Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/23/21

Area Forecast Discussion

National Weather Service Detroit/Pontiac MI

 1146 PM EDT Fri Oct 22 2021


.AVIATION...

The passage of a mid level short wave overnight will help drive some
of the showers ongoing across the west side of the state into Se Mi,
primarily after 09Z. Any showers that make it into the terminals
will remain light. The wave will also drive a little better moisture
into Se MI. This will primarily result in cloud bases in the 4k-6k
foot range, although some brief MVFR ceiling conditions are
possible.

For DTW...Upstream observations remain supportive of sub 5000 foot
clouds returning to metro shortly after 06Z. Some early afternoon
dry air advection will then support some improvement in the ceiling
heights.

.DTW THRESHOLD PROBABILITIES...

*  High in ceilings at or below 5000 feet Saturday morning. Low
   Saturday afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 818 PM EDT Fri Oct 22 2021

UPDATE...

Thus far this evening the response off Lake Mi has been fairly
decent, with ample shower coverage over srn Lake Mi and portions of
SW Lower Mi. The low level wind fields will bring some added lake
moisture into Se Mi overnight as they become oriented more west-
southwesterly. This along with mid level short wave energy and
latest runs of the HRRR and RAP will support a slight upward
adjustment to precip chances overnight, mainly into the scattered
category. Otherwise, no other forecast updates appear warranted at
this time.

PREV DISCUSSION...
Issued at 310 PM EDT Fri Oct 22 2021

DISCUSSION...

Today will end up being the first day of below normal temperatures
for the month of October. The stretch from Oct 1-21 was warmest on
record at Flint/Saginaw and second at Detroit (1879 being the
first). The below normal temperatures look to carry through the
weekend.

Large upper level low near James Bay will be slow to move and break
down as we head into the Weekend, but a drift to the south should
occur. Meanwhile, shortwave/mid level cold pool (-24 C at 500 MB)
over the Midwest will slide east close to the southern Michigan
border this evening/tonight. Mid level dry slot in place should help
limit shower activity tonight, but there will be an increase in low
level westerly flow coming off Lake Michigan, with favorable 850 MB
temps falling below -2 C. Looks like just enough weak low level
convergence/isentropic ascent (284 K) and modest capes/supersaturation
with respect to ice (albeit mostly below -10 C) to support isolated
light shower activity (supported by latest HRRR/RAP/ARW/FV3).

Renewed drop in 500 MB temps on Saturday (especially north of M46)
will likely maintain isolated-scattered showers with surface based
capes rising above 50 J/kg, as high temperatures look to reach into
the lower 50s.

Blocking/strong high pressure over northern Ontario for the second
half of the weekend, but cyclogensis over the Central Plains
ejecting northeast sending a excellent surge of Pacific and Gulf of
Mexico moisture north toward the southern Lower Michigan border.
Still some key differences amongst the Euro ensemble members where
strong FGEN will reside, but bulk of solutions suggest areas south
of M-59 will reside in the 850-700 MB FGEN/baroclinic zone, with 6-8
g/kg of specific humidity to work with Sunday evening/night.
Widespread rainfall expected, but extent of convection/thunderstorms
over the Ohio Valley late in the day potentially disrupting the
transport into the State. Thus, low confidence on where exactly the
heavy rainfall axis will reside, and how narrow it will be as well.

As the low pressure system exits the Midwest, should be gradually
weakening/dampening/becoming stretched out as it runs into the
blocking high/upper level confluent flow over the Great Lakes region
as we head into Monday. Still, deformation will support
numerous/widespread showers tracking through southeast Michigan
during the day, with the brisk low level northeast winds coming off
Lake Huron. Local probabilistic guidance indicating 30+ mph gusts,
especially near Saginaw Bay/Lake Huron shorelines, where 40 mph is
in play with the increased marine layer mixing.

Upper level ridge arriving for mid week period looks to be short
lived, as next batch of Pacific upper level energy spins up a large
cyclone over the Midwest/western Ohio Valley by Thursday. However,
there is some indication (12z Euro) the system will develop faster
(absorbing TD seventeen-E) and potentially cutting off farther south
and attempting to become detached from the northern stream. Thus,
only chance pops will go out with the going forecast for Thursday,
despite the soaking rain advertised by the 12z GFS.

MARINE...

Weak high pressure across the central Great Lakes will continue to
remain in place through the first half of the weekend. Light and
variable winds will exist through at least the first half of
Saturday trending southwesterly by Saturday night in response to
developing low pressure in the central Plains. Cold air continuing
to feed down from northern Ontario coupled with light winds will
favor the potential for waterspouts over portions of the Lake Huron
basin Saturday. The Plains low pressure system will continue
deepening as it tracks northeastward towards the northern Ohio
Valley Sunday into Monday bringing an extended period of wet and
unsettled weather. Winds will flip northeasterly with the approach
of the low and strengthen in response to the tightening pressure
gradient. Gusts to at least small craft criteria certainly look
plausible during this time with a small potential for sporadic gusts
to gales over the open Lake Huron waters. Northeast flow decreases
but remains moderate then heading into the middle of next week as
the low departs off to the east.

HYDROLOGY...

A moisture laden low pressure system will track northeast out of the
Central Plains during the second half of the weekend, and track
close to the southern Michigan border on Monday. A long duration
rainfall appears likely in the late Sunday through late Monday time-
frame. Event total rainfall in excess of 1 inch appears likely along
and south of M-59, with the potential of up to 3 inches toward the
southern Michigan. The peak hourly rainfall rates of a quarter to
possibly half an inch looks to be late Sunday evening/early Monday
morning, but will be dependent out how the thunderstorms developing
over the Ohio Valley alter the rainfall pattern, as the heavy rain
axis may hold just to our south. Due to the long duration, just minor
flooding of urban/poor drainage/low lying areas anticipated. Leaves
clogging sewers/drains could cause localized issues as well.

Rainfall will likely struggle to make significant inroads north of I-
69 Sunday evening/night, and bulk of the rainfall for those areas
looks to be on Monday, but only around half an inch.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&

$$

AVIATION.....SC
UPDATE.......SC
DISCUSSION...SF
MARINE.......IRL
HYDROLOGY....SF


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



Area Forecast Discussion...UPDATED

National Weather Service Memphis TN

 905 PM CDT Fri Oct 22 2021

.UPDATE...

Slightly adjusted temps for this evening to more closely reflect
latest guidance and trends. Otherwise, forecast looks good. Clear
skies and calm winds tonight as surface high pressure gradually
migrates to our east.

CAD

&&

.DISCUSSION.../issued 301 PM CDT Fri Oct 22 2021/

Much cooler across the area today thanks to yesterday`s cold
front. Current temperatures are in the mid 60s, and will gradually
warm to the low 70s today. A low pressure to our northeast is
allowing clouds to spill into our eastern counties which has
caused temperatures to take awhile to increase around the
Tennessee River. Otherwise, temperatures tonight will be in the
lower 50s to upper 40s.

By the weekend a warm front will lift northeast from Texas
through the Mid-South. This will provide showers to the area and
possibly a few thunderstorms by Saturday afternoon. By Sunday
night, another front will swing through the Mid-South.
thunderstorms will return to Sunday night and increase in coverage
by Monday before tapering off Monday night. Thunderstorm
development looks to be favorable over eastern Arkansas and the
Missouri Bootheel. Models show modest MLCAPE over eastern
Arkansas by sundown in conjunction with 30kts of shear and modest
PWAT values. With that being said, with the increasing low level
jet, storms have a short time frame to tap into these ingredients.
As the night progresses kinematics will begin to decrease, as
with the threat of severe weather. All severe hazards will be
possible including damaging winds and hail, and perhaps some
tornadic activity.

By Wednesday another front will bring widespread showers and
thunderstorms to the Mid-South. Confidence is still low on timing
and intensity but there could be a chance of severe storms.
Confidence will increase as the week progresses. Moisture return
is the largest concern, especially with the aforementioned front
moving through on Sunday/Monday. Also, models continue to
disagree with the orientation of the system. We`ll continue to
monitor.

Temperatures this weekend will begin to increase to the upper 70s,
then low 80s by Sunday. By Tuesday expect temperatures to moderate
back to normal, to the low 70s. Lows will be in the 50s by
Saturday then increase to the low 60s Sunday and mid to upper 60s
by Monday.

SWB

&&

.AVIATION...

00Z TAFs

Light/calm winds to prevail tonight, with surface high pressure
recentering from AR to the TN River valley. PVE and SNH, both
near the TN River, were reporting fog prior to sunset and persisting
at discussion time. This may be a local effect, with no apparent
signature yet appearing on GOES nighttime microphysics imagery.
Despite HREF and HRRR depictions of VFR across the region
overnight, MKL TAF includes a mention of fog.

West of the MS River, NAM Bufr sounding depicts a fairly steep
near surface inversion to develop at JBR late this evening, which
may trap some of the smoke from agricultural burning. This also
was not depicted in short range model guidance.

VFR and strengthening low level southerly return flow to develop
Saturday, perhaps with enough mixing to preclude visibility
reductions at JBR, due to fog or haze prior to sunrise. No fog
concerns for MEM at this time.

PWB

&&

.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&

$$



Area Forecast Discussion

National Weather Service Marquette MI

 756 PM EDT Fri Oct 22 2021

.SHORT TERM...(This evening through Saturday)
Issued at 421 PM EDT FRI OCT 22 2021

Water vapor imagery and RAP analysis show an expansive mid-level low
centered near southern James Bay. The northern Great Lakes are now
firmly under the circulation of this low, but the deep cyclonic flow
is weak. CAA regime into the fcst area ended last night, leaving
850mb temps settled into the -3 to -5C range across Lake Superior.
With Lake Superior sfc water temp roughly around 12C, but locally
higher, sct lake effect -shra are occurring under nnw low-level
flow. Last evening, Upper MI`s first snowflakes of the season were
observed at some locations. So, this season`s first snowflakes
occurred almost exactly 3 weeks later than last year (Oct 1, 2020).
At the sfc, high pres centered over far northern Manitoba is ridging
s into the Upper Mississippi Valley while low pres is located in
central Quebec. Resulting weak pres gradient has led to a day of
light winds across Upper MI. Temps are currently in the 40s F.

Thru Sat, the mid-level low near southern James Bay will wobble
slightly to the sw while 850mb temps generally hold in the -3 to -5C
range. A weak shortwave extending w from the low across northern
Ontario will pivot across the area tonight. As a result, there
should be some uptick in lake effect pcpn coverage. Deep moisture
profile upwards of 15kft or more will further aid the lake effect
convection. Otherwise, nnw flow lake effect showers will continue
into Sat. Moisture depth begins to fall on Sat from the w, so pcpn
should end over at least the far w in the aftn. Since wetbulb zero
heights tonight/Sat are similar to last night and today, the -shra
will mix with or change to -shsn in similar locations to last night
and this morning. Deeper convection could produce graupel, no matter
the elevation. As has been the case, lake effect pcpn will continue
to be more nmrs into n central Upper MI e of Marquette due to longer
fetch and Lake Nipigon preconditioning. With lake induced
equilibrium levels to 10-15kft and winds under 20kt thru the layer,
conditions thru Sat morning remain somewhat supportive for the
potential of waterspouts on Lake Superior, mainly on the e half of
the lake. Low temps tonight will be similar to last night (upper 20s
to upper 30s F), but if clouds scatter out long enough in the
interior, temps will easily fall into the mid 20s. Highs on Sat will
be similar to today, ranging thru the 40s, maybe reaching 50F s
central.

.LONG TERM...(Saturday night through Friday)
Issued at 301 PM EDT FRI OCT 22 2021

Blocking pattern across much of NOAM will continue through this
weekend as an upper-level low remains btwn James Bay and the Great
Lakes and anomalous ridging persists across central Canada northward
into the Arctic. This low will begin to fill in by Sunday as a
shrtwv ejects from the Rockies, spinning up a sfc low across the
Central Plains into the Ohio River Valley by Monday. Further
upstream, a strong trof will reach the Pac NW Sunday evening,
"running into" the downstream ridging extending from north central
CONUS northward through Canada. This strong trof will begin to shift
this ridging eastward, as the low north of the Great Lakes combines
with trof shifting through the Ohio River Valley Monday night.
Sfc high pressure dropping south from northern Canada will increase
the pressure gradient for Monday as the sfc low tracks through the
Ohio River Valley...which will bring stronger easterly winds across
the area for Monday into Monday evening. By Tuesday evening, the
ridge axis will begin to move over the western UP as southerly flow
begins to increase. This will bring a warm up by the middle of the
week, with high temps 5 to 10 degrees above normal as our normal
high falls from 49 to 44 over the next 6 days. Model and ensemble
spread increase on Wednesday, with confidence for the second half of
the week quite low.

Saturday night, light NW flow with 850mb temps near -4C will lead to
continued LER across parts of the Keweenaw and ern Upper Michigan.
Inversion heights and saturation will range from near 8kft across
the west to near 9kft across the east. Despite 850mb temps remaining
near -4C through the day Sunday, saturation and inversion heights
will decrease, falling to around 4kft by 18Z Sunday. As winds begin
to veer from the NW to NE ahead of an approaching wave to our south,
LER will begin to diminish in coverage through the morning hours,
with only an isolated shower or two possible by late aftn on Sunday.
Despite sfc temps remaining above or near freezing, higher inversion
heights into the DGZ may allow for some wet snow or graupel to mix
in.

Heading into Monday, shrtwv and sfc low will pass to the south of
Upper Michigan as the pressure gradient and easterly winds increase.
While there could be some fgen rain along Lk Michigan, the UP is
expected to remain dry with this system. Should be a raw feeling day
with breezy conditions and highs in the 40s to potentially up to 50.

Ridging and sfc high pressure move overhead for Tuesday, with
southerly winds bringing a warmer trend with highs 5 to 10 degrees
abv normal. As the strong wave from the Pac NW reaches the central
CONUS by Wednesday, associated sfc low develops across the Central
Plains. Pcpn chances will then increase across the wern UP by
Wednesday evening, before spreading over the UP into Thursday. Model
spread increases by the middle of the week and with a blocking ridge
across central Canada, inherent uncertainty exists for pcpn chances
so chance PoPs will exist Thursday into the weekend.
&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 742 PM EDT FRI OCT 22 2021

It`s anticipated that all three terminals will be dominated by
primarily MVFR cigs, but KIWD and KCMX have been bouncing around
categories over the last 12 to 24 hours, and KSAW has been
reporting VFR conditions throughout the day. Given how close the
LER/S is to KSAW, didn`t feel comfortable going VFR but an
amendment/update may be required if these trends continue to
indicate KSAW will remain free of the ongoing bands. More
confidence exists at KIWD and KCMX, with it worth noting that
there are indications KIWD could perhaps drop into lower
categories, so will monitor that as well. NW winds will remain
fairly light (topping out to around 10 knots on Saturday) to calm
(overnight) through this TAF period.

&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 421 PM EDT FRI OCT 22 2021

With high pres ridge extending se toward the Upper Lakes, northerly
winds on Lake Superior will remain under 20kt thru Sat night, but
will be strongest across the e half of the lake. On Sun and Mon,
high pres will build across northern Ontario as low pres moves e to
the Upper Ohio River Valley. Increasing pres gradient btwn these 2
features will probably lead to wind gusts increasing to at least 20-
25kt over portions of Lake Superior later Sun into Mon. Winds will
then diminish to under 20kt into Tue morning as high pres ridge
moves across Lake Superior. Some increase in winds will occur Wed as
the ridge moves e and low pres moves across the central Plains.

On another note, conditions will remain somewhat supportive for
waterspout development on mainly the e half of Lake Superior
into Sat morning.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Rolfson
LONG TERM...JAW
AVIATION...lg
MARINE...Rolfson