Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 08/12/22
Area Forecast Discussion
National Weather Service Boston/Norton MA
1053 PM EDT Thu Aug 11 2022
Mainly dry, seasonable weather expected Friday with a low chance
for showers across Cape Cod, southeast MA, and RI. Shower
chances linger into Saturday morning across this region, but
our first shot of drier, cooler fall like air comes Saturday
morning, as lows drop into the 50s across much of interior
southern New England! Broad low may brush southeast New England
early on Saturday, but overall high pressure builds in keeping
the weather dry and quiet. Unsettled for much of the upcoming
week with the potential for a multiple day rain event. Cooler
than normal temperatures anticipated.
.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
1045 PM Update...
Monitoring a strong thunderstorm capable of producing small hail
and locally heavy downpour across Hartford into Tolland county
in CT. Made some adjustments to the PoPs for the next few hours
based on radar trends. Forcing is weak but there is around 20 kt
of effective bulk shear across CT and RI to help organize
updrafts. Also noted around 700-900 J/kg of downdraft CAPE so
there is a low probability of gusty winds from the downpours or
Additionally, trimmed the areal and temporal coverage of the
fog across southeast MA based on obs and near-term trends.
745 PM Update...
Have added slight chances of precip across SW MA/CT to account
for the showers and perhaps an isolated thunderstorm or two
bubbling up across eastern NY/far western MA. Leaned toward the
latest ARW, which is doing well based on the current situation.
Otherwise the forecast remains on track at this point, but will
need to monitor the stratus/fog pushing into the Cape/Islands
and perhaps eastern MA. Some guidance suggests it could be dense
at times especially across the Cape/Islands, but think this
will be short lived as flow shifts and becomes more NW/N late.
Rain showers have all but come to an end across Cape Cod and
Nantucket as clearing continues to push east. Fog and stratus
is expected to redevelop over Cape Cod and the Islands given
high SSTs, low dewpoint depressions, at or below 1F in some
cases, and light winds. Fog is anticipated to be limited to the
Cape, Islands, and immediate southeast coastal plains as dry air
will begin to filter into interior southern New England this
evening and overnight. As of this writing, daytime mixing has
allowed dewpoints to drop into the 50s across portions of
interior southern New England, in areas such as Fitchburg and
Orange. While a brief surge in dewpoints is expected this
evening along an approaching cold front from the northwest,
conditions will remain sub-optimal for fog formation away from
The aforementioned cold front is currently located over upstate
New York, but will begin to push into our region around sunset.
CAMs are in agreement that this front will bring the possibility
of a spot shower or weak thunderstorm to our area overnight. The
12Z CAMs present two likely scenarios with both the FV3 and NAM
3K showing the development of a more potent line of showers
across the north shore of Massachusetts, and the HRRR draping a
line of showers across Connecticut and central MA. Embedded
thunder cannot be ruled out in the strongest cells with elevated
CAPE values approaching 1000 J/KG. Overall, not expecting a
widespread convective event this evening, but cannot rule out
Winds will be variable again overnight, but will ultimately take a
northerly stance by sunrise. With high astro-tides in the mix and a
high tide expected around midnight, it is possible that some minor
splashover may be experienced in our most coastal flood prone
locations. This evening`s tide looks to be our only shot for
splashover/minor flooding in the foreseeable future.
.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
A rather "fall-like" 500mb trough begins to dig into our region on
Friday behind Thursday evening`s cold front. While conditions look
to stay mostly dry during the day on Friday, the trough will begin
to invert, which coupled with a few weak bubbles of low pressure to
our east may bring unsettled, showery weather to parts of our
region. Cape Cod and the Islands again have the best chance for
showers on Friday due to their proximity to the best available
moisture and forcing, but shower chances may expand into southeast
MA and RI during the day Friday. Even so, we are not expecting a
washout, with just the chance for scattered showers. Cloudiness will
accompany the chance for showers across eastern MA and Rhode Island,
but much of western MA and central CT will experience much sunnier
skies; similar to what we have experienced the last few days.
Fog will dissipate across southeast and Coastal MA after sunrise as
we begin to mix out. Given mostly sunny to partly cloudy skies
across our western zones, daytime mixing will again allow dewpoints
to drop into the 50s west of the Worcester area. This drop in
dewpoints will be aided by much drier 850mb air rushing into the
region behind the departing cold front. Some guidance, namely the
ECMWF, actually mixes high dewpoints out all the way to the coastal
plain , opening the door for dews in the upper 40s late Friday
afternoon and evening! While the ECMWF presents the most aggressive
solution, other guidance, like the GFS, Canadian, and NAM, are all
in line with a substantial drop in humidity by Friday afternoon; in
general widespread dewpoints in the 50s can be expected, especially
west of I-495.
Hi-res guidance, along with the ECWMF, keeps these low dewpoints
with us overnight Friday, which opens the door for some of the
chilliest overnight lows we have seen in weeks! Widespread sub 60F
lows will be observed Saturday morning across interior southern New
England, but clear skies, relatively light winds, and nice radiative
cooling across western MA may drop temperatures into the upper 40s
across the highest elevations of Franklin and Worcester
Cape Cod looks to stay immune to these almost September like lows as
cloud cover and moisture from the inverted trough set-up keep shower
chances alive overnight Friday into Saturday. Overnight low
temperatures across the Cape and coastal plain will remain above
60F. Shower chances look to be limited the this region.
.LONG TERM /SATURDAY THROUGH THURSDAY/...
* Could see spotty showers across eastern areas especially early
Sat, but overall should be dry and quiet through the weekend.
* Unsettled for much of the upcoming week as the pattern becomes
more fall-like. Chances of rain especially in the Tue-Thu
timeframe. Temps near to below seasonable.
Saturday through Sunday...
Trough/cutoff over New England initially lifts into northern New
England/Nova Scotia by late Saturday. Behind the trough a shortwave
ridge builds into the eastern Great Lakes late on Saturday and over
New England on Sunday. Will have a broad low offshore lifting toward
Nova Scotia on Saturday as high pressure builds in. The high pushes
offshore on Sunday, but will still nudge into southern New England.
Expecting much of this period to be dry and quiet weather wise
across southern New England. Do think there is the opportunity for
some spotty showers across the Cape/Islands and southeast MA due to
the broad low offshore especially during the AM. Expect this
activity to push offshore as the low lifts further off. Even the
current PoPs could be a bit overdone given the NW flow aloft drying
out the mid levels, but slight chance to chance does not seem
unreasonable at this point.
Will see cooler than seasonable temps across the region on Saturday.
Expecting NW cold air advection to keep temps in the roughly 8-10
degree Celsius range. Not completely out of the question we are a
bit cloudier than currently forecast as well given the cutoff
overhead combined with diurnal heating, but have not adjusted from
the NBM at this point. May need to in future updates. The result
will be cooler than normal highs with readings in the mid/upper 70s
for most. Anticipate there will be some 80 degree readings over the
CT River Valley.
Drier weather in store for Sunday, but warmer as the high shifts
offshore and flow becomes more W/SW due to the position of the high.
This will result in 850 hPa temps warming to roughly 10-13 degrees
Celsius. Temps will be more seasonable for this time of year with
highs in the upper 70s to mid 80s.
Monday through Thursday...
Unsettled through much of this period. A trough digs into the
eastern Great Lakes/New England on Monday. This feature then cuts
off and remains nearby/overhead for much of the week.
At this point appears that early on Monday will start off relatively
dry, but will have increasing chances of rain as the day progresses
due to low pressure developing to the south of us. At this point
think that the activity over our region will be more spotty on
Monday precip wise and should not be a washout especially as the
best upper forcing should be to the west of us. The NBM seems
reasonable at this point with increasing chances of precip and temps
in the mid 70s to low 80s. Do suspect this may need to be lowered
due to persistent onshore flow, but will have to get a better handle
on the sky cover in place.
Have still stuck with the NBM in the Tuesday-Thursday timeframe. It
is here where we will have the best shots for potentially
significant beneficial rains. Expecting the cutoff to slide closer
or over southern New England on Tuesday into Wednesday before
potentially lifting out on Thursday. There is some question with how
quickly this feature lifts out, which at this point is where most of
the uncertainty lies especially later in this period. Think that the
greatest chance for widespread rains is on Tuesday and Wednesday as
we will have PWATs rising to roughly 1-2 inches with the highest
values across eastern areas. Warm cloud layers depths appear to be
in roughly the 3-4 km range and given the forcing there could
potentially be some heavy downpours at times. Instability appears
limited and honestly looks more like a stratiform rain pattern, so
have kept out thunder at this point. Temperatures generally in the
70s on Tue/Wed, but may become more seasonable by Thu.
.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Expecting most terminals to remain VFR tonight. The exception is
the Cape/Islands and perhaps the immediate eastern MA coast.
Expecting MVFR to LIFR stratus/fog to spread in due to onshore
flow. Should see visby fall to roughly 1-2 SM other than ACK
where it may go down to 1/2 SM to 1/4 SM at times. Was not
confident enough at this point to bring down to 1/4SM, but may
be necessary at ACK. Will note that BOS appears to be on the
edge of this MVFR/IFR stratus deck. Have hinted at this point,
but keep VFR for now. Should see this risk go away at BOS as
winds flip to the W/NW between 5-6Z.
More immediately will need to keep an eye on the shower activity
spreading into SW MA and CT. Leaned toward ARW which slides this
activity through BAF/BDL. Not out of the question there could be
a rumble of thunder or two, but anticipate the activity to
diminish as instability wanes. Winds will remain rather light
and variable overnight, but will trend NW to N by sunrise.
Friday...High confidence; moderate confidence for Cape and
Mainly VFR, with areas of MVFR lingering across the Cape and
Islands for much of the day. Think the best shot of breaking out
will be late AM into the afternoon. Cannot completely rule out a
spot shower across RI/SE MA. Winds N to NE at 5-10 kts.
Friday night...High confidence.
VFR with increasing chances for showers across RI and southeast
MA. Winds out of the N/NNE at 5-10 kts. Could see a few gusts of
15-20 kts across the Cape/Islands toward daybreak.
KBOS...High confidence in trends, moderate in exact timing. Main
concern is the MVFR and borderline IFR stratus leaking in
between 00-06Z. Once winds shift to the W/NW should see this
threat go away. Have hinted at the possibility for now, but keep
KBDL... Moderate confidence. May see a spot shower and perhaps a
rumble of thunder between 01-04Z. Have as VCSH for now, but may
need to up to VCTS. Uncertain due to the waning instability.
Afterwards confidence high with VFR conditions and light N/NW
Outlook /Saturday through Tuesday/...
Saturday through Sunday Night: VFR.
Monday: VFR. Slight chance RA.
Monday Night: VFR. Chance RA.
Tuesday: Mainly MVFR, with areas VFR possible. Chance RA.
Forecaster Confidence Levels:
Low - less than 30 percent.
Medium - 30 to 60 percent.
High - greater than 60 percent.
Tonight into Friday...High confidence.
Winds and seas will remain below SCA criteria during this period.
Low pressure will track across the far southern waters today,
bringing light and variable winds along with periods of rain showers
during the day into the early evening hours. Localized fog is
also possible overnight tonight into Friday morning especially
across the southern waters into Cape Cod and the Islands.
Friday night...High confidence.
Increasing N to NNE winds. Should see speeds of 10-15 kts late
with gusts up to 20 kts. Seas 2-4 ft. Will have shots of
scattered rain mainly across the south coast.
Outlook /Saturday through Tuesday/...
Saturday: Winds less than 25 kt. Slight chance of rain showers.
Saturday Night through Sunday Night: Winds less than 25 kt.
Monday: Winds less than 25 kt. Slight chance of rain.
Monday Night: Winds less than 25 kt. Chance of rain.
Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
Chance of rain.
A Coastal Flood Advisory in place from 01Z to 07Z this evening
due to high astro tides and developing northerly flow. Winds are
expected to remain light overnight, but splashover and
inundation of up to one half foot is possible in our most
coastal flood prone areas such as Morrissey Boulevard and
Nantucket Harbor. Tonight`s high tide is expected to be the only
high tide of concern for the foreseeable future.
MA...Coastal Flood Advisory until 3 AM EDT Friday for MAZ007-015-
Area Forecast Discussion
National Weather Service Jacksonville FL
921 PM EDT Thu Aug 11 2022
Rain ended much earlier due to prior convective overturning and
stabilizing conditions. Weak sfc high pressure is over the forecast
area with some low level convergence to our west, which is where
mid level troughing is noted, from central GA to the FL panhandle
and northeast Gulf. This is also where isolated convection is
occuring this evening.
As shortwave energy gradually shifts eastward, a few showers and
potential storms will probably move into the Suwannee Valley area
after about 2-3 AM through sunrise. This is noted by the HRRR and
HREF guidance. So for the update, just included this potential of
slight chance of a showers in that area, and also dropped lows
1-2 degrees based on the fact the airmass has cooled nicely in
the wake of the cool outflow boundaries from Thursday afternoon.
Almost all sites are already in the 70s. Given this, some patchy
fog is possible but clouds and stirring winds just above the sfc
may hinder fog intensity.
Fairly quiet conditions overnight with winds generally 5-10 kt
and seas 2-3 ft. Will update 1st period of the forecast based on
latest observations and radar data.
.PREV DISCUSSION [743 PM EDT]...
.NEAR TERM [Through Tonight]...
An early start to Gulf convection pushed an outflow NNE across
the forecast area through mid-afternoon which brought strong to
isolated severe storms. The airmass has stabilized now with an
early end to deep convection across the area today as stronger
storms were pressing offshore of the local Atlantic coast and
north of the Altamaha River basin this hour. Lingering showers and
possibly an isolated storm across western SE GA or the Suwannee
River Valley will be possible in the wake of this stronger storms
through early evening, but coverage will be discrete and generally
fading stratiform with embedded lightning through 5-6 pm. Temps
cooled with strong outflows today and ranged in the 70s to low 80s
after high temps reached near 90 generally east of Highway 301
prior to convection.
Cloudy skies with a low chance of showers will continue through
about 8 pm, then mostly dry conditions and lingering debris clouds
are expected through about 3-4 pm, then the next batch of Gulf
convection will begin to fire and edge eastward toward the Gulf
Coast through sunrise under moist, westerly steering flow and
continued weak PVA aloft under a deepening mid/upper level trough
across the eastern CONUS as the surface front edges southward
across N GA. Minimal fog is expected tonight due to lingering
.SHORT TERM [Friday Through Saturday Night]...
A front will move south across Georgia Friday and approach north
Florida early Saturday. West to southwest winds will precede the
front Friday morning which will bring an early start to showers
and isolated storms across the Suwannee River Valley and portions
of southeast Georgia. Into the early and mid afternoon, showers
and storms will move toward the Atlantic coast, where a weak east
coast sea breeze will be near the I-95 corridor across St. Johns
and Flagler counties which could trigger stronger storms. Late
afternoon and evening showers and storms approach southeast
Georgia ahead of the front. Heavy rainfall potential increases
Friday night and into Saturday as the front slowly edges southward
across the local area under moist, westerly flow. Winds
transition to NNE late Saturday near the Atlamaha River Basin as
the front settles farther south and winds will become onshore near
Strong to isolated severe storms will be possible through Friday
evening especially across the lower St. Johns Basin from SGJ to
GNV southward where cooler temps aloft and stronger short wave
energy is expected to override the most low level instability mid-
afternoon as a weak east coast sea breeze drifts inland toward
the I-95 corridor.
Strong storm potential will fade with the loss of diurnal
instability Friday evening, but a chance of showers and isolated
storms, including locally heavy rainfall, will continue for SE GA
and the I-10 corridor of NE FL through daybreak Saturday morning
as the frontal zone drifts slowly south across the local forecast
area. With the slow moving front across the area under lobes of
passing vorticity under WNW flow, heavy rainfall potential will
focus near the frontal axis, especially for NE FL where the deepest
moisture fetch from the GOMEX is expected to override low level
convergence along the front into Saturday. The Weather Prediction
Center continues to highlight a "Marginal Risk" of heavy rainfall
across the local area Friday through Saturday, with widespread
rainfall amounts of 0.5-1 inches Friday through Saturday for many
areas, with locally higher amounts possible. Localized flooding
rainfall, especially near urban areas, will be possible with
Temperatures will trend near to below normal with highs near 90
toward the I-95 corridor Friday to the mid/upper 80s across the
Suwannee River Valley and SE GA. Temps will trend cooler Saturday
with the front settling across the area and range from the
mid/upper 80s across most locations to near 90 across our north-
central FL zones (Marion-Flagler). Low temps will range in the
.LONG TERM [Sunday Through Thursday]...
On Monday, with a high pressure to the northeast, northerly flow
will bring drier mid level air, likely suppressing afternoon
convective activity. Some isolated convection may be possible from
onshore flow in the afternoon/evening. The drier air mass will
move south to central Florida while another front is approaching
SE GA from the northeast early Tuesday. The front will gradually
push through Georgia into Florida, bringing higher precipitation
chances especially in NE FL. Dominating flow will gradually shift
from northerly to westerly on Wednesday, allowing seasonably
average PWAT values to return. By Thursday, a SW steering flow
will allow the Gulf sea breeze to push inland. With the front
lingering in central FL mid week, scattered to numerous afternoon
and evening thunderstorm development is likely to occur Tuesday
After a slightly cooler weekend, temperatures will return to near
normal highs and lows next week, with highs in the lower 90s
inland and upper 80s/near 90 on the coast. Low temperatures will
be in the mid 70s on the coast and lower 70s inland.
[Through 00Z Saturday]
Prevailing VFR clouds expected to continue into Friday morning
with most of the convection aftn/evening dissipated already, and
just a very small chance of some low clouds or brief patchy fog
toward sunrise. Due to low confidence, will not put this in the
TAFs. A good chance of showers and thunderstorms again on Friday
and may start early likely today, so started some VCSH between
about 12Z-16Z Friday. Guidance is a bit uncertain on thunderstorms
during the mid to late part of the day so for now just include
PROB30 group and will leave any TEMPO groups for later TAF
issuances. Wind will be light south to southwest tonight, and then
prevailing southwest 5-10 kt Friday.
A cold front will settle south across Georgia Friday into Friday
night and then across north Florida early Saturday. Waves of
showers and storms will move across the local waters through this
time frame, with locally heavy rainfall at times along the
frontal boundary. The front will move south of the local waters
late Saturday as north to northeast flow develops in the wake of
the front into Sunday. High pressure will briefly build across the
local waters Monday then winds veer south southwest in advance of
the next front that will approach from the north Tuesday.
Rip Currents: Low rip current risk expected Friday and Saturday.
.PRELIMINARY POINT TEMPS/POPS...
AMG 71 89 70 89 69 / 10 70 40 50 10
SSI 76 89 74 87 75 / 10 70 60 60 20
JAX 73 91 72 87 73 / 10 60 40 70 30
SGJ 73 90 74 87 74 / 10 50 30 70 40
GNV 71 89 71 88 71 / 10 50 30 80 30
OCF 73 90 73 90 72 / 10 40 30 80 40
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
1054 PM CDT Thu Aug 11 2022
Issued at 857 PM CDT Thu Aug 11 2022
Only real change we`ve seen with the forecast this evening is a
slight westward shift in where the heaviest band of rain is expected
to setup Friday morning. This makes sense as it brings the higher QPF
closer to where blends show the surface moisture gradient setting up
overnight. It`s not huge, but the 11.12 HREF had the heaviest rain
falling almost right over Hennepin county. A band of rain like this
is still expected, but looks to be more from near Alexandria southeast
across western Carver and Scott continues, and down toward Owatonna.
We expect a very sharp rainfall gradient across the west side of the
rain shield, with a more gradual gradient to the east of the heavier
band across much of the Twin Cities metro and western WI.
.DISCUSSION...(This evening through Thursday)
Issued at 310 PM CDT Thu Aug 11 2022
- Heavy rainfall possible late tonight into Friday morning.
A very good setup overnight and early Friday morning of heavy
rainfall potential as a storm system begins to organize across the
Northern Plains and moves east-southeast across the Upper Midwest
through Friday evening. This main setup for the heavy rainfall
potential is a strong moisture advection axis associated with an
increasing low level jet tonight, a fairly strong jet streak at mid-
levels of the atmosphere, and PWATs near 1.75" or greater by Friday
morning. Although there will be timing and placement issues based on
which the these parameters are maximized, the potential is high that
heavy rainfall will occur. HREF 12-24 hr QPF ensemble localized
probability-matched mean suggest eastern Mn and parts of western Wi
could see localized 1 to 2 inches before noon Friday. WPC has
highlighted this region with a marginal risk of excessive rainfall,
but the overall threat is low (Flash Flooding Risk) based on current
moisture conditions. Temperatures will have a high range Friday
afternoon with 90s in the far western MN, with just 60s in a cloudy w
est-central WI. I wouldn`t be surprised to see some minor changes
based on cloud cover and when the rainfall exits our region. There
remains some residual shower and thunderstorm activity Friday night,
especially over western WI where the surface low and upper level
forcing remains in close proximity.
Beyond Saturday, the general trend is to remain near seasonable
norms with highs in the 80s and lows in the 60s. There are no big
signals of any strong storm system moving across our region. Global
models also suggest a very anomalous deep trough forming across the
eastern 1/2 of the nation with a general north/northeast flow aloft
next week. This means cooler than normal over the eastern CONUS, and
parts of the Great Lakes.
Models also suggest a weak frontal boundary mid to late week slowly
affecting the Upper Midwest. However, models are not consistent on
areal coverage of the precipitation and upper level forcing.
Therefore, the NBM will be used which leans toward climatology
anyway. Another disturbance moves across the area by late in the week
which is just a reinforcement shot of the cooler airmass from the
deep trough over the eastern CONUS.
.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1046 PM CDT Thu Aug 11 2022
Few changes needed to going TAFs. Continued to favor a blend of the
NAM and HRRR (and away from the GFS) for timing of precip in the
TAFs, which still looked good from the 00z TAFs with only some minor
timing changes. A band of storms is still expected to develop during
the morning, likely impacting STC and MSP, with MKT either getting
in on the storms or remaining just west of them. For EAU/RNH it just
looks like a light rain for most of the morning. The one change we`ve
seen with the 00z guidance is more of them starting to develop some
MVFR cigs in the morning with the heavier rain. STC has the most
guidance hitting them with MVFR cigs, though MSP could get in that
for a bit.
KMSP...We`re starting to really hone in on 10z for seeing precip
breaking out at MSP, with some lightning looking likely between 11z
/OUTLOOK FOR KMSP/
SAT...VFR. Wind NE 5 kts.
SUN...VFR. Wind NE 5 kts.
MON...VFR. Wind SE 5-10 kts.
Area Forecast Discussion
National Weather Service Phoenix AZ
412 PM MST Thu Aug 11 2022
.UPDATE...UPDATED 00Z AVIATION DISCUSSION...
A 15 percent chance of widely isolated to scattered mostly
distant and high terrain storms continues this afternoon in
Phoenix, with better 30 to 50 percent chances across the high
terrain areas. Storm chances then gradually increase this evening
through tomorrow and the weekend with locally heavy rainfall,
localized flash flooding, gusty winds and patchy blowing dust
possible. Near to slightly below normal highs will fall further
below normal over the weekend and through early next. Storm
chances for next week remain moderate.
The midlevel anticyclone remains favorably located near the S-Cent
Rockies with moist SE-E undercutting flow through the mid-upper
levels aloft. WV imagery reveals a very moist airmass across the
region with upstream E wave disturbance(S) advancing W through NM.
Early afternoon radar revealed convection sparking E-NE of Phoenix, N
and SE AZ. Afternoon ACARS soundings showed an anomalously moist
airmass with PW maintaining near 1.7->1.9" along with a near moist
adiabatic, slightly worked-over and conditionally unstable
profile. Mesoscale analysis indicated PW of 1.5->2" and mean W of
12->14 g/kg across the region. MU and SB CAPE readings were to
~1.3K->1.5K j/kg around Phoenix and >2-2.5k j/kg across the W
Under mostly clear skies, morning heating across Phoenix and the
lower deserts has been stronger today than recent mornings. Models
also indicate temporary subsidence around Phoenix and the lower
deserts this afternoon. A 15 percent chance of widely isolated to
scattered mostly distant and high terrain storms continues this
afternoon in Phoenix, with better 30 to 50 percent chances across
the high terrain areas. Recent HRRR runs have latched onto a late
afternoon E outflow pushing into the Phoenix Metro with the
potential for locally gusty winds. This is in good agreement with
current radar trends.
Storm chances then gradually increase this evening through tomorrow
and the weekend with locally heavy rainfall, localized flash
flooding, gusty winds and patchy blowing dust possible. The WPC day
2 ERO for tomorrow/Fri also features a large "Slight Risk" area
of excessive rain fall for most of AZ. This is associated with the
next E wave out of NM.
HREF and members are fairly bullish on pronounced convection with
locally heavy rainfall developing tomorrow/Fri afternoon across S
Gila Cty and near/E of Globe and burn scar areas (and the
Mogollon Rim and SE AZ) before descending into the lower deserts
and parts of the Phoenix Metro during the evening hours. HREF wind
speeds for Fri evening feature a pair of fairly robust converging
outflows, one from the NE and the other from the SSE. The
resulting low level convergence through Pinal and Maricopa Cty,
coupled with the UL disturbance, would support pronounced
storms/convection for the Phoenix Metro and lower deserts
spreading west of Phoenix, including into parts of W-SW AZ and SE
CA, well into the night. The preferred WPC storm total QPF for
Phoenix on Fri is ~0.10-0.15" and ~0.3-0.5" for both the E AZ high
elevations and parts of the western deserts. The HREF shows a
50-70% chance for 3-hr QPF >1.0" for the E AZ high terrain for
Fri evening and a corresponding 10-30% chance for Phoenix and the
lower deserts. This represents a good signal for locally heavy
rainfall and additional localized flash flooding in the high
country and the lower deserts.
For the weekend, ensembles are latching onto a slightly larger E
wave on Sat evening and Sun moving from NM to AZ in general. The
preferred NBM and WPC solutions feature an increase in POPs while
maintaining healthy storm total QPF for Sat evening and Sun
morning comparable to the aforementioned Fri evening/Sat morning
storm total QPF.
At some point early next week, the pattern will begin to shift
with the sub-tropical high to our northeast weakening, while a
weak trough possibly sets up off the southern California coast.
This scenario may not bring much of a change to our area with
models continuing to show adequate moisture levels for storms, but
overall forecast confidence is low due to the change in the upper
level pattern and some model differences. Temperatures are
expected to cool off slightly at some point over the weekend into
early next week with forecast highs closer to 100 degrees due to
anticipated more active monsoon conditions.
South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Winds are variable across the metro area, with areas of southerly
winds in the southeast and north valley areas. Closer to KPHX
winds have been southwest. Wind directions will shift between 0-1Z
across the metro area as an outflow from the northeast moves in.
Winds may shift again to the southeast later this evening due to
additional storm activity. Thunderstorms are expected to stay out
of the valleys, but there is a 10-20% chance a storm could develop
close to a terminal. Due to the expectation of multiple outflow
boundaries, wind directions will be gusty and erratic at times
with periods of relatively low predictability. Overnight winds
will become southeasterly with another small 10-20% chance of
virga showers near dawn. Additional thunderstorm activity appears
likely Friday afternoon, with a 30% chance of spreading into
Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will generally favor the south-southeast. KIPL will have a
westerly wind shift for a few hours later this evening but speeds
will mostly remain below 10 kts. Chances for showers and
thunderstorms this afternoon and evening are 15% or less at the
terminals. However, any thunderstorm that develops would be
capable of gusty erratic winds, blowing dust, and locally heavy
rainfall. Skies will remain mostly cloudy through the TAF period
with ceilings mainly aoa 10 kft.
Ample monsoonal moisture is expected to persist through at least
the first half of next week keeping the fire danger threat low.
This moist airmass will continue to yield elevated humidities
with afternoon minimum RH values mostly in a 30-35% range,
locally higher, and good overnight recovery. Chances for wetting
rains will continue for most areas almost daily. Winds for the
most part will remain light, with the exception of thunderstorm
outflows generating stronger gusts.