Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/26/20

Area Forecast Discussion...Updated

National Weather Service Phoenix AZ

 430 PM MST Fri Sep 25 2020

.UPDATE...Updated aviation Discussion.

&&

.SYNOPSIS...
Dry conditions and clear to mostly clear skies will continue through
late next week as strong high pressure builds over the West Coast
and low pressure passes to the northeast this weekend and early next
week. Temperatures will remain mostly above normal through the
period although with a slight cooling trend through the first half
of next week.

&&

.DISCUSSION...
A mostly dry and stable airmass remains in place with a flattened
ridge of high pressure in control of the region. The upper air
analysis showed weak anticyclonic flow aloft along a horizontal ridge
axis over N Baja extending E-NE through E-central AZ. Pronounced
W-NW flow was in place north of the region associated with the
zonal jet stream further north, and E-NE flow across NW MX. The
early afternoon ACARs soundings exhibited westerly component flow
aloft with a mean PW of 0.78" and a slightly elevated moist layer
near 650 mb. The result is clear skies and plenty of insolation
with lower desert highs expected to stay above normal and reach
103 to 106 degrees across the region today.

The dry conditions with clear to mostly clear skies will continue
through the weekend and well into next week. From Saturday night
through Monday models are in good agreement on a high amplitude
ridge anomaly developing from the NE PAC into the West Coast and SW
Canada setting up somewhat of a high amplitude blocking pattern.
Near the same time a low pressure trough drops through the Plains
and also digs into the Central Rockies late this weekend into early
next week. This provides the region with dry northwesterly flow
aloft keeping the region dry.

There is also growing/good confidence on a gradual slight cooling
trend for the late weekend into the first half of next week due
to the influence of backdoor cooling from the system to the east.
The model spread for NBM highs for early next week is now quite
minimal with the coolest (near normal) highs expected on Tuesday.
As a result, highs on Tuesday are now expected in the upper 90s
in and around Phoenix and the lower deserts, and the upper 90s to
low 100s out west. The current 3 to 5 day 500 mb height Clusters
favor the main ridge axis and H5 anomalies to remain centered
more to the west and northwest of the area from central CA to the
PAC NW.

If this forecast pattern trend holds it should mitigate high heat
risk and excessive heat from reemerging for the area next week.
However, there is more uncertainty on low temperatures for the
coming week. For example, for early next week forecast lows
around Phoenix could be anywhere from the mid 60s to the mid 70s.
Either way these lows would offer some overnight relief from the
near to above normal highs.

&&

.AVIATION...Updated at 2330Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT;
Southeast California/Southwest Arizona including KIPL and KBLH:

Strong high pressure aloft will keep skies clear area-wide for the
next 24 hours. Gradients are weak and we can expect a very
persistence based forecast in the Phoenix area; TAFs will reflect
typical diurnal wind patterns with west winds through midnight
becoming light/variable and then east in the 08-10z window. Speeds
generally 8kt or less. There may be an occasional west wind gust
into the low/mid teens thru about 02z this evening. Winds should
return to the west after 20z Saturday. Out west winds will favor
southeast to south with strongest southerly winds along the lower
Colorado River valley affecting KBLH. Look for a few gusts to 20kt
through about 02z this evening and maybe some gusts into the teens
again Saturday afternoon. Less wind expected at KIPL, and winds
there will tend more towards the southeast than south. Overall there
are no aviation concerns at the TAF sites for at least the next 24
hours.

&&

.FIRE WEATHER...
Monday through Friday:
Dry conditions and mainly above normal temperatures will continue
through the period as strong high pressure builds along the West
Coast early in the period. High temperatures across the lower
deserts will mostly range from the upper 90s to the low 100s under
clear to mostly clear skies. Daily minimum RHs will be quite low,
mainly falling to around 10% or less each day, while overnight max
RHs mostly top out between 20-35%. Winds will remain mostly light
through Monday before a potential cold front moves in from the
east early Tuesday bringing breezy easterly winds and gusts up to
25 mph across the region Tuesday. Winds for Wednesday and
Thursday should return to a light and diurnal pattern.

&&

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

&&

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

$$

DISCUSSION...Sawtelle
AVIATION...CB
FIRE WEATHER...Sawtelle/Kuhlman



Area Forecast Discussion

National Weather Service Blacksburg VA

 1000 PM EDT Fri Sep 25 2020

.SYNOPSIS...
Clouds with showers and fog will persist across the
Appalachians and central mid Atlantic region tonight. High
pressure will then build in over the weekend with warmer
temperatures and drier weather expected through Sunday. Our
weather pattern turns active again early next week with the
approach and passage of a strong cold front.

&&

.NEAR TERM /THROUGH SATURDAY/...
As of 1000 PM EDT Friday...

Our last wave of showers should start to finish up here between 10pm-
1am out over the Piedmont and off into central Virginia. In it`s
wake some leftover pockets of mist and drizzle especially out east
of Roanoke to Boone and along the crest of the Blue Ridge. Areas of
dense fog look to be the bigger concern as visibilities continue to
drop especially in areas west of the I-81 corridor and back into the
Greenbrier/New River Valleys. Low to mid level clouds remain
plentiful so uncertainty remains to if a Dense Fog Advisory may be
needed. For now we will hand that over to the incoming overnight
shift for further evaluation.

Low clouds and fog will slowly lift  across the area by mid to late
Saturday morning with a return to some sunshine late afternoon.
Clearing will be gradual from west to east across the area as high
pressure builds in late Saturday afternoon and evening.


Overnight lows should stay steady with most locations out west in
the mid to upper 50s, while areas out east sit right around 60
degrees. Highs by Saturday will range from the low to mid 70s out
west to mid to upper 70s out east.

&&

.SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/...
As of 200 PM EDT Saturday...

Weak high pressure will dominate the area Saturday, with an almost
summer like pattern in place for a change. Beta will have left a
warm and humid air mass in place with little cooling in its wake
indicated. Differential heating and orographic lift may spark a few
showers across the western mountains, but this does warrant more
than a 15-20% pop at this point confined to the afternoon and
evening hours only. Temperatures will be above normal and humidity
levels certainly will with highs in the 70s west to 80s east and
lows mostly in the 50s west to 60s east.

High pressure will drift toward the east coast Sunday. Southerly
flow and decent warm air advection will boost temperatures upward by
Sunday afternoon. This extra heating may spark isolated showers
along the southern Blue Ridge and western mountains once again, but
still only warrants a slight chance pop at this point. Sunday
temperatures will be well above normal

On Monday, a broad upper level trough will dig southward across the
Plains and push a cold front eastward to the Mississippi River on
Monday. This will result in upper ridging across the eastern U.S.
with 500mb heights rising toward 588dm and 850mb temps pushing
upward of +18C. Moisture will remain abundant as the region resides
solidly in the warm sector and a warm/humid air mass. Again, the
western areas will be the most favored with respect to afternoon
convection and a thunderstorm or two is possible at this point as
the instability increases. However, dynamics and synoptics are too
weak at this point for anything more than scattered showers and
isolated thunderstorms.
Temperatures and humidity levels will remain well above normal for
late September with highs largely in the 75 to 85 range and lows
mostly in the 60s.

Confidence in this portion of the forecast is moderate to high.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
As of 200 PM EDT Thursday...

By Tuesday, the strengthening and deepening trough to our west will
lead to deepening south to southwesterly flow aloft and thus an
increase in shower activity, especially in the western part of the
CWA. The front finally comes through in some form/fashion by late
Tue into Wed. Unfortunately, significant differences remain between
the ECMWF and the GFS/Canadian solutions as to how quickly, how
negatively, and any secondary disturbances are associated with the
deep trough. The ECMWF solution of developing a secondary low back
in deep south TX and then sweeping another strong negatively tilted
upper trough through the eastern U.S. by Thursday is an anomalous
solution and I have disregarded for this forecast. There, leaning
heavily toward the more progressive GFS/Canadian solution which
moves the front through Wed. Thus, the best chance for widespread
convection, some possibly strong to severe mainly in the form of
wind gusts and brief heavy rainfall, would be late Tuesday into
early Wednesday. The remainder of the forecast period should be
mostly dry and cooler with perhaps some linger upslope western
mountain showers, but confidence is low due to the opposing mostly
dry/cool GFS solution versus the wet and very unsettled ECMWF
solution throughout the extended periods. Tuesday and Wednesday
should continue with mostly above normal temperatures trending
toward more normal in the west, but closer to normal or perhaps even
slightly below normal temperatures may ensue by the end of the week,
but this does not yet appear to be a clear frost/freeze event for
the region with the upper trough lagging back to the west until late
week.

Confidence in the extended portion of the forecast remains low to
moderate.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
As of 757 PM EDT Friday...

Poor flying conditions settling in overnight despite a few pockets
of VFR and MVFR showing up from KLWB to KBCB and KTNB. IFR/LIFR
conditions still prevail though east of KROA toward KLYH and KDAN as
our last band of moderate to heavy rain pushes on through. Most of
this precipitation looks to move east around 01-03z(9-11PM) with
pockets of drizzle setting in at all the TAF sites through 06z(2AM)
Saturday.

Widespread IFR/LIFR cigs/vsbys will continue through Saturday
morning especially in the west from KLWB-KROA-KBCB-KBLF where vsbys
looks to tank to LIFR due to fog and drizzle. Conditions will
gradually improve to MVFR by late Saturday morning into Saturday
midday. Cigs and vsbys should improve back to VFR conditions by
Saturday afternoon starting in the west from KLWB to KBCB then
pushing east toward KROA-LYH-KDAN by Saturday evening.

Winds will remain light through the period with no significant
impacts to aircraft operations.

Confidence remains high for winds and low vsbys/cigs.

.Extended Aviation Discussion...

High pressure slowly builds into the area by late Saturday
afternoon and evening. Some leftover sub-VFR conditions are expected
through the evening before a bounce back to VFR Sunday. Another
front arrives Monday with the threat of showers and even a few
thunderstorms. Even here though conditions continue as VFR, but
confidence remains low at this time.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.

&&

$$
SYNOPSIS...DS/MBS
NEAR TERM...ET
SHORT TERM...RAB
LONG TERM...RAB
AVIATION...ET/MBS