Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 09/27/21
Area Forecast Discussion
National Weather Service Quad Cities IA IL
711 PM CDT Sun Sep 26 2021
...AVIATION UPDATE...
.SYNOPSIS...
Issued at 154 PM CDT Sun Sep 26 2021
As expected, a warm and somewhat breezy day is taking place under
a mainly sunny sky. There is patchy cirrus streaming over the
northern 1/2 of the area, and a very narrow stripe of mid clouds,
extending from Webster City Iowa to the Quad Cities. The
trajectory of the mid clouds is helping it persist an hour or two
in locations from Iowa City through the Quad Cities. Temperatures
are in the lower to mid 80s north to mid 80s south. Though the air
is dry, dewpoint in the upper 40s to lower 50s are resulting in RH
values of 28-38 percent, which is less supportive of fire
potential than yesterday.
&&
.SHORT TERM...(This Evening through Monday)
ISSUED AT 154 PM CDT Sun Sep 26 2021
Dry weather is certain, and our forecast will be just focusing on
winds and temperatures through tomorrow.
Tonight, the south winds will continue to blow around 10 mph
through the night, resulting in temperatures staying higher than
last night, in the mid 50s north to mid 60s south. As stated in
the aviation section, wind aloft will be rather strong, and this
should help keep the surface winds going through the night.
Monday will be dry, and at least in the morning, south winds will
be 10 to 20 mph. In the afternoon, a back door cold front / lake
boundary should move southwest, which will decrease the south
winds over much of the area. Despite this front, the timing
suggests we`ll get a strong warming day, several degrees higher
than today. With highs reaching the 86 to 88 range, many sites are
near record highs for September 27. Please see the climate section
below.
.LONG TERM...(Monday Night through Sunday)
ISSUED AT 154 PM CDT Sun Sep 26 2021
Warm and dry conditions are expected through much of the work week,
with above normal temperatures.
Monday night-Thursday night...building upper level ridge over the
Midwest will be the main weather feature through the period. This
will bring ideal harvest conditions for area farmers with warm and
dry weather forecast. Highs in the 80s and lows in the upper 50s/low
60s are expected. Latest RAP and HRRR show a backdoor cold
front/lake boundary will push into northern IL late Monday afternoon
and evening. Model 1000-500mb RH progs are below 45% along the
front, so not anticipating much more than a wind shift to the
northeast and perhaps a wind gust around 20 mph. The latest 12z GFS
continues to show moisture return and precip chances coming back to
the area as early as Wednesday night, but feel this is still too
soon given our dry airmass and ridge axis overhead. The bulk of the
GEFS ensemble members support a dry forecast, with the 12z
deterministic run falling on the higher end of the QPF spectrum
currently. NBM QPF probabilities have also lowered owing to a higher
confidence dry forecast.
Friday-Sunday...the amplified omega block will start to break down,
as several shortwaves lift out of the northern Plains. Still a lot
of model uncertainty on when this will occur and how quickly we can
saturate the column. Slight chance PoPs were maintained for now
across eastern IA, with the better storm track further to the west.
However, it is very possible that we will remain dry through most if
not all of the weekend.
&&
.AVIATION...(For the 00Z TAFS through 00Z Monday Evening)
ISSUED AT 658 PM CDT Sun Sep 26 2021
Low-level wind shear is expected tonight as winds increase aloft
but decrease on the surface. SW to WSW winds at 2000 ft AGL are
forecast to reach 40 - 50 kts, and persist into early Monday
morning at MLI and BRL before diminishing. No other impacts are
expected through the period with clear skies and unrestricted
visibility.
&&
.CLIMATE...
ISSUED AT 154 PM CDT Sun Sep 26 2021
Record Highs for September 27...
Moline.........90 in 1990
Cedar Rapids...89 in 1954
Dubuque........88 in 1954
Burlington.....91 in 1905
Week 2...
The latest 8-14 day temperature outlook from the Climate Prediction
Center shows high probabilities of above normal temperatures across
most of the Midwest for the Oct 3rd-9th time frame. Normal highs for
this period are in the upper 60s and normal lows are in the middle
40s.
&&
.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&
$$
SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...Gross
AVIATION...Uttech
CLIMATE...Ervin/Gross
Area Forecast Discussion
National Weather Service El Paso TX/Santa Teresa NM
607 PM MDT Sun Sep 26 2021
.AVIATION...00Z TAF CYCLE
Deteriorating conditions ongoing around the area bringing heavy
rain and gusty winds to TAF sites. Thunderstorms expected to
continue through the evening and generally ending around 04Z
except for KELP where storms should end at 06Z. Winds will taper down
this evening and become 220-280 at 5-10KT outside of
thunderstorms. CIGs will be BKN200-OVC250. Tomorrow afternoon
should have less thunderstorm activity compared to today.
&&
.PREV DISCUSSION...313 PM MDT Sun Sep 26 2021...
.SYNOPSIS...
An active weather pattern will continue through this week. The
upper-level low over northern New Mexico will brings chances of
rain to mountain areas and areas along and west of the Rio this
afternoon and evening. Rain chances remain in place across the
mountain areas on Monday and Tuesday before we dry out on
Wednesday. Widespread rain chances increase on Thursday and Friday
as another system develops over the Desert Southwest.
&&
.DISCUSSION...
.SHORT TERM...Tonight and Monday
A large and vigorous upper low pressure storm system continues to
spin to our southwest. During the previous 12 hours it has unhitched
from it`s anchor spot off the west coast of the Baja, and it is
slowly tracking ENE across the heart of Arizona. Increasing
instability and dynamics, associated with the approaching low are
beginning to shift east over our western zones with increasing
convection, and stronger strength in some of them. We are seeing
better cooling aloft, PVA, diffluence aloft, and fair daytime
heating of the surface with better sunshine through midday. All
areas do have POPs and mention of showers and storms, but the better
chances are over areas west of the Rio Grande. As usual, the CAMs
show a mixed bag of storm coverages into the evening and overnight
hours across the region. The latest, 18Z, HRRR is a bit bullish with
more storms moving in later this evening from the SW. It also does
bring them into central and eastern potions of the CWFA. That does
make sense with the main storm system slowly easing east toward our
region. thus we keep storms in through midnight and then trim back.
For Monday the large upper low is projected to sit right over the
entire state of NM. This puts our region directly under the main
dynamics of the system. We could see a bit of dry-slotting, and the
models do drop our PWATs a bit, but not enough to rule out storm/
shower activity. With the drop in surface moisture the instability
parameters do drop a bit. Models tend to want to keep a good portion
of the SW deserts dry, but do keep pcpn/tstms forming over the W
zones, N zones, Gila region, and maybe the Sacs and SE Hudspeth
areas. Thus our POP fields mimic that pattern. Again, with low
pressure over the area, abundant moisture in place, and a fair
amount of clouds temperatures will be below seasonal averages by a
few degrees.
&&
.LONG TERM...Monday Night through Saturday
By Monday night and Tuesday morning, the upper-level cutoff low
will be centered over north-central New Mexico. As it gradually
treks towards the northeast. In response, a small ridge will
slowly move into the area on Tuesday and 500-mb heights will rise.
Winds aloft and at the surface will be generally out of the
west/northwest, pushing in drier air. That being said, rain
chances remain in place for our northern counties/mountain areas.
The weakening low will be over the CO/NM state border, bringing
those areas enough forcing to tap into the leftover, wrap around
moisture that`s still in place. Scattered showers and
thunderstorms can be expected mainly focused over the Gila and
Sacramento Mountains. Wednesday looks to be the driest day this
next week. Our winds will continue to be out of the west with dry
air filtering in across the Borderland. Skies will be mostly sunny
with temperatures in the low-to-middle 80s in the lowlands,
cooler over the higher terrain.
On Thursday and Friday our focus turns to a upper-level trough
that will dig, strengthen, and become a cutoff low across the
Desert Southwest. Ahead of the approaching trough, a cold front
will dive in from the north across New Mexico. Differences between
the GFS and ECMWF arise on how this front will interact with the
approaching trough. The ECMWF is showing a weaker, more diffuse
front than what the GFS is showing. However, an increase in
moisture is expected across the area, as the CWA is in the eastern
periphery of the low where the most moisture gets advected in.
The WPC Cluster Analysis continues to dial in on this approaching
storm system and its likelihood of it impacting the Borderland
region. The only discrepancies that arise between clusters, is the
QPF. Overall, with the increase in moisture, an increase in
widespread rain can be expected Thursday into Friday. I won`t get
into too much detail with regard to rainfall amounts due to how
many days away we are from the event. But most areas across the
CWA could receive 1+ inches of rain. As we progress through the
week we will be watching the trends closely. By Saturday, the
cutoff low opens up and gets absorbed into the main steering flow
aloft and quickly moves northeast.
&&
.FIRE WEATHER...
A large low pressure storm system remains to our southwest, with a
good amount of moisture continuing to stream in over the region from
the south. This system will be a slow mover, and track across the
western areas Monday, and slowly move away to the NE on Tuesday. A
second low pressure system moves into the region on Thursday, and
passes Friday as a backdoor front also moves in. All this means an
unsettled weather pattern through the week. Showers and
thunderstorms are likely across the region, with the Gila favored
Monday and Tuesday, and eastern and central regions favored with the
second storm system. Wednesday, and possibly Tuesday, look to be
generally drier, storm/rain free days. Overall fire weather concerns
will remain low, with cooler temperatures, topping out each
afternoon near and below seasonal averages. In addition, the bump in
dewpoints and precipitable water will help to keep variable cloud
cover, and elevated relative humidity over the area. Winds will be
generally light to only moderate with minor increases to near breezy
as the storms pass.
&&
.PRELIMINARY POINT TEMPS/POPS...
El Paso 85 63 83 63 / 40 40 0 0
Sierra Blanca 82 57 77 56 / 40 40 10 10
Las Cruces 81 56 80 56 / 30 30 0 10
Alamogordo 82 57 81 56 / 30 30 10 0
Cloudcroft 65 43 58 40 / 30 40 30 10
Truth or Consequences 79 57 77 55 / 40 40 30 10
Silver City 74 53 68 51 / 60 50 40 20
Deming 81 54 80 55 / 50 40 20 10
Lordsburg 81 56 76 55 / 60 40 30 20
West El Paso Metro 87 63 84 63 / 40 40 0 0
Dell City 87 58 83 55 / 30 30 10 0
Fort Hancock 90 60 86 59 / 40 40 10 10
Loma Linda 80 57 76 56 / 30 40 0 0
Fabens 88 61 84 60 / 40 40 0 0
Santa Teresa 85 57 82 57 / 40 40 0 0
White Sands HQ 86 60 80 60 / 30 30 10 10
Jornada Range 83 57 78 56 / 30 30 10 0
Hatch 84 56 79 55 / 30 30 10 0
Columbus 82 57 80 58 / 40 40 10 0
Orogrande 86 57 81 57 / 30 30 10 0
Mayhill 75 50 69 47 / 30 30 30 10
Mescalero 75 47 68 45 / 30 40 30 10
Timberon 73 47 67 44 / 30 40 30 10
Winston 75 45 71 42 / 60 50 40 20
Hillsboro 80 53 76 53 / 50 40 30 10
Spaceport 82 55 77 53 / 30 30 20 10
Lake Roberts 74 45 69 44 / 60 60 40 20
Hurley 74 51 72 49 / 60 40 30 20
Cliff 81 49 75 47 / 60 50 30 30
Mule Creek 75 52 70 51 / 70 60 50 40
Faywood 78 52 73 51 / 50 40 30 10
Animas 82 54 79 54 / 60 50 30 10
Hachita 80 53 77 53 / 60 40 20 0
Antelope Wells 81 55 78 53 / 60 50 10 0
Cloverdale 76 53 74 53 / 60 40 30 0
&&
.EPZ WATCHES/WARNINGS/ADVISORIES...
NM...None.
TX...None.
&&
$$
14/38/37
Area Forecast Discussion
National Weather Service New Orleans LA
931 PM CDT Sun Sep 26 2021
.EVENING UPDATE...
No changes needed to forecast package at this time. 35
&&
.PREV DISCUSSION... /issued 252 PM CDT Sun Sep 26 2021/
SHORT TERM (This evening through Tuesday Night)...
Another quiet and beautiful day in the books as we close out the
weekend. Only item worth mentioning this evening is some thin,
patchy upper-level cirrus advecting east, downstream of a closed
upper- low over Arizona. We will continue to see patchy, thin
cirrus tonight but overall another peaceful night. Meanwhile at
the surface, we were greeted with a reinforcing area of high
pressure following a decaying front to our north, but will
continue to drift east. This will in turn allow for surface winds
to clock more from the ESE to eventual SE overnight tonight. Not
seeing any increasing vertical depth with this subtle return flow
starting up just yet, which may allow for larger scale subsidence
to win over vertically. However, seeing some indications of
enough of a nudge of dewpoints to cause another night of very
patchy surface fog to develop, with the better chances for western
areas from Reserve to New Roads, perhaps close to Baton Rouge
then also across McComb, but this should be very minor. Elsewhere,
very thin, patchy fog will be possible, just not impactful enough
to mention in the forecast. While dewpoints will ever so slightly
drag up through the overnight hours and into daybreak Monday,
just not seeing enough moisture advection or enough depth to
offset larger-scale subsidence and radiative cooling processes
with mostly clear skies and calm winds come daybreak, because of
that, have decided to place MinT`s on the lower side of the NBM
Ensemble spread biasing a few degrees cooler than deterministic
(similar trend to the previous few days). But regardless, it will
still be a few degrees warmer than last night with many areas in
the upper 50`s to lower 60`s, mid/upper 60`s southshore and SE LA.
Monday will start off very nice, with some patchy upper-level
clouds around. But starting early tomorrow, we begin to see more
of a vertical extent of the moist return flow to take over. This
in turn decays the near surface to low-level subsidence inversion
transitioning into a moistening PBL, enough to produce patchy
cumulus between the LCL and base of the secondary/stronger
subsidence inversion from H8 to H5. Meanwhile, deeper flux moist
transport sets up to our west from southern/Southwestern LA to the
SE TX coastline. There, strengthening WAA in a veering vertical
wind profile will be enough to spark some scattered to isolated
showers and a few storms. Noticing the latest extended synoptic
hour run of the HRRR develop some isolated showers or a storm or
two as far east as Houma to Baton Rouge. This is an outlier, but
leaned the NBM enough in the short-term to mention 20-30% PoPs in
this region. Local soundings (particularly LFT) shows enough deep
moist ascent to erode the stronger H8 subsidence inversion, which
makes sense but the eastward extent will be greatly determined by
how fast deeper tropospheric moist air can pull into our region
from the southwest. Overall, Monday should largely be primarily
dry with some patchy Cu or upper-level clouds but overall another
very nice day, just watch for an isolated shower/storm or two for
far west areas.
Monday night into Tuesday, we have to take a step back and look
at the entire US mid-level pattern. That same aforementioned
upper-low over the southwest nudges east underneath ridging in
control of the western US, but a very strong Pac NW trough comes
on shore and amplifies the ridge over the central US and
absorbs/weakens the upper-low in a progressive SW to NE flow
aloft. For here, as it has been mentioned, pulses of mid-level
energy advects in from the west underneath a generalized zone of
weakness aloft. GFS continues to trend more moist with time, as
mean SFC to 400mb flow from the southwest wins over, dragging
1.8-2"+ PW`s east into our area. NBM caught on increasing PoP`s
yet again as confidence continues to increase as well bringing now
60-80% PoPs for areas along and west of I-59. Still going to
message doubt on the eastward extent (generally coastal MS) but
will only mention less confidence in this region while keeping a
mention of PoPs going. This increase in moisture reveals a few new
things to monitor for looking at soundings on Tuesday.
Instability is much higher thanks to more available moisture,
meaning thunderstorms will be more likely, especially for western
areas. Not seeing any severe weather issues as the wind field
remains extremely weak (yet veering from the surface to H7).
However, H5 temperatures in the -10C range with H7 to H5 LR`s in
the 6 to -6.5C/km could reveal a stronger storm or two. Also,
with PW`s in the 1.8 to 2.0 inch range with weak steering flow
(mean storm motion ~280/4kts), cant rule out locally heavy
downpours leading to minor flooding. Overall, not a significant
risk in severe weather or flash flooding, but at trend that will
require monitoring especially as we get closer and are able to
reveal small-scale details. Most of this activity will come to an
end by sunset Tuesday with dry and partly to mostly cloudy skies
overnight. KLG
LONG TERM (Wednesday through Saturday Night)...
Wednesday will be a similar story to Tuesday, with much of the
same PVA underneath a moist SW to NE flow aloft bringing waves of
showers and storms yet again. Same environmental conditions exist
with weak, but veering winds aloft but enough instability to
bring thunderstorms. Once gain, can`t rule out localized heavy
rain/minor flooding due to weak steering flow (mean storm motion
~255/3kts) but safe to say, good idea to have your umbrella both
Tuesday and Wednesday and monitor for minor flooding issues
possible, depending on where heaver storms set up.
Thursday through the rest of the week and weekend, it has been
mentioned before that the upper-level pattern becomes a bit
chaotic, as long-wave troughing out west eventually breaks off a
tail upper-low over the SW US, ridging (~588dm) builds into the SE
US and multiple strong impulses dive into the upper MS valley
region. A wee bit complicated, but the good news here is the trend
of this ridge staying tight in control of our area which leads to
a drier trend, with near to slightly above climatology in regards
to forecast temperatures. Fingers crossed for another stretch of
nice weather hopefully in this time frame, but will need to keep a
close eye on this upper-level pattern if any changes in trends do
occur. KLG
AVIATION (18Z DISCUSSION)...
Expect VFR conditions to prevail through today and overnight
tonight with SKC/FEW250 and light surface winds. Some indication
of light patchy surface fog daybreak Monday, primarily for western
terminals (BTR, HDC to MCB) with temporary MVFR flight
categories possible, but should refrain from becoming a
significant impact at this time as conditions should improve
shortly after sunrise. KLG
MARINE...
Light easterly winds will steadily transition towards the
southeast later tonight, persisting through the rest of the week
ahead with generally calm seas expected. Isolated showers and
storms start off on Monday, with better chances west of the MS
river. Thereafter, coverage of showers and storms will increase
Tuesday through Thursday with several rounds of heavy showers and
storms likely. ESE to SE winds pick up late in the week which
allows for a slow increase in waves/seas across outer 20-60nm
zones to around 2 to 4 feet late this week, increasing to 3 to 6
by next weekend. KLG
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 58 85 67 84 / 0 0 10 60
BTR 59 85 68 84 / 0 20 30 80
ASD 60 86 67 86 / 0 10 10 60
MSY 66 87 73 87 / 0 20 20 70
GPT 62 84 69 84 / 0 0 10 40
PQL 60 85 66 85 / 0 0 10 30
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&
$$
Area Forecast Discussion
National Weather Service San Francisco Bay Area
638 PM PDT Sun Sep 26 2021
.SYNOPSIS...Region will undergo additional cooling during the
beginning of the this week. Unsettled weather is expected to move
into the Bay Area on Monday which will increase onshore winds and
bring the potential for light rain, mainly in the North Bay. Expect
coastal stratus and increasing humidity values to spread inland
again tonight into Monday morning. Warmer and drier trend for the
second half of the work week.
&&
.DISCUSSION...as of 02:45 PM PDT Sunday...Smoke aloft in the sky
continues to create a milky haze overhead. Fortunately, the near
surface concentrations of smoke continue to be very low due to the
onshore flow bringing in fresh, marine air. Current temperatures
are running similar to yesterday or up to 7 degrees cooler.
Expecting highs today to be a little below average with coastal
temperatures peaking in the 60s to low 70s and inland areas
peaking in the mid 70s to mid 80s except for a few hotter spots
reaching the upper 80s to low 90s. Cooler air is being brought in
by an approaching trough over the eastern Pacific that has
deepened our marine layer to 2000 ft. That cooling effect will
continue into Tuesday as the trough tracks eastward.
So the main weather event in the short term is the trough moving
inland on Monday. Hi-res models have been fairly persistent that
our region will get the weaker end of that frontal passage. The
best confidence in getting light rain in our CWA is for the North
Bay coastal areas where precipitation looks to start late
morning/afternoon. Some models hint that some spotty showers may
make their way into the South Bay and Monterey Bay late Monday
night, but confidence is not high. Have kept slight chance PoPs in
the forecast for the Monterey Bay shorelines to cover the
potential of either light rain or drizzle as this system moves
through. Rain totals will likely remain less than a tenth of an
inch.
In addition to precipitation, increasing winds associated with
this system will bring breezy to locally gusty conditions to the
region. Luckily, the incoming airmass will be very moist so there
is lower concern for fire weather as winds increase. Even so,
winds are not expected to be super gusty. At most, we should see
our highest elevations peak at gusts around 35 mph, possibly up to
40 mph in very localized areas. Meanwhile, the lower elevations
will generally have gusts ranging 15 to 25 mph at times. The
trough remains over our area through Tuesday which will bring
another round of breezy to locally gusty winds (similar to
Monday). Plus, the trough will maintain below normal temperatures
as our highs range from the upper 50s to upper 70s across our
entire CWA (not just near the coast). And that cooler airmass also
means you can expect a bit of a chill early Wednesday morning as
many locations dip down into the low 40s to low 50s.
By Wednesday afternoon, high pressure reestablishes itself over
the eastern Pacific. The ridge axis will begin nudging into the
west coast by Wednesday evening and then strengthen inland on
Thursday. This will cause an uptick in the daytime thermometer as
our Wednesday highs become more seasonable and Thursday highs are
near to a few degrees above normal. This means a drier and warmer
trend with highs back in the 70s along the coast and in the 80s
to low 90s inland to round out the work week.
&&
.AVIATION...as of 6:38 PM PDT Sunday...For the 00z TAFs. Wildfire
smoke will steadily clear out from the cwa per recent hrrr smoke
forecasts, lingering longest to the south. Slant range visibility
will be reduced due to smoke aloft, otherwise localized MVFR mainly
inland and south in smoky/hazy conditions. Coastal low clouds will
advance inland, though there is a dry pocket of air arriving near
925 mb (2,500 feet) per satellite imagery and model forecasts. Cooler
air at this level will continue to weaken the already weakened and
deepened marine layer tonight and Monday. Mainly MVFR ceilings tonight
and Monday morning, with localized IFR possible late tonight and
Monday morning. Light rain arriving over the North Bay Monday, a
mix of light rain or drizzle to the south along the coast to San
Mateo County Monday.
Vicinity of KSFO...VFR, west wind near 20 knots easing back to
around 10 knots tonight and Monday morning. MVFR forecast 07z-18z
Monday. VFR to MVFR Monday evening and night.
KSFO Bridge Approach...Similar to KSFO. Slant range visibility
possibly reduced in wildfire smoke, however model forecasts
improvement through the period, especially Monday.
Monterey Bay...MVFR-IFR ceilings developing tonight and continuing
into Monday morning. Conditions improving to VFR by late Monday
morning and afternoon.
&&
.MARINE...as of 02:10 PM PDT Sunday...Generally light to locally
moderate northwest winds will continue into tonight. Breezy
afternoon and evening winds expected where coastal jets form
south of Pigeon Point and along the Big Sur coast south of Point
Sur. Winds will briefly shift out of the south to southwest into
Monday over much of the waters as a weak cold front moves
through. Northwest winds will quickly return by Monday night and
then increase into mid week. Seas remain mixed with a moderate
west to northwest swell and a longer period southerly swell. A
second larger northwest swell will arrive Monday night with seas
building into Tuesday. The combination of stronger winds and
building swell will result in hazardous seas conditions,
particularly for smaller vessels.
&&
.MTR WATCHES/WARNINGS/ADVISORIES...
.Tngt...SCA...Pigeon Pt to Pt Pinos 0-10 nm until 9 PM
SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm
&&
$$
PUBLIC FORECAST: Bingaman
AVIATION: Canepa
MARINE: AS
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Area Forecast Discussion
National Weather Service Pendleton OR
850 PM PDT Sun Sep 26 2021
.UPDATE...The latest radar was showing a band of rain along the
wa/or cascades. This band of rain is forecast to drift east and
may lean somewhat toward the more aggressive gfs soln than both
the hrrr and rap with pushing the showers into portions of the
basin toward morning. Meanwhile pressure gradients tighten and
surface winds may increase some overnight. Otherwise minor changes
were done to the low temps and the present short term forecast
appears on track. Furthermore and into Monday the models were
even more aggressive with a cold front tracking through the region
and another round of showers along with increasing qpf amounts are
expected into Monday night and the current forecast reflects
this.
&&
.PREV DISCUSSION... /issued 458 PM PDT Sun Sep 26 2021/
SHORT TERM...Tonight through Tuesday...An upper level trough with
a leading cold front will continue to approach the forecast area
tonight. Out ahead of the frontal boundary, showers are starting
to form along the WA coast as a shortwave in the southwest flow
aloft is coming onshore. These showers will continue to push east
into tonight, with light precipitation starting along the WA
Cascades late this evening. Early tomorrow, the cold front will
slowly move across the western half of OR/WA and stall against the
Cascades for a couple of hours. This will allow a good chance of
precip along the Cascade crests, with some spillover on the east
slopes. By tomorrow afternoon, the cold front will cross the
Cascades and move southeast across the forecast area, bringing a
chance of rain showers across most of the forecast area. Ahead and
behind the cold front, breezy winds will develop across the
lowlands, with strongest winds in central OR. Tuesday, in the wake
of the aforementioned cold front, the trough will swing across the
forecast area starting in the morning, and sustain rain showers
mainly across the mountains through the evening. Snow showers may
be possible across the Cascade Crests and the Wallowas, as snow
levels behind the cold front will drop to around 5,500ft in the
morning. Breezy westerly winds will redevelop with trough axis
passage, especially in portions of the Basin and the Simcoe
Highlands where gusts may get up to 30-35 mph. The trough axis
will exit to the east by Tuesday evening, with most precipitation
chances sharply declining and skies clearing in the Basin behind
the trough axis passage. Temperatures will be near normal for
today and tomorrow, while below normal temperatures can be
expected for Tuesday. Lawhorn/82
LONG TERM...Wednesday through Sunday...Mean ensembles show a
shortwave ridge developing in the wake of the aforementioned trough
in the short-term. The ridge peaks Wednesday afternoon as southwest
flow develops ahead of the next trough over the eastern Pacific. The
trough pushes onshore Thursday, weakens, and exits the region by
Friday afternoon. Weak ridging is expected to develop in it`s wake
Saturday and Sunday. There are some discrepancies between the models
with the EOFs showing differences, mainly in timing. However, these
differences become quite large in the developing trough for next
week.
The deterministic models are in fairly good agreement showing the
trough pushing through the area by Friday evening. At this time,
the ECMWF is a little slower than the GFS in pushing it eastward.
The best chance for precipitation will be over the Cascades Wednesday
night into Thursday and over the northeast Oregon mountains Thursday
evening. Both models show an upper level ridge developing over
Oregon by the weekend. The GFS is stronger and centered over Oregon
while the ECMWF is flatter/weaker and centered off the Oregon coast.
As mentioned earlier, the EOFs show a large discrepancy in timing
and strength of the through next week which will have an impact on
the strength of this developing ridge. Despite these differences,
daytime highs will begin below normal Wednesday but they will remain
above normal through the rest of the period. Earle
AVIATION...vfr conditions should prevail at most taf sites through
the next 24 hours. Meanwhile showers may develop after 06z at most
taf sites except for kpdt and kalw. Also lcl mvfr conditions could
be approached at taf site kdls after 06z in any heavier showers.
&&
.PRELIMINARY POINT TEMPS/POPS...
PDT 54 74 46 62 / 10 30 80 30
ALW 58 76 49 63 / 10 20 80 30
PSC 60 75 53 67 / 20 30 70 20
YKM 54 68 43 64 / 20 40 30 20
HRI 56 74 49 66 / 20 30 70 20
ELN 53 64 43 59 / 30 50 30 30
RDM 49 68 37 58 / 30 60 70 20
LGD 49 75 43 56 / 10 20 80 50
GCD 48 76 41 57 / 10 20 80 40
DLS 59 67 50 64 / 50 70 60 40
&&
.PDT WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
&&
$$
SHORT TERM...97
LONG TERM....99
AVIATION...97
Area Forecast Discussion
National Weather Service Phoenix AZ
504 PM MST Sun Sep 26 2021
.UPDATE...Updated aviation discussion.
&&
.SYNOPSIS...
A slow moving low pressure system will bring good chances for
showers and isolated thunderstorms this evening across much of southern
and central Arizona with lingering chances mainly over the
Arizona high terrain on Monday and Tuesday. A second slow moving
weather system is then expected to affect the region during the
latter half of the week bringing more intermittent chances for
rain. Below normal temperatures are also anticipated for much of
the area through the coming week.
&&
.DISCUSSION...
Latest RAP analysis indicates mid-tropospheric streamlines
associated with the low have become more elongated and less
symmetrical. The center of the low extends roughly from Pima
County into southern Gila County. Several smaller vort maxes are
also evident on water vapor imagery within the larger circulation.
One of those vort maxes has been largely responsible for a
decaying MCS and its stratiform rain which have persisted across
central Arizona nearly all day. With the thick cloud cover,
temperatures have also struggled to make it out of the upper 60s
and lower 70s, which is a remarkable 25 to 30 degrees below
normal.
Rain amounts since early morning have generally ranged from a
tenth to a half of an inch across the Valley, while amounts near
an inch have been observed across far northeastern Maricopa and
southern Gila Counties. This has caused a spike in Tonto Creek,
though levels in Tonto Basin remain just below action stage at
this time.
Latest mesoanalysis indicates the greatest instability and
strongest storms have been displaced east of the aforementioned
low and mainly relegated to southeastern Arizona this afternoon.
CAMs have struggled somewhat today, including the HRRR which
continues to initialize the precipitation and then quickly kill it
off. General consensus from the CAMs including the HREF indicated
the rain would taper off this afternoon before redeveloping
tonight. However, latest radar trends clearly show that wraparound
precipitation has already developed, likely due to the faster
northeastward translation of the low. Conditions will likely
become less favorable for precipitation after sunset, as
instability wanes and subsidence increases behind the low.
&&
.PREVIOUS DISCUSSION...
The upper level low will be quite slow to exit the region as
models show the low center only making it into north-central New
Mexico by Monday night. Plenty of moisture will still be present
across Arizona on Monday before gradual drying conditions take
place into Tuesday. With the moisture still in place on Monday,
scattered showers and likely a few afternoon thunderstorms are
expected to impact the area, first initiating across the high
terrain north of Phoenix before possibly tracking southward into
the south-central Arizona deserts. NBM PoPs for Monday range from
60% across the high terrain to 20-30% into the Phoenix area,
before lowering to 30-50% across the high terrain on Tuesday and
less than 10% for Phoenix.
Model ensembles are in very good agreement the active weather
pattern will continue across the Southwestern U.S. through the end
of the coming week as a deep eastern Pacific trough tracks
southeastward into our region beginning Tuesday night. Ensembles
largely agree this trough will eventually become somewhat cut off
from the progressive flow across the northern CONUS, likely
stalling out briefly over our region late in the week.
Determining rain chances and the timing is still a bit early, but
for now the NBM is placing the highest PoPs on Wednesday night
into Thursday. As with the current weather system, cut-off lows
are difficult to forecast so the timing and placement of the low
and subsequent rain chances are still uncertain. However, this
system looks more like a traditional fall type system, so
moisture levels are likely be more limited.
Due to the active weather pattern expected during the coming
week, temperatures are likely to remain below normal across much
of area. High temperatures across the south-central Arizona lower
deserts should mostly top out in the upper 80s to lower 90s,
while highs across southeast California and southwest Arizona
mostly range between 90-95 degrees.
&&
.AVIATION...Updated at 0000z
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Showers have shown a downtrend in coverage this evening across the
Phoenix area, with more extensive showers expected to move into
western Maricopa County this evening. Low CIGS of 7-10 kft are
persisting, but have showed some gradual improvement with the
reduction in showers. Expecting areas of VCSH to persist through
most of the evening and overnight, but uncertain if any more
widespread redevelopment occurs. Some model guidance is showing
this happening, with potentially heavier showers and a few
thunderstorms affecting the western half of the Phoenix metro area
(potentially DVT), but this scenario is still uncertain and has a
20-30% chance of materializing. Winds will generally favor a
northeasterly direction and could be gusty at times (to near 15
kt). Improving CIGs and falling precip chances are expected after
16Z Monday morning as the upper low slowly exits the region.
Southeast California/Southwest Arizona including KIPL and KBLH:
Chances for showers and thunderstorms should remain east of the
Lower Colorado River Valley this evening, but outflows from
showers approaching La Paz County may affect KBLH after 03Z.
Otherwise, winds will generally favor a southerly component at
both sites with extended periods of light and variable winds. FEW-
SCT, and at times BKN, clouds will continue aoa 10 kft through
the period.
&&
.FIRE WEATHER...
Tuesday through Saturday:
An unsettled weather pattern will be in place for much of the
period with lingering rain chances across eastern Arizona on
Tuesday. This will be followed up by another slow moving weather
system likely affecting the region throughout a good portion of
the latter half of the week. Moisture levels will remain quite
elevated for much of the period with min RHs mostly ranging from
around 20% across the western districts to 25-40% from Phoenix and
areas east of Phoenix. Aside from fairly breezy conditions on
Tuesday, winds will be fairly light most days favoring local
diurnal/terrain influences.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...Rogers/Smith
FIRE WEATHER...Kuhlman