Forecast Discussions mentioning any of
"HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 07/27/17
Area Forecast Discussion
National Weather Service La Crosse WI
545 PM CDT Wed Jul 26 2017
.SHORT TERM...(Tonight thru Thursday night)
Issued at 235 PM CDT Wed Jul 26 2017
Main fcst concerns this period are lingering SHRA/TSRA chances this
evening then small mainly SHRA chances Thu afternoon/evening.
18z data analysis had a cold front from NE WI to near KLSE to KOMA,
pushing slowly SE across the region. Per WV imagery and radar
reflectivity, a shortwave was moving east across IA. Abundant cloud
cover across IA, and most of WI and southern MN has limited CAPE
development over much of the region today. Thus, in spite of it
being July, convection with the front and shortwave has generally
decreased since 12-14z. Models and SPC meso-analysis indicating a
general lack of moisture transport/theta-e convergence across WI/IA
and nearby areas this afternoon, thus mainly sct SHRA and isolated
TSRA these areas.
No problems noted with 26.12z model initializations. Models in good
agreement for the IA shortwave to quickly pass east of the area this
evening. A stronger shortwave to then drop into northern WI by 00z
Fri and toward lower MI by 12z Fri. Trend favors a tighter consensus
of earlier runs on timing/strength of this feature as it drops SE
across the western great lakes. Short-term fcst confidence is
generally good this cycle.
In the short term, the IA shortwave energy moves well E/SE of the
area by 03z with the weak cold front slipping SE of the area as
well. With limited CAPE today due to the cloud cover and decreasing
forcing/lift, trend among models (including hi-res/CAMs models) is
for the bulk of the SHRA/TSRA to be exiting/out of the fcst area by
or shortly after 00z. Short-term forecaster has already reduced
SHRA/TSRA chances tonight, and depending on mid afternoon WSR-88D
trends, may need to reduce them more. Given a mostly cloudy/cloudy
day, some rain most areas, then a decrease of clouds tonight, patchy
late night/early morning BR/FG seems reasonable. Some increase of
pressure gradient/BL winds later tonight as the main sfc low
migrates to northern IL, but this may not be enough for BL mixing
and will leave the patchy fog in the 06-13z grids as is for now. Can
high pressure builds in Thu/Thu night, but some moist BL air (sfc
dew points in the 60s) progged to be slow to scour out. And there is
the shortwave dropping into northern WI by 00z Fri. Depending on how
much BL/low level moisture remains Thu afternoon, models progging
some MUCAPE over much of the fcst area around 00z Fri. Soundings
showing this mainly capped between 700-600mb. With approach of the
shortwave in the afternoon, continued some small SHRA chances across
the NE end of the fcst area. May yet need some small SHRA chances
across the NE side of the fcst area into Thu evening but will it dry
for now to maintain a good blend with neighboring grids.
925-850mb cold advection spreads across the area for Thu. With a
decent amount of sunshine and mixing to about 850mb, the blend of
guidance highs mostly in the upper 70s-lower 80s looks good.
Considered adding a mention of valley BR/FG to late Thu night/early
Fri morning grids but area remains on the leading edge of the high
thru 12z Fri, with some gradient sfc-925mb winds to keep BL stirred.
.LONG TERM...(Friday thru Wednesday)
Issued at 235 PM CDT Wed Jul 26 2017
For Friday thru Saturday night: main fcst concerns this period are
Model runs of 26.12z continue to advertise rising hgts/shortwave
ridging to build across the Upper Midwest Fri thru Sat night, for
what is expected to be a dry, quiet, seasonable period. Fcst
confidence remains on the good side for this period.
As the ridging aloft builds in, drier and cooler Can high pressure
builds SE across the region under it, with the center of the
high/ridge axis near/over the area Fri night thru Sat night. Model
soundings showing diurnal mixing to around 850mb both Fri/Sat,
with this mixed lower portion of the column supporting highs
mostly in the upper 70s to lower 80s. These temps near the late
July normals, along with an influx of drier BL air and sfc dew
points mostly in the 50s, to make Fri/Sat a couple of rather
comfortable days. The one other concern this period may well be
late night/early morning valley fog. A well watered landscape,
plus evapo- transpiration near its seasonal max and the center of
the high near/ overhead, parameters would be favorable for valley
fog formation these nights. Plenty of time to detail any fog
possibilities as Fri night/Sat nights approach.
For Sunday thru Wednesday (days 4-7): main fcst concerns this period
are small SHRA/TSRA chances much of Sun afternoon thru Wed.
26.00z/26.12z medium range model runs in rather good agreement on NW
flow aloft to remain over the Upper Midwest Sun thru at least Wed.
What they disagree on, which is no real surprise, are various
shortwaves to be rippling SE thru this flow during the day 4-7
period. Confidence is above average for temps to be near normal Sun-
Wed, but given the detail differences with shortwaves, confidence is
average at best on any of the SHRA/TSRA chances this period.
Under the NW flow aloft, 925/850mb temps over the region remain
seasonable with the warmer air held off to the west over the
rockies/western plains. Consensus highs/lows a few degrees either
side of normal for Sun-Wed looking well trended at this time. Model
consensus holds the sfc high over the region Sun/Mon, with the high
then being pushed off into the OH valley Tue/Wed as a stronger
shortwave and a sfc front would approach from the NW. For Sun/Mon,
main moisture plume on the west side of the high generally remains
west of the fcst area. However a model run here and there does try
to drop a shortwave in later Sun or Mon, bringing the moisture plume
and a small chance of SHRA/TSRA east and SE toward the area.
Stronger approaching shortwave and sfc trough/front Tue/Wed offering
a bit more consistency to bring the moisture plume into MN/IA/WI for
the middle of next week. With little confidence in the shortwave
details, the small consensus SHRA/TSRA chances later Sun thru Wed a
reasonable place to start at this point.
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 545 PM CDT Wed Jul 26 2017
Cigs: bkn mvfr-vfr cigs hanging around a sfc front sagging south
early this evening, and clouds should slip south of the taf sites
between 03-06z. MVFR likely comes in and out - no solid signal in
satellite/sfc obs. Generally skc overnight, with some diurnal cu
development for Thu afternoon.
WX/Vsby: still some threat for an isold shra/ts around the boundary
that could impact krst/klse through about 02z - per latest HRRR
runs. Won`t include in the forecast for now, rather monitor and add
With clouds most of today, the T/Td spread relatively small at early
evening. Should see a fall off in dewpoints tonight, but spread
looks to stay close, and with light winds/clear skies added to the
mix, some mvfr br looks likely overnight. Will continue mention.
Wind: generally light northerly tonight, picking up just a bit but
staying north Thu afternoon.
.HYDROLOGY...through Wednesday night
Issued at 235 PM CDT Wed Jul 26 2017
Bulk of the locally heavy rain threat this afternoon/evening has
passed or shifted south of the fcst area. Any additional rains
thru this evening no longer expected to create renewed hydro
Flood Warnings continue along the Kickapoo River from Gays Mill to
Steuben. River levels at these sites are expected to fall below
flood stage within the next day or so.
Area Forecast Discussion
National Weather Service Denver/Boulder CO
826 PM MDT Wed Jul 26 2017
Issued at 826 PM MDT Wed Jul 26 2017
A very moist airmass is in place with precipitable water value of
1.34 inches from the 00Z sounding at DNR. This is the highest
ever recorded for July 27th. Very heavy rain from the
thunderstorms is occurring with rainfall rates of up to 1 inch in
15 minutes with the strongest thunderstorms. The heavy rain and
flash flooding threat will continue through the evening as the
thunderstorms progress eastward.
.SHORT TERM...(This evening through Thursday)
Issued at 400 PM MDT Wed Jul 26 2017
An abnormally moist and marginally unstable atmosphere covering the
forecast area today will continue to fuel shower and thunderstorm
formation over and along the mountains. Storm motions this afternoon
have been quite slow, generally in the 10 to 20 mph range.
Instability is generally lower across northern sections of the CWA
as is evident by the poor organization and relatively short duration
of storms drifting off the foothills in Larimer and Boulder
Counties. However, a few of these storms before moving off the
foothills managed to deposit 0.25 to 0.50 inch of rain in under 45
minutes. The HRRR and RAP mesoscale models have done a pretty decent
job predicting the formation and slow progression of these storms,
although storm QPF has been over done. Will keep that in mind going
forward with storms downstream on the adjacent plains is evening.
Turning to areas farther south, such as along and south of
Interstate 70. Over the next few hours, should see storm coverage
expand eastward off the foothills as low-level moisture is fed into
the area by a deepening northeast flow. Should see the convection
drifting off the high terrain tapping into this moist and relatively
unstable environment resulting in scattered to numerous showers and
embedded t-storms. Slow easterly storm motions and mean layer PW
values in the 1.1 to 1.5 inch range should have little problem
producing storms capable of locally heavy rainfall. High res models
show storm coverage expanding eastward along the Palmer Divide
during the early evening hours with rainfall of 0.50 to 1.5 inch per
hour possible. Through the evening, high res models show this
activity moving across Elbert and Lincoln counties where higher
theta-e and PW could result in local rain totals in excess of 2
inches. This area will bear watching this evening. No flash flood
watch at this time, but local flash flooding is a fair bet. Further
more could see scattered storms in this area linger beyond midnight.
Late tonight, showers and storm activity will drop off and with
partial clearing could see patchy dense fog form in eastern
sections toward morning.
On Thursday...the moist atmosphere is expected to shift west of the
Front Range with the upper high pressure ridge migrating westward
over Utah and western Colorado. Should see few storm tomorrow with
PW values on the decline. And with winds on the plains turning
southerly, upslope will play less of a role in producing storms
along the Front Range. Still, the high country should see scattered
showers and t-storms form after the noon hour with locally heavy
rainfall still a possibility during the afternoon west of the Cont
Divide. Temperatures in the next 24 hours should be little
.LONG TERM...(Thursday night through Wednesday)
Issued at 400 PM MDT Wed Jul 26 2017
The upper ridge remains over Colorado Thursday night into
Saturday. Models still show it to move westward the rest of
Saturday and Saturday night. There is very weak upward vertical
motion on the QG Omega fields much of the time. Models hang on to
southeasterly low level flow Friday and Saturday. There is
substantial moisture to remain over the CWA through Saturday
night. Precipitable water values stay in the 0.75 to 1.50 inch
range Thursday night through Saturday night. The surface dew point
progs have 60s F readings over the plains all five periods. The
mountains and foothills have mid 40s F to upper 50s F through
Saturday night. There is pretty high CAPE values over much of the
CWA late day Friday and a little less late day Saturday. The QPF
fields show some fairly decent measurable rainfall, mostly over
the foothills Thursday evening. There are higher amounts progged
for much of the CWA later friday afternoon and much of the night.
There is a bit less coverage and amounts late day Saturday, but
still plenty. It appears the higher amounts of moisture will be
sticking around for a while. Will keep decent pops going, and
"likely"s in the high country. For temperatures, Friday`s highs
warm up 1-4 C from Thursday`s highs. Saturday`s highs will be
0-1.5 C cooler than Friday`s. For the later days, Sunday through
Wednesday, models have the upper ridge center well west of
Colorado through Wednesday. The moisture the models show is still
significant through Tuesday, then there is some drying Wednesday.
.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 826 PM MDT Wed Jul 26 2017
Thunderstorms are expected to continue across the Denver area
through about 05Z. Airmass will remain moist with low clouds
likely after 08Z through Thursday morning, 18Z. Ceilings are
expected to be drop into the 2000 to 4000 foot range. There is a
slight chance for lower ceilings and reduced visibility due to fog
around 12Z. There will be a chance for thunderstorms again
Thursday afternoon, after 21Z.
Area Forecast Discussion
National Weather Service Charleston SC
1031 PM EDT Wed Jul 26 2017
Broad low pressure will remain across far southern Southeast
Georgia through tonight. A weak cold front will stall over or
near Southeast South Carolina through Thursday. Another cold
front will move into the area this weekend, then likely stall
just offshore into early next week.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
As of 1025 PM: Convection continued to slowly slide north across
SE GA along with AMZ 354 and 374. The latest few runs of the
HRRR have indicated that convection will linger across the
southern forecast area through most of the night. However,
beginning during the pre dawn hours, convection may drift
northward, partially due to outflow boundaries. I will adjust
PoPs to reflect the last guidance and radar trends.
As of 925 PM: Convection across SE GA and adjacent waters has
increased since the last update. It appears that the majority of
the activity remains as showers, however, a few lightning
strikes are occurring out 20-30 miles. I will update the
forecast to increase PoPs heading into the late night hours.
As of 745 PM: A few isolated showers remained across the
forecast area. The greatest coverage was over McIntosh County
and adjacent waters, a rounds of convection develops on the east
side of a mid level low. I will update the PoPs to lower values
north of the Savannah River through the late night hours, then
indicate an increase towards dawn.
To start, numerous/widespread showers and
thunderstorms across far southern counties will gradually
diminish and/or gradually shift south of the Altamaha River.
Here, likely/categorical POPs will diminish to chance POPs as we
transition into the evening. Until then, locally heavy rain
could occur. At most other locations farther north/west, slight
chance/chance POPs early will diminish to less than 15 percent
with no mention of precipitation for several hours especially
Overnight, guidance suggests that northern/western locations
away from the coast will remain rain-free. South of I-16,
scattered showers/thunderstorms could persist into the overnight
and could even increase in coverage late due to the persistent
influence of a slow-moving upper low. Over coastal waters and
adjacent coastal counties, coverage of showers/thunderstorms
could also increase late tonight. Thus, chance POPs return
along the coast well after midnight.
.SHORT TERM /6 AM THURSDAY MORNING THROUGH SATURDAY/...
Troughing will prevail through the period. The deepest moisture is
likely through Thursday before a mid-level low weakens and shifts
southeast of the area and again Friday night into Saturday ahead of
an approaching cold front. The main concern this time period will be
the threat for severe storms, mainly late Friday into Friday night
as deep layer shear increases. At this time however the risk appears
low given that the storms should be arriving at night when
instability will be less. Temperatures will warm into Friday ahead
of the front before dropping again Saturday.
.LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/...
Deep moisture characterized by PWATS up to 2.0 inches will persist
over the Southeast United States Saturday night into Sunday while a
cold front slowly progresses south and eventually stalls just
offshore and/or south of the region. The pattern becomes more
difficult to predict early next week with some guidance suggesting
that the stationary front drifts back near the Southeast coast or
low pressure develops along it and lifts northeast along/near the
Southeast coast. Regardless of the outcome, it appears chances of
showers/thunderstorms will be possible early next week with greatest
precip coverage anticipated near coastal areas.
Temps will generally be a few degrees below normal this weekend and
early next week given extensive cloud cover and precip activity. In
general, temps should peak in the mid/upper 80s. Overnight lows will
range in the low/mid 70s.
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
VFR conditions through the 0Z TAF period. Light east winds are
expected through late tonight, then becoming calm for KSAV by
7z. Spokes of mid level forcing may rotate around the center of
a low during the daylight hours Thursday. I will indicate PROB30
for TSRA at KSAV during the mid day and KCHS during the
Extended Aviation Outlook: VFR conditions should prevail into
Friday. Higher chances of flight restrictions should return late
Friday through Sunday as showers and thunderstorms occur with a
cold front that slowly progresses over the region.
Tonight: Wind direction could remain changeable to start, but
more uniform east winds 10 kt or less are still expected to
develop, accompanied by seas 1-3 ft. Thunderstorms could
produce locally hazardous conditions, including brief
waterspouts, especially later tonight.
Thursday through Monday: A cold front looks to stall near the SC
waters through Thursday and then dissipate before another cold front
moves into the area this weekend. Conditions are expected to remain
below Small Craft Advisory levels through the period. However, a
southwest/south flow could gust around 20 knots Friday night into
early Saturday until cold fropa occurs. Seas will build a bit, up to
4 ft near the Gulf Stream, before subsiding a bit over the weekend
as the front pushes through, and then increasing again early next
week behind the front.
AREA FORECAST DISCUSSION
National Weather Service Eureka CA
303 PM PDT Wed Jul 26 2017
.SYNOPSIS...An upper level low will bring the potential for a few
thunderstorms this afternoon and evening over Trinity and northern
Mendocino county. High pressure will build across the region for
the remainder of the week, bringing drier and warmer conditions to
the area. Coastal clouds and patchy fog will develop each night
and persist through the morning for the next few days.
.Short Term (Through Friday)...The upper level low has started to
move out of the area this afternoon and is now over the Central
Valley. Water vapor shows more mid level moisture over the area,
but as of 3pm there has only been CU build ups over the mountains
of Trinity county and northeastern Mendocino county. Any storms
that do form will likely dissipate around sunset as the heating of
the day diminishes. This evening the marine stratus is expected
to spread inland quickly once the daytime heating diminishes. Low
temperatures will be near seasonal levels tonight.
Thursday dry weather is expected across the area as high pressure
builds in. At the coast the inversion looks slightly weaker behind
the upper level low. This should allow the stratus to mix out a
bit more quickly tomorrow than today. Inland temperatures will
warm a few degrees over today and will be slightly above normal.
The marine layer will likely shrink a bit as well. Thursday night
the marine layer will return and will be similar to the previous
night. Friday inland temperatures will remain above normal and the
coastal stratus will push back to the coast in the afternoon. MKK
.LONG TERM.../Friday evening through Tuesday night/
Hot weather in store for the interior through early next week, with
highs in the low triple digits in Weaverville area, and highs near
100 degrees in Ukiah. This will be about 5 to 10 degrees above
normal. So far this month, temperatures in the area have been
running above 3 to 5 degrees above. Thus, the warmer than normal
trend will continue.
The 500 mb heights will continue to rise through the weekend, as
the upper level ridge builds into NW California from the south.
The height rise will be subtle, however, as there is an upper
level trough holding strong over Gulf of Alaska. There will be no
precipitation potential through the weekend into early next week.
There maybe a few weak upper level disturbances passing through
the area. This may bring slight increase in sky cover. Don`t
expect the weather pattern to change much in this typical summer
pattern. Hot and dry inland, marine stratus along the coast.
Changes to the previous forecast package is minor.
.Fire Weather...There is still a slight chance some showers and
thunderstorms this afternoon over Trinity and northeastern
Mendocino county. CU has been building and the HRRR forcasted
reflectivity is showing some storms building over Trinity county
late this afternoon/early evening. Once the heating of the day is
over the thunderstorms are expected to come to an end. Thursday
dry weather is expected along with warming temperatures. In the
afternoon 5 to 10 mph west to northwest winds are expected.
Thursday night northerly winds will increase slightly over the
higher terrain in Mendocino county. Poor recoveries are also
expected, mainly in southern Mendocino county. MKK
.AVIATION...The upper low has moved to the east of the region
today. There is still the potential for thunderstorms this
afternoon and evening over northeast Mendocino county and Trinity
county. This threat will diminish this evening. The marine stratus
has pushed back to the immediate coast this afternoon, but is
expected to move back in tonight. It will be fairly widespread,
but is not expected to make it into Ukiah. Thursday the inversion
looks a bit weaker due to being on the backside of the low. This
should help clear skies a bit earlier than today. MKK
.MARINE...Summertime maritime pattern will continue over NW
California waters through the weekend. There is a quasi-stationary
ridge of high pressure set up over the East Pacific, and a thermal
low over Central Valley. The combined weather systems will generate
strong north winds over the coastal waters through the forecast
period. There is a potential to see some gale force wind gusts
Friday through Sunday, especially over the outer waters.
Seas are expected to remain fairly steep and elevated for the outer
waters through the work week into the weekend. There will be a
healthy northerly wind waves, bringing wave heights of 6 to 8 feet
to the outer waters. For the inner waters, wave heights will be
around 4 to 6 feet. Starting on Sunday, a decent south swell will
move into the coastal waters and linger through early next week. The
south swell will have a wave period of around 15 seconds at around 5
to 6 feet. This swell is caused by Hurricane Hiary and Tropical
Storm Irwin, as these systems are expected to head north, and the
southerly swell will be generated on the east side of these tropical
systems. The south swell will be worth watching for the next few
NORTHWEST CALIFORNIA COASTAL WATERS...
Small Craft Advisory until 5 PM PDT Saturday for PZZ470-475.
Visit us at http://www.weather.gov/eureka
Follow us on Facebook and Twitter at:
For forecast zone information
see the forecast zone map online:
Area Forecast Discussion
National Weather Service Gray ME
1019 PM EDT Wed Jul 26 2017
High pressure will move offshore tonight. A cold front moves
across the area on Thursday bringing scattered showers and
thunderstorms. High pressure will attempt to build into the
region Friday and into the weekend as low pressure moves south
of the area. This high will remain established over the
Northeast through early next week.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
1000 PM Update...
Quick update to adjust temp/td/sky grids. Showers pushing into
northwest Vermont beginning to fade and IR sat PIC showing
warming tops so not looking for this activity to hold together
as it continues east. Second batch moving through the eastern
Great Lakes will likely enter northwest zones after midnight
and will continue to push east through the early morning hours.
Current pops still looking good at this point so no changes
700 PM Update... Clouds continue to advance from the
west early this evening and will quickly overspread the region
through midnight. Area radar composite showing precipitation
moving into northern New York ahead of cold front back over the
Great Lakes. Looking for showers to edge into far northwest
zones after midnight and will gradually drop southeast through
the remainder of the forecast area through daybreak. HRRR seems
to be doing a good job on timing and extent and current pops
looking good. Have made minor adjustments to temps/tds but no
major changes planned to current forecast attm. Next update will
be around 1000 pm.
Clouds will advance eastward during the night. This will limit
the patchy fog as compared to last night. Nevertheless, there
will be some fog, especially before midnight.
Showers will work their way east ahead of an approaching cold
front. This front will reach the Saint Lawrence River Valley by
With the cloud cover and light southerly gradient, temperatures
will stay in the upper 50s to lower 60s for overnight lows.
There will be a couple readings in the mid 50s over far northern
.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
As the surface cold front approaches the region Thursday,
scattered showers and thunderstorms will break out across the
region. Dependent on the amount of morning sunshine, the
atmosphere will destabilize through the morning and early
afternoon, yielding CAPE values of over a 1000 J/KG. The threat
will primarily be in areas away from the immediate shoreline
where conditions will be more stable. A few of the storms may be
sufficiently strong to produce damaging wind gusts. Hail is
less of a threat on Thursday.
Increasing surface dew points and precipitable water values will
allow for locally heavy rainfall. The slow moving nature to the
front may allow for training of storms over any particular
As the precipitation ends Thursday night, patchy fog may form
over areas that receive heavy rainfall during the day.
Scattered convection expected to continue until sunset at the
slow moving front remains over central and northern areas.
.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
The front drops south of the area on Friday with low pressure
forming and moving eastward along that front south of New
England Friday night into Saturday. It is looking like the rain
from this system will stay to our south, with our area remaining
under high pressure with seasonable temperature and low
humidity this weekend.
The center of high pressure shifts east across the area on
Monday, with a westerly flow developing aloft which will
transport warmer, slightly more humid air from the center of
the continent eastward into New England. There are no
significant rain chances in the forecast through midweek as we
will broadly be under the influence of high pressure.
.AVIATION /02Z THURSDAY THROUGH MONDAY/...
Short Term...Mainly VFR conditions will yield to lowering
ceilings and visibilities in showers and storms on Thursday.
Locally, IFR and LIFR conditions expected in any of those storms
which will last into Thursday evening. Patchy fog develops
Long Term...VFR conditions are expected with fog possible each
morning in the usual locations, Lebanon and Whitefield.
Short Term...Winds and seas will remain below Small Craft
Long Term...Expect light winds and low seas through the weekend
and into next week as high pressure builds through the area.
Area Forecast Discussion
National Weather Service Houston/Galveston TX
845 PM CDT Wed Jul 26 2017
.DISCUSSION... A weak 850 mb high was located over south central
Louisiana and 850 temps were 1-2 degrees warmer tonight and
moisture levels at 850 mb were a bit lower than last night. 00z
soundings showed PW values near 1.56 inches at LCH and moisture
was lacking in the 850-700 layer. The 00z CRP sounding showed PW
values around 1.73 inches. GOES-R PW imagery shows the high PWAT
air over SE TX is being shunted westward with drier air working
into the region from the east and the south. At 300 mb, a
sprawling ridge of high pressure extended from eastern AZ into
western AR with a lobe of the upper high extending south into LA.
A weak inverted upper trough extended from SE TX into Deep South
Texas. So what does it all mean? The drier air working into the
region and the loss of heating should keep things dry overnight
with generally clear skies. Not enamored with rain chances for
Thursday as moisture levels drop further and the inverted upper
trough pushes west and becomes less defined. However, am concerned
with afternoon max temps and heat index values. The proximity of
the upper ridge and warm 850 temps suggest high temps between
95-100 and heat index values between 105-109 degrees tomorrow
afternoon. A Heat Advisory may be required for tomorrow afternoon.
Not seeing a lot of change for Friday and Saturday with very warm
temperatures and high heat index values. Will tweak Temp/Sky and
Dew Pt grids but the overall integrity of the previous forecast is
on track. 43
.PREV DISCUSSION... /ISSUED 632 PM CDT Wed Jul 26 2017/
The main area of scattered showers and thunderstorms were between
KSGR/KIAH and KCLL. These were drifting northwestward and should
diminish around 01Z. Other isolated showers are possible before
01Z given the outflow boundaries evident on radar. There are some
showers and thunderstorms about 100 nm offshore. Do not think
these will make it to KGLS or KLBX but there is an outside chance
they will begin to affect either site between 02Z and 06Z and
possibly later. For now think the possibility is too small to
include in the forecast.
VFR conditions are expected overall although there is a slight
chance for MVFR conditions around 12Z. The models show some slight
potential for isolated showers and thunderstorms once again on
Thursday, mainly after 15Z at the coast and after 18Z further
PREV DISCUSSION... /ISSUED 352 PM CDT Wed Jul 26 2017/
Scattered showers and thunderstorms just south of I-10 near the
Houston Metroplex continuing to push north this afternoon with the
help of the seabreeze and outflow from earlier convection. Based
on short term guidance such as the HRRR and RAP, still believe
that most of the convection should dissipate around sunset this
The big story for Thursday and Friday will be the heat. High
temperatures Thursday will approach the mid to upper 90s further
inland and the low 90s around the coast by mid afternoon.
Tomorrow, forecast soundings bring PWs between 1.9 to 2.1 inches,
therefore, moisture will be available with dew points in the low
to mid 70s inland and upper 70s along the coast. The combination
of elevated high temperatures and moisture will result in heat
indices approaching near heat advisory criteria ranging between
104 to 109 degrees. On the contrary, these heat indicies could be
on the lower side depending on how far inland the sea breeze
reaches tomorrow afternoon. It is possible that a heat advisory
will have to be issued for tomorrow afternoon depending on how the
dew points trend. A similar situation will be possible on Friday,
with high temperatures reaching up into the 90s and dew points in
the mid 70s.
Next best chance for showers and thunderstorms push back in
Saturday and Sunday, as the upper level ridge that was centered
over northern Texas slides west. A trough begins to push into the
area late Saturday and a frontal boundary will slide through the
region. Expecting a majority of this precipitation associated with
this boundary to be east of the forecast area, but still will see
some showers and thunderstorms across our eastern zones late
Saturday and through the day Sunday. Most of the precip should
clear out by early Monday. Dewpoints will lower slightly behind
this feature, though temperatures should still stay around normal
for this time of year.
High pressure situated over the north central Gulf will slowly
meander to the west into the late week. This will suppress shower
and thunderstorm potential, and maintain light onshore winds and
low seas. Towards the weekend, winds may veer towards
southwesterly, but remain light. A weak frontal boundary will sag
into east Texas late in the weekend and may droop close to the
coast into early next week. Barring the boundary pushing over the
waters, the primary impact of this would be for shower and storm
coverage to increase modestly and force winds back towards the
southeast or east-southeast. Marine concerns should be fairly
limited, though winds and seas can become agitated in the vicinity
of any storms that may manage to crop up.
.PRELIMINARY POINT TEMPS/POPS...
College Station (CLL) 76 99 76 99 77 / 20 10 10 10 10
Houston (IAH) 77 96 78 97 78 / 30 10 10 10 10
Galveston (GLS) 84 92 82 91 83 / 30 20 10 10 10
Area Forecast Discussion
National Weather Service Indianapolis IN
940 PM EDT Wed Jul 26 2017
The NEAR TERM Section has been updated below.
Issued at 325 PM EDT Wed Jul 26 2017
A cold front will drop southeast across central Indiana Thursday and
Thursday evening. The front will interact with a warm, very moist
and unstable atmosphere and trigger widespread thunderstorms
overnight and Thursday. A few storms will linger into Friday as an
upper waves dives southeast over the Great Lakes. Then, high
pressure will bring dry weather and cooler temperatures to the area
for the weekend.
Temperatures will warm back up to near normal next week, and a few
storms are possible south by Wednesday as an upper wave moves across.
.NEAR TERM /Rest of Tonight and Thursday/...
Issued at 936 PM EDT Wed Jul 26 2017
IR satellite imagery shows growing MCS with cooling tops over northern
and central IL this evening. Showers and thunderstorms are over
the northwest corner of IL and this activity is expected to cross
the state line between 06Z and 08Z. Question now is whether the
latest HRRR is slower than it should be bring the rain into
central IN between 10Z and 12Z. Latest upper air analysis using
SPC Mesoanalysis shows axis of Precipitable Water (PW) extending
from STL east and southeast through EVV. The PW values actually
lower as the IL complex tries to move eastward. So, the question
now remains whether there is some low level moisture transport
northeastward to increase PW values to forcast levels over 2.0",
or if the IL complex builds southward effecting more of areas
south of the proverbial I-70 line.
Timing and coverage of thunderstorms as well as location of heavy
rain axis will be the main concerns for the short term. Severe
weather can also not be ruled out.
Models are having some timing difficulties regarding an approaching
weak cold front, that currently is residing over Lake Superior into
Nebraska. The 12z NAM and GFS both have it over our northern
forecast area 00z Friday. However, the 00z ECMWF has it near the
Ohio River at that time. The 00z Canadian was something of a
compromise with the front over south central Indiana. This goes
along better with the WPC frontal position and is thus preferred but
with low confidence. Models also have timing differences with a pair
of weak impulses set to move through the area tonight and Thursday.
At any rate, the synoptic forcing will interact with precipitable
water values to 2.4 inches, courtesy of a 30 to 40 knot low level
jet, which is above the daily max line of 2.1 inches for ILN from
the SPC Sounding Climatology Page. In addition, despite extensive
cloud cover, the instability will be plenty enough with surface
based CAPES to around 200 J/KG overnight and over 1000 J/KG
Current forecast has small chance pops this evening, except far east
and likely pops all but far south and far east by 11z Thursday.
Despite some timing differences in model QPF, this looks to be a
good compromise and better to leave things as is with the
uncertainty that goes with those timing concerns. For Thursday, all
models and would suggest widespread thunderstorms. Confidence is
high with the front moving in.
With the moisture so impressive and freezing levels above 15,600
feet, there is certainly a threat for heavy rain overnight and
Thursday. Models are not surprisingly having issues with placement
of the heaviest rain axis. However, model trends are now a little
further south with the heaviest rainfall axis across our far
southern counties and into Kentucky. So, will go along with adjacent
offices and mostly use the 18z WPC QPF which reflects this thinking.
The Day 1 Excessive Rainfall Potential Outlook has parts of our
northwestern counties in a marginal or slight risk. However, Flash
Flood guidance has recovered with 1 hour numbers mostly 2 to 2.3
inches and 3 hour numbers mostly 2.5 to 3.2 inches. Taking that into
account along with the model consensus issues but further south
trends, and after coordinating with adjacent offices, will hold off
on a Flash Flood Watch, but include heavy rain in the grids
overnight and Thursday south and hit that and localized flooding
hard in the Hazardous Weather Outlook and Weather Story.
Due to extensive cloud cover, confidence in severe weather is not
great for Thursday. However, with nice veering with height, the low
level jet and a 70 plus knot upper jet over Michigan, can not rule
it out. The SPC Day2 Outlook has a Marginal Risk over our southern
Blended temperatures look ok. Prefer temperatures at or below a
blend Thursday with the widespread convection opted to keep it from
warming up as much as otherwise.
.SHORT TERM (Thursday night through Saturday)...
Issued at 325 PM EDT Wed Jul 26 2017
The main concerns with the short term will be timing the convection
of the area.
Models and ensembles all suggest the front will move south of the
area Thursday evening. This should result in the bulk of the
thunderstorms ending from northwest to southeast before Midnight.
For the evening, good chance pops look good close to the front
tapering off to slight chance northwest. After that, a distinct
upper wave will drop southeast across the Great Lakes on Friday.
This supports model small pops, despite limited moisture. There
should be just enough instability to justify thunder.
By Friday night, should see little to no clouds and cooler
temperatures, per model blend as high pressure builds in from the
.LONG TERM /Saturday night through Wednesday/...
Issued at 228 PM EDT Wed Jul 26 2017
A strong upper level low pressure system will exit the Midwest and
move into the Appalachians Saturday night leaving behind northerly
flow that will persist through much of the long term period. At
the surface, north to northeasterly winds will keep temperatures in
the low to mid 80s and keep dewpoints in the low to mid 60s.
There is high confidence for dry weather through Tuesday. A weak
upper level disturbance will move across the Midwest on Monday and
Tuesday, but with very dry air aloft, chances for precipitation are
low. Better chances for rain for Wednesday with several models
showing an upper level shortwave strengthening over the High
Plains and moving east into the Midwest.
.AVIATION /Discussion for 27/0000Z TAF Issuance/...
Issued at 606 PM EDT Wed Jul 26 2017
VFR conditions this evening will give way to increasing clouds and
lowering ceilings towards later this evening into the early
morning hours. Right now, looking for rain and scattered
thunderstorms to move into the region after midnight with IFR/VIFR
chances increasing after 27/06Z especially in the the vicinity of
TSRW through 27/13Z and the later morning hours.
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
907 PM CDT Wed Jul 26 2017
854 PM CDT
Monitoring a line of showers and storms marching east through
northern IL. My overall impression is the line is falling apart,
but slower than I originally thought it would. The latest RAP
analysis has a ridge of 1000+ J/kg through north central IL, but
the 0-6km shear axis has shifted further east. Surface CIN is also
increasing over the Chicago metro area. IR imagery shows cloud top
warming over northern IL and cloud top cooling over central IL.
Therefore, expecting the storms over northern IL to continue to
weaken and remain unorganized as they continue east. However,
cannot rule out an isolated cell or two pulsing up and producing
sub-severe wind gusts.
Also closely monitoring areal and flash flooding as PWAT values
are 1.5-2 inches. Storm motion is the key. If storms begin to
train or slow, flooding is much more likely. Upstream reports from
the Davenport office indicated as much as 2 inches of rain falling
in an hour. Not expecting rates that high since storms are falling
apart, but heavy rainfall still may lead to localized ponding or
229 PM CDT
For the remainder of the afternoon conditions should remain
relatively quiet with increasing mid and high cloudiness in advance
of an area of pcpn extending from srn WI, through ern Iowa and nrn
Missouri. This activity is largely in response to a modest
shortwave tracking across the middle Mississippi Valley. Warm,
moist, unstable conditions with MU CAPE of 2000-3000 J/kg,
temperatures climbing into middle to upper 80s and sfc dewpoints in
the middle to upper 70s. Latest radar trends are for more sct
shra/isold tsra and in spite of a well defined MCV generated by
earlier convective activity over the cntrl plains, Extensive cloud
cover is likely helping to inhibit stronger, more widespread
thunderstorms this afternoon.
Looking into the evening hours, focus will shift to timing and
location of a swatch of heavy rainfall. The 12Z DVN sounding
indicated pwats of 1.3 inches and the short range guidance indicates
that pwats should climb to slightly in excess of 2 inches as the
shortwave tracks east across the region. Latest guidance is
suggesting that the shortwave should take a more sely track across
the region, which would suggest that the heaviest pcpn should be
suppressed a little farther south than previously anticipated. While
locally heavy rainfall is still likely with some of the stronger
storms, the areal average heavier rainfall should be confined to
areas generally south of the I-80 corridor. The overall severe
threat is also diminishing, but not totally out of the question,
with marginal mid level lapse rates and extensive cloud cover
somewhat limiting sfc based destabilization. Also, with relatively
weak mid level flow, there primary weather threat will be more for
locally heavy rainfall, with an isolated wind threat more related to
wet microbursts than any kind of upscale thunderstorm development.
222 PM CDT
Thursday through Wednesday...
Main forecast concerns/challenges are with lingering chances for
showers and thunderstorms on Thursday, with a low chance for an
isolated strong storm mainly along/southeast of I-57.
Any lingering showers and thunderstorms Thursday morning will be
confined to areas south of I-80, but will be steadily southeast
out of the CWA through mid morning. Mainly dry conditions expected
for much of the cwa then anticipated through midday. Anticipate
cloudier conditions to continue throughout the day and with these
clouds likely to remain, have maintained similar high temp
forecast of highs around 80 with slightly cooler temps near the
There remains a chance for additional showers and thunderstorms
by early afternoon mainly for areas along and southeast of I-57.
Higher dewpoints pooling along surface trough still in place
across the southern CWA could serve as focus for additional
development. Coverage should remain widely scattered with any
development, with some isolated development possible further to
the north in northern Illinois. Most development likely to remain
subsevere, however, there is some potential for an isolated
stronger storm. This will be conditional on any clearing
occurring, and if that occurs, isolated areas of higher
instability are not out of the question. Storm chances will
quickly diminish by late afternoon and early evening, as focus
quickly shifts south of the area. High pressure then expected to
build across the region late in the work week into the weekend and
early next week, with no significant weather expected.
For the 00Z TAFs...
648 pm...Main forecast concern is thunderstorm chances this
evening into early Thursday morning.
Scattered thunderstorms near the Mississippi River will continue
moving east/southeast over the next few hours and the overall
trend is for these storms to weaken with the bulk of the activity
moving southeast into central IL. Additional thunderstorms across
southern WI may continue to move south into far northern IL by
mid/late evening and also are expected to weaken. Maintained
thunder at rfd but confidence further east at the Chicago area
terminals is low and trends will need to be monitored over the
next few hours. Some shower activity is possible overnight and
there is a some small chance of showers Thursday morning.
Light southerly winds will turn more southeasterly this evening
but speeds should remain well under 10kts. Winds will likely
become variable overnight and turn northeasterly Thursday morning.
The gradient will tighten and northeast winds will increase along
with some gusts Thursday afternoon into Thursday evening. An
outflow boundary across southeast WI currently will need to be
monitored as it moves into far northeast IL early this evening.
With the moist low levels and light winds...some fog is possible
overnight into Thursday morning along with mvfr cigs. Confidence
is low and trends will need to be monitored later tonight. cms
222 PM CDT
As surface trough moves across the northern part of the lake this
evening, will likely see a diminishing trend with the winds.
Expect these lighter winds to persist for a time tonight but as
the surface trough/low depart to the southeast late tonight
through early Thursday, will see increasing northerly winds across
the entire lake. Increasing northerly winds will be the trend
across the lake during the day Thursday, with winds of 15 to 25 kt
returning Thursday afternoon and evening. Occasional gusts to 30
kt could still be a possibility. These stronger winds and higher
waves will likely support hazardous conditions for small craft
late Thursday and Thursday night. However, given the time frame,
have not issued a small craft advisory at this time. Northerly
winds will then likely continue into the start of the weekend,
with speeds periodically bouncing from 15 to 25 kt, to 30 kt
during this time. Hazardous conditions for small craft will likely
continue as well.
VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)
FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
Area Forecast Discussion
National Weather Service Midland/Odessa TX
1000 PM CDT Wed Jul 26 2017
Area radars show convection has dwindled to a few cells in wrn
Eddy county, and all indications are that these will continue to
diminish w/loss of daytime heating. Convection further north
moving into SE NM after midnight is still in question, but the
latest NAM and HRRR suggest it won`t make it. We`ll do a quick
update to lower pops, and adjust other parameters as needed.
Updates out shortly.
.PREV DISCUSSION... /issued 638 PM CDT Wed Jul 26 2017/
Please see the 00Z aviation discussion below.
VFR conditions will prevail the next 24 hours. Thunderstorms
across the west will weaken/dissipate after sunset, and while
mention was not included early in the forecast period at CNM, will
monitor and amend if needed. Winds will remain out of the S/SE,
with a few gusts to around 20kt possible through this evening.
PREV DISCUSSION... /issued 201 PM CDT Wed Jul 26 2017/
Typical summer pattern in place into this weekend with the upper
ridge overhead providing hot temperatures with storms confined to
the higher terrain. Convective coverage will be less than yesterday
as increasing heights and subsidence help to suppress most CU
development. Hi-res models show an outflow boundary sparking a
few storms very late tonight across parts of SE NM so have kept
PoPs going there through Thursday morning. Even though
temperatures will be above normal, it will only be by 3-5
degrees. Midland Intl has only hit 100 degrees once this month
which is far from our hottest month on record last July!
Not much change through the weekend until the upper ridge weakens
and shifts slightly west. By this time a weak front will penetrate
the ridge and could backdoor into the region late Sunday. This will
be highly dependent on the amount of convection to our north
which could push the front in sooner. Models have delayed the
onset of midlevel northerly flow by a day or so. While showers and
storms will increase early next week, greater chances hold off
until the middle to latter part of next week. Latest models have
also backed off on the much cooler temperatures for next week.
Will have to wait and see if this trend continues, but more clouds
and rain around should at the very least help temperatures fall
back toward normal.
.PRELIMINARY POINT TEMPS/POPS...
Big Spring 75 100 74 100 / 0 0 0 0
Carlsbad 74 98 72 98 / 10 10 10 10
Dryden 74 99 75 99 / 0 10 0 0
Fort Stockton 73 98 72 98 / 0 0 0 0
Guadalupe Pass 70 89 68 89 / 10 10 10 10
Hobbs 71 96 69 96 / 10 10 0 0
Marfa 63 91 63 91 / 10 10 10 10
Midland Intl Airport 74 99 74 99 / 0 0 0 0
Odessa 74 99 74 99 / 0 0 0 0
Wink 74 101 73 100 / 0 0 0 0
Area Forecast Discussion
National Weather Service Pendleton OR
855 PM PDT Wed Jul 26 2017
.SHORT TERM...Tonight through Saturday...Sat WV loop shows upper
low moving into nw Nevada at mid evening. Still looks like a
closed circulation and 00z model initialization confirms this as
so. Movement to the northeast over the next 12 hours will continue
to bring moisture into eastern Oregon mainly east of John Day to
LaGrande line. Daytime heating, of course, has ended and
thunderstorms are weakening. Will eliminate the chance for
thunderstorms to the west of this line and allow the Red Flag
Warning to expire at 11 pm. 00Z NAM shows upper low opening into a
wave and moving into SW ID Thursday morning. Thus the POPs on
Thursday will be considerably lower across the southern tier of
counties compared to today. A more westerly flow will bring
increasing winds to areas near the Cascade east slopes including
the Gorge and Kittitas valley, but below advisory criterion.
Slight ridging will begin on Friday and continue Saturday for
continued dry conditions and above normal temperatures.
.AVIATION...06z TAFs...As upper low moves east away from TAF
sites, VFR conditions will prevail with SKC at DLS,BDN,RDM,YKM.
SCT-BKN150 will gradually become SKC at PSC, ALW, AND PDT after
12z. DLS will have G25kts after 18z.
.PREV DISCUSSION... /issued 242 PM PDT Wed Jul 26 2017/
SHORT TERM...Tonight through Saturday...An upper low remains over
northern California at this time and is circulating moisture and
disturbances around and through our area. Instability from the low
and daytime heating is starting to generate some thunderstorms over
the higher terrain of the eastern Oregon mountains and the Cascades
of central oregon. Expect that this will continue through the
evening with isolated to scattered thunderstorm coverage. The number
of thunderstorms should decrease but probably not end overnight.
Have kept a slight chance of showers and thunderstorms over the
eastern Oregon mountains through the night and into early tomorrow
morning. Precipitable water amounts are over an inch (which is well
above normal), so believe storms will have rainfall amounts up to a
quarter inch, perhaps up to a half inch with the stronger cells. The
storms may have gusty outflow winds as well. The combination of
lightning and the possibility of outflow winds has lead to the
issuance of a Red Flag Warning for Central Oregon and the eastern
Oregon mountains. See the Fire Weather Discussion below for
additional details. Late tonight the low will weaken and open up
into a wave. It will get absorbed into the main upper flow and move
northeast just to the south and east of our area. Despite it`s
weakened state, have kept a slight chance of showers and
thunderstorms over the higher terrain of the eastern Oregon
mountains south of the Blue Mountains. Elsewhere in the area, the
main impact of the low passage will be breezy 10 to 20 mph winds in
the Columbia Gorge and Kittitas Valley as the pressure gradient
pulls a weak marine flow into the area. By tomorrow evening the
remnants of the low will be over the Idaho panhandle and aside from
a few showers over the Wallowa mountains, the impact of that low
will be over. By Friday, a ridge over the desert southwest will try
to expand north but will be countered by a large low in the Gulf of
Alaska. This will keep a dry west to slightly southwest flow over
the area Friday through Saturday and fair and sunny weather is
expected. Temperatures will be a few degrees cooler tomorrow with
highs in the lower to mid 90s in the Columbia Basin and in the mid
80s to lower 90s elsewhere. Friday will be a couple of degrees
cooler then Saturday will warm back to the mid 80s to mid 90s. Perry
LONG TERM...Saturday night through Wednesday...Models in good
agreement in building an upper level ridge over the Great Basin
through the period. This will result in southwest flow becoming more
westerly across our forecast area as the weekend gives way to the
workweek. There are differences in how each model handles a weak
disturbance riding over the ridge Tuesday. GFS is stronger with this
system and produces an area of convection over Oregon while ECMWF is
much weaker and drier with no convection. At this time, prefer the
drier ECMWF solution as it seems to be the more consistent from run
to run. In addition, more members of the GFS Ensemble show a weak
open trough which lines up better with the EMWF`s solution. In
summary, outside a few possible buildups over the mountains on
Tuesday, we should be dry and hot through the extended period. Earle
AVIATION...00Z TAFs...VFR conditions can be expected for the next
24 hours. Mid/High level clouds will stream over the area tonight as
a system in northern California moves eastward. BDN/RDM may see a
thunderstorm before the evening is done. However, thunderstorm
coverage is expected to remain scattered so will use VCTS for now.
Winds will be generally less than 10 kts, except KDLS where winds
will be 10 to 15 kts with a few gusts to 25 kts. Winds are expected
to decrease overnight, but increase to 10 to 15 kts Thursday
FIRE WEATHER...In the past hour, thunderstorms have developed east
of Prairie City and over southwest Deschutes County. Visible
satellite shows the towering cumulus across east central Oregon that
will soon become buildups over the next few hours. The Red Flag
Warnings (RFW) currently in effect appear on track based on the HRRR
composite reflectivity through midnight. For Oregon Fire Zones 611
and 640 that cover the southern Deschutes National Forest and the
Prineville District, the RFWs are in effect through 11 PM. For
Oregon Fire Zones 642, 644 and 645 that cover Grant County, the
southern Blue Mountains, the Grande Ronde Valley, and Wallowa
County, the RFWs are in effect until 9 AM Thursday. Thunderstorms
will decrease in coverage after midnight, and there may only be
isolated thunderstorms around sunrise. The upcoming shifts may
decide to cancel the warnings if storms have dissipated and are no
longer a threat.
A dry southwest flow will remain over our eastern Washington and
north central Oregon zones through Thursday. An onshore flow west
of the Cascades will allow some marine air to filter through the
Columbia River Gorge where winds will increase to around 15-25 mph
during the afternoon. Winds will also increase to around 10-20 mph
along the I-84 corridor to as far east as Arlington or Boardman and
south toward Condon around sunset. The relative humidity will range
from 18-30 percent. The combination of winds and RHs will not be
enough to warrant a RFW but will be highlighted in the forecast.
.PRELIMINARY POINT TEMPS/POPS...
PDT 64 93 59 90 / 10 10 0 0
ALW 69 95 64 93 / 10 0 0 0
PSC 64 96 60 94 / 0 0 0 0
YKM 64 94 60 94 / 0 0 0 0
HRI 66 94 61 93 / 0 0 0 0
ELN 61 88 58 89 / 0 0 0 0
RDM 53 90 51 91 / 30 0 0 0
LGD 56 92 54 92 / 20 10 10 10
GCD 59 92 58 93 / 20 10 10 10
DLS 65 88 61 89 / 0 0 0 0
OR...Red Flag Warning until 9 AM PDT Thursday for ORZ642-644-645.
Red Flag Warning until 11 PM PDT this evening for ORZ611-640.
Area Forecast Discussion
National Weather Service Pocatello ID
123 PM MDT Wed Jul 26 2017
.SHORT TERM...Tonight through Thursday night. Upper low over
northern CA today. Mid-level dry slot working through Great Basin
ahead of low into East Idaho with good clearing. Showers continue
over eastern highlands early this afternoon with a few embedded
thunderstorms. Air mass within clearing behind mass of showers
showing signs of destabilization again, and expect another round
of thunderstorms to develop this afternoon/evening across the
region. Models continue to have a difficult time with placement of
convection, but HRRR consistent this morning on rather widespread
swath of convection redeveloping between 2 and 4pm, shifting
northeast through early evening. Strongest cells in HRRR over
higher terrain regions so concentrated precip chances there. Upper
low opens and shifts northeast through Thursday, sliding across
East Idaho during the afternoon and early evening. Better shear
associated with passage of the shortwave could lead to slightly
more organized convection, so have reserved highest precip chances
for Thursday afternoon. As shortwave axis shifts east overnight,
expect precip to drop off significantly after midnight. DMH
.LONG TERM...Friday through Wednesday. Upper ridge rebounds
slightly heading into the weekend with resurgence of high pressure
over the Great Basin. Plenty of moisture lingers through the
remainder of the week, and thus have kept some chance of
convection each afternoon and evening through the period. Look for
temperatures to rebound back into the 90s for lower elevation
areas by Saturday, continuing into next week. DMH
.AVIATION...Monsoon moisture will continue to invade eastern Idaho
through tomorrow. TAFs contain -SHRA VCTS or VCTS through this
evening, with the potential of heavy rain and gusty winds over
25kts. We can`t rule out small hail either. We went with VCSH
overnight as instability decreases BUT it does appears the potential
for showers and even thunderstorms is there overnight. More of the
same tomorrow. Overall, expect VFR although with storms containing
heavier rain ceilings and visibility COULD drop into MVFR. Keyes
.FIRE WEATHER...We are seeing clearing slowly from west to east
today with showers and isolated/widely scattered storms continuing
or redeveloping back to the west. Gusty winds and locally heavy rain
(over 0.25") are possible with stronger storms. Small hail is also
possible. With the next storm moving into our area later tonight and
Thursday, the risk of lightning/thunderstorms will persist into
tonight and obviously tomorrow. Heavy rain is still possible
overnight and Thursday, with perhaps a little better chance of gusty
winds or small hail tomorrow. At the moment, coverage SHOULD still
remain below scattered. As mentioned over the past couple of days,
advanced warning on scattered coverage and Red Flag conditions could
be pretty short as we`ve been nowcasting (a few hours ahead of time
vs 12+ hours) areas of clearing and storm development. Heading into
the weekend, the models are still a bit chaotic (in other words, no
major agreement) in terms of storm coverage after Saturday. We are
expecting isolated Friday and Saturday as no real trigger is there
plus lack of deeper moisture. The ridge tries to rebuild northward
and the extent of that will determine how much moisture rotates
around the center of it and where it will go. We may easily be back
into the Monsoon soup early next week depending on how things pan
Area Forecast Discussion
National Weather Service Phoenix AZ
900 PM MST Wed Jul 26 2017
Drier air moving into the region will result in a lower chance of
storms for much of the work week. Decreasing cloudiness and
moisture will support a warming trend through Thursday with near
normal highs. Moisture begins increasing late Thursday and will
usher in an increased chance of storms across the CWA Thursday
night through the weekend. Subsequently, high temperatures
decrease as well...most noticeably over south-central Arizona.
A very quiet day across our cwa, with virtually all convective
activity remaining well off to the north and east. The combination
of ridging/warming in the 500-700mb layer and southwesterly flow
through much of the column that has advected drier air into the
region was responsible for the lack of convective activity over the
region today. The latest HRRR high-res model runs continue to show a
very quiet overnight and early morning forecast for Thursday. Thus,
have reduced POPS to below 10% over virtually all of our cwa through
early Thursday. The latest (00Z) GFS model output, which is just
staring to come in, shows a bit more drying across the region
through Thursday evening, with near-zero POPS likely across the
lower elevations, with thunderstorm chances being relegated to the
easternmost/highest elevations of our cwa. Other than the changes to
the POPS, inherited forecasts are still looking good.
Quiet weather will continue through the day where our most
concerning question is to see just how hot temperatures will
climb. Phoenix has already hit a high of 103 degrees, before 1PM,
so adding three or perhaps four degrees to that figure is not out
of the question. A study of the GOES-16 visible satellite reveals
mostly clear skies but for some high clouds filtering through the
area. The 500 millibar high pressure situated over central New
Mexico is allowing for drier southwesterly air aloft to filter
over the area. This morning, surface dew points were still in the
mid 60s through parts of central Arizona while the sounding
revealed a much more delightful 1.6 inches of precipitable water.
Even better, we should see the PW values drop a little more
through the next day or two. The lower desert will have very
little, if any, CAPE to work with during the next two days.
In addition, the atmosphere over much of Arizona will endure some
warming aloft. At 12Z, the Phoenix sounding indicated the 500 mb
temperature was a little cooler than -4 deg C, and the
southwesterly flow aloft will help warm that layer an additional
degree or two by tomorrow. An isolated storm or two might be
possible over the mountains in Gila County tonight and Thursday,
but with nearly no CAPE and warming aloft, one would be hard
pressed to find much convection over the lower desert. However,
the drier atmosphere will lead to slightly warmer temperatures
peaking 2-5 degrees above normal.
Thunderstorm chances creep back into the area by Friday evening.
The center of the 500 mb high migrates a closer to the Four Corners
which will induce a more storm-favorable southeasterly wind flow,
and allow additional moisture to penetrate into the area. There
are also a few disturbances rotating around the 250 mb high, which
is centered over the south-central US, that will enhance
atmospheric dynamics to be more supportive for storm development
as they move closer to the region. While day-to-day variability
will matter, storm chances will remain in the forecast into early
next week. Although the best chances for rain will remain over the
higher elevations, all places across the CWA will have at least a
shot at some rain. Moreover, the additional moisture will also
usher in high temperatures a few degrees below the seasonal
South-Central Arizona including KPHX, KIWA, and KSDL:
Very quiet period weatherwise to continue through midday Thursday as
a rather stable airmass keeps convective activity well north and
east of the Greater Phoenix area. Some increase in convective
activity is possible Thursday afternoon/evening over the higher
terrain north and east of Phoenix, but the only impact that is
expected from these storms is a slight chance of some outflows
moving down into the Phoenix area. However, confidence is far to low
at this point to include any wind shifts in the tafs. Cigs are
expected to remain mainly aoa 10k feet through the taf period.
Southeast California/Southwest Arizona including KIPL and KBLH:
Winds will remain relatively light and favor a southerly direction.
No real chance for storms through the taf period, with only a few
passing high clouds. Otherwise, no major aviation weather concerns
Aviation discussion not updated for amended TAFs.
Saturday through Wednesday:
Thunderstorm chances will remain in the forecast through the
weekend with all locations having at least a decent chance and
rain. Storm chances decrease through Wednesday, with the best
chances by then being confined mostly to the higher terrain north
and east of Phoenix. Given the moisture levels, minimum relative
humidities will stay well above 15 percent with good overnight
recoveries. Winds will otherwise be light outside of any
thunderstorm related winds.
.SPOTTER INFORMATION STATEMENT...
Spotters should follow standard reporting procedures.
Visit us on Facebook, Twitter, and at weather.gov/phoenix