Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/05/21

Southeast Alaska Forecast Discussion

National Weather Service Juneau AK

 251 PM AKDT Sun Jul 4 2021

.SHORT TERM...For days a murky layer of moisture has teased
forecasters across the northern Inner Channels. Models have
supported offshore flow and clearing for the last two or three
days, but the offshore never materializes, and hopes dash as
clouds may thin, yet persist into the afternoon/evening. After
multiple runs of suggesting the same thing, offshore winds began
making appearances in AMDAR soundings from Sitka into Juneau. And
the clouds began visibly eroding first from Upper Lynn Canal, then
to Downtown Juneau, and now only linger from Glacier Bay,
Chichagof, and Baranof west. Confidence increases now that many of
these locations may remain clear this evening, thus adding the
need for sunscreen for many celebratory activities. Along the
immediate coast, marine stratus might push back inland tonight,
but we feel stronger that it halts at Gustavus and stands
prevented from advancing any more eastward.

The southern Panhandle has enjoyed another day in full sun. Some
localized low clouds developed along the western edge of Prince of
Wales quickly burned away by mid-morning. A thermally driven
trough has been stationed days across the southern Panhandle and
Dixon Entrance. Thus persistent northwest flow through the
southern Inner Channels continues to insulate communities from the
cooler air masses across Hecate Strait. This afternoon/evening,
as the marine layer finally erodes across the north, that thermal
trough could migrate northward, inviting a possible evening
southeasterly into Ketchikan. This would definitely cause us to
shift gears in the forecast and draw in more marine stratus
through our southern entrances.

Now to what`s happening in central BC. The High CAPE values,
convection that initiated around noon, as well as some weak
vorticity for some lift have sparked several lightning strikes
east of Hyder. After a morning assessment, we had convinced
ourselves to remove it late this afternoon--after, of course,
monitoring trends. However, the early convective initiation caught
our eye, and with coordination from our friends in Vancouver, we
continue to support a slight risk of thunderstorms late this
afternoon and early this evening in Misty Fjords. The setup looks
more impressive Monday afternoon/evening, and thus its mention
Monday remains unchanged.

Changes to temperatures were reserved to increasing highs for
Ketchikan this afternoon and a slight warmup for Monday with
greater confidence of less cloud cover throughout the Inner
Channels. By Tuesday, the predicted pattern change shifts into
gear. A system in the western gulf spawns a front that brings a
chance of rain Tuesday with rain likely Tuesday night for Yakutat.
Chances of rain spread east into Gustavus Tuesday night as clouds
drive back into the Panhandle late Tuesday. Thus, we did lower
high temperatures on Tuesday much more significantly: by 2 to 7
degrees in most locations. With greater projected sun Monday and
a ridge migrating east from the gulf into the Panhandle, we raised
southerlies through Lynn Canal to 20 kt. Lynn Canal has been an
underachiever until this afternoon, as it has finally caught up
with our forecast due in part to a better sky forecast. Otherwise,
small craft advisories continue for 41/42 through Monday
morning/Sunday night respectively.

.LONG TERM.../Monday through Sat/ Upper level and surface ridging
continues to be the dominate weather makers for at least the
first half of the long range. The second half of the long range is
mainly dominated by a broad upper low dropping SE into the
Western gulf from the Bering Sea area mid week. The overall trend
is toward wetter weather for most of the panhandle by mid next
week as the upper level and surface ridge get pushed E.

The main areas of contention for the long range remains how long
the ridging (and dry weather) hangs on before giving way to the
upper low (and the precip it will bring), and where that upper low
eventually ends up toward the end of the extended. For the
former, guidance has again pushed the onset of precip back another
12 to 18 hours. Rain is now expected to push into the Yakutat area
on Tue with the rest of the panhandle getting in on the act Tue
night into Wed. Forecast confidence is still about average or
lower though as future model runs could continue to delay the rain
even further into the week.

As for where the upper level low goes, possibilities range from
the central gulf to S of the Alaska Peninsula late next week. The
farther w solutions are hinting at a return of dry weather for
late next week as the system will be far enough w to allow the
surface ridge to rebuild over the eastern gulf keep rain over the
western gulf. On the other hand, the central gulf solutions keeps
the panhandle wet into the weekend as no surface ridge develops
and southerly flow dominates. A chance of rain and mostly cloudy
skies remains in the forecast as a result of this uncertainly on
where the upper low eventually goes.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ041-042.

&&

$$

JWA/KRT

Visit us at http://www.weather.gov/Juneau



Area Forecast Discussion

National Weather Service Denver/Boulder CO

 802 PM MDT Sun Jul 4 2021

.UPDATE...
Issued at 757 PM MDT Sun Jul 4 2021

Most convection has ended except across sern Lincoln county and
srn Park county. This convection will end in the next or two.
Overall will only make a few minor changes to current fcst.

&&

.SHORT TERM...(This evening through Monday)
Issued at 227 PM MDT Sun Jul 4 2021

Convection has initiated over the higher terrain with moderate to
heavy rain and isolated severe hail with lightning being the main
impacts. With the strengthening ridge upper level flow has slowed
allowing for slower moving storms and slightly increased flood
potential. Current CAM projections show the storms moving over the
urban corridor and east ward through the early evening hours.
Dewpoints still sit in the upper 40s to lower 50s with ACARs
soundings showing little cap left to detour storms moving across the
area. Improving conditions along the foothills and I-25 corridor are
anticipated after 8 pm with clearing across all areas after 9 pm.
Overnight lows will continue to be on the more mild side with
temperatures in the lower 60s with partly cloudy skies.

For Monday, the upper ridge will be in place over the four corners
region with PW values still hovering over an inch across the plains
into the afternoon. Weak flow aloft and 700 mb temperatures a few
degrees higher then today will bring highs into the lower to mid-90s
once again for the plains. A shortwave embedded in the upper west to
northwest flow aloft will push through later in the evening
increasing storm coverage over the higher terrain starting around
noon and then moving onto the plains after 4 pm. Current CAMs show a
few rounds of storms from the influence of the shortwave keeping
storms developing and moving eastward well into the overnight hours.
With high PW values, skinny CAPE signatures, and weak steering winds
of less than 10kts through 500 mb there is increased potential for
flash flooding across area burn scars and lower elevations. Will
continue to to monitor model trends with these parameters, however a
watch may be needed.

.LONG TERM...(Monday night through Sunday)
Issued at 227 PM MDT Sun Jul 4 2021

For Monday night, Northern Colorado will still be under a slow
moving upper disturbance which will have lingering impacts into
Tuesday. Moisture levels will remain quite high Monday night with
precipitable water values close to 1.25" over the Front Range and
plains and slightly less west of the Continental Divide. Main
impacts will be a flash flood potential for the stronger storms
over the burn areas Monday evening. Beyond the evening, expect
lingering scattered rain showers a good bet through the night and
potentially into Tuesday morning. Expect quite a bit of low level
moisture/low clouds through Tuesday morning. The trof axis looks
to move through the area Tuesday morning with a more subsident and
drying airmass moving in Tuesday afternoon. Focus for any
stronger convection on Tuesday would likely shift over southern
portions of the county warning area. Cross sections and forecast
soundings showing substantial drying above 700mb for the
afternoon. There is some inconsistencies within the models, as the
European solution is slower moving the trof across on Tuesday so
will blend some compromise solution and will keep some low pops
over Northern Colorado into Tuesday afternoon.

For the rest of the week, Colorado weather will be dominated by a
broad ridge of high pressure building over the Great Basin and
interior western U.S. This will lead to mainly dry conditions expect
just isolated late day showers/thunderstorms. Temperatures will
remain above normal with afternoon readings well into the 90s. There
is a trof which will sweep across the northern high plains on late
Thursday and Friday which will cause the high pressure ridge to
retrograde westward. This will result in some cooling on Friday and
into the weekend, closer to seasonal normals. Moisture still looks
limited so only slight chances of late day storms.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 757 PM MDT Sun Jul 4 2021

Winds have become south at DIA and should stay that general
direction overnight. Otherwise VFR conditions thru 12z.

&&

.HYDROLOGY...
Issued at 227 PM MDT Sun Jul 4 2021

Increased flash flood threat for Monday on the burn areas starting
after 1 pm and continuing into the evening hours. Storms will be
slower moving and could produce a tenth up to 4 tenths of rain
within 30 min or less with the stronger storms. These conditions
warrant an elevated threat across the burn areas.

Flash flood threat will be higher Monday evening with deep
moisture in place. Expect a drying trend from late Tuesday
through the end of the week with a much lower threat for flash
flooding in the burn scars.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...RPK
SHORT TERM...Bowen
LONG TERM...Entrekin
AVIATION...RPK
HYDROLOGY...Bowen/Entrekin



Area Forecast Discussion

National Weather Service Phoenix AZ

 410 PM MST Sun Jul 4 2021

.SYNOPSIS...
Good chances for showers and thunderstorms will continue today
across eastern Arizona with isolated storms possible into the south-
central Arizona deserts. Heavy rainfall capable of producing flash
flooding will be the main impact. Much drier conditions will then
settle in for Monday through at least Wednesday with only isolated
storm chances over the eastern Arizona high terrain. Temperatures
will also warm to a few degrees above normal for much of the coming
week with highs mostly in a 109 to 112 degree range across the lower
deserts. A gradual return of monsoon moisture should bring back more
widespread rain chances by next weekend.

&&

.DISCUSSION...
Central Arizona is currently situated between two smaller mid-
tropospheric anticyclonic circulations, one across the central Baja
peninsula and another south of the Four Corners. Latest satellite
imagery also reveals the lingering vort max across northern Sonora,
which has helped to already initiate convection across southern
Arizona. Meanwhile, latest observations reflect what is typically
seen the day after widespread shower and thunderstorm activity.
Temperatures across south-central Arizona are struggling to reach
the 100 degree mark, while dewpoints are well above normal in the
mid to upper 60s. PWATs are also running near all-time daily records
with the PSR morning sounding registering 2.01 inches. Theres been
little change during the day indicated by the latest KPHX ACARS
sounding at 2.08 inches.

The abundant moisture is yielding a widespread area of MLCAPE above
1000 J/kg across southern and eastern Arizona, while mid-level lapse
rates are weak and near moist adiabatic. Latest mesoanalysis
indicates a dearth of DCAPE and consequently the chance of strong
winds and blowing dust is low. Convective parameters essentially
point to the potential for heavy rain this afternoon and evening.
Weak steering flow will also result in slow-moving storms capable of
producing flash flooding, particularly across the burn scars in the
higher terrain east of Phoenix.

Convection has already initiated across far southwestern Maricopa
County and additional isolated storms are likely to develop across
the higher terrain north and east of Phoenix this afternoon.
However, CAMs including the time-lagged HRRR continue to trend
towards less overall coverage. This is largely due to a pronounced
warm and dry layer evident around 800 mb, which is resulting in
detrimental convective inhibition, generally from Phoenix westward.
Nevertheless, an isolated cell or two in the Valley remains a
possibility, given the excessive moisture. PoP for this evening has
been lowered based on the latest trends in the NBM and several CAMs.
A few models also hint at the possibility of early morning shower
activity across the lower deserts and this certainly cant be ruled
out, considering there will likely be areas of leftover instability.

&&

.PREVIOUS DISCUSSION...
The westerly drying will continue Monday into Tuesday with a
capping inversion aloft likely shutting down storm chances in all
but the high terrain on Monday. By Tuesday, afternoon surface dew
points are seen dropping into the 40s areawide and PWATs lower to
around 1.00" resulting in only a few isolated storms possible over
far eastern Arizona. The upper level ridge center is forecast to
shift into Nevada Tuesday before drifting back over southern Utah
and northern Arizona later in the week. H5 heights will also
increase slightly reaching 591-594dm across the Desert Southwest.
The drying boundary layer and increased heights aloft should push
daytime highs to around 110 degrees in the Phoenix area to 110-113
degrees across the western deserts for Tuesday and Wednesday.

After the somewhat dry period during the half of the week, models
remain in good agreement showing modest moisture return out of the
east and northeast once the high center shifts closer to the Four
Corners area. The moisture advection may start as early as
Wednesday, expanding through much of southern Arizona on Thursday
and Friday. This should expand storm chances westward by next
weekend, but as usual chances will be greater over the eastern
Arizona high terrain. Temperatures may also begin to moderate
slightly late in the week as moisture increases, but we will be
going against a strengthening ridge as ensemble output agrees the
ridge center strengthens and H5 heights increase to around 598dm
just to our north.

&&

.AVIATION...Updated at 2310Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
West winds 10-15kt will continue through mid evening, then looking
at the possibility of a distant outflow boundary turning the
direction to east. HREF guidance shows a 30-40% probability of
outflow winds exceeding 30 kts this evening during a 02Z-05Z time
frame. NBM output shows around 15% chance of storms this evening and
overnight, but have no mention in these TAFs. SCT-BKN clouds mostly
aoa 10 kft will continue throughout much of the period. NBM storm
chances at any site Monday is less than 10%.

Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will continue to favor a southeast to southwest component at
the terminals through the next 24 hours with speeds mostly remaining
aob 12kts. FEW clouds are expected through the period with bases
remaining aoa 10 kft.

&&

.FIRE WEATHER...
Wednesday through Sunday:
Moisture will decrease gradually through the midweek period, which
will generally confine the threat of storms to the eastern Arizona
high terrain. A return of deeper moisture looks likely late in the
week with storm chances potentially increasing and expanding
westward across Arizona. Temperatures for the bulk of the period
will run a few to several degrees above normal. Min RH values will
generally be in a 10-20% range midweek with higher values over the
higher terrain before improving to 15-25% late in the period. Max
RHs will recover into the 30-45% range for most locations. Apart
from thunderstorms, wind patterns will follow diurnal patterns.

&&

.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.

&&

$$

DISCUSSION...Hirsch
PREVIOUS DISCUSSION...Kuhlman
AVIATION...Smith/18
FIRE WEATHER...Hirsch/Kuhlman