Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/23/20
Area Forecast Discussion
National Weather Service Bismarck ND
946 PM CDT Sat Aug 22 2020
.UPDATE...
Issued at 944 PM CDT Sat Aug 22 2020
For late evening update have removed precipitation chances over
the north since the only activity from the boundary, one little
shower, quickly dissipated a few hours ago with nothing since
then. High-res models have also backed off on the potential for
precipitation. Otherwise, going forecast remains in good shape.
UPDATE Issued at 636 PM CDT Sat Aug 22 2020
For early evening update have adjusted winds a bit, particularly
over the northwest, with the approaching boundary pushing through
far northeastern Montana. Have also added some very low
precipitation chances over the north while this boundary pushes
through. Only other change was to put areas of smoke through the
CWA as satellite shows smoke has pushed almost across all of
western and central North Dakota. Still unsure how much will make
it to the surface, but well worth mentioning.
&&
.SHORT TERM...(This evening through Sunday)
Issued at 215 PM CDT Sat Aug 22 2020
This afternoon, a stationary front extended across north central
North Dakota and will remain nearly in this location tonight.
A cold front in Montana will move into western North Dakota
tonight. This front will be initially dry, but should pick up
some low chances for showers and thunderstorms along the front
late tonight and Sunday.
Sunday afternoon the front and associated baroclinic zone will be
across south central ND into Northwest SD.
The RAP13 continues to show low to mid level frontogenetic
forcing increasing along the boundary Sunday afternoon and
evening. This will be the focus for lift across southwest into
central North Dakota Sunday afternoon and evening. While the
shear remains moderate at 50 kts, the GFS boundary layer CAPE is
still marginal at 500-1000. Current thinking is this will be
sufficient for some widely scattered strong to isolated severe
thunderstorms late in the afternoon and evening Sunday.
Areas of smoke from the Montana and Colorado fires will become
more prevalent across the west and central this afternoon and
tonight. Initially the smoke will be aloft. We used the HRRR
smoke model as an initial input for this.
Lows tonight will be in the mid 50s to lower 60s. It should be
cooler across the north on Sunday, with highs there around 80, to
the lower 90s south.
.LONG TERM...(Sunday night through Saturday)
Issued at 215 PM CDT Sat Aug 22 2020
The broad features in the h500 pattern continue to persist, with
a strong h500 upper high across the southwest US, with a band of
moderate westerly flow over the top of the ridge into the
northern plains. This will bring a above average convective
pattern for the region though the period.
Warm temperature will persist through midweek, followed by a
cooling trend into the weekend as a shortwave trough finally
moves through the ridge and forces it down.
Wednesday may see a potential for severe weather, as the shear and
cape are sufficient, as depicted by the GFS. However, the capping
may still present an obstacle, especially central and east.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 636 PM CDT Sat Aug 22 2020
A few showers or thunderstorms will be possible overnight over
northwest and north central North Dakota, but coverage is expected
to be sparse if storms even do develop, so have refrained from
mentioning in TAFS. Low chances for storms spread over most
locations on Sunday, but again coverage is expected to be quite
low and timing remains questionable, so have refrained from
mentioning in the TAFS at this point. Smoke from western wildfires
has spread across the area. So far no visibility restrictions have
been noticed over North Dakota. Will continue to monitor
observations and will amend if smoke results in visibility
restrictions.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
UPDATE...JJS
SHORT TERM...WAA
LONG TERM...WAA
AVIATION...JJS
Area Forecast Discussion
National Weather Service Columbia SC
755 PM EDT Sat Aug 22 2020
.SYNOPSIS...
An upper trough axis to our west will continue to bring deep
moist southwesterly flow over the region today. An upper ridge
over the western Atlantic will build into the area late in the
weekend into early next week. Tropical Storm Laura is forecast
to move into the Gulf of Mexico early next week.
&&
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Mesoanalysis as of 23z shows a stable airmass remains in place over
the area with only some light showers over the CSRA. Generally
expect showers to decrease into the overnight as the upper trough to
the west begins to lift into the Tennessee Valley while upper
ridging over the Atlantic begins to build over coastal SC. Even with
lingering moisture, expect conditions to remain mostly dry tonight,
outside of some isolated light shower activity mainly in the south
and southeast forecast area along weaknesses in the ridge and where
moisture is higher. High level clouds will persist over most of
the region through tonight with some patchy low stratus
developing late tonight. Overnight lows once again in the upper
60s and low 70s.
&&
.SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY NIGHT/...
Sunday and Sunday Night: A weakening upper level trough to the west
will lift into the Ohio valley, allowing the subtropical ridge to
extend farther west across the region. As the ridge extends
westward, channeled vorticity along the western periphery of the
ridge will shift inland from the coast, likely acting as a trigger
for showers and thunderstorms. Even to start the day, there could be
some isolated showers along a weak surface trough, but expect the
showers and thunderstorms to increase in coverage, becoming
scattered during the afternoon and early evening. Lingering showers
could persist into the overnight hours. Temperatures will remain
slightly below normal, with highs in the upper 80s. Nighttime lows
should be in the lower 70s, with a good deal of cloud cover
expected.
Monday and Monday Night: Ridging will strengthen over the area, but
an onshore low level flow off the Atlantic will ensure an ample
amount of moisture advects into the area, with precipitable water
values rising upwards of 2.3 inches in some areas. The moisture and
an active seabreeze will result in scattered to numerous showers and
thunderstorms in the afternoon/evening, with the greatest coverage
across the lower CSRA and eastern Midlands. Highs will be around 90
most areas.
&&
.LONG TERM /TUESDAY THROUGH SATURDAY/...
An upper level ridge digging across New England and part of the Mid-
Atlantic will flatten the ridge some on Tuesday, but the ridge will
restrengthen Wednesday and Thursday. Increased uncertainty for late
week into the weekend as much of the synoptic weather pattern will
depend on the eventual track of TS Laura.
Best chances of rainfall appear to be on Tuesday as the ridge
flattens, but more of a typical summertime pattern with diurnal
scattered convection expected Wednesday into Thursday. Have
maintained a forecast favored by climatology for late week given the
uncertainty with Laura. Temperatures appear to rise above normal
levels mid-late week.
&&
.AVIATION /00Z SUNDAY THROUGH THURSDAY/...
VFR conditions expected through most of the TAF period, although
some restrictions possible Sunday morning with stratus and
patchy fog possible.
Ridge extending inland from offshore. Relatively deep moisture
across the area in southwest flow aloft. Satellite indicating
mainly mid and high level ceilings at the moment but some
scattered lower strato-cumulus possible this evening. Showers in
east central Ga appears to be dissipating near the CSRA and any
showers should be limited overnight. Low-level moisture appears
higher tonight which may result in stratus toward morning. With
some clearing possible at times, there may be fog although some
mixing possible in the boundary layer through at least 09z.
HRRR model does not hit stratus too hard but lamp and mos
suggesting at least a limited threat so including restrictions
in a tempo group toward morning with lower ceiling and
visibility to IFR at AGS. Light mainly south and southeast winds
Sunday with increasing low to mid level moisture. Scattered
showers mainly in the afternoon in weakly to moderately unstable
air mass.
EXTENDED AVIATION OUTLOOK...Scattered mainly diurnal shower and
thunderstorm activity through the period. Patchy late
night/early morning fog/stratus possible.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
Area Forecast Discussion
National Weather Service Des Moines IA
630 PM CDT Sat Aug 22 2020
...Aviation Update...
.DISCUSSION.../Tonight through Saturday/
Issued at 250 PM CDT Sat Aug 22 2020
The focus for the near-term is lingering convection this
afternoon into the evening hours. Otherwise, the primary story is
the long- duration heat next week with little relief until
possibly Friday.
This afternoon into tonight...weakening convection across the
northeast where there is a little more deep moisture convergence
present and very weak mid-level theta-e advection. MUCAPE values
range from 2000-3000 J/kg but effective shear and lapse rates
remain weak and as mentioned with the lack of significant
forcing, expecting these storms to gradually wan into the early
evening. The latest HRRR run does suggest a couple of isolated
storm to trickle south and even possibly impact the DSM Metro, but
much of the storm threat should diminish by 04-06z at the latest.
Sunday through Thursday...It`s gonna be HOT! The saving grace
during this time frame is the lower dew points than what is
typical for late August. Thus, the extreme heat index values are
not anticipated. Still can`t rule out the afternoon hours each day
in a few locations getting close to 100 for a heat index,
especially Monday with less mixing. Tuesday and Wednesday are
forecast to be the hottest days, wrt temperatures. Good mixing
each afternoon should help push temperatures well into the middle
and upper 90s both afternoons. Other than the Des Moines Metro,
there should be some overnight relief as lows barely dip into the
upper 60s. The heat island effect looks to keep low temperatures
in the 70s Tuesday night and Wednesday night and there might need
a headline for the long duration heat for just the metro area.
By Friday, models are in agreement with the upper ridge breaking
down and conditions cooling off into next weekend. Precipitation
chances however look fairly bleak as any significant moisture is
being pinched off by the tropical remnants of Laura moving up
through the Ohio Valley. Thus, unfortunately the drought
conditions are likely to worsen/expand with this hot and dry week
ahead.
&&
.AVIATION.../For the 00Z TAFS through 00Z Sunday evening/
Issued at 627 PM CDT Sat Aug 22 2020
Prevailing VFR conditions generally expected at all sites, but
could see some brief MVFR conditions around KFOD/KALO/KMCW through
around 03z this evening with showers/storms in their vicinities.
Otherwise light, variable to southerly/southwesterly, winds will
be seen throughout the period.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
DISCUSSION...Podrazik
AVIATION...Curtis
Area Forecast Discussion
National Weather Service El Paso TX/Santa Teresa NM
604 PM MDT Sat Aug 22 2020
...Updated for 00Z TAF Discussion...
.AVIATION...00Z TAF CYCLE
A pretty quiet evening so far. There are a few thunderstorms near
KLSB moving west, but the short term models are indicating that
once those storms move into Arizona, we will be done for the
night. We could still see some gusty outflow winds affecting KDMN
as those storm exit the region, but generally our winds tonight
will be variable at less than 10 knots. We will see some high
ceilings of BKN250 west of the Rio Grande, but east of the river
we will have unlimited ceilings tonight. The skies west of the
river will clear later tonight. Our weather pattern won`t change
much, so tomorrow will be much like today, with just a slight
chance for rain and our winds from the southeast at less than 10
knots.
&&
.PREV DISCUSSION...235 PM MDT Sat Aug 22 2020...
.SYNOPSIS...
Scattered mountain and isolated storms will remain possible
through Monday. On Tuesday and Wednesday, most locations will be
dry with only the Gila wilderness seeing a chance for rain. By
next weekend, the Sacramento mountains may see storm chances
return as well. Temperatures will remain much above normal
throughout the period, and most lowland locations will see zero
rain.
&&
.DISCUSSION...
.SHORT TERM...
Tonight and Sunday...
Very little movement of upper high currently located over the Four
Corners region through Sunday. Moisture over the area is currently
deepest over the far west where dew points remain in the 55-60
degree range but will be mixing out into the 50-55 range by late
afternoon. Decent disturbance should allow for isolated to
scattered storms to develop by mid to late afternoon over the Gila
with some surface convergence allowing for a few storms on the
lowlands west of the Continental Divide for this evening. Less
moisture and instability over the east so think isolated coverage is
the best that can be expected there. Convection should be done by
06Z or earlier. Overnight lows look close to last night, maybe just
a few degrees cooler out west where lows remained in the upper 60s
to lower 70s.
For Sunday, with little change in the pattern and an easterly low
level continental trajectory, do not see much increase in storm
activity although there will be a disturbance affecting the eastern
zones in the afternoon and may get a couple storms to move onto the
lowlands toward far west Texas which is what the longer range HRRR
is indicating. High temperatures will be around 100 degrees for the
lowlands but should remain a few degrees short of records.
&&
26
.LONG TERM...
On Monday the upper-level high/ridge axis centered over the Four
Corners will take on more of a NE-SW orientation, and this will
cause flow aloft to take on more of an easterly component over our
area. Dry air is upstream on this trajectory, so moisture will
begin to exit. Thus, Monday looks to be the last day for lowland
storms, perhaps, through the remainder of the period. Even then
for Monday, coverage looks scattered for mountains and isolated
for lowlands, at best.
On Tuesday, enough dry air moves in that PWAT values drop well
below one inch and instability drops to near zero. Even the
Sacramento Mountains may struggle to see any convection though at
least Wednesday. Enough moisture will linger over the Gila/Black
range for isolated storms. The pattern will bring a couple of
possible bright-spots. The reorientation of upper-level flow will
allow temperatures to come down below 100 for the lowlands, and
it may also give us a break from the smoke or at least a reduction
in it.
Forecast guidance diverges some beginning later Thursday. The GFS
moves the high just enough to the north and west, aided by a weak
tropical low (which may at least be partially attributed to
Marco) to allow some recycled low-caliber monsoonal moisture to
move back in across NM and far W TX. The high then shifts back
overhead, but the GFS keeps moisture trapped beneath it. This
would allow scattered mountain and isolated lowland storms back
into the picture as soon as Thursday. The Euro does not move the
high as much as the GFS and is quicker to bring it overhead.
Moisture is not allowed to be trapped beneath it. In the Euro`s
solution we would be hotter and drier than the GFS. Given how
this summer has gone and neither pattern are really conducive for
much rain, I kept pops out of the forecast for much of the
lowlands Tuesday onwards with lowland highs back within a couple
degrees of 100.
&&
34
.FIRE WEATHER...
Upper high over the Four Corners region will move little through
Monday with hot and dry conditions generally the story with just
some isolated lowland and widely scattered mountain storms expected
with greatest coverage next couple days. As the high moves shifts
east by midweek, high temperatures will fall into the lower to mid
90s, but still remain above normal. Relative humidities through much
of the week will remain in the teens to lower 20s lowlands with 20s
and 30s mountains. Winds will not be a big concern except near
thunderstorms.
&&
26
&&
.PRELIMINARY POINT TEMPS/POPS...
El Paso 75 100 74 97 / 0 10 10 0
Sierra Blanca 72 95 65 91 / 0 0 0 0
Las Cruces 70 98 69 95 / 0 20 20 0
Alamogordo 71 99 68 96 / 0 20 20 10
Cloudcroft 46 75 50 73 / 20 40 20 30
Truth or Consequences 72 98 70 96 / 20 20 20 10
Silver City 66 90 65 91 / 30 40 20 20
Deming 69 100 69 98 / 20 20 20 0
Lordsburg 72 99 70 98 / 20 20 20 0
West El Paso Metro 75 103 76 100 / 0 10 10 0
Dell City 69 100 67 96 / 0 10 10 0
Fort Hancock 72 102 71 98 / 0 0 0 0
Loma Linda 73 94 70 91 / 0 20 10 0
Fabens 74 100 74 97 / 0 0 0 0
Santa Teresa 71 100 71 97 / 0 10 10 0
White Sands HQ 72 100 71 96 / 0 20 20 0
Jornada Range 67 98 69 96 / 10 20 20 0
Hatch 71 100 69 97 / 10 20 20 0
Columbus 73 101 71 99 / 20 10 10 0
Orogrande 72 99 69 96 / 0 20 20 0
Mayhill 54 88 56 83 / 10 40 20 30
Mescalero 52 87 55 83 / 10 40 20 30
Timberon 52 85 54 81 / 10 30 20 20
Winston 57 91 57 89 / 20 40 20 30
Hillsboro 67 96 64 96 / 20 30 20 20
Spaceport 66 98 68 96 / 10 20 20 0
Lake Roberts 54 92 57 90 / 30 40 20 30
Hurley 66 93 64 93 / 20 30 20 10
Cliff 62 98 64 97 / 30 40 20 30
Mule Creek 58 94 66 93 / 30 40 20 30
Faywood 65 95 66 93 / 20 30 20 10
Animas 67 100 67 100 / 20 20 20 0
Hachita 68 99 66 97 / 20 20 20 0
Antelope Wells 67 98 66 96 / 20 20 10 0
Cloverdale 66 93 66 92 / 30 20 10 0
&&
.EPZ WATCHES/WARNINGS/ADVISORIES...
NM...None.
TX...None.
&&
$$
99/99/15
Area Forecast Discussion
National Weather Service Elko NV
237 PM PDT Sat Aug 22 2020
.SYNOPSIS...Haze and areas of smoke will continue into Sunday,
especially in northern Nevada. Temperatures will remain much above
normal this weekend and through next week. Tropical moisture will
increase Sunday from the south and make its way northward on
Monday and Tuesday, bringing the chance for Thunderstorms to the
region.
&&
.SHORT TERM...Today through Monday
High pressure centered over the four corners region will lead to
continued southwesterly flow aloft across northern and central NV
through Sunday morning. This will mean ongoing hazy or smokey
conditions in NV due to the wildfires burning in California. A
Smoke Advisory remains in effect through Sunday morning for
northwestern counties, with lowest visibility expected to continue
there. There will start to be a wind shift more from the south on
Sunday in central Nevada, which will cut off the transport of
smoke to that area leaving the thicker haze to be more limited to
northern Nevada by Sunday afternoon.
There will also be a gradual push of mid-level moisture and weak
instability spreading up into portions of central NV this
afternoon and evening, then over most of central and portions of
northern NV on Sunday. Any thunderstorms that may develop this
afternoon and evening should be very limited, and centered over
the southern portions of NE Nye County and in White Pine County
in the Great Basin National Park region. Today being the initial
push of moisture, not expecting much if any precipitation to reach
the ground in any cells that may develop. Latest guidance
continues to show the ongoing surge of moisture and instability to
be gradual. By Sunday, mainly isolated thunderstorms will form in
central Nevada and in southern sections of Northern Nevada,
though there could be some pockets of a mix of wet and dry
scattered thunderstorms around Hwy 50 and south. There looks to be
enough instability to perhaps fire off a few strong storms there
as well.
Some showers may linger into the nighttime hours overnight on
Sunday and lasting into Monday morning with perhaps a few
lightning strikes. The moisture is expected to make its way
northward into northern Nevada on Monday. There will be an area of
isolated to scattered mix of wet and dry storms from around Elko
County southwestward into Eureka and Lander counties. Outside of
this area looks to mainly be isolated drier storms.
As for temperatures, analysis indicates that the smoke is
shielding the high temperatures just a little bit from reaching
the NBM highs and therefore highs were dropped a degree or two for
this afternoon and Sunday afternoon. Regardless, temperatures are
still well above normal.
.LONG TERM...Monday night through Saturday
Upper ridging extends out to a good portion of the CONUS at the
start of the long term period. Overnight Monday into Tuesday
morning some nocturnal convection is possible once again. Isolated
thunderstorms are expected once again on Tuesday afternoon and
evening as tropical moisture persists, with the focus on eastern
Nevada, with a few strong storms possible in northeastern Elko
County. Troffing in the Pacific northwest on Wednesday looks to
begin moving onshore and flattens the ridge some on Wednesday
night through Thursday night as it quickly moves eastward across
the northern CONUS. Thunderstorm coverage wanes on Wednesday and
Thursday, though some isolated mainly dry thunderstorms will still
be possible in eastern Nevada. On Friday and Saturday, the ridge
could rebuild some, though likely only temporarily as a deeper and
cooler Low looks poised to move into the West the following week.
Isolated thunderstorms are once again possible for eastern nevada
Friday, then all moisture may shift east of the area for
Saturday.
While cloud cover on Tuesday and Wednesday should damper high
temperatures a little on Tuesday and Wednesday, much above normal
temperatures persist, with highs mainly in the 90`s throughout
the long term period.
&&
.AVIATION...
Smoke continues to stream across northern Nevada with the lowest
visibility observed at KWMC at less than 2 miles earlier in the
day. Trends offered by the vertically integrated smoke and
visibility per HRRR model do not show any hints of improvement,
particularly northwest Nevada and KWMC. Smoke will be thick enough
with periods of IFR possible at KWMC. The smoke is less dense at
KBAM and KEKO, but prevailing visibility is likely to stay in the
3-5 SM range. KTPH has better visibility but periods of MVFR Vis
may still occur. KELY is the farthest from the smoke source and
should stay VFR.
By late Sunday afternoon, a few thunderstorms could be in the
vicinity of KELY that generate erratic gusty winds.
&&
.FIRE WEATHER...
Dry and stable air mass today means no convection this afternoon.
This changes Sunday as higher level moisture increases over
central Nevada with the best chance for storms over the higher
terrain surrounding Ely, or zone 425.
Monday, moisture spreads over northern Nevada with an ejecting
Pacific short wave to enhance convection. Possible that a few late
afternoon convection may persist after sunset. Isolated cells may
generate brief showers, but most storms will be dry or do not
produce any significant rainfall.
Tuesday, dew point values do rise into the 40s in the morning
meaning higher humidity values, supporting an environment for
mixed dry and wet storms. Will need to make another assessment on
lightning potential for Monday and Tuesday and whether fire
weather hazards exist, but confidence is lacking today on the
areal extent of lightning potential.
&&
.LKN WATCHES/WARNINGS/ADVISORIES...
Dense Smoke Advisory until 9 AM PDT Sunday for Humboldt County-
Northern Lander County and Northern Eureka County-Southern
Lander County and Southern Eureka County.
&&
$$
90/90/88/88
Area Forecast Discussion
National Weather Service Marquette MI
633 PM EDT Sat Aug 22 2020
.SHORT TERM...(This evening through Sunday)
Issued at 414 PM EDT SAT AUG 22 2020
Water vapor imagery and RAP analysis show a shortwave trof moving
over the the western Great Lakes. This trof is largely made up of a
well-defined MCV that spun up from convection in MN last night.
Center of this MCV is currently located w of KGRB, and it is slowly
moving ene toward far northern Lake MI. Plenty of cloud cover has
kept instability from building much this aftn ahead of this feature.
Latest SPC mesoanalysis has MLCAPE under 500j/kg underneath and
directly downstream of the feature. In the last couple of hrs, shra
have been developing/expanding near the center of the MCV, though no
lightning has been detected yet. Farther upstream, greater
instability w of Upper MI combined with subtle shortwave has been
supporting sct tsra from near KDLH sse along the backside of the
MCV.
MCV will move ene toward the Straits/far eastern Upper MI tonight.
Expect shra, and eventually some thunder, to continue increasing in
coverage around the MCV over the next few hrs. Given the expected
track of the feature, greatest coverage of shra/tsra will occur
across the e half of the fcst area, especially Menominee County out
to Luce County. Some breaks in the clouds are forming over western
Upper MI. So, some increase in instability combined with weak
upstream shortwave may support isold/sct shra/tsra development there
into the evening. At the moment, not expecting any svr storms this
evening given shear under 25kt and instability on the lower side.
There is a pocket of shear up to 35kt noted over Menominee County
toward Manistique. If for some reason clouds break for a time over
the next couple of hrs (looks doubtful), there could be a svr risk
in that area. During the night, pcpn will diminish/end from w to e.
Conditions should be favorable for fog/stratus to develop overnight.
Fog could become locally dense.
Expect fog/stratus to lift during Sun morning. During the day,
height rises in the wake of the shortwave trof should offer a drier
day. However, weak pres gradient will allow lake breeze development.
With low-level air mass not drying out, fcst soundings suggest there
may be enough moisture for parcels to slip past a weak cap, if
present, per some fcst soundings. Thus, fcst will reflect isold to
sct aftn convection over the w half ahead of the Lake Superior lake
breeze. Fcst soundings suggest less potential for convection over
the e, but converging lake breezes over the interior could spark
isold convection. Expect high temps mostly in the 75-80F range. Will
be slightly cooler lakeside.
.LONG TERM...(Sunday night through Saturday)
Issued at 338 PM EDT SAT AUG 22 2020
The upper level pattern of persistent ridging over the western
CONUS and the western Atlantic will continue this week, allowing
for a period of more zonal flow to establish itself over the
northern CONUS. A parade of shortwaves will move through the Upper
Great Lakes within this flow as these large synoptic features
vary in strength and position. By the end of the week, troughing
looks to reestablish itself southward out of an upper level low
over Hudson Bay. This overall pattern will give the region
multiple opportunities of showers and thunderstorms this week as
well as near normal to above normal temperatures most days. As
the omega pattern develops early this weekend, expect cooler
temperatures.
Beginning Sunday night, a shortwave and warm front north of Lake
Superior may bring some showers parts of Lake Superior late, but
overall, Upper Michigan looks dry. Expect lows to be in the low and
mid 60s. Some upper 50s could be seen in the traditional cooler
spots of the interior.
Monday into Monday night, a weak shortwave and surface cold front
will move into the west early and continue east through the day and
evening. Models vary on the evolution of precip and have dialed back
on precip potential ahead of the front. Given the model`s pulling
back some, limited PoPs to chance and slight chance. Guidance is
still queuing in on 1000-2000 j/kg MLCAPE coupled with 30-40kts of
deep layer sheer though, so if showers do develop, there is will be
a chance for some organized thunderstorms, mainly across the south-
central and east. Inverted V and steep mid-level lapse rates suggest
both large hail and gusty winds could be possible if an organized
updraft develops. Guidance also suggests PWATs above 1.5 inches,
which coupled with favorable MBE velocities, could lead to some
training and localized flooding in any organized thunderstorms.
Some guidance is suggesting that as the front exits, its east-west
elongation may allow for some additional showers early on Tuesday
in the south, but confidence is low.
High pressure will build in across Ontario behind the front as upper
level ridging shifts eastward across the northern Plains. With the
exception of any morning showers associated with the lingering
front, Tuesday looks to be mostly dry for Upper Michigan under
increasing heights. Expect highs in the 70s.
Tuesday night, another shortwave looks to ride the top of the upper
level ridge, bringing the region another shot for showers and
thunderstorms early on. At the moment, the timing of the wave in the
region looks like it could outrun its instability before reaching
the forecast area, but will still be accompanied by a good amount
of deep shear, suggesting that much of the impacts across the
forecast area will largely depend on upstream development.
Wednesday, warm front lifting through the region could again lead
to the development of some strong to severe thunderstorms. Another
shortwave could lead to more showers and storms Thursday.
On Friday, as upper level troughing begins to establish itself over
eastern North America, guidance is suggesting a deepening clipper
moving through Ontario, with potential phasing resulting in cyclogenesis
over the Upper Great Lakes. Details about this evolution are
still uncertain, including phasing with another system to the
south or any tropical system contributions into this development.
Model consensus does highlight the CAA on the lee side of the low,
allowing for a period of northerly flow and cooler temperatures
for the weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 633 PM EDT SAT AUG 22 2020
Combination of a stalled frontal boundary and a disturbance moving
ene from WI will result in shra and some tsra developing this
evening. Expect KSAW to be most directly impacted with KCMX least
likely to see any shra. VFR conditions should generally prevail into
this evening at all sites. At KIWD, MVFR cigs should largely be the
rule. Fog and stratus are likely to develop tonight, leading to
deteriorating conditions to IFR at all terminals. Slow improvement
expected Sun morning.
&&
.MARINE...(For the 4 PM Lake Superior forecast issuance)
Issued at 414 PM EDT SAT AUG 22 2020
With a weak pressure gradient over the area thru Sun, winds across
Lake Superior will remain mostly under 15kt. Winds should then be
mostly under 20kt Mon thru midweek. A humid air mass over the area
combined with some showers moving across the lake will lead to some
fog patches tonight and Sun. The fog could be locally dense.
&&
.MQT WATCHES/WARNINGS/ADVISORIES...
Upper Michigan...
None.
Lake Superior...
None.
Lake Michigan...
None.
&&
$$
SHORT TERM...Rolfson
LONG TERM...JP
AVIATION...07
MARINE...Rolfson
AREA FORECAST DISCUSSION...UPDATED
National Weather Service Morristown TN
913 PM EDT Sat Aug 22 2020
.UPDATE...
EVENING UPDATE.
&&
.DISCUSSION...
An upper trough axis will remain just west of the region through
the next 24 hours. Weak waves will rotate around this trough
enhancing areas of isentropic lift but overall activity will
mainly be diurnal in nature as dynamics are limited. Scattered
showers and isolated thunderstorms will slowly diminish overnight.
Main question is how much cloud cover will remain. If enough
breaks in the clouds occur, greater likeihood of low cloud/fog
development.
Will continue with patchy/areas of fog across the region given the
recent rains, wet soils and calm winds.
Made some minor changes to forecast lows and hourly temperatures.
&&
.AVIATION...
00Z TAF DISCUSSION.
Main concerns through the forecast period are mainly diurnal
convection from now through 03Z and again mainly late morning
through the afternoon Sunday. Also, potential of low cloud and fog
development producing IFR and possibly LIFR conditions mainly at
TRI and TYS between 08-13Z.
An upper trough axis across Kentucky and Tennessee will remain
producing periods of mainly diurnal showers and storms. Winds will
decouple this evening but return of south to southwest winds of 5
to 10kts expected Sunday.
&&
.PREV DISCUSSION...
/ISSUED 319 PM EDT Sat Aug 22 2020/
SHORT TERM...(Tonight and Sunday)...
The H70-H50 wave that has persisted across the Tennessee valley
continues to slowly move north into the Ohio valley this afternoon.
Most of the convection this morning and early afternoon has remained
well to the north across the Ohio river where a weak theta-e axis
developed. While synoptic scale lift should be maintained across the
area today, the lack of SHRA/TSRA coverage across the local area
can likely be explained by very poor lapse rates and slight mid-
level warming. The boundary layer does continue to destabilize
this afternoon with a couple thousand j/kg of CAPE. Differential
heating should be enough to maintain isolated to scattered
convection across the higher terrain. This activity will have a
northerly forward motion. Strong to severe chances look very low
today as the better shear exists to the east of the area
associated with slightly stronger southerly mid level flow.
Overnight, showers and thunderstorms will likely continue with some
uncertainty regarding the coverage. The NAM and RAP continue to
favor precipitation across the area just downstream of the H70-H50
shortwave axis...in an environment of mid-level PVA and weak
isentropic ascent on the 310-315K surfaces. Hi-res CAMs also feature
isolated SHRA overnight but coverage is much less impressive. Will
continue to favor PoPs overnight with a decreasing trend. Some heavy
rainfall and isolated flash flooding is a possibility given
increasing 0-2km moisture flux convergence...although PW values are
not overly impressive and some drier air aloft will exist. Will
leave out the mention of heavy rainfall and isolated flash
flooding as coverage is uncertain. Lows will drop into the mid
60s to near 70 degrees.
Will not see many changes to the synoptic pattern on Sunday as
the H70-H50 shortwave continues to slowly move through the
Tennessee valley. Continued moisture advection in southwest flow
aloft combined with synoptic scale ascent will bring another day
of showers and thunderstorms to the area. Weak lapse rates and
warming aloft should limit any strong or severe thunderstorm
chances. Only hazard would be additional heavy rainfall and
possibly flash flooding as PW values remain elevated. Highs on
Sunday will rise into the upper 70s to mid 80s still several
degrees below average. Again, the low probability of hazardous
weather will preclude the mention of any hazards in the HWO.
Diegan
LONG TERM...(Sunday night through Saturday night)...
The extended begins with weak troughing across the Tennessee and
Ohio Valleys between two large anticyclones across the Mountain West
and the western North Atlantic. TC Marco will be nearing landfall
across the Gulf Coast on Monday before slowing and dissipating
across the lower Mississippi Valley on Tuesday with very high PW
values remaining near the remnant system. An old/remnant moisture
boundary across SC/GA/AL will be a focus for low-level convergence
and diurnal thunderstorm development. There is some uncertainty in
the exact location of this boundary, but with it generally being
near or south of the forecast area, PoPs will be highest across our
southern zones with a diurnal trend in probs and coverage each day.
With this general summer-like pattern, kept temperatures near or
slightly above normal.
Late in the extended, uncertainty is high. Much depends on the
tracks of TC Marco and TC Laura. Landfalling tropical systems across
the norther Gulf Coast occasionally impact the Tennessee Valley and
Southern Appalachians with remnant heavy rainfall and breezy
conditions. Current global model guidance is coming into better
agreement with TC Laura approaching the northern Gulf Coast by
Wednesday and then moving northward through the Mississippi Valley.
The remnants of Laura would then merge with a shortwave trough and
amplify troughing across the Eastern CONUS. This scenario would
bring abundant moisture into our forecast area ahead of a surface
cold front moving southeast on Friday and Saturday with the
potential for locally heavy excessive rainfall. However, QPF and
PoPs will be highly dependent on the remnant tracks of TC Laura and
the TC Marco. Guidance is beginning to include likely PoPs on Friday
and Saturday, but with the uncertainty of tropical system tracks 5
to 7 days out, did not include any higher than high chance PoPs at
this time. If better run to run consistency develops over the next
24 hours, PoPs could be trended higher late week in future forecast
issuances.
JB
&&
.PRELIMINARY POINT TEMPS/POPS...
Chattanooga Airport, TN 70 86 70 88 72 / 40 40 20 40 20
Knoxville McGhee Tyson Airport, TN 68 85 68 87 70 / 40 40 20 30 10
Oak Ridge, TN 68 85 68 88 69 / 40 40 20 30 10
Tri Cities Airport, TN 64 84 66 85 66 / 40 40 20 30 10
&&
.MRX WATCHES/WARNINGS/ADVISORIES...
NC...NONE.
TN...NONE.
VA...NONE.
&&
$$