Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 04/28/18
Area Forecast Discussion...Updated
National Weather Service Billings MT
843 PM MDT Fri Apr 27 2018
No changes needed to the going forecast. Convection over KBOI`s
area this evening was well-depicted by the HRRR, and was being
driven by difluence and jet divergence ahead of the SW OR/N CA
Pacific low, and by orographics. Models either dissipate the
convection or keep it over ID. HRRR dissipated it. Some convection
will redevelop over the western mountains Saturday morning as
dynamics move over this area. Forecast has some PoPs over the high
peaks of the Beartooths/Absarokas in the morning. These PoPs may
need to be expanded if models start showing more QPF. Dry forecast
for tonight looked fine. Low-level jet will turn winds in the E
to the SE, and increase their speeds a bit overnight. Expect
mainly clear skies overnight. Temperatures were in good shape
given observed temperature and dew points and expected trends
.SHORT TERM...valid for Sat and Sun...
Strong high pressure aloft will bring continued dry and warm
weather through tomorrow. As ridge axis shifts east, thermal low
will move to south central MT, bringing what will be the warmest
day yet of 2018 for our western and central cwa, including
Billings which should see its first taste of 80 degrees. Sheridan
should push the mid 80s.
Height falls and backed SW flow aloft will open the door to
isolated showers/tstm potential across our western mountains and
foothills by late Saturday. Low levels across our west will be dry
and well-mixed, and forcing will be weak, so will keep coverage
at isolated, though could see some erratic surface wind gusts near
any weak storms that develop. Eastern areas will see increasing
boundary layer moisture, but air mass will be capped w/ increasing
SE winds. Far eastern areas from Baker to Ekalaka will see gusts
of 35-45 mph tomorrow.
Shortwave and west-to-east passage of a weak cold front will keep
the risk of showers going through the night and Sunday morning
across the western two-thirds of our forecast area. Latest models
are a little more aggressive w/ the surface front, so have
expanded pops further east by late Saturday night.
Better potential for showers and thunderstorms is Sunday afternoon
and evening as a stronger shortwave lifts through WY, ahead of a
fairly deep upper low over ID. Likely pops across the region look
good and will keep this forecast going. As for the potential for
strong storms, eastward passage of surface front will result in NW
surface winds and decreased instability across our western and
central areas. It looks as if greatest chance of strong storms is
in our east in vicinity of surface trof, and this is something
to watch as we get closer to Sunday. Shear and instability, along
with PV lifting thru WY at a favorable time of day, could support
a few severe storms if the surface trof is slow to exit into the
Dakotas. Regardless of this, Sunday will be an active day of
weather and anyone with outdoor plans should take note. Temps on
Sunday will be warmest in our far east, maybe near 80 degrees, and
post-frontal/cooler in our west (mid 60s to lower 70s).
Chance of precip will continue through Sunday night as upper trof
to our west moves slowly east. Freezing levels will fall slowly
during this time and elevations above 7kft could see some snow
accumulation by early Monday.
.LONG TERM...valid for Mon...Tue...Wed...Thu...Fri...
An unsettled weather pattern will persist through the middle of
the coming week as an upper trough and associated low dominate the
weather over the western US. A weak shortwave looks to lift into
the region on Monday spreading precipitation across the area
Monday into Monday night. While the precipitation looks to remain
mainly rain at the lower elevations, snow accumulations across the
higher elevations look possible. Heading into Tuesday, general
troughiness continues, with models digging a cutoff low over the
desert southwest and dropping another shortwave into the area out
of the northwest. This will continue shower chances over the area
for Tuesday, possibly into Wednesday. Uncertainty remains high for
this time frame as models continue to struggle with placement and
timing of waves and associated precipitation. High pressure then
looks to build over the region Thursday into Friday diminishing
High temperatures will range from the 50s to lower 60s through
midweek with the unsettled weather pattern, potentially warming
back into the 70s by Friday as high pressure builds back over the
region. Low temperatures in the 30s can be expected most
Strong high pressure aloft will bring continued VFR flight
conditions tonight and Saturday. Southeast winds will increase in
far southeast MT, with gusts of 30-40 kts at KBHK tomorrow. Expect
isolated showers and thunderstorms across western areas by late
.PRELIMINARY POINT TEMP/POPS...
Sat Sun Mon Tue Wed Thu Fri
BIL 046/082 053/071 043/056 038/057 037/057 037/063 040/071
00/U 26/T 64/W 33/W 32/W 11/B 11/B
LVM 041/080 045/065 037/052 034/054 034/053 032/059 034/066
02/T 35/T 54/W 44/W 33/W 11/B 11/B
HDN 042/084 052/074 044/058 038/058 037/059 037/063 040/071
00/U 26/T 75/W 43/W 22/W 11/B 11/B
MLS 044/079 052/075 047/058 038/055 036/059 037/062 040/070
00/N 12/T 64/W 33/W 12/W 11/B 11/U
4BQ 043/077 054/075 046/057 039/054 037/056 037/058 039/068
00/N 13/T 64/W 43/W 12/W 21/B 11/U
BHK 039/071 048/077 046/060 036/052 033/057 035/059 037/067
00/N 02/T 63/W 33/W 11/B 11/B 11/U
SHR 043/083 051/072 042/054 037/054 037/053 034/057 036/065
00/U 26/T 66/W 53/W 23/W 21/B 11/U
Area Forecast Discussion
National Weather Service Wilmington NC
1045 PM EDT Fri Apr 27 2018
Weak high pressure will prevail tonight into Sat. A dry cold
frontal passage will occur Saturday night, followed by cool
Canadian high pressure for Sunday into Monday. The center of the
high will drift across the area Tuesday and slowly offshore
from the Southeast U.S. Coast during the mid to late week period
of next week. This will result in a substantial warm up to occur
during the mid to late week period of next week, with continued
dry conditions under mainly clear skies.
.NEAR TERM /THROUGH SATURDAY/...
As of 830 PM Friday...The sfc based inversion should develop
but later this evening or overnight then the usual right after
sunset. This due to an active boundary layer. As the sfc pg
further relaxes this evening and overnight, winds, especially
away from the coast, will eventually decouple. Enough low level
moisture remains given current and overnight progged sfc
dewpoints. In addition, sfc dewpoint depressions will run 0 to
3 degrees F. All of this is enough to atleast include patchy
ground fog for most locations mainly during the pre-dawn Sat
As of 300 PM Friday...A beautiful day ongoing across behind this
mornings weak low pressure and rain showers. Much drier air
advecting overhead noted on WV imagery and evident on visible is
combining with weak subsidence and a capping inversion to
prevent any showers locally. Despite the HRRR insistence that
showers will develop across SE NC this aftn, have kept POP below
mentionable as even the Cu field outside looks flat due to dry
air entrainment from above. For this reason do not anticipate
anything more than maybe 1 isolated shower in Pender County, not
worth a POP addition. Otherwise, dry air aloft will eventually
win out, and other than some scattered mid-level cloud cover
tonight expect mostly clear sky conditions with winds becoming
light. As mins fall into the mid and upr 50s, good radiational
cooling, light winds, and still a moist ground could support
some fog overnight. Text bulletins keep visibility mostly
unrestricted, and soundings show only shallow saturation despite
favorable low-level hydrolapse rates. Could see some shallow
fog overnight, but otherwise do not expect widespread or dense
On Saturday, the region enters a warm sector ahead of a cold front
which will be on the doorstep Saturday evening. Despite continued
broad troughing aloft, WAA on SW winds near the surface will drive
temps up towards 80 on Saturday, but have forecast temps slightly
below guidance to account for expected diurnal Cu and lowered
thicknesses beneath the upper trough, but still a beautiful and dry
day forecast for Saturday!
.SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 300 PM Friday...What a difference a day makes. Although
sunshine will be plentiful, Sunday will be much cooler than
Saturday. The mid to upper trough will dig down and push a dry
cold front through and then finally swing off the coast Sun
night. The main shortwave energy will remain north Sat night but
should see some passing clouds as front passes through. The pcp
water is up to .75 inches Sat night but plummets down to a
quarter of an inch or less through Sun. The low level westerly
flow will swing around to the NW and N with a dip in 850 temps
from 10C Sat eve down near 2C Sun morning. Overall, plenty of
cool and dry air will make its way in Sat night into Sun.
Temps Sat night will begin to drop in CAA, ending up in the low
to mid 50s by daybreak. Late April sunshine will work against
the CAA to push temps to near 70, but most of the day will be in
the 60s with a cool northerly wind. By Sun night the atmosphere
will decouple over most of the area leaving near calm to calm
winds overnight. This will combine with clear skies to produce
temps down in the 40s most places.
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 300 PM Friday...H5 low over New England will drift
farther east during Monday while a ridge axis begins to push
east of the MS valley. Overall, this pattern change will result
in increasing heights aloft, subsequent warming trend, and a
continued lack of support for rainfall. Additional height
increases are likely the latter half of the week as a
subtropical high builds across the northeast Gulf of Mexico and
ridges across the southeastern United States. The precipitable
water will only be a half inch or less Monday and Tuesday,
gradually increasing to around 1 inch by Friday. While the long
term period will start below normal on Monday look for
temperatures to get back above normal by Tuesday and each day
thereafter through Friday.
.AVIATION /03Z SATURDAY THROUGH WEDNESDAY/...
As of 00Z...Mostly VFR conditions expected through the forecast
period. With good radiational conditions developing overnight,
there is always the threat of MVFR BR. With most guidance
pointing to this, I did use prevailing groups for all sites for
a couple of hours during the early morning. A little longer for
NEAR TERM /THROUGH SATURDAY/...
As of 830 PM Friday...Based on latest buoy reports and trends,
included SW gusts up to 20 kt during this evening and then
followed previous fcst dropping it back down to the West at 10
kt or less. Significant seas have kept widespread 2 to 3 ft for
the overnight with some 4 footers off Cape Fear via latest 41013
reports. These 4 footers will become less apparent as the wind
driven wave portions of the seas subsides as previously
mentioned. The ESE-SE, 8 to 9 second period swell will continue
to very slowly subside but remain the dominant input to the
As of 300 PM Friday...SW winds will persist across the waters
through this evening at 10-15 kts, before easing and veering to the
west late as a weak trough pushes offshore. Winds will return to the
SW Saturday as flow around the high pressure offshore and ahead of
an approaching cold front reaches 10-15 kts, with slightly higher
gusts likely within the near shore sea breeze during the aftn. The
front will still be well west of the waters by the end of the period
so SW winds will persist into Saturday night. A slowly decaying SW
wind wave and 8-9 sec 2 ft SE swell will combine through the period
to produce the wave spectrum this period. Seas currently of 3-4 ft
will fall slowly to around 2 ft late as the wind wave contribution
SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
As of 300 PM Friday...Seas will drop to less than 3 ft through
Sat eve in a lighter SW to W flow but a cold front will move
through overnight. Winds will swing around to the north behind
the front, increasing up to 15 to 20 kts through daybreak Sun.
Seas will increase to 3 to 4 ft Sunday morning. The slight surge
in northerly winds will diminish through late Sun leaving a NW
to N wind around 10 kts. This will allow seas to drop to less
than 3 ft by Sun night.
LONG TERM /MONDAY THROUGH WEDNESDAY/...
As of 3 PM Friday...High pressure will build over the waters during
Monday with a period of light and variable winds. The high will be
positioned off the SC coast Tuesday through Wednesday with light
southwesterly flow prevailing. No issues with seas as they remain 3
ft or less through the period.
Area Forecast Discussion
National Weather Service Lincoln IL
856 PM CDT Fri Apr 27 2018
Issued at 856 PM CDT Fri Apr 27 2018
Skies remain partly to mostly cloudy this evening and as the cold
front and associated light showers/virga continues to move
southeast across the CWA. Winds have also started to subside and
gusts are fewer and speeds are less. Current forecast has good
handle on this so far. Only concern is overnight low temps across
the area. Dwpts are in the 30s across the area, but winds of
10-15 mph should keep things mixed enough that overnight lows
should not fall down to dwpts. Current forecast lows of upper 30s
to lower 40s looks fine. Since forecast is handling current trends
good, will not be updating at this time.
.SHORT TERM...(This evening through Saturday)
ISSUED AT 250 PM CDT Fri Apr 27 2018
High-based CU field is becoming more robust along an advancing
cold front across eastern Iowa/northern Illinois this afternoon.
Despite developing radar echoes, have not yet seen any reports of
precip reaching the ground. Cloud bases are generally around
10,000ft...similar to what 12z forecast soundings showed. High-res
models such as the HRRR have been consistently suggesting widely
scattered showers developing along the front late this afternoon
into the evening, and based on current satellite/radar trends,
have no reason to doubt that. Given the very dry airmass below
800mb, any showers that develop will have the capability of
bringing higher momentum air down to the surface via evaporative
cooling...potentially producing wind gusts of 30-35mph. Have
included slight chance PoPs along/north of a Canton to Bloomington
line late this afternoon...then as far south as I-70 this evening
before the showers completely dissipate after sunset. The cold
front will settle southward into the Ohio River Valley late
tonight, allowing a chilly airmass to settle into the region. Low
temperatures tonight will range from the upper 30s north...to the
middle 40s far south around Lawrenceville. Highs on Saturday will
generally remain in the middle to upper 50s.
.LONG TERM...(Saturday night through Friday)
ISSUED AT 250 PM CDT Fri Apr 27 2018
As has been advertised for the past few days, the coldest period
of the entire forecast will be coming up Saturday night as a 1028mb
high builds into Illinois. Winds will become light/variable and
skies will be clear, allowing excellent radiational cooling
conditions to develop. Resulting low temperatures will bottom out
in the lower to middle 30s, with areas of frost likely developing.
If trends continue, a Frost Advisory will eventually be needed
for parts or all of the KILX CWA Saturday night into early Sunday
After one more cool day on Sunday, high pressure will shift east
of the region and southerly winds will bring a marked warming
trend next week. High temperatures will soar well into the 70s on
Monday...then will climb into the upper 70s and lower 80s by
Tuesday and Wednesday. Meanwhile, a deep upper trough will dig
across the western CONUS...then will slowly begin ejecting
eastward as the week progresses. Latest trends suggest this
process will take place in several phases and will be slightly
slower than previously thought. The first wave and its associated
rain chances will arrive Tuesday night into Wednesday: however,
model consensus suggests that the best rain chances will hold off
until Thursday/Thursday night as a significant portion of the
western trough pushes eastward into the Midwest. Have therefore
kept PoPs in the chance category through Wednesday...before
increasing to high chance/likely late Wednesday night through
Thursday night. After that, a cold front will slowly settle into
the Ohio River Valley by Friday, shifting the best rain chances
off to the E/SE at that time.
.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 630 PM CDT Fri Apr 27 2018
VFR conditions will prevail at all TAF sites next 24hrs. Broken AC
around 8-9kft will move across the sites this evening, ending
first at PIA, then BMI and then around 4z at SPI/DEC/CMI. Then
clear skies to scattered clouds expected remainder of the night
and into the early morning hours. Then scattered AC around 10kft
will move back into the area during the morning hours and will
continue into the afternoon. Winds will be quite gusty this
evening with possible showers so have higher winds gusting to over
25kts this evening with VCSH. Once showers moves out and sunsets,
winds will decrease some out of the northwest. Winds become
northerly tomorrow but with speeds of only 10-15kts.
Area Forecast Discussion
National Weather Service Mount Holly NJ
929 PM EDT Fri Apr 27 2018
Several low pressure systems will move into the northeast this
weekend and combine into one and remain across New England
through early next week. A cold front is expected Saturday, with
additional surface troughs Sunday into Tuesday. High pressure
across the Mid Mississippi and Ohio Valley Sunday will build to
our south Monday, before shifting offshore of the Carolinas
Monday night where it remains through Thursday of next week. A
cold front is forecast to approach the east coast next Friday.
.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
With the 930 PM update, made some adjustments to weather and PoP
for later tonight. The area of showers and thunderstorms in
central PA continues to show organization in two separate
lines. It should weaken some as it gets closer to our area; much
of our area did not clear out before sunset, therefore, we are
starting out with lower temperatures as compared to central PA
and thus lower instability. None the less, there is some
elevated instability in RAP model soundings at 06Z enough to
support isolated thunderstorms. These showers are associated
with a leading mid and upper level short wave trough that is
expected to lift northeast over PA overnight.
The wind should become light and variable overnight as the weak
surface low departs our region. The lingering low level
moisture is expected to manifest itself in the form of low
clouds and areas of fog. We did see some clearing, though low
clouds are starting to build back in. If this trend continues,
this could be more of a low stratus event, but given dew point
depressions already less than 5 degrees F for many sites, did
not have enough confidence to reduce the mention of fog across
Minimum temperatures are forecast to range from the middle 40s
to the lower 50s in much of southeastern Pennsylvania, New
Jersey, Delaware and northeastern Maryland. Lows should be in
the lower 40s in the Poconos and in far northern New Jersey.
.SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/...
The sky should become mostly sunny over much of our region on
Saturday morning after any lingering low clouds and fog lift and
dissipate. However, clouds should be on the increase again
during the afternoon as a cold front approaches from the west.
The wind is expected to be from the southwest around 10 mph.
The cold front is forecast to begin moving into eastern
Pennsylvania toward evening. We have mentioned the potential for
rain showers as the boundary nears.
The southwest flow should result in slightly above normal
daytime temperatures. Highs will favor the upper 60s and lower
70s in much of our region. Readings should not get above the
lower and middle 60s in the elevated terrain up north.
.LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
On Sunday high pressure will be moving out of the Mid
Mississippi Valley and across the Tennessee River Valley, before
shifting across the southern Applachians and offshore of the
Carolinas Monday. Meanwhile, low pressure will remain across New
England. This will keep our area under the influence of a west
to northwest flow, with a couple of weak surface troughs and
short wave/vorticity impulses moving across the area both Sunday
and Monday. Most of the area will remain dry with the passage
of the surface troughs. However, an area of enhanced low-mid
moisture will slide across portions of northeast Pennsylvania
and northern New Jersey, which could lead to a chance of
isolated showers. Gusty conditions are expected to develop both
Sunday and Monday with winds gusting 20-30 mph at times.
The high will remain to our south Tuesday into Wednesday,
keeping dry conditions in the forecast. Winds could remain gusty
at times, but likely not as gusty as Sunday or Monday;
generally 15-25 mph.
Late in the week a cold front is expected to move toward the
area from the west. Right now it looks like the front will not
make it fully into the area Thursday, but more likely Friday.
There will be a chance of isolated showers starting Wednesday
night through Friday as multiple short wave/vorticity impulses
will be sliding across the area. However, the most likely period
for showers is Friday with the passage of the actual cold
After an up and down forecast to the temperatures Saturday and
Sunday, a warming trend will begin Monday and continue through
the upcoming week. Temperatures in the 80s are forecast for the
end of the week from Wednesday through Friday.
.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG,
KILG, KMIV, KACY and surrounding areas.
Tonight...High confidence that the wind will be light and
variable through the overnight period. However, for the
remainder of the forecast elements, have low confidence. First,
ceilings will be between MVFR and VFR through the evening hours.
Timing of changes between MVFR and VFR is uncertain. After
midnight, expect a round of fog and possibly low clouds to lower
conditions to IFR at most places, though LIFR is also possible.
May have a better idea in the next few hours as we monitor
temperature and dew point trends after sunset.
Saturday...VFR after early morning low clouds and fog.
Southwest wind 6 to 10 knots. Showers arriving from the west
very late in the afternoon. Moderate confidence in most aspects
of the forecast, but low confidence in the return to VFR
Saturday night-Wednesday...VFR. Gusty west to northwest winds
20-25 knots Sunday and Monday. Gusty west to southwest winds
15-20 knots Tuesday and Wednesday.
Winds and seas are expected to remain below small craft advisory
conditions tonight and Saturday. A cold front is forecast to
approach from the west on Saturday.
Wind speeds are expected to remain less than 15 knots with
gusts not exceeding 20 knots.
Saturday night...Conditions expected to remain below advisory
Sunday-Monday...Winds may approach Small Craft Advisory levels
on Sunday into Monday.
Monday night-Wednesday...Conditions expected to remain below
Area Forecast Discussion
National Weather Service Pocatello ID
206 PM MDT Fri Apr 27 2018
.SHORT TERM...Tonight through Monday afternoon. Low pressure
disturbance to our west has a embedded disturbance rotating through
California and Nevada, part of which may sneak into southern Idaho
late this afternoon and this evening with a slight chance of
thunderstorms that could move into the Sawtooth Mountains. The GFS
and the RAP both have an indication of some limited moisture after
midnight tonight moving towards Pocatello and then onto Palisades by
Saturday morning. Looks like high level moisture and late hour so
chose to not include any showers with that patch of clouds. The high
pressure ridge slips east as the low moves inland, we remain under
southerly flow and should stay on the warm side, a little more
cloud cover and cooler air aloft. Late Saturday afternoon and
evening we could fall under the influence of a spoke of energy
rotating around that low. Kept a slight chance of thunderstorms in
the forecast for the Central Mountains, Snake Plain, and Eastern
Highlands as it is real hard to pin point the activity. Overnight
Saturday and through Sunday, the bulk of the disturbance moves
across Idaho. Moisture deepens and even snow levels drop by Sunday
to near 6000 feet, then rebounds by afternoon with highs in the 50s.
Best snow should be in the Central Mountains with 1 to 4 inches
possible and most of that on the upper elevations. What ever shows
up below 7000 feet will not last long. RS
.LONG TERM...Monday night through Friday. Showers continue into
Tuesday as a trough remains over the state, with a new low carving
itself out to our southwest. At this point, trying to get into
details would be futile as the amount of showers and precipitation
varies among the models. It will remain pretty cool across the board
with snow levels in the general 6000-7000ft range. The low shifts
east on Wednesday, but close enough to keep showers going with a
better chance east of I-15. Confidence is low enough right now to
not go terribly high with the chance of rain or snow. That storm
will finally move far enough east by the end of next week to dry
things out PERHAPS. The ECMWF wants to set up a stronger blocking
pattern over the West, keeping us dry by then. The GFS has a ridge
but weaker in comparison and allows limited moisture for a few
showers and thunderstorms. We followed with a blended forecast that
keeps isolated development over the central mountains and along the
Montana border. Keyes
.AVIATION...The question over the next 24 hours is how extensive
will shower and thunderstorm coverage will be across eastern Idaho.
Higher resolution models seem to indicate that any real threat will
be isolated tonight from around Twin Falls through the central
mountains. There MIGHT be a few showers/storms that develop farther
east but that could be stretching it, and we end up with just some
mid level clouds. We did keep VCTS for a few hours this evening at
KSUN based on current trends. We DON`T have it for any other TAF
sites but that could change based on what happens this evening and
tonight. For Saturday, it looks like there are two potential areas
for showers and storms with a dry slot over the Snake Plain. The
first is over the central mountains to south of KBYI. At the moment,
it looks like VCTS would be warranted in the afternoon at KBYI and
potentially KSUN. For the latter, trends point toward most of this
staying to the north and west. Therefore, we left it out...for now.
The other area would be in the eastern highlands, affecting KDIJ at
some point for at least VCTS. We have dry air in place at the
surface, so we are looking at a potential gusty wind threat through
tomorrow with convection. Otherwise, VFR weather is anticipated.
Area Forecast Discussion
National Weather Service Phoenix AZ
855 PM MST Fri Apr 27 2018
Very warm conditions will continue through the weekend with
widespread high temperatures in the mid to upper 90s at lower
elevations. A slight chance for thunderstorms will exist across
southern Gila County on Friday and Saturday afternoon, but most
locations will not see measurable rainfall. A distinct cooling
trend will occur for at least the first half of next week, with a
slight chance of showers possible on Tuesday into early Wednesday
morning. Breezy winds will be possible on Sunday and Monday, with
stronger wind gusts on Tuesday.
At 8 pm this evening, a large upper low could be seen spinning just
off the Pacific northwest coast allowing the high pressure ridge
over the desert southwest to shift east; 00z plot data showed the
ridge axis near the New Mexico border. Ahead of the approaching low,
dry southwest flow aloft was spreading into the western deserts and
IR imagery showed generally clear skies from Phoenix west into far
SE CA. East of Phoenix, flow was more south/southeast and modest
amounts of mid level moisture had advected into the higher terrain
allowing high based cumulus to form over portions of southern Gila
county as well as the eastern mountains. So far no high based storms
or lightning strikes were noted over the high terrain east of Phoenix
despite the modest mid level instability present. High temp today in
Phoenix reached 100 degrees under sunny skies and this should be the
last day where high temperatures threaten the triple digit mark; the
low to our west will gradually push inland and drop heights leading
to a substantial cooling trend that will eventually drop deserts
highs to around 80 by the early to middle part of next week. For the
rest of tonight expect the clouds to our east to continue to
dissipate while skies remain genly clear from Phoenix westward.
Current forecasts look to be in good shape and no updates are needed.
Temperatures have once again climbed into the 90s for most areas
with a few spots in the Colorado River valley near 100 degrees as
Central Arizona and southeast California remains under a mid-to-
upper level ridge of high pressure. Some parts of Phoenix will
reach 100 today as skies continue to remain clear with relatively
strong subsidence. Clouds continue to develop over the higher
terrain in Gila County where cooler temperatures generally in the
80s are in place along a dissipating back door cold front.
Additional daytime heating and increasing MUCAPE values above 100
J/kg may allow for a few isolated thunderstorms to develop there
late this afternoon into the evening hours, but most hi-res models
including the HRRR keep this activity well northeast or just
south of our area. Any thunderstorm that does develop will most
likely not produce measurable rainfall, but there is a threat of
lightning that could initiate wildfires.
Thunderstorm chances still appear to peak tomorrow afternoon for
locations northeast of our region, but most hi-res models suggest
this activity will be northeast of Gila County. However, global
models continue to suggest the potential for measurable QPF over
far northeast Gila County, and MUCAPE values will be a little
higher tomorrow with greater moisture in place. Thus, we have
retained the mention of thunderstorms over this area, with the
biggest hazard remaining lightning strikes with a low chance of
measurable rainfall. Temperatures tomorrow may be a little cooler
tomorrow with this slight increase in moisture, but a more
substantial 3-5 degree cooling will occur on Sunday as the ridge
weakens further and heights fall ahead of a slowly digging trough
centered over the Pacific Northwest.
Temperatures will decrease to near or slightly below normal by
Monday as a vorticity maximum breaks off and rapidly digs along
the California coast and a dissipating front moves into western
Arizona. Global models show this low becoming cutoff along the
southern CA-AZ border on Tuesday, with dynamic forcing associated
with this cold core possibly triggering isolated thunderstorms
over higher terrain in southeast California. This trough should
lift northeast over Arizona Tuesday night into Wednesday morning,
which should allow for some shower activity at higher elevations
with perhaps some isolated showers into the I-10 corridor as weak
SW-NE isentropic ascent overspreads the region. Thus, we have
increased POPs closer to 15-20 percent for the Phoenix metro with
20-30 POPs further northeast and below 10 percent further west.
This forecast is dependent on the low tracking directly over or
just west of the region with enough moisture aloft, with an
eastward deviation making measurable rainfall more unlikely. At
the current moment, we only have a few hundredths of an inch of
rain well northeast of the Phoenix metro, but models trending even
cooler continues to look more likely.
Breezy winds will be possible on Sunday and Monday, with stronger
wind gusts in excess of 30 mph at higher elevations possible on
Tuesday mainly due to dynamic forcing from the low. Temperatures
for Tuesday and Wednesday were decreased a few degrees from the
previous forecast. Temperatures are close to the previous forecast
for the second half of next week as the model ensemble exhibits
considerable spread in whether or not a more progressive pattern
will occur or additional shortwaves will break off from the main
flow and push through the region. For now, we sided with the more
progressive pattern shown by the GFS, leading to a fairly rapid
warmup in temperatures closer to climatological normals.
South-Central Arizona including KPHX, KIWA, and KSDL:
Expect skies in the greater Phoenix area to remain genly clear until
Saturday afternoon when another round of high-baed cumulus will
develop over the higher terrain off to our east. Should any storms
develop over the mountains tomorrow afternoon/evening, we do not
expect any outflow winds or dust to reach into the Phoenix area or
affect the terminals. Winds next 24 hours will follow typical
diurnal tendencies, with potential for some afternoon southwest
gusts tomorrow reaching into the teens or low 20s.
Southeast California/Southwest Arizona including KIPL and KBLH:
Upper low approaching from the west will provide dry southwest flow
aloft and result in genly clear skies through Saturday evening.
Expect winds to favor the west at KIPL next 24 hours, with gusts to
around 25kt thru midnight tonight and again tomorrow late afternoon
and evening. Winds to favor the south to southwest at KBLH with some
gusts also expected Saturday afternoon. Do not expect any blowing
dust with the gustiness.
Aviation Discussion not updated for amended TAFs.
Monday through Friday:
Breezy to windy conditions will impact the districts Monday and
Tuesday with the strongest gusty winds of 20 to 35 mph Tuesday
afternoon. Cooler than average temperatures along with modestly
increased moisture values will keep humidity values elevated
slightly above critical thresholds. Afternoon minimum humidity
values will generally fall in a 15 to 25% range during the first
half of the week, falling to a 10-15% range by the end of the week.
Overnight recovery will generally be good. Wind speeds will decrease
substantially later in the week as temperatures warm back up near
and above the seasonal normal.
.SPOTTER INFORMATION STATEMENT...
Spotters are encouraged to follow standard reporting procedures.