Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/06/21
Area Forecast Discussion
National Weather Service Aberdeen SD
848 PM CDT Thu Aug 5 2021
.UPDATE...
Issued at 848 PM CDT Thu Aug 5 2021
Surface obs upstream in northeast winds showing 3 to 6 miles in
smoke/haze. Aberdeen had also come down to 5 miles this evening.
The hrrr surface smoke also indicated a higher smoke concentration
coming in from the north tonight. Thus, added in patchy smoke for
the night for the cwa.
UPDATE Issued at 637 PM CDT Thu Aug 5 2021
00z aviation discussion updated below.
&&
.SHORT TERM...(This Evening through Friday Night)
Issued at 244 PM CDT Thu Aug 5 2021
Northwest flow aloft with ample shortwave activity embedded in the
flow will keep the pattern active tonight through Friday morning
with persistent non-zero chances for showers. Chances for
thunderstorms will increase a bit late Friday with southeast flow at
the sfc drawing up llm ahead of a lee side low. A 25 kt llj will
develop across the east Friday evening as the sfc low pushes into
central SD.
Elevated smoke from western U.S. fires will remain over the region,
but temperatures are still expected to climb into the 90s on Friday
as the upper ridge builds during peak heating. The ridge will
collapse Friday night under the influence of an upper trough over
the western Dakotas.
.LONG TERM...(Saturday through Thursday)
Issued at 244 PM CDT Thu Aug 5 2021
An area of low pressure and associated frontal boundaries will
cross the region on Saturday, bringing the potential for strong to
severe storms, mainly in eastern SD and western MN. Low level
moisture advection ahead of the surface low could produce dew points
in the mid to upper 60s, creating a moderately unstable environment.
With about 30-40 knots of shear, along with upper level support from
a trough, convection should develop over eastern SD during the mid
to late afternoon hours. Increasing 850 mb winds could aide with
producing a few severe storms with hail and damaging winds the main
threats. Convection should progress into MN before 12Z Sunday with
mostly dry conditions expected for the rest of the period. A few
models are supporting a potential cool down during the middle of
next week with highs in the 70s. Boundary layer dew points off the
12Z GFS drop into the mid 30s over a good portion of the CWA on
Wednesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday Evening)
Issued at 637 PM CDT Thu Aug 5 2021
Terminals KABR,KATY,KPIR,KMBG
VFR conditions are expected through tonight and Friday at all
airports.
&&
.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&
$$
UPDATE...Mohr
SHORT TERM...Wise
LONG TERM...SD
AVIATION...Mohr
Area Forecast Discussion
National Weather Service La Crosse WI
1030 PM CDT Thu Aug 5 2021
.UPDATED...
Issued at 825 PM CDT Thu Aug 5 2021
Convection firing to the west/northwest along a cold front, enhanced
in areas co-located with upper level shortwave support. Latest
RAP/HRRR mostly keeps the northern bit of energy north while diving
the bit to the west southeast. Effectively, this skirts the forecast
area. However, the sfc front continues to sag southeast, and while
the RAP suggests the convergence will weaken as the night wears on
areas devoid of the shortwave energy, a MUCAPE pool upwards of 1500
J/kg travels with the boundary. Might be enough to continue
isold/sct convection. Have adjusted rain chances up a bit
tonight/fri morning and will continue to monitor/adjust as needed.
At this time, don`t see a severe threat. Storms will be elevated
limiting any wind concerns. Perhaps small hail in a stronger storm.
Mostly locally heavy rain and lightning.
.SHORT TERM...(Tonight)
Issued at 201 PM CDT Thu Aug 5 2021
Recent radar imagery showed a band of showers stretching from north
central Wisconsin back towards southeast Minnesota then down nearly
along the Mississippi River Valley into northwestern Illinois with a
separate small cluster working its way through northcentral Iowa.
These showers are expected to continue their northeastward
progression. The northern portion of this band has held relatively
steady since this morning as a mid-level shortwave trough moved
through the region being co-located with decent moisture transport
pushing northeastward. Whereas the southern portions of the band
have slightly weakened into this afternoon as they moved away from
the better forcing. Although low, isolated thunder is possible, but
the greatest instability near 3000 J/kg remains off to the west of
the region in southwest Minnesota into southeastern South Dakota.
The surface boundary was draped from northwest Minnesota into
central South Dakota. Several of the convective allowing models
(CAMs) are showing thunderstorms initiating off of this boundary as
it slowly moves southeastward into central Minnesota tonight. The
storms progress to the southeast away from the boundary. Moving away
from the pool of higher instability, the storms are then anticipated
to weaken by the time they would reach the local area. If the storms
hold together as they progress to the east, just general
thunderstorms would be expected with little 0-6 km shear limiting
severe development.
With the recent rainfall and decreasing winds overnight, this could
lead to areas of fog developing by sunrise Friday morning. Was not
fully confident to include this in the forecast at this time as
clouds are expected to linger over the region which would limit the
radiational cooling.
.LONG TERM...(Friday through Thursday)
Issued at 201 PM CDT Thu Aug 5 2021
FRIDAY...Pulses of shortwave energy could cause lingering showers
and storms into Friday morning, especially the trough identified
clearly in the GOES-east water vapor imagery over nern MT. Clouds
should dissipate from west to east into the early afternoon. Surface
warming throughout the day and the passage of a weak warm front from
the south help build a pool of CAPE into the area south of I-90. The
lack of shear and forcing limits widespread organized convection,
but a late afternoon isolated strong storm could occur. If cloud
cover persists later into Friday, it will decrease instability and
strengthen the cap/CIN, acting to limit storm initiation in our
region Friday night.
As the low level jet noses its way into southwestern Wisconsin
Friday night it could initiate isolated showers and storms,
especially along the southeastern border of our forecast area. There
is fairly consistent signal of scattered storm activity on the warm
front arc from sw WI into central MN by Saturday morning in the
latest hi-res CAMS.
SATURDAY...As the deeper trough, now over nrn CA, ejects into the
High Plains Saturday, surface low pressure deepens over the
Dakotas. Warm frontal lifting late Friday night into Saturday
morning poses a threat for another round of showers and
thunderstorms. A break in the precipitation Saturday afternoon is
likely, but skies seem remain cloudy keeping temps in the low to mid
80s.
Saturday night, the low level jet and 850 mb moisture transport
strengthen along a warm front on the periphery of the deeper trough
approaching from the Northern Plains. Isolated storms may form along
the warm front in the very early evening. 0-3km shear supports more
organized, multicell storms with the potential for damaging winds
and isolated large hail. This may be the best chance at severe
storms for the weekend. As the night progresses, this will likely
develop into a region of widespread rain and storms. Precipitable
water values of 2.0 inches and prolonged moisture advection from
northeastern Iowa into northwest Wisconsin signal a prolonged heavy
rain event across the region is possible. This is supported by
ensemble agreement from the 05.00z EC, GEFS, and Canadian ensemble
systems.
SUNDAY...The broader trough will continue its eastward propagation
into our area Sunday morning resulting in continued forcing as the
low level jet dissipates keeping showers and storms active. By
Sunday morning, some areas could see 3-5 inches of rain if the heavy
rain signal verifies. Southwesterly flow causes a constant moisture
flow into the area, continually feeding widespread showers
throughout the day Sunday. Overall a rainy day it appears, with any
clearing allowing more CAPE to build and showers/storms to result.
Sunday night through Thursday...Forecast confidence lowers into this
period as the trough over the Great Lakes has large spread in the
model guidance on the exit speed - which could prolong the
rainfall/chances into Monday...with the 05.00Z ECMWF ensemble family
being the slowest and wettest. Shortwave ridge building then occurs
into midweek with a drier day(s) possible. The large scale
readjustment occurring next week over the CONUS is causing a variable
forecast outcome with ensembles 180 degrees out of phase. For now,
the consensus model blends seem the best to use in this lower
confidence time period.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1030 PM CDT Thu Aug 5 2021
Challenging forecast when it comes to cigs and pcpn chances. Several
upper level shortwaves and sfc boundaries will meander across the
region over the next few days, bringing a variety of cigs with
occasional shra/ts chances. Confidence is not high with pinpointing
the higher impacts periods at this time.
Cigs: another plume of high/mid level clouds moving in thanks to a
line of convection approaching from the northwest. Could see some
increase in low level RH, mostly across WI by 12z. Some models more
robust, other suggest it will stay farther east. For now, will add
some MVFR at KLSE and keep RST VFR. Looking at mostly sct-bkn mid
clouds then for tomorrow as front slips southward. However, if it
holds farther north, greater chance for a bkn CU deck that could
flirt with MVFR.
WX/vsby: a cold front/upper level shortwave was firing bkn line of
shra/ts across northwest WI/southeast MN at late evening. Trends
favor continuing the storms over northern WI where forcing is
strongest, weakening/diminishing the activity as it nears KRST/KLSE
where forcing wanes. Will follow this with VCTS at KRST and keep
KLSE dry for now. Could still see some BR toward 12z, but chances
decreasing with more cloud cover anticipated.
Later in the day Friday, a few models suggest the cold front will
hang closer to I-90 rather than sinking farther south. That would
bring shra/ts back into the forecast. More support for driving the
front to the south though, especially in the CAMS, and going this
way. If we stay rain free, could stay that way until later Fri
night/Sat morning when the front moves back north with a shortwave
trough ejecting out of the southern plains.
Winds: mostly light southerly through the period, although with some
bagginess in the sfc pressure gradient, there could be some
variability in direction from time to time. Winds will pick up for
Sat as said gradient tightens.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
UPDATED...Rieck
SHORT TERM...Peters
LONG TERM...Baumgardt/KAA
AVIATION....Rieck
Area Forecast Discussion
National Weather Service Denver/Boulder CO
927 PM MDT Thu Aug 5 2021
.UPDATE...
Issued at 852 PM MDT Thu Aug 5 2021
There are a few showers and storms over the northeast corner of
Colorado this evening. PoPs were added to the forecast through
midnight to account for these showers and storms. They should end
around midnight as stability increases. There were a couple storms
in Grand County as well so PoPs were added there too but these
will have even less instability to work with and should end soon.
Some of the high resolution models are starting to show a good
signal for strong outflow winds across the northeast corner
tomorrow afternoon. There was not high enough confidence at the
moment to change the forecast but a severe wind gust is possible
across the northeast corner tomorrow.
&&
.SHORT TERM...(This evening through Friday)
Issued at 211 PM MDT Thu Aug 5 2021
The upper level ridge has pushed in over the Great Basin and is
pulling northwest flow into the region. This is also bringing
increased levels of smoke down from fires across California and the
northwest. Some CU has developed across the higher elevations but
mid-level drying will help to keep convection at bay and conditions
dry for the late afternoon and evening. Current HRRR smoke
projections have elevated smoke sticking around through the evening
ahead of the incoming shortwave. This and the aforementioned upper
flow will keep overnight lows more mild in the mid-60s across the
plains.
Looking to Friday, a shortwave embedded in the upper flow aloft that
is currently pushing into western WY will move into CO during the
morning hours. There is some weak forcing associated with it that
will help to fire off some afternoon convection across the higher
terrain that will move onto the plains by the late afternoon. Model
upper air soundings indicate more high-based storms with DCAPE
values from 1400-1500 J/kg that will equate to more gusty wind
impacts then intense rainfall. Some storms could produce winds up to
50 mph with outflows into the evening hours. Outside of the storms
winds will stay elevated with subsidence increasing behind the
disturbance with gusting from 35 to 45 mph across the higher
elevations with mixing by the afternoon. In return, this will help to
scour out the low lying smoke and provide some relief over the next
few days. Highs will continue their upward climb with temperatures
in the mid to upper 90s across the lower elevations and 70s to low
80s in the mountains and high mountain valleys.
.LONG TERM...(Friday night through Thursday)
Issued at 211 PM MDT Thu Aug 5 2021
FRIDAY NIGHT INTO SATURDAY, AN UPPER LEVEL TROUGH OF LOW PRESSURE
WILL MOVE ACROSS THE NORTHERN AND CENTRAL ROCKIES WITH A DRY WEST TO
NORTHWESTERLY FLOW ALOFT OVER COLORADO. THIS PATTERN WILL BRING
MOSTLY DRY, COOLER AND BREEZY CONDITONS TO NORTH CENTRAL AND
NORTHEASTERN COLORADO WITH ONLY A FEW HIGH BASED SHOWERS POSSIBLE
MAINLY OVER THE MOUNTAINS and far northeastern plains. With low
relative humidity, gusty winds and dry fuels, fire danger will be
elevated across the far northeastern corner of Colorado.
FOR SUNDAY AND MONDAY, DRY WEATHER AND ABOVE NORMAL TEMPERATURES are
expected AS UPPER LEVEL HIGH PRESSURE DOMINATES THE SOUTHERN TIER OF
THE U.S and ANOTHER UPPER LEVEL TROUGH OF LOW PRESSURE MOVING ACROSS
THE NORTHERN ROCKIES.
For Tuesday through Thursday, upper level high pressure begins to
build over the Western U.S. with a northwesterly flow aloft over
Colorado. There is some differences between the models in how they
handle an upper level low pressure system over the Central Plains
States. The ECMWF shows an upper level low centered over the Black
Hills by 00Z Friday with the GEM solution having a deeper low
centered over Eastern South Dakota. The GFS solution shows no such
low and has an open trough covering much of the Central and Eastern
U.S. Both the ECMWF and GEM solutions show some increase in
subtropical moisture and QPF during this period, while the GFS keeps
things dry. For now will go with the forecast model blend and make
some tweaks to lower the pops somewhat.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 852 PM MDT Thu Aug 5 2021
Smoke will continue to impact visibility through this evening but
it will improve during the early morning hours as clearer air will
move in. It`s possible some smoke may linger into the daylight
hours tomorrow but it should be low enough to avoid ILS. Drainage
winds will be a bit stronger than normal tonight. A weak boundary
will move through midday tomorrow which may shift winds towards a
northerly component. There is a good chance that some showers will
produce strong outflow winds and impact the terminals.
&&
.FIRE WEATHER...
Issued at 211 PM MDT Thu Aug 5 2021
Elevated fire weather conditions will be possible Friday afternoon
across the northeast plains with RH values dropping below 15% with
some wind gusts from 20 to 25 mph. Fuel status across the
northeastern plains counties are cured enough to promote fire
spread so caution is advised.
Dry fuels combined with gusty winds to 30 mph and low relative
humidity will lead to elevated fire danger across Sedgwick and
Phillips Counties on Saturday. Despite marginal relative humidity
values, have decided to go with a Fire Weather Watch for those
areas after coordinating with adjacent offices. The fire danger
will remain elevated through early next week.
&&
.HYDROLOGY...
Issued at 211 PM MDT Thu Aug 5 2021
The threat of burn area flash flooding will be quite low on Friday.
Only scattered but high based showers/storms can be expected.
Limited moisture, a dry and deep sub-cloud layer, and relatively
fast storm movement will support only light rainfall amounts (less
than 0.25 inch).
Mostly dry weather is expected through Monday with a slight
increase in shower and thunderstorm activity beginning on Tuesday.
With limited moisture available, the flash flood threat at this
time looks to limited.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
Fire Weather Watch from Saturday afternoon through Saturday
evening for COZ250-251.
&&
$$
UPDATE...Danielson
SHORT TERM...Bowen
LONG TERM...Kalina
AVIATION...Danielson
FIRE WEATHER...Bowen/Kalina
HYDROLOGY...Bowen/Kalina
Area Forecast Discussion
National Weather Service Dodge City KS
450 PM CDT Thu Aug 5 2021
...UPDATE TO AVIATION...
.SHORT TERM...(This evening through Friday)
Issued at 248 PM CDT Thu Aug 5 2021
Northwest flow aloft is increasing the subsidence over the region
during this short term period. With clear conditions the
temperatures will drop evenly across the area, influenced by surface
dew points higher in the east than in the west. Overall a mild
overnight with more midsummerlike lows than the last several nights.
Mid to upper 60s should be common in the lower plains/eastern
counties while farther west perhaps as low as 60 degrees will likely
be found through the Arkansas River valley. As a weak surface trough
slips southeast across the area this afternoon, the winds will
gradually switch back out of a southeasterly direction pretty much
area-wide. The HRRR model will still have elevated concentrations of
smoke in the atmosphere through Friday afternoon, therefore some
degree of haziness will be noticeable at times, especially in the
early morning. Hotter temperatures are expected Friday. Triple
digits will not be out of the question in a few locations, and
the entire forecast area will see temperatures in the upper 90s at
minimum for the afternoon lows.
.LONG TERM...(Friday night through Thursday)
Issued at 248 PM CDT Thu Aug 5 2021
Friday night, a buckle in the upper 500 mb flow is noted as an upper
jet moves though Colorado with the nose of the jet moving into
western Kansas overnight. Models are not particularly together on
good probability of precipitation occurring and the warm air
aloft may be part of it, additionally potential in the wrong jet
dynamics region (subsidence). This will be something better suited
for the mesoscale modes to resolve in another 24 hours. By
Saturday afternoon a cold front will be moving into the forecast
area with potential for surface based convection developing along
the moisture convergence axis, The area will likely be generally
lacking deep shear however given the moderate CAPE available on
the order of 1500-2000 J/kg, a few severe storms may be possible
over the more moisture rich eastern counties, tied closely to the
boundary. Beyond Saturday the heat surges back with 100+ degrees
likely both Sunday and Monday. Even at 102 or so the highs
temperatures in context would still likely fall short of record
highs for the historical period, which are around 106 degrees for
Saturday through Monday. Although the forecast confidence is not
as great with increasing time, the model consensus is for still
warm highs in the 90s into midweek as the strong mid level
westerly flow remains over southern Canada. The main 3 globals
spectral models hint at another Plains frontal boundary impacting
the general Central High Plains region Monday night and late
Tuesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 445 PM CDT Thu Aug 5 2021
VFR conditions will prevail in the vicinity of all TAF sites through
early Friday afternoon. Light and variable winds will persist through
early Friday morning as a weak surface trough of low pressure edges
eastward through western into central Kansas. Southerly winds 10 to
20kt return mid/late Friday morning as lee side troughing redevelops
in eastern Colorado.
&&
.PRELIMINARY POINT TEMPS/POPS...
DDC 65 98 72 99 / 0 0 10 10
GCK 61 98 69 97 / 0 0 10 10
EHA 61 99 68 97 / 0 0 0 10
LBL 61 98 70 97 / 0 0 0 10
HYS 65 100 71 97 / 0 0 10 20
P28 66 98 73 99 / 0 0 0 20
&&
.DDC WATCHES/WARNINGS/ADVISORIES...
NONE.
&&
$$
SHORT TERM...Russell
LONG TERM...Russell
AVIATION...JJohnson
Area Forecast Discussion
National Weather Service Grand Forks ND
659 PM CDT Thu Aug 5 2021
.UPDATE...
Issued at 656 PM CDT Thu Aug 5 2021
Showers have moved to the east of the area this evening, with
clouds remaining in place for areas east of the Red River. Smoke
continues to cause poor air quality, and will likely remain in
the forecast through the remainder of the night and into Friday.
North winds are generally light this evening.
&&
.SHORT TERM...(This evening through Friday night)
Issued at 255 PM CDT Thu Aug 5 2021
The main challenges in this portion of the forecast are air
quality issues and the next chance for rain.
Surface visibilities due to smoke remain restricted in the 3 to 6
mile range across the FA. The north-northwest winds of late
afternoon will becoming light this evening. The HRRR near surface
smoke model shows pretty stagnant conditions tonight, with some
slight improvement on Friday. The Air Quality Alert for our
northwest Minnesota counties is in effect until 9 pm Friday.
A few showers or storms remain possible across the Lake of the
Woods to Upper/Lower Red Lakes region through the late afternoon.
By evening, all activity should be east of the FA. The thicker
cloud cover should start to decrease by late afternoon into the
evening, with more filtered sun (because of the smoke) expected on
Friday. The next chance for rain arrives on Friday night, but
details are still fairly uncertain. At this point, another surface
low is expected somewhere over South Dakota, with a warm front
extending out to its east. Models show the best low level jet
focused over southern Minnesota. However, will maintain some low
precipitation chances along and south of Interstate 94 for now.
.LONG TERM...(Saturday through Thursday)
Issued at 255 PM CDT Thu Aug 5 2021
Impactful weather chances could present on Sat/Sat night as a risk
for some severe tstms will be in place during that time.
Sat into Sat night still offers the best chances for potentially
impactful weather during the extended period as a stronger short
wave will traverse the forecast area during this time. SPC has the
extreme southern valley and part of the MN Lakes Country in SLIGHT
RISK as of this writing. The signal remains well reflected in our
clustered and other ensemble data. Instability is still pegged to be
in the 1500 to 2000 J/Kg range over the valley and adjacent MN
region with surface dewpoints projected to be in the 65 to 70 degree
range. 0 to 6 Km bulk shear still not off the charts, maxing at
about 30 Kts for the most part. So the question mark remains as to
the sufficiency to sustain much strong to severe activity. The
action could continue into Sat night before moving east of our
region on Sun.
Ridge breaking down early next week will yield to more zonal flow
limiting pcpn to more isolated to scattered variety dependent on the
timing of short waves. This will tend to keep temps closer to
seasonal averages.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 630 PM CDT Thu Aug 5 2021
MVFR conditions prevail across much of the area this evening with
scattered stratus and low to mid-level smoke. Showers have pushed
to the east of the region along with the upper low. For the TAF
period, we will see gradual clearing of the cloud deck, with at
least occasional MVFR CIGs through sunrise. The mention of smoke
continues as surface flow remains out of the north and generally
less than 10 knots. Visibility will range from 3 to 5 SM in most
cases.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$
UPDATE...Lynch
SHORT TERM...Godon
LONG TERM...WJB
AVIATION...Lynch
AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
1051 PM CDT Thu Aug 5 2021
.SHORT TERM...(This Evening through Friday)
Issued at 244 PM CDT Thu Aug 5 2021
Attention for the remainder of the daytime hours revolves around any
thunderstorm chances and a low chance of strong to severe storms. As
of mid afternoon, a weak boundary/convergence zone was located from
south central SD into west central MN with a small cluster of weak
convection located just ahead of it in Lyon County MN. Radar and
satellite intensity trends have been exhibiting a downward trend
however. MLCAPE ahead of this cluster is generally on the order
of 1000-1500 J/kg with still some weak SBCIN. Effective deep layer
shear is unimpressive at less than 25 kts and thus suspect we
won`t see much organization to any convection through the evening
hours. Any severe risk would likely originate from gusty wind
potential with DCAPE values up to 1300 J/kg. Not out of the
question to get some smaller hail on any initial updrafts but wind
gusts to 60 mph appear to be the primary risk (again, if any
stronger storms to develop).
Overnight, another bout of mid level WAA may drive additional weak
showers/storms into the morning hours Friday but not expecting
anything approaching severe levels with this activity. Depending
on overnight cloud cover, may see some patchy fog with SREF
probabilities favoring NW IA.
Bulk of the day Friday should remain dry as shortwave ridge axis
moves overhead. HRRR smoke model again painting upper level wildfire
smoke providing for hazy skies. Afternoon high temperatures likely
sneak a couple degrees higher than today`s values or mid 80s to mid
90s.
.LONG TERM...(Friday Night through Thursday)
Issued at 244 PM CDT Thu Aug 5 2021
A lead wave begins to approach Friday night into Saturday and again
may bring some scattered showers or weak convection. How long this
activity sticks around will have significant impacts on Saturday`s
temperatures and as a result any afternoon convection chances. For
now, will stick close to the NBM which is just above the 50th
percentile or 80s to near 90 for highs. By mid to late afternoon
Saturday, models have come into better agreement with a surface
low positioned just off to our NW with a west to east warm front
and north to south cold front emanating from it. Guidance perhaps
keying in on a couple of different zones of potential convective
initiation. One with the surface trough east of I-29 and the other
closer to the surface front and main upper wave across central
SD. Better 850:700 mb flow resides across NW IA and points
southeast with weak and messy shear profiles northwest of there
across the remainder of the forecast area. Dewpoints in the upper
60s to near 70 will help drive moderate MLCAPE but the lack of
shear may prevent a more organized severe threat. What may instead
occur is any initial development may carry a marginal severe hail
risk with one or more cold pool driven multicell clusters
presenting a wind risk thereafter. Still a lot of questions to be
answered regarding the convective evolution Saturday afternoon and
evening but for now SPC has highlighted areas along and east of
the James River in a Slight risk with a Marginal risk of
excessive rainfall from WPC east of I-29.
Sunday and Monday again look to be a period influenced by shortwave
ridging and thus mostly dry conditions. Our far east counties may
get clipped by lingering precipitation chances Sunday as the upper
level wave spins east but ensemble probabilities favor this staying
just east. Temperatures again from the mid 80s to mid 90s look
common.
Next wave running along the International Border swings through
Tuesday and Wednesday and will likely carry some precipitation
chances with it. Poor model agreement precludes much more specifics
than that however. Temperatures a few degrees either side of normal
from the NBM still seem appropriate at this time.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1043 PM CDT Thu Aug 5 2021
Strong thunderstorms will sink south through northwest IA and
northeast NE through about 1 am. After this more garden variety
isolated showers and thunderstorms will be possible through about
sunrise. Most of Friday into Friday evening should be dry with
soem chance for showers and thunderstorms returning later Friday
night.
&&
.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&
$$
SHORT TERM...Kalin
LONG TERM...Kalin
AVIATION...08
AREA FORECAST DISCUSSION
National Weather Service Hastings NE
729 PM CDT Thu Aug 5 2021
...Short Term and Aviation Update...
.UPDATE...
Issued at 727 PM CDT Thu Aug 5 2021
Some comments on convective trends for the remainder of tonight
and also a summary of the past few hours (essentially just adding
more detail to preceding day shift discussion which already had a
good handle on things):
- Remainder of this evening-overnight:
Before 10 PM: at least for now, will carry the assumption that
the activity working south toward the Dawson County of our far
western CWA as of this writing will continue to gradually weaken
(or at least not notably strengthen) as it potentially enters that
area over the next hour or so. However, will keep a close eye on
things as we are still a couple hours from true nightfall/darkness
and there might be time for a brief flare up before low-level
instability/CAPE really starts to drop off. Would be fairly
surprised though to see any of this activity survive very far
south of the I-80 corridor...and would also be surprised to see it
linger past 10 PM (especially given lack of a strong low level
jet).
After 10 PM: have maintained a dry forecast CWA-wide for several
hours, before another slight chance for very late night/early Fri
AM convection enters the picture mainly after 4 AM mainly in our
extreme northeast zones (mainly northeast of a Greeley-Osceola
line). It`s far from a sure thing that any of this potential
activity even clips our CWA (much of it could remain slightly
northeast of us altogether), but the latest HRRR supports keeping
the small PoPs from inherited day shift forecast going in that
area, as this area could catch the western edges of activity
driven by modest warm air/theta-e advection in the 850-700
millibar layer. It appears anything that might develop into our
area would be fairly weak/non-severe, with elevated CAPE averaging
less than 500 J/kg.
- Past few hours:
Despite some often-reliable models (such as HRRR) earlier
insisting on a storm-free late afternoon/early evening CWA-wide,
the combo of subtle surface convergence, decent mixed-layer CAPE
1500-2000 J/kg and a fairly weak cap (700 millibar temps only
8-10C) was enough to pop some very isolated convection in our
northern zones, including a briefly severe-warned storm in
northwestern Buffalo County around 445 PM (only known ground truth
report was dime size hail west of Pleasanton). Since that brief
local flare up quickly faded (possibly owing to fairly poor mid
level lapse rates and large scale subsidence in wake of shortwave
trough departing off to our southeast, we have been keeping an eye
on earlier-severe convection over north central NE that has been
drifting south toward our northern/northwest zones, but recent
radar trends have been on the decline for this activity (even
despite increasing deep layer shear now as high as 40-50KT), which
largely suggests that this activity is primarily diurnally-
driven.
&&
.DISCUSSION...(This evening through Thursday)
Issued at 309 PM CDT Thu Aug 5 2021
Main concerns include a small chance of pop-up storms this
afternoon/evening from insolation, then a shot at some strong to
severe storms Saturday afternoon/evening. Also, back to some
hotter/sultry conditions for Sunday into Tuesday.
There is a weak surface boundary detected at the surface from
interpreting LAPS streamline, dewpoints, and instability axis
stretching from the northeast into the northern half of the CWA.
This could be the focus of a couple of pop-up thunderstorms if we
wind up breaking the cap today. Models indicate a potential sunrise
surprise in our northeast late tonight and early Friday morning as
well with a little bit of support from low-level jet convergence
for a short time.
The next shot at precip may be as soon as Friday night as a stout
low-level jet develops and could help maintain shower/thunderstorm
activity.
For Saturday, a wave trekking across the northern Plains could spark
some convection in the afternoon/evening, depending on timing of the
wave. Bulk shear of 25-30 KTS and MLCAPE near 2500 J/kg near the
associated surface boundary could touch off some strong to severe
storms, especially in our east as the timing of the boundary will be
highly influential.
Heat and humidity will continue to build, especially during the
Sunday-Tuesday time frame, with Monday potentially being the warmest
with heat indexes getting into the 100-105 degree range. By mid-week
next week, the trough in the west shifts to the central part of the
country and could give us some at least spotty chances of more rain
and slightly cooler temps.
As for smoke, plan on more hazy skies with continued large burning
wildfires upstream.
&&
.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Saturday)
Issued at 727 PM CDT Thu Aug 5 2021
Ceiling/visibility/precipitation:
High confidence in VFR ceiling, although quite a bit of mid-high
level cloud will likely be present at times (mainly at/above 12K
ft.). Confidence is also fairly high in VFR visibility, as long as
any "sneaky" haze from distant wildfire smoke doesn`t unexpectedly
come into play. As for precipitation/thunderstorms, have gone with
a very generic "vicinity thunderstorm" (VCTS) these very first 3
hours to account for the outside chance of isolated convection
currently over north central NE surviving southward into the
KGRI/KEAR vicinity, but odds of a storm directly affecting either
location currently looks fairly low. Beyond this evening, kept out
any official shower/thunderstorm mention, although there may be a
non-zero chance for a rogue shower sometime Friday morning.
Winds (including low level wind shear/LLWS):
This evening-overnight, fairly light (under 10KT) and generally
southerly breezes will prevail (assuming no convective outflow
influences). Then during the day Friday, southerly winds will be
on the increase, with the afternoon featuring sustained speeds
generally 15-20KT/gusts up to around 25KT. As for LLWS, have opted
to introduce a formal group from 09-14Z Friday morning, as latest
model data is suggesting that winds in about the lowest 1K ft.
will pick up to around 35KT from the southwest, resulting in
roughly 30KT of shear magnitude between the surface and this
level.
&&
.GID WATCHES/WARNINGS/ADVISORIES...
NE...NONE.
KS...NONE.
&&
$$
UPDATE...Pfannkuch
DISCUSSION...Heinlein
AVIATION...Pfannkuch
Area Forecast Discussion
National Weather Service Grand Junction CO
538 PM MDT Thu Aug 5 2021
.SHORT TERM...(Tonight through Friday night)
Issued at 250 PM MDT Thu Aug 5 2021
Conditions continue to dry across eastern Utah and western
Colorado, as noted by the downward trend in Precipitable Water
from GJT`s 12Z sounding. Lack of cloud cover across much of the
region is also detectable in current visible imagery, with the
exception of convection developing over the eastern Uintas and the
Southwest San Juans. As previously mentioned in this morning`s
discussion, a shortwave trough rippling through the ridge of high
pressure has triggered thunderstorms over northeast Utah, with
storm coverage mainly confined along the Uinta Range. Meanwhile,
residual moisture has fueled isolated afternoon thunderstorms just
southwest of Telluride. Expect this activity to continue across
the favored ranges through this evening, with all activity
diminishing shortly after sunset.
A low pressure system sliding over the Northern Rockies overnight
will shift winds from the southwest and tighten the pressure
gradient aloft. We may also see an uptick in cloud cover in
response to the approaching disturbance, which will act as
insulation and moderate radiational cooling tonight. Strong pre-
frontal winds will set the stage for critical fire weather
conditions Friday afternoon across portions of eastern Utah and
much of northwest Colorado where fuels are still considered
susceptible (despite recent rains!). Red Flag Warnings have been
issued for these areas, in coordination with fuel specialists for
vulnerable vegetation, as discussed in the Fire Weather Section
below. However, southwest wind gusts in excess of 35 mph are
possible by mid afternoon to evening hours for much of the area.
In addition, isolated convection firing (mainly north of I-70) in
the afternoon will likely enhance surface winds from associated
outflow boundaries. These storms will be fast moving and
relatively high based, so the potential for mud and debris flows
is low. The low`s associated cold front is anticipated to push
across the region overnight, which abruptly shifts winds from the
northwest. Unfortunately, this strong wind shift will carry a
thick plume of smoke from ongoing fires in Oregon and Northern
California. Notably higher concentrations of smoke will trickle
southeast over the entire region by sunrise.
High temperatures will remain above normal Friday afternoon in
prefrontal conditions, though, overnight lows will feel some
relief from the frontal passage Friday night and drop 3 to 8
degrees cooler than temps tonight.
.LONG TERM...(Saturday through Thursday)
Issued at 250 PM MDT Thu Aug 5 2021
A drier northwest flow will set up following Friday`s shortwave
trough. While this would normally bring mostly sunny skies and
slightly cooler temperatures, the latest HRRR smoke model is showing
the western skies being filled with widespread deep layer smoke
across all of eastern Utah and western Colorado. This smoke is
originating from the numerous wildfires burning in northern
California, with smoke reaching as far south as northwest New
Mexico/Four Corners and as far east as the Front Range...almost to
the western Kansas border by sunrise Saturday morning. Highs will be
closer to normal on Saturday, maybe a little cooler given the
widespread smoke in the atmosphere. Conditions could be a bit breezy
across the north this weekend as a few weak shortwaves associated
with an upper level trough moving across the Intermountain West and
Northern Rockies. This trough stays north of us with dry conditions
expected this weekend into early next week, with above normal
temperatures returning Sunday and beyond.
Previous model runs were hinting at potential return of monsoonal
moisture mid to late next week. However, latest model guidance and
ensembles seem to favor a ridge of high pressure building back over
the region or further west over the Great Basin, with this moisture
becoming suppressed to the south of the Four Corners, pooling in
Arizona and New Mexico. This is likely due to the trough moving
across the Intermountain West and Northern Rockies, helping suppress
the high further south and west. Regardless, the best potential for
any convection may be across the southern mountains and up the
southern/central divide mid to late next week, as some moisture
tries to sneak in under the high, but most areas look to remain dry.
Low confidence in this potential moisture return as there are still
differences in placement of the high and subtle features that would
trigger convection. Sticking with the ensembles which favor the
ridge of high pressure maintaining its position over the Great Basin
and drier conditions with isolated afternoon convection favoring
high terrain along the divide.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 535 PM MDT Thu Aug 5 2021
A few showers and storms have fired over the San Juans and Uintas
this afternoon but, aside from KVEL, don`t anticipate any effects
to TAF sites. KVEL might see a passing shower over the next hour
or two with some gusty surface winds up to 30kts, give or
take. Remaining TAF sites will see few to scattered skies and
staying that way overnight. Clouds will increase somewhat tomorrow
afternoon ahead of the next system but they will stay well in the
VFR category. Expect gusty southwesterly winds after 18Z tomorrow
with gusts reaching between 25 to 30 kts at times.
&&
.FIRE WEATHER...
Issued at 250 PM MDT Thu Aug 5 2021
High pressure centered overhead today will maintain warm and dry
conditions across much of eastern Utah and western Colorado this
evening. Exceptions include the Southwest San Juans where a few
isolated thunderstorms have developed from residual low level
moisture. In addition, a weak disturbance drifting over northeast
Utah, has initiated a few storms along the eastern Uintas. High
based storms will minimize rainfall reaching the ground, with
lightning and gusty outflow winds remaining the primary concerns.
Expect all thunderstorm activity to wane this evening and diminish
after sunset.
Conditions begin to shift gears tomorrow as strong prefrontal
winds drape across much of the region by Friday afternoon. In
combination with already drying low levels, critical conditions
will be reached for areas with susceptible fuels. Thus, Fire
Weather Watches have been upgraded to a Red Flag Warning for the
areas determined critical in coordination with fuel specialists.
Winds taper off by 8 PM MDT, however an abrupt wind shift to the
northwest is anticipated with the frontal passage overnight.
Through the weekend, localized fire weather conditions may
resurface each afternoon while high pressure remains suppressed
to the south and a series of troughs pass over the region to the
north.
&&
.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Red Flag Warning from noon to 8 PM MDT Friday for COZ200-202-203.
UT...Red Flag Warning from noon to 8 PM MDT Friday for UTZ490.
&&
$$
SHORT TERM...ERW
LONG TERM...MDA
AVIATION...TGR
FIRE WEATHER...ERW
Area Forecast Discussion
National Weather Service San Francisco Bay Area
904 PM PDT Thu Aug 5 2021
.SYNOPSIS...Smoke from fires in Siskiyou and Trinity counties
will drift southward into the Bay Area late today into tomorrow.
Tomorrow will be tangibly warmer than today as high pressure
nudges into the area. Then, a cooling trend through the weekend
and into next week.
&&
.DISCUSSION...as of 09:03 PM PDT Thursday...Temperatures across
the region this afternoon ended up being around 2 to 7 degrees
cooler across the interior while coastal areas saw slight warming.
This was as a mid/upper level trough pushing inland over the
region, cooling temperatures aloft but also mixing out the marine
layer and associated clouds near the coast. Meanwhile, low clouds
have already returned to coastal areas this evening while
spreading inland across San Francisco, into the East Bay and
around the southern Monterey Bay. Expecting the marine layer to
once again become better defined overnight with stratus spreading
inland into the region`s valley locations.
One thing to monitor overnight is smoke aloft forecast to advect
southward on the back side of the exiting trough. This may
eventually mix down closer to the surface to produce smoky and/or
hazy conditions on Friday. For more on this and the rest of the
forecast, please see the previous discussion below.
&&
.PREV DISCUSSION...as of 02:30 PM PDT Thursday... The synoptic scale
pattern primarily features low pressure influences over the area
today. A deeper 558dm Gulf of Alaska low is farther to the
northwest while a weaker low pressure circulation in the base of
trough skirted over the region last night and is now located over
the eastern OR/CA border. To our southeast, a weak 594dm high
pressure ridge is elongated from San Diego to the Four Corners,
but is playing no significant role in the local surface conditions
today.
In response to this low pressure influence, a fairly robust
marine layer of 2000 feet depth formed overnight and provided a
reservoir for the arriving trough to wring out a significant
amount of drizzle to the point it could be considered light
rainfall. Numerous locations along the coast and coastal facing
slopes have reported a few to several hundredths of an inch of
precipitation as a result, with local amounts for direct coastal
faces approaching a tenth of an inch.
Early afternoon satellite imagery depicts that the trough axis
has now shifted to our east which is resulting in a larger
northerly component in the wind field. As a result, wildfire
smoke, primarily from the fires burning in remote portions of
Siskiyou and Trinity counties, is showing signs of advancing
southwards through Mendocino county and towards Sonoma county. The
latest HRRR near-surface and vertically integrated smoke appears
to line up somewhat well with current observations, however, model
estimates may be a bit on the early side. That said, most likely
scenario is to see some mid to upper level smoke generate hazy
late today into this evening for those along the North Coast,
North Bay, and in proximity of the Golden Gate gate through the
Delta given the forecast onshore winds there. Lesser amounts may
expand into the East Bay/South Bay overnight. Lower level smoke
may then filter down to the near surface levels in patches
beginning tomorrow morning. We will continue to post modeled smoke
estimates on our twitter feed, but be sure to follow the Bay Area
Air Quality Management District (or your local air quality
district) for official air quality forecasts.
Otherwise, for tomorrow, expect dry air on the lee side of the
trough to entrain into the region and provide some suppression of
the marine layer. At the same time, the aforementioned ridge to
the southeast will briefly build onshore and into Central
California in the wake of todays passing trough. Both of these
factors will contribute to tangible one day warming trend of 5 to
10 degrees from today into tomorrow.
Gradually cooler, wetter conditions will arrive with each
successive day from Saturday onward as high pressure weakens in
favor of an advancing trough that finally pushes ashore early next
week. For now, though, our focus will be on the short term
impacts of the near surface smoke over the next few days, if any.
&&
.AVIATION...as of 5:34 PM PDT Thursday...For the 00z TAFs. It`s
VFR except /MVFR-IFR/ along the coastline in areas of stratus and
fog. Slant range visibilities at sunset/sunrise possibly reduced
in the Bay Area due to wildfire smoke and hazy conditions aloft,
hrrr near smoke model output shows the amount of smoke uptrending
on Friday. Otherwise the marine layer remains intact, plenty of
water vapor remains trapped beneath the marine layer temperature
inversion, some compression of the marine layer tonight and
Friday. Patchy light coastal drizzle possible tonight and Friday
morning.
Vicinity of KSFO...VFR then MVFR ceiling developing by 08z this
evening. West wind 18 to 27 knots until mid evening then gradually
settling back to near 10 knots overnight. Slant range and surface
vsbys possibly reducing to 6 miles in smoky and hazy conditions,
especially Friday.
KSFO Bridge Approach...Similar to KSFO.
Monterey Bay...VFR except areas IFR in stratus and fog. IFR
due to stratus and fog becoming more widespread tonight and Friday
morning. IFR lifting to MVFR-VFR Friday. Slant range visibility
reductions possible, especially Friday.
&&
.MARINE...as of 09:03 PM PDT Thursday...Increasing northwest
winds across the coastal waters creating hazardous conditions for
smaller vessels through Friday night. Gusty afternoon and early
evening west winds will also develop through the Golden Gate and
into the Delta. Steep short period locally generated northwest
waves at 5 to 7 seconds continue to dominate the sea state along
with a moderate period southerly swell.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...SCA...Pt Reyes to Pigeon Pt 0-10 nm
SCA...Pigeon Pt to Pt Pinos 0-10 nm
SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm
SCA...Pt Arena to Pt Reyes 0-10 nm
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
SCA...Pt Arena to Pigeon Pt 10-60 nm
&&
$$
PUBLIC FORECAST: RGass/DRP
AVIATION: Canepa
MARINE: Canepa
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Area Forecast Discussion
National Weather Service Sacramento CA
156 PM PDT Thu Aug 5 2021
.SYNOPSIS...
Periods of critical fire weather conditions through this evening.
Mainly dry weather and near-normal temperatures are forecast
through the weekend with occasional breezy onshore winds. Gradual
warming trend will begin next week.
&&
.DISCUSSION...
GOES-West visible and infrared imagery show a very active day with
northern California`s wildfires. Numerous hotspots on the Dixie
Fire continue to pump out smoke, lofting towards the northeast.
Relative humidity values this afternoon are forecast to plummet
again to the single digits / teens this afternoon. This combined
with gusty winds and the extraordinarily dry fuels will result in
continued critical fire weather conditions. The Red Flag Warning
for portions of the Sacramento Valley, Coastal Range, all of
Shasta County, the southern Cascades, and the Sierra Nevada into
Tuolumne County goes through 9 PM PDT this evening. Residents are
urged to have a plan in place if required to evacuate, and to
quickly follow any/all evacuation orders issued by law
enforcement.
Upper level low presently located near Redding will lift northeast
toward northwestern Nevada and southern Idaho over the next 24
hours. On the backside of this low, Valley winds will become more
northerly tonight and into Friday. Main consequence of this wind
shift will be the smoke-related impacts up and down the Sacramento
Valley. Latest HRRR near-surface smoke model increases smoke
concentration from north to south in the Valley tonight through
tomorrow afternoon. Main impacts with the smoke will air quality
as well as visibility restrictions for aviation. Another forecast
challenge that the smoke will present would be slightly cooler
afternoon temperatures. Depending on the concentration and timing,
tomorrow`s afternoon high temperatures ranging from the middle
90s to near 100 deg F in the Valley may be too hot. Will closely
monitor temperatures over the next subsequent shifts and adjust
accordingly. Some onshore flow will return at some point later
tomorrow which would help clear out potential smoke in/around the
Delta. Dry, west/northwest flow will prevail overhead northern
California through the weekend. // Rowe
&&
.EXTENDED DISCUSSION (Monday THROUGH Thursday)...
Clusters and ensembles advertise an upper level trough over the
Pacific Northwest early next week. This low will push inland and
be replaced with a building ridge over the West Coast by
Wednesday/Thursday. If this verifies, would expect to see a
gradual day-to-day warming trend next week with dry conditions
expected. The latest Climate Prediction Center`s 6-10 temperature
outlook (valid August 11-15) heavily favors the increased
likelihood of above normal temperatures for northern California.
&&
.AVIATION...
SW surface winds 10-15 kt with gusts up to 25 kt, locally up to
35 kt through the Delta and over higher terrain. VFR conditions
expected over interior NorCal through Thursday evening except
local MVFR/IFR possible in smoke in vicinity of wildfires in
Shasta, Plumas, and Butte counties. Widespread MVFR possible after
03-06z Friday as winds shift to the north and bring smoke south
of the wildfires.
&&
.STO WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM PDT this evening for Burney Basin
and Northeast Plateau in Shasta County Including Northwest
Lassen NF north of Lassen NP-Central Sacramento Valley in Glenn,
Colusa, Yuba, Northern Sutter, and Butte County Below 1000 Ft-
Eastern Mendocino NF-Eastern Portion of Shasta/Trinity NF-
Northern Sacramento Valley to Southern Tehama County Line Below
1000 Ft-Northern Sierra Foothills from 1000 to 3000 Ft. Includes
portions of Shasta-Trinity and Butte Units-Northern Sierra
Including Lassen NP and Plumas and Lassen NF/S West of the
Sierra Crest (West of Evans Peak-Grizzly Peak-Beckworth Peak)-
Northern Sierra Including the Tahoe and ElDorado NF/S West of
the Sierra Crest-Southeast Edge Shasta-Trinity NF and Western
Portions of Tehama-Glenn Unit-Stanislaus NF West of the Sierra
Crest.
&&
$$