Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/23/20

Area Forecast Discussion

National Weather Service La Crosse WI

 1101 PM CDT Thu Oct 22 2020

.SHORT TERM...(This evening through Friday)
Issued at 345 PM CDT Thu Oct 22 2020

Tonight and Friday... Forecast concerns in the short term will be
showers and thunderstorms this afternoon and tonight, track of
the surface low and potential for some strong to severe storms
with hail/damaging winds, then ending of precipitation with a mix
or some light snow possible before ending.

At 18Z the latest subjective surface analysis had northeast
surface flow across much of the forecast area with an inverted
trough near KOLZ and KPVB. By 20Z..the surface front had lifted
north with temperatures approaching 80 degrees at DVN. The warm
front was farther south toward Ottumwa IA and Moline IL...but had
lifted north of DVN by 20Z. Surface dewpoints were in the 60s to
lower 70s south of the warm front with dewpoints in the 30s and
40s farther north. Temperatures across the forecast area ranged
from the lower 30s from KRST toward KMDZ with other readings in
the 30s to mid 40s. A mix of precipitation fell across the area
this morning with the wide range in temperatures. Some light
glazing on elevated surfaces where temperatures were near or below
freezing, some sleet thundershowers and showers and thunderstorms
farther south. Precipitation amounts through 1pm were variable
with trace to half inch amounts common from far northern Iowa into
west central Wisconsin and points north. South of this area,
rainfall was more 0.6 to 1 inch with a few smaller bands from 1 to
1.5 inches. With the storms already this afternoon, we have had
pea to dime-sized hail with the limited instability available.

The pattern through Friday morning is for the 500mb trough over
the eastern Rockies to deepen as it moves into the western High
Plains this evening and swing through the upper Mississippi Valley
Friday morning.

Surface low pressure toward Kansas is forecast to
track northeast toward Dubuque into southern Wisconsin overnight.
The low level jet is forecast to strengthen to around 45-50kts
near the front by 21Z- 00z...the veer to 60kts more toward
southern WI. Sfc instability around 2500 J/kg was over far
southern Iowa and per the SPC meso- graphics forecast to lift
north with around 500 J/kg toward DBQ by 00Z with MLCAPE of 2000
J/kg just south of the forecast area and MUCAPE spreading farther
north into southern MN and parts of west central WI. Effective
bulk shear is around 45-55kts near the surface front and effective
helicity of 200-400m2/s2. With this increasing low level jet,
surge of low level jet and instability, there is good agreement in
the re-development of convection late this afternoon along and
north of the front. The trends in the HRRR MUCAPE have been to
decrease the northward extent of the higher MUCAPE from the 16Z to
the 18Z run...so this trend will need to be monitored. SPC has
placed part of northeast Iowa and southwest Wisconsin into the
slight risk of severe weather. Farther north there remains a
marginal risk. The severe weather threat especially for hail seems
reasonable based on the strength of the low level jet,
instability and shear.

As the trough pushes through Friday morning with the colder
temperatures some mixed precipitation is possible. Forecast
soundings point toward a little light snow/snow showers over parts
of southeast Minnesota into western Wisconsin, but the snow would
be patchy.

Gusty northeast winds will become northwest once the surface low
passes to the southeast. Northwest winds should gust to around 30
mph with temperatures only in the 30s resulting in wind chills in
the 20s.

.LONG TERM...(Friday night through Thursday)
Issued at 345 PM CDT Thu Oct 22 2020

Surface high pressure will build in through Saturday with
temperatures in the lower 30s to lower 40s...well below the
normal high in the mid 50s. The next trough over Montana Saturday
is beginning to spread snow across the Dakotas. The storm system
continues to spread snow eastward across the Plains into the
forecast area. There is good agreement with the global models and
the ensembles on accumulating snow Sunday into Sunday night. The
GEFs for LSE is around 2 inches with a spread of 1 to 5 and is
similar at RST with slightly higher amounts with the mean of 2 to
3 inches. Cold temperatures continue Monday and Tuesday with only
slight warming later in the week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1059 PM CDT Thu Oct 22 2020

A low pressure system will move northeast through southeast
Wisconsin overnight. Visibilities will likely remain MVFR through
23.14z for KRST. Ceilings will remain IFR/MVFR into Friday
morning and then become MVFR on Friday afternoon and stay MVFR of
Friday evening.

&&

.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&

$$

SHORT TERM...Zapotocny
LONG TERM...Zapotocny
AVIATION...Boyne



Area Forecast Discussion

National Weather Service Des Moines IA

 641 PM CDT Thu Oct 22 2020

...Updated for 00z Aviation...

.DISCUSSION.../Tonight through Thursday/
Issued at 314 PM CDT Thu Oct 22 2020

Today and Tonight (Previous 12:01 PM CDT Update):

Key Points:
- Warm Front Surging Northward
- Narrow Window For Severe Threat
- Conditional Threat for Supercells

Technical Details:

Warm front is oriented east-west across  extreme north-central
Missouri as of a 16z analysis. Dewpoints with this warm airmass have
been in the mid to upper 60s, rather anomalous for late October.
Visible satellite imagery is showing breaks in the cloud cover in
far southern portions of the forecast area. In north central
Missouri, insolation from clear skies well behind the warm front
have allowed SBCAPE values to jump to near 2000 J/kg. This will
likely keep going up this afternoon, and will slowly work its way
into southern and southeastern portions of the forecast area after
19z. There is some limited CIN, especially close to the stratus
shield that starts in central Iowa and is expansive northward. And
there are some wave-like characteristics within the vicinity of the
boundary, which would indicate there is cap vertical motion if
fighting. However, HRRR soundings mix the boundary layer out rather
well, and it appears that this is happening in Missouri so far, and
will continue to move north. As this happens, lapse rates will
continue to steepen, increasing the strength of the thermodynamic
environment. There is still some uncertainty with respect to how far
north the warm front will surge as the surface cyclone tracks toward
the northeast. Synoptic scale models like the GFS and NAM limit the
northward extent, while a few of the CAMs go a little bit further
north. The northward push of the warm front will be important in
clearing skies this afternoon. The HREF does have mean SBCAPE sneak
up north up to about Hwy. 30 with values near 2000 J/kg. On the back
side of the surface cyclone is a strong cold front that will be the
key source for convergence this afternoon and into evening, as it
pushes up against the warm unstable airmass. Given the
aforementioned stratiform shield over the greater part of central,
western and northwestern Iowa, the severe threat with thunderstorms
initiated appears to have a narrow window of opportunity both in
time and areal coverage. The areal coverage will be confined to
mainly southeast Iowa, and perhaps portions of east-central Iowa, or
east of Interstate 35 and from the IA-MO state line to somewhere
between Interstate 80 and Hwy 30. CAM guidance is suggesting initial
development after 19z in western Iowa, but holds off on any robust
convection until 21z when convergence increases in the clear sky
region. Deep layer shear values are high enough for supercell
development, 0-6 km values at 40-60 kts. 0-1 km SRH values in
southern and southeast Iowa may reach as high as 300 m^2/s^2, which
would support a tornado threat. However, this window of opportunity
if very narrow, and also extremely conditional on discrete
convection starting. Even though there is a great amount of deep
shear, the vector will quickly become parallel to the initiating
boundary, creating an environment more favorable for a linear
convective event. With steep lapse rates and deep layer shear, there
also will be a threat for large hail with initial discrete storms.
As the system becomes more linear, it will quickly turn into more of
a damaging wind threat. The cold front will then sweep through the
late evening, before eventually exiting the state. There does appear
to be signal for lingering elevated instability, which may lead to
trailing elevated convection on the back side of the cold front.
Precipitation should completely clear the area after 8-9z Friday
morning.

Friday and Saturday:

Short-wave trough axis will shift eastward of the region Friday and
move into the Great Lakes Region by Saturday. Weak AVA over the
northern Plains will help to develop surface high pressure behind
the cold front. Persistent north-northwesterly flow will allow cold
air to continue to filter into the region. This will send high
temperatures into the lower 40s for central and southern Iowa, with
mid to upper 30s for northern portions of the state. Most of the
precipitation should be out of forecast area by the mid morning on
Friday, some lingering light showers may still be on going in the
far east. For the rest of Saturday and Sunday, high pressure will
help to keep conditions dry. Moderate pressure gradient will be in
place with the surface high pressure and exiting low, making for
breezy winds for the first part of the weekend.

Sunday Snow:

Another trough will develop late Saturday Night into early Sunday
morning across the southern Canadian Prairie Provinces, and surface
lee cyclogenesis will again occur in response to this. This system
will have rather robust dynamics with it, and likely will have areas
with enhanced frontogenetical forcing. Convergence in Iowa will not
be hard to come by on Sunday. What is interesting, is that the 12z
GFS has tracked the surface cyclone further south, but the ECMWF
tracks the center further north through the Ozarks Region.
Regardless, it is still looking like a widespread precipitation
event for Iowa on Sunday. Ensemble means for Sunday with respect to
QPF have a widespread 0.10", but several members in multiple
locations depict as much as 0.40". If a track similar to the GFS
occurs, the air will be quite cold, and most of the precipitation
would likely be snow. However, if the track remains further north,
there likely will be periods of rain followed by snow, dependent on
when the temperatures drop again after the center of the low has
pushed east. In addition, a north vs. south solution will also
impact how much moisture works back into Iowa ahead of the low
pressure. As mentioned at the top of this section, there likely will
be frontogenetical bands that develop as this system passes by, and
could result in some locations of the forecast area having snow
accumulations that would require headlines. For now, will be
conservative with the forecast and let today`s system pass by, and
allow subsequent runs to better depict the dynamics and additional
ensembles address the uncertainty with QPF and temperatures for
Sunday. But, be prepared for wintry impacts Sunday and maybe early
into Monday morning.

Extended:

Long range guidance in decent agreement with with trough acquiring
positive tilt as it propagates away from the Rockies. Closed low
over Hudson Bay moves south, forcing the flow further south and
allowing the trough to dig toward the Gulf Coast. This will allow a
strong Polar Airmass to move into the Upper Midwest, making for
unseasonably cold conditions across the state. This will lead to a
high potential for daily overnight low temperature records, and may
even lead to a few locations achieving daily record low maximum
temperatures. There may also be a few perturbations in this flow
leading to wintry precipitation. More details on precipitation in
the extended will be better known at a later time.

&&

.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 641 PM CDT Thu Oct 22 2020

Scattered showers and thunderstorms are moving across the state
this evening and will continue through the overnight hours. IFR to
LIFR cigs and occasionally decreased vis will continue to impact
most sites through the overnight and Friday morning before
gradually improving. North winds will also increase Friday,
gusting between 20 to 25 kts.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

DISCUSSION...Krull
AVIATION...Hagenhoff



Area Forecast Discussion

National Weather Service Marquette MI

 634 PM EDT Thu Oct 22 2020

.SHORT TERM...(This evening through Friday)
Issued at 511 PM EDT THU OCT 22 2020

Water vapor imagery and RAP analysis continue to show a mid-level
trof dominating Canada from coast to coast. Shortwave that was
dropping into the Pacific NW 24hrs ago has amplified this trof
southward toward the central Rockies. Response downstream has been
for increasing waa/isentropic ascent spreading into the Upper Great
Lakes today. Forcing for upward motion is further being aided by
right entrance of 140kt upper jet across northern Ontario. Northward
surge of deep moisture has brought precipitable water up to a little
over 200pct of normal at KOAX/KDVN per 12z raobs. Thus, with the
forcing, widespread pcpn has developed/lifted n into Upper MI this
aftn, though dry lower levels have delayed pcpn onset over nw Upper
MI. Lightning is also being noted to the s in WI.

Fcst today is no easier than yesterday, and it has been a huge
challenge trying to get weather and snow accumulations into a
gridded format that represent expectations. Initial surge of pcpn
across the nw 1/2 to 2/3rds of fcst area has been snow or rain
changing to snow. To the s, pcpn is becoming much more showery with
embedded thunder. Expect this pcpn to lift ne generally impacting
areas from Iron/Marquette counties eastward. This showery pcpn is
likely accompanied by a warm nose above 0C roughly positioned in the
6-10kft layer per NAM/RAP fcst soundings. Parcels will have have
some CAPE when lifted from near the top of this warm layer, so
expect some of the thunder to the s to lift across roughly the se
half of the fcst area this evening. Where the warm layer above 0C is
less pronounced, this showery pcpn with embedded thunder may produce
some bursts of mdt to possibly hvy sleet. The area from roughly
Crystal Falls/Iron Mtn ne to Gwinn/Munising will probably be most
susceptible to bursts of sleet. So, the advy for Dickinson and Alger
counties will remain in place for this potential. Farther e and s,
rainfall may become locally hvy at times. To the w, expect periods
of snow thru the evening. Radar imagery upstream does not look too
concerning and with the positive tilt of the trof, not likely to see
any significant pcpn develop to the w of the warm conveyor pcpn
lifting across the e half of the fcst area. So after periods of snow
for the next several hrs, pcpn will diminish. Mid-level drying may
end up leading to pcpn diminishing to -dz/-ra for at least a brief
time overnight as ice nucleation processes are lost. Temps will
change little thru the night.

Shortwave will lift across the Upper Lakes on Thu. With it, deeper
moisture will return to areas that had some mid-level drying
overnight. Combined with a period of deep layer forcing and 850mb
temps falling to -5 to -7C, lake enhancement will kick in. Should be
a well-defined upslope component to this pcpn under brisk nne winds
backing nw. DGZ will be largely placed above the moist layer, and at
a minimum, the upward motion will occur blo the DGZ even where the
DGZ drops into the moist layer. Thus, not expecting significant snow
accumulations on Thu in the n wind lake effect snow belts. Did opt
to extend advy for Baraga/Marquette given the sharper upslope and
longer fetch that will for a time have a streamline extending to
Lake Nipigon during the time of best forcing. A few inches of wet
snow may accumulate on the high terrain zone favored by strongest
upslope under nne wind backing nnw. Away from the lake effect areas,
expect some -shsnra. Will be a blustery day closer to Lake Superior
where winds will gust 25-35mph, especially from the Keweenaw
eastward.

.LONG TERM...(Friday night through Thursday)
Issued at 414 PM EDT THU OCT 22 2020

A cold front should be past and headed se towards MI`s Lower
Peninsula by Friday night. Temperatures will take a plunge as CAA
moves into the area. As the CAA pushes through, this will cause a
period of consistent nw winds at the sfc and 850 mb level which,
given the difference in the 850 mb and lake sfc temperature, will
bring about lake effect rain/snow from Friday night into Saturday.
Expect mostly, if not all snow in the west, whereas the east may see
some rain mix in at times, particularly during the daytime hours
Saturday. A small sfc high pressure looks to develop over eastern
Lake Superior Saturday, which will bring in some wind shear between
the sfc and 850 mb level. This, in turn, should stop most of the
lake effect precip, although a few remnant bands may remain in the
east early Saturday night.

As we move from Saturday night into Sunday, a shortwave associated
and on the north side of a low pressure system down in the Southern
Plains will move through and bring mixed precip into the area. The
west again should see more snowfall, whereas the east may see more
rainfall mixed in during the afternoon hours. Once this shortwave
moves through the area as the low pressure it is associated with
moves ne, expect some lake effect snow in the central and east, with
rain mixing in east. By Monday night, winds will shift quickly
again, cutting off the lake effect process. However, there may be
some stray lake effect showers early in the evening east.

Models diverge late in the fcst period. What is predicted is a
shortwave that looks to come into Upper MI, the only problem is
pinpointing when. The Euro has the shortwave moving through
Wednesday and Wednesday night, whereas the Canadian and GFS have the
shortwave arriving later (Wednesday night into Thursday).
&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 634 PM EDT THU OCT 22 2020

A mixture of pcpn, mostly snow will continue this evening with all
sites remaining at LIFR/VLIFR. Vsbys will depend on when snow is
present at the terminals, as periods of rain, snow, and possible
sleet will create varying vsby conditions this evening. Gusty winds
(gusting to 25-30 knots, especially at CMX and SAW) will develop
late tonight as winds increase from the NE as a sfc low moves over
Lake Michigan and the pressure gradient increases. Winds back more N
toward 12Z Fri and then further to the NW tomorrow with lake-effect
precipitation remaining, but generally diminishing. Conditions will
slowly improve Fri morning at all sites.
&&

.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 531 PM EDT THU OCT 22 2020

Strong high pres building into the Dakotas combined with a low pres
wave lifting ne to Lower MI late tonight/Fri morning and into Quebec
late Fri will lead to strengthening ne winds across Lake Superior
tonight. Winds will back n to nw on Fri. Winds will increase to 20-
30kt across the lake tonight with some gale force gusts to around
35kt. While winds will diminish to under 20kt over western Lake
Superior Fri aftn, expect 20-30kt winds to continue over the e half
along with some gale gusts to around 35kt. By Sat, winds should be
20kt or less across the lake. These lighter winds will linger thru
Sun as a very weak trof drifts acros the lake. Winds will then
increase some for Mon as a strong high pres builds se into the
Plains. Low pres heading e toward Hudson Bay on Tue will bring a
further increase in winds to 20-30kt, at the very least over western
Lake Superior.
&&

.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
  Winter Weather Advisory until 8 AM EDT /7 AM CDT/ Friday for
     MIZ002-003-006-009>011-084.

  Winter Weather Advisory until 4 PM EDT Friday for MIZ004-005.

  Lakeshore Flood Advisory until 3 AM CDT Friday for MIZ012.

Lake Superior...
None.
Lake Michigan...
None.
&&

$$

SHORT TERM...Rolfson
LONG TERM...TAP
AVIATION...07
MARINE...Rolfson




Area Forecast Discussion

National Weather Service Nashville TN

 803 PM CDT Thu Oct 22 2020

.UPDATE...
FOR EVENING DISCUSSION.

&&

.DISCUSSION...

Pleasant and mild evening across Middle Tennessee with current
temperatures in the mid 60s to low 70s with dewpoints in the
upper 50s to low 60s. Temperatures won`t fall much overnight as a
southerly LLJ increases to 30 kts across the area, with lows
ranging from the upper 50s east to mid 60s west. The strengthening
LLJ should also keep any fog formation quite patchy at best.
Latest short term models such as the HRRR and CONSShort show
isolated showers breaking out in parts of the area between 10-12Z
tomorrow morning, with showers gradually increasing in coverage
through the day and a few thunderstorms mixing in by late morning
and afternoon. Have adjusted hourly pops based on latest short
term guidance.

Cold front progged to reach our northwest counties by 00Z Friday
evening then be east of the Plateau by 12Z Saturday morning, with
highest precip chances along and ahead of the boundary. Forecast
soundings don`t show anything noteworthy, but MLCape near/over 500
J/Kg, mid level lapse rates around 6 C/km, and deep layer shear
around 20 kts might be enough for a strong storm or two - mainly
in our northwest counties late Friday afternoon into early Friday
evening. Models are not very enthusiastic about this potential,
however.

&&

.AVIATION...
00Z TAF DISCUSSION.

BNA/MQY/CKV/CSV...Clear skies and high pressure cover the mid
state this evening, but it won`t stay that way much longer.
We`ll leave radiation fog out of the TAF`s for now. Even though
we`ve experienced widespread radiation fog the last few nights,
look for surface winds to increase during the next few hours as
the pressure gradient starts to tighten up ahead of an approaching
cold front. LLWS can also be expected after 06Z as the low-level
jet strengthens. Also, t-over values don`t support significant fog
development, but we`ll evaluate more closely with the 06Z TAF`s.
Tomorrow, look for widespread showers to develop and also a few
storms during the afternoon as the surface front pushes into
Middle Tennessee.


&&

.OHX WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

DISCUSSION......Shamburger
AVIATION........08