Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/09/22
Area Forecast Discussion
National Weather Service Denver/Boulder CO
937 PM MDT Thu Sep 8 2022
.UPDATE...
Issued at 929 PM MDT Thu Sep 8 2022
Pesky outflow boundaries have been the problem this evening. The
convection has been pretty weak. The outflow winds speeds have not
been significant. Currently, the much anticipated cooler air has
just reached Cheyenne, Wyoming: at least the wind shift. A bit
north of Cheyenne, temperatures have fallen into the mid 50s at
this time. Some of the models have low Stratus for some of the
plains on Friday morning. Will make some minor updates to the
sky, pops and wind GFE grids this update. Nothing significant.
&&
.SHORT TERM...(This evening through Friday)
Issued at 322 PM MDT Thu Sep 8 2022
Looking at GOES-16 mid to low level water vapor, high clouds are
building into the northern I-25 corridor. Hard to believe 2 years
ago today, Denver broke its daily snowfall record of 1 inch in 2020.
Additionally, Denver broke its daily high temperature record of 94
set in 1959 this afternoon reporting 99 currently. Storms are
developing in the foothills pushing into the plains but these storms
are more likely to produce significant wind gusts up to 40-50 mph
with isolated rogue gusts of 50-60 mph (near the Cheyenne Ridge)
as DCAPE reaches 1000 J/kg from the ACARS soundings. Storms should
decrease in coverage by 8 PM.
Tonight through Friday, the upper level trough axis will dip into
southeastern Wyoming which will weaken the upper level ridge.
This should limit majority of wildfire smoke entering the region
Friday. This will allow cooler air to enter our region from the
US-Canadian border. Cooler air (40-50F) behind this system
arrives Friday morning bringing some relief from the recent
record breaking heat. Friday afternoon highs will drop to the 60s
to lower 70s for the urban corridor, foothills, and plains. Parts
of the mountains and valleys will be similar with higher peaks
above 10k ft dropping to the lower 50s.
.LONG TERM...(Friday night through Thursday)
Issued at 322 PM MDT Thu Sep 8 2022
A shortwave trailing the main trough axis will give another push
to the cooler air, while the associated jet streak helps produce a
little QG lift over the front. This isn`t terribly strong or
organized, but looks to be enough to produce some shower
activity Friday night into Saturday as the trough passes. The most
likely area for this will be over the northeast plains on
Saturday, but there is also a good chance of some light rain or
drizzle along the east slopes of the Front Range from saturated
upslope winds. It doesn`t look cold enough for snow in the deep
moisture which looks to stay at or below the freezing level, but
there could be a slight chance of some snow above timberline from
the elevated showers. Clouds should be thick enough to limit
heating fairly well on Saturday, and we`ve nudged the temperatures
on the plains down a little more.
The moisture clears out pretty quickly late Saturday, and the cold
air will shrink in depth as well. There should still be a shallow
layer of cold air Sunday morning, especially if there`s pretty
good clearing early in the night. There`s probably enough drying
to prevent fog, but it could cool enough for frost in more of the
coldest spots of the northern mountains where that has been very
patchy so far.
With the warm dry air over us again for the early part of next
week, we`ll accept our model blend`s fairly aggressive warming
with temperatures back into the 80s Monday and near 90 by Tuesday
under the ridge axis. There`s better agreement on the ridge
shifting slowly eastward and southwest flow aloft developing by
Tuesday, but differences upstream affect the timing and amount of
moisture that comes in from the southwest. Consensus looks to be
keeping any deep moisture plume in the southerlies on the east
side of the Hurricane Kay remnants from getting here, but giving
us some high moisture first on Tuesday or Wednesday and then some
further increase for another day or two after that. It should be
enough for a late summer convective pattern with a fair amount of
moderately strong storms over the mountains, and more limited
activity fighting the warmth aloft over the plains.
&&
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 930 PM MDT Thu Sep 8 2022
Numerous outflows have tortured the TAF this evening. The cold
front/wind shift should get to DIA around 06Z. Models keep an
upslope component to the winds all day Friday. Concerning low
clouds, the new 00Z NAM is hanging onto some Stratus on the cross
sections from mid/late morning onward into Friday night. Went
with a BKN030 ceiling but until late day Friday. Not sure at low
cloudiness for DIA at this time. Also went with VCSH for the rest
of the this evening and after 00Z Friday evening/night.
&&
.FIRE WEATHER...
Issued at 322 PM MDT Thu Sep 8 2022
The red flag warning continues through 8 PM but all areas
across the region will recover tonight reaching 60-80% relative
humidity. No fire weather concerns through Friday with minimum
relative humidity trend above 30% for all areas. Scattered storms
and showers will occur mainly for South Park and the Palmer Divide.
There could be some high based showers in the eastern plains which
will produce wind gusts up 30-40 mph.
It will be cooler with higher humidities over the weekend,
especially on the plains, but significant rain is not likely.
There will be a warm and dry day or two early next week, but
strong winds are not expected, than a gradual increase in moisture
through the rest of next week.
&&
.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE.........RJK
SHORT TERM.....AD
LONG TERM......Gimmestad
AVIATION.......RJK
FIRE WEATHER...AD/Gimmestad
Area Forecast Discussion
National Weather Service Phoenix AZ
500 PM MST Thu Sep 8 2022
.UPDATE...Updated Aviation Discussion.
.SYNOPSIS...
Copious amounts of moisture will spread into the region through the
weekend with widespread moderate to heavy rainfall forecast across
southeast California and southwest Arizona Friday into Saturday.
Shower and thunderstorm activity may be more scattered towards the
Phoenix metro with not everyone seeing rainfall, however a few
locations potentially seeing brief heavy downpours. Storm chances
may persist in south-central Arizona early next week. Temperatures
will be substantially cooler over the weekend, and most lower
elevation communities will struggle to reach 100 degrees through
next week.
&&
.DISCUSSION...
Tracking tropical system Kay and associated surge of higher theta-e
airmass preceding the circulation center will be the primary
forecast challenge and major hazard over the next several days.
Early this afternoon, NHC places the center of Kay just offshore of
the Baja near 26N 115W in its last vestiges of a hurricane. The
system has already moved over cooler, unsupportive waters; and most
recent satellite imagery depicts drier air being absorbed into the
western half of the storm. Recent aircraft reconnaissance suggests a
downgrade in afternoon updates as the system continues its NW
trajectory hugging the Baja peninsula. Modeling remains very
consistent in rapid deterioration of this system as it stalls and
wobbles off the southern California coast before being absorbed into
the westerlies and a remnant negative PV center propagates through
Arizona early next week.
Global modes, ensemble members, and a full suite hi-res CAMs all
depict the outer, midlevel banding features periodically passing
into parts of the CWA and steadily lowering in the troposphere with
time. This afternoon and evening moisture was almost exclusively
concentrated above 700mb with dry, continental flow dominating the
H8-H7 layer. Thus, only virga, sprinkles and light showers have been
an issue in advance of the tropical system. However, there is
excellent agreement that a pronounced theta-e surge will occur
around or just after sunrise Friday where any remaining drier air
will be rapidly overcome by a record breaking type of deep moisture
profile (PWATs 2.00-2.50 inches). Tropical rainfall should advance
into SW AZ and SE CA behind this surge and have serious impacts
through the remainder of the day.
While the most serious impact will be the excessive rainfall
amounts, the trajectory of Kay and pressure gradient will support a
period of stronger winds along and immediately behind the initial
theta-e surge. HREF data supports H8 winds 40-45kt spreading across
the international border early Friday morning though the northern
extent of any stronger winds will be limited by the stalled nature
of the tropical system and weakening gradient. The moist environment
and limited lapse rates should restrict convective potential and
coverage, such that not all this momentum transfer will be realized.
However, enough evidence exists that a few areas could experience
very strong winds and an advisory has been issued along the
international border.
HREF membership supported by BUFR forecast soundings suggest the
pronounced moisture surge and most significant rainfall rates will
envelop SW AZ/SE CA late Friday morning with the critical time frame
Friday afternoon/evening. WPC indicates a moderate risk of excessive
rainfall resulting in flash flooding where rainfall amounts of 1-2
inches may be common. NBM probabilities of over 1 inch accumulations
are quite high at 35%, but by no means unrealistic. There are many
hi-res models supporting 2-4 inch rainfall totals across the western
half of Imperial County and even NBM odds show better than a 10%
chance of 2 inches or more at any given point. Keep in mind, this is
a region where the average annual rainfall in only 2-3 inches, so
these types of amounts (if realized) would create seriously
hazardous situations. In all likelihood, the rainfall accumulation
gradient will be steep expanding northeast from southern Imperial
and Yuma counties and the theta-e surge, and the greater areal
extent of 0.50-1.00 inches amounts will be more common than the
extreme, record breaking amounts to the south.
Farther away from the center of Kay`s circulation, lobes of
vorticity may bring a band or two of showers and embedded
thunderstorms into south-central Arizona Friday evening through
overnight. Although this activity (if it comes to fruition) should
be isolated to scattered in coverage, localized training of storms
could result in heavy rainfall in some spots, including the Phoenix
metro. At this time, probabilities are quite low for excessive
rainfall with NBM odds of greater than one inch in Phoenix under 5%.
The most obvious impact in eastern zones will be thick clouds,
increased humidity, and much lower temperatures (falling to a below
normal range).
As Kay continues to weaken Saturday, the circulation will slowly
drift west over the cooler waters of the East Pacific, however still
remain close enough to provide areas of ascent over the western
forecast area. While this could bring some additional shower
activity on Saturday, somewhat drier air wrapping into the
circulation could provide more breaks and more scattered coverage.
However, total column moisture levels will remain above average
keeping a slight threat for heavy rainfall with any shower/storm
activity. Elsewhere, persistent cloud cover and restricted surface
temperatures should hamper instability, and deep convection may be
restricted even over higher terrain.
Confidence is good that the remnants of Kay will spin nearly
stationary off the southern California coast through early next
week, with the remnant midlevel circulation and PV anomaly tracking
back through the SW Conus. Although considerable midlevel drying
will continue, abundant low level moisture should remain with
chances for showers and thunderstorms becoming focused again over
mountain areas. Conceptually, this pattern looks like a monsoon
transition event as deep troughing and stronger westerly flow will
accompany this remnant low. NBM POPs in a 20-40% range seem
applicable to such a transition event.
By the middle of next week, westerly dry flow is likely to spread
across the region ending rain chances once again. Temperatures next
week may warm back into the normal range with the drying, but
ensembles suggest H5 heights will mostly remain around 585dm as
broad upper level troughing moves into much of the Western U.S. and
lower elevation communities struggling to reach the 100F threshold.
&&
.AVIATION...Updated 0000Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Due to the influence of the approaching storm Kay, an atypical wind
pattern will prevail through the period. Current thinking is that
westerly winds will prevail thru at least the midnight-2 am
timeframe, then shift to easterly until around late morning-midday
on Friday, then gradually shift thru southerly then southwesterly
thru the afternoon hours. Periods of light/variable winds are also
possible as well. There is a chance for virga, or even a light
sprinkle thru tonight and Friday morning as well. Better chances for
showers are anticipated by Friday afternoon as deeper moisture from
the remains of Hurricane Kay move into the region. Chances for
showers and t-storms increase further Friday evening/night. At this
point, not confident enough to introduce anything more then VCTS in
the TAFs at this point, given the uncertainty of the timing of any t-
storms that do develop. Any t-storms that do develop will be capable
of producing gusty winds/brief heavy downpours.
Southeast California/Southwest Arizona including KIPL and KBLH:
At KIPL, light to moderate SE component winds will prevail through
this evening along with episodes VCSH. Tonight and Fri wind speeds
will increase to 10-15 kt with gusts of 20-35 kts along with showers
and even a period of steady rain by mid morning and low cloud CIGS
near 5 kft in/near showers. There is potential for winds gusts as
high as 40 kts Friday afternoon, periods of moderate-heavy rainfall,
and even an isolated t-storm as the low-level circulation (remains
of hurricane Kay) makes its closest approach. At KBLH, breezy SW-SE
winds to develop tonight and Friday with gusts of 20-30 kts. Periods
of VCSH today will be replaced with showers by mid Fri morning. BKN-
OVC cloud deck generally AOA 10-15 kft can be expected through the
period. However, CIGs may briefly lower to less 10 kft in shower
activity.
&&
.FIRE WEATHER...
A return of higher humidities will continue into the weekend as
moisture surges northward into the region as a result of a tropical
system tracking northward along the Baja peninsula. The rapid
increase of humidity and mostly cloudy skies starting today will
lead to cooler temperatures through the rest of the week. For Friday
into Saturday, much of the area will see very good chances (above
50%) for wetting rains with significant rainfall possible across
southeast California. Starting Sunday, wetting rain chances drop to
below 10% across the entire area as conditions begin to dry out
again. Minimum afternoon humidity levels will quickly improve over
the next couple days rising from 20-30% today to mostly above 40%
for Friday and Saturday. Winds Friday are expected to be driven by
the passing tropical system, leading to gusty southeasterly winds of
25-35 mph across the western deserts. Other than Friday, winds
should not pose any significant concerns with the typical diurnal
upslope gusts.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Wind Advisory from 2 AM to 5 PM MST Friday for AZZ532-535-536.
Flood Watch from Friday morning through Saturday evening for
AZZ530>533-535-536.
CA...Flood Watch from Friday morning through Saturday evening for
CAZ560>570.
Wind Advisory from 5 AM to 5 PM MST Friday for CAZ562-563-
565>567.
&&
$$
DISCUSSION...18/Kuhlman
AVIATION...Percha/Sawtelle
FIRE WEATHER...Kuhlman