Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/05/24
Area Forecast Discussion
National Weather Service Bismarck ND
1014 PM CDT Sun Aug 4 2024
.KEY MESSAGES...
- There is a low chance of strong to severe thunderstorms in
southwest North Dakota late tonight.
- Widespread showers are expected across western and southern
North Dakota tonight through Monday morning, with a few
thunderstorms along and south of Interstate 94. Localized
heavy rainfall of at least one inch is possible.
- Below normal temperatures are expected through the upcoming
week, especially on Monday when highs could be limited to the
60s.
&&
.UPDATE...
Issued at 942 PM CDT Sun Aug 4 2024
We made some updates to pops overnight. Currently, a cluster of
strong to severe storms was located near Billings Montana and
south into northern Wyoming. This convection was the convection
mentioned in earlier discussions that would make it`s way
towards southwest ND tonight, with 18Z Cams showing stronger
convection holding together as it moves into southwest ND. This
trend has continued for the most part. The HRRR UH tracks are
not as strong moving into southwest ND, compared to 18 UTC, but
reflectivities remain robust into southwest ND. The NAM Nest is
also not as strong with the UH tracks moving into ND, but does
strengthen one over Adams County ND towards morning. Both are
later moving stronger convection into the state and both area
stronger with convection/and or maintain convection along the
southern tier counties overnight and into Monday morning.
Utilized a blend of 00Z guidance with our previous forecast for
pops through tonight. This delays pops into the southwest
tonight, with likely pops not making it to the Bismarck area
until a little before sunset. Although a marginally severe wind
gust or hail stone can not be ruled out, the probability still
remains low.
There is also an area of convection that has developed along
the SD border over McIntosh and into Dickey County. This
convection is in an are of 850-700mb FG forcing and although
there were some indications earlier today of the happening, the
latest 00z CAMS did not pick this up. Expect non-severe
convection in this area of warm advection, but this general
area, along the ND/SD border may be a focus for convection,
which remains through Monday morning.
Lastly, an area of 700-500 mb FG forcing to the north is
producing an area of showers that continues from around
Williston to around Minot and southeast to Harvey and
Carrington. Expect this area to linger through the night with
only light accumulations.
Updated text products will be transmitted shortly.
UPDATE
Issued at 549 PM CDT Sun Aug 4 2024
No significant changes to the early evening update. The main
concern tonight will be strong to severe thunderstorms over
southeast Montana making their way into southwest North Dakota
after midnight. Some Cams continue to show more robust
convection holding on as it moves into southwest ND after
midnight MDT. Current pops from the day shift cover this well
and with a lot of time before convection would move into the
area can see how the 00Z Cams resolve convection late tonight.
Updated text products will be transmitted shortly.
&&
.DISCUSSION...
Issued at 308 PM CDT Sun Aug 4 2024
The Northern Plains sit under northwest flow aloft this afternoon,
with downstream troughing from Hudson Bay to the Great Lakes and an
upstream ridge over the Rockies. A few weak disturbances embedded in
the northwest flow are generating some scattered light showers
across the region, most prevalent near Williston and Watford City
and also south of Interstate 94 between the Missouri and James
Rivers. There were a few instances of lightning earlier this
afternoon from southeast Dunn to western Oliver Counties, but most
of the ongoing precipitation as of this writing was displaced north
of any appreciable buoyancy. Surface flow this afternoon is mostly
easterly with high pressure centered over southwest Manitoba and a
lee cyclone between the Bighorn Mountains and Black Hills. Outside
of southwest North Dakota, where greater sunshine is expected,
afternoon temperatures will be limited to the 70s.
A shortwave riding near the top of the upstream ridge will eject
east along the international border tonight into Monday. This wave
is expected to generate widespread showers along a band of mid level
frontogenesis from northwest to southeast North Dakota late tonight
through Monday morning, with rain dissipating from west to east
Monday afternoon. The associated cloud cover, which could persist
all day in the aforementioned areas, and antecedent cooler near-
surface air mass could keep high temperatures on Monday near record
cold values of lower to mid 60s.
Prior to the development of the widespread showers, some convection
is possible across southwest and far south central North Dakota
later this evening through tonight. First, CAMs are in strong
agreement on a complex of strong to severe thunderstorms crossing
southeast Montana this evening. The storms` motion into southwest
North Dakota around midnight would bring them into an increasingly
stable air mass, but there could be just enough elevated buoyancy in
a moderately to highly sheared environment for a strong to severe
storm in southwest North Dakota overnight. Most CAMs have been
consistent in advertising a weakening trend as the convection
crosses the border, but a couple of recent HRRR runs maintain
detectable UH tracks as far east as Adams County. Given the marginal
at best CAPE, we will continue to message only base severe hazards
of hail up to quarter size and winds up to 60 mph. Separately, some
CAMs show a latitudinal line of sub-severe convection flaring up
along the South Dakota border late tonight, near and east of Lake
Oahe. But this seems a little too far displaced poleward from the
nose of the low level jet.
Given the orientation of storm motions parallel to the baroclinic
zone and seasonably high precipitable water, the potential for
training convection causing localized excessive rain will need to be
monitored tonight through Monday morning. NBM and WPC deterministic
QPF project one half to one inch of rain along a broad axis from
between Watford City and Beach to between Jamestown and Ellendale,
but HREF localized probability-matched mean and maximum QPF show
potential for localized amounts as high as 3 inches.
Northwest flow aloft will persist Monday night into Tuesday
afternoon, but surface high pressure will provide a break from
shower and storm chances. Another shortwave reaching the Northern
Rockies by Tuesday evening will push subtle height rises over the
Northern Plains through peak heating, allowing for a one-day return
to closer to normal high temperatures in the mid 70s to mid 80s.
Synoptic scale forcing from the upstream shortwave will begin
reaching western North Dakota late Tuesday evening into Tuesday
night, and may be accompanied by ongoing convection. Current model
projections show uncertainty in the eastward extent and degree of
buoyancy, but there is high confidence in very strong deep layer
shear on the order of 50 kts. While the severe potential in western
North Dakota late Tuesday evening through Tuesday night remains
unclear, a few severe storms are a plausible outcome, and forecast
trends will need to be monitored closely.
Chances for showers and storms remain in the forecast on Wednesday,
but will likely be dependent on the timing of a cold frontal passage
attendant to a southern Manitoba low. A closed upper low over
Saskatchewan is then forecast to slowly plunge into the Northern
Plains on Thursday, with uncertainty in its path and evolution
thereafter. This pattern keeps lower chances for rain in the
forecast through the weekend, though a larger scale surface high
pressure could eventually form and reduce the prospects of
precipitation. The bigger story for the latter half of the week is a
consistent ensemble signal for below normal temperatures. For
Thursday and Friday, the NBM is only advertising highs in the mid
60s to lower 70s, with just a slight warmup to 70s across the state
for the weekend. A few nighttime periods could be quite cool as
well. Wednesday through Friday nights already have forecast lows in
the 40s across western North Dakota, and there are hints in the
ECMWF EFI that near-record cold cannot be ruled out.
&&
.AVIATION /00Z TAFS THROUGH 00Z TUESDAY/...
Issued at 549 PM CDT Sun Aug 4 2024
VFR conditions are expected through this evening, with
scattered light showers possible. There has been some MVFR
cloudiness with shower activity moving through KBIS this
afternoon and it`s possible a brief MVFR ceiling could occur
early this evening at KJMS.
Later tonight into Monday morning, chances for rain will
increase from southwest to northeast. A few thunderstorms are
possible across southern North Dakota, with the highest
probability of TS at KDIK overnight. We added a Tempo for
thunder at KDIK and a VCTS at KBIS. Ceilings are also expected
to lower to MVFR to IFR levels across western and southern North
Dakota Monday morning, with LIFR ceilings possible at KDIK.
Winds will generally be northeast to east around 10-15 kts
through the forecast period.
&&
.BIS WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...TWH
DISCUSSION...Hollan
AVIATION...TWH
Area Forecast Discussion
National Weather Service Glasgow MT
238 PM MDT Sun Aug 4 2024
.DISCUSSION...
KEY MESSAGES:
- Isolated showers this afternoon will become more widespread
overnight. This may affect harvesting operations across the
area.
- A strong storm or two may affect areas south of the Missouri
River into the early evening hours, but the better chances
appear to be over southeast Montana.
- Thereafter, a cooling trend is expected this week with
occasional chances for showers.
WEATHER PATTERN OVERVIEW:
A pattern change has taken place as disturbances over Canada will
begin dropping into the area. Rainshowers will move into the area
tonight that will be the first significant rainfall for most in
about a month. See our social media pages for percentages on
amounts but most should end up getting at least a tenth of an
inch by Monday.
The severe storm threat looks to mainly stay south of the CWA
later today with the latest HRRR indicating the possibility of a
bow echo type of storm structure developing from Billings to Miles
City from about 4 pm till 8 pm. The Storm Prediction Center has
upgraded the area to a Slight Risk.
The next chance of severe thunderstorms appear to be Tuesday (Day
3) as another disturbance clashes with a warm and unstable airmass
ahead of it.
The other big story this week will be the cooldown as temperatures
look to plunge! Look for highs later this week to be below normal
and feeling more like September! Highs Thursday and Friday are
expected to be in the 60s and 70s and lows dropping into the 40s
(Friday morning).
FORECAST CONFIDENCE & DEVIATIONS:
Confidence is moderate to high on cooling temperatures through
the week and also the rainfall tonight.
Rainfall chances linger into the coming week but amounts and
location remain low confidence. TFJ
&&
.AVIATION...
VFR becoming MVFR early Monday.
DISCUSSION: An area of rainshowers with embedded thunderstorms
will move in from the southwest this evening. Brief visibility
reductions may occur tonight but the expected MVFR conditions
will come with lowering ceilings Monday morning.
WIND: East wind tonight of 10-20 kts will diminish Monday. Expect
gusty and erratic winds in and around any thunderstorms this
evening. TFJ
&&
.GGW WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
weather.gov/glasgow
Area Forecast Discussion
National Weather Service Goodland KS
945 PM MDT Sun Aug 4 2024
.KEY MESSAGES...
- Very high grassland fire danger for the remainder of the
afternoon today.
- Hot again Monday in the triple digits along with some
thunderstorm potential during the late afternoon and through
evening.
- Mid-week system is expected to bring some storms, potentially
continuing into the weekend.
- Below average temperatures in the 70`s may return to the area
Thursday/Friday.
&&
.SHORT TERM /THROUGH TUESDAY NIGHT/...
Issued at 209 PM MDT Sun Aug 4 2024
NW upper level flow continues across the region today as clear skies
are in place. As mentioned in this mornings update guidance did come
in drier and hotter across western portions of the area which is
leading to near critical to locally critical fire weather conditions
especially across Yuma, Cheyenne (KS), and Dundy counties as
winds have remained breezy with sustained southerly winds of
15-20 mph with occasional gusts of 25-30 mph.
This evening and tonight will be watching a cluster of storms move
off of the Front Range. Guidance has been fairly consistent
with indicating the potentially for outflow from these storms
to move across Yuma county with 35-45 mph wind gusts.
Precipitation is not expected with that activity. However the
RAP and the NAM continue to saturate the 700-500 mb layer
starting around 09Z through at least mid morning Monday where
some showers may be possible. Current thinking is that they may
be more spotty than anything given the strong subsidence and
weak forcing so am going to go with silent pops for now.
Temperatures for tonight look to remain warm in the mid 60s to
mid 70s as a LLJ again kicks in with SSW winds remaining around
15 mph through the night. Did increase the temperatures some
especially near sunrise as winds turn to the 200-220 degree
range which typically does help warm temperatures with the wind
from that direction.
Moving on into Monday, ridging and high pressure remain across most
of the area for the majority of the day. Will be watching a wind
shift boundary that looks to move into the area and perhaps stall
across the area during the afternoon hours. This does lead to a
somewhat difficult temperature forecast as temperatures will be in
the 100s to the south of the boundary and in the 90s to the
north.With the latest guidance it does appear that corridor of
slight warmer temperatures looks to occur roughly from a Tribune to
Norton line which would have the best potential for heat indices
around 105. Did contemplate a Heat Advisory but opted to hold
off due to continued discrepancies of where exactly the
boundary does set up and the quality of the dew points as well
with guidance suggesting that mid 50 dewpoints would be most
likely across that area. We would need around 60 dew points for
heat indices of 105 to become a concern. So with all of that
considered did opt to hold off for now.
Also continuing to monitor thunderstorm potential for Monday
afternoon. The first focus will be along the wind shift boundary
that looks to be draped from roughly the Cheyenne Wells to
McCook area. Strong capping will be in place with 700mb around
17C which does lead me to believe that if anything were to
develop it would be isolated in nature. A concern I do have is
for landspout potential due to very strong surface vorticity and
very high lapse rates in place. Winds will also be around 10-20
knots converging on this boundary. Convective temperatures are
in the upper 90s to low 100s as well so do think that updraft
attempts will occur. There also may be some additional
streamwise vorticity in place to help stretching according to
hodographs during the 22Z-01Z time frame along the CO/KS line
south of I-70. My higher confidence in rainfall comes from the
west from convection off of the Front Range during the afternoon
and evening hours. At this time severe weather potential looks
low with perhaps wind being the primary hazard but have concerns
about outflow getting to far out of it for severe winds to
occur. RAP does indicate a potential MCV developing by looking
at 700mb vorticity levels which would support additional
redevelopment of showers and storms through the night Monday and
into the morning hours Tuesday. This does look a little
conditional as it will depend on the placement of the MCV but
the RAP and NAM both do support moisture in the 700-500 mb
levels so have added in silent pops for now.
A cold front pushes through the area Monday night into Tuesday as
well which will bring Tuesday morning temperatures into the upper
50s to low 60s for lows across the area.This front will help bring
highs down to normal to slightly below normal for Tuesday in the mid
80s to low 90s. High pressure then quickly redevelops across the
area as western locales will be the warmest. Another wave moves off
of the Front Range bringing another slight chance of showers and
storms across NW portions of the area.
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
Issued at 200 PM MDT Sun Aug 4 2024
The long term period continues to be forecast to see higher
precipitation chances and near to potentially below average
temperatures.
The upper pattern is forecast to start with an upper ridge over the
Southwestern CONUS while an upper low/trough begin moving into
Southern Canada. With this, Wednesday remains the only day of the
period currently forecast to have well above average temperatures in
the upper 90`s and 100`s. Will need to watch for potential heat
issues, but the current forecast timing of the front should keep
temperatures just low enough to keep heat index values around 100.
Once the front passes, storm chances are forecast for the remainder
of the period as moisture advects into the area. The area is
forecast to go under northwest flow which will allow for storm
chances every day from off the higher terrain in Colorado. Severe
weather could possibly occur on any of these days, but may be more
likely with the frontal passage Wednesday. Ensemble guidance
generally favors rain totals remaining below an inch each day with
only a few suggestions of stronger storms producing heavier rain.
Even if storms do produce 2-3" in a day, flooding concerns will
remain low given how dry it has been lately.
As for temperatures, this is the trickiest part of the forecast.
Ensemble guidance continues to show the upper trough/low delaying
now more into Friday. However, even the trough/low moving into
Canada is forecast to deamplify the upper ridge and the surface
front is forecast to bring some cooler air in. The main batch of
cooler air may not move through more until Friday if the slower
solutions are indeed what occurs. For most of the period, highs are
forecast to be in the 80`s with lows in the upper 50`s. Friday may
be the coolest day with highs currently forecast in the 70`s and low
80`s. If enough low level moisture lingers, northeastern portions of
the area may be under fog/cloud cover through most of the day and
stay in the 60`s. There is still about a 30% chance that the
trough/low moves too quickly and/or too far east to where the storm
chances lower a bit and high temperatures warm more into the 90`s.
The weekend is also a bit more likely to see temperatures try and
warm back into the 90`s as the current forecast favors the upper
ridge reamplifying over the Rockies.
&&
.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 945 PM MDT Sun Aug 4 2024
KGLD...VFR conditions are expected through the period. Southerly
winds, occasionally gusting up to 25kts are anticipated from taf
issuance through 11z. After 12z, winds steadily veer to the
southwest, west, northwest, north and northeast at speeds up to
10kts or so. Thunderstorms may impact the terminal but given
spacial issues and overall coverage being rather low, will not
include a mention at this time. Window of opportunity for this
to occur is roughly from 23z-03z. Primary hazard is gusty
outflow winds followed by sub VFR conditions due to locally
heavy rainfall given very slow storm motions and high
precipitable water.
KMCK...VFR conditions are expected through the period. Southerly
winds around 11kts are expected through 14z. After 15z, winds
steadily veer to the southwest, west, northwest and north at
speeds up to 11kts. Presently, convection or precipitation is
not expected.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...None.
CO...None.
NE...None.
&&
$$
SHORT TERM...Trigg
LONG TERM...KAK
AVIATION...99
Area Forecast Discussion
National Weather Service Gray ME
1037 PM EDT Sun Aug 4 2024
.SYNOPSIS...
Showers and thunderstorms will diminish this evening. A cold
front will cross the region on Monday, bringing chances for
showers and thunderstorms, some of which could produce locally
heavy rainfall, damaging winds and large hail. A weak area of
low pressure will track off the southern New England coastline
on Tuesday and Wednesday, bringing scattered showers to southern
Maine and New Hampshire while high pressure allows for dry
conditions for northern areas. Another frontal system will bring
scattered showers to the region late in the week as tropical
activity remains across the Southeastern US.
&&
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
1030 PM...Mainly adjusted POPs to cover the last line of showers
moving E across the CWA and weakening as it does so, with only
the far N zones seeing another round of showers thru about 06Z.
Otherwise the main issue will be fog, because it rain across
much of the area at some point, and very heavy in some spots.
Therefore given even slightly lower Tds (~2F) tonight, and calm
conds with clearing skies, squeezing out some moisture will be
easy. Otherwise lows will range from the low 60s in the mtns to
the upper 60s in the S.
755 PM...Updated the POPs to better time the convection this
evening, and overnight, although most of the CWA should be done
by midnight, with the exception the N zones along the
international border which could see occasional shower moving
through in the pre-dawn hours, but should see a break by
daylight. Otherwise overnight temps not changed much.
Previously...Showers and thunderstorms will move off the
Seacoast region this evening while another set of showers and
storms diminishes after sunset in the mountains. A few of these
thunderstorms may produce locally heavy rainfall and flooding as
they remain in a very moisture rich environment as well as
strong gusty winds.
Overnight lows will drop into the 60s in all areas. Locations
that did record heavy rainfall today may be more prone to the
development of fog than other locations.
&&
.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
An upper level trough and its associated surface cold front will
move across the region on Monday from northwest to southeast.
Ahead of this system, ample moisture will remain in place,
albeit, slightly lower PWATs and surface dew points across the
region. Nevertheless, increased dynamics with the front and the
upper trough will allow for destabilization of the atmosphere
with thunderstorm containing locally very heavy rainfall once
again. SPC continues to have a threat for damaging winds and
hail as well through the afternoon and into the early evening
hours.
It will be quite warm and humid Monday. Apparent temperatures
will approach Heat Advisory criteria, but may come up just
short. Expect air temperatures to top 90 degrees over portions
of interior York County and southern New Hampshire.
The latest NamNest and HRRR solutions keep the showers and
storms into the evening hours before the precipitation exits the
coastline. More patchy fog will develop, however dew points
will become noticeably lower during the night.
&&
.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...
Tuesday and Wednesday...one thing to watch will be frontal wave
moving to our south. It may affect southern NH with additional
rainfall Tue and Tue night, with a fairly tight S-N gradient
possible. It could also remain dry with the precip just south of
the MA border. Chance PoPs for now. Either way we will be in a
post frontal air mass which will be cooler and drier (dewpoint-
wise). Drier weather for Wednesday into Thursday but a return to
more unsettled weather possible late week and weekend.
&&
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Short Term...Localized IFR and LIFR conditions in early evening
storms followed by patchy fog development. VFR Monday morning
before more showers and storms form from northwest to southeast.
LIFR conditions possible in any precipitation which will end
during the evening hours Monday.
Long Term...
Showers and storms could linger into Monday evening
and Monday night, but conditions will be variable on Tuesday
with showers possibly developing along the exiting cold frontal
boundary (mainly for southern terminals) through Tue night.
Drier air follows Wed before more showers enter the region late
in the week.
&&
.MARINE...
Short Term...Southwesterly winds will veer to the west and
northwest by Monday night. Winds and seas will remain below SCA
thresholds.
Long Term...No issued noted as far as winds and seas go Tue-Fri.
&&
.HYDROLOGY...
Convection on Monday afternoon and evening will be focused along
and ahead of a surface cold front. Locally heavy rainfall can be
expected once again with a flash flood threat still possible.
Portions of the mountains, southern New Hampshire and far
southwestern Maine may have an elevated threat from the already
soaked grounds, creeks and small rivers from the weekend
rainfall.
&&
.GYX WATCHES/WARNINGS/ADVISORIES...
ME...None.
NH...None.
MARINE...None.
&&
$$
SYNOPSIS...
NEAR TERM...Cannon/Cempa
SHORT TERM...Cannon
LONG TERM...Ekster
AVIATION...
MARINE...
HYDROLOGY...
Area Forecast Discussion
National Weather Service Phoenix AZ
410 PM MST Sun Aug 4 2024
.UPDATE...
Updated Aviation
&&
.SYNOPSIS...
Excessive heat conditions will persist through Monday for the lower
deserts with forecast highs around 115 degrees across the typically
hotter locales, and overnight lows from the middle 80s to lower 90s.
Daily thunderstorms chances will exist through the next 7 days
primarily focused over the Arizona high terrain. A westward moving
disturbance is expected to approach the region early this week
bringing better potential for more robust and greater coverage of
storms during the middle of the week, particularly on Tuesday.
Temperatures should be closer to seasonal normals during the middle
of the week before heating back up into the weekend.
&&
.DISCUSSION...
Excessive heat conditions continue across the lower deserts. Phoenix
Sky Harbor Airport even reported a temperature of 100F before 8 AM
MST this morning, so with a record daily high set yesterday and
morning lows in the upper 80s to low 90s across the region, there
has been very little relief from the heat so far this weekend.
Forecast highs today and tomorrow will again range between 110-116
degrees for the typically hotter lower desert locations. Given all
these factors, an Excessive Heat Warning will continue to be in
effect through Monday at 8 PM MST. There is however a potential to
see some storms in the South-Central AZ lower deserts this evening,
and with this, some locations could receive welcome respite from the
heat or at least a more rapid cooldown with any scattered pockets of
showers/storms.
Mid-level water vapor imagery this morning revealed a filament of
drier air aloft moving over southwestern AZ, with a broad swath of
more abundant moisture in place across the eastern half of the state
and rotating around the Four Corners subtropical high. RAP analysis
also shows a local maximum in PWAT and surface mixing ratio values
at this hour (~1.5" and 9-10 g/kg, respectively) centered over South-
Central AZ, with moisture dropping off rather quickly towards the
western deserts. Greater coverage of storms to the south/southwest
of the Phoenix area yesterday likely helped to heighten boundary
layer moisture locally, and so RAP analysis and CAMs have begun to
pick up on this. Storms have already fired up along the high terrain
of Northern/Central AZ and Southeastern AZ. Development of new
storms will trend westward as the afternoon goes on, and with up to
1500 J/kg DCAPE in forecast soundings over the foothills and values
increasing to the west, strong, long-lived outflows out of the east
and southeast look likely for the lower deserts of South-Central AZ
this evening. New convection could initiate along a strong
east/southeast outflow over the lower deserts as indicated by
several 12Z HREF members. This is not an unreasonable solution, as
there will be little CIN early in the evening, and HREF mean MUCAPE
values around 750 J/kg will be in place. The main hazards for any
storms that form today will be strong, gusty outflow winds, patchy
blowing dust, and brief heavy downpours.
Starting tomorrow, the monsoon pattern is expected to shift as the
Four Corners subtropical high begins to orient itself east-west and
an inverted trough approaches the region along the southern edge of
the high. Easterly flow aloft will increase over the course of the
day tomorrow along/ahead of the inverted trough, with ensemble mean
500 mb wind speeds increasing upwards of 20-25 kt by the evening
over the southeastern portion of AZ. Easterly flow should remain
enhanced through Tuesday over southern AZ, with 500 mb wind speeds
in the 90th percentile of NAEFS climatology. This stronger east flow
aloft could allow slightly better chances for storms to survive off
the high terrain into the lower deserts tomorrow through the middle
of the week, and linear storm modes/weak organization could be
favored at times. As the inverted trough nears our region, moisture
and convection are expected to pick up across northern Mexico
setting the stage for a considerable increase in moisture into the
boundary layer across Southwest and South-Central Arizona Monday
night into Tuesday. Forecast PWATs are shown to increase to around
1.6" from Phoenix through Yuma with modest 1-1.2" PWATs stretching
into the higher terrain east of Phoenix. This increase in moisture
should boost MUCAPE to between 1000-1500 or higher J/kg Tuesday
afternoon over much of the area, while the inverted trough moves
into far southern Arizona and Sonora Mexico. Given the potential
strong instability and increased flow aloft, we could be in for a
round of strong to potentially severe thunderstorms impacting
portions of the south-central Arizona lower deserts late Tuesday
afternoon and evening.
The inverted trough is likely to stick around through at least
Wednesday, maybe even Thursday providing chances for showers and
thunderstorms across the lower deserts of Arizona to as far west as
southeast California. Beyond Wednesday, forecast uncertainty
increases as it will depend on how long the inverted trough sticks
around and how much moisture remains in place. NBM guidance does
suggest best chances for rain are likely to shift back higher
terrain areas by around Thursday as some drier air may push back
into the western deserts, but given the uncertainty this decrease in
monsoon activity may not pan out as the NBM PoPs suggest.
Temperatures are also expected to increase again later this week
into next weekend, with widespread Moderate HeatRisk and areas of
Major HeatRisk indicated on Saturday.
&&
.AVIATION...Updated at 2310Z.
South Central Arizona including KPHX, KIWA, KSDL, and KDVT:
The primary weather issue will be an outflow boundary with an abrupt
E/NE wind shift this evening followed by the potential for
isolated/scattered SHRA/TSRA across eastern gates and subsequent
multiple wind shifts, erratic directions, and locally enhanced
gusts. While a subtle wind shift to a NW direction is possible
during the early evening (likely not affecting operations),
confidence is good that a long traveling outflow from the NE will
sweep through the Phoenix airspace during the 02-04Z time frame.
Gusts in a 20-30kt range seem reasonable. Lower confidence exists
regarding the redevelopment of any TSRA along/behind this boundary
off higher terrain with somewhat more likely chances at KIWA/KSDL.
Models suggest some storms forming well to the S/SE of the
terminals in which case another outflow may be possible mid/late
evening.
Confidence in specific timing and directions of subsequent wind
shifts after the initial NE switch is low, though model evidence
eventually shows and predominant easterly wind developing shortly
after midnight. Similar to today, the switch back to a W/SW
component should occur around or just after noon Monday with far
less outflow/storm influences likely into the afternoon and evening.
Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather concerns will exist through Monday afternoon under
mostly clear skies. Wind will generally follow a S/SE component
during afternoon hours with a tendency to veer W/SW during the
evening and overnight. Variability in wind direction may be common
around and after sunrise
&&
.FIRE WEATHER...
Scattered thunderstorms will mainly be possible across the AZ high
terrain through Monday before chances increase areawide on Tuesday.
Although thunderstorm chances remain low in most lower desert
locations today and Monday, there will still be the risk for strong
outflow boundaries which could result in a sudden wind shift and
gusty winds at active burn areas. Aside from thunderstorm outflows,
winds will should remain light and diurnal with afternoon gusts into
the teens. Minimum RH values will mostly reside in the 10-20% range
through Monday with overnight recovery to 30-50% most areas.
Temperatures through Monday will be several degrees above normal,
with lower desert highs reaching the 110-116F range. Temperatures
will cool down closer to normal by Tuesday with the arrival of
better moisture and cloud cover.
&&
.CLIMATE...
Phoenix Daily Record Temperatures
High Warm Low
---------- ----------
8/4 116 (1975) 91 (2018)
8/5 116 (2023) 95 (2009)
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Monday for AZZ530>555-559-
560.
CA...Excessive Heat Warning until 8 PM PDT Monday for CAZ560>570.
&&
$$
DISCUSSION...Whittock
AVIATION...18
FIRE WEATHER...Kuhlman
CLIMATE...Benedict
Area Forecast Discussion
National Weather Service Reno NV
117 PM PDT Sun Aug 4 2024
.SYNOPSIS...
* A few isolated showers and storms are possible later this
afternoon and evening, then mainly dry conditions prevail for
this week.
* Above average temperatures continue through the work week, with
a moderate HeatRisk seen in most lower elevations.
* Temperatures look to start a slight cooling trend going through
next weekend.
&&
.DISCUSSION...
* Today, forecast models show a shortwave trough traveling through
the flow over the CWA which is on the western side of an upper
air ridge controlled by a Four Corners upper air high. As a
result of this upper air patten along with residual moisture in
the area, the latest run of the HRRR shows some chances (15-30%)
for possible isolated showers and thunderstorms during the late
afternoon and evening hours for areas generally south of US-50
with some clouds already starting to develop on current
satellite imagery. Severe weather is not anticipated at this
time, but lightning strikes and some gusty outflow winds could
be possible with storms. These precipitation chances today look
to be the best chances for moisture for this entire week at this
time as models show the CWA staying underneath a broadening
upper air ridge through the week. Cannot completely rule out
some late afternoon isolated showers through the week due to
diurnal heating, but chances currently look low.
* As forecast models project an upper air ridge to reside over the
CWA through the week, the temperatures across the region look to
be around 3-6 degrees above normal with highs in the upper 90s
to near the 100 degree mark for lower elevations and the middle
to upper 80s for Sierra communities. The latest HeatRisk
assessment shows the CWA within the Minor to Moderate category
through the work week as a result with some localized areas of
High HeatRisk in western NV on Tuesday. While the region expects
the typical afternoon breezes through the week, there may be an
hour or two of fire weather concerns during Monday afternoon for
Lassen and northern Washoe counties with low relative humidity
values in the forecast. As for smoke/haze from the CA
wildfires, the latest HRRR model has backed off on coverage over
the region as air quality has improved a bit according to the
latest readings from the region`s sensors.
* Forecast guidance shows an upper air trough moving into the
Pacific Northwest beginning late Friday pushing the ridge
eastward a bit which may signal daytime temperatures to start to
cool slightly going through next weekend. Daytime highs by next
Sunday currently look to be in the upper 80s to middle 90s range
in the valleys while the Sierra Mountain areas are forecast to
be in the middle 70s to upper 80s range. -078
&&
.AVIATION...
VFR conditions are expected for the REV terminals today going into
tomorrow with some breezes between 21-03Z generally out of the west
(the exception being KTVL with south-southwest afternoon winds).
While mostly dry conditions are expected for the region today,
there is a chance (15-30%) for an isolated shower or two in areas
south of US-50 during the late afternoon and evening hours today.
Haze from the Park Fire may produce minor reductions in slantwise
visibility especially for areas north of I-80 though the latest
HRRR model has back off on smoke/haze in the region following
yesterday`s precipitation. -078
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
Area Forecast Discussion
National Weather Service Tucson AZ
113 PM MST Sun Aug 4 2024
.SYNOPSIS...Chances for thunderstorms and scattered showers will
continue through this week, with potential for heavy rainfall and
strong wind gusts. Hot temperatures continue into Monday, before
cooling by a few degrees by early next week.
&&
.DISCUSSION...Another hot afternoon across southeast Arizona with
highs well into the triple digits across the lower elevations from
Tucson westward. Adequate moisture remains in place for convection
per latest GOES Total PWAT with around 1 inch PWAT eastern areas to
around 1.5 inches for the western deserts. Latest SPC RAP
mesoanalysis shows 1000-1500 J/KG from Tucson westward and a bit
less eastern areas. We`re already seeing scattered showers and
thunderstorms developing as of now primarily across the higher
terrain south and east of Tucson. Mid level steering flow is fairly
slow at around 5 to 10 kts from the east to northeast so these
storms will be more dependent on westward moving outflows rather
than cell movement to generate additional thunderstorm activity into
the lower elevations from Tucson westward. With that said, expect a
continuation of scattered showers and thunderstorms with gusty winds
and locally heavy rainfall the main threats.
Over the next couple of days the pattern will start to transition as
an inverted trough, now over west Texas approaches from the east.
Monday is still looking fairly similar to today as the inverted
trough will be far enough away to not really influence our weather
just yet. With that said, still expect another round of mainly
afternoon and evening showers and thunderstorms Monday. Hot
temperatures continue Monday, though perhaps a degree or two cooler
than today. The inverted trough will then move into adjacent
northern Sonora Tuesday and the additional lift ahead of this system
should result in a nice uptick in convection Tuesday afternoon into
evening. Strong gusty winds and heavy rainfall with areas of flash
flooding are a concern with the storms Tuesday and the WPC has
outlined much of southeast Arizona ins a slight risk area for
excessive rainfall.
While we remain in a fairly typical monsoon regime Wednesday and
beyond into next weekend, there is a considerable uncertainty in the
day to day specifics including the more active days. Near normal
temperatures Wednesday and Thursday will transition to temperatures
4 to 7 degrees above normal next weekend.
&&
.AVIATION...Valid through 06/00z.
SCTD -SHRA/-TSRA thru 05/04z then diminishing overnight. Another
round of SCTD -SHRA/-TSRA aft 05/18Z. MVFR conds and local gusts to
50 kts near thunderstorms. Outside of thunderstorms expect wind
speeds less than 12 kts and following typical diurnal trends.
Aviation discussion not updated for TAF amendments.
&&
.FIRE WEATHER...Scattered showers and thunderstorms continue each
day through the forecast period. Some drier air today and Monday
will keep min RHs in the upper teens to lower twenties in the lower
locations and thirties in the higher elevations. Min RHs will trend
upward thereafter during the midweek period due to thunderstorm
influences. Outside of thunderstorm winds, 20-foot winds will
generally be 15 mph or less, with afternoon/early evening gusts to
20-25 mph and light winds overnight.
&&
.TWC WATCHES/WARNINGS/ADVISORIES...None.
&&
$$
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