of this may creep into the RGV
impacting the airports for a couple of hours tomorrow morning
possibly resulting in some MVFR/IFR vsbys. This should be pretty
short lived after sunrise with increasing daytime heating. The sea
breeze tomorrow may fire up some afternoon conv in the BRO area
and will include a PROB30 group during the afternoon hours.
&&
.PREV DISCUSSION... /issued 307 PM CDT Thu Oct 21 2021/
SHORT TERM (Tonight through Friday Night): Quasi-zonal mid-level
flow will persist through much of the short-term period. Tonight
should be mostly clear to partly cloudy, with generally a dry and
stable atmosphere in place. However, latest run of the HRRR was
indicating showers/storms developing just south of the river late
this afternoon or early this evening, then dissipating before
crossing over into the RGV. Currently kept PoPs out of the
forecast tonight, but will continue to monitor trends. Otherwise,
a fairly inactive night is in store with low temperatures dropping
into the upper 60s or lower 70s. Patchy to areas of fog may
develop again after midnight tonight, mainly across the Northern
Ranchlands and western portions of the CWA. At this time, a Dense
Fog Advisory is not anticipated.
As surface ridging over the Plains continues to slide southeast over
the lower Mississippi Valley over the next 24 hours, winds will
begin to veer from east to southeast by Friday evening, but will
remain generally light. Conditions look favorable for seabreeze
activity to get going in the afternoon, though still some
questions remain on just how convectively active the seabreeze
will be as low to mid-level dry air begins to erode by the
afternoon. Weak shortwave troughs embedded in the mid-level flow
may help to assist in shower development, mainly in the afternoon.
So, decided to keep in 20-30% PoPs for most inland locations
tomorrow in the form of spotty showers and thunderstorms. Slightly
better rain chances will occur Friday night into Saturday
morning, especially near the coast, as a shortwave trough slides
closer to the CWA. There is still some uncertainty on how Friday
night will play out, but will keep PoPs generally 20-30% Friday
night.
A Coastal Flood Advisory remain in effect between 3 PM today and 4
AM Friday morning. High tide is scheduled to occur at 6:17 PM CDT this
evening. As of this writing, water levels at SPI Brazos Santiago
are still about 0.8 feet above predicted levels (observed at 0.68
feet MHHW). Minor flooding will be possible, especially along
narrow parts of SPI and Boca Chica beaches this evening and
overnight tonight. Another Coastal Flood Advisory may be needed
for Friday afternoon/evening.
LONG TERM (Saturday through Thursday): A nearly zonal flow will
prevail over deep south Texas with the weekend as a pair of modest
short waves transverse over the CWA in the mid to upper level flow.
However, rain chances should remain fairly limited as PWATs between
1.5 to 1.7 inches with isolated convection possible over the coastal
waters. Rain chances are expected to increase Monday into Tuesday as
deep tropical moisture surges into the region. The latest GFS
suggest PWATs quickly jump to near 2.4 inches, especially along the
coast, by Monday night. The deep moisture then shifts northeast late
Tuesday as drier air filters into the area. A large 500mb trough
will swing over the Plains mid to late week pushing the associated
cold front into deep south Texas by late week. Above normal
temperatures are expected through much of the period, except
temperature may be lower on Tuesday due to increase cloud cover and
rain chances.
MARINE (Now through Friday night): Broad surface ridging over the
Gulf will keep marine conditions mostly favorable through the
short term period. Light to moderate east/northeast winds will
gradually shift southeasterly by Friday night. Gulf seas will
likewise remain tame, with significant wave heights ranging
between 2 and 3 feet. Showers and thunderstorms will be possible
beginning on Friday as weak surface & midlevel troughing
approaches the waters.
Saturday through Tuesday...Moderate onshore flow and low to moderate
seas will prevail along the lower Texas coast through the period.
However, brief periods of small craft exercise caution conditions
may be possible at times this weekend.
&&
.PRELIMINARY POINT TEMPS/POPS...
BAYVIEW/PORT ISABEL 71 85 73 87 / 10 30 20 20
BROWNSVILLE 71 89 73 89 / 10 30 20 20
HARLINGEN 68 89 71 89 / 10 20 20 20
MCALLEN 71 91 73 91 / 10 20 20 20
RIO GRANDE CITY 70 92 71 94 / 10 20 20 10
SOUTH PADRE ISLAND 77 82 78 83 / 10 30 20 20
&&
.BRO WATCHES/WARNINGS/ADVISORIES...
TX...Coastal Flood Advisory until 4 AM CDT Friday for TXZ256-257-351.
GM...None.
&&
$$
This product is also available on the web at:
https://weather.gov/rgv
60-Speece/69-Farris
Area Forecast Discussion
National Weather Service State College PA
1116 PM EDT Thu Oct 21 2021
.SYNOPSIS...
Low pressure will track north of Pennsylvania through tonight,
dragging a cold front through the area. This will result in
showers and a few thunderstorms late this afternoon and evening,
followed by cooler conditions this weekend. An upper level
trough will swing over Pennsylvania Saturday, then begin lifting
out by late in the weekend.
&&
.NEAR TERM /UNTIL 7 AM FRIDAY MORNING/...
Radar at 03Z shows a weakening line of convection preceding a
cold front, running from the Potter/Tioga Co border south
through KUNV and KCBE. Although strong wind shear will continue
to accompany the fropa late this evening, diminishing low level
instability should limit the severe wx threat. Latest HRRR
supports this scenario, depicting dwindling convection along
front, as it sweeps through the eastern part of the forecast
area between 03Z-05Z. Post-FROPA NW flow regime sets in late
tonight, with plenty of lake clouds and scattered showers over
the Allegheny Plateau. The arrival of a secondary cold front
should enhance the shower threat across Warren/Mckean counties
late tonight.
&&
.SHORT TERM /7 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/...
No changes seen for Friday in high confidence post-FROPA NW
flow regime, with plenty of lake clouds and scattered showers
expected over the Allegheny Plateau. The focus for showers will
be along and just ahead of a secondary cold front, which will
push through the northwest mountains early in the day, then
settle into the Laurel Highlands by afternoon.
&&
.LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/...
An upper level trough will pivot across the area Friday into
Saturday, accompanied by cooler temperatures and scattered
showers across the northern and western mountains.
By early next week, the focus will shift to a slow-moving area
of low pressure lifting out of the midwest. Differences exist
among med range guidance as to the track and timing of this
feature. However, the latest ECENS and GEFS support a chance of
rain sometime between late Sunday and late Tuesday, with the
best chance of rain coming Monday night into part of Tuesday.
A surface low track south of Pa, combined with a surface high
to the north, should result in chilly daytime conditions early
next week. Have undercut NBM high temps based on its warm bias
in cold air damming scenarios.
Drier and seasonable conditions appear possible Wednesday, as
ridging builds in at the surface and aloft. However, all medium
range guidance signals unsettled conditions returning by
Thursday in association with a deepening upstream trough over
the midwest and potential coastal low.
&&
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
A line of gusty showers is moving across PA at the time of the
3Z update. MVFR to IFR restrictions likely in SHRA. TSRA
remains possible for the next few hours. It looks more likely
that JST will stay IFR to LIFR through Friday.
Prev..
Later tonight conditions will deteriorate in NW flow behind the
front at JST and BFD with low vis and cigs. Scattered
SHRA and DZ possible during the overnight hours.
Elsewhere, conditions briefly improve before going MVFR for the
day Friday. Western terminals will likely stay IFR through the
day.
Outlook...
Fri...MVFR to IFR cigs in NW flow. SHRA possible SW.
Sat...Conditions gradually improving to VFR. SHRA possible NW.
Sun...AM valley fog. SHRA possible SW.
Mon-Tue...Restrictions in SHRA and low cigs.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Guseman/DeVoir/RXR
NEAR TERM...Fitzgerald
SHORT TERM...DeVoir/Fitzgerald/RXR
LONG TERM...Fitzgerald/Gartner
AVIATION...Wagner
Area Forecast Discussion...UPDATED
National Weather Service Austin/San Antonio TX
829 PM CDT Thu Oct 21 2021
.UPDATE...
Thunderstorms continue to develop across the Big Bend area and
northeast Mexico. However, latest HRRR keeps the thunderstorm
activity west of the area for the rest of tonight. Therefore, decided
to remove the mentioning of showers and storms along the Rio Grande
for the tonight period.
For this update, added patchy fog to begin an hour before than
previously forecasted for the Coastal Plains. The patchy fog and even
areas of fog should stay south of I-35 late tonight through 16Z
Friday.
&&
.PREV DISCUSSION... /ISSUED 651 PM CDT Thu Oct 21 2021/
AVIATION...
/00Z TAFS/
VFR conditions are expected across area sites for the most part.
There is a slight chance for MVFR cigs to develop around 15Z across
the KDRT for a short period of time. Otherwise, VFR conditions to
prevail for this forecast cycle. Light and variable winds are
expected tonight into Friday morning. A southeasterly flow around 5
to 10 knots is forecast for Friday afternoon and evening. A weak cold
front is forecast to stay nearby the northern Hill Country for most
of the period with HiRes models pushing back on chances for rain per
latest runs and therefore no impacts to area terminals.
PREV DISCUSSION... /ISSUED 242 PM CDT Thu Oct 21 2021/
SHORT TERM (Tonight through Friday Night)...
A decently complex setup is in place for the short term despite the
forecast generally being dry and warm. A cold front is situated just
to the north of our area this afternoon. Based on surface
observations and the 15z WPC frontal analysis the front is roughly
stalled from San Angelo to Temple to Palestine. Across West Texas a
dryline may spark off some thunderstorms through the evening and
overnight hours. On top of those features a weak shortwave moving
trough the zonal flow aloft produced a few showers earlier in the
day across Val Verde and Edwards County. These showers are now
moving through Mason and San Saba County and could impact some folks
in Llano and Burnet county through the late afternoon. All of these
showers are generally light, and while a rumble of thunder is
possible, it is unlikely. Partly to mostly cloudy skies have hung on
through the afternoon with temperatures in the low to mid 80s.
As discussed in the morning short term AFD there are a few questions
about whether convection across West Texas (Davis Mountains) and
Mexico (Sierras del Burro) from the dryline and orographic
influences will make it east into our Rio Grande Plains. Some of the
high resolution models hint it is possible, but think that most
areas will stay dry so have only included a sliver of 20% PoPs for
these areas. Equally, some of the synoptic models show additional
showers developing along the front tonight as it attempts to sag
south into some of our Hill Country counties. The overwhelming
majority of the high resolution models keep the Hill Country dry
this evening and into the overnight so have left the forecast dry
overnight with lows dropping into the mid to low 60s.
The front is forecast to lift back north as a warm front on Friday.
Warm, humid southeasterly flow will prevail Friday. With this moist
atmosphere surging back northward another round of morning fog is
possible across the Coastal Plains as well as low lying areas of the
Hill Country. Think any shower activity will remain close to the
coast during Friday afternoon so a warm (mid to upper 80s) and dry
forecast will hold out for Friday.
LONG TERM (Saturday through Thursday)...
The upper level pattern this weekend remains of a nearly zonal flow
but an occasional subtle disturbance or ripple within the flow may
be possible. Shortwave ridging then builds over the region from
Monday into early Tuesday. At the surface, winds will remain light
to moderate out of the south and southeast. Combination of these
features will result in continued above average temperatures. High
temperatures may approach the daily record highs Monday and again
Tuesday for some locations. The afternoon heat indices, with the
elevated dew points, are expected to peak in the mid to upper 90s.
While rainfall looks slim across the majority of the region into
Tuesday, the far eastern portions of the area along highway 77 do
have the chance for isolated showers and/or a thunderstorm this
weekend. Otherwise, anticipate low morning clouds each day before
scattering out into or through the afternoon.
Midweek will continue to focus on an upper level trough advancing
out of the western US. Latest models, including the last 2 runs of
the GFS, are more progressive and a bit flatter with the trough as
it moves across the CONUS. While uncertainty does still exist, any
tropical moisture from the eastern Pacific that the recent runs of
the GFS are picking up, quickly advances eastward given the more
progressive nature of the trough. Otherwise, this parent trough
allows for a Pacific front to move across the region into or during
the day on Wednesday. The front could yield to some small chances
for rain along and east of highway 281. Temperatures for Wednesday
may be tricky depending on the timing of the surface front as the
most recent 12Z GFS run came in a bit weaker and slower with the
boundary, resulting in some rather strong compressional heating
across portions of the area. With these hotter temperatures being
more of an outlier solution among the guidance, I elected to trend
only a tad warmer compared to the NBM. Breezy northwest winds and
building surface high pressure behind the front is to bring a much
drier airmass. Temperatures should also drop closer to seasonable
average.
&&
.PRELIMINARY POINT TEMPS/POPS...
Austin Camp Mabry 66 84 68 86 69 / - - 0 10 -
Austin Bergstrom Intl Airport 65 84 66 84 67 / - - 0 10 -
New Braunfels Muni Airport 65 84 66 85 67 / - - - 10 -
Burnet Muni Airport 65 82 65 84 67 / - - 0 - -
Del Rio Intl Airport 67 87 68 91 70 / 10 - - - -
Georgetown Muni Airport 65 84 66 85 68 / - - 0 - -
Hondo Muni Airport 65 85 65 87 68 / - - - - -
San Marcos Muni Airport 65 84 65 85 67 / - - 0 10 -
La Grange - Fayette Regional 68 86 68 86 69 / - 10 - 20 10
San Antonio Intl Airport 66 83 68 85 69 / - - - 10 -
Stinson Muni Airport 68 86 69 87 70 / - - - 10 10
&&
.EWX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Short-Term/Aviation...17
Long-Term...09
Area Forecast Discussion
National Weather Service Medford OR
751 PM PDT Thu Oct 21 2021
.DISCUSSION...A mature cutoff low continues to drive moist SW
flow into the region along a slowly moving cold front, which is
now roughly along a line from Roseburg, OR to Eureka, CA. The main
cutoff low off the coast of B.C. will retrograde into the Gulf of
Alaska and absorbed into the next low to approach the region.
A portion of breakaway energy in the base of the upper level
trough will negatively tilt the axis and move it across the
interior of the PNW and ultimately reform into a cyclone in the
lee of the Rockies.
Stratiform rain will persist into Friday morning, but the heaviest
rain is likely still to come. Thus far, the heaviest returns have
remained north of the the Umpqua Divide, but the most
concentrated area of water vapor is still offshore. At the
moment, radar derived hydrophobic streamflow suggests that rain
rates have been low enough that hydro concerns over the burn scars
of western Siskiyou County remain very low. 1hr accumulations
over Douglas county have remained below our concern thresholds, so
hydro concerns over the burn scars there also remain low. We will
continue to monitor rain rates and estimated streamflows as the
more concentrated water vapor moves onshore as this preceding
stratiform rain will only prime conditions for excess runoff and
hydro concerns.
An addition to the previous discussion is for the slight chance of
thunderstorms in the Mt. Shasta area on Friday. During the early
afternoon the breakaway energy will be pushing the base of the
trough over and east of the Cascades. The upper level dynamics
combined with strong up-slope flow point to the Mt. Shasta area as
a prime place for deep convection. Thunderstorms also remain
possible over the coastal waters, along the coast, and coast
range north of Cape blanco at the same time. -Miles
&&
.AVIATION...22/00Z TAFs...A cold front will continue across the area
through Friday morning with light to moderate precipitation.
Southerly winds ahead of the front, generally in northern California
and from the Cascades eastward, will remain gusty and strong with
low level gusts up to 45 kt. Meantime, numerous light showers are
expected behind the front through Friday evening. This will continue
a varying mix of MVFR and VFR visibilities and ceilings with areas
of mountain obscuration. Freezing levels around 10000 ft msl ahead
of the front will fall to 6500 ft msl behind it. -DW
&&
.MARINE...Updated 800 PM PDT Thursday, 21 October 2021...Southerly
gales have ended, but a secondary disturbance will provide advisory
strength southerly winds overnight into early Friday morning.
Meantime, a mix of fresh swell and longer period west swell will
continue high to very high and very steep seas at 12 to 20 ft into
Friday.
Another front will follow Friday night into Saturday morning with
winds again approaching gales. The active weather pattern will
continue next week with the potential for another episode of very
high and very steep seas Sunday through Tuesday. Seas Sunday night
into Monday are likely to build to 25 to 30 feet with breaking wave
heights around 35 feet possible. BTL/DW
&&
.PREV DISCUSSION... /Issued 320 PM PDT Thu Oct 21 2021/
SHORT TERM...An active wet and windy pattern will persist into
the weekend and early next week as a series of strong, moist
fronts move across the region. The first of these fronts is
moving into the coast this afternoon and evening and will
gradually move eastward across the area tonight into Friday
morning. This front is bringing strong, gusty winds ahead of it,
with winds expected to peak later today into tonight. This front
will also bring widespread moderate to locally heavy rain to the
area. Showers are expected behind the front on Friday. Then, a
weaker front will bring additional light to moderate rainfall on
Saturday along with breezy winds. On Sunday a second strong and
moist front will move into the area with another round of strong,
gusty winds and moderate to heavy precipitation. Precipitation and
winds with this front are expected to last longer from late
Saturday night into Monday.
Satellite imagery shows the frontal band just offshore this
afternoon and moderate rain is beginning to move into the coast
and coastal mountains. Winds have increased ahead of this front
with strongest winds at the coast, over the mountains, in the
Shasta and southern Rogue Valleys as well as east of the Cascades
near Summer Lake and over the higher terrain. Wind gusts of 55 to
69 mph have been recorded at the coast this afternoon across
headlands with gusts of around 50 mph along the coast near Gold
Beach. A high wind warning is in effect for portions of the coast
between Bandon and Gold Beach and wind advisories remain in effect
for affected inland areas. Please see the NPWMFR for details.
Models continue to show widespread moderate to locally heavy
rainfall spreading across the area late today through Friday
morning with high snow levels of 10000 feet, lowering to 6000 feet
behind the front. Rainfall amounts ranging from 0.75-2.00 inches
are expected over much of the area, except 2.00-4.00 inch amounts
in areas where upslope flow and orographic enhancement is
maximized (coast ranges and in western and southern portions of
Siskiyou County). Also expect lighter precipitation in eastern
Lake and eastern Modoc Counties with amounts of 0.3 to 0.75
inches. With the heavy rainfall, there is a potential for ponding
of water on roadways and in urban areas where there may be blocked
storm drains. We are also monitoring the potential for flash
flooding or debris flow in and near burn scars, especially for
the McCash and River Complex burn scars in northern California.
The high resolution HRRR and HREF continue to show some locally
heavy hourly rainfall rates of around 0.5 to 0.6 inches in Western
Siskiyou County. Heavy precipitation rates are below the guidance
criteria for flash flood in the McCash and River burn scars.
However, this will be closely monitored through the event. The
coastal mountains and Mount Shasta areas are also expected to see
possibly heavy rainfall rates of 0.5 to 0.8 inches per hour with
this frontal passage.
On Friday, the frontal band will shift east of the Cascades in
the morning then east of the area by early afternoon. Winds are
expected to lower overnight for areas west of the Cascades and in
the late morning and early afternoon for areas east of the
Cascades.
Also with this front and behind the front there is a slight chance
for thunderstorms over the waters, near the coast and then on Friday
in the Mount Shasta area.
Friday night into Saturday another weaker front will arrive. This
front will bring light to moderate precipitation across the area.
Snow levels will be around 6000 feet as this front moves into the
area.
On Sunday, a second strong and very moist frontal system is
expected to move into the area. Integrated water vapor
transport(IVT) values, which show how effectively water vapor is
transported by the wind within the atmosphere, are high between
750 and 1000, indicating high potential for moderate and heavy
precipitation with this system. Expect heaviest rainfall in the
coastal mountains and across western and southern Siskiyou County,
similar to the front today with peak rain rates late Saturday
night into early Sunday afternoon. However, the moist onshore flow
pattern will last longer in duration and may result in higher
total rainfall amounts across the area. Current models show
widespread rainfall Saturday night through Sunday night with
amounts of 1 to 2 inches with heavier amount of 2.5 to 4 inches
in the coastal mountains and western Siskiyou and 3 to 5 inches in
the Mount Shasta area. Snow levels are expected to be high around
7000 feet or higher ahead of the front, lowering to 5000 to 6000
feet behind the front Sunday night and Monday morning. With
the heavy rainfall, expect rivers and stream flows to increase and
potential impacts with ponding on roadways or urban areas. We will
continue to assess the flash flood potential for burn scars as
well. Also with the front, weak instability and upper level dynamics
favor a slight chance to chance for thunderstorms over the
coastal waters and for areas along the coast and into the coastal
mountains on Sunday. Strong, gusty winds with and ahead of the
front will also bring potential impacts, especially to the coast
and for inland areas such as the mountains, Shasta Valley and
Summer Lake areas on Sunday. Additionally, strong winds across the
marine waters and very high seas will result in impacts for
mariners and those at the coast. We will continue to monitor and
update the forecast as confidence increases in the details of this
event.
LONG TERM...From Monday 12Z until Saturday 12Z.
A mature and well developed cyclone will move inside 130 W late
Sunday night into Monday morning well off the coast of Washington.
Looking at some of the deterministic models, the low surface pressure
rises from 945 mb to roughly 965 mb mid day Monday. Although this
doesn`t communicate any weather impacts, it should help demonstrate
how strong the south westerly flow will remain on Monday behind the
cold front. Ensembles suggest the precipitation will persist into
Monday, yet at a lower rate/intensity compared to Sunday.
With cooler air filtering in behind this front, we`ll see snow
starting to accumulate above 5500 feet within the region. We`re
forecasting about 10 inches of snow over the Cascades and Siskiyous,
so popular destinations like Crater Lake and Mt Ashland should start
adding to a snow pack this fall. It should be noted that the NBM
probability greater than 8 inches over 48 hours is pretty low, so
perhaps that 10 inch snow forecast is on the high side. In any
case, we do have high confidence in 2 to 4 inches of snow
accumulating snow above 5500 feet through Monday night.
This zonal onshore moist flow continues into Tuesday with more
precipitation continuing to fall across the region. It appears a
moist warm front and moisture plume smacks right into the Oregon
coastline with a weak surface low rising the upper level wave. With
the air becoming warmer, snow levels will likely rise up to 7000
feet, yet it`s unclear how much of our area will get that warmer
air. This warm moist plume could move farther north or south as new
model data comes in. For now, simply count on more precipitation as
the NBM is forecasting a probability of precipitation near 90
percent on Tuesday.
The good news is it appears Wednesday or Thursday conditions will
dry out. The NBM is forecasting 10 to 20 percent chance of rain
over sections our region with 50 percent chance along the coast. In
addition, the deterministic models are also hinting at high pressure
building in briefly during this time frame.
-Smith
&&
.MFR WATCHES/WARNINGS/ADVISORIES...
OR...Hazardous Seas Warning until 11 PM PDT this evening for
ORZ021-022.
Wind Advisory until 8 AM PDT Friday for ORZ030-031.
Wind Advisory until 11 PM PDT this evening for ORZ026.
CA...Wind Advisory until 8 AM PDT Friday for CAZ085.
Wind Advisory until 2 AM PDT Friday for CAZ081.
Pacific Coastal Waters...
Hazardous Seas Warning until 11 PM PDT this evening for
PZZ350-356-370-376.
Gale Watch from late Friday night through Saturday afternoon for
PZZ350-356-370-376.
$$
Area Forecast Discussion
National Weather Service Marquette MI
801 PM EDT Thu Oct 21 2021
.SHORT TERM...(This evening through Friday)
Issued at 454 PM EDT THU OCT 21 2021
Water vapor imagery and RAP analysis show a mid-level low over
northern Ontario, centered just sw of James Bay. Shortwave that was
near Sioux Falls, SD 24hrs ago is tracking into the Lower Great
Lakes region. Shra associated with that feature exited the fcst area
late this morning. In the wake of the pcpn, abundant stratocu is
streaming off Lake Superior on northerly flow and under 850mb temps
that have fallen from roughly a -1 to 1C range at 12z to roughly -3
to -5C now. With Lake Superior sfc water temp roughly around 12C,
-shra are developing under increasing overwater instability into
mainly n central Upper MI. With the clouds and caa today, temps have
not risen much. Current readings are in the 40s F, warmest s
central.
Thru Fri, the mid-level low over northern Ontario will wobble around
near its current location. However, its influence over the fcst area
will increase as heights slowly fall and the circulation expands to
the w and s. Subtle shortwaves will rotate thru the circulation, but
it won`t be until late Fri/Fri night that a more notable wave
reaches the area, resulting in some synoptic forcing spreading
across Lake Superior. CAA will essentially end this evening, leaving
850mb temps across Lake Superior generally in the -3 to -6C range
thru Fri. With Lake Superior sfc water temp roughly around 12C, but
locally higher, overlake instability will be favorable for lake
effect pcpn. Inversions tonight will be in the 3-5kft range but will
increase over eastern Lake Superior to around 7kft overnight. With
longer fetch that also includes preconditioning from Lake Nipigon,
lake effect pcpn coverage will be greatest into n central Upper MI
tonight, centered over far eastern Marquette County into the w half
or so of Alger County. Not only will the preconditioning streamline
extend to that area, but low-level convergence will also be
maximized there. These -shra will extend inland to Lake MI though
with diminishing coverage. To the w, low inversions suggest limited
pcpn development. If pcpn develops, it won`t be until late tonight
during the more favorable min of the diurnal temp cycle. Wet bulb
zero heights falling blo 1500ft over the w half and far e, even to
the sfc, indicate pcpn will mix with or change to snow at times, but
lowest wet bulb zero heights are over the interior w where pcpn is
not likely to occur. Typical for early season lake effect, the more
vigorous convection into the n central later tonight under the
rising inversion may produce graupel at times. Expect low temps
tonight of 30-40F, lowest interior w. If there are sufficient breaks
in the clouds, temps could fall toward the mid 20s interior w.
More of the same expected on Fri. However, with the inversion rising
toward 10kft, lake effect pcpn will tend to expand in coverage
despite the negative impact of the early lake effect season higher
sun angle. Although fcst reflects rain ptype after the morning hrs,
increasing depth of convection and local boundary layer cooling
during pcpn will probably result in some snow mixing in at times
over higher terrain. More likely scenario may be seeing more graupel
ptype with stronger convection, no matter elevation. Approaching
shortwave late in the day should further aid pcpn development. As is
the case tonight, pcpn coverage will be more widespread and heavier
into areas e of Marquette. With the increasing convective cloud
depth to around 10kft and winds under 20kt thru the layer,
conditions could become somewhat supportive for waterspout
development on the e half of Lake Superior, particularly later in
the day. Expect high temps in the 40s F across the board, warmest s
central.
.LONG TERM...(Friday night through Thursday)
Issued at 337 PM EDT THU OCT 21 2021
Upper low over eastern Ontario will be the primary weather player
Friday night into early Sunday before the low opens up and shears
eastward. Several shortwaves rotating around the low will enhance
the lake effect process Friday night into Saturday and again
Saturday night. As temperatures cool each evening lake effect rain
showers will transition to some light snow showers or rain/snow mix
for higher terrain areas across the central U.P. No snow
accumulations are expected.
With 85H temperatures between -4C and -6C temperatures will remain
cool...40s during the day...but not out of the ordinary for this
time of year.
Shortwave moving through the mid-Mississippi Valley will spin up a
surface low over the Lower Lakes on Monday. Most of the
precipitation from that should remain south of the U.P.
Strong warm advection ahead of upper trough moving out of the
western U.S. will yield milder days for Tuesday into Wednesday
before a cold front with a band of showers crosses the area on
Wednesday. Temperatures will cool back to normal behind the front
for late in he week.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 741 PM EDT THU OCT 21 2021
Although KIWD and KSAW are reporting VFR conditions to start this
TAF period, it`s anticipated not to last long with MVFR cigs
returning. Moisture assist from the Great Lake Superior (plus Lake
Nipigon) will continue to feed into the formation and retention
of clouds, plus associated LER. Persistent low clouds look to
remain at least in the vicinity of all three terminals through
much of the period, with NW winds prevailing.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 454 PM EDT THU OCT 21 2021
Across the w half of Lake Superior, expect northerly winds under
20kt tonight. Meanwhile, northerly winds gusting to 25-30kt across
the e half of Lake Superior will fall back to mostly under 20kt
tonight. With high pres ridging building toward Lake Superior during
Fri and Sat, winds should remain mostly under 20kt, but will be
strongest across the e half of the lake. On Sun and Mon, high pres
will build across northern Ontario as another low moves to the Ohio
River Valley. Increasing pres gradient btwn these 2 features will
probably lead to wind gusts increasing to at least 20-25kt over at
least portions of Lake Superior later Sun into Mon. Winds should
diminish some on Tue.
On another note, conditions could become somewhat supportive for
waterspout development on the e half of Lake Superior late Fri into
Sat morning.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...Rolfson
LONG TERM...MZ
AVIATION...lg
MARINE...Rolfson