Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/01/23
Area Forecast Discussion
National Weather Service Caribou ME
914 PM EDT Thu Aug 31 2023
.SYNOPSIS...
High pressure builds across the area today and remains over the
area into the middle of next week.
&&
.NEAR TERM /THROUGH FRIDAY/...
9:12 PM Update...A band of clouds has crossed the north and the
sky is now mostly clear. Adjusted sky cover to show this and
adjusted temps down just a bit in the NW where the clear dry air
is allowing the air to cool quickly.
Clouds are already beginning to diminish especially over southern
areas. Winds are still gusting from the northwest but with high
building east and diurnal mixing diminishing around 22z they should
begin to lighten and remain light through the overnight. Deeper
valleys over the northwest should be able to decouple late tonight
and will allow temps to dip toward 30 degrees, which will result in
mins dropping toward the 30-degree mark. Frost formation appears
likely but does not appear to be widespread enough to warrant a
Frost Advisory but will mention in the HWO and highlight in social
media. In addition to the frost there will be patchy river valley
fog so how much of an impact this has on frost formation remains up
in the way.
Skies will be clear in the morning but latest HRRR and RAP smoke
models giving us a layer of smoke aloft. Have updated the sky grids
to account for this with a thin cloud layer over the CWA late
morning into the afternoon. This may have some impact on temps but
have gone with NBM given uncertainty of how much sky cover will be
present.
&&
.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
Upper level and surface high pressure will be over the area
Friday night through early Saturday, then the high pressure
shifts east as a weak shortwave upper trough approaches in NW
flow Saturday/Saturday night and is over the area Sunday. This
upper trough will be quite weak and the airmass will be quite
warm over the area through the weekend with highs in the
vicinity of 80. Still somewhat cool Friday night with mid 40s to
mid 50s, but milder Saturday night with around 60 thanks to
increasing southerly flow ahead of the approaching upper trough.
Dewpoints will rising through the weekend, with mid to upper 50s
Saturday and low to mid 60s Sunday. Dry until potentially
Saturday night and Sunday, when there is a slight chance of
showers with the upper trough. Upper trough won`t have much deep
moisture to work with though, thus the low 20 percent PoPs.
&&
.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
Looking very warm to potentially even hot Monday to Wednesday
with upper ridging centered a bit west of us and generally weak
surface high pressure over our area. Best guess is for highs in
the mid to upper 80s, but can`t rule out some spots getting to
90. Cooler immediate coast as is often the case in the warm
season. Fairly high confidence in the very warm temperatures.
Little to no rain chances through Wednesday thanks to subsidence
with the upper ridging. Surface dewpoints will be fairly high
with mid to upper 60s during the day. Can`t rule out some areas
getting close to heat advisory criteria.
Weather pattern begins to become more unsettled toward Thursday
and Friday, although confidence decreases significantly. Some
models/ensembles have an upper trough approaching from the west,
while others actually have what`s left of Idalia moving NW to
near or in the Gulf of Maine.
&&
.AVIATION /01Z FRIDAY THROUGH TUESDAY/...
NEAR TERM: VFR next 24 hours. Gusty northwest winds diminish by
00z this evening. Cannot rule out IFR patchy fog at PQI and HUL
late tonight but confidence is too low.
SHORT TERM: VFR, though can`t rule out late night and early
morning fog BGR/BHB and the Downeast coast Saturday night
onward. Generally S/SW winds 5-15 kts.
&&
.MARINE...
NEAR TERM: Extended SCA for the outer waters through 12z Fri and
have dropped the intracoastal zone. Seas will remain above 5ft
over the outer waters late tonight before dropping below small
craft levels on Friday.
SHORT TERM: Winds and seas remain below advisory levels through
next week, though SW winds and seas could approach advisory
levels Saturday night. Patchy marine fog is possible from
Saturday night on, but not expecting it to be that widespread.
&&
.TIDES/COASTAL FLOODING...
Long period swells associated with Hurricane Franklin are
gradually diminishing this afternoon but may impact the Maine
coast into this evening.
&&
.CAR WATCHES/WARNINGS/ADVISORIES...
ME...None.
MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ050-051.
&&
$$
Near Term...Buster/Bloomer
Short Term...Foisy
Long Term...Foisy
Aviation...Buster/Foisy
Marine...Buster/Foisy
Tides/Coastal Flooding...
Area Forecast Discussion
National Weather Service Glasgow MT
308 PM MDT Thu Aug 31 2023
.DISCUSSION...
AFTERNOON UPDATE:
Smoke and haze is starting to filter in from Alberta/Saskatchewan
with slight reductions in visibility (<10 mi) already being
observed along the hi-line. Based on the latest run of the RAP
near- surface smoke, this smoke is expected to filter further
south as the day progresses, covering most of northeastern
Montana by midnight tonight. The worst of the smoke is expected
tomorrow morning in the 6 AM to 12 PM timeframe. Reductions to air
quality as low as unhealthy levels, as well as reductions in
visibility down to 4 miles are possible during this time.
Otherwise, the Lake Wind Advisory is still going strong. Winds may
not quite last until 9 PM but the decision to cut it off will be
made by the next shift as conditions change.
The main change to the long-term forecast with this update were
the QPF totals for the upcoming low pressure moving through Sunday
through Tuesday. QPF north of the Missouri River backed off a bit
while areas in south central Montana saw a decent increase.
There`s still a bit of model disagreement on this but, for now,
it seems generally likely that the highest chance of wetting rains
will be south of the Missouri River.
-thor
MORNING DISCUSSION:
Synoptic Setup: Forecast begins with hot high pressure situated
over the Desert Southwest and a ridge jutting northeast through
the Great Plains and Upper Mississippi Valley. A large
disturbance that dragged the front through yesterday has allowed
its surface low to dwell over southern Saskatchewan letting some
lingering moisture enter northeast Montana. Farther west a trough
over the coast of the Pacific Northwest is beginning to retrograde
and drop southwest off the coast of California.
Today into tonight: Strong west winds behind the front are
expected along with possible lingering showers across the northern
zones as the low exits to the east early today.
RAP Model is hinting toward a resurgence of haze across the area
Friday morning though the strength/intensity of particle
concentration does appear to be less than the last 2 events and does
not appear to be much more impactful than haze and limited health
concerns in comparison. Timing for the worst of it looks to be
around 3AM to Noon across northern zones.
Friday through Saturday night: Heat from the Desert Southwest will
move itself over the Great Plains and backbuild a ridge northwest
over central Montana and the CWA. This will stabilize and cap the
atmosphere for dry warmer weather (widespread 90s for highs) into
the early weekend. Meanwhile a new trough off he coast of British
Columbia will use its momentum to barrel into the back built
ridge and form a cold front over central Alberta as it links up
with the more southern trough over the California coast.
Sunday to Monday night: The cold front is expected to drop down
the high Plains of Alberta hitting northeast Montana roughly
Sunday afternoon to Sunday evening. If sufficient pacific or
monsoonal moisture can gather ahead of the front from the new
southwest flow aloft there is a high chance for thunderstorms with
a slight chance for severe weather due to mainly gusty winds.
However, frontal timing will have to remain in sync with afternoon
heating to remain severe. After the thunder exits Sunday night,
general shower chances with possible wetting rains should survive
through Monday night
Tuesday onward: Cool high pressure at the surface and a warming
profile with height should generate stable, dry, and partly cloudy
conditions through early next week. This warming will be followed
with a shortwave ridge axis crossing the area Wednesday and maybe
a shortwave trough right behind on Thursday. Though those last two
days are currently low confidence being 7 to 8 days out. GAH
&&
.AVIATION...
UPDATED: 2100Z
FLIGHT CAT: MVFR-VFR
DISCUSSION: Smoke and haze is starting to move into the area this
afternoon and linger through the day on Friday. Haze has already
started reducing visibility at KGGW and is expected to continue
with haze reaching KOLF by 00Z, KSDY and KGDV by 06Z.
WINDS: West to southwest at 15 to 25 kts, gusting to 30 kts this
afternoon. Calming to less than 10 kts overnight.
-thor
&&
.GLASGOW WATCHES/WARNINGS/ADVISORIES...
Lake Wind Advisory until 9 PM MDT this evening For Fort Peck
Lake for Central and Southeast Phillips...Central and Southern
Valley...Garfield...McCone...Petroleum.
&&
$$
weather.gov/glasgow
Area Forecast Discussion
National Weather Service Goodland KS
521 PM MDT Thu Aug 31 2023
.SHORT TERM...(This evening through Saturday Night)
Issued at 303 PM MDT Thu Aug 31 2023
At the beginning of the short term period, the latest RAP analysis
shows the CWA being underneath an upper air ridge with an upper air
high over NM along with upper air lows over LA and southern SK
during the Thursday afternoon hours. Current surface observations
and satellite imagery report dry conditions underneath sunny skies
with southerly winds gusting up to around 20 kts in the eastern half
of the CWA while the western portions see lighter winds with a
surface trough in eastern CO. Models show this upper air pattern
pretty much continuing through the rest of the day with the ridge
staying over the CWA. At the surface, models show the CWA having a
mostly southerly flow through the rest of the day being on the
eastern side of a surface trough in CO. Model forecast soundings
are showing some possible wind gusts up to around 25 kts mixing
down overnight in some portions of the CWA. Minimum RH values
look to stay above critical fire weather criteria for the rest of
today, but these gusty winds could cause a dangerous situation
within the region should a wildfire occur. Upon looking at blowing
dust parameters, widespread blowing dust is not anticipated with
unsupportive lapse rates but localized blowing dust may be
possible. Also, the latest HRRR model run of the vertically
integrated smoke product looks to show some patchy smoke in the
eastern half of the CWA during the afternoon that looks to clear
out by the evening hours. Slightly reduced visibilities are
possible as well as some unhealthy air quality in those areas
during the remainder of the afternoon. For the Thursday night
temperature forecast, overnight lows expect to be in the lower to
middle 60s.
On Friday, forecast guidance depicts the CWA remaining underneath
the upper air ridge during the day though the ridge starts to move
slightly eastward due to an upper air low moving over the coast of
northern CA and the upper air low over LA moving into eastern TX by
the evening hours. At the surface, another surface trough is
expected throughout the day in CO making southerly wind gusting
up to around 25 kts during the afternoon and evening hours
possible. Models also show up gusts up to around 30 kts mixing
down overnight as well. There does not look to be a widespread
blowing dust concern throughout Friday based on blowing dust
parameters, but cannot rule out some localized blowing dust once
again. The main concern for Friday though is the near critical to
critical fire weather conditions expected during the afternoon
and into the evening hours. The Fire Weather Watch has been
upgraded to a Red Flag Warning for counties along the CO border
as the forecast calls for the criteria being met. Portions of
adjacent counties to the east look to possibly reach criteria as
well, but it does not look to be widespread enough to merit a Red
Flag Warning at this time. Continued to trend dewpoint
temperatures towards the NBM 25th percentile as it appears to be
lining up best with what dewpoint temperatures have been reaching
as of late. Will continue to monitor conditions going forward in
case an expansion is needed. For the temperature forecast, near
record highs are possible as Friday`s daytime highs look to range
between middle 90s and lower 100s followed by overnight lows in
the lower to upper 60s range.
For Saturday, models do not show too much change in the upper air
pattern as the CA and TX upper air lows do not move too much
though the CWA looks to be more underneath the rear of the upper
air ridge over the Central Plains. At the surface, models show a
slight change with a surface trough setting up more over the CO
border during the day. The CWA continues to expect a southerly
surface flow though models have gusts during the day to be
slightly slower compared to previous days due to the trough
placement. Minimum RH values look to be in the lower to middle
teens supporting possible near critical fire weather concerns
across the region though the wind criteria for critical fire
weather does not look to be met at this time. Winds do look to
pick up a bit overnight gusting up to around 25 kts in some
locations. With the lack of moisture seen in the environment on
Saturday, no precipitation is anticipated currently continuing the
dry spell for another day. Daytime highs look similar to those on
Friday being near record highs ranging between the middle 90s and
lower 100s. Overnight lows expect to be similar to Friday night`s
lows as well being between the lower and upper 60s. Forecasted
maximum heat indices look to be in sub-100 degrees as well which
is similar to what is expected on Friday afternoon.
.LONG TERM...(Sunday through Thursday)
Issued at 1240 PM MDT Thu Aug 31 2023
Persistent warm and dry conditions will last through the weekend,
leading to potentially critical fire weather conditions. Cooler
temperatures and precipitation next week are possible.
Sunday, and potentially Monday, could see near-critical to critical
fire weather conditions as we remain under a ridge. With maximum
temperatures reaching near triple digits east of highway 27, RH
values are expected to be near 13% or lower on Sunday. Winds are
still the questionable category to support critical fire weather
conditions. Southerly winds at 15-20 kts on Saturday and Sunday,
with gusts up to 25 kts on Sunday, are forecast. Confidence for
multiple counties meeting critical fire weather conditions is
increasing, with winds being the limiting factor.
There is an upper and mid level low pressure system that moves over
eastern Kansas Sunday evening through Monday evening. This could do
a couple of things depending on its track and intensity. Option 1,
it could increase mid level moisture, which would lower temperatures
and increase PoPs. Option 2, it could lower the mid level moisture
and reduce PoPs while keeping temperatures nearly the same. Based on
current NMB and GEFS guidance, both options are equally possible.
Monday morning the ridge will slowly be pushed east by a trough
coming in from the west. The placement and speed of the 250 mb
trough around 12Z Tuesday is another wild card for the period. The
current runs of the GFS, ECMWF, and CMC-NH are aligning and show a
FROPA around 6Z Tuesday. Since the models are differing less than
previous days, confidence in timing and other impacts has increased.
The associated surface FROPA is looking likely to occur in the later
evening and overnight hours Monday. This could allow some moisture
to potentially move in with the LLJ and give us a chance of
precipitation. However, as mentioned in the previous paragraph, the
mid level low pressure system could cutoff the supply of moisture.
Confidence for precipitation is low but slightly increasing as PoPs
are only 15-40 across the area after 0Z Tuesday. The highest PoPs
are in northern Yuma County with values lowering to the southeast.
Tuesday onward will see a weak ridge attempt to build back into the
region, but it will be fighting against a trough in Canada.
Depending on the strength of the two features, the Tri-State area
could be under the weak ridge, have zonal flow, or have
northwesterly flow. At this point, any of these three options are
possible and will impact temperatures the most. There is a slight
chance of some showers Wednesday and Thursday evening, once again,
dependent on the ridge`s behavior.
Sunday, high temperatures will be in the mid 90s to lower 100s.
Monday will slightly cool down with highs staying under 99F in the
CWA. After the cold front, Tuesday`s highs will be cooler with
high`s in the mid 80s and 90s. Wednesday, depending on the
aforementioned ridge, could start a warming trend through the
period. The current forecast calls for most locations reaching the
lower and mid 90s. Overnight temperatures will follow a similar
trend, but to a lesser extent. Temperatures are expected to remain
in the 60s to low 70s with the potential of northwestern CWA cooling
into the upper 50s Tuesday and Wednesday morning.
&&
.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 519 PM MDT Thu Aug 31 2023
VFR expected to prevail at both KGLD and KMCK through the TAF
period. Nocturnal low level jet will develop later tonight and
through the overnight, with southwesterly winds between 1-2kft AGL
of 40-50kts.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Red Flag Warning from noon MDT /1 PM CDT/ to 8 PM MDT /9 PM CDT/
Friday for KSZ001-013-027-041.
CO...Red Flag Warning from noon to 8 PM MDT Friday for COZ252>254.
NE...Red Flag Warning from noon to 8 PM MDT Friday for NEZ079.
&&
$$
SHORT TERM...076
LONG TERM...CA
AVIATION...024
Area Forecast Discussion
National Weather Service Memphis TN
942 PM CDT Thu Aug 31 2023
...New UPDATE...
.UPDATE...
Issued at 937 PM CDT Thu Aug 31 2023
Mild and dry conditions with low relative humidity will continue
for another few days across most of the Midsouth. A few showers
and thunderstorms may creep into north Mississippi tomorrow
afternoon and over the weekend as moisture levels trend slightly
higher. High temperatures should remain below 90 degrees across
most of the Midsouth into early next week.
30/Sirmon
&&
.SYNOPSIS...
Issued at 300 PM CDT Thu Aug 31 2023
Precipitation chances return to the forecast due to a low
pressure system that will meander over the Lower Mississippi Valley
through the weekend. Shower and thunder chances will be mainly
confined to north Mississippi through Sunday. Temperatures will warm
slightly each day prior to reaching the low to mid 90s mid week
ahead of another cold front.
&&
.DISCUSSION...
(This evening through next Wednesday)
Issued at 300 PM CDT Thu Aug 31 2023
Subsidence from Tropical Storm Idalia and a cold frontal
passage granted a sunny, dry, and below normal temperature day to
the Mid-South. Dry air, clear skies, and light winds are expected to
continue overnight causing overnight lows to dip into the 50s and
lower 60s.
Tomorrow, an upper level low pressure system is expected to form
over the ArkLaMiss region and remain in this location through the
weekend. To the northwest, high pressure will build in and make its
track east across the Mid-South. As the low pressure system
meanders, moisture returns to the region bringing showers and
thunderstorm chances back to the forecast. The GFS and ECMWF have
widespread coverage for tomorrow afternoon and evening, while the
HRRR has very isolated coverage and is confined to the evening
hours. The HRRR coverage also looks to be confined to a shortwave
trough that will stretch across the region tomorrow. Due to the
subsidence and location of the trough and low pressure system,
small PoPs were carried tomorrow mainly across north Mississippi
and the Tennessee River Valley. QPF values are generally
negligible, 0.10" or below, so the HRRR was more closely followed.
The battle of the two systems will be brought to a halt as a trough
will move across the CONUS with enough forcing to embed the upper
level low on its track eastward, and exit the region by Tuesday.
High pressure is anticipated to settle in Wednesday resulting in
temperatures to begin a small warming trend. Temperatures will
return to the low to mid 90s briefly ahead of another cold frontal
passage late next week.
DNM
&&
.AVIATION...
(00Z TAFS)
Issued at 603 PM CDT Thu Aug 31 2023
VFR conditions will continue across the Mid-South for much of the
forecast period. 00Z HRRR brings some thunderstorms into portions
of northeast Mississippi by late Friday afternoon as moisture
returns to the region but have low confidence that this activity
will reach KTUP area before 00Z on Friday. Winds will be mainly
from the northeast at 5 to 10 knots this evening before
diminishing to around 5 knots later tonight.
&&
.MEG WATCHES/WARNINGS/ADVISORIES...
AR...None.
MO...None.
MS...None.
TN...None.
&&
$$
PUBLIC FORECAST...DNM
AVIATION...ARS
Area Forecast Discussion
National Weather Service Melbourne FL
922 PM EDT Thu Aug 31 2023
...New UPDATE, MARINE, AVIATION...
.UPDATE... (Next 24 Hours)
Issued at 922 PM EDT Thu Aug 31 2023
Key Messages:
-Another Round of Showers & Storms Friday
-Worsening Boating Conditions Over The Atlantic
-Rain Chances Drop Considerably This Weekend
Through Tonight...
Beneath a canopy of mid and high debris clouds, showers and
storms continue to wane across the Florida Peninsula this evening.
Extremely rich tropical moisture remains situated across the
district: the 31/20Z XMR (Cape) sounding revealed a 2.3" PW
value. The RAP initialized with 0-3km mixing ratios between 14-16
g/kg. In fact, H85 mixing ratios are near the climatological
maximum! However, with nocturnal stabilization, only isolated
(10-25%) showers are forecast overnight with balmy lows in the
mid and upper 70s.
Friday...
One more decent round of showers/storms appear to be on the way
before big changes overtake the pattern across Florida this
weekend (see below). A weak back-door front / subtle convergence
zone will push ashore from the northeast by mid-morning north of
Cape Canaveral, causing E/NE breezes to become common area-wide by
afternoon. Deep moisture remains overhead, so this convergence
should act to spark isolated/scattered (30-40%) showers along the
coast in the mid and late morning before better (60-80%) coverage
of rain and lightning storms fire up over the interior by
afternoon. Gusty winds from 35-45 mph and torrential rain
potentially leading to temporary lowland flooding could occur from
the strongest storms. High temps generally low 90s, except upper
80s at the coast. Heat indices 100-107.
&&
.PREVIOUS DISCUSSION... (Extended)
Issued at 255 PM EDT Thu Aug 31 2023
Saturday-Wednesday...
Northeasterly flow will largely dominate in the low levels
between high pressure to the north and TC Idalia over the western
Atlantic. Drier air will move into the region in this NE flow,
with PW values dropping as low as 1.2-1.3" into Monday in both the
GFS/ECMWF models. However, the GFS is a little bit faster with
the drier air moving into the area. Decreasing PoPs therefore
expected through the period, with rain chances up to 30-40 percent
on Saturday and generally around 20-30 percent from Sunday into
early next week. Highs will be closer to normal for this time of
year, around the upper 80s to low 90s, with dewpoints dropping to
the lower 70s and at least not making it feel quite as humid as it
has been lately. Overnight lows will range from the low to mid
70s.
Main weather related concern will be with increasing swell from
Idalia that will impact the beaches through the holiday weekend,
producing rough surf and a high risk of rip currents.
&&
.MARINE...
Issued at 922 PM EDT Thu Aug 31 2023
Tonight-Friday... It won`t last long, but area boating conditions
have improved for now, courtesy of light winds. Seas 1-2 ft
nearshore, 2-4 ft offshore by sunrise. Post-Tropical Cyclone
Idalia will approach Bermuda over the next couple days, with
swells increasing across the local waters beginning Friday
afternoon. By evening, 3-5 ft seas nearshore, and 5-7 ft seas
beyond 20 nm where a Small Craft Advisory has been issued.
Inshore/intracoastal waters hang onto a light/moderate chop as
winds become E/NE during the day, 8-14 kt.
Saturday-Monday... NE winds around 10-15 knots through much of
the period. Boating conditions will deteriorate into the weekend
as swells from Idalia over the western Atlantic increase seas up
to 6 to 8 feet. The Small Craft Advisory for offshore waters
beyond 20 nm continues through Saturday evening, but this will
likely be extended through much of the weekend and perhaps even to
our nearshore waters.
&&
.AVIATION...
(00Z TAFS)
Issued at 922 PM EDT Thu Aug 31 2023
VCSH diminish late evening with most areas quiet overnight as
winds become LT/VRB. Winds will become E/NE 5-12 kt on Friday,
with another round of showers/storms anticipated. Showers are
forecast to develop by late morning near DAB/TIX before spreading
toward the west/south eventually approaching most terminals by
the afternoon. Highest confidence in TSRA was reflected with
TEMPOs for Greater Orlando terminals (incl. MCO) mid-late
afternoon (roughly 17-22Z depending on the terminal).
&&
.PRELIMINARY POINT TEMPS/POPS...
DAB 89 76 86 76 / 60 50 60 30
MCO 91 77 90 76 / 70 50 80 30
MLB 92 78 89 78 / 70 50 70 40
VRB 93 76 90 76 / 60 50 70 40
LEE 91 76 91 75 / 70 50 80 30
SFB 91 77 90 76 / 70 50 70 30
ORL 90 78 90 76 / 70 50 80 30
FPR 94 77 90 77 / 60 40 70 40
&&
.MLB WATCHES/WARNINGS/ADVISORIES...
FL...None.
AM...Small Craft Advisory from 5 PM Friday to 8 PM EDT Saturday for
AMZ570-572.
Small Craft Advisory from 8 PM Friday to 8 PM EDT Saturday for
AMZ575.
&&
$$
FORECASTS/AVIATION...Heil
RADAR................Sedlock
IDSS.................Haley
Area Forecast Discussion
National Weather Service Phoenix AZ
521 PM MST Thu Aug 31 2023
.UPDATE...Updated 00z Aviation Discussion.
&&
.SYNOPSIS...
Rain chances will be increasing today with some strong to severe
thunderstorms possible across south-central Arizona later this
evening. Isolated to scattered showers and thunderstorms are
likely to persist mainly across south-central Arizona tonight into
Friday morning before more widespread showers and thunderstorms
are expected Friday afternoon and evening. Heavy rainfall with
localized flash flooding will be the primary threat on Friday, but
localized strong winds will still be a concern. A Flood Watch has
been issued for much of the area from this evening through Friday
evening. Near to below normal temperatures are expected starting
Friday with drier conditions settling in by Sunday.
&&
.DISCUSSION...
Now that the heat is abating as the strong high pressure system is
starting to shift east of the region, forecast attention has
turned toward increasing storm chances by later today. Boundary
layer moisture has been on the increase since yesterday and will
continue through Friday afternoon as deep southerly flow sets up
across the region. PWATs have already risen to near 1.7" across
southwest Arizona with guidance indicating PWATs increasing to
1.5-1.7" across all of the southern Arizona deserts this evening,
but DCAPEs remaining very high at 1500-1800 J/kg. Forecast MUCAPE
of 1000-1500 J/kg for late this afternoon and evening across the
lower deserts will support strong to possibly severe storms where
minimal CIN is expected centered over Pima into Maricopa
counties. Morning and early afternoon runs of the HRRR has been
consistently depicting a cluster of storms developing across Pima
County late this afternoon with a light southeasterly steering
flow pushing the storms through the Phoenix area during the latter
half of the evening. It seems very plausible this cluster of
storms will produce strong to possibly localized severe winds,
areas of blowing dust, and localized heavy rainfall. SPC also has
this area in a marginal risk of severe thunderstorms.
As moisture continues to increase into tonight and then on Friday,
PWATs are expected to increase to 1.7-1.9" across the majority of
the lower deserts. This will create an increasing threat for heavy
rainfall and flash flooding, possibly as early as this evening
across south-central Arizona if the cluster of storms is quite
robust. Broad scale ascent will also be increasing starting
tonight in response to a deep upper level trough digging southward
through the Pacific Northwest into California and the Great Basin.
There is also another weak shortwave trough currently over Baja
which is forecast to move northward through Arizona on Friday
which will bring PV energy for further enhancement of ascent over
our area Friday afternoon/evening. Given the more than adequate
moisture levels, good instability, and upper level support
portions of the area on Friday are likely to see strong
thunderstorms producing heavy rainfall. The 12Z HREF shows a
corridor of persistent QPF starting this evening and lasting
through Friday morning focused over Maricopa County. With expected
better instability by Friday afternoon, scattered to numerous
thunderstorms are likely to develop across the area with the HREF
focusing on an swath from Tucson through Phoenix into the Lower
Colorado River Valley. A Flood Watch has been issued starting this
evening across south-central and much of southwest Arizona before
expanding into portions of Gila County for Friday afternoon and
evening.
Aside from the rain chances, temperatures will top out around 105-
110 degrees today across the lower deserts before quickly dropping
off for Friday. For Friday, the NBM has high temperatures struggling
to climb into the triple digits with highs expected to stay in the
90s across the Valley. Overall confidence in temperatures will be
more uncertain Friday due to factors such as cloud cover and rain
with this uncertainty reflected in the greater spread in the
interquartile range of the NBM.
Chances for showers and thunderstorms will linger around for
Saturday before much drier air is ushered into the region as the low
pressure system along the West Coast shifts eastward during the
latter part of the weekend into early next week. This will lead to
rain chances falling to near 0% for the start of next week.
Temperatures then looking to gradually trend back upward next week
as ensembles favor ridging building back in with heights climbing
above 590 dm by the middle part of next week.
&&
.AVIATION...Updated at 0020Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Thunderstorm activity remains well south of the metro area late
this afternoon, thus the timing on outflow/thunderstorm potential
remains generally 03-07z range from south to north going through
this evening and into the early overnight hours. A weak outflow
out of the easterly direction may precede the strong southerly
outflow, but confidence was too low to include any change groups
with that potential. With the main outflow out of the southerly
direction, strong winds of 30 kts or greater is likely (at least
70%) and reduced visibilities in blowing dust will be the expected
outcomes. TS conditions remains around a 40-50% potential in the
04-07z time range will follow the expected outflow traversing
through the metro with CB`s around 10 kft. VCSH conditions will
prevail into early tomorrow morning, with VCTS or TS conditions
not out of the question during this period. Winds will eventually
become generally southeasterly by tomorrow morning before gusty
southerly cross winds developing in the late morning to early
afternoon hours. VCTS conditions will once again be developing by
early to mid afternoon and last into the early evening hours
tomorrow.
Southeast California/Southwest Arizona including KIPL and KBLH:
Storms off the Baja Peninsula remain well south to warrant any
VCSH/VCTS concerns at IPL this evening. Generally southerly flow
will persist across the region. At BLH, winds will remain strong
with gusts in the 20-25 kt range through the overnight period.
VCSH/VCTS conditions anticipated to develop at both terminals late
tomorrow morning with CB`s around 10 kft, with higher chances at
BLH around 30-40%. Stronger winds gusting in excess of 30 kts
expected at BLH during this period.
&&
.FIRE WEATHER...
Increasing moisture will translate to cooler temperatures and
quite good chances for rain through Friday. The best chances for
thunderstorms today will be across south-central Arizona with
strong winds a good possibility along with localized heavy
rainfall. Chances for wetting rains will further increase for
Friday with greater chances for seeing flash flooding, primarily
across central Arizona. Outside of thunderstorm winds, breezy
southerly winds are expected through Friday, particularly across
southeast California and southwest Arizona. Min RHs today will be
around 20-30% before increasing into the 35-45% range Friday.
Rain chances linger around Saturday before much drier air is
ushered in, eliminating rain chances by the start of next week.
Min RHs are expected to fall to around 15-25% by early next week.
Below normal temperatures will gradually trend upward again next
week as ridging is expected to build back into the region.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Flood Watch through Friday evening for AZZ530-531-533-534-
536>544-546-548>551-553>555-559.
Blowing Dust Advisory until 11 PM MST this evening for AZZ539-
550-551-553>555-559.
Flood Watch from Friday afternoon through Friday evening for
AZZ545-547-552-556>558-561-562.
CA...Flood Watch through Friday evening for CAZ569.
&&
$$
DISCUSSION...Smith/Kuhlman
AVIATION...Young
FIRE WEATHER...Smith/Kuhlman