Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 05/22/21
Area Forecast Discussion
National Weather Service La Crosse WI
1050 PM CDT Fri May 21 2021
.SHORT TERM...(This evening through Saturday)
Issued at 219 PM CDT Fri May 21 2021
GOES water vapor imagery continued to show a plume of deep
moisture extending northward from the Gulf Coast through the Upper
MS Valley on the western fringe of strong mid-level ridging
across the Ohio Valley. Clouds remain extensive over the region
with persistent moisture transport and precip water values over
1.6 inches. Scattered showers and a few storms will continue into
early evening as a shortwave trough lifts across the region. With
moist profiles/weak lapse rates and abundant cloud, instability
has been slow to increase, with the RAP indicating 500+ J/kg of
MLCAPE through late afternoon. Deep layer shear is quite a bit
weaker today, although some 0-1 km shear is still present with the
stronger low-level flow. This environment isn`t very favorable
for strong/severe storms, and in fact, more showery conditions are
expected than organized storms. Given the low-level shear,
though, any stronger more persistent cells could at least exhibit
transient rotation.
As ridging builds across the area tonight into Saturday, GEFS
integrated water vapor transport shows a relaxing of the moisture
fetch into the area. In the absence of any coherent large scale
lift signal, later tonight into Saturday looks predominantly dry.
A weak shortwave trough possibly could bring a few showers to far
southern areas by later Saturday, however. With potential for more
sunshine on Saturday and 925 mb temps climbing into the 20-22C
range, expect high temps into the 80s for much of the area. That
said, if clouds do remain more stubborn, highs could hold in the
70s in some areas.
.LONG TERM...(Saturday night through Friday)
Issued at 219 PM CDT Fri May 21 2021
It looks like the potential for another extended period of rain
chances is setting up for next week. The upper level ridging the
builds over the Midwest for the weekend will get flattened as the
western U.S. upper level low lifts to the north/northeast. As this
low reaches southern Canada Monday and then weakens and move
east, the upper level flow will transition to a quasi-zonal
pattern over the Upper Midwest. This looks like it will return the
pattern of several short wave troughs moving across the region,
especially in the first half of the work week. At the surface, the
nearly stationary boundary currently set up across the Dakotas
and northern Minnesota, will sink south into the region by Sunday.
An area of low pressure should develop with the upper level low
and help to lift this front back to the north Monday. However, as
the low moves to the east, it will quickly push a weak cold front
into the region to help maintain a boundary/focus for convective
development. This boundary may not exit the region until Tuesday
night given the rather slow eastward movement of the parent area
of low pressure across Canada. With the potential for several
short wave troughs to move across the area and the presence of the
surface boundaries, there will be an extended period of on and
off rain chances from Sunday into Tuesday night. As of now, the
periods with the best chances for some widespread rain looks to
Sunday afternoon and night and Monday afternoon and night. Current
indications are that any severe threat should be pretty minimal
Sunday. While there may be some modest ML CAPE in place ahead of
the boundary, on the order of 750 J/Kg or so, the deep layer shear
will be lacking as it stays well to the north. Some heavy
downpours might occur as warm cloud depths reach 3.5 to 4 km, but
the moisture transport into the boundary does not look very
impressive at this point.
Looking out into the middle and end of next week, an area of high
pressure should briefly build in from the north for some dry
weather Wednesday. The should then move off to the east Thursday
as another short wave trough approaches from the west to bring in
a return for some additional rain.
&&
.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1047 PM CDT Fri May 21 2021
Clouds have decreased through the evening and should see
scattered clouds overnight. Moisture transport has weakened,
however relative humidities are still expected to be on the high
side. There may be some MVFR ceilings that spread northward around
12Z. With low confidence left the clouds scattered for now and can
adjust if the ceiling develop northeastward. Low level winds of
20 to 35kts overnight should help mitigate the fog at the TAF
sites. Southeast to southwest winds 5 to 15 kts with some stronger
gusts at KRST Saturday.
&&
.ARX WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
IA...None.
&&
$$
SHORT TERM...JM
LONG TERM...04
AVIATION...Zapotocny
Area Forecast Discussion
National Weather Service Denver/Boulder CO
854 PM MDT Fri May 21 2021
.UPDATE...
Issued at 850 PM MDT Fri May 21 2021
Weakening thunderstorms over the northeast plains no longer
warrant the Severe Thunderstorm Watch, therefore the watch has
been cancelled. Also added the potential for patchy fog late
tonight into Saturday morning, from the I-25 corridor eastward
onto the plains.
UPDATE Issued at 657 PM MDT Fri May 21 2021
Overall the timing of the thunderstorms in the grids this evening
remains on track. Main line of storms over western Logan,
Washington and Lincoln counties as this time, with the overall
line moving slowly east this evening. No longer expect
thunderstorms over Weld County this evening so I cancelled the
Severe Thunderstorm Watch there. We may cancel the watch for
Morgan County as well within the hour. Generally weak showers and
a isolated thunderstorms over the mountains the rest of the
evening, so flood threat in the burn areas will be very low the
rest of tonight. Gusty south to southeast winds will persist
across the northeast plains this evening, but gradually weaken
further west. Only short term adjustments were made to the pops
this evening, the rest of the grids look good.
&&
.SHORT TERM...(This evening through Saturday)
Issued at 323 PM MDT Fri May 21 2021
We`re still expecting strong to severe storms to develop over the
eastern part of the plains on the redeveloping dryline over the
next few hours. The area from east of Limon to north or northwest
of Sterling looks like it`s almost warm/moist enough to break the
cap. CAPEs in this area are 1000-1500 J/kg. The wind profile will
favor large hail while the background 30 knots or so of low level
flow will make it easier to get severe wind gusts as well. A
tornado can`t be ruled out but once again some deviant motion
would likely be required as there`s even less environmental
helicity than yesterday. Storms should race northwards and while
there may be a couple of nice focal points to start with, the
environment will likely become messier with time and more likely
to have linear or cluster types than quasi-supercells. There will
likely still be enough CAPE/shear for large hail through early
evening then later it should be mostly a wind threat as the low
level flow stays brisk even as the convection weakens. The latest
HRRR shows some redevelopment just after sunset. It seems possible
for there to be some refocus at some point but I wouldn`t count
on any of the detail.
Meanwhile, the surface pressure falls near Denver delayed the
south wind`s arrival, but it has spread across most of the city
now. There`s still a battle going on up against the foothills
around Broomfield which will likely continue. Eventually the
northerly winds will wind, but this evening we`ll see conflicting
forcing from the decreasing flow off the ground, the tendency for
southerly drainage winds over most of the city, and a larger
tendency for northerly winds as the synoptic pressure falls should
shift out onto the plains a bit.
By morning the cooler but moist air should have pushed southward
across Denver. We prefer the models that are more aggressive with
this, pushing it well south past Colorado Springs. This scenario
keeps the area from Denver northwards too cool for surface based
convection most of the day with northeast to east low level winds.
The GFS is really aggressive with this and suggests the area will
be capped all day, with a high in the mid 60s in Ft Collins.
We`re not ready to go all the way with that solution and are still
concerned with an intermediate solution that would be just warm
enough and moist enough for the upslope winds to trigger late
afternoon or evening convection that could be anchored or
repetitive over the foothills presenting a flash flood threat.
The convergence area south and southeast of Denver should be the
focus for strong to severe convection Saturday afternoon. Models
suggest this activity would likely start in El Paso and Elbert
counties and then stream northward. How far north depends on the
strength of the cool air surge, though the area east of Denver
could be recharging as the plains southerlies push richer air into
that area during the afternoon and early evening. There`s a lower
threat of strong storms up along the northern border, though it
will be moist enough that there is some threat if it gets warm
enough. For temperatures, we`ve gone toward the cooler end of
guidance across most of the area, but not as cold as the frigid
GFS north of Denver.
.LONG TERM...(Saturday night through Friday)
Issued at 323 PM MDT Fri May 21 2021
A few severe storms with high winds and large hail will likely
continue to race north/northeast across the plains Saturday
evening. A couple showers and thunderstorms may also linger across
the mountains and I-25 Corridor for a few hours in the evening
due to sufficient instability, mid level moisture, and weak
synoptic scale forcing. However, the primary severe threat should
be pushing farther east, driven by the low level (untapped)
instability axis. Some of these showers and storms may even linger
past the midnight hour thanks to the above mentioned factors.
Sunday will likely bring another severe storm threat, this time
shifting farther east across the plains versus tomorrow. Timing
will be everything here, with the latest models in fair agreement
driving a well pronounced dryline east across the plains and
roughly reaching a Sterling to Akron line by early to mid
afternoon. Anywhere along and east of that line will see MLCAPE
near 1500-2000 J/kg, coinciding with bulk shear at a whopping
45-60 knots. Hodographs are close to straight-line, with some
curvature and effective Storm Relative Helicity (SRH) near 100
m2/s2. That said, a deviating storm to the east/northeast would
support a rapid increase in SRH and larger tornado threat.
Otherwise, very high winds and damaging/destructive hail would be
the primary storm threats. Models can sometimes be too fast with
the dryline, so will also watch this for any potential slowing and
thus threat somewhat west of the above mentioned Sterling to
Akron line. We do have higher confidence that the I-25 corridor
and points west through the mountains will be dry, in fact - very
dry, as the deep dry slot and downslope drying ensue the short
wave/dryline passage.
We`ll then see mostly dry conditions persist Monday and Tuesday.
By Wednesday through the latter half of next week, we should begin
to see more convective activity and stronger storms as MLCAPE
builds and weak troughing is advertised by operational and
ensemble averages.
&&
.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 850 AM MDT Fri May 21 2021
VFR through tonight with gusty southerly winds gradually
decreasing this evening. Saturday morning around 09z the models
show more switch to north/northwest winds. This could result in
patchy fog toward 12z but may just address this with vcfg in the
next taf update. The winds are expected to become more easterly
Saturday afternoon. Scattered thunderstorms are expected Saturday
afternoon with a chance of wind shifts with gusts to 40 knots and
localized MVFR conditions. Instrument approaches to KDEN may be
needed after 18z due to ceilings and the thunderstorms.
&&
.HYDROLOGY...
Issued at 657 PM MDT Fri May 21 2021
Scattered showers and isolated thunderstorms will be possible
over the mountains this evening. Just some brief light rain
showers the rest of this evening so the flash flood threat will be
very low the rest of tonight.
On Saturday, moisture will increase but instability will be
limited. If thunderstorms do develop over the foothills burn
areas, heavy rain is possible. Storms are expected to be moving,
but there would be potential for enough rain to cause flooding.
Areas west of the divide will have a lower threat as storms should
be moving faster. The main threat would be in the late afternoon
through mid evening.
A much drier airmass will develop across the mountains and
foothills Sunday, with only a slight chance of a passing light
shower over the burn areas. The far northeast corner of the state
could still see locally heavy rain due to strong/severe storms.
Drier weather should persist Monday and Tuesday, with scattered
storms entering the picture again for Wednesday into the latter
half of next week.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Cooper
SHORT TERM...Gimmestad
LONG TERM...Barjenbruch
AVIATION...Cooper/Gimmestad
HYDROLOGY...Cooper/Gimmestad/Barjenbruch
Area Forecast Discussion
National Weather Service Caribou ME
915 PM EDT Fri May 21 2021
.SYNOPSIS...
A cold front will approach overnight and slowly move across the
region into Saturday night. A second cold front will move
across the area Sunday. High pressure will build in through
early week before another cold front approaches by the middle of
next week.
&&
.NEAR TERM /THROUGH SATURDAY/...
9:15 PM Update: A mild and muggy evening inland with dew points
well into the 60s. It is much cooler along and near the coast
owing to the cold ocean waters. The 00z Caribou sounding was
very moist with a PWAT of 1.62" which is a daily record and not
far from the May record of 1.73". Area radars showing showers
pushing south across the Downeast Region and additional showers
across the northern zones. No lightning has been detected in the
past few hours. Made some adjustments based on the current
conditions as well as for increased rain chances Downeast during
the next few hours as showers move through the area.
Previous discussion:
Disturbance moving through the upper ridge kicking off showers
and tstms this afternoon w/the most significant action being
across eastern Aroostook County. Still expecting some activity
to continue into the evening. Sounding data and convective
parameters still showing MU CAPE Values into the evening of
500-700 joules, w/the best chance for storms from the
Piscataquis region up into SE Aroostook County. Onshore wind has
kept things cooler across the Bangor and Downeast region
helping to negate the convective potential. As the night wears
on, atmosphere is expected to stabilize which help to alleviate
any further convection. The latest runs of the RAP and NAM show
a pre-frontal trof apchg the region by early Saturday morning
w/some upper support to set off some more showers across the far
n and nw. The 12Z GFS showed this setup too. The RAP is the
most robust w/the showers and placement which looks overdone as
the NAM is weaker w/forcing. GFS is similar to the RAP and does
show some mid level forcing to support the showers. Decided on
the blend and leaned w/highest pops across the northern border
and 20--40% elsewhere. Kept the mention of patchy fog in there
for the Downeast areas and across the n where rainfall occurred.
Some showers or perhaps drizzle expected in the morning, then a
break as the trof lifts off to the e. Some partial clearing is
possible which will allow for the atmosphere to destabilize by
late morning, especially for the northern and central areas.
This will lead to the potential for tstms w/CAPE values hitting
700-1000 joules. The steepest lapse rates are in the late
morning across the Maine Highlands and Northern Maine, which
would support updraft potential. However, those lapse rates
shift to east as the cold front apchs and showers and storms get
going. Looking at the latest Showalter Index and EHI placement,
best potential looks to line up across the Southern Aroostook
region down into the Piscataquis and Penobscot region by early
to mid afternoon. In this region there a better chance for some
heating leading to convective development. Soundings do support
some hail, heavy rainfall w/the stronger storms given the PWS
of >/= 1.50" WBZs around 10k ft. Inverted V in the llvls coupled
w/dry air aloft leads to threat of some strong wind gusts too.
Another item to be mindful is that since it is the weekend,
folks being out on area lakes/streams and still relatively
colder water temps led to the issuance of a Special Weather
Statement for cold water temperatures.
&&
.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/...
The first cold front will slowly exit the area Saturday evening
with a few lingering thunderstorms possible and most precip
should be over by later in the evening. Conditions will remain
quite humid overnight with dew points near 60F and that will
limit low temps...and perhaps generate some fog. Fog would be
most likely in the coastal Downeast region. The next cold front
will be arriving in the Saint John Valley early Sunday morning
and sweep southward across the forecast area by mid-afternoon.
It appears to be an anafrontal set up with a baroclinic zone
lagging behind the surface front. This structure and the early
timing will limit convective potential in northern zones. Have
maintained a chance of thunderstorms in the southern half of
the forecast area for a narrow window from the midday into mid
afternoon. There`s still some guidance suggesting a more robust
convective environment with strong wind gusts as shear will be
favorable, but most guidance favors the cooler and more stable
scenario. The cold front will rapidly bring much cooler air into
the area later Sunday and northeasterly winds will be gusting as
high as 40 mph in the afternoon. A 1028mb high in Canada
quickly builds overnight and suggests winds will die off enough
to produce some frost later Sunday night. This will be mostly in
the northern half of the area and the lowest temps will be in
the North Woods where the frost/freeze program is not in effect.
Monday looks like a sunny day with very low humidity and
pleasant temperatures in the 60s. Did make some efforts to lower
dew points below guidance.
&&
.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Temperatures will likely cool off fairly quickly Monday evening
in the cool air mass, but may warm later in the night as the
high moves offshore and warming southwest winds commence. Highs
on Tuesday will be around 10F warmer than Monday and a strong
pressure gradient generating gusty southwest winds. Gusts could
reach up to 30kt. In the absence of any significant rainfall
this weekend, fire weather would be a prime concern on Tuesday.
The strong winds continue Tuesday night and keep lows from
dropping out of the 50s. Guidance suggests some shower or
thunderstorm activity in northern zones on Tuesday night along a
thermal ridge axis, but could be just convective debris moving
into very dry air over the state. Temps warm back towards the
upper 70s to lower 80s on Wednesday ahead of another cold front.
Timing will be critical for convective activity as the spread on
frontal passage currently ranges from Wednesday afternoon to
later Wednesday night. Once again, this front will bring a fresh
supply of cool Canadian air and a return to seasonable temps and
dry weather for late week into the Memorial Day weekend.
&&
.AVIATION /01Z SATURDAY THROUGH WEDNESDAY/...
NEAR TERM: VFR late this evening. There is a threat for MVFR
and possible IFR by early Saturday morning, especially for KBGR
and KBHB. S winds 5-10 knots overnight.
For Saturday, some IFR cigs in the morning, and then conditions
improving to VFR by mid to late morning mainly n of KHUL.
Further s. MVFR hangs on longer. SHRA/TSRA possible in the
afternoon for the region w/potential for MVFR and TEMPO IFR.
SHORT TERM:
Saturday night...VFR except a chance of IFR fog towards the
coast to include BHB. Isolated thunderstorms possible in the
evening. Light winds.
Sunday...VFR with the exception of MVFR cigs in rain north of
PQI in the morning. Isolated afternoon thunderstorms south of
MLT and HUL. Winds becoming NW gusting to 25kt.
Sunday night through Wednesday...VFR. Isolated thunder possible
north of GNR and HUL on Tuesday night. Southwest winds gusting
to 25kt on Tuesday.
&&
.MARINE...
NEAR TERM: Beach Hazards Statement issued per collaboration
w/USCG and GYX. This will most likely be needed again for
Sun. SCA in effect for swells of 5-6 ft for the outer waters
into Sun morning. SSW winds 10-15 kt w/ocnl gusts hitting 20+
kts by late Sat w/the apch of the cold front.
SHORT TERM: Fog expected Saturday night into Sunday morning.
Can`t rule out an isolated thunderstorm Sunday evening. Long
period SE swell will be diminishing Saturday night into Sunday
with seas maxing out around 4 ft. A Small Craft Advisory seems
likely to develop Tuesday and carry into Wednesday morning...in
spite of stable conditions and little gustiness under an
inversion.
&&
.CLIMATE...
The high of 85F in Caribou today was the warmest temperature
since August 14, 2020.
&&
.CAR WATCHES/WARNINGS/ADVISORIES...
ME...Beach Hazards Statement from 8 AM EDT Saturday through
Saturday evening for MEZ029-030.
MARINE...Small Craft Advisory from 4 AM Saturday to 4 AM EDT Sunday for
ANZ050-051.
&&
$$
Near Term...CB/Hewitt
Short Term...MCW
Long Term...MCW
Aviation...CB/Hewitt/MCW
Marine...CB/Hewitt/MCW
Climate...CB
Area Forecast Discussion
National Weather Service Grand Forks ND
921 PM CDT Fri May 21 2021
.UPDATE...
Issued at 921 PM CDT Fri May 21 2021
The front is being picked up by the radar, with the latest image
showing it along a line from Thief River Falls to Hillsboro to
Cooperstown. The north winds to the north of the boundary have
been fairly gusty, which has limited the fog so far. If the front
keeps moving as it has been, it should push down into the Fargo
Moorhead area in the next couple of hours, and could well continue
even further southward. This has been bringing low clouds and
north winds behind it, as well as falling temperatures. This
southward push is a bit faster than expected, which will play into
Saturday`s forecast too. The new model guidance for Saturday is
looking cooler, with north winds across the entire FA. High
resolution model guidance continues to show the precipitation
developing over western South Dakota right now....lifting north-
northeast overnight, mainly into the Devils Lake region, so that
remains on track.
UPDATE Issued at 655 PM CDT Fri May 21 2021
Tricky forecast again tonight, due to fog, spotty showers and
storms, the possibility of an area of showers and storms moving
into the Devils Lake region after midnight, and wind speeds and
directions. The surface front sits along a Jamestown to Grand
Forks to Warroad line, with south winds on one side and north
winds on the other. Like last night at this time, there are some
4 to 5 mile visibilities already developing north of the boundary.
This gives a little more confidence to fog developing again
overnight, but not sure if it will become dense, or it will just
stay in the 2 to 5 mile range. Did add the mention of fog to some
areas behind the boundary. Spotty showers and storms continue to
form along the boundary as well. After dark last night, they
became elevated well north of the surface boundary, and that may
happen again this evening. Already had some low precipitation
chances along and north of highway 2, just spread them a little
more eastward. Finally, high resolution models still show a more
organized band of showers and storms forming over the western
Dakotas and lifting up toward the Devils Lake region around or
after midnight. If this occurs, it would finally bring a little
more widespread rain to that parched area. However, convection is
variable, and a lot could happen between now and then.
&&
.SHORT TERM...(This evening through Saturday night)
Issued at 315 PM CDT Fri May 21 2021
Frontal placement will continue to play havoc with sky cover and
temperatures/winds into Saturday. South-southeast winds have made
up to near a Hallock-Grafton-Devils Lake line at mid aftn. Winds
have turned back north at KDVL at 20z. HRRR and blended model
solutions indicate north winds dropping back southward as the
front moves south behind exiting wave now in eastern Manitoba.
Airmass in warm sector thru SE/EC ND into MN is quite warm and
humid with man sites in the 80s and dew pts in the low-mid 60s.
There have been some elevated shower/t-storms within the warm
sector along the NE SD/SE ND/MN border region but they are
diminishing. A narrow region of t-storms in NW MN, north of TRF to
Roseau associated with southern edge of upper level wave in
Manitoba will exit in the next few hours.
Overall for most of the area a quiet start to the evening. Upper
level wave and sfc low is progged to move north on the east side
of the larger 500 mb low in Nevada. This system will showers and
t-storms into south central and southwest ND this evening with a
complex moving NE or ENE thru central and into NE ND and southern
Manitoba overnight, exiting Saturday AM. Severe risk seems quite
low but some gusty wind threat does exist into the DVL basin
overnight. Behind this wave the north winds will drop south thru
most areas Saturday as a front moves south. Scattered t-storms are
possible along the front during the day Saturday as it moves into
WC MN and SE ND in the aftn. Risk of a strong storm or two at that
time, but upper ridge in place and lack of wind shear should
prevent organized supercells from developing.
Weak high will build into the north Saturday afternoon and
evening. A chc for showers or psbly a t-storm continues over SE ND
and WC MN Sat night.
.LONG TERM...(Sunday through Friday)
Issued at 315 PM CDT Fri May 21 2021
SUMMARY...Primary headline is the severe potential on Sunday night
into Monday morning, primarily over the western CWA. The primary
question to resolve is placement of the surface cyclone and
connected warm front, as model guidance has been variable on
positioning along the North Dakota-South Dakota border. The rest of
the long term period is characterized by progressive shortwaves
embedded within zonal flow and variable temperatures.
SUNDAY THROUGH MONDAY...An interesting dynamic is setting up for
Sunday. Ridging begins to deamplify and push eastward, allowing
the strong cutoff low spinning over the northwest to push
northward. This will provide for a very broad area of synoptic
ascent over the northern high plains, facilitating surface cyclone
development. Ensemble guidance has struggled with the position of
this surface cyclone, which unfortunately puts warm frontal
placement in a precarious situation, ranging from as far north as
the south RRV to east central South Dakota. Isentropic ascent
north of the warm front will likely facilitate cloud cover over
the area, inhibiting boundary layer destabilization and limiting
opportunities for thunderstorms, although showers north of the
warm front cannot be ruled out, especially as ensemble members
show the potential for weak shortwave troughs aloft in advance of
the upper low Sunday morning.
A very warm and relatively moist warm sector will set up south of
the warm front, with dewpoints in the 50s and 60s with southerly
flow. Within the warm sector, guidance suggests MLCAPE within the
range of 1000-2500 J/kg. North of the warm front, elevated
instability does exist, with lapse rates aloft in the range of 7
K/km. CI will likely occur upstream, so the primary question will be
how far east ongoing convection gets and how far north it gets with
the warm front. As the cold front sweeps through the area,
convection will push eastward and diminish Monday morning into the
afternoon. A dry clear day is expected behind the front, with
increasing winds as mixing brings rather stout momentum down to the
surface.
TUESDAY THROUGH FRIDAY...Another breezy day on Tuesday is expected
as strong flow aloft will mix down once again to the surface.
Shortwave ridging will prevent any further activity on Wednesday,
although guidance varies in the strength of this shortwave ridge,
which will play a role in the evolution of Thursday and Friday. For
now, leaving NBM due to high uncertainty in upper air evolution
towards the end of the period.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 655 PM CDT Fri May 21 2021
Have stuck with the 18z TAF idea of fog and stratus forming again
tonight into Saturday morning. Exact timing and locations when
this happens is always hard to nail down, but went with the best
trends and will adjust as need be. There have been isolated
showers and weak storms along and north of the frontal boundary
from Jamestown to Grand Forks Warroad this evening. There are
some high resolution models that continue to show isolated shower
and storm activity from where it is now all the way to the
Canadian border this evening. However, coverage is not enough to
warrant mention in any of the TAFs. The best chance for more
organized showers and storms looks to arrive around or after
midnight at KDVL. This may only last for a few hours before it
continues to lift north-northeast into Canada. Not looking likely
that the MVFR or IFR ceilings will lift on Saturday.
&&
.FGF WATCHES/WARNINGS/ADVISORIES...
ND...None.
MN...None.
$$
UPDATE...Godon
SHORT TERM...Riddle
LONG TERM...Perroux
AVIATION...Godon
Area Forecast Discussion
National Weather Service Goodland KS
559 PM MDT Fri May 21 2021
.UPDATE...
Issued at 434 PM MDT Fri May 21 2021
A severe thunderstorm watch is currently in effect for Yuma, Kit
Carson, and Cheyenne counties until 10 PM MDT. Possible hazards
include large hail and damaging winds.
&&
.SHORT TERM...(This evening through Saturday night)
Issued at 231 PM MDT Fri May 21 2021
500mb RAP analysis and satellite imagery showed southwest flow above
the region this afternoon as a large closed low spun over western
Nevada with upper ridging across the eastern half of the country. At
the surface, a dryline extended from north to south along the Front
Range in Colorado with some low to mid level clouds developing in
its vicinity. Generally the region is under mostly sunny skies
midday, with windy conditions as south winds gust up to 50 mph along
a tight pressure gradient. At 2 PM MT, temperatures ranged mainly in
the low to mid 80s.
A north-south oriented line of thunderstorms is anticipated to
initiate along the aforementioned dryline mid afternoon in north
central/northeast Colorado. This line should enter the western
portion of our area in the late afternoon and progress eastward into
the evening hours. Am not anticipating this line to make it very far
into southwest Nebraska and northwest Kansas before dissipating this
evening. At this point, have kept thunderstorm chances in eastern
Colorado and the first western tier of Kansas and Nebraska counties.
Severe parameters including very steep mid level lapse rates, shear
of 30 to 40 knots or so, and CAPE nearing 2000 J/kg support a
potential for severe weather. While the threat exists along and west
of Highway 27, the area of most concern will be Yuma and Kit Carson
counties in Colorado where the mentioned severe parameters are at
the highest levels. This setup suggests that large hail and damaging
winds will be the main threats. Also cannot rule out a tornado or
two with any initial discrete thunderstorms that develop this
afternoon before they congeal into the line.
Otherwise for tonight, south winds stay breezy through the evening,
slightly tapering off early Saturday morning. Temperatures fall into
the mid 50s to low 60s under mostly cloudy skies.
On Saturday, the system over the western CONUS progresses very
little, with the closed low lingering near Nevada. Southwest flow
prevails aloft while breezy southerly winds gust around 30-35 mph.
As temperatures rise into the mid 70s to mid 80s, we could see a
little break in cloud cover before thunderstorms develop and clouds
increase once again.
Timing for thunderstorm initiation is uncertain at this point, with
some guidance showing early development (around Noon MT) and others
following similar timing to today. What is throwing me off is that
we could see some thunderstorm activity billowing up from
southeastern Colorado midday, which will then intensify as daytime
heating is underway in the afternoon. Not sure which solution is
correct, so this will have to be monitored. Nevertheless,
thunderstorms look to form along the dryline once again in the
afternoon, starting out as discrete cells and merging into a line or
two through the evening. While severe weather will be possible
across the entire region, the area that appears to have the higher
threat is west of a line from Trenton, NE to Tribune, KS (roughly)
due to the upper ridging pushing in from the east. Hazards are large
hail, damaging winds, and a tornado or two. Dry weather should
return to the region by midnight, with temperatures falling into the
mid 50s to low 60s.
.LONG TERM...(Sunday through Friday)
Issued at 200 PM MDT Fri May 21 2021
Upper low will be over the northern Rockies on Sunday with
negatively tilted shortwave trough moving over the central High
Plains Sunday afternoon and evening. Front/surface trough appears
to be likely location for convective initiation, which will be
roughly along/just east of the Kansas/Colorado border area.
Environment will be strongly sheared, up to 60 kts, with weak to
moderate instability forecast. The set up would suggest severe
storms likely, with still some uncertainty on exact locations for
greatest risk, and perhaps some uncertainty due to lack of better
instability. Nonetheless, SPC slight risk seems appropriate, might
even bump it up a category due to the strong shear. Storms will
continue into Sunday evening before weakening/moving east out of
the area by midnight or so. Also expecting breezy to windy south
winds Sunday afternoon, with gusts of 40-50 mph in Colorado and
west of Highway 25 in Kansas/Nebraska.
Front slowly moves through the area on Monday and becomes nearly
stationary in central/eastern part of the forecast area. Exact
location will ultimately determine where storms initiate in the
afternoon. Another shortwave trough will be moving through the
base of the upper low now in the northern plains. Deep layer
shear/instability forecasts continue to support organized
convection along/east of the front for Monday afternoon and
evening, with shear forecast at 40-60 kts, with another round of
severe storms possible.
Upper flow becomes more zonal on Tuesday but appears to be another
impulse coming out of the central Rockies in the afternoon. In
addition, old surface front may still be in the area, but
difficult to say where as mesoscale influences from previous days
convection will have an influence. Deep layer shear continues to
be around 40-50 kts, although some question on amount of
instability if models forecasts are correct. Appears eastern areas
will be favored due to timing of upper wave and where better
instability currently forecast, but confidence in timing and
location details is not that great at this time.
For the Wednesday through Friday time period, very persistent
upper pattern with southwesterly flow over the plains and
embedded impulses. Instability and deep layer shear will be
sufficient for severe storms should they develop. Surface pattern
will basically feature a moist southeasterly flow each day, with
perhaps a hint of a dry line on Thursday which may dry out
southwestern areas. However, surface pattern highly uncertain at
this time range.
Temperatures will continue to be above normal through the long
term period, with highs in the 80s and lows mainly in the 50s.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 550 PM MDT Fri May 21 2021
KGLD expects see VFR conditions to begin the forecast period with
south-southeasterly winds at 28G37 kts. At 04Z, KGLD winds look
to turn more southerly and slow to 23G30 kts with southerly LLWS
of 45 kts introduced at 2 kft. At 09Z, KGLD winds slow to 18G23
kts as LLWS expects to end. MVFR conditions begin at KGLD by 13Z
as the cloud ceiling drops to 2400 ft followed by VFR conditions
returning at 14Z when the cloud ceiling rises to 5 kft.
KMCK begins the forecast period with VFR conditions and south-
southeasterly winds at 21G33 kts. At 04Z, KMCK winds expect to slow
to 15G25 kts with southerly LLWS of 45 kts introduced at 2 kft. By
11Z, MVFR conditions begin at KMCK as cloud ceilings drop to 1700
ft with wind shear ending and winds slowing to 12 kts. At 15Z,
KMCK winds turn southerly and increase to around 14G22 kts before
VFR conditions return at 17Z with cloud ceilings rising to 3500
ft. KMCK winds then turn back south-southeasterly and slow to
around 17 kts.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...NONE.
CO...NONE.
NE...NONE.
&&
$$
UPDATE...076
SHORT TERM...JBH
LONG TERM...024
AVIATION...076
Area Forecast Discussion
National Weather Service Gray ME
1028 PM EDT Fri May 21 2021
.SYNOPSIS...
Warm conditions will continue Saturday away from the coast. A cold
front will cross the region on Sunday bringing a line of showers and
thunderstorms. Canadian high pressure will build in to start next
week bringing much cooler conditions to the region. Another warm up
will arrive next week.
&&
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
1025 PM Update...Little change to the going forecast at this
time. Most scattered shower activity should remain over eastern
zones for the next couple of hours then move offshore.
Otherwise, a mostly cloudy and relatively warm night.
615 PM Update...Scattered showers continue in them mountains
and foothills as well a portions of Grafton County NH early this
evening. Have kept isolated in for the next couple of hours as
a strike or two will be possible. Otherwise, just some minor
adjustments to the going forecast at this time with the forecast
remaining on track.
Previously...
Weak upper wave passing over the top of an upper ridge over the
eastern CONUS will bring a slight chance of showers and isolated
thunderstorm through this evening. Current satellite imagery shows
cumulus building over the mountains with radar showing some
convective showers over Aroostook County and southeast Canada.
Latest RAP analysis shows a few hundred J/kg of SBCAPE over the
mountain and foothills, but overall expectations are for
showers to be limited in coverage with best chances across the
mountains. Chances for any thunder will wane after sunset with
the loss of heating.
Tonight there will be slight chances for showers across eastern
zones as the weak upper wave tracks into the Canadian Maritimes.
It will be a mild night with lows staying in the 60s away from
the coast with mostly cloudy skies. Closer to the coast lows
will dip into the 50s and with plenty of low level moisture
there will be areas of patchy fog near the Mid-Coast through the
Capital District of Maine.
&&
.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Another upper wave passes over the top of the ridge Saturday.
Despite mostly cloudy skies it will be warm away from the coast
with highs into the 80s and parts of southern New Hampshire
climbing to near 90F. Closer to the coast onshore winds will
keep temperatures in the 70s with the Mid-Coast likely staying
in the 60s. Due to the warm weather expected and water
temperatures still in the 50s will be issuing a Beach Hazard
Statement and Special Weather Statement to highlight the dangers
of cold water.
Dewpoints will climb to near 60F during the day and CAMs
continue to show several hundred J/kg of SBCAPE developing over
much of the area with the exception being the Mid-Coast. As the
upper wave passes to our north scattered showers on
thunderstorms will develop near the International Border and
mountains just after noon and will track southeast across the
area. Mid-level lapse rates will generally be less the 6C/km and
effective shear looks to be around 25 kts so the overall severe
threat looks low. PWATs will be will above normal for this time
of year around 1.5 inches so there is potential for some heavy
downpours with stronger cells.
Showers and thunderstorms will diminish around sunset with
another mild night expected. Parts of southern New Hampshire
will only drop into the mid 60s with the rest of the area
dropping to near 60F.
&&
.LONG TERM /SUNDAY THROUGH FRIDAY/...
A strong cold front will approach New England from Canada to start
out the long term portion of the forecast on Sunday. Ahead of this
front, an increasing southwesterly gradient will allow for a warm
and moist atmosphere in the region. H8 readings top out near +14C.
With good mixing, warm temperatures will make it to most of the
region including the southwest coast of Maine and the Seacoast of
New Hampshire where readings will be in the 80s in most locations
outside the mountains. The southwesterly flow will allow for cooler
readings along the Midcoast as winds will remain onshore.
A strong and fast moving upper level trough will cross region
Sunday. This will aid in thunderstorm development, some of which may
contain gusty winds as dew point values climb into the lower 60s
during the morning. CAPE values climb into the 500-1000 J/KG range
aiding in the development of convection along and near the front.
Timing is critical for the FROPA however as it may cross the region
a little on the early side on Sunday.
Canadian high pressure will bring much cooler and drier air into the
region Sunday night into Monday. In fact, frosts may occur in the
northern mountains where the growing season has begun.
Temperatures will be seasonable as winds switch out of the west on
Tuesday. A couple showers may clip northern areas during the day.
More warmth and moisture arrives on Wednesday as a strong
southwesterly gradient sets up throughout the atmosphere, both at
the surface and aloft. Readings will once again climb into the 80s
in all areas including much of the coastline. The Midcoast region
will be cooler do to an onshore component.
Scattered showers and possibly a thunderstorm may accompany this
warm air advection pattern.
Another strong cold front will cross the region late Wednesday night
and early Thursday morning. A few strong storms may accompany this
system as wind fields once again increase over the region. However
the time of day should minimize significant activity.
&&
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
Short Term...Mainly VFR through tonight with perhaps the
exception being KRKD where low cigs will bring periods of IFR
late tonight through sunrise. Scattered SHRA and -TSRA will
develop across the mountains tomorrow just afternoon and will
track southeastward bringing brief periods of restrictions.
Long Term...A cold front will cross the region on Sunday, with
thunderstorms moving through briefly dropping conditions to MVFR or
IFR. High pressure will build in Sunday night into Monday with the
next potential for rainfall on Tuesday night.
Another strong frontal system will cross the region Wednesday night.
&&
.MARINE...
Short Term...Winds generally stay at or below 25 kts through
the weekend while a subtropical system well offshore send in
building swells tonight. Sea build to 5 feet tonight and will be
in the 5-7 ft range through Saturday night.
Long Term...Swell from a subtropical storm near Bermuda will
continue over our waters late this weekend and into early next week.
A strong cold front will also allow for gusty northwesterly winds
Sunday night, possibly exceeding SCA thresholds. Seas will build
also Tuesday night into Wednesday as a southwesterly gradient
strengthens over the waters.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...Beach Hazards Statement from 8 AM EDT Saturday through
Saturday evening for MEZ023>028.
NH...Beach Hazards Statement from 8 AM EDT Saturday through
Saturday evening for NHZ014.
MARINE...Small Craft Advisory from 2 AM Saturday to 8 AM EDT Sunday for
ANZ150-152-154.
&&
$$
NEAR TERM...Ekster/Schroeter
SHORT TERM...Schroeter
LONG TERM...Cannon
Area Forecast Discussion
National Weather Service North Platte NE
631 PM CDT Fri May 21 2021
.SHORT TERM...(This evening through Saturday night)
Issued at 221 PM CDT Fri May 21 2021
Today the CWA remains with an upper level low to its west and a high
pressure system to its east. At the sfc, there is an inverted trough
over eastern WY that will move into the area with an accompanied
frontal boundary and be the initiator for storms this evening. Also,
there continues to be southeasterly flow which is advecting Gulf
moisture into the state with PWATs reaching ~1-1.5". Given the
abundance of moisture, it is possible for up to an inch of rainfall,
especially in Sheridan county which the models agree will see the
heaviest amounts. Additionally, if there are any slow moving storms,
they may end up causing some areas of heavier rainfall.
The area of concern for tonight is primarily the Panhandle and
western Sandhills as here some of these storms may turn severe. Both
the RAP and HRRR are showing SCP around 4-6 in the Panhandle where
there are steep lapse rates (~8-9deg/km) and about 1000 J/kg of
MUCAPE. There is also some decent 0-6km bulk shear near 40kts or so.
As such, expecting some supercells to develop with the primary
concerns being hail, strong winds, and locally heavy rainfall. As
with previous fcsts, expecting most of the storms to stay west of
HWY 83.
Storms are expected again tomorrow afternoon and evening, with the
area of concern again being the Panhandle and Sandhills. There is
strong FGEN at 850 and 700mb, which is expected to be the basis for
these storms, as the moisture advection continues from the SSE.
There is a chance tomorrow night as well for up to an inch of
rainfall over the northern Sandhills, and locally heavier amounts
if storms stall out over an area. The severe threat is being
monitored as there seems to be ample 0-6km bulk shear (40-50kts)
and over 60kt winds at 700mb. ATTM the main concern is heavy
rainfall and strong winds, but this will continue to be evaluated
with new model runs.
.LONG TERM...(Sunday through Friday)
Issued at 221 PM CDT Fri May 21 2021
The potential for storms will return again Sunday evening and
into the overnight.
Into the day Sunday, the closed upper level low will move over the
Rockies and lift northeastward to the WY/Nebraska border. By this
time, it is expected to have developed an associated sfc cold front
due to some lee FGEN IVO the Rockies. This will be the main
initiator for storms, along with support from a small upper level
jet. At this time, the region will still be in southeasterly flow at
the surface, and receiving a good amount of moisture from the Gulf,
resulting in PWAT values near 1-1.5". Given the lift provided, and
the ample moisture via advection, there is potential for some
localized areas of heavy rainfall (near 1+") or more. Additionally,
there is a chance that some of these storms may become severe, with
the biggest area of concern being the Panhandle and western
Sandhills ATTM. There is looking to be near 70kts of 0-6 km of bulk
shear, steep lapse rates, and moderate DCAPE...all which would
support the storms turning severe. The severe potential will
continue to be monitored through the weekend.
The front seems to stall out in eastern Nebraska, and may linger for
a few days. No present wx impacts are detected, but something to
keep an eye on as confidence in location is low. Into the early
morning Monday, winds will shift to southwesterly, pushing storms
northeastward and bringing some drier SW air into western Neb. This
will help fend off storms and keep skies clear through Tuesday.
As this low treks into Canada by Wednesday, the Plains will be left
in an area of ridging at upper levels, with a sfc high pressure
system working its way through from the northwest. This will bring
moisture advection back into the area, and increase PWATs once
again.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 631 PM CDT Fri May 21 2021
Multiple aviation weather concerns exist for western Nebraska,
including thunderstorms and gusty winds this evening, low ceilings
overnight into the morning, and another round of precipitation
for Saturday. The ongoing strong south/southeast winds will
continue into the early overnight hours with frequent gusts over
30 kts. Once surface speeds begin to wane, low level wind shear
conditions will likely arise, then subside by daybreak. Scattered
thunderstorms will affect the panhandle and western terminals
(KOGA to KVTN) this evening, with some being capable of large hail
and wind gusts 40+ kts. A stratus deck will also build into the
area to coincide with the lighter surface winds. Most terminals
will drop to MVFR or IFR ceilings. Northern terminals (KVTN) may
remain in stratus for much of Saturday, while southern terminals
(KLBF) will break mid-morning with increasing thunderstorm chances
heading into the afternoon.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SHORT TERM...Meltzer/Sinclair
LONG TERM...Meltzer/Sinclair
AVIATION...Snively
AREA FORECAST DISCUSSION
National Weather Service Raleigh NC
910 PM EDT Fri May 21 2021
.SYNOPSIS...
High pressure will strengthen over the Carolinas and southern
Appalachians through Saturday. A strong high pressure aloft will
continue to dominate the pattern for our region Sunday through next
week with predominately hot and dry conditions.
&&
.NEAR TERM /THROUGH TONIGHT/...
As of 910 PM Friday...
Current forecast on track for the overnight period. High pressure
over far eastern VA will move southwestward into central NC
overnight, resulting in excellent radiational cooling. Lowered
minimum temperatures a few degrees with generally mid to upper 50`s
and some lower 50`s in the typical colder spots. Some high clouds
will drift into the area by the early morning hours as a mid-level
ridge over the Ohio Valley drifts south into the Tennessee Valley.
Latest guidance from the SREF and HRRR show potential for some fog
across the far eastern Coastal Plain, perhaps clipping Rocky Mount
and southern Sampson County as some low-level moisture, currently
present near Kitty Hawk, drifts southwestward under the easterly
flow. Any fog would be patchy and lift by sunrise.
&&
.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 350 PM Friday...
A mid/upper shortwave rotating around the ridge centered over the
Deep South will move south from the Great Lakes region into the Mid-
Atlantic on Saturday and Saturday night. At the surface, an
associated trough will develop along the East Coast, shunting the
high pressure system farther west over the Deep South. While no
precipitation is expected in central NC with this shortwave, it will
likely result in increased cloudiness during the day and into
Saturday night. With 1000-850mb thicknesses around 1400-1410m
(roughly 15m higher than Friday), and the flow shifting to a more
westerly direction, temperatures on Saturday will climb into the
upper-80s to near 90 (5-10 degrees above normal). Increased clouds
will help keep lows Saturday night warmer than previous nights as
well, in the lower-to-mid-60s.
&&
.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 240 PM Friday...
...Record hot temperatures possible for part of next week (mainly
Wednesday, May 26 and possibly Thursday, May 27).
...Little if any short term relief from the abnormally dry
conditions through the next 7-10 days.
Strong upper level high pressure is expected to weaken slightly and
drift slowly westward (retrograde) but still located just to our
west, over the TN Valley region Sunday into Monday. Our moisture
sources will be cut off with strong ridging to our west. The mean
flow will be from the NW-N aloft which will be susceptible to
remnant/decayed convection well to our NW (Great Lakes etc...).
However, there should be some periods of mid/upper level cloudiness
with any of these remnant vort maxes. The surface flow will be light
from the west (downslope) which will aid drying and heating during
the day. Highs both days should be in the upper 80s to lower 90s.
These temps may have to be adjusted at any point given the chance of
mid/high clouds affecting temps especially early Sunday, then again
late Monday. The chance of any convection looks meager, at best.
Lows will be in the mid to upper 60s.
A backdoor cool front may make a run into NC from the NE later
Monday into Tuesday. This may allow it to be a few degrees cooler in
the NE Tuesday with some additional cloudiness. Other than a slight
chance of a shower or thunderstorm near the front, expect dry
conditions. Highs Tuesday should range in the mid 80s NE to lower
90s south.
The hottest days during this late May heat wave should be Wednesday
and Thursday as the ridge remains strong with little in the way of
cloudiness to inhibit heating. Highs Wednesday should soar into the
lower 90s NW, mid 90s for the central areas, and upper 90s in the
Sandhills. If this forecast holds, new daily record highs will have
a potential to be tied or broken in some areas.
Finally, some relief should develop late week with the approach of a
cold front from the NW-N as the ridge aloft weakens somewhat.
However, the chance of thunderstorms still remains questionable with
the lack of low level moisture. Convection may remain isolated to
widely scattered even with the front on Friday. We will keep POP
very low until the pattern shows some definitive signs of changing.
Highs should drop back 4-7 degrees into the upper 80s to lower 90s
by Friday.
&&
.AVIATION /00Z FRIDAY THROUGH WEDNESDAY/...
As of 737 PM Friday...
24 hour TAF period: Aside for a brief period of some sub-VFR
conditions in fog/stratus at KRWI between 10 to 12z Sat, expect VFR
predominately VFR conditions through the forecast period. Otherwise,
high clouds/cirrus is expected to increase late tonight through
Saturday.
Looking beyond 18z Saturday: VFR conditions will continue through
Sunday, with partly to mostly sunny skies. There is a low chance of
showers and storms from Monday through Wednesday, with sub-VFR
conditions also possible. The best chance will be across the
northern Piedmont.
&&
.CLIMATE /
...Possible high temperatures that have a chance to be broken next
week.
Raleigh: Wednesday, May 26, (94 set in 2019)
Thursday, May 27, (96 set in 1916)
Greensboro: Wednesday, May 26, (95 set in 1926).
Fayetteville: Wednesday, May 26 (100 set in 1953)
.RAH WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Badgett
NEAR TERM...Kren/Danco
SHORT TERM...Danco
LONG TERM...Badgett
AVIATION...CBL/Danco
CLIMATE...Badgett
Area Forecast Discussion
National Weather Service Riverton WY
513 PM MDT Fri May 21 2021
.SHORT TERM...(This evening through Saturday night)
Issued at 128 PM MDT Fri May 21 2021
Cold front pushed south overnight and is now stalled essentially
along the continental divide from Yellowstone to Dubois to South
Pass to south of Casper. North of the front temperatures are well
below normal with low clouds over the lower elevations, and fewer
clouds over the higher elevations. Southwest of the front,
temperatures are more seasonal to below normal (farther north),
though instability is greater, so showers this morning are
becoming heavier and more numerous this afternoon. Latest model
guidance has widespread precipitation occurring from Sweetwater
County northwest into Sublette, Lincoln, and Teton Counties. The
heaviest amounts are expected along the west side of the Wind
River Mountains with the strong southerly flow converging along
the divide. SPC has introduced an area of marginal risk of severe
thunderstorms across eastern ID and barely into western WY. The
slightly stronger storms look most likely late this afternoon as
the dry slot over UT moves north and noses into SW WY for the
storm from Star Valley to the Tetons. Late this afternoon and
early evening, the showers over SW WY are expected to move NNE
over the dome of cooler air to bring showers to areas east of the
divide. The convective activity looks to diminish after midnight
over much of the area, with isolated chances through the morning.
Counter to model suggestions yesterday, the warm dry southerly
flow is not likely to push the stationary front northward, so
below normal temperatures with low clouds are likely east of the
divide into Saturday.
The upper level low over west central Nevada will move toward NW
Nevada Saturday morning, tightening the gradient from NE Utah into
SW WY. Easterly flow will continue east of the divide, while SW WY
should again see strong dry southerly flow with gusts 30-40 mph.
Saturday morning from 6am to noon looks to be mostly quite
precipitation wise. In this situation, thunderstorms are expected
to develop early Saturday afternoon along the boundary and move
northward. The northern Wind Rivers and Absarokas as well as
around the Bighorns appear to be the most favorable locations.
Some areas may see 0.25 to 0.50" of precipitation during the
afternoon and early evening, with a couple of inches snow in the
highest elevations. The HRRR is suggesting that the cold air will
push over the divide Saturday evening and move into SW WY as the
strong southerly flow subsides. Moderate precipitation should
continue Saturday evening into Sunday morning as the upper level
low becomes negatively tilted to provide much better mid and upper
level support. Saturday night could see some areas see up to an
inch of precipitation as the upper level low becomes more
negatively tilted and the 300 mb jet gets focused from south
central WY toward NW WY. With the low moving toward NW WY early
Sunday morning, winds across southern and central WY may be gusty
as 700mb winds over 40 kts start to move in.
Overall, another very active short term period the next 48 hours
to bring precipitation to western and central WY. Temperatures
will either be quite cool or near normal, depending on the
location!
.LONG TERM...(Sunday through Friday)
Issued at 1248 PM MDT Fri May 21 2021
Sunday through the beginning of next week, the trough to the west of
the region begins to lift as the trough negatively tilts and the low
center moves east. The trough will lift over the Cowboy State
through the day Sunday and Monday. This will increase the pressure
gradient and bring very strong winds into the region beginning
Sunday morning. Will likely need some kind of wind highlights Sunday
morning through Monday afternoon where the SSW flow will be
strongest along the pressure gradient. MOS Guidance is pushing winds
sustained 30+ kts from Rock Springs to Buffalo, especially Sunday
afternoon. 50 to 60kt 700mb winds will also be present across
Sweetwater county Sunday morning, moving east into Natrona and
Johnson County by early afternoon, where it will stall into Monday
morning. Despite southerly flow, the wind will keep temperatures
moderated through the early part of the week.
By Tuesday morning, the low should finally have lifted up and out of
the region. Warmer zonal flow will fill in behind it, bumping
temperatures back into the 70s east of the Divide by later in the
week. In terms of precipitation, models show a good bit of
uncertainty through the second half of the week. In general, looks
like zonal flow with weak ridging that could bring shortwaves across
the region. Will likely see scattered convection throughout the
week as the instability and generally active pattern continues.
&&
.AVIATION...(For the 00Z TAFS through 00Z Sunday)
Issued at 510 PM MDT Fri May 21 2021
Rain showers (and snow showers for the higher terrain) will continue
over the region into the evening hours, with far west-central WY
(including KJAC) having the best chance of isolated thunderstorms
before 22/0500z. Expect lower ceilings and some visibility reduction
when showers move through.
Winds are expected to decrease after sunset, with most valleys
decoupling. Those sites close to terrain (e.g. KPNA) may continue to
see some gusts, but less than the winds seen during the daytime
hours. After midnight, precipitation decreases across the region.
Light north and northeast flow resumes east of the Divide.
Winds increase late morning for those west of the Divide on Saturday
morning. Showers and isolated thunderstorms are again possible
during the afternoon hours Saturday.
Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for
the latest information on icing and turbulence forecasts.
&&
.FIRE WEATHER...
Issued AT 137 PM MDT Fri May 21 2021
A very unsettled pattern the next 2-3 days over western and
central WY As a large upper level low pressure system over Nevada
moves toward Montana. A cold front aught up on the continental
divide is complicating the situation. Much of the area will see
showers and thunderstorms, with some areas seeing strong storms
and heavy precipitation. This afternoon and evening, the strong
southerly flow across SW WY will focus the precipitation into the
Wind Rivers and western mountains. Showers will continue through
midnight. Temperatures are below normal east of the divide and
near normal over SW WY. Saturday morning looks to be fairly quite,
with more showers and thunderstorms developing over central WY
early in the afternoon. Stronger storms and showers with moderate
precipitation is expected from the Wind Rivers into the Absarokas
and NW WY Saturday afternoon and evening, with some areas likely
seeing 0.50" to 1.0" of precipitation. Look for strong southwest
winds Sunday for much of the state as the core of the system goes
over Yellowstone.
&&
.RIW WATCHES/WARNINGS/ADVISORIES...NONE.
&&
$$
SHORT TERM...McDonald
LONG TERM...Fisher
AVIATION...VandenBoogart
FIRE WEATHER...McDonald
Area Forecast Discussion
National Weather Service Las Vegas NV
425 PM PDT Fri May 21 2021
.SYNOPSIS...A large low pressure system will circulate over our
region today and Saturday bringing considerably cooler
temperatures with scattered showers across the southern Sierra and
south central Nevada with light snow accumulations possible above
6000 feet. Winds diminish Saturday and Sunday, though
temperatures will remain below normal as the system slowly lifts
away to the north. Near normal temperatures and dry conditions
will return early next week. &&
.SHORT TERM...Today through Sunday.
The broad upper-level trough currently centered over southwest NV
will continue to dig southeast through Saturday. However, the board
low will continue to circulate overhead through Sunday morning
before it lifts northeast. As a result, breezy west to southwest
winds are expected again tomorrow, with gusts to around 15-25 mph.
Slightly stronger winds will be possible across western San
Bernardino County near Barstow tomorrow afternoon, where gusts to
around 30 mph will be possible.
As the low shifts southeast through tomorrow, moisture associated
with the low center will also push south, similar to today, leading
to another day of isolated to scattered light showers/high elevation
snow showers. Precipitation is expected to again be light tomorrow,
but elevations above 7000-7500 feet may see some light dusting of
snow where temperatures will be cold enough and showers are
expected. Otherwise, accumulating snow is only expected above 9500
feet. An additional 1-3 inches will be possible along the higher
elevations of the eastern Sierra and up to 1-2 inches along the
higher elevations of the Spring Mountains tomorrow. Decent
instability associated with the low center will also be in place
tomorrow afternoon, so isolated thunder will be possible with some
of the stronger updrafts that develop. Smoke plume associated with
the Cherrywood fire is expected to overspread across parts of
western Lincoln County this afternoon, per the latest HRRR smoke
runs.
By Sunday, the low will begin to wrap up and lift northeast, allow
for height increase, resulting in increasing temperatures. Though, a
weak piece of energy along the backside of the trough will move
across central NV, leading to a slight increase in pressure
gradients, creating breezy west winds across Lincoln County.
.LONG TERM...Height fields will be rising fairly rapidly during
the day Monday and in turn so will surface temperatures.
Generally zonal flow and some additional warming taking place on
Monday, bringing temperatures back to closer to their seasonal
normals. WPC Clusters indicate another weak upper low moving into
northern California on Tuesday which, at this point looks to have
only very modest impacts to the Great Basin and Mojave Desert.
Southwest winds may increase a bit ahead of the approaching system
and temperatures will climb a few more degrees in most locations.
The upper level trough will be slow to make much progress on
Wednesday and Thursday, basically keeping the status quo with
temperatures at or slightly above their normals, which in Las
Vegas is in the lower 90s, along with breezy and dry conditions.
&&
.FIRE WEATHER...A belt of west to southwest winds gusting 35 to 45
mph will combine with low relative humidity to create another round
of critical fire weather conditions over the San Bernardino County
deserts up across the Lake Mead National Recreation area and
northwest Arizona. A Red Flag Warning is in effect for these areas
until 8 PM this evening. &&
.AVIATION...For McCarran...Continued minor to moderate impacts to
the terminal through about sunset as isolated showers continue to
occur in the vicinity of the Valley. While there could be brief
shifts to the west, southwest direction is favored through the
overnight period with a stark drop off in wind gusts after 03Z.
Relatively light and variable winds expected early tomorrow morning
before another round of isolated showers bring virga and outflow
concerns again tomorrow afternoon and more westerly wind gust
potential. PIREP solicitation is recommended through at least 12Z
due to low level turbulence up to 12kft.
For the rest of southern Nevada, northwest Arizona and southeast
California...Continued gusty winds and isolated -SHRA expected
across much of the region through the first few hours of the TAF
period. By sunset, winds and showers should diminish resulting in a
relatively quiet night overall. Winds will increase again tomorrow
afternoon but much less than the last couple days. Isolated -SHRA
again possibly tomorrow afternoon for KBIH and the LV Valley.
&&
.SPOTTER INFORMATION STATEMENT...Spotters are encouraged to report
any significant weather or impacts according to standard operating
procedures.
&&
$$
Short Term...Peters
Long Term...Czyzyk
Aviation...TB3
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