Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 11/07/20
Area Forecast Discussion...Updated
National Weather Service Phoenix AZ
500 PM MST Fri Nov 6 2020
.UPDATE...Updated aviation discussion.
&&
.SYNOPSIS...
Well above normal temperatures will continue today, but a cooling
trend will also begin. A much more drastic cool down is then
expected Saturday as a low pressure system moves through the
region. It will also bring breezy to windy conditions and a chance
of rain with the best chances over the high terrain. Another
system will follow closely behind later on Sunday bringing a
better chance of precipitation. That second system is expected to
exit the region by Monday afternoon. Below normal temperatures
will continue through much of next week.
&&
.DISCUSSION...
Latest water vapor imagery depicts the remnant moisture of
post-tropical cyclone Odalys advancing northeastward into the Desert
Southwest. Consequently, it is not entirely surprising the PWAT of
0.7 inches from this morning`s KPHX ACARS sounding is considerably
above normal. Mostly cloudy skies persist across the area today and
an isolated thunderstorm has even managed to develop near El Centro
in the Imperial Valley. Latest HREF indicates the threat for showers
and isolated thunderstorms will persist across southeastern
California and southwestern Arizona into this evening.
Elsewhere, latest runs of the HRRR suggest sprinkles and isolated
showers will also be possible further east across portions of central
Arizona. Despite the clouds and isolated precipitation, well-above
normal temperatures are expected again this afternoon after setting a
new high minimum of 72 degrees in Phoenix this morning. Forecast
high temperature of 93 degrees would fall only one degree shy of the
daily record of 94 degrees set in 2007.
The focus for precipitation will shift eastward tonight and Saturday
as an anomalously strong low pressure system dives into southern
California. The higher terrain north and east of Phoenix will be
favored for precipitation, given the widespread vorticity-forced
ascent and localized orographic lift due to the strong level-wind
fields. This will translate into generally breezy conditions, which
could result in areas of blowing dust, particularly across
southeastern California.
WPC QPF will be utilized which indicates a few hundredths of an inch
of rain in the Valley, but up to an inch of rain in the Superstitions
through Sunday morning. Models then depict a discernible break in the
action before precipitation redevelops ahead of the next anomalous
Pacific closed low. Although PWATs will be considerably lower with
this system Sunday, it will also be colder and capable of producing
beneficial rainfall, given the well-defined jet-forced ascent,
particularly Sunday night and early Monday.
Highest rainfall totals are again expected across the higher terrain
north and east of Phoenix, however rainfall coverage will likely
extend further into the lower deserts. Precipitation is expected to
taper off Monday morning and with much cooler air behind the cold
front, very light snow accumulations will be possible across eastern
Gila County above 5500 ft in elevation. Across the lower elevations,
latest NBM guidance is exhibiting a tight spread and suggests
temperatures will likely struggle to reach the lower 60s.
Overall pattern next week will feature a longwave trough across the
western CONUS. This will result in a continuation of the below
normal temperatures, though a warming trend is likely as thicknesses
gradually increase.
&&
.AVIATION...Updated at 0000Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
There are several aviation issues over the next 24 hours as a series
of low pressure systems impact the central deserts: wind, wind
shear, CIGs and precip. First short wave to quickly move northeast
and across the area this evening will result in isolate high based
showers through about 07z. As such, have VCSH in the TAFs starting
around 02-03z. CIGS will be on the high side tonight, mostly 10k
feet or higher with this weaker wave. As another stronger wave
approaches Saturday, lower cloud decks develop with SCT-BKN decks 6k
or above develop during the morning. There will be a chance of
showers developing during the afternoon, confidence is not overly
high on when they will start but based on a variety of high res
models, will put PROB30 groups into the TAFs with precip starting by
around 21z Saturday. Do not expect any thunder, and precip amounts
should be rather light. May see CIGs lower a bit under the heavier
showers and down to around 5k feet at times.
Wind and wind shear will be the other issues. After a few hours of
rather light west/southwest wind early this evening, the wind will
start to back and then become stronger and locally gusty after
midnight. Wind shifts to southeast at KPHX likely to be starting
around 03z. Sustained speeds after midnight could exceed 10kt at
times with some gusts into the teens possible. During the evening,
after about 02z, we may still have some LLWS as south/southwest
winds from 2 to 5k feet pick up to 30kt or higher. Thus some TAFs
will see LLWS for several hours. After midnight, as winds increase
the shear should start to taper off. By late morning Saturday winds
should turn more to the south and become locally gusty, then
becoming southwest to west by 21z with gusts over 20kt possible.
Southeast California/Southwest Arizona including KIPL and KBLH:
For the most part, weather issues over the western deserts should
mainly be confined to winds, as precip should be minimal and mainly
impacting KIPL during the afternoon on Saturday. Look for elevated
southwest winds tonight at KBLH with gusts up to 20kt during the
evening. Stronger south/southwest winds expected Saturday afternoon
ahead of an approaching low pressure system; look for gusts over
25kt possible during the afternoon. At KIPL we will see southwest
winds develop and increase early this evening with gusts over 20kt
at times overnight and by noon Saturday they should continue to
increase with gusts over 30kt likely by 20z. Although there may be
some patchy blowing dust with stronger gusts, confidence in amount
of dust and effects on visibility are on the low side so no mention
of restricted vis made in the TAFs with the latest issuance. At KIPL
there may be a few showers developing in the afternoon with SCT-BKN
decks in the 8-12k range for the most part. No heavy rain expected.
&&
.FIRE WEATHER...
Monday through Friday:
Valley rain and high-elevation snowfall associated with
a cold front will taper off Monday. In its wake, a gradual
warming trend is anticipated, however well-below normal temperatures
will persist through the week. Winds will also return to more
seasonable speeds, generally between 5 and 10 mph for most locations
through the week. Meanwhile, moist conditions Monday will give way
to min RHs in the 20s by Tuesday.
&&
.CLIMATE...
Record highs this week:
Date Phoenix Yuma El Centro
---- ------- ---- ---------
Nov 6 94 in 2007 96 in 1988 96 in 1988
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...Wind Advisory until 7 PM PST Sunday for CAZ562.
&&
$$
DISCUSSION...Hirsch
AVIATION...CB
FIRE WEATHER...AJ/Kuhlman
CLIMATE...MO
Area Forecast Discussion
National Weather Service Great Falls MT
814 PM MST Fri Nov 6 2020
.SYNOPSIS...
Some rain and snow showers will continue for the Rocky Mountain
Front and adjacent plains this evening, then diminish briefly
overnight. Precipitation, mostly rain at lower levels, will
return south of the Canadian border tomorrow morning, and expand
in coverage through the day. The developing potent winter storm
will then change the rain to all snow Saturday night, which will
continue through Sunday night, as temperatures fall to around 20
degrees below normal. Strong northerly winds will also cause
widespread blowing snow over the plains. Snow will move out on
Monday, but cold temperatures will linger through the week.
&&
.UPDATE...
The expected upper level trough digs southward through southern
California along the U.S. west coast, as The Treasure State awaits a
major winter storm. The forecast is transpiring as expected, with
observed grids in very close agreement with forecast grids;
therefore, no update to the forecast will be made, at this time.
- Fogleman
&&
.DISCUSSION...
Rest of today through Monday...Confidence is very high that a major
winter storm will bring significant impacts to portions of the
Northern Rockies from Saturday through Monday morning. Models
continue to be in very good agreement with the track and evolution
of both the upper level low/troughs and surface low over the period.
Models also remain very aggressive with the surface high building
south along the Canadian Rockies behind the re-enforcing cold front
Saturday night through Sunday morning, which will send a surge of
pressure rise across the region and lead to a period of strong
northwest winds following its passage. Furthermore, as the main
storm lifts northeast into/over Eastern Montana and the Western
Dakotas it will rapidly strengthen, with additional strong northwest
to north surface winds expected across Central and North Central
Montana (H850 winds are expected to reach 35-45kts from Saturday
night through Sunday night).
The combination of these strong surface winds and intense
snowfall rates is expected to lead to whiteout conditions over a
large portion of Central and North Central Montana, which has
necessitated the need to upgrade the Winter Storm Watch to a
Blizzard Warning for the Rocky Mountain Front, Eastern Glacier,
Toole, Liberty, Hill, Eastern Pondera, Chouteau, Eastern Teton,
and Cascade. Travel within the Blizzard Warning is expected to
become very hazardous, if not impossible Saturday night through
Sunday. The Winter Storm Watch for Blaine, Judith Basin, and
Fergus Counties was also upgraded to a Winter Storm Warning due to
the expected snowfall totals and reduced visibilities; however,
these areas will need to be monitored closely as winds/visibility
could approach blizzard criteria. The Winter Storm Watch for
Central and Southern Lewis and Clark, Meagher, Jefferson, and
Broadwater Counties was also upgraded to a Winter Storm Warning,
with the remaining watch for Beaverhead, Madison, and Gallatin
Counties being left as is due to lower confidence in snowfall
amounts and ultimate impacts.
The main takeaways with this major winter storm over the weekend are
as follows : (1) conditions will rapidly deteriorate Saturday
afternoon/evening; (2) northwest-to-north winds will increase
significantly Saturday night and remain strong through Sunday night
over Central and North Central Montana, which will lead to
significant reductions in visibility due to blowing snow and cause
widespread drifting snow; (3) some rural and non-maintained roadways
could become impassable due to drifting snow; (4) snowfall rates
could approach 1-2" per hour Saturday night through Sunday
afternoon, especially over Central and North Central Montana; (5) a
50-100 mile band of 16-24" of snow is possible along/near the US Hwy
87 corridor, but confidence in its ultimate placement is still a
little uncertain; and (6) 2-day November snowfall records could fall
across much of Central and North Central Montana when this storm
finally wraps up Monday. - Moldan
Monday through next Friday...A brief period of upper level
ridging Mon keeps the area dry with a chance of breezy westerly
downslope winds on the Plains. The downslope winds may continue
some for north-central MT on Tues, with temperatures at lower
elevations getting into the low to mid 30s. However, a new
shortwave will push into western MT on Tues, and work into our
CWA by Tues evening and night. As of now, it looks like it should
be cold enough for precip with this system to be almost all snow.
However, for now it appears that most snow will remain in the
mountains Tues and Wed, with limited QPF and accumulations at
lower elevations. The progressive pattern continues with another
shortwave ridge quickly sliding across the area Thu and Fri,
possibly bringing most areas into the 30s by Fri. However, yet
another trough may start working into W & SW MT on Friday, though
there remains substantial disagreement among models on the speed
of this feature. Some are holding off precip over our area until
Sat, so POPs east of the Divide are kept on the lower side for
Friday. -Kredensor
&&
.AVIATION...
550 PM MST Fri Nov 6 2020 (07/00Z TAF period)
North-central Montana (KCTB/KHVR):
Begin this TAF period with IFR conditions at KCTB. Conditions
increase to the MVFR range by 07/02Z and continue MVFR until toward
the end of this TAF period when IFR conditions are forecast, again.
Additionally, gusty north-northwesterly winds to 25KT are forecast
for the end of this TAF period, impacting light aircraft.
VFR conditions prevail at KHVR until 07/14Z when this airfield
experiences reduced visibility in precipitation and lowering
ceilings. MVFR conditions are forecast for the remainder of this TAF
forecast period.
Central to Southwest Montana (KHLN/KGTF/KLWT/KBZN/KEKS/KWYS):
KGTF begins this forecast period MVFR due to low ceilings, and
continues MVFR for the duration of this TAF period. All other
central to southwest Montana airfields begin VFR. Between 07/18Z and
07/22Z, all of these airfields fall into the MVFR range in
association with the onset of precipitation. Gusty winds to 32KT are
forecast at KEKS and KWYS after 07/16Z. Additionally, low level wind
shear is included in the KLWT, KEKS and KWYS TAFs. Expect the
associated turbulence.
Throughout the region:
Expect mountain obscuration and aircraft icing conditions.
Refer to weather.gov/zlc for more detailed regional aviation weather
and hazard information.
&&
.PRELIMINARY POINT TEMPS/POPS...
GTF 34 44 17 20 / 10 80 100 100
CTB 31 34 14 18 / 60 90 100 100
HLN 34 52 18 22 / 0 80 100 100
BZN 33 61 20 23 / 10 60 100 100
WYS 30 53 22 28 / 10 70 100 100
DLN 34 59 18 21 / 20 60 100 100
HVR 36 47 18 25 / 10 70 100 100
LWT 34 54 18 22 / 10 60 100 100
&&
.TFX WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning from 8 PM Saturday to 6 AM MST Monday
Broadwater...Central and Southern Lewis and Clark...Jefferson...
Meagher.
Blizzard Warning from 2 PM Saturday to 6 AM MST Monday Eastern
Glacier...Eastern Pondera...Eastern Teton...Liberty...Northern
Rocky Mountain Front...Southern Rocky Mountain Front...Toole.
Winter Storm Watch from Saturday evening through late Sunday
night Beaverhead...Gallatin...Madison.
Winter Storm Warning from 10 PM Saturday to 8 AM MST Monday
Blaine...Fergus...Judith Basin.
Blizzard Warning from 6 PM Saturday to 8 AM MST Monday Cascade...
Chouteau...Hill.
Small Stream Advisory for Western Glacier County until Saturday
morning.
&&
$$
http://www.weather.gov/greatfalls