Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/27/20
Area Forecast Discussion
National Weather Service State College PA
1112 PM EDT Wed Aug 26 2020
.SYNOPSIS...
A slow moving frontal boundary in the vicinity of Pennsylvania will
bring the potential for scattered showers and locally strong to
severe thunderstorms each afternoon or evening into the
weekend. The remnants of Hurricane Laura are forecast to track
across Virginia on Saturday with limited rainfall impacts
expected in central Pennsylvania at this time.
&&
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
A warm and mainly dry late evening across central PA with
increasing humidity. Severe weather threat for late tonight
appears to be waning but will still see scattered coverage of
showers and thunderstorms moving across portions of NC and NE
PA now through 2-3 AM or so. HRRR and WRF have backed off a bit
on earlier solutions and still track a cluster of showers and
likely isold tsra over NE PA after midnight. Elsewhere an
isolated shower or storm is possible, but most areas will remain
dry overnight.
With dewpoints forecast to surge back into the 60s, min temps
tonight will be much warmer/muggy than last night in the low 60s
to around 70F.
&&
.SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/...
Little change at this time for Thursday, as D2 outlook
conts to indicate significant severe thunderstorm enhanced risk
for north central/northeast PA. SPC defines significant severe
tstms as any storm that may produce one or more of the following
elements: tornado with EF2 or greater damage, damaging winds 75
mph or greater, hail 2" in diameter or larger. The D3 outlook
downshifted to MRGL (from D4 15% or SLGT equivalent) for the
southern 3/4 of the CWA.
The setup for Thursday will continue to feature a robust low
level moisture recovery in the wake of northeastward-lifting
warm front. The rich mid 60s to low 70s dewpoints combined with
peak heating (max temps in the 80s to low 90s) should yield
moderate instability. The ENH risk area will reside within a
belt of stronger NW flow aloft with 30-40kts of effective bulk
shear supporting fast- moving organized storms, including bowing
segments and supercells. There is some uncertainty with storm
initiation due to potential capping inversion with 700mb temps
around 10C in the warm sector. HREF updraft helicity tracks are
focused over southern NY which may suggest a greater svr potential
there. While the primary threats are sig svr damaging winds and
large hail, all severe hazards are possible from mid afternoon
through early evening. Max HX values should get close to 100F
across the lower Susq. Valley Thursday afternoon.
Additional strong storms with gusty to locally damaging wind
threat are possible on Friday afternoon - mainly to the south
of q-stationary boundary extending from the Great Lakes into the
northern Mid-Atlantic. There is a broad model signal for
moderate to perhaps locally heavy QPF amounts across the
northwest part of the area heading into Friday night/Saturday
morning. This would be the point where moisture from Laura
would be transported northward along cold front pushing east
from the Great Lakes/Ohio Valley. Therefore, increased POPs in
conjunction with the latest NBM and upped QPF as well.
&&
.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
A cold front accompanying a progressive northern-stream trough
will advance southeast through the OH Valley and Northeast
States, reaching the Middle Atlantic during the evening on
Saturday. Showers and thunderstorms will be ongoing along and
ahead of the front. Additional storms will likely develop as the
warm sector destabilizes during the afternoon, posing a threat
for mainly damaging wind. SPC has maintained the 15% or SLGT
risk equivalent area over central and eastern PA.
The remnants of Laura are forecast to track to the south of PA
Saturday and Saturday night. Some moisture entrainment is
possible along/ahead of aforementioned cold front. At this time,
rainfall impacts appear to be limited especially given the
ongoing drought conditions across much of west-central PA and
any soaking rain would most likely be welcome to help ease the
drought conditions. We will continue to monitor for shifts in
the track and an increase in heavy rainfall potential.
Behind the front and Laura, much cooler air will move into the
region late this weekend and into next week. Expect high temps
to be more in the 70s and lower 80s with low humidity.
&&
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
At 03z, most of central PA is experiencing VFR conds, although
BFD just saw its vsby drop below 2 miles. Have to think that
this will only be a temporary drop in vsby there, as clouds are
thickening quickly over nrn PA.
Lowering cigs are expected overnight as a warm front edges into
the region, with possible MVFR cigs across the nrn and wrn
highlands based on model guidance. SHRA/TSRA are projected to
drop southeastward from the eastern Great Lakes and slide
across north-central and northeastern PA overnight, and have
added VCSH to the BFD and IPT TAFs. Additionally, strong winds
a couple thousand feet off the surface will result in LLWS
over much of the area overnight.
Conds should become VFR area-wide after sunrise Thursday
morning. However, TSRA are expected to develop Thursday aftn
and continue into the evening hours, some of which could
produce locally gusty winds and hail.
Outlook...
Fri...AM low cigs possible wrn highlands. Sct PM tsra impacts
possible.
Sat...Widespread showers and reductions are expected.
Sun-Mon...Generally VFR w/ no sig wx expected.
&&
.CTP WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...DeVoir/Gartner
NEAR TERM...DeVoir/Gartner
SHORT TERM...DeVoir/Gartner/Travis
LONG TERM...DeVoir/Travis
AVIATION...Evanego
Area Forecast Discussion
National Weather Service Duluth MN
957 PM CDT Wed Aug 26 2020
.SHORT TERM...(This evening through Thursday night)
Issued at 353 PM CDT Wed Aug 26 2020
We will continue to see chances of showers and thunderstorms
increase this afternoon and evening as a cold front passes through
the region. A very humid air mass has settled across the Northland
this afternoon, characterized by dew point temperatures in the upper
60s and lower 70s. Cloud cover has been rather tough to diminish
this afternoon, with partly to mostly cloudy skies across the
region. This has likely helped to keep instability slightly lower
than what many of the global models are progging, with the RAP model
indicating mixed-layer CAPE between 1000 to 2000 J/kg. Despite the
lower-end instability, deep-layer shear is supportive of organized
convective updrafts, with values in the 35 to 45 knot range. With
this convective parameter space, the Storm Prediction Center
continues to have a Slight Risk across the southern portions of the
region, including along and south of a line from Poplar, MN to
French River, MN to Sand Bay, WI. The CAMs do appear to be progging
at least some strong to severe storms later this evening, although
they appear to be more isolated in nature, at the moment.
Once the cold front passes through the region tonight, drier
conditions are expected for Thursday as an area of high pressure
noses into the region from the Canadian Prairies. Expect sunny skies
to start the day, with increasing cloud cover from the west in the
afternoon as a precursor to increasing chances of showers and storms
for Thursday night, as a mid-level shortwave trough shifts eastward
into the region. No severe storms are expected at that time. High
temperatures for Thursday will be in the mid 70s north to the lower
80s south.
.LONG TERM...(Friday through Wednesday)
Issued at 353 PM CDT Wed Aug 26 2020
The long-term forecast will have a few chances for showers and
thunderstorms Friday and Monday, but overall will remain mostly dry.
The first of these chances of precipitation will be Friday as the
Northland is progged to be between a warm front to our south and an
amplifying upper-level shortwave trough, with a decent positive
vorticity maxima. The high-resolution models are generally
indicating that the activity along the front will remain to the
south, but activity along the shortwave trough will scrape across
the Borderland region Friday afternoon. The global models show this
scenario, as well. Severe potential appears very low as this time,
with very marginal instability of mixed-layer CAPE up to 500 J/kg
possible. Deep-layer shear is a bit better, with values in the 40 to
45 knot range. The Day 3 convective outlook from SPC only has the
region under a General Thunderstorm risk.
Once this shortwave passes through, much calmer conditions are
expected for the weekend, with partly to mostly sunny skies across
the region. As the shortwave trough departs to the east,
northwesterly upper-level flow will help support cold air advection
for Friday night. This cooler air will linger with us through much
of next week, leading to high temperatures Saturday through
Wednesday in the upper 60s and lower 70s, along with more
comfortable dew point temperatures.
There will be another opportunity for showers and thunderstorms for
Sunday night through the day Monday as a high-amplitude upper-level
trough will sweep along the International Border region. Despite
some decent large-scale forcing, instability appears to be very
minimal, with most-unstable CAPE values of a few hundred J/kg - not
very supportive of strong thunderstorms. This trough will likely
bring a rather wet and soggy Monday due to the prolonged period of
rainfall.
The global models begin to diverge for Tuesday and Wednesday, with
with discrepancies in terms of precipitation chances. There appears
to be some phasing differences regarding an upper-level trough.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 642 PM CDT Wed Aug 26 2020
A cold front moving through the region is currently causing
showers and thunderstorms in the Northland. After this line moves
east, VFR conditions are present behind it. Precipitation chances
are already minimal for INL and BRD from this point onward, and
HIB and DLH are quickly decreasing as well. Conditions at HIB and
DLH should improve in the next couple hours to MVFR or VFR. HYR
will be affected by the front into tonight as the line moves
through. Fog is possible tonight at DLH and HIB and could lower
conditions to MVFR or IFR.
&&
.MARINE...
Issued at 942 PM CDT Wed Aug 26 2020
Showers and thunderstorms have moved out of the area, and no
further precipitation is expected out over the lake through the
rest of tonight. But we are not done yet! More showers and
thunderstorms are expected Thursday night into Friday over western
Lake Superior. These storms are not expected to be severe. Other
than storms, conditions are quiet with light winds and waves below
2 ft over the next 48 hours.
&&
.PRELIMINARY POINT TEMPS/POPS...
DLH 59 78 58 71 / 40 0 50 60
INL 53 75 55 72 / 10 0 50 60
BRD 59 80 58 76 / 50 10 50 50
HYR 62 82 59 75 / 50 0 70 70
ASX 62 78 58 73 / 40 0 60 70
&&
.DLH WATCHES/WARNINGS/ADVISORIES...
WI...None.
MN...None.
LS...None.
&&
$$
SHORT TERM...JTS
LONG TERM...JTS
AVIATION...Kossen
MARINE...LE/Kossen
Area Forecast Discussion
National Weather Service Northern Indiana
607 PM EDT Wed Aug 26 2020
.SYNOPSIS...
Issued at 328 PM EDT Wed Aug 26 2020
Another warm and muggy night is in store tonight, with partly cloudy
skies and lows in the 70s. Highs Thursday will climb up into the
upper 80s and low 90s again. There are chances for showers and
thunderstorms Thursday into Saturday morning, with the greatest
chances Friday into Friday night. Strong to severe storms are
possible late Thursday afternoon and evening, then again on Friday,
though confidence is low.
&&
.SHORT TERM...(This Evening through Thursday)
Issued at 328 PM EDT Wed Aug 26 2020
Another warm and muggy night is in store for the forecast area, with
temps only falling into the low 70s under partly cloudy skies. We
saw a record warm minimum temperature at KSBN last night, and
suspect we`ll be close again tonight.
Focus turns to Thursday into Thursday night. Expect we`ll see mostly
dry conditions through the first part of the day, with capping
inversion in place and generally weaker forcing. Some of the
guidance outputs some shower activity in the morning/early afternoon
for areas south of US 30 thanks to a push of WAA ahead of a weak
shortwave moving through the flow aloft, but doesn`t look too
impressive at this point. Have slight chance pops to account for
this activity. The best chance for storms and severe weather would
be in the late afternoon/evening generally along/north of the toll
road (I 80-90) as the cold front sinks southward from Central Lower
Michigan and upper level forcing increases. By the 18-21z timeframe
DCAPE in the north and central CWA is around 1500-2000 J/kg and bulk
0-6 km shear is on the order of 20-30 knots in our N-NE (along/north
of I 80-90). Front is expected to become stationary and linger
overnight, so what we get as far as storms in general or even severe
weather Thursday into Thursday night will depend on how far south it
makes it and where exactly it sets up. If severe weather does
develop, the main threat would be damaging winds-though hail and
heavy rain can`t be ruled out. Some of the guidance, including the
NAM suggests the fronts stays north of our CWA and we remain
underneath the upper level ridge longer, which would mean we`re
mostly dry Thursday with the exception of the morning chances south
of US 30. Overall, confidence is low.
&&
.LONG TERM...(Thursday Night through Wednesday)
Issued at 328 PM EDT Wed Aug 26 2020
Our chances for severe weather Friday into Friday night will in part
depend on how things set up Thursday into Thursday night with the
frontal boundary. Additionally, how remnants of hurricane Laura are
absorbed into the northern stream flow. The surface low projected to
develop to our northwest over NW IA/MN Friday morning should shift
eastward along the stationary boundary into southern Ontario by
Saturday morning. This will bring a cold front through the CWA.
Current model runs suggest the remnants of Laura will mainly focus
to the south of our CWA, which is depressing given that we really
need rain around here. This could also stunt some of the moisture
and forcing needed to really kick things off severe-weather wise.
Expect we`ll see rain and chances for storms Friday, with severe
weather potential conditional on the aforementioned factors.
Overall, agree with SPC`s slight risk outlook for Friday, though
confidence is low at this point.
Dry conditions are expected Saturday afternoon into early Monday as
high pressure builds into the region. Highs will be cooler, only
reaching into the 70s and low 80s. In the wake of the cold front,
forecast to be out of the area by Saturday morning, expect gusty
north-northwest winds which will whip up waves to around 5 to 6 feet
on Lake Michigan. Direct onshore wave angles of approach in addition
to wave periods of 5 to 6 seconds will be extremely supportive for
the development of dangerous currents. Anticipate a beach hazards
statement/high swim risk for Saturday, and at least a moderate risk
on Sunday (could be high swim risk still despite slightly lower
forecasted wave heights).
The forecast for Monday afternoon into Tuesday is a little
uncertain, with models disagreeing on the timing/strength of an
upper level trough and subsequent surface low and frontal
boundaries. The GFS has a steeper and more progressive solution
(big surprise) and brings us a decent shot of rain (and t-storm
potential) where the ECMWF is less amplified and keeps us mostly
dry (with main precipitation areas north and south of our CWA).
Kept the consensus pops for now, as a lot will depend on how
remnants of hurricane Laura are absorbed earlier in the week.
Wednesday appears mostly dry with a surface high over the CWA and
either zonal or slightly ridged flow aloft, per both the
GFS/ECMWF, but Thursday the ECMWF brings another trough into the
central plains and lifts a surface low and associated
precipitation into our CWA starting in the morning. Kept pops low
given lower confidence at this point out. Highs should be in the
mid-upper 70s to around 80F.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday Evening)
Issued at 541 PM EDT Wed Aug 26 2020
An upper level ridge continued over the area and was helping to
limit storm development. Low level moisture should increase
overnight and may help to bring MVFR ceilings to the terminals
(especially FWA). Given the latest NAM and HRRR runs, have kept
just scattered lower clouds with VFR conditions prevailing. Can
not rule out a brief 2000 ft ceiling between 10Z and 15Z, but
for now will leave low ceilings out.
&&
.IWX WATCHES/WARNINGS/ADVISORIES...
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.
&&
$$
SYNOPSIS...MCD
SHORT TERM...MCD
LONG TERM...MCD
AVIATION...Skipper
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Area Forecast Discussion
National Weather Service North Platte NE
707 PM CDT Wed Aug 26 2020
.SYNOPSIS...
Issued at 324 PM CDT Wed Aug 26 2020
H5 analysis from earlier this morning had high pressure
anchored over the Four Corners and a secondary area of high pressure
was located over western Georgia. A low amplitude ridge of high
pressure extended north of these two features into the upper
Mississippi valley. Further west, a trough of low pressure extended
from the Oregon coastline, south southwest to a point approximately
700 miles off the central California coast. A strong low was located
over eastern Quebec with a trough extending south toward Bermuda.
Hurricane Laura was approximately 200 miles southeast of the mouth
of the Sabine river. At the surface, a weak frontal boundary
extended from the western Nebraska Panhandle into northeastern South
Dakota. Winds behind this boundary were northerly, while south of
the boundary, winds were either southwesterly or southerly. Skies
remained mostly clear this afternoon, with a few higher clouds in
western portions of the forecast area. Temperatures as of 2 PM CT
ranged from 91 at Gordon to 98 at Thedford.
&&
.SHORT TERM...(This evening through Thursday night)
Issued at 324 PM CDT Wed Aug 26 2020
The main forecast
challenges in the next 36 hours are precipitation chances tonight,
then again on Thursday night. Over the next 24 hours, there will be
a gradual weakening of the persistent ridging across the northern
plains and northern Rockies. This will allow shortwaves to enter the
Dakotas Thursday into Thursday night, increasing the threat for
thunderstorms (more on this later). For tonight, there was some
indication with this morning`s HRRR of thunderstorm development in
the panhandle late this afternoon into the evening hours. Some of
this activity was progged to move into the northwestern forecast
area early this evening, then dissipate. The 12z NAM12 and NAMNest
develop some limited convection off to the west of the forecast area
and dissipate it before it reaches the western forecast area. As has
been the case in this regime the past few days, the HRRR is the most
"ambitious" with development of precipitation with its morning runs,
then it backs off of it as you trend into the afternoon hours. The
same thing is occurring right now as the latest 18z HRRR develops
convection over the Cheyenne ridge which never makes it into the
eastern panhandle. This model trend was echoed by the NAM12 and
NAMNest from this morning which are dry for us tonight. That being
said, decided to strip out pops in the NW Sandhills for tonight and
keep them confined to the eastern panhandle. With respect to the
weak frontal boundary which is currently draped across the northern
forecast area. This feature is expected to lift slowly north as a
warm front Thursday morning, becoming oriented across far Southern
South Dakota by 21z Thursday. Late in the day Thursday, a northern
stream disturbance will track from Montana into North Dakota. This
will force the frontal boundary south into northern Nebraska
Thursday evening increasing the threat for thunderstorms in the
Dakotas and northern Nebraska. A decent low level jet will develop
Thursday night from central Nebraska into northeast Nebraska. The
nose of this feature will extend across northern Nebraska. Larger
scale forcing will be even stronger across South Dakota Thursday
night and am expecting the best chances for pcpn to be north of the
forecast area with some chances in northern portions of the forecast
area. Unfortunately, given weak forcing further south, pcpn chances
are going to be minimal along and south of Interstate 80. As for
highs Thursday, I went ahead and increased them some over guidance
in northern Nebraska given the expected location of the surface
front over southern South Dakota late in the afternoon.
.LONG TERM...(Friday through Wednesday)
Issued at 324 PM CDT Wed Aug 26 2020
The cool front will be
pushed south into Kansas Friday resulting in cooler and drier
conditions across western and north central Nebraska. The threat
for precipitation will increase Saturday into Saturday night as mid
level warm air advection and a surface warm front lifts across the
area. Temperatures will warm back to more seasonal levels Sunday
behind the warm front with highs in the mid 80s to lower 90s. This
brief warmup will be followed by the threat for thunderstorms Sunday
night as a strong cold front tracks through the forecast area.
Behind the front, highs Monday and Tuesday will be in the 70s, with
upper 70s to lower 80s for Wednesday.
&&
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 706 PM CDT Wed Aug 26 2020
Fairly quiet aviation conditions are expected across the region
through Thursday afternoon. There is a low chance of some
thunderstorms across northern Nebraska Thursday evening. Confidence
remains low in development at this time and any thunderstorms that
do develop will only impact KVTN mainly after 00Z Friday.
&&
.LBF WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
SYNOPSIS...Buttler
SHORT TERM...Buttler
LONG TERM...Buttler
AVIATION...Kulik
Area Forecast Discussion...UPDATED
National Weather Service Portland OR
840 PM PDT Wed Aug 26 2020
Updated aviation discussion
.SYNOPSIS...Typical summertime pattern to continue through the week.
Potential for rain late in the weekend before returning to seasonal
trends.
&&
.SHORT TERM...Tonight through Friday...Current satellite is showing
smoke from California and Oregon wildfires moving northeastward.
Upper level winds will be in our favor for the most part but patchy
smoke across the Lane and Linn county Cascades is likely through the
tomorrow morning. The HRRR is showing a clearing of smoke
on the west side of the Cascades by Thursday morning.
Otherwise, typical summertime pattern is expected to continue through
the end of the week. Weak influence from the Northeast Pacific high
will keep skies clear and temperatures will trend upward by Friday.
Weak east winds and building heights will produce inland high
temperatures into the upper 80s on Friday. Expect late night to early
morning marine stratus to form in coastal river valleys and lower
Columbia River. Strengthening of the thermal low over the OR/CA
border will bring gusty northerly winds in the afternoon across the
Willamette Valley and along the coast. -BPhillips
.LONG TERM...Friday night through Wednesday...Temperatures will trend
down by Saturday as a weakening front pushes into the region Friday
night. Inland locations should expect low 80s and coastal locations
will see upper 60s. Most ensemble members show zero QPF associated
with this disturbance so the region will likely stay dry. A second
disturbance is expected to dip south Sunday night into Monday which
has a greater chance of bringing some precipitation to the area.
Light rain is possible across the northern half of the CWA and will
dissipate by Monday afternoon. By Monday night, high pressure will
build back bringing temperatures up into the mid to upper 80s by the
middle of next week. -BPhillips
&&
.AVIATION...High pressure will maintain mainly VFR conditions in the
interior the next 24 hours under mostly clear skies. The exception
will be a few hours of MVFR cigs in the vicinity along the Lower
Columbia River between 10-17Z. Will also see another round of breezy
northwest to north winds with occasional gusts to 20 kt between 19-
04Z.
Onshore flow along the coast will allow MVFR or lower conditions to
redevelop over the next few hours and persist into Thursday morning.
Expect conditions similar to last night with a period of vsbys below
2SM and cigs at or below 500 ft. Any reduced flight conditions look
to improve by late Thursday morning with VFR conditions thereafter.
Refer to http://weather.gov/zse for detailed regional aviation
weather and hazard information.
KPDX and APPROACHES...Mainly VFR the next 24 hours under mostly
clear skies, but a few hours of MVFR cigs in the vicinity is
possible between 12-15Z. Breezy northwest winds with occasional
gusts to 20 kt likely between 19-04Z. /64
&&
.MARINE...High pressure remains anchored over the Pacific through
the next several days. Winds are northerly as the inverted
thermal trough, that stems from California to Oregon, persists
through
the weekend. Winds will likely be strongest in the afternoons as
the thermal gradient increases. Expect gusts up to 25 mph
through all of the waters, with the more consistent and stronger
winds in the central outer waters. The Small Craft Advisory
remains in effect through Thu morning. There is a chance for
another round of small craft winds Thu afternoon but at this
time, models are showing winds staying just below thresholds.
Seas at 4 to 5 ft with a northwesterly swell at 7 to 9 seconds
will continue through the middle of next week. -Muessle
&&
.PQR WATCHES/WARNINGS/ADVISORIES...
OR...None.
WA...None.
PZ...Small Craft Advisory until 2 AM PDT Thursday for coastal waters
from Cape Shoalwater WA to Florence OR from 10 to 60 NM.
Small Craft Advisory from 5 PM this afternoon to 2 AM PDT
Thursday for Coastal waters from Cascade Head to Florence
OR out 10 NM.
&&
$$
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Area Forecast Discussion
National Weather Service Phoenix AZ
430 PM MST Wed Aug 26 2020
.SYNOPSIS...
Temperatures will remain unseasonably hot for the majority of the
week with readings exceeding excessive heat thresholds for many
communities through Thursday. Thunderstorm chances will decrease
today into Friday, mainly favoring high terrain areas to the east of
Phoenix. Monsoon moisture looks to gradually return this weekend
into early next week leading to an increase in thunderstorm chances
along with their associated weather hazards such as strong wind,
heavy rain and blowing dust. Given the increase in moisture,
temperatures will cool over the weekend and into next week and fall
to near seasonal normal levels.
&&
.DISCUSSION...
Latest water vapor imagery shows mid-upper level moisture embedded
within the anticyclonic flow. Mesoanalysis places the mid-
tropospheric Monsoon High over north-central Arizona, which is
resulting in a very weak flow through the column. Meanwhile,
sounding and model-based PWATs are near 1.4 inches, which is near or
slightly below normal while surface dewpoints are generally in the
50s. Latest visible satellite imagery reveals some areas of mid
clouds and even some light showers across the Imperial Valley.
Morning run of the HREF generally pointed to only isolated activity
along the periphery of the Monsoon High, across the Mogollon Rim and
across Pima County in southern Arizona. However, earlier runs of the
HRRR suggested a southward propagating outflow boundary would
possibly collide with another boundary to initiate convection across
the Valley this evening. The HRRR has since backed off, owing to a
weaker or even non-existent boundary from Yavapai County.
Nevertheless, it can`t be ruled out entirely and the NBM guidance
indicates a 10-20% chance of rainfall. However, CAM-based
reflectivities remain modest, suggesting only strong wind gusts at
most. Another low probability but possible scenario per the latest U
of A GFS-based WRF suggests convection will develop across the
Valley, but late this evening associated with the weak moisture
convergence.
Models continue to indicate excessive heat will continue through at
least tomorrow across much of the Desert Southwest. Subtle cooling
is then anticipated Friday, as the aforementioned Monsoon High
weakens, while drifting to the south and east. Today is the average
day for the last 110 degree temperature in Phoenix, but it appears
110 degrees will be reached again Thursday, which would equal 49
days so far this summer!
&&
.PREVIOUS DISCUSSION...
As we move from Thursday into Friday, guidance is very consistent in
calling for a continued downward trend in convection across the area
as an upper low moves into position along the central California
coast; this serves to shunt the high to the east and set up a weak
southerly steering flow. Moisture also appears to gradually diminish
along with instability and temperatures. For the most part storms
will be quite isolated and should only affect high terrain areas
well to the east and southeast of Phoenix with POPs in the single
digits each day across most of the lower elevations.
As we move through the weekend and into the early part of next week,
there are clear model signals that moisture will gradually make a
return, and the monsoon will begin to heat up again. As the upper
low near the California coast has more of an impact, steering flow
gradually turns from weak southerly to stronger southwest or
west/southwest. Despite the more "unfavorable" nature of the
steering flow, significant tropical moisture pooling off Baja
associated with a passing system begins to be pulled north and
spreads into much of southern Arizona with time. Both the ECMWF and
GFS/GEFS reflect this trend and we have correspondingly raised POPs
with time; by Sunday and Monday isolated to scattered showers and
storms are expected favoring high terrain but still likely affecting
lower deserts as far west as the lower Colorado River Valley. Model
guidance as well various ensemble member output begin to sort of go
off the rails and diverge early next week with some solutions
arguing for a drying northwest flow aloft while others keep a very
moist southwest flow in place. There is way to much inconsistency
that far out in time so we will keep a rather broad brush moderate
grade monsoon forecast in place thru the end of the forecast period -
Tuesday afternoon.
&&
.AVIATION...Updated at 2330Z.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Very similar weather scenario through Thursday evening as has been
experienced the past couple days. Competing outflows from the
northeast and southwest may create frequent wind shifts this evening
though the weaker storms to the north as compared to yesterday may
limit (or negate) the potential for the northerly wind shift to
actually develop. Stronger storms to the southwest have a better
chance of sending outflow into terminals later this evening.
Nevertheless, speeds do not look that impressive and any gusts (if
there are any) certainly look below 20kt. Chances for actual SHRA
at any aerodrome is 10% or less. Confidence is good that the typical
easterly wind should settle in after midnight and persist into mid
afternoon Thursday.
Southeast California/Southwest Arizona including KIPL and KBLH:
No major weather impacts will exist through Thursday evening under
mostly clear skies. Trends in wind directions and speeds should be
similar to the past several days with the typical diurnal switches,
and with speeds below 12kt.
&&
.FIRE WEATHER...
Saturday through Wednesday:
A cooling trend is likely this weekend through early next week.
Storm coverage looks to stay diminished on Saturday, but will start
to increase again Sunday into next week. Occasional wetting rains
are possible starting Sunday evening continuing into next Wednesday.
Afternoon humidity levels will generally fall into a 15-25% range
while morning humidity levels will generally be 30-45% at lower
elevations and 45-70% higher terrain. Outside of thunderstorm areas,
winds should be weak and follow typical diurnal patterns.
&&
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
&&
.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...Excessive Heat Warning until 8 PM MST Friday for AZZ534-537-
540>553-555-556-560>562.
Excessive Heat Warning until 8 PM MST Thursday for AZZ530>533-
535-536-538-539-554-559.
CA...Excessive Heat Warning until 8 PM PDT Thursday for CAZ561>563-
565>570.
&&
$$
DISCUSSION...Hirsch
PREVIOUS DISCUSSION...CB
AVIATION...Smith/Percha
FIRE WEATHER...Hirsch/Feldkircher
Area Forecast Discussion
National Weather Service Reno NV
142 PM PDT Wed Aug 26 2020
.SYNOPSIS...
Thunderstorms are expected through the evening for northeast
California and portions of western Nevada. Typical westerly winds
will also increase this afternoon across the region. Chances for
isolated to scattered thunderstorms continue over high terrain
and northeast California through the end of the week, least likely
on Thursday. The air quality will continue to be a concern due
to smoke from regional wildfires.
&&
.DISCUSSION...
Satellite data (and a quick peek out the window) is showing
cumulus beginning to develop mainly along the Sierra/Sierra Front
into northeast CA and far northern NV. With plenty of lingering
moisture and added forcing from the jet stream draped across this
region, we`ll see thunderstorms once again this afternoon and
evening. Storms will mainly be isolated in coverage, but we could
see a bit more coverage in far northeast CA, generally between
Susanville, Burney, and Alturas north and east toward Rome,
Oregon.
One change to the forecast was to add a slight chance for
thunderstorms overnight across portions of northern Nevada, mainly
from near Pyramid Lake north and east. The lingering jet streak
along with a subtle upper level wave could bring the necessary
forcing for storms. The HRRR and the HREF are both hinting at
nocturnal storms as well. While storms will be putting down rain,
the concern is the increased storm motions with the potential for
dry lightning strikes outside of thunderstorm cores.
The trough remains centered over northern California, but begins
to weaken, with drier air moving into the area Thursday. This
should keep thunderstorm chances at bay, but with general
troughiness and PWATs creeping back up, a few storms will once
again be possible Friday, mainly along the Sierra.
Still seeing quite a range of possibilities in ensemble guidance
for next week. The big message is that it will remain dry, but
the question is whether or not we`ll be seeing a developing low
and cold frontal passage the early part of next week, or if this
feature remains well to the east. There is better agreement it
will remain east, however, there is enough evidence to give the
trough feature a second look. Next Monday could be rather windy
if we see this feature, or we could be seeing typical afternoon
breezes. The current NBM high temperature guidance for lower
valleys next Tuesday range from mid 70s to low 90s, not
instilling a lot of confidence in the overall forecast.
Otherwise, smoke and haze will remain a concern as long as the
wildfires are ongoing. The latest HRRRx smoke runs are indicating
the worst conditions in northeast California and northern Nevada
north of I-80. -Dawn
&&
.AVIATION...
Typical westerly afternoon winds today with gusts 18-25 kts at
terminal sites.
Thunderstorms are possible this afternoon and evening, but
coverage will be less than what we have seen recently. Very
isolated storms are possible along the Sierra and Sierra Front,
with a 10% chance of seeing a storm in the vicinity of
KRNO/KCXP/KTVL/KMEV/KTRK. Storms are more likely to form in
northeast California into far northern Washoe County. We could
also see isolated nocturnal storms tonight north and east of
Pyramid Lake. The greatest concern for storms today will be gusty
and erratic outflow winds along with brief heavy rainfall
obscuring terrain.
Otherwise, smoke and haze remains a problem due to a large number
of ongoing wildfires. Pockets of MVFR conditions are possible,
especially just before to a few hours after sunrise, with
improvement during the day as mixing improves. The worst
conditions remain in northeast California and far western Nevada
north of I-80. Slantwise visibility will be degraded across the
entire region. -Dawn
&&
.FIRE WEATHER...
Storms this afternoon are still expected across northeast
California, the Sierra, and far western Nevada. For the most part
storms will be isolated, with the greatest coverage likely to be
in between Susanville, Burney, and Alturas north and east toward
Rome, Oregon. Storm motions through this region are slowing as we get
into the evening, from around 20-25 mph to around 15 mph, which
will lessen, but not negate, the risk of new fire starts.
One change to the forecast was to add a slight chance for
thunderstorms overnight across portions of northern Nevada, mainly
from near Pyramid Lake north and east. While storms will be
putting down rain, the concern is the increased storm motions with
the potential for dry lightning strikes outside of thunderstorm
cores. Storms should remain isolated in coverage, so between this
and the fact is will be raining, we are not planning a Red Flag
Warning at this time. -Dawn
&&
.REV Watches/Warnings/Advisories...
NV...None.
CA...None.
&&
$$
For more information from the National Weather Service visit...
http://weather.gov/reno