Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/02/23
Area Forecast Discussion
National Weather Service Flagstaff AZ
905 PM MST Fri Sep 1 2023
.SYNOPSIS...Subtropical moisture will continue to overspread the
Grand Canyon State this weekend with the chance for heavy rain
and potentially flash flooding through the first half of the
weekend. The latter half of the weekend and into the first full
week of September will bring rain- free conditions and warmer
daytime temperatures.
&&
.UPDATE...Scattered showers and isolated thunderstorms continue to
move northward across northern Arizona this evening. Updated
forecast earlier to increase the PoPs over eastern portions of
northern Arizona. These showers will slowly dwindle as the
evening progresses. Water vapor imagery is showing a rotation
moving north-northeastward across central Arizona this evening and
a decaying thunderstorm complex near Yuma...moving north-
northeast. This will keep chances of showers higher in our western
zones through the night.
&&
.PREV DISCUSSION /202 PM MST/...For the rest of this afternoon,
showers and thunderstorms continue to lift northward out of
northern Mexico and adjacent portions of Arizona. This convection
is rather robust (-70 C degree cloud tops), and the near-storm
environment---per ACARS data from Phoenix Sky Harbor---suggests
MLCAPE values just under 1500 J/kg. This is a bit higher than
suggested by the 12 UTC HREF CAPE probabilities, so some
adjustments to the near term forecast have been warranted with a
slight trend upward in PoPs across mostly Yavapai County where
the PHX ACARS is likely sampling a similar environment. There`s
been a consistent signal in some of the hi-res NWP, including
experimental Warn-On-Forecast output, in more vigorous convection
across the western Coconino Plateau and up toward the Glen/Marble
Canyon areas. Fortunately, the cloud bearing flow is around 20-30
knots which should foster swift storm motions and minimize the
flash flood threat. However, training storms (especially over any
burn scars or slot canyons) can still present a flash flood
threat and individuals should remain vigilant.
For this evening and tonight...There remains a mixed signal from
guidance regarding the potential for a couple of late evening and
overnight rounds of convection. Recent iterations of the HRRR
have suggested an increase in showers/storms across two areas of
northern AZ over the next 4-8 hours; 1) eastern Yavapai County and
adjacent parts of Gila and Coconino counties and 2) across Navajo
and Apache counties. While I do believe the trends in the HRRR to
be reasonable, the magnitude of convection in area #1 seems
overdone as widespread cloud cover has gripped the region, thereby
resulting in a sharp gradient between the higher instability
closer toward the Phoenix Metro area and more stable air farther
north. For now, I`ll nudge PoPs upward to show a greater coverage
of mostly showers here. Area #2 is a bit more realistic in terms
of more robust convection as daytime heating has helped to
generate a bit more in the way of instability (satellite supports
this with the deeper cumuliform clouds). PoPs have been adjusted
here accordingly as well. Another round of convection may develop
as additional moisture streams northward, largely across eastern
Yavapai and adjacent parts of Gila and Coconino counties.
For Saturday, the focus for heavy rainfall appears that it`ll be
confined to Yavapai and western Coconino counties (and points
westward). Sufficient mid/upper level moisture will continue to
funnel northward with even indications from the latest Extreme
Forecast Index or EFI of QPF anomalies (compared to the model
climatology) across these areas. In short, confidence is high from
model guidance that heavy rainfall will transpire on Saturday
across this area. As a result, the Flash Flood Watch is in fine
shape and no alterations are needed with this forecast cycle.
Sunday and into next week will feature moderating temperatures
and rain-free conditions as dry southwesterly flow envelops the
Pacific Southwest. In fact, the dry airmass will result in some
anomalously low precipitable water values (approaching 20-30% of
normal in some of the ensemble guidance). This translates to PoPs
of 5% or less across much of the High Country. A welcomed sign for
some (not me)! Temperatures at the start of the work week will
initially remain 5 to 10 degrees below normal before climbing to 5
to 8 degrees above normal by the middle to end of next week.
&&
.AVIATION...For the 06Z TAF Package...VFR and occasional MVFR
conditions will continue through the next 24 hours. Scattered to
numerous showers and thunderstorms are forecast tonight and
Saturday, with best coverage west of a KPAN-KFLG-KPGA line. Some
thunderstorms will produce heavy rainfall and gusty, erratic winds
in excess of 30 knots. Otherwise, mainly southwest winds of 5 to 15
knots, with gusts up to 25 knots are expected. Aviation discussion
not updated for TAF amendments.
&&
.FIRE WEATHER...Saturday and Sunday...Cooler with scattered to
numerous showers and thunderstorms on Saturday with the best
coverage west of a Payson-Flagstaff-Page line. Decreasing coverage
on Sunday with mainly isolated activity. Heavy rainfall and gusty,
erratic outflow winds of 30 mph or more are expected at times. Away
from showers and storms, expect mainly southwest winds at 10 to 20
mph.
Monday through Wednesday...Breezy and dry. Southwest winds at 10 to
20 mph with afternoon gusts up to 30 mph.
&&
.FGZ WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Saturday evening for AZZ004-006>008-015-037-
038.
&&
$$
PUBLIC...MAS/Bain
AVIATION...McCollum
FIRE WEATHER...McCollum
For Northern Arizona weather information visit
weather.gov/flagstaff
Area Forecast Discussion
National Weather Service North Platte NE
1002 PM CDT Fri Sep 1 2023
.SYNOPSIS...
Issued at 219 PM CDT Fri Sep 1 2023
Key Messages:
- Heat builds in this holiday weekend, with record breaking
temperatures possible. A Heat Advisory has been issued for
portions of far north central Nebraska from 1 PM Saturday
through 8 PM CT Sunday. Precautions must be taken to avoid heat
related illness. Protect, hydrate, and plan!
- Near-critical to critical fire weather conditions are possible
tomorrow across southwest Nebraska (Fire Weather Zones 210 and
219) where a Fire Weather Watch is now in effect from 12 to 7
PM MT/1 to 8 PM CT Saturday. For more information refer to the
Fire Weather Discussion.
- Hot, dry, and windy conditions persist Sunday and Monday
resulting in continued increased fire weather concerns across
portions of the area for both days.
- A cold front is expected to sweep across the area Monday night
bringing relief from the seasonally hot temperatures for the
middle of next week and the next shot for rain and/or
thunderstorms to portions of northwest Nebraska.
Recent GOES-16 WV and RAP 500-mb analysis showed high pressure
building across the southern Rockies and southern Plains. Further
northwest of this feature, an upper-level closed low pressure system
was centered across Washington/Oregon with a trough extending south
into southern California. Another upper-level low was centered
across Manitoba with a trough extending southeast across the Upper
Midwest. A weak shortwave was apparent on the northwest periphery of
the ridge, tracking across the central Rockies and Laramie Range.
All of these features has led to west-southwesterly flow aloft
across western and north central Nebraska. At the surface, low
pressure was centered across the Panhandle of Nebraska with a trough
extending southwest across eastern Colorado. Surface high pressure
was anchored across New England, encompassing the eastern third of
the US.
A tight surface pressure gradient (SPG) has set up between
the two surface features across the region, resulting in gusty
southerly winds with recent area observations of 20 to 25 mph. At
3 PM CT, temperatures ranged from 83 degrees at Gordon to 100
degrees at Imperial. Combination of the gusty winds, low relative
humidity, and hot temperatures has resulted in critical fire
weather conditions across far southwest Nebraka where a Red Flag
Warning remains in effect through 7 PM MT/8 PM CT this evening for
Fire Weather Zone 210.
&&
.SHORT TERM...(This evening through Sunday)
Issued at 311 PM CDT Fri Sep 1 2023
The southerly breezy winds currently being observed across the area
will continue into the overnight period as the nocturnal low-level
jet (LLJ) ramps up across the region. This combining with the tight
SPG across the area will lead to wind gusts of 20 to 25 mph being
common for north central and southwest Nebraska with localized gusts
up to 30 mph possible. The Panhandle and northwest Nebraska are the
exception to these breezy winds due to the SPG/LLJ being maximized
further to the southeast. Overnight lows will fall into the 10 to 20
degree above normal range in the 60s to near 70 degrees. This
anomalous heat builds in further as we head into Saturday and
Sunday.
The aforementioned upper-level low currently across Manitoba will
exit eastward, allowing the pesky upper-level ridge to build further
into the region Saturday. This will allow September and
Meteorological Fall to kick off with well-above normal temperatures
for the Holiday Weekend. Daytime high temperatures in the upper 90s
to low 100s will be felt across western and north central Nebraska
Saturday and Sunday. Though forecast heat indicies are not as high
as the August 21st - 24th period, heat of this magnitude is unusual
for this time of year and will pose a health risk to those who do
not take precautions to avoid heat related illness. The signal for
anomalous heat across central and western Nebraska is highlighted by
the EFI/SoT (Extreme Forecast Index/Shift of Tails) for Saturday and
Sunday. Given this, have decided to issue a Heat Advisory for
portions of far north central Nebraska from 1 PM Saturday afternoon
to 7 PM CT Sunday. If you plan to spend time outside during the
holiday or participate in school year outdoor activities, make
sure to stay hydrated and dress in loose-fitting, lightweight, and
light colored clothes. Though it will not bring much relief from
the heat, breezy southerly winds are expected to continue across
north central and southwest Nebraska for both days with gusts up
to 25 mph and locally higher gusts of 30 mph possible.
.LONG TERM...(Sunday night through Friday)
Issued at 311 PM CDT Fri Sep 1 2023
The aforementioned PNW upper-level trough will will swing into
the Great Basin late Sunday into Monday, shunting the stubborn
upper-level ridge further east. With decreased influence from the
heat dome and the approach of a surface cold front temperatures
fall back just a few degrees. High temperatures are forecast to
range from near 90 degrees across northwest Nebraska to near 100
degrees across the southwest. The previously mentioned cold front
will sweep across the area through Monday night bringing much
relief from the heat on Tuesday and Wednesday where highs fall
back to at or slightly above normal. The next shot of
precipitation is expected late Monday into early Tuesday as the
cold front tracks through western and north central Nebraska
bisecting PVA off the upper- level trough moving across the
northern Rockies. This will result in scattered rain and/or
thunderstorm development off the higher terrain to the west to
move into the local area. Despite these chances, widespread
wetting rainfall is not expected and locations who do see
precipitation are forecast to see a few tenths of an inch at best.
Additional disturbances eject across the area through the latter
end of the week which may lead to sporadic isolated rain and/or
thunderstorms chances. However, limited lift and forcing results
in lowered confidence in this potential with dry conditions likely
to continue well into next weekend. Unfortunately (at least for
those who don`t like anomalous heat), ensemble solutions are in
general agreement that the ring of fire builds into the Desert
Southwest for the latter end of the week into the weekend bringing
more days of above normal temperatures. This is in agreement with
the CPC 6-10/8-14 Day Temperature Outlook favoring above normal
temperatures for the region.
&&
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 648 PM CDT Fri Sep 1 2023
Expect VFR conditions and dry weather across central and western
Nebraska through Saturday with mid/high clouds increasing from the
west. However, winds and wind shear will impact aircraft operations
this TAF period.
Winds will be gusty this evening into early tonight. The gusts may
become a bit sporadic as time goes on, but will maintain the gusts
through around 06Z. A robust southerly/southwesterly low level jet
will once again become established overnight into early Saturday
morning. Low level wind shear can be expected with winds just off
the surface around 45kt from about Midnight through daybreak.
However, based on trends last night do not expect much opportunity
for mixing in the boundary layer after Midnight so will not
mention gusts overnight at KLBF or KVTN. Onset of diurnal heating
and boundary layer mixing Saturday morning will eventually
generate some gusty conditions by late morning/early afternoon.
Gusts persist Saturday afternoon with good mixing thorugh the end
of the valid period.
&&
.FIRE WEATHER...
Issued at 219 PM CDT Fri Sep 1 2023
Dry, hot, and windy conditions will result in increased fire
weather concerns through the weekend and the start of next week.
Widespread near-critical (and locally critical) fire concerns are
expected Saturday across southwest Nebraska. Though the breezy
winds will be more marginal on Saturday as compared to today,
minimum relative humidity values bottom out as low as 13 percent.
After discussing fuel status with local fire officials, fuels have
reached a volatile state and additional drying is certain over
the next few days further increasing concerns. Per fire weather
officials, any fires that develop will likely spread rapidly even
if criteria is not being met for winds. Thus, in collaboration
with neighboring offices, did decide to issue a Fire Weather Watch
for Fire Weather Zones 210 and 219 across southwest Nebraska for
Saturday afternoon into Saturday evening.
Fire weather concerns remain elevated to near-critical on Sunday
and Monday with continued low humidity and gusty winds. However,
limited overlap of strongest winds and lowest relative humidity
minimums will preclude any headlines for both days.
&&
.CLIMATE...
Issued at 334 AM CDT Fri Sep 1 2023
Forecast Highs/Record Values (Years set)
Sat 09/02 | Sun 09/03
North Platte 102/101 (1947) | 100/ 99 (1960/`54)
Valentine 102/103 (1983) | 101/102 (1990)
Broken Bow 100/ 99 (2022/`39)| 99/ 99 (1960)
Imperial 102/106 (1922) | 101/103 (2017)
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM CDT /noon MDT/ Saturday to 7 PM CDT /6
PM MDT/ Sunday for NEZ005>010.
Fire Weather Watch from Saturday afternoon through Saturday
evening for NEZ210-219.
&&
$$
SYNOPSIS...Viken
SHORT TERM...Viken
LONG TERM...Viken
AVIATION...MBS
FIRE WEATHER...Viken
CLIMATE...CDC/Viken